Other forming processes

Shear rates during calendering range typically from 10 to 10 sec. The pressure and forces encountered within the nip region are affected by the characteristics of the material (rheology, 

A number of polyolefin blends are routinely calendered. TPO s consisting of blends of PP or PE with a-olefin random copolymer Oleflex ) are suitable. The copolymer is finely dispersed as a rubbery phase in the polyolefin matrix. The blend is processed at conditions similar to polyolefins. For calendering, typical melt temperature is 165-175°C. 

PP/EPDM blends Santoprene ), with their high melt viscosity and melt strength, are easily calendered. The material is normally premixed in a Banbury or other intensive mixer. The melt temperature should be about 190°C. Roll temperature should be about 70-120°C. Conventional four-roll calenders can produce quality sheet with thickness 0.4 to 1 mm. 

Thermoforming consists of forming a preheated plastic sheet or film into a desired shape against a mold surface. Forming can take place pneumatically or mechanically. In the first case, a differential air pressure is used, either vacuum on the mold side, compressed air on the other, or both. In the second case, the preheated sheet of material is pressed into the mold using either a preform, a plug, or by a combination of both. Viitually all thermoplastics can be thermoformed. However, because of limitations in the material characteristics, some can only be used for simple shapes with small draw ratios. 

Temperature of HIPS (Polystyrol ) or PS/PB blends (Styroplus ) during thermoforming is usually within the range 130-150°C. High draw ratios, e.g., 5 1, are common. It should be noted that PS, being an amorphous polymer with low heat capacity, requires less heat to reach the processing temperature than other commonly used plastics, thus it is a thermally efficient resin. 

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This review on vacuum thermoforming can be related to most of the other forming processes. With a vacuum system a sheet is subjected to heat to meet its optional processing temperature, or technique that forces it against the shape of a mold. The hot, pliable material is moved rapidly to the mold (for example, by gear drives) and/or is moved by an air pressure differential, which holds it in place as it cools. When the proper set temperature is reached, the formed part can be removed and still retain its shape. 

Electroformed mold n. A mold made by electroplating a model, which is subsequently removed from the metal deposit. The deposit is sometimes reinforced with cast or sprayed metal backings to increase its strength and rigidity. Such molds are used in slush casting of vinyl plastisols and other forming processes done at low pressures. 

It is possible with solvents of a particular composition to determine quantitatively the level of stress existing in certain TP moldings where molded-in stresses exist. The stresses need not be applied ones but can be residual (internal) stresses resulting from the molding or other forming process that was used to shape the plastic part. Solvent mixtures suitable for this type of test are available for materials such as PSs, PCs, and acrylics through resin suppliers, who can provide details. 

Can incorporate other forming processes, for example knurling, thread rolling and bending to produce complex parts at one machine. 

Under certain conditions of temperature and pressure, and in the presence of free water, hydrocarbon gases can form hydrates, which are a solid formed by the combination of water molecules and the methane, ethane, propane or butane. Hydrates look like compacted snow, and can form blockages in pipelines and other vessels. Process engineers use correlation techniques and process simulation to predict the possibility of hydrate formation, and prevent its formation by either drying the gas or adding a chemical (such as tri-ethylene glycol), or a combination of both. This is further discussed in SectionlO.1. 

Speckle shearing interferometry, or shearography, is a full field optical inspection teclmique that may be used for the nondestructive detection of surface and, sometimes, subsurface defects. Whilst being more sensitive in the detection of surface defects, it may also be considered for pipe inspection and the monitoring of internal conoslon. In contrast, laser ultrasound and other forms of ultrasound, are point by point measurement techniques, so that scanning facilities and significant data processing is required before information on local defects is extracted from any examination of extensive areas [1 - 3]. 

Direct Reduction. Direct reduction processes are distinguished from other ironmaking processes in that iron oxide is converted to metallic iron without melting. Because this product, called direct reduced iron (DRI), is soHd, it is most suitable for melting in an electric arc furnace (EAF) as a substitute for scrap (see Furnaces, electric). The briquetted form of DRI, hot briquetted iron (HBI) is used when the product is to be transported. Briquetting increases density and chemical stabiUty. The predominant direct reduction processes (MIDREX and HyL III) are based on natural gas as a fuel and reductant source. They are economically attractive in regions where natural gas is cheap and abundant, especially if iron ore is available nearby (see Iron BY DIRECT reduction). ... 

Arc wire utilizes two continuously fed 1.6-mm dia intersecting wires with a d-c arc maintained between the wire tips as they meet. Compressed gas (usually air) strips the molten metal from the tips and forms a directional spray stream. This process is widely used to spray most metals. Arc wire is the most economical process because of the wire feedstock. Moreover, it utilizes - 10% of the thermal energy of the other spray processes (0.4 vs 6.6 kWh/kg using stainless steel) because of the direct arc heating of the wire tips. 

Sulfur is produced from a variety of sources using many different techniques in many countries around the world. Worldwide changes have affected not only the sources of sulfur, but also the amounts consumed. Sulfur sources in the United States underwent significant changes during the 1980s. Voluntary sulfur from the Frasch process (mines) suppHed only 25% of the sulfur in the United States in 1995, compared to about 53% in 1980, whereas recovered or involuntary sulfur suppHed 63% of the sulfur in the United States in 1995, compared to 34% in 1980. About 12% is suppHed from other forms, primarily by metallurgy (21,33). 

Processing of baked and graphitized carbon. Properties of manufactured graphite, Appbcations of baked and graphitized carbon. Other forms of carbon and graphite. 

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