Category Archives: food service

Vacuum packing

Vacuum packing is a method of packaging that removes air from the package prior to sealing. This method involves (manually or automatically) placing items in a plastic film package, removing air from inside, and sealing the package.[1]Shrink film is sometimes used to have a tight fit to the contents. The intent of vacuum packing is usually to remove oxygen from the container to extend the shelf life of foods and, with flexible package forms, to reduce the volume of the contents and package.[2]

Vacuum packing reduces atmospheric oxygen, limiting the growth of aerobic bacteria or fungi, and preventing the evaporation of volatile components. It is also commonly used to store dry foods over a long period of time, such as cereals, nuts, cured meats, cheese, smoked fish, coffee, and potato chips (crisps). On a more short term basis, vacuum packing can also be used to store fresh foods, such as vegetables, meats, and liquids, because it inhibits bacterial growth.

Vacuum packing greatly reduces the bulk of non-food items. For example, clothing and bedding can be stored in bags evacuated with a domestic vacuum cleaner or a dedicated vacuum sealer. This technique is sometimes used to compact household waste, for example where a charge is made for each full bag collected.

Vacuum packaging products, using plastic bags, canisters, bottles, or mason jars, are available for home use.

For delicate food items which might be crushed by the vacuum packing process (such as potato chips), an alternative is to replace the interior gas with nitrogen. This has the same effect of inhibiting deterioration due to the removal of oxygen.

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External sealers[edit]

External vacuum sealers involve a bag being attached to the vacuum-sealing machine externally. The machine will remove the air and seal the bag, which is all done outside the machine. A heat sealer is often used to seal the pack.

Single Vacuum Chamber Machines[edit]

File:Vacuum Packaging Machine.webm

This video shows vacuum packaging of organic rice.

Tabletop Vacuum Packaging Machine

Single chamber sealers require the entire product to be placed within the machine. Like external sealers, a plastic bag is typically used for packaging. Once the product is placed in the machine, the lid is closed and air is removed. Then, there is a heat seal inside the chamber that will seal the bag, after sealing the bag the chamber is refilled with air by the automatic opening of a vent to the outside. This oncoming pressure squeezes all remaining air in the bag. The lid is then opened and the product removed. Chamber sealers are typically used for low-to-medium-volume packaging, and also have the capability to vacuum seal liquids.

Double Vacuum Chamber Machines[edit]

Double Chamber Vacuum Packaging Machine

Double chamber sealers require the entire product to be placed in a plastic bag within the machine. Once the product is placed in the machine on the seal bar, the lid is closed and air is removed. Then a seal bar inside the chamber seals the product in the bag, after sealing the bag the chamber is refilled with air by the automatic opening of a vent to the outside. This oncoming pressure squeezes all remaining air in the bag. The lid is then opened and the product removed. Double chamber sealers are typically used for medium-volume packaging, and also have the capability to vacuum seal liquids. The lid generally swings from one side to another, increasing production speed over a single chamber model. Double chamber vacuum packaging machines generally have either spring-weighted lids or fully automatic lids.

Double chamber vacuum packaging machines are commonly used for:

  • Fresh Meat
  • Processed Meat
  • Cheese (hard and soft)
  • Candy & Chocolate
  • Empty Cans (it’s a example of atmospheric pressure)

Automatic Belt Vacuum Chamber Machines[edit]

Automatic Belt Vacuum Chamber Machine. Automatic belt vacuum chamber machines offer vastly increased speed and automation and accommodate large products.

Automatic belt chamber sealers require the entire product to be placed in a plastic bag or flow wrapped pouch within the machine. The product travels on the conveyor belt, it is automatically positioned in the machine on the seal bar, the lid is closed and air is removed. Then a seal bar inside the chamber seals the product in the bag. After sealing the bag, the chamber is refilled with air by the automatic opening of a vent to the outside. This oncoming pressure squeezes all remaining air in the bag. The lid is then opened and the product removed. Automatic belt vacuum chamber machines are typically used for high-speed packaging of large items, and also have the capability to vacuum seal liquids. The lid generally travels straight up and down.

Automatic belt vacuum chamber packaging machines are commonly used for:

  • Fresh Meat (large portions)
  • Processed Meat
  • Large Sausage logs
  • Cheese (hard and soft)

Thermoforming (rollstock) Vacuum Packaging Machines[edit]

Thermoform packaging machines are used in larger production facilities for vacuum packaging products.

Vacuum Packaging in large production facilities can be done with thermoforming machines. These are Form-Fill-Seal style machines that form the package from rolls of packaging film (webbing). Products are loaded into the thermoformed pockets, the top web is laid and sealed under a vacuum, producing vacuum packaged products. Thermoforming can greatly increase packaging production speed. Thermoformed plastics can be customized for size, color, clarity, and shape to fit products perfectly, creating a consistent appearance. Some common uses for Thermoforming in vacuum packaging include:

  • Fresh & Marinated Meat
  • Sausage
  • Cheese
  • Candy / Chocolate
  • Grain
  • Grab-and-Go Snacks (beef jerky, snack sticks)
  • Pharmaceutical and Medical Products
  • Coins / Collectables

Shelf life[edit]

Depending on the product, the shelf life of vacuum packaged products can exceed normal bagged or wrapped packages. Beef can last up to six weeks refrigerated, and much longer when frozen.[citation needed]

High Barrier Shrink Vacuum Bags[edit]

The amount of shelf life enhanced by a vacuum bag is dependent on the structure in the material. A standard vacuum bag is composed of a PA/PE structure where PA is for puncture resistance and PE is for sealing. The high barrier category includes the usage of more layers focused on the prevention of oxygen permeability, and therefore shelf life protection. There are two materials used in high barrier structures, polyvinylidene chloride (PVDC) and ethylene vinyl alcohol (EVOH). Shelf life indication can be effectively measured by how many cubic centimeters of oxygen can permeate through 1 square meter of material over a 24-hour period. A standard PA/PE bag allows on average 100 cubic centimeters, PVDC allows on average over 10, and EVOH on average 1 cubic centimeter. Multi-layer structures allow the ability to use strong oxygen-barrier materials for enhanced shelf life protection. The PremiumPack structure is a good example of EVOH based high barrier shrink material.

Preventing freezer burn[edit]

When foods are frozen without preparation, freezer burn can occur. It happens when the surface of the food is dehydrated, and this leads to a dried and leathery appearance. Freezer burn also ruins the flavor and texture of foods. Vacuum packing reduces freezer burn by preventing the food from exposure to the cold, dry air.

Sous-vide cooking[edit]

Vacuum packaging also allows for a special cooking method, sous-vide. Sous-vide, French for under vacuum, involves poaching food that is vacuum sealed in a plastic bag.

Food safety[edit]

In an oxygen-depleted environment, anaerobic bacteria can proliferate, potentially causing food-safety issues. Vacuum packing is often used in combination with other packaging and food processing techniques.

from wikipedia

Glass

Glass is a non-crystalline amorphous solid that is often transparent and has widespread practical, technological, and decorative usage in, for example, window panes, tableware, and optoelectronics. The most familiar, and historically the oldest, types of glass are “silicate glasses” based on the chemical compound silica (silicon dioxide, or quartz), the primary constituent of sand. The term glass, in popular usage, is often used to refer only to this type of material, which is familiar from use as window glass and in glass bottles. Of the many silica-based glasses that exist, ordinary glazing and container glass is formed from a specific type called soda-lime glass, composed of approximately 75% silicon dioxide (SiO2), sodium oxide (Na2O) from sodium carbonate (Na2CO3), calcium oxide, also called lime (CaO), and several minor additives.

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Many applications of silicate glasses derive from their optical transparency, giving rise to their primary use as window panes. Glass will transmit, reflect and refract light; these qualities can be enhanced by cutting and polishing to make optical lenses, prisms, fine glassware, and optical fibers for high speed data transmission by light. Glass can be coloured by adding metallic salts, and can also be painted and printed with vitreous enamels. These qualities have led to the extensive use of glass in the manufacture of art objects and in particular, stained glass windows. Although brittle, silicate glass is extremely durable, and many examples of glass fragments exist from early glass-making cultures. Because glass can be formed or moulded into any shape, it has been traditionally used for vessels: bowls, vases, bottles, jars and drinking glasses. In its most solid forms it has also been used for paperweights, marbles, and beads. When extruded as glass fiber and matted as glass wool in a way to trap air, it becomes a thermal insulating material, and when these glass fibers are embedded into an organic polymer plastic, they are a key structural reinforcement part of the composite material fiberglass. Some objects historically were so commonly made of silicate glass that they are simply called by the name of the material, such as drinking glasses and reading glasses.

Scientifically, the term “glass” is often defined in a broader sense, encompassing every solid that possesses a non-crystalline (that is, amorphous) structure at the atomic-scale and that exhibits a glass transition when heated towards the liquid state. Porcelains and many polymer thermoplastics familiar from everyday use are glasses. These sorts of glasses can be made of quite different kinds of materials than silica: metallic alloys, ionic melts, aqueous solutions, molecular liquids, and polymers. For many applications, like glass bottles or eyewear, polymer glasses (acrylic glass, polycarbonate or polyethylene terephthalate) are a lighter alternative than traditional glass.

Silicate glass

Ingredients

Silica (the chemical compound SiO2) is a common fundamental constituent of glass. In nature, vitrification of quartz occurs when lightning strikes sand, forming hollow, branching rootlike structures called fulgurite.

Fused quartz is a glass made from chemically-pure SiO2 (silica). It has excellent thermal shock characteristics, being able to survive immersion in water while red hot. However, its high melting-temperature (1723 °C) and viscosity make it difficult to work with.[1]Normally, other substances are added to simplify processing. One is sodium carbonate (Na2CO3, “soda”), which lowers the glass transition temperature. The soda makes the glass water-soluble, which is usually undesirable, so lime (calcium oxide [CaO], generally obtained from limestone), some magnesium oxide (MgO) and aluminium oxide (Al2O3) are added to provide for a better chemical durability. The resulting glass contains about 70 to 74% silica by weight and is called a soda-lime glass.[2] Soda-lime glasses account for about 90% of manufactured glass.

Most common glass contains other ingredients to change its properties. Lead glass or flint glass is more ‘brilliant’ because the increased refractive index causes noticeably more specular reflection and increased optical dispersion. Adding barium also increases the refractive index. Thorium oxide gives glass a high refractive index and low dispersion and was formerly used in producing high-quality lenses, but due to its radioactivity has been replaced by lanthanum oxide in modern eyeglasses.[citation needed] Iron can be incorporated into glass to absorb infrared energy, for example in heat absorbing filters for movie projectors, while cerium(IV) oxide can be used for glass that absorbs UV wavelengths.[3]

The following is a list of the more common types of silicate glasses, and their ingredients, properties, and applications:

  1. Fused quartz, also called fused silica glass, vitreous silica glass: silica (SiO2) in vitreous or glass form (i.e., its molecules are disordered and random, without crystalline structure). It has very low thermal expansion, is very hard, and resists high temperatures (1000–1500 °C). It is also the most resistant against weathering (caused in other glasses by alkali ions leaching out of the glass, while staining it). Fused quartz is used for high temperature applications such as furnace tubes, lighting tubes, melting crucibles, etc.
  2. Soda-lime-silica glass, window glass: silica + sodium oxide (Na2O) + lime (CaO) + magnesia (MgO) + alumina (Al2O3). Is transparent, easily formed and most suitable for window glass (see flat glass). It has a high thermal expansion and poor resistance to heat (500–600 °C). It is used for windows, some low temperature incandescent light bulbs, and tableware. Container glass is a soda-lime glass that is a slight variation on flat glass, which uses more alumina and calcium, and less sodium and magnesium which are more water-soluble. This makes it less susceptible to water erosion.
  3. Sodium borosilicate glass, Pyrex: silica + boron trioxide (B2O3) + soda (Na2O) + alumina (Al2O3). Stands heat expansion much better than window glass. Used for chemical glassware, cooking glass, car head lamps, etc. Borosilicate glasses (e.g. Pyrex) have as main constituents silica and boron trioxide. They have fairly low coefficients of thermal expansion (7740 Pyrex CTE is 3.25×10–6/°C[4] as compared to about 9×10−6/°C for a typical soda-lime glass[5]), making them more dimensionally stable. The lower coefficient of thermal expansion (CTE) also makes them less subject to stress caused by thermal expansion, thus less vulnerable to cracking from thermal shock. They are commonly used for reagent bottles, optical components and household cookware.
  4. Lead-oxide glass, crystal glass: silica + lead oxide (PbO) + potassium oxide (K2O) + soda (Na2O) + zinc oxide (ZnO) + alumina. Because of its high density (resulting in a high electron density) it has a high refractive index, making the look of glassware more brilliant (called “crystal”, though of course it is a glass and not a crystal). It also has a high elasticity, making glassware “ring”. It is also more workable in the factory, but cannot stand heating very well.
  5. Aluminosilicate glass: silica + alumina + lime + magnesia + barium oxide (BaO) + boric oxide (B2O3). Extensively used for fiberglass, used for making glass-reinforced plastics (boats, fishing rods, etc.) and for halogen bulb glass.
  6. Germanium oxide glass: alumina + germanium dioxide (GeO2). Extremely clear glass, used for fiber-optic waveguides in communication networks.[6] Light loses only 5% of its intensity through 1 km of glass fiber.[7]

Another common glass ingredient is crushed alkali glass or “cullet” ready for recycled glass. The recycled glass saves on raw materials and energy. Impurities in the cullet can lead to product and equipment failure. Fining agents such as sodium sulfate, sodium chloride, or antimony oxide may be added to reduce the number of air bubbles in the glass mixture.[2] Glass batch calculation is the method by which the correct raw material mixture is determined to achieve the desired glass composition.

Physical properties

Optical properties

Glass is in widespread use largely due to the production of glass compositions that are transparent to visible light. In contrast, polycrystalline materials do not generally transmit visible light.[8] The individual crystallites may be transparent, but their facets (grain boundaries) reflect or scatter light resulting in diffuse reflection. Glass does not contain the internal subdivisions associated with grain boundaries in polycrystals and hence does not scatter light in the same manner as a polycrystalline material. The surface of a glass is often smooth since during glass formation the molecules of the supercooled liquid are not forced to dispose in rigid crystal geometries and can follow surface tension, which imposes a microscopically smooth surface. These properties, which give glass its clearness, can be retained even if glass is partially light-absorbing—i.e., colored.[9]

Glass has the ability to refract, reflect, and transmit light following geometrical optics, without scattering it. It is used in the manufacture of lenses and windows. Common glass has a refraction index around 1.5. This may be modified by adding low-density materials such as boron, which lowers the index of refraction (see crown glass), or increased (to as much as 1.8) with high-density materials such as (classically) lead oxide (see flint glass and lead glass), or in modern uses, less toxic oxides of zirconium, titanium, or barium. These high-index glasses (inaccurately known as “crystal” when used in glass vessels) cause more chromatic dispersion of light, and are prized for their diamond-like optical properties.

According to Fresnel equations, the reflectivity of a sheet of glass is about 4% per surface (at normal incidence in air), and the transmissivity of one element (two surfaces) is about 90%. Glass with high germanium oxide content also finds application in optoelectronics—e.g., for light-transmitting optical fibers.

Other properties

In the process of manufacture, silicate glass can be poured, formed, extruded and molded into forms ranging from flat sheets to highly intricate shapes. The finished product is brittle and will fracture, unless laminated or specially treated, but is extremely durable under most conditions. It erodes very slowly and can withstand the action of water. It is resilient to chemical attack and is an ideal material for the manufacture of containers for foodstuffs and most chemicals.

Contemporary production

Following the glass batch preparation and mixing, the raw materials are transported to the furnace. Soda-lime glass for mass production is melted in gas fired units. Smaller scale furnaces for specialty glasses include electric melters, pot furnaces, and day tanks.[2]After melting, homogenization and refining (removal of bubbles), the glass is formed. Flat glass for windows and similar applications is formed by the float glass process, developed between 1953 and 1957 by Sir Alastair Pilkington and Kenneth Bickerstaff of the UK’s Pilkington Brothers, who created a continuous ribbon of glass using a molten tin bath on which the molten glass flows unhindered under the influence of gravity. The top surface of the glass is subjected to nitrogen under pressure to obtain a polished finish.[10]Container glass for common bottles and jars is formed by blowing and pressing methods. This glass is often slightly modified chemically (with more alumina and calcium oxide) for greater water resistance. Further glass forming techniques are summarized in the table Glass forming techniques.

Once the desired form is obtained, glass is usually annealed for the removal of stresses. Surface treatments, coatings or lamination may follow to improve the chemical durability (glass container coatings, glass container internal treatment), strength (toughened glass, bulletproof glass, windshields), or optical properties (insulated glazing, anti-reflective coating).

Color

Color in glass may be obtained by addition of electrically charged ions (or color centers) that are homogeneously distributed, and by precipitation of finely dispersed particles (such as in photochromic glasses).[11] Ordinary soda-lime glass appears colorless to the naked eye when it is thin, although iron(II) oxide (FeO) impurities of up to 0.1 wt%[12] produce a green tint, which can be viewed in thick pieces or with the aid of scientific instruments. Further FeO and Cr2O3 additions may be used for the production of green bottles. Sulfur, together with carbon and iron salts, is used to form iron polysulfides and produce amber glass ranging from yellowish to almost black.[13] A glass melt can also acquire an amber color from a reducing combustion atmosphere. Manganese dioxide can be added in small amounts to remove the green tint given by iron(II) oxide. When used in art glass or studio glass is colored using closely guarded recipes that involve specific combinations of metal oxides, melting temperatures and “cook” times. Most colored glass used in the art market is manufactured in volume by vendors who serve this market, although there are some glassmakers with the ability to make their own color from raw materials.

History of silicate glass

Main article: History of glass

Bohemian flashed and engraved ruby glass (19th-century)

Wine goblet, mid-19th century. Qajar dynasty. Brooklyn Museum.

Roman cage cup from the 4th century CE

Studio glass. Multiple colors within a single object increase the difficulty of production, as glasses of different colors have different chemical and physical properties when molten.

Naturally occurring glass, especially the volcanic glass obsidian, has been used by many Stone Age societies across the globe for the production of sharp cutting tools and, due to its limited source areas, was extensively traded. But in general, archaeological evidence suggests that the first true glass was made in coastal north Syria, Mesopotamia or ancient Egypt.[14] The earliest known glass objects, of the mid third millennium BCE, were beads, perhaps initially created as accidental by-products of metal-working (slags) or during the production of faience, a pre-glass vitreous material made by a process similar to glazing.[15]

Glass remained a luxury material, and the disasters that overtook Late Bronze Age civilizations seem to have brought glass-making to a halt. Indigenous development of glass technology in South Asia may have begun in 1730 BCE.[16] In ancient China, though, glassmaking seems to have a late start, compared to ceramics and metal work. The term glass developed in the late Roman Empire. It was in the Roman glassmaking center at Trier, now in modern Germany, that the late-Latin term glesum originated, probably from a Germanic word for a transparent, lustrous substance.[17] Glass objects have been recovered across the Roman empire in domestic, industrial and funerary contexts.[citation needed]

Glass was used extensively during the Middle Ages. Anglo-Saxon glass has been found across England during archaeological excavations of both settlement and cemetery sites. Glass in the Anglo-Saxon period was used in the manufacture of a range of objects including vessels, beads, windows and was also used in jewelry. From the 10th-century onwards, glass was employed in stained glass windows of churches and cathedrals, with famous examples at Chartres Cathedral and the Basilica of Saint Denis. By the 14th-century, architects were designing buildings with walls of stained glass such as Sainte-Chapelle, Paris, (1203–1248)[18] and the East end of Gloucester Cathedral.[19] Stained glass had a major revival with Gothic Revival architecture in the 19th-century. With the Renaissance, and a change in architectural style, the use of large stained glass windows became less prevalent. The use of domestic stained glass increased until most substantial houses had glass windows. These were initially small panes leaded together, but with the changes in technology, glass could be manufactured relatively cheaply in increasingly larger sheets. This led to larger window panes, and, in the 20th-century, to much larger windows in ordinary domestic and commercial buildings.

In the 20th century, new types of glass such as laminated glass, reinforced glass and glass bricks have increased the use of glass as a building material and resulted in new applications of glass. Multi-storey buildings are frequently constructed with curtain walls made almost entirely of glass. Similarly, laminated glass has been widely applied to vehicles for windscreens. While glass containers have always been used for storage and are valued for their hygienic properties, glass has been utilized increasingly in industry. Optical glass for spectacles has been used since the late Middle Ages. The production of lenses has become increasingly proficient, aiding astronomers as well as having other application in medicine and science. Glass is also employed as the aperture cover in many solar energy systems.

From the 19th century, there was a revival in many ancient glass-making techniques including cameo glass, achieved for the first time since the Roman Empire and initially mostly used for pieces in a neo-classical style. The Art Nouveau movement made great use of glass, with René Lalique, Émile Gallé, and Daum of Nancy producing colored vases and similar pieces, often in cameo glass, and also using luster techniques. Louis Comfort Tiffany in America specialized in stained glass, both secular and religious, and his famous lamps. The early 20th-century saw the large-scale factory production of glass art by firms such as Waterford and Lalique. From about 1960 onwards there have been an increasing number of small studios hand-producing glass artworks, and glass artists began to class themselves as in effect sculptors working in glass, and their works as part fine arts.

In the 21st century, scientists observing the properties of ancient stained glass windows, in which suspended nanoparticles prevent UV light from causing chemical reactions that change image colors, are developing photographic techniques that use similar stained glass to capture true color images of Mars for the 2019 ESA Mars Rover mission.[20]

Chronology of advances in architectural glass

  • 1226: “Broad Sheet” first produced in Sussex.
  • 1330: “Crown glass” for art work and vessels first produced in Rouen, France. “Broad Sheet” also produced. Both were also supplied for export.
  • 1500s: A method of making mirrors out of plate glass was developed by Venetian glassmakers on the island of Murano, who covered the back of the glass with a mercury-tin amalgam, obtaining near-perfect and undistorted reflection.
  • 1620: “Blown Plate” first produced in London. Used for mirrors and coach plates.
  • 1678: “Crown Glass” first produced in London. This process dominated until the 19th century.
  • 1843: An early form of “Float Glass” invented by Henry Bessemer, pouring glass onto liquid tin. Expensive and not a commercial success.
  • 1874: Tempered glass is developed by Francois Barthelemy Alfred Royer de la Bastie (1830-1901) of Paris, France by quenching almost molten glass in a heated bath of oil or grease.
  • 1888: “Machine Rolled” glass introduced allowing patterns to be introduced.
  • 1898: “Wired Cast” glass invented by Pilkington for use where safety or security was an issue.[citation needed]
  • 1959: “Float Glass” launched in UK. Invented by Sir Alastair Pilkington.[21]

Other types of glass

New chemical glass compositions or new treatment techniques can be initially investigated in small-scale laboratory experiments. The raw materials for laboratory-scale glass melts are often different from those used in mass production because the cost factor has a low priority. In the laboratory mostly pure chemicals are used. Care must be taken that the raw materials have not reacted with moisture or other chemicals in the environment (such as alkali or alkaline earth metal oxides and hydroxides, or boron oxide), or that the impurities are quantified (loss on ignition).[22] Evaporation losses during glass melting should be considered during the selection of the raw materials, e.g., sodium selenite may be preferred over easily evaporating SeO2. Also, more readily reacting raw materials may be preferred over relatively inert ones, such as Al(OH)3 over Al2O3. Usually, the melts are carried out in platinum crucibles to reduce contamination from the crucible material. Glass homogeneity is achieved by homogenizing the raw materials mixture (glass batch), by stirring the melt, and by crushing and re-melting the first melt. The obtained glass is usually annealed to prevent breakage during processing.[22][23]

To make glass from materials with poor glass forming tendencies, novel techniques are used to increase cooling rate, or reduce crystal nucleation triggers. Examples of these techniques include aerodynamic levitation (cooling the melt whilst it floats on a gas stream), splat quenching (pressing the melt between two metal anvils) and roller quenching (pouring the melt through rollers).

Network glasses

A CD-RW (CD). Chalcogenide glasses form the basis of rewritable CD and DVD solid-state memory technology.[24]

Some glasses that do not include silica as a major constituent may have physico-chemical properties useful for their application in fiber optics and other specialized technical applications. These include fluoride glasses, aluminosilicates, phosphate glasses, borate glasses, and chalcogenide glasses.

There are three classes of components for oxide glasses: network formers, intermediates, and modifiers. The network formers (silicon, boron, germanium) form a highly cross-linked network of chemical bonds. The intermediates (titanium, aluminium, zirconium, beryllium, magnesium, zinc) can act as both network formers and modifiers, according to the glass composition. The modifiers (calcium, lead, lithium, sodium, potassium) alter the network structure; they are usually present as ions, compensated by nearby non-bridging oxygen atoms, bound by one covalent bond to the glass network and holding one negative charge to compensate for the positive ion nearby. Some elements can play multiple roles; e.g. lead can act both as a network former (Pb4+ replacing Si4+), or as a modifier.

The presence of non-bridging oxygens lowers the relative number of strong bonds in the material and disrupts the network, decreasing the viscosity of the melt and lowering the melting temperature.

The alkali metal ions are small and mobile; their presence in glass allows a degree of electrical conductivity, especially in molten state or at high temperature. Their mobility decreases the chemical resistance of the glass, allowing leaching by water and facilitating corrosion. Alkaline earth ions, with their two positive charges and requirement for two non-bridging oxygen ions to compensate for their charge, are much less mobile themselves and also hinder diffusion of other ions, especially the alkalis. The most common commercial glasses contain both alkali and alkaline earth ions (usually sodium and calcium), for easier processing and satisfying corrosion resistance.[25] Corrosion resistance of glass can be achieved by dealkalization, removal of the alkali ions from the glass surface by reaction with e.g. sulfur or fluorine compounds. Presence of alkaline metal ions has also detrimental effect to the loss tangent of the glass, and to its electrical resistance; glasses for electronics (sealing, vacuum tubes, lamps…) have to take this in account.

Addition of lead(II) oxide lowers melting point, lowers viscosity of the melt, and increases refractive index. Lead oxide also facilitates solubility of other metal oxides and is used in colored glasses. The viscosity decrease of lead glass melt is very significant (roughly 100 times in comparison with soda glasses); this allows easier removal of bubbles and working at lower temperatures, hence its frequent use as an additive in vitreous enamels and glass solders. The high ionic radius of the Pb2+ ion renders it highly immobile in the matrix and hinders the movement of other ions; lead glasses therefore have high electrical resistance, about two orders of magnitude higher than soda-lime glass (108.5 vs 106.5 Ohm·cm, DC at 250 °C). For more details, see lead glass.[26]

Addition of fluorine lowers the dielectric constant of glass. Fluorine is highly electronegative and attracts the electrons in the lattice, lowering the polarizability of the material. Such silicon dioxide-fluoride is used in manufacture of integrated circuits as an insulator. High levels of fluorine doping lead to formation of volatile SiF2O and such glass is then thermally unstable. Stable layers were achieved with dielectric constant down to about 3.5–3.7.[27]

Amorphous metals

Samples of amorphous metal, with millimeter scale

In the past, small batches of amorphous metals with high surface area configurations (ribbons, wires, films, etc.) have been produced through the implementation of extremely rapid rates of cooling. This was initially termed “splat cooling” by doctoral student W. Klement at Caltech, who showed that cooling rates on the order of millions of degrees per second is sufficient to impede the formation of crystals, and the metallic atoms become “locked into” a glassy state. Amorphous metal wires have been produced by sputtering molten metal onto a spinning metal disk. More recently a number of alloys have been produced in layers with thickness exceeding 1 millimeter. These are known as bulk metallic glasses (BMG). Liquidmetal Technologies sell a number of zirconium-based BMGs. Batches of amorphous steel have also been produced that demonstrate mechanical properties far exceeding those found in conventional steel alloys.[28][29][30]

In 2004, NIST researchers presented evidence that an isotropic non-crystalline metallic phase (dubbed “q-glass”) could be grown from the melt. This phase is the first phase, or “primary phase”, to form in the Al-Fe-Si system during rapid cooling. Interestingly, experimental evidence indicates that this phase forms by a first-order transition. Transmission electron microscopy (TEM) images show that the q-glass nucleates from the melt as discrete particles, which grow spherically with a uniform growth rate in all directions. The diffraction pattern shows it to be an isotropic glassy phase. Yet there is a nucleation barrier, which implies an interfacial discontinuity (or internal surface) between the glass and the melt.[31][32]

Electrolytes

Electrolytes or molten salts are mixtures of different ions. In a mixture of three or more ionic species of dissimilar size and shape, crystallization can be so difficult that the liquid can easily be supercooled into a glass. The best-studied example is Ca0.4K0.6(NO3)1.4.

Aqueous solutions

Some aqueous solutions can be supercooled into a glassy state, for instance LiCl:RH2O in the composition range 4<R<8.

Molecular liquids

A molecular liquid is composed of molecules that do not form a covalent network but interact only through weak van der Waals forces or through transient hydrogen bonds. Many molecular liquids can be supercooled into a glass; some are excellent glass formers that normally do not crystallize.

A widely known example is sugar glass.

Under extremes of pressure and temperature solids may exhibit large structural and physical changes that can lead to polyamorphic phase transitions.[33] In 2006 Italian scientists created an amorphous phase of carbon dioxide using extreme pressure. The substance was named amorphous carbonia(a-CO2) and exhibits an atomic structure resembling that of silica.[34]

Polymers

Important polymer glasses include amorphous and glassy pharmaceutical compounds. These are useful because the solubility of the compound is greatly increased when it is amorphous compared to the same crystalline composition. Many emerging pharmaceuticals are practically insoluble in their crystalline forms.[35]

Colloidal glasses

Concentrated colloidal suspensions may exhibit a distinct glass transition as function of particle concentration or density.[36][37][38]

In cell biology there is recent evidence suggesting that the cytoplasm behaves like a colloidal glass approaching the liquid-glass transition.[39][40] During periods of low metabolic activity, as in dormancy, the cytoplasm vitrifies and prohibits the movement to larger cytoplasmic particles while allowing the diffusion of smaller ones throughout the cell.[39]

Glass-ceramics

A high-strength glass-ceramic cooktop with negligible thermal expansion.

Glass-ceramic materials share many properties with both non-crystalline glass and crystalline ceramics. They are formed as a glass, and then partially crystallized by heat treatment. For example, the microstructure of whiteware ceramics frequently contains both amorphous and crystalline phases. Crystalline grains are often embedded within a non-crystalline intergranular phase of grain boundaries. When applied to whiteware ceramics, vitreous means the material has an extremely low permeability to liquids, often but not always water, when determined by a specified test regime.[41][42]

The term mainly refers to a mix of lithium and aluminosilicates that yields an array of materials with interesting thermomechanical properties. The most commercially important of these have the distinction of being impervious to thermal shock. Thus, glass-ceramics have become extremely useful for countertop cooking. The negative thermal expansion coefficient (CTE) of the crystalline ceramic phase can be balanced with the positive CTE of the glassy phase. At a certain point (~70% crystalline) the glass-ceramic has a net CTE near zero. This type of glass-ceramic exhibits excellent mechanical properties and can sustain repeated and quick temperature changes up to 1000 °C.[41][42]

Structure

As in other amorphous solids, the atomic structure of a glass lacks any long-range translational periodicity. Due to chemical bonding characteristics glasses do possess a high degree of short-range order with respect to local atomic polyhedra.[43]

The amorphous structure of glassy silica (SiO2) in two dimensions. No long-range order is present, although there is local ordering with respect to the tetrahedral arrangement of oxygen (O) atoms around the silicon (Si) atoms.

Formation from a supercooled liquid

Main article: Glass transition

In physics, the standard definition of a glass (or vitreous solid) is a solid formed by rapid melt quenching.[44][45][46][47][48] The term glass is often used to describe any amorphous solid that exhibits a glass transition temperature Tg. If the cooling is sufficiently rapid (relative to the characteristic crystallization time) then crystallization is prevented and instead the disordered atomic configuration of the supercooled liquid is frozen into the solid state at Tg. The tendency for a material to form a glass while quenched is called glass-forming ability. This ability can be predicted by the rigidity theory.[49] Generally, the structure of a glass exists in a metastable state with respect to its crystalline form, although in certain circumstances, for example in atactic polymers, there is no crystalline analogue of the amorphous phase.[50]

Some people consider glass to be a liquid due to its lack of a first-order phase transition[51][52] where certain thermodynamic variables such as volume, entropy and enthalpy are discontinuous through the glass transition range. The glass transition may be described as analogous to a second-order phase transition where the intensive thermodynamic variables such as the thermal expansivity and heat capacity are discontinuous.[45] Nonetheless, the equilibrium theory of phase transformations does not entirely hold for glass, and hence the glass transition cannot be classed as one of the classical equilibrium phase transformations in solids.[47][48]

Glass is an amorphous solid. It exhibits an atomic structure close to that observed in the supercooled liquid phase but displays all the mechanical properties of a solid.[51][53] The notion that glass flows to an appreciable extent over extended periods of time is not supported by empirical research or theoretical analysis (see viscosity of amorphous materials). Laboratory measurements of room temperature glass flow do show a motion consistent with a material viscosity on the order of 1017–1018 Pa s.[54]

Although the atomic structure of glass shares characteristics of the structure in a supercooled liquid, glass tends to behave as a solid below its glass transition temperature.[55] A supercooled liquid behaves as a liquid, but it is below the freezing point of the material, and in some cases will crystallize almost instantly if a crystal is added as a core. The change in heat capacity at a glass transition and a melting transition of comparable materials are typically of the same order of magnitude, indicating that the change in active degrees of freedom is comparable as well. Both in a glass and in a crystal it is mostly only the vibrational degrees of freedom that remain active, whereas rotational and translational motion is arrested. This helps to explain why both crystalline and non-crystalline solids exhibit rigidity on most experimental time scales.

Question dropshade.png Unsolved problem in physics :

What is the nature of the transition between a fluid or regular solid and a glassy phase? “The deepest and most interesting unsolved problem in solid state theory is probably the theory of the nature of glass and the glass transition.” —P.W. Anderson[56]
(more unsolved problems in physics )

Behavior of antique glass

The observation that old windows are sometimes found to be thicker at the bottom than at the top is often offered as supporting evidence for the view that glass flows over a timescale of centuries, the assumption being that the glass has exhibited the liquid property of flowing from one shape to another.[57] This assumption is incorrect, as once solidified, glass stops flowing. The reason for the observation is that in the past, when panes of glass were commonly made by glassblowers, the technique used was to spin molten glass so as to create a round, mostly flat and even plate (the crown glass process, described above). This plate was then cut to fit a window. The pieces were not absolutely flat; the edges of the disk became a different thickness as the glass spun. When installed in a window frame, the glass would be placed with the thicker side down both for the sake of stability and to prevent water accumulating in the lead cames at the bottom of the window.[58] Occasionally such glass has been found installed with the thicker side at the top, left or right.[59]

Mass production of glass window panes in the early twentieth century caused a similar effect. In glass factories, molten glass was poured onto a large cooling table and allowed to spread. The resulting glass is thicker at the location of the pour, located at the center of the large sheet. These sheets were cut into smaller window panes with nonuniform thickness, typically with the location of the pour centered in one of the panes (known as “bull’s-eyes”) for decorative effect. Modern glass intended for windows is produced as float glass and is very uniform in thickness.

Several other points can be considered that contradict the “cathedral glass flow” theory:

  • Writing in the American Journal of Physics, the materials engineer Edgar D. Zanotto states “…the predicted relaxation time for GeO2 at room temperature is 1032 years. Hence, the relaxation period (characteristic flow time) of cathedral glasses would be even longer.”[60] (1032 years is many times longer than the estimated age of the universe.)
  • If medieval glass has flowed perceptibly, then ancient Roman and Egyptian objects should have flowed proportionately more—but this is not observed. Similarly, prehistoric obsidian blades should have lost their edge; this is not observed either (although obsidian may have a different viscosity from window glass).[51]
  • If glass flows at a rate that allows changes to be seen with the naked eye after centuries, then the effect should be noticeable in antique telescopes. Any slight deformation in the antique telescopic lenses would lead to a dramatic decrease in optical performance, a phenomenon that is not observed.[51]
  • There are many examples of centuries-old glass shelving that has not bent, even though it is under much higher stress from gravitational loads than vertical window glass.[citation needed]

Gallery

from wikipedia

Borosilicate glass

Borosilicate glass is a type of glass with silica and boron trioxide as the main glass-forming constituents. Borosilicate glasses are known for having very low coefficients of thermal expansion (~3 × 10−6 K−1 at 20 °C), making them resistant to thermal shock, more so than any other common glass. Such glass is less subject to thermal stress and is commonly used for the construction of reagent bottles. Borosilicate glass is sold under such trade names as Borcam, Borosil, Suprax, Simax, Heatex, Endural, Schott, or Refmex, Kimble, and some (but not all) items sold under the trade name Pyrex.

click the link below to buy any of your home products from a needle to a sowing mechine from a spoon to refrigerator from a funnel to a wine cooler  at the best prices

Homes Products Store

History[edit]

Borosilicate glass was first developed by German glassmaker Otto Schott in the late 19th century. Otto Schott is also founder of today’s SCHOTT AG, which has sold borosilicate glass under the brand name DURAN since 1893. Another manufacturer of DURAN is the DURAN Group. After Corning Glass Works introduced Pyrex in 1915, the name became a synonym for borosilicate glass in the English-speaking world. However, borosilicate glass is the name of a glass family with various members tailoring completely different purposes. Most common today is borosilicate 3.3 glass like SCHOTT Duran and Pyrex by Corning.

The European manufacturer of Pyrex, Arc International, uses borosilicate glass in its Pyrex glass kitchen products;[1] however, the U.S. manufacturer of Pyrex kitchenware uses tempered soda-lime glass.[2] Thus Pyrex can refer to either soda-lime glass or borosilicate glass when discussing kitchen glassware, while Pyrex, Bomex, Duran, TGI and Simax all refer to borosilicate glass when discussing laboratory glassware. The real difference is the trademark and the company that owns the Pyrex name. The original Corning ware made of borosilicate glass was trademarked in capital letters (PYREX). When the kitchenware division was sold, the trademark was changed to lowercase (pyrex) and switched to low thermal-expansion soda-lime glass. The bottom of new kitchenware and old kitchenware can be inspected for an immediate difference.[citation needed] The scientific division of Pyrex has always been using borosilicate glass.[citation needed]

In addition to quartz, sodium carbonate and aluminium oxide traditionally used in glassmaking, boron is used in the manufacture of borosilicate glass. The composition of low-expansion borosilicate glass, such as those laboratory glasses mentioned above, is approximately 80% silica, 13% boric oxide, 4% sodium oxide and 12–13% aluminium oxide. Though more difficult to make than traditional glass due to the high melting temperature required (Corning conducted a major revamp of their operations to manufacture it), it is economical to produce. Its superior durability, chemical and heat resistance finds excellent use in chemical laboratory equipment, cookware, lighting and, in certain cases, windows.

Manufacturing process[edit]

Borosilicate glass is created by adding boric oxide[3] to the traditional glassmaker’s frit of silica sand, soda, and ground lime. Since borosilicate glass melts at a higher temperature than ordinary silicate glass, some new techniques were required for industrial production. Borrowing from the welding trade, burners combining oxygen with natural gas were required. The manufacturing process depends on the product geometry and can be differentiated between different methods like floating, tube drawing or moulding.

Physical characteristics[edit]

The common type of borosilicate glass used for laboratory glassware has a very low thermal expansion coefficient (3.3 × 10−6 K−1),[4] about one-third that of ordinary soda-lime glass. This reduces material stresses caused by temperature gradients, which makes borosilicate a more suitable type of glass for certain applications (see below). Fused quartzware is even better in this respect (having a fifteen times lower thermal expansion than soda-lime glass), however the difficulty of working with fused quartz makes quartzware much more expensive; borosilicate glass is a low-cost compromise. While more resistant to thermal shock than other types of glass, borosilicate glass can still crack or shatter when subjected to rapid or uneven temperature variations. When broken, borosilicate glass tends to crack into large pieces rather than shattering (it will snap rather than splinter)[citation needed].

The softening point (temperature at which viscosity is approximately 107.6 poise) of type 7740 Pyrex is 820 °C (1,510 °F).[5]

Borosilicate glass is less dense (about 2.23 g/cm3) than typical soda-lime glass due to the low atomic mass of boron.

The temperature differential that borosilicate glass can withstand before fracturing is about 165 °C (329 °F). This compares well with soda lime glass, which can withstand only a 37 °C (99 °F) change in temperature and is why typical kitchenware made from traditional soda-lime glass will shatter if a vessel containing boiling water is placed on ice, but Pyrex or other borosilicate glass laboratory will not.[6]

Optically, borosilicate glasses are crown glasses with low dispersion (Abbe numbers around 65) and relatively low refractive indices (1.51–1.54 across the visible range).

Glass families[edit]

For the purposes of classification, borosilicate glass can be roughly arranged in the following groups, according to their oxide composition (in mass fractions). Characteristic of borosilicate glasses is the presence of substantial amounts of silica (SiO2) and boric oxide (B2O3, >8%) as glass network formers. The amount of boric oxide affects the glass properties in a particular way. Apart from the highly resistant varieties (B2O3 up to a maximum of 13%), there are others that – due to the different way in which the boric oxide is incorporated into the structural network – have only low chemical resistance (B2O3 content over 15%). Hence we differentiate between the following subtypes.

Non-alkaline-earth borosilicate glass (borosilicate glass 3.3)

The B2O3 content for borosilicate glass is typically 12–13% and the SiO2 content over 80%. High chemical durability and low thermal expansion (3.3 × 10–6 K−1) – the lowest of all commercial glasses for large-scale technical applications – make this a multitalented glass material. High-grade borosilicate flat glasses are used in a wide variety of industries, mainly for technical applications that require either good thermal resistance, excellent chemical durability, or high light transmission in combination with a pristine surface quality. Other typical applications for different forms of borosilicate glass include glass tubing, glass piping, glass containers, etc. especially for the chemical industry.

Alkaline-earth-containing borosilicate glasses

In addition to about 75% SiO2 and 8–12% B2O3, these glasses contain up to 5% alkaline earths and alumina (Al2O3). This is a subtype of slightly softer glasses (as compared with non-alkaline-earth borosilicate glass), which have thermal expansions in the range (4.0–5.0) × 10–6 K−1.

High-borate borosilicate glasses

Glasses containing 15–25% B2O3, 65–70% SiO2, and smaller amounts of alkalis and Al2O3 as additional components, have low softening points and low thermal expansion. Sealability to metals in the expansion range of tungsten and molybdenum and high electrical insulation are their most important features. The increased B2O3 content reduces the chemical resistance; in this respect, high-borate borosilicate glasses differ widely from non-alkaline-earth and alkaline-earth borosilicate glasses. Among this glasses are also borosilicate glasses that transmit UV-ray down to 180 nm, which combine the best of the borosilicate glass- and the quartz world.[7]

Usage[edit]

Borosilicate glass has a wide variety of uses ranging from cookware to lab equipment, as well as a component of high-quality products such as implantable medical devices and devices used in space exploration

Health and science[edit]

Borosilicate beakers

Virtually all modern laboratory glassware is made of borosilicate glass. It is widely used in this application due to its chemical and thermal resistance and good optical clarity, but the glass can react with sodium hydride upon heating to produce sodium borohydride, a common laboratory reducing agent. Fused quartz is also found in some laboratory equipment when its higher melting point and transmission of UV are required (e.g. for tube furnace liners and UV cuvettes), but the cost and difficulty of working with quartz make it excessive for the majority of laboratory equipment.

Additionally, borosilicate tubing is used as the feedstock for the production of parenteral drug packaging, such as vials and pre-filled syringes, as well as ampoules and dental cartridges. The chemical resistance of borosilicate glass minimizes the migration of sodium ions from the glass matrix, thus making it well suited for injectable-drug applications. This type of glass is typically referred to as USP / EP JP Type I.

Borosilicate is widely used in implantable medical devices such as prosthetic eyes, artificial hip joints, bone cements, dental composite materials (white fillings)[8] and even in breast implants.

Many implantable devices benefit from the unique advantages of borosilicate glass encapsulation. Applications include veterinary tracking devices, neurostimulators for the treatment of epilepsy, implantable drug pumps, cochlear implants, and physiological sensors.[9]

Electronics[edit]

During the mid-twentieth century, borosilicate glass tubing was used to pipe coolants (often distilled water) through high-power vacuum-tube–based electronic equipment, such as commercial broadcast transmitters.

Borosilicate glasses also have an application in the semiconductor industry in the development of microelectromechanical systems (MEMS), as part of stacks of etched silicon wafers bonded to the etched borosilicate glass.

Cookware[edit]

Glass cookware is another common usage. Borosilicate glass is used for measuring cups, featuring screen printed markings providing graduated measurements. Borosilicate glass is sometimes used for high-quality beverage glassware. Borosilicate glass is thin and durable, microwave- and dishwasher-safe.

Lighting[edit]

Many high-quality flashlights use borosilicate glass for the lens. This increases light transmittance through the lens compared to plastics and lower-quality glass.

Several types of high-intensity discharge (HID) lamps, such as mercury-vapor and metal-halide lamps, use borosilicate glass as the outer envelope material.

New lampworking techniques led to artistic applications such as contemporary glass marbles. The modern studio glass movement has responded to color. Borosilicate is commonly used in the glassblowing form of lampworking and the artists create a range of products such as jewelry, kitchenware, sculpture, as well as for artistic glass smoking pipes.

Lighting manufacturers use borosilicate glass in their refractors.

Organic light-emitting diode (for display and lighting purposes) also uses borosilicate glass (BK7). The thicknesses of the BK7 glass substrates are usually less than 1 millimeter for the OLED fabrication. Due to its optical and mechanical characteristics in relation with cost, BK7 is a common substrate in OLEDs. However, depending on the application, soda-lime glass substrates of similar thicknesses are also used in OLED fabrication.

Optics[edit]

Most astronomical reflecting telescope use glass mirror components made of borosilicate glass because of its low coefficient of thermal expansion. This makes very precise optical surfaces possible that change very little with temperature, and matched glass mirror components that “track” across temperature changes and retain the optical system’s characteristics.

The optical glass most often used for making instrument lenses is Schott BK-7 (or the equivalent from other makers), a very finely made borosilicate crown glass[citation needed]. It is also designated as 517642 glass after its 1.517 refractive index and 64.2 Abbe number. Other less costly borosilicate glasses, such as Schott B270 or the equivalent, are used to make “crown-glass” eyeglass lenses. Ordinary lower-cost borosilicate glass, like that used to make kitchenware and even reflecting telescope mirrors, cannot be used for high-quality lenses because of the striations and inclusions common to lower grades of this type of glass. The maximal working temperature is 268 °C (514 °F). While it transitions to a liquid starting at 288 °C (550 °F) (just before it turns red-hot), it is not workable until it reaches over 538 °C (1,000 °F). That means that in order to industrially produce this glass, oxygen/fuel torches must be used. Glassblowers borrowed technology and techniques from welders.

Rapid prototyping[edit]

Borosilicate glass has become the material of choice for fused deposition modeling (FDM), or fused filament fabrication (FFF), build plates. Its low coefficient of expansion makes borosilicate glass, when used in combination with resistance-heating plates and pads, an ideal material for the heated build platform onto which plastic materials are extruded one layer at a time. The initial layer of build must be placed onto a substantially flat, heated surface to minimize shrinkage of some build materials (ABS, polycarbonate, polyamide, etc.) due to cooling after deposition. The build plate will cycle from room temperature to between 100 °C and 130 °C for each prototype that is built. The temperature, along with various coatings (Kapton tape, painter tape, hair spray, glue stick, ABS+acetone slurry, etc.), ensure that the first layer may be adhered to and remain adhered to the plate, without warping, as the first and subsequent layers cool following extrusion. Subsequently, following the build, the heating elements and plate are allowed to cool. The resulting residual stress formed when the plastic contracts as it cools, while the glass remains relatively dimensionally unchanged due to the low coefficient of thermal expansion, provides a convenient aid in removing the otherwise mechanically bonded plastic from the build plate. In some cases the parts self-separate as the developed stresses overcome the adhesive bond of the build material to the coating material and underlying plate.

Other[edit]

Aquarium heaters are sometimes made of borosilicate glass. Due to its high heat resistance, it can tolerate the significant temperature difference between the water and the nichrome heating element.

Specialty glass smoking pipes for cannabis and tobacco are made from borosilicate glass. The high heat resistance makes the pipes more durable.

Most premanufactured glass guitar slides are also made of borosilicate glass.

Borosilicate is also a material of choice for evacuated-tube solar thermal technology, because of its high strength and heat resistance.

The thermal insulation tiles on the Space Shuttle were coated with a borosilicate glass.[10]

Borosilicate glasses are used for immobilisation and disposal of radioactive wastes. In most countries high-level radioactive waste has been incorporated into alkali borosilicate or phosphate vitreous waste forms for many years, and vitrification is an established technology.[11] Vitrification is a particularly attractive immobilization route because of the high chemical durability of the vitrified glass product. This characteristic has been used by industry for centuries.[citation needed] The chemical resistance of glass can allow it to remain in a corrosive environment for many thousands and even millions of years.

Borosilicate glass tubing is used in specialty TIG welding torch nozzles in place of standard alumina nozzles. This allows a clear view of the arc in situations where visibility is limited.

Trade names[edit]

Borosilicate glass is offered in slightly different compositions under different trade names:

  • Borofloat of Schott AG, a borosilicate glass, which is produced to flat glass in a float process.
  • BK7 of Schott, a borosilicate glass with a high level of purity. Main use in lens and mirrors for laser, cameras and telescopes.
  • Duran of DURAN Group, similar to Pyrex, Simax or Jenaer Glas.
  • Fiolax of Schott, main use for containers for pharmaceutical applications.
  • Ilmabor of TGI (2014 insolvency), main use for containers and equipment in laboratories and medicine.
  • Jenaer Glas of Zwiesel Kristallglas, formerly Schott AG. Main use for kitchenware.
  • Pyrex of Arc International Cookware, formerly Corning. Main use for kitchenware
  • Rasotherm of VEB Jenaer Glaswerk Schott & Genossen, for technical glass
  • Simax of Pegasus Industrial Specialties or Kavalier Glaswerke, similar to Pyrex or Jenaer Glas
  • Willow Glass is an alkali free, thin and flexible borosilicate glass of Corning

Borosilicate nanoparticles[edit]

It was initially thought that borosilicate glass could not be formed into nanoparticles, since an unstable boron oxide precursor prevented successful forming of these shapes. However, in 2008 a team of researchers from the Swiss Federal Institute of Technology at Lausanne were successful in forming borosilicate nanoparticles of 100 to 500 nanometers in diameter. The researchers formed a gel of tetraethylorthosilicate and trimethoxyboroxine. When this gel is exposed to water under proper conditions, a dynamic reaction ensues which results in the nanoparticles.[12]

In lampworking[edit]

Borosilicate (or “boro”, as it is often called) is used extensively in the glassblowing process lampworking; the glassworker uses a burner torch to melt and form glass, using a variety of metal and graphite tools to shape it. Borosilicate is referred to as “hard glass” and has a higher melting point (approximately 3,000 °F / 1648 °C) than “soft glass”, which is preferred for glassblowing by beadmakers. Raw glass used in lampworking comes in glass rods for solid work and glass tubes for hollow work tubes and vessels/containers. Lampworking is used to make complex and custom scientific apparatus; most major universities have a lampworking shop to manufacture and repair their glassware. For this kind of “scientific glassblowing”, the specifications must be exact and the glassblower must be highly skilled and able to work with precision. Lampworking is also done as art, and common items made include goblets, paper weights, pipes, pendants, compositions and figurines.

In 1968, English metallurgist John Burton brought his hobby of hand-mixing metallic oxides into borosilicate glass to Los Angeles. Burton began a glass workshop at Pepperdine College, with instructor Margaret Youd. A few of the students in the classes, including Suellen Fowler, discovered that a specific combination of oxides made a glass that would shift from amber to purples and blues, depending on the heat and flame atmosphere. Fowler shared this combination with Paul Trautman, who formulated the first small-batch colored borosilicate recipes. He then founded Northstar Glassworks in the mid-1980s, the first factory in the world devoted solely to producing colored borosilicate glass rods and tubes for use by artists in the flame. Trautman also developed the techniques and technology to make the small-batch colored boro that is used by a number of similar companies. [13] By the time Trautman sold Northstar in 2002, he had composed hundreds of his own recipes for colored borosilicate that are still in production today. In 2004, Trautman came back to making glass, founding Trautman Art Glass. At TAG he developed a number of newer colors that are also industry standards for the boro art community. [14] Fowler continues to teach lampworking and hand-mixing of color in the “Burton style” around the US and Europe.

Beadmaking[edit]

In recent years, with the resurgence of lampworking as a technique to make handmade glass beads, borosilicate has become a popular material in many glass artists’ studios. Borosilicate for beadmaking comes in thin, pencil-like rods. Northstar, Trautman Art Glass, Glass Alchemy and Momka’s Glass are popular manufacturers, although there are other brands available. The metals used to color borosilicate glass, particularly silver, often create strikingly beautiful and unpredictable results when melted in an oxygen-gas torch flame. Because it is more shock-resistant and stronger than soft glass, borosilicate is particularly suited for pipe making, as well as sculpting figures and creating large beads. The tools used for making glass beads from borosilicate glass are the same as those used for making glass beads from soft glass. Type 1 glass is used for buffer solution

from wikipedia

Bar stools

Bar stools are a type of tall chair, often with a foot rest to support the feet. The height and narrowness of bar stools makes them suitable for use at bars and high tables in pubs or bars. In the 2010s, bar stools are becoming more popular in homes, usually placed at the kitchen counter or at a home bar.[citation needed] Bar stools are becoming more popular in homes because they are available in varied styles. As well, bar stools allow for a higher view when eating, drinking, or socializing.

click the link below to buy any of your home products from a needle to a sowing mechine from a spoon to refrigerator from a funnel to a wine cooler  at the best prices

Homes Products Store

Types[edit]

There are many different types, construction materials and models. Bar stools are often made of wood or metal. There are bar stools with and without armrests, backs, and padding or upholstery on the seat surface. Bar stools can range from basic wooden designs to more complex ones with adjustable height. Extra tall and extra short are common features, as well as indoor bar stools and outdoor bar stools. Some bar stools have backs, while most do not. In commercial settings, swivel and floor mounted bar stools are common. Floor mounting renders the stool immovable, so it cannot be stolen or used as a weapon in a bar fight. Floor-mounted stools generally are mounted on a column, but stools with legs can also be secured to the floor using metal brackets.

The normal seat height for a bar stool is 30 in (76 cm) with a 26 in (66 cm) stool being used against kitchen counters. Extra tall 36 in (91 cm) stools are increasingly used in contemporary styles with high pub tables to create a visual effect in modern interiors. Counter height bar stools have a seat height of 24″ (61cm). By comparison a conventional dining chair seat height is 18 in (46 cm). Some bar stools use polyurethane foam as padding for comfort[citation needed]. Bar stools can be made from rattan or bamboo and these stools can be used to create a tiki bar effect. The retro styling of the 1950 and 1960s is popular in some bars and restaurants,[citation needed] which use chrome and vinyl stools combined with matching benches or diner chairs. Stacking stools are often favored for their space-saving qualities. Some establishments use matching bar stools and chairs.

Aluminum is often used outdoors. Stacking aluminum stools and patio chairs are used by commercial premises. Indoors, wood and upholstery are popular in traditional settings. Bar stools are used in pool or billiard halls and the style of chair customized for such use is often called a “spectator chair”. Bar stools are used in Ireland during weekends by followers of the English Premier League, a practice which led to the creation of the pejorative term “barstoolers” by supporters of the League of Ireland. Bar stools are a growth area in the consumer market and online purchasing is on the increase[citation needed]. Bar stools can be made to order and customers can specify a wide range of fabrics and finishes as well as specifying other options such as height and custom foot rests. Both wooden and metal bar stools, including stainless and chrome styles and adjustable height features are popular.[citation needed]

from wikipedia

Rubbing alcohol

Rubbing alcohol refers to either isopropyl alcohol (propan-2-ol) or ethanol based liquids,[1] or the comparable British Pharmacopoeia defined surgical spirit, with isopropyl alcohol products being the most widely available.

They are liquids used primarily as a topical antiseptic.[2] They also have many industrial and household uses.[3][4] The term “rubbing alcohol” has become a general non-specific term for either isopropyl alcohol (isopropanol) or ethyl alcohol (ethanol) rubbing-alcohol products.

The United States Pharmacopeia defines ‘isopropyl rubbing alcohol USP‘ as containing approximately 70 percent by volume of pure isopropyl alcohol and defines ‘rubbing alcohol USP’ as containing approximately 70 percent by volume of denatured alcohol.[5][6] In Ireland and the UK, the comparable preparation is surgical spirit B.P., which the British Pharmacopoeia defines as 95% methylated spirit, 2.5% castor oil, 2% diethyl phthalate, and 0.5% methyl salicylate.[7]Under its alternative name of “wintergreen oil”, methyl salicylate is a common additive to North American rubbing alcohol products.[8] Individual manufacturers are permitted to use their own formulation standards in which the ethanol content for retail bottles of rubbing alcohol is labeled as and ranges from 70-99% v/v.[9]

All rubbing alcohols are unsafe for human consumption: isopropyl rubbing alcohols do not contain the ethyl alcohol of alcoholic beverages; ethyl rubbing alcohols are based on denatured alcohol, which is a combination of ethyl alcohol and one or more bitter poisons that make the substance toxic.

Properties[edit]

All rubbing alcohols are volatile and flammable. They have an extremely bitter taste from additives. The specific gravity of Formula 23-H is between 0.8691 and 0.8771 at 15.56 °C (60.01 °F).

Isopropyl rubbing alcohols contain from 50% to 99% by volume of isopropyl alcohol, the remainder consisting of water. Boiling points vary with the proportion of isopropyl alcohol from 80 °C (176 °F) to 83 °C (181 °F); likewise freezing point vary from −32 °C (−26 °F) to −50 °C (−58 °F).[10] Surgical spirit BP boils at 80 °C (176 °F).[11]

Naturally colorless, products may contain color additives. They may also contain medically-inactive additives for fragrance, such as wintergreen oil (methyl salicylate),[12] or for other purposes.

US legislation[edit]

Main article: Denatured alcohol

To protect alcohol tax revenue in the United States, all preparations classified as Rubbing Alcohols (defined as those containing ethanol) must have poisonous additives to limit human consumption in accordance with the requirements of the US Treasury Department, Bureau of Alcohol, Tobacco, and Firearms, using Formula 23-H (8 parts by volume of acetone, 1.5 parts by volume of methyl isobutyl ketone, and 100 parts by volume of ethyl alcohol). It contains 87.5–91% by volume of absolute ethyl alcohol. The rest consists of water and the denaturants, with or without color additives, and perfume oils. Rubbing alcohol contains in each 100 ml more than 355 mg of sucrose octaacetate or more than 1.40 mg of denatonium benzoate. The preparation may be colored with one or more color additives. A suitable stabilizer may also be added.[13]

Warnings[edit]

Product labels for rubbing alcohol include a number of warnings about the chemical, including the flammability hazards and its intended use only as a topical antiseptic and not for internal wounds or consumption. It should be used in a well-ventilated area due to inhalation hazards. Poisoning can occur from ingestion, inhalation, absorption, or consumption of rubbing alcohol.[14][15]

from wikipedia

Rubber

Natural rubber, also called India rubber or caoutchouc, as initially produced, consists of polymers of the organic compound isoprene, with minor impurities of other organic compounds, plus water. Malaysia and Indonesia are two of the leading rubber producers. Forms of polyisoprene that are used as natural rubbers are classified as elastomers.

Currently, rubber is harvested mainly in the form of the latex from the rubber tree or others. The latex is a sticky, milky colloid drawn off by making incisions in the bark and collecting the fluid in vessels in a process called “tapping”. The latex then is refined into rubber ready for commercial processing. In major areas, latex is allowed to coagulate in the collection cup. The coagulated lumps are collected and processed into dry forms for marketing.

Natural rubber is used extensively in many applications and products, either alone or in combination with other materials. In most of its useful forms, it has a large stretch ratio and high resilience, and is extremely waterproof.[1]

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Hevea brasiliensis[edit]

The major commercial source of natural rubber latex is the Pará rubber tree (Hevea brasiliensis), a member of the spurge family, Euphorbiaceae. This species is preferred because it grows well under cultivation. A properly managed tree responds to wounding by producing more latex for several years.

Congo rubber[edit]

Congo rubber, formerly a major source of rubber, came from vines in the genus Landolphia (L. kirkii, L. heudelotis, and L. owariensis).[2] These cannot be cultivated, and the intense drive to collect latex from wild plants was responsible for many of the atrocities committed under the Congo Free State.

Dandelion[edit]

Dandelion milk contains latex. The latex exhibits the same quality as the natural rubber from rubber trees. Yet in the wild types of dandelion, latex content is low and varies greatly. In Nazi Germany, research projects tried to use dandelions as a base for rubber production, but failed.[3] In 2013, by inhibiting one key enzyme and using modern cultivation methods and optimization techniques, scientists in the Fraunhofer Institute for Molecular Biology and Applied Ecology (IME) in Germany developed a cultivar that is suitable for commercial production of natural rubber.[4] In collaboration with Continental Tires, IME began a pilot facility.

Other[edit]

Many other plants produce forms of latex rich in isoprene polymers, though not all produce usable forms of polymer as easily as the Pará. Some of them require more elaborate processing to produce anything like usable rubber, and most are more difficult to tap. Some produce other desirable materials, for example gutta-percha (Palaquium gutta)[5] and chicle from Manilkara species. Others that have been commercially exploited, or at least showed promise as rubber sources, include the rubber fig (Ficus elastica), Panama rubber tree (Castilla elastica), various spurges (Euphorbia spp.), lettuce (Lactuca species), the related Scorzonera tau-saghyz, various Taraxacum species, including common dandelion (Taraxacum officinale) and Russian dandelion (Taraxacum kok-saghyz), and perhaps most importantly for its hypoallergenic properties, guayule (Parthenium argentatum). The term gum rubber is sometimes applied to the tree-obtained version of natural rubber in order to distinguish it from the synthetic version.[1]

History[edit]

The first use of rubber was by the indigenous cultures of Mesoamerica. The earliest archeological evidence of the use of natural latex from the Hevea tree comes the Olmec culture, in which rubber was first used for making balls for the Mesoamerican ballgame. Rubber was later used by the Maya and Aztec cultures – in addition to making balls Aztecs used rubber for other purposes such as making containers and to make textiles waterproof by impregnating them with the latex sap.[6][7]

The Pará rubber tree is indigenous to South America. Charles Marie de La Condamine is credited with introducing samples of rubber to the Académie Royale des Sciences of France in 1736.[8] In 1751, he presented a paper by François Fresneau to the Académie (published in 1755) that described many of rubber’s properties. This has been referred to as the first scientific paper on rubber.[8] In England, Joseph Priestley, in 1770, observed that a piece of the material was extremely good for rubbing off pencil marks on paper, hence the name “rubber”. It slowly made its way around England. In 1764 François Fresnau discovered that turpentine was a rubber solvent. Giovanni Fabbroni is credited with the discovery of naphtha as a rubber solvent in 1779.

South America remained the main source of the limited amounts of latex rubber used during much of the 19th century. The trade was heavily protected and exporting seeds from Brazil was a capital offense, although no law prohibited it. Nevertheless, in 1876, Henry Wickham smuggled 70,000 Pará rubber tree seeds from Brazil and delivered them to Kew Gardens, England. Only 2,400 of these germinated. Seedlings were then sent to India, Ceylon (Sri Lanka), Indonesia, Singapore, and British Malaya. Malaya (now Peninsular Malaysia) was later to become the biggest producer of rubber. In the early 1900s, the Congo Free State in Africa was also a significant source of natural rubber latex, mostly gathered by forced labor. Liberia and Nigeria started production.

In India, commercial cultivation was introduced by British planters, although the experimental efforts to grow rubber on a commercial scale were initiated as early as 1873 at the Calcutta Botanical Gardens. The first commercial Hevea plantations were established at Thattekadu in Kerala in 1902. In later years the plantation expanded to Karnataka, Tamil Nadu and the Andaman and Nicobar Islands of India. India today is the world’s 3rd largest producer and 4th largest consumer.[9]

In Singapore and Malaya, commercial production was heavily promoted by Sir Henry Nicholas Ridley, who served as the first Scientific Director of the Singapore Botanic Gardens from 1888 to 1911. He distributed rubber seeds to many planters and developed the first technique for tapping trees for latex without causing serious harm to the tree.[10] Because of his fervent promotion of this crop, he is popularly remembered by the nickname “Mad Ridley”.[11]

Pre-World War II[edit]

Charles Goodyear developed vulcanization in 1839, although Mesoamericans used stabilized rubber for balls and other objects as early as 1600 BC.[12][13]

Before World War II significant uses included door and window profiles, hoses, belts, gaskets, matting, flooring and dampeners (antivibration mounts) for the automotive industry. The use of rubber in car tires (initially solid rather than pneumatic) in particular consumed a significant amount of rubber. Gloves (medical, household and industrial) and toy balloons were large consumers of rubber, although the type of rubber used is concentrated latex. Significant tonnage of rubber was used as adhesives in many manufacturing industries and products, although the two most noticeable were the paper and the carpet industries. Rubber was commonly used to make rubber bands and pencil erasers.

Rubber produced as a fiber, sometimes called ‘elastic’, had significant value to the textile industry because of its excellent elongation and recovery properties. For these purposes, manufactured rubber fiber was made as either an extruded round fiber or rectangular fibers cut into strips from extruded film. Because of its low dye acceptance, feel and appearance, the rubber fiber was either covered by yarn of another fiber or directly woven with other yarns into the fabric. Rubber yarns were used in foundation garments.

While rubber is still used in textile manufacturing, its low tenacity limits its use in lightweight garments because latex lacks resistance to oxidizing agents and is damaged by aging, sunlight, oil and perspiration. The textile industry turned to neoprene (polymer of chloroprene), a type of synthetic rubber, as well as another more commonly used elastomer fiber, spandex (also known as elastane), because of their superiority to rubber in both strength and durability.

Properties[edit]

Rubber latex

Rubber exhibits unique physical and chemical properties. Rubber’s stress–strain behavior exhibits the Mullins effect and the Payne effect and is often modeled as hyperelastic. Rubber strain crystallizes.

Due to the presence of a double bond in each repeat unit, natural rubber is susceptible to vulcanisation and sensitive to ozone cracking.

The two main solvents for rubber are turpentine and naphtha (petroleum). Because rubber does not dissolve easily, the material is finely divided by shredding prior to its immersion.

An ammonia solution can be used to prevent the coagulation of raw latex.

Rubber begins to melt at approximately 180 °C (356 °F).

Elasticity[edit]

Main article: Rubber elasticity

On a microscopic scale, relaxed rubber is a disorganized cluster of erratically changing wrinkled chains. In stretched rubber, the chains are almost linear. The restoring force is due to the preponderance of wrinkled conformations over more linear ones. For the quantitative treatment see ideal chain, for more examples see entropic force.

Cooling below the glass transition temperature permits local conformational changes but a reordering is practically impossible because of the larger energy barrier for the concerted movement of longer chains. “Frozen” rubber’s elasticity is low and strain results from small changes of bond lengths and angles: this caused the Challenger disaster, when the American Space Shuttle‘s flattened o-rings failed to relax to fill a widening gap.[14] The glass transition is fast and reversible: the force resumes on heating.

The parallel chains of stretched rubber are susceptible to crystallization. This takes some time because turns of twisted chains have to move out of the way of the growing crystallites. Crystallization has occurred, for example, when, after days, an inflated toy balloon is found withered at a relatively large remaining volume. Where it is touched, it shrinks because the temperature of the hand is enough to melt the crystals.

Vulcanization of rubber creates disulfide bonds between chains, which limits the degrees of freedom and results in chains that tighten more quickly for a given strain, thereby increasing the elastic force constant and making the rubber harder and less extensible.

Chemical makeup[edit]

Chemical structure of cis-polyisoprene, the main constituent of natural rubber. Synthetic cis-polyisoprene and natural cis-polyisoprene are derived from different precursors, isopentenyl pyrophosphate and isoprene.

Latex is the polymer cis-1,4-polyisoprene – with a molecular weight of 100,000 to 1,000,000 daltons. Typically, a small percentage (up to 5% of dry mass) of other materials, such as proteins, fatty acids, resins, and inorganic materials (salts) are found in natural rubber. Polyisoprene can also be created synthetically, producing what is sometimes referred to as “synthetic natural rubber”, but the synthetic and natural routes are different.[1] Some natural rubber sources, such as gutta-percha, are composed of trans-1,4-polyisoprene, a structural isomer that has similar properties.

Natural rubber is an elastomer and a thermoplastic. Once the rubber is vulcanized, it turns into a thermoset. Most rubber in everyday use is vulcanized to a point where it shares properties of both; i.e., if it is heated and cooled, it is degraded but not destroyed.

The final properties of a rubber item depend not just on the polymer, but also on modifiers and fillers, such as carbon black, factice, whiting and others.

Biosynthesis[edit]

Rubber particles are formed in the cytoplasm of specialized latex-producing cells called laticifers within rubber plants.[15] Rubber particles are surrounded by a single phospholipid membrane with hydrophobic tails pointed inward. The membrane allows biosynthetic proteins to be sequestered at the surface of the growing rubber particle, which allows new monomeric units to be added from outside the biomembrane, but within the lacticifer. The rubber particle is an enzymatically active entity that contains three layers of material, the rubber particle, a biomembrane and free monomeric units. The biomembrane is held tightly to the rubber core due to the high negative charge along the double bonds of the rubber polymer backbone.[16] Free monomeric units and conjugated proteins make up the outer layer. The rubber precursor is isopentenyl pyrophosphate (an allylic compound), which elongates by Mg2+-dependent condensation by the action of rubber transferase. The monomer adds to the pyrophosphate end of the growing polymer.[17] The process displaces the terminal high-energy pyrophosphate. The reaction produces a cis polymer. The initiation step is catalyzed by prenyltransferase, which converts three monomers of isopentenyl pyrophosphate into farnesyl pyrophosphate.[18] The farnesyl pyrophosphate can bind to rubber transferase to elongate a new rubber polymer.

The required isopentenyl pyrophosphate is obtained from the mevalonate pathway, which derives from acetyl-CoA in the cytosol. In plants, isoprene pyrophosphate can also be obtained from the 1-deox-D-xyulose-5-phosphate/2-C-methyl-D-erythritol-4-phosphate pathway within plasmids.[19] The relative ratio of the farnesyl pyrophosphate initiator unit and isoprenyl pyrophosphate elongation monomer determines the rate of new particle synthesis versus elongation of existing particles. Though rubber is known to be produced by only one enzyme, extracts of latex host numerous small molecular weight proteins with unknown function. The proteins possibly serve as cofactors, as the synthetic rate decreases with complete removal.[20]

Production[edit]

Rubber is generally cultivated in large plantations. The image shows a coconut shell used in collecting latex, in plantations in Kerala, India.

Close to 28 million tons of rubber were produced in 2013, of which approximately 44% was natural. Since the bulk is synthetic, which is derived from petroleum, the price of natural rubber is determined, to a large extent, by the prevailing global price of crude oil.[21][22][23] Asia was the main source of natural rubber, accounting for about 94% of output in 2005. The three largest producers, Thailand, Indonesia (2.4 million tons)[24] and Malaysia, together account for around 72% of all natural rubber production. Natural rubber is not cultivated widely in its native continent of South America due to the existence of South American leaf blight, and other natural predators.

Cultivation[edit]

Rubber latex is extracted from rubber trees. The economic life period of rubber trees in plantations is around 32 years — up to 7 years of immature phase and about 25 years of productive phase.

The soil requirement is well-drained, weathered soil consisting of laterite, lateritic types, sedimentary types, nonlateritic red or alluvial soils.

The climatic conditions for optimum growth of rubber trees are:

  • Rainfall of around 250 centimetres (98 in) evenly distributed without any marked dry season and with at least 100 rainy days per year
  • Temperature range of about 20 to 34 °C, with a monthly mean of 25 to 28 °C
  • Atmospheric humidity of around 80%
  • About 2000 hours sunshine per year at the rate of six hours per day throughout the year
  • Absence of strong winds

Many high-yielding clones have been developed for commercial planting. These clones yield more than 2,000 kg of dry rubber per hectare per year, under ideal conditions.

Collection[edit]

A woman in Sri Lanka in the process of harvesting rubber.

In places such as Kerala where coconuts are in abundance, the half shell of coconut was used as the latex collection container. Glazed pottery or aluminium or plastic cups became more common in Kerala and other countries. The cups are supported by a wire that encircles the tree. This wire incorporates a spring so it can stretch as the tree grows. The latex is led into the cup by a galvanised “spout” knocked into the bark. Tapping normally takes place early in the morning, when the internal pressure of the tree is highest. A good tapper can tap a tree every 20 seconds on a standard half-spiral system, and a common daily “task” size is between 450 and 650 trees. Trees are usually tapped on alternate or third days, although many variations in timing, length and number of cuts are used. The latex, which contains 30–40% dry rubber, is in the bark, so the tapper must avoid cutting right through to the wood, else the growing cambial layer is damaged and the renewing bark becomes deformed, making later tapping difficult. It is usual to tap a pannel at least twice, sometimes three times, during the tree’s life. The economic life of the tree depends on how well the tapping is carried out, as the critical factor is bark consumption. A standard in Malaysia for alternate daily tapping is 25 cm (vertical) bark consumption per year. The latex-containing tubes in the bark ascend in a spiral to the right. For this reason, tapping cuts usually ascend to the left to cut more tubes.

The trees drip latex for about four hours, stopping as latex coagulates naturally on the tapping cut, thus blocking the latex tubes in the bark. Tappers usually rest and have a meal after finishing their tapping work, then start collecting the liquid “field latex” at about midday.

Field coagula[edit]

Mixed field coagula.

Smallholder’s lump at a remilling factory

The four types of field coagula are “cuplump”, “treelace”, “smallholders’ lump” and “earth scrap”. Each has significantly different properties.[25] Some trees continue to drip after the collection leading to a small amount of “cup lump” that is collected at the next tapping. The latex that coagulates on the cut is also collected as “tree lace”. Tree lace and cup lump together account for 10–20% of the dry rubber produced. Latex that drips onto the ground, “earth scrap”, is also collected periodically for processing of low-grade product.

Cup lump[edit]

Cup lump is the coagulated material found in the collection cup when the tapper next visits the tree to tap it again. It arises from latex clinging to the walls of the cup after the latex was last poured into the bucket, and from late-dripping latex exuded before the latex-carrying vessels of the tree become blocked. It is of higher purity and of greater value than the other three types.

Tree lace[edit]

Tree lace is the coagulum strip that the tapper peels off the previous cut before making a new cut. It usually has higher copper and manganese contents than cup lump. Both copper and manganese are pro-oxidants and can damage the physical properties of the dry rubber.

Smallholders’ lump[edit]

Smallholders’ lump is produced by smallholders who collect rubber from trees far from the nearest factory. Many Indonesian smallholders, who farm paddies in remote areas, tap dispersed trees on their way to work in the paddy fields and collect the latex (or the coagulated latex) on their way home. As it is often impossible to preserve the latex sufficiently to get it to a factory that processes latex in time for it to be used to make high quality products, and as the latex would anyway have coagulated by the time it reached the factory, the smallholder will coagulate it by any means available, in any container available. Some smallholders use small containers, buckets etc., but often the latex is coagulated in holes in the ground, which are usually lined with plastic sheeting. Acidic materials and fermented fruit juices are used to coagulate the latex — a form of assisted biological coagulation. Little care is taken to exclude twigs, leaves, and even bark from the lumps that are formed, which may also include tree lace.

Earth scrap[edit]

Earth scrap is material that gathers around the base of the tree. It arises from latex overflowing from the cut and running down the bark, from rain flooding a collection cup containing latex, and from spillage from tappers’ buckets during collection. It contains soil and other contaminants, and has variable rubber content, depending on the amount of contaminants. Earth scrap is collected by field workers two or three times a year and may be cleaned in a scrap-washer to recover the rubber, or sold off to a contractor who cleans it and recovers the rubber. It is of low quality.

Processing[edit]

Removing coagulum from coagulating troughs.

Latex coagulates in the cups if kept for long and must be collected before this happens. The collected latex, “field latex”, is transferred into coagulation tanks for the preparation of dry rubber or transferred into air-tight containers with sieving for ammoniation. Ammoniation preserves the latex in a colloidal state for longer periods of time.

Latex is generally processed into either latex concentrate for manufacture of dipped goods or coagulated under controlled, clean conditions using formic acid. The coagulated latex can then be processed into the higher-grade, technically specified block rubbers such as SVR 3L or SVR CV or used to produce Ribbed Smoke Sheet grades.

Naturally coagulated rubber (cup lump) is used in the manufacture of TSR10 and TSR20 grade rubbers. Processing for these grades is a size reduction and cleaning process to remove contamination and prepare the material for the final stage of drying.[26]

The dried material is then baled and palletized for storage and shipment.

Vulcanized rubber[edit]

Main article: Vulcanization

Torn latex rubber dry suit wrist seal

Natural rubber is often vulcanized, a process by which the rubber is heated and sulfur, peroxide or bisphenol are added to improve resistance and elasticity and to prevent it from perishing. Before World War II, carbon black was often used as an additive to rubber to improve its strength, especially in vehicle tires.

Transportation[edit]

Natural rubber latex is shipped from factories in south-west Asia, South America, and North Africa to destinations around the world. As the cost of natural rubber has risen significantly and rubber products are dense, the shipping methods offer the lowest cost per unit weight are preferred. Depending on destination, warehouse availability, and transportation conditions, some methods are preferred by certain buyers. In international trade, latex rubber is mostly shipped in 20-foot ocean containers. Inside the container, smaller containers are used to store the latex.[27]

Uses[edit]

Compression molded (cured) rubber boots before the flashes are removed

Uncured rubber is used for cements; for adhesive, insulating, and friction tapes; and for crepe rubber used in insulating blankets and footwear. Vulcanized rubber has many more applications. Resistance to abrasion makes softer kinds of rubber valuable for the treads of vehicle tires and conveyor belts, and makes hard rubber valuable for pump housings and piping used in the handling of abrasive sludge.

The flexibility of rubber is appealing in hoses, tires and rollers for devices ranging from domestic clothes wringers to printing presses; its elasticity makes it suitable for various kinds of shock absorbers and for specialized machinery mountings designed to reduce vibration. Its relative gas impermeability makes it useful in the manufacture of articles such as air hoses, balloons, balls and cushions. The resistance of rubber to water and to the action of most fluid chemicals has led to its use in rainwear, diving gear, and chemical and medicinal tubing, and as a lining for storage tanks, processing equipment and railroad tank cars. Because of their electrical resistance, soft rubber goods are used as insulation and for protective gloves, shoes and blankets; hard rubber is used for articles such as telephone housings, parts for radio sets, meters and other electrical instruments. The coefficient of friction of rubber, which is high on dry surfaces and low on wet surfaces, leads to its use for power-transmission belting and for water-lubricated bearings in deep-well pumps. Indian rubber balls or lacrosse balls are made of rubber.

Around 25 million tonnes of rubber are produced each year, of which 30 percent is natural.[28] The remainder is synthetic rubber derived from petrochemical sources. The top end of latex production results in latex products such as surgeons’ gloves, condoms, balloons and other relatively high-value products. The mid-range which comes from the technically specified natural rubber materials ends up largely in tires but also in conveyor belts, marine products, windshield wipers and miscellaneous goods. Natural rubber offers good elasticity, while synthetic materials tend to offer better resistance to environmental factors such as oils, temperature, chemicals and ultraviolet light. “Cured rubber” is rubber that has been compounded and subjected to the vulcanisation process to create cross-links within the rubber matrix.

Allergic reactions[edit]

Main article: Latex allergy

Some people have a serious latex allergy, and exposure to natural latex rubber products such as latex gloves can cause anaphylactic shock. The antigenic proteins found in Hevea latex may be deliberately reduced (though not eliminated)[29] through processing.

Latex from non-Hevea sources, such as Guayule, can be used without allergic reaction by persons with an allergy to Hevea latex.[30]

Some allergic reactions are not to the latex itself, but from residues of chemicals used to accelerate the cross-linking process. Although this may be confused with an allergy to latex, it is distinct from it, typically taking the form of Type IV hypersensitivity in the presence of traces of specific processing chemicals.[29][31]

Microbial degradation[edit]

Natural rubber is susceptible to degradation by a wide range of bacteria.[32][33][34][35][36][37][38][39]

from wikipedia

Box

Box (plural: boxes) describes a variety of containers and receptacles for permanent use as storage, or for temporary use, often for transporting contents.

Boxes may be made of durable materials such as wood or metal, or of corrugated fiberboard, paperboard, or other non-durable materials. The size may vary from very small (e.g., a matchbox) to the size of a large appliance. A corrugated box is a very common shipping container. When no specific shape is described, a box of rectangular cross-section with all sides flat may be expected, but a box may have a horizontal cross section that is square, elongated, round or oval; sloped or domed top surfaces, or non-vertical sides.

A decorative or storage box may be opened by raising, pulling, sliding or removing the lid, which may be hinged and/or fastened by a catch, clasp, or lock.

 

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Packaging box[edit]

An empty box made of corrugated fiberboard

A corrugated folder for pizza

Several types of boxes are used in packaging and storage.

  • A corrugated box is a shipping container made of corrugated fiberboard. These are most commonly used to transport and warehouse products during distribution, and are rated according to the strength of the material or the capacity of the finished box.
  • A folding carton (sometimes called a box) is fabricated from paperboard. The paperboard is printed (if necessary), die-cut and scored to form a blank. These are transported and stored flat, and erected at the point of filling. These are used to package a wide range of goods, intended either for one-time (non-resealable) use or as a storage box for the remaining goods.
    • A type of the folding carton is the gift box, used for birthday or Christmas gifts and often wrapped in decorative wrapping paper; this type is usually of much lighter construction than a similar-sized paperboard box meant for packaging and distribution.
  • A “set up” box (or rigid paperboard box) is made of stiffer paperboard, permanently glued together with paper skins that can be printed or colored. Unlike folding cartons, these are assembled at the point of manufacture and transported already “set-up”. Set-up boxes are more expensive than folding boxes and are typically used for protecting high value items such as cosmetics, watches or smaller consumer electronics.
  • A crate is a heavy duty shipping container originally made of wood. Crates are distinct from wooden boxes, also used as heavy duty shipping containers. For a wooden container to be a crate, all six of its sides must be put in place to result in the rated strength of the container. The strength of a wooden box, on the other hand, is rated based on the weight it can carry before the top or opening is installed.
    • A variant of the wooden box is the wooden wine box or wine crate, originally used for shipping and storing expensive wines,but nowadays for decorative or promotional purposes or as a storage box instead of for protection during shipping.
  • A bulk box is a large box often used in industrial environments. It is sized to fit well on a pallet.

Depending on locale and specific usage, the terms carton and box are sometimes used interchangeably.

The invention of large steel intermodal shipping containers has helped advance the globalization of commerce.[1][2]

Storage boxes[edit]

18th century German gold and mother of pearl snuffbox

Cake box

Boxes for storing various items in can often be very decorative, as they are intended for permanent use and sometimes are put on display in certain locations.

  • A jewelry (AmE) or jewellery (BrE) box, is a box for trinkets or jewels. It can take a very modest form with paper covering and lining, covered in leather and lined with satin, or be larger and more highly decorated.
  • A humidor is a special box for storing cigars at the proper humidity, by means of absorbent materials that retain and moderate moisture coming from the cigars. Powered boxes can also maintain the right temperature.[citation needed]
  • A “strong box” or safe, is a secure lockable box for storing money or other valuable items. The term “strong box” is sometimes used for safes that are no longer portable boxes but are installed in a wall or floor for increased security.
  • A toolbox is used for carrying tools of various kinds. The term implies a container meant for portability rather than just storage, for instance with hinged lids, clasps or locks, reinforced corners, and handles. Toolboxes are usually very sturdy, but unlike a shipping box containing dunnage, are not expected to fully protect their contents if the box is inverted or upended.
  • The common storage box for tools, instruments, glassware, artworks, etc. is a sturdy box made to be longer-lasting and better-finished than a shipping box or crate. For instance, a box might be a rigid paperboard box instead of a corrugated box. Or it could be a wooden box with a sanded surface and mitered corners instead of a crude crate construction. A storage box may or may not have dunnage or cushions that protect the contents if the box is upended or shaken, and usually does not have hinges, latches or locks, but simply a cover. Boxwood gets its name from its superior properties for manufacturing this type of box, although those properties are equally useful when making a decorative box.
  • A boxfile is used commonly in offices for storing papers and smaller files.

Electrical boxes[edit]

In electrical terminology, a “box” is used to contain and protect connections, thus:

Postal service boxes[edit]

  • Post box (British English and others, also written postbox), or mailbox (North American English and others) is a physical box used to collect mail that is to be sent to a destination. Variants of post boxes for outgoing mail include:

Boxes where postal workers deposit incoming mail for the recipient include:

  • Letter box (in the US usually called mailbox), positioned near or on the mail recipient’s home or place of work.
  • Post office box, (often abbreviated P.O. box or PO box), a box rented by the mail recipient to be an independent postal address, located in a post office or in the premises of a company offering such facilities. Self-service boxes are unlocked by the recipient, otherwise a postal clerk retrieves the mail.

A relay box is similar to a post or mail box, but totally locked; post office trucks deposit mail that is then retrieved and delivered by pedestrian mail carriers. In the United States, they are painted differently from collection boxes.

Booths that are sometimes called boxes[edit]

  • Call box
  • Police box, a booth for use by police in 20th century Britain.
  • Penalty box, a booth used in many ball-team sports where a player sits to serve the time of a given penalty.
  • Signal box, a building by a railway to coordinate and control railway signals.
  • Telephone box, a booth containing a public telephone.

Other boxes[edit]

Library book drop box

  • Ammunition box metal can or box for ammunition
  • Ballot box, a box in which votes (ballot papers) are deposited during voting.
  • Black box, something for which the internal operation is not described but its function is.
  • Event data recorder, commonly called a “black box”, a durable data-recording device found in some vehicles, used to assist in the investigation of an accident.
  • Box, informal reference to large box-shaped parts of a computer, such as the base unit or tower case of a personal computer.
  • Check box, on paper, normally to check off as opinion or option.
  • Coach Box or the driver’s seat on a carriage coach.
  • Dispatch box, (or despatch box), a box for holding official papers and transporting them.
  • Kōbako decorative storage box
  • First aid box is a collection of supplies and equipment for use in giving first aid to someone.[3]
  • Glory box or Hope Chest, a box or chest containing items typically stored by unmarried young women in anticipation of married life.
  • Jack-in-the-box, a children’s toy containing a surprise.
  • Lunch box, or “lunch pail” or “lunch kit”, a rigid container used for carrying food. Can also be decorative.
  • Mitre box, a woodworking tool used to guide a hand saw to make precise mitre cuts in a board.
  • Nest box, a substitute for a hole in a tree for birds to make a nest in.
  • Pandora’s box, in Greek mythology, a box containing the evils of mankind and also hope.
  • Pillbox, a special container for storing scheduled doses of one’s medications
  • Set-top box, a device used to decode and display TV signals.
  • Singing bird box, an objet d’art which contains within a miniature automaton singing bird.
  • Squeezebox, a musical instrument
  • Female box is a vulgar referral to the entire pubic area below the stomach usually for large hipped females.

Notes[edit]

Weighing scales

Weighing scales (or weigh scales or scales) are devices to measure weight or calculate mass. Spring balances or spring scales measure weight (force) by balancing the force due to gravity against the force on a spring, whereas a balance or pair of scales using a balance beam compares masses by balancing the weight due to the mass of an object against the weight of a known mass or masses. Either type can be calibrated to read in units of force such as newtons, or in units of mass such as kilograms, but the balance or pair of scales using a traditional balance beam to compare masses will read correctly for mass even if moved to a place with a different (non-zero) gravitational field strength (but would then not read correctly if calibrated in units of force), while the spring balance would read correctly in force in a different gravitational field strength (but would not read correctly if calibrated in units of mass).

Scales and balances are widely used in commerce, as many products are sold and packaged by weight. Very accurate balances, called analytical balances are used in scientific fields such as chemistry.

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History[edit]

Although records dating to the 1700s refer to spring scales for measuring weight, the earliest design for such a device dates to 1770 and credits Richard Salter, an early scale-maker.[1] Spring scales came into wide usage in the United Kingdom after 1840 when R. W. Winfield developed the candlestick scale for weighing letters and packages, required after the introduction of the Uniform Penny Post.[2] Postal workers could work more quickly with spring scales than balance scales because they could be read instantaneously and did not have to be carefully balanced with each measurement.

By the 1940s various electronic devices were being attached to these designs to make readings more accurate.[1][3] Load cells, small nodes that convert pressure (or force) to a digital signal, have their beginnings as early as the late nineteenth century, but it was not until the late twentieth century that they became accurate enough for widespread usage.[4]

Mechanical scales[edit]

Spring scales[edit]

Main article: Spring scale

A spring scale measures weight by reporting the distance that a spring deflects under a load. This contrasts to a balance, which compares the torque on the arm due to a sample weight to the torque on the arm due to a standard reference weight using a horizontal lever. Spring scales measure force, which is the tension force of constraint acting on an object, opposing the local force of gravity. They are usually calibrated so that measured force translates to mass at earth’s gravity. The object to be weighed can be simply hung from the spring or set on a pivot and bearing platform.

In a spring scale, the spring either stretches (as in a hanging scale in the produce department of a grocery store) or compresses (as in a simple bathroom scale). By Hooke’s law, every spring has a proportionality constant that relates how hard it is pulled to how far it stretches. Weighing scales use a spring with a known spring constant (see Hooke’s law) and measure the displacement of the spring by any variety of mechanisms to produce an estimate of the gravitational force applied by the object. Rack and pinion mechanisms are often used to convert the linear spring motion to a dial reading.

Spring scales have two sources of error that balances do not: the measured weight varies with the strength of the local gravitational force (by as much as 0.5% at different locations on Earth), and the elasticity of the measurement spring can vary slightly with temperature. With proper manufacturing and setup, however, spring scales can be rated as legal for commerce. To remove the temperature error, a commerce-legal spring scale must either have temperature-compensated springs or be used at a fairly constant temperature. To eliminate the effect of gravity variations, a commerce-legal spring scale must be calibrated where it is used.

Hydraulic or pneumatic scale[edit]

It is also common in high-capacity applications such as crane scales to use hydraulic force to sense weight. The test force is applied to a piston or diaphragm and transmitted through hydraulic lines to a dial indicator based on a Bourdon tube or electronic sensor.[5]

Digital scales[edit]

Digital bathroom scale[edit]

A digital bathroom scale is a type of electronic weighing machine, which is used to measure many readings including body fat, BMI, lean mass, muscle mass, water ratio along with body weight. The digital bathroom scale is a smart scale which has many functions like smartphone integration, cloud storage, fitness tracking, etc.[6]

Strain gauge scale[edit]

In electronic versions of spring scales, the deflection of a beam supporting the unknown weight is measured using a strain gauge, which is a length-sensitive electrical resistance. The capacity of such devices is only limited by the resistance of the beam to deflection. The results from several supporting locations may be added electronically, so this technique is suitable for determining the weight of very heavy objects, such as trucks and rail cars, and is used in a modern weighbridge.

Supermarket and other retail scale[edit]

These scales are used in the modern bakery, grocery, delicatessen, seafood, meat, produce and other perishable goods departments. Supermarket scales can print labels and receipts, mark weight/count, unit price, total price and in some cases tare.[7] Some modern supermarket scales print an RFID tag that can be used to track the item for tampering or returns. In most cases these types of scales have a sealed calibration so that the reading on the display is correct and cannot be tampered with. In the USA the scales are certified by the National Conference on Weights and Measures’ NTEP, in South Africa by the South African Bureau of Standards and in the UK by the International Organization of Legal Metrology.

Testing and certification[edit]

Scales used for trade purposes in the state of Florida, as this scale at the checkout in a cafeteria, are inspected for accuracy by the FDACS’s Bureau of Weights and Measures.

Most countries regulate the design and servicing of scales used for commerce. This has tended to cause scale technology to lag behind other technologies because expensive regulatory hurdles are involved in introducing new designs. Nevertheless, there has been a recent[when?] trend to “digital load cells” which are actually strain-gauge cells with dedicated analog converters and networking built into the cell itself. Such designs have reduced the service problems inherent with combining and transmitting a number of 20 millivolt signals in hostile environments.

Government regulation generally requires periodic inspections by licensed technicians using weights whose calibration is traceable to an approved laboratory. Scales intended for non-trade use such as those used in bathrooms, doctor’s offices, kitchens (portion control), and price estimation (but not official price determination) may be produced, but must by law be labelled “Not Legal for Trade” to ensure that they are not re-purposed in a way that jeopardizes commercial interest.[citation needed] In the United States, the document describing how scales must be designed, installed, and used for commercial purposes is NIST Handbook 44. Legal For Trade (LFT) certification usually approve the readability as repeatability/10 to ensure a maximum margin of error of 10%.[clarification needed][citation needed]

Because gravity varies by over 0.5% over the surface of the earth, the distinction between force due to gravity and mass is relevant for accurate calibration of scales for commercial purposes. Usually the goal is to measure the mass of the sample rather than its force due to gravity at that particular location.

Traditional mechanical balance-beam scales intrinsically measured mass. But ordinary electronic scales intrinsically measure the gravitational force between the sample and the earth, i.e. the weight of the sample, which varies with location. So such a scale has to be re-calibrated after installation, for that specific location, in order to obtain an accurate indication of mass.

Sources of error[edit]

Some of the sources of error in weighing are:

  • Buoyancy – Objects in air develop a buoyancy force that is directly proportional to the volume of air displaced. The difference in density of air due to barometric pressure and temperature creates errors.[8]
  • Error in mass of reference weight
  • Air gusts, even small ones, which push the scale up or down
  • Friction in the moving components that causes the scale to reach equilibrium at a different configuration than a frictionless equilibrium should occur.
  • Settling airborne dust contributing to the weight
  • Mis-calibration over time, due to drift in the circuit’s accuracy, or temperature change
  • Mis-aligned mechanical components due to thermal expansion or contraction of components
  • Magnetic fields acting on ferrous components
  • Forces from electrostatic fields, for example, from feet shuffled on carpets on a dry day
  • Chemical reactivity between air and the substance being weighed (or the balance itself, in the form of corrosion)
  • Condensation of atmospheric water on cold items
  • Evaporation of water from wet items
  • Convection of air from hot or cold items
  • Gravitational differences for a scale which measures force, but not for a balance.[9]
  • Vibration and seismic disturbances

Balance scales[edit]

Finely crafted Pan Balance or scales with boxed set of standardized gram weights.

The original form of a balance consisted of a beam with a fulcrum at its center. For highest accuracy, the fulcrum would consist of a sharp V-shaped pivot seated in a shallower V-shaped bearing. To determine the mass of the object, a combination of reference masses was hung on one end of the beam while the object of unknown mass was hung on the other end (see balance and steelyard balance). For high precision work, such as empirical chemistry, the center beam balance is still one of the most accurate technologies available, and is commonly used for calibrating test weights.

Mechanical balances[edit]

The balance (also balance scale, beam balance and laboratory balance) was the first mass measuring instrument invented.[10] In its traditional form, it consists of a pivoted horizontal lever with arms of equal length – the beam – and a weighing pan[11] suspended from each arm (hence the plural name “scales” for a weighing instrument). The unknown mass is placed in one pan and standard masses of known weight are added to the other pan until the beam is as close to equilibrium as possible. In precision balances, a more accurate determination of the mass is given by the position of a sliding mass moved along a graduated scale. Technically, a balance compares weight rather than mass, but, in a given gravitational field (such as Earth’s gravity), the weight of an object is proportional to its mass, so the standard “weights” used with balances are usually labeled in units of mass (g, kg, etc.).

Two 10-decagram masses

Masses of 50, 20, 1, 2, 5 and 10 grams

Unlike spring-based scales, balances are used for the precision measurement of mass as their accuracy is not affected by variations in the local gravitational field. (On Earth, for example, these can amount to ±0.5% between locations.[12]) A change in the strength of the gravitational field caused by moving the balance will not change the measured mass, because the moments of force on either side of the beam are affected equally. A balance will render an accurate measurement of mass at any location experiencing a constant gravity or acceleration.

Very precise measurements are achieved by ensuring that the balance’s fulcrum is essentially friction-free (a knife edge is the traditional solution), by attaching a pointer to the beam which amplifies any deviation from a balance position; and finally by using the lever principle, which allows fractional masses to be applied by movement of a small mass along the measuring arm of the beam, as described above. For greatest accuracy, there needs to be an allowance for the buoyancy in air, whose effect depends on the densities of the masses involved.

Aluminum, mass-produced balance scale (steelyard balance) sold and used throughout China: the scale can be inverted and held by the larger ring beneath the user’s right hand to produce greater leverage for heavier loads (Hainan Province, China)

To reduce the need for large reference masses, an off-center beam can be used. A balance with an off-center beam can be almost as accurate as a scale with a center beam, but the off-center beam requires special reference masses and cannot be intrinsically checked for accuracy by simply swapping the contents of the pans as a center-beam balance can. To reduce the need for small graduated reference masses, a sliding weight called a poise can be installed so that it can be positioned along a calibrated scale. A poise adds further intricacies to the calibration procedure, since the exact mass of the poise must be adjusted to the exact lever ratio of the beam.

For greater convenience in placing large and awkward loads, a platform can be floated on a cantilever beam system which brings the proportional force to a noseiron bearing; this pulls on a stilyard rod to transmit the reduced force to a conveniently sized beam.

One still sees this design in portable beam balances of 500 kg capacity which are commonly used in harsh environments without electricity, as well as in the lighter duty mechanical bathroom scale (which actually uses a spring scale, internally). The additional pivots and bearings all reduce the accuracy and complicate calibration; the float system must be corrected for corner errors before the span is corrected by adjusting the balance beam and poise.

A Roberval balance. The pivots of the parallelogram understructure makes it insensitive to load positioning away from center, so improves its accuracy, and ease of use.

Roberval balance[edit]

Main article: Roberval balance

In 1669 the Frenchman Gilles Personne de Roberval presented a new kind of balance scale to the French Academy of Sciences. This scale consisted of a pair of vertical columns separated by a pair of equal-length arms and pivoting in the center of each arm from a central vertical column, creating a parallelogram. From the side of each vertical column a peg extended. To the amazement of observers, no matter where Roberval hung two equal weight along the peg, the scale still balanced. In this sense, the scale was revolutionary: it evolved into the more-commonly encountered form consisting of two pans placed on vertical column located above the fulcrum and the parallelogram below them. The advantage of the Roberval design is that no matter where equal weights are placed in the pans, the scale will still balance.

A gear balance: A = Axle, F = Frame, G = Generator, GL = geared linkage, WL = weighted lever; counter weight added for balance, all the gear linkages free running on the rotating frame

Further developments have included a “gear balance” in which the parallelogram is replaced by any odd number of interlocking gears greater than 1 with alternating gears of the same size and with the central gear fixed to a stand and the and outside gears fixed pans, as well as the “sprocket gear balance” consisting of a bicycle-type chain looped around an odd number of sprockets with the central one fixed and the outermost two free to pivot and attached to a pan.

Because it has more moving joints which add friction, the Roberval balance is consistently less accurate than the traditional beam balance, but for many purposes this is compensated for by its usability.

Electronic devices[edit]

Microbalance[edit]

Main article: Microbalance

A microbalance is an instrument capable of making precise measurements of weight of objects of relatively small mass: of the order of a million parts of a gram.

Analytical balance[edit]

Main article: Analytical balance

Mettler digital analytical balance with 0.1 mg readability

An analytical balance is a class of balance designed to measure small mass in the sub-milligram range. The measuring pan of an analytical balance (0.1 mg or better) is inside a transparent enclosure with doors so that dust does not collect and so any air currents in the room do not affect the balance’s operation. This enclosure is often called a draft shield. The use of a mechanically vented balance safety enclosure, which has uniquely designed acrylic airfoils, allows a smooth turbulence-free airflow that prevents balance fluctuation and the measure of mass down to 1 μg without fluctuations or loss of product.[citation needed] Also, the sample must be at room temperature to prevent natural convection from forming air currents inside the enclosure from causing an error in reading. Single-pan mechanical substitution balance maintains consistent response throughout the useful capacity is achieved by maintaining a constant load on the balance beam, thus the fulcrum, by subtracting mass on the same side of the beam to which the sample is added.[citation needed]

Electronic analytical scales measure the force needed to counter the mass being measured rather than using actual masses. As such they must have calibration adjustments made to compensate for gravitational differences.[13] They use an electromagnet to generate a force to counter the sample being measured and outputs the result by measuring the force needed to achieve balance. Such measurement device is called electromagnetic force restoration sensor.[14]

Pendulum balance scales[edit]

Pendulum type scales do not use springs. This design uses pendulums and operates as a balance and is unaffected by differences in gravity. An example of application of this design are scales made by the Toledo Scale Company.[15]

Symbolism[edit]

The Ancient Egyptian Book of the Dead depicts a scene in which a scribe’s heart is weighed against the feather of truth.

The scales (specifically, a two-pan, beam balance) are one of the traditional symbols of justice, as wielded by statues of Lady Justice. This corresponds to the use in metaphor of matters being “held in the balance”. It has its origins in ancient Egypt.[citation needed]

Scales are also the symbol for the astrological sign Libra.

History of the balance scale[edit]

The balance scale is such a simple device that its usage likely far predates the evidence. What has allowed archaeologists to link artifacts to weighing scales are the stones for determining absolute weight. The balance scale itself was probably used to determine relative weight long before absolute weight.[10]

The oldest evidence for the existence of weighing scales dates to c. 2400–1800 B.C. in the Indus River valley (modern-day Pakistan). Prior to that, no banking was performed due to lack of scales. Uniform, polished stone cubes discovered in early settlements were probably used as weight-setting stones in balance scales. Although the cubes bear no markings, their weights are multiples of a common denominator. The cubes are made of many different kinds of stones with varying densities. Clearly their weight, not their size or other characteristics, was a factor in sculpting these cubes.[1] In Egypt, scales can be traced to around 1878 B.C., but their usage probably extends much earlier. Carved stones bearing marks denoting weight and the Egyptian hieroglyphic symbol for gold have been discovered, which suggests that Egyptian merchants had been using an established system of weight measurement to catalog gold shipments and/or gold mine yields. Although no actual scales from this era have survived, many sets of weighing stones as well as murals depicting the use of balance scales suggest widespread usage.[1]

Variations on the balance scale, including devices like the cheap and inaccurate bismar (unequal-armed scales),[16] began to see common usage by c. 400 B.C. by many small merchants and their customers. A plethora of scale varieties each boasting advantages and improvements over one another appear throughout recorded history, with such great inventors as Leonardo da Vinci lending a personal hand in their development.[3]

Even with all the advances in weighing scale design and development, all scales until the seventeenth century AD were variations on the balance scale.

Hybrid spring and balance scales[edit]

Elastic arm scale[edit]

The prototype of an elastic arm scale measuring a weight.

In 2014 a concept of hybrid scale has been introduced, the elastically deformable arm scale,[17] which is a combination between a spring scale and a beam balance, exploiting simultaneously both principles of equilibrium and deformation. In this scale, the rigid arms of a classical beam balance (for example a steelyard) are replaced with a flexible elastic rod in an inclined frictionless sliding sleeve. The rod can reach a unique free of sliding equilibrium when two vertical dead loads (or masses) are applied at its edges. Equilibrium, which would be impossible with rigid arms, is guaranteed because configurational forces develop at the two edges of the sleeve as a consequence of both the free sliding condition and the nonlinear kinematics of the elastic rod. This weight measuring device can also work without a counterweight.

from wikipedia

Plate

From Wikipedia, the free encyclopedia

Plate may refer to a range of objects, which have in common being thin and flat and also food or other products can be set on them.

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Cooking[edit]

Science[edit]

Biology / Medicine
Geology
Physics
  • A physical approximation of a theoretical plate in separation processes
  • Plate electrode, a type of electrode used in vacuum tubes
  • Plate theory, a theory used in continuum mechanics to explain thin solids
  • Wilhelmy plate, used to measure tension at an interface between air and a liquid or between two liquids

Technology[edit]

  • Wall plate, a vertical component used in building construction

Printing and photography[edit]

  • Printing plate, a printing medium:
    • in intaglio
    • in lithography
    • Plate, a (part of a) “tipped-in page“, a separately-printed page in a book used to carry one or more images rather than text.
      • Folding plate, a tipped-in, folded, larger-than-a-page illustration
    • Approach plate, a chart used by a pilot to perform an instrument approach and landing on a runway

Rairoading[edit]

  • Plate B, Plate C, … , Plate H, different loading gauges used on North American railroads. I

Metal plates[edit]

  • Plate (metal), a rectangular flat metal stock that is more than 6 mm or 0.25 in thick, not as thin as sheet metal

Places[edit]

Sport[edit]

Other uses[edit]

Cup

A cup is a small open container used for drinking and carrying drinks.[1][2] It may be made of wood, plastic, glass, clay, metal, stone, china or other materials,[3] and may have a stem, handles or other adornments. Cups are used for quenching thirst across a wide range of cultures and social classes,[4] and different styles of cups may be used for different liquids or in different situations.[5]

Cups have been used for thousands of years for the purpose of carrying food and drink, as well as for decoration.[6] They may also be used in certain cultural rituals and to hold objects not intended for drinking such as coin.

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Types[edit]

Names for different types of cups vary regionally and may overlap. Any transparent cup, regardless of actual composition, is likely to be called a “glass”; therefore, while a cup made of paper is a “paper cup”, a transparent one for drinking shots is called a “shot glass”, instead.

Cups for hot beverages[edit]

Teacups on saucers

While in theory, most cups are well suited to hold drinkable liquids, hot drinks like tea are generally served in either insulated cups or porcelain teacups.

Disposable cups[edit]

Disposable cups are intended to be used only once. They are often used by fast-food restaurants and coffee shops to serve beverages. Institutions that provide drinking water, such as offices and hospitals, may also use disposable cups for sanitary reasons.

Cups for alcoholic beverages[edit]

Some styles of cups are used primarily for alcoholic beverages such as beer, wine, cocktail, and liquor. There are over a dozen distinct styles of cups for drinking beer, depending on the precise variety of beer. The idea that a certain beer should be served in a cup of a certain shape may have been promulgated more for marketing purposes, but there very well may be some basis in fact behind it.[7] Wine glasses also come in different shapes, depending on the color and style of wine that is intended to be served in them.

Cultural significance and use of cups[edit]

Since cups have been an integral part of dining since time immemorial, they have become a valued part of human culture. The shape or image of a cup appears in various places in human cultures. Solo cups (especially red ones) carry strong cultural connotations, especially in America, generally referring to the consumption of alcoholic beverages.[9]

Religious use[edit]

A two-handled Natla (נַטְלָה) cup used for ritual washing in Judaism

In the Christian ritual of Communion, adherents drink from a cup of wine (or a wine substitute) to commemorate the Last Supper of Jesus.[10] A chalice is often used for this purpose.

Ancient Greek religious practices included libations. The rhyton was one cup used for libations.

Culinary use[edit]

The measuring cup, an adaptation of a simple cup, is a standard tool in cooking that has been in use at least as far back as Roman times. Apart from serving as drinking vessels, cups can be used as an alternative to bowls as a receptacle, especially, for soup. Recipes have been published for cooking various dishes in cups in the microwave.[11]

Heraldry[edit]

Chalices are sometimes used in heraldry, especially ecclesiastical heraldry. A Kronkåsa is a type of elaborate wooden cup which was used by the Swedish nobility during the Renaissance.

Child development[edit]

Drinking from a cup is a significant step on a baby’s path to becoming a toddler; it is recommended that children switch from bottles to cups between six months and one year of age.[12][13] Sippy cups are sometimes used for this transition.

Sports trophies[edit]

Many trophies take the form of a cup, often a loving cup. In sports, competitions themselves often take on the name of the cup-shaped trophy awarded.

Many trophies take the form of a large, decorated cup. In the case of the FIFA World Cup or the Sprint Cup Series, the competition itself may grow to take on the name of the trophy that is awarded to the winner. Owing to the common usage of cup-shaped trophies as prizes for the winners, a large number of national and international competitions are called “cups”.[14]

Games[edit]

In Tarot divination, the suit of cups is associated with the element of water and is regarded as symbolizing emotion, intuition, and the soul.[15][16] Cards that feature cups are often associated with love, relationships, fears, and desires.[15][17]

Various cups have been designed so that drinking out of them without spilling is a challenge. These are called puzzle cups.

The cup game involves rhythmically striking plastic cups.[18]

Promotional cups[edit]

In the developed world, cups are often distributed for promotional purposes. For example, a corporation might distribute cups with their logo at a trade show, or a city might hand out cups with slogans promoting recycling. There are companies that provide the service of printing slogans on cups.[19]

Antiquity[edit]

Cups improve on one’s hands for holding liquids

Cups are an obvious improvement on using cupped hands to hold liquids. They have almost certainly been used since before recorded history, and have been found at archaeological sites throughout the world. Prehistoric cups were sometimes fashioned from shells and hollowed out stones.[20]

An ancient stoneware (terracotta) cup from the Sa Huynh culture (modern Viet Nam)

In Mesopotamia, cups were made for a variety of purposes, possibly including the transportation and drinking of alcoholic beverages.[21] There is evidence the Roman Empire may have spread the use of cups throughout Europe, with notable examples including silver cups in Wales and a color-changing glass cup in ancient Thrace.[22][23] In England, cups have been discovered which date back to several thousand years, including the Rillaton Gold Cup, about 3,700 years old. Cups were used in the Americas several centuries prior to the European arrivals.[24] Around the Gulf of Mexico, Native American societies used the Horse conch for drinking cups, among other purposes.[25]

The King’s cup[edit]

Historically, monarchs have been concerned about assassination via poisoning. To avoid this fate, they often used dedicated cups, with cup-bearers to guard them. A “divining cup” was supposed to be able to detect poison. In the Bible, Joseph interprets a dream for Pharaoh‘s cup-bearer,[26] and a silver divining cup plays a key role in his reconciliation with his brothers.