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Pyrex glass is the material of choice for many laboratories due to affordability as quartz products are more expensive. Glassware products for lab use includes tubes, beakers and graduated cylinders.
The manufacturing process can be broken down into two phases. First, a large batch of molten glass composition is made. Next, the glass is fed into shaping machines to create different types of glassware. The process moves at tremendous speeds and is quite efficient.
Batching: Large batches of Pyrex glass are produced in a specified compounding area of the production plant. Here, glassmakers follow formula instructions and add the required raw materials in the correct proportions into large tanks. Prior to use, the raw materials are pulverized and granulated to a uniform particle size. They are stored in batch towers. The materials are mixed together and heated to temperatures over 2,912°F (1,600°C). This high temperature melts the ingredients and allows them to thoroughly mix to create molten glass. However, the mixture typically requires longer heating—up to 24 hours—to remove excess bubbles that can lead to a weaker structure.
Forming: The batch tanks are designed so that the molten glass will flow slowly toward the working end of the tank. This end of the tank is connected to continuous feed forming machines. As the glass moves from the tank, it looks like a thick, red-orange syrup. The forming machines work the material quickly because as it cools it becomes rigid and unworkable. Typical glass processing machines blow, press, draw, and roll it into various shapes. The forming process used depends on the final product. Glass blowing is used to create thin-walled products like bottles. A bubble of the molten glass is put inside a two-piece mold. Air is forced into the mold, which presses the glass against its sides. The glass cools inside the mold and conforms to the shape. Glass pressing is used to create thicker pieces of glass. The molten glass is put into a mold and a plunger is lowered which forces the glass to spread and fill the mold. Drawing is used to create tubing or rods. In this process molten glass is drawn down over a hollow cone called a mandrel. Air is blown through it to keep the tube from collapsing until the glass becomes rigid. For glass sheets, like windows, a rolling process is used.• After the product is formed, it is cooled and polished. It may then be decorated with various printing or markings and fitted with plastic pieces if necessary. The glass product is then checked for imperfections, put in protective boxes and shipped out to customers. Depending on the size of the batching tank, as much as 700,000 lb. (317,520 kg) of glass product can be produced in one year.
Quality control: Since the quality of the glass depends on the purity of the raw materials, manufacturers employ quality control chemists to test them. Physical characteristics are checked to make sure they adhere to previously determined specifications. For example, particle size is measured using appropriately meshed screens. Chemical composition is also determined with an IR or GC. Other simple checks that are done on the raw materials include color checks and odor evaluations. During production of a glass product, inspectors watch the glass products at specific points on the manufacturing line to ensure that each product looks correct. They notice things such as cracks, flaws or other imperfections. For certain products, the thickness of the glass is measured.
By products/waste: Since Pyrex is made from compounds that become oxides when heated, air pollution is a potential problem. A variety of byproducts may be released during manufacture including nitrates, sulfates, and chlorine. These chemicals can react with water to form acids. Acid rain has been shown to cause significant damage to manmade structures as well as natural ecosystems. One method glassmakers use to reduce pollution is by making glass compositions that have lower melting temperatures. Lower temperatures reduce the amount of volatilization thereby reducing the amount of gaseous pollutants. Another pollution control is the use of precipitators that are installed in chimneys. These devices help reduce air pollution by filtering out solids that persist in smoke and vapor created by the melting process. Waste-disposal drains are monitored to ensure that only allowable amounts of factory waste are released into the environment. This helps prevent water pollution. An additional method of pollution control is the use of ventilators. These devices are also called regenerators because they help recover and recycle heat energy consumed during manufacture. This has the double effect of reducing air pollution and lowering production costs. Other cost reducing and environmentally sound techniques employed include the use of electric heat instead of gas heat, and the incorporation of broken recycled glass during the production of new glass.
Applications and uses of pyrex (borosilicate) glass
Pyrex glass has a wide variety of applications ranging from cookware to lab equipment. Some are summarized below: Health and Science: 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. 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) 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 sensor.
Electronics: 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: 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: Lighting manufacturers use Pyrex glass in their refractors. Many high-quality flashlights use it for the lens to improve 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.
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: Pyrex glass is extensively used in optics. Many scientific lenses require a glass that remains both clear and strong when exposed to heat. Borosilicate microscope lenses and microscope slides allow scientists to analyze tiny organisms right under their nose and astronomers use it in telescopes that bring far off galaxies much closer to home. 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. Thus, Pyrex glass is often the material of choice for reflective optics in astronomy applications.
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. It is also designated as 517642 glass after its 1.517 refractive index and 64.2 Abbe number. Other less costly Pyrex 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: Pyrex 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.
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. The chemical resistance of glass can allow it to remain in a corrosive environment for many thousands and even millions of years.
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