Extrusion equipment

The most chemical-resistant plastic commercially available today is tetrafluoroethylene or TFE (Teflon). This thermoplastic is practically unaffected by all alkahes and acids except fluorine and chlorine gas at elevated temperatures and molten metals. It retains its properties up to 260°C (500°F). Chlorotrifluoroethylene or CTFE (Kel-F, Plaskon) also possesses excellent corrosion resistance to almost all acids and alkalies up to 180°C (350°F). A Teflon derivative has been developed from the copolymerization of tetrafluoroethylene and hexafluoropropylene. This resin, FEP, has similar properties to TFE except that it is not recommended for continuous exposures at temperatures above 200°C (400°F). Also, FEP can be extruded on conventional extrusion equipment, while TFE parts must be made by comphcated powder-metallurgy techniques. Another version is poly-vinylidene fluoride, or PVF2 (Kynar), which has excellent resistance to alkahes and acids to 150°C (300°F). It can be extruded. A more recent development is a copolymer of CTFE and ethylene (Halar). This material has excellent resistance to strong inorganic acids, bases, and salts up to 150°C. It also can be extruded. 

Acetal resins may be processed without difficulty on conventional injection moulding, blow moulding and extrusion equipment. The main points to be considered are ... 

Polyaryl ether ketones may be processed on conventional injection moulding and extrusion equipment, providing sufficiently high temperatures can be achieved. Melt temperatures required are typically 370°C for unreinforced PEEK, 390°C for reinforced PEEK and both unreinforced and reinforced PEK and unreinforced PEEKK, and 410°C for reinforced PEEKK. For the latter material a temperature profile from feed zone to nozzle would be... 

One type of block polymer is known as thermoplastic elastomers. They consist of a number of rubber blocks tied together by hard crystalline or glassy blocks. These materials can be processed in injection molding and extrusion equipment since the crystalline blocks melt or the glassy ones soften at high temperatures. However, at lower temperatures, such as at room temperature, the hard blocks behave very much as cross-links to reduce creep and stress relaxation. Thermoplastic elastomers have creep behavior between that of very lightly cross-linked rubbers and highly cross-... 

A profile extrusion line was required to increase its rate from the current 75 kg/h to about 230 kg/h in order to meet business demand. The extruder was 88.9 mm in diameter and was running a HIPS resin. Operation of the existing extrusion equipment, however, caused the extrudate temperature to be too high at rates higher than about 80 kg/h. The objective of this project was to increase the rate of the profile line from the current 75 kg/h to a maximum rate of 230 kg/h while maintaining the extrudate temperature below 195 °C. 

Brookfield, Ct., 2002, Session II, p.47-54, 27cm, 012 SEQUENTIAL REACTIVE BLENDING/ FOAMING OF PET IN EXTRUSION EQUIPMENT... 

A comparison is made between a 3.5 melt flow conventional polypropylene homopolymer (Profax 6523) and a 7.0 melt flow, high-melt-strength, foamable PP homopolymer in extensional flow. The importance of extensional or elongational viscosity in the foam process is demonstrated and the way in which the rheological differences permit the production of low-density foam on tandem extrusion equipment is shown. 6 refs. 

Usually antistatic agents develop their full activity only after a couple of days. The almost instantaneous antistatic action is extremely important during the production of films where operators are exposed with static built up on the extrusion equipment. Thus, the additive is useful in applications where dissipative properties are important, such as supported or unsupported sheets forming... 

V. M. Hovey, History of Extrusion Equipment for Rubber and Plastics, Wire and Wire Prod., 36, 192 (1961). 

Reactive extrusion is a new tool in polymer reaction engineering. From an environmental viewpoint, the need for only small quantities of volatile solvents, and consequent reduced cost, are positive aspects. From an economical point of view, the expensive extrusion equipment is compensated by there being no need to separate the polymer from the solvent The process is largely complicated by the occurrence of various nonlinear effects that may introduce instabilities into the process, these being of thermal, hydrodynamic, and chemical origin. 

Vinylidene Chloride Copolymer Foams. Low density, fine-celled VDC copolymer foams can be made by extrusion of a mixture of vinylidene chloride copolymer and a blowing agent at 120—150°C (190). The formulation must contain beat stabilizers, and the extrusion equipment must be made of noncatalytic metals to prevent accelerated decomposition of the polymer. The low melt viscosity of the VDC copolymer formulation limits the size of the foam sheet that can be extruded. 

The mixing process for concentrate pellet product production via Leistritz-type extrusion equipment is essentially identical to that of dry color product mixing. Once weigh-out has been completed, the formula is usually transported to a mixer where the ingredients must be mixed to uniformity. The ingredients are usually manually dumped into the mixer, after which the lid is sealed and the mixer is operated until the formula reaches the desired uniformity. After mixing, the formula is manually removed from the mixer and placed into a hopper or container with a controlled outlet and is ready for the next operation. 

The majority of thermoforming production is by roll fed machines. Sheet fed machines are used for the smaller volume applications. Larger production units have in house sheet extrusion equipment. Because of the complexities in synchronising sheet extrusion equipment and the thermoforming machines, the two processes can be carried out independently of each other, the extruded sheet being produced in advance of production schedules. 

Almost exclusively used for extrusion of PVC-U into pipe profile and sheet, extrusion equipment consists of a cylindrical barrel containing two close fitting, intermeshed, Archimedean screws. PVC dry blend is fed in via a hopper at the start of the screws and is conveyed forward, softened, sheared and finally gelled by rotation of the screws and the heat of the barrel. The resulting homogeneous viscous melt is forced through a heated die fitted to the exit end of the barrel. Thereafter the downstream equipment sizes or calibrates, cools and pulls off the product which is also cut to desired lengths. 

FEPR). A copolymer of tetrafluoroethylene, F2C CF2 and hexafluoropropylene, F8C.CF CF2, which can be melt processed in conventional molding and extrusion equipment for use as wire insulation, cable jacketing, shaped objects, gaskets, seals, etc. Stands temps up to 200°C and is tough at low temps... 

The large-scale manufacture of suppositories and pessaries uses either the fusion method where the drug is dispersed in a molten base and the mixture poured into molds to solidify, or the cold compression methodJ In the latter process, the medicament and cold-grated base, usually theobroma oil or witepsol base, are intimately mixed and placed in a cylinder. The mass is extruded by means of a piston through small holes that connect with the mold. The cavities are filled by pressure with the mass which is prevented from escaping by movable end plates. The plates are removed and the suppositories ejected by further extrusion. The extrusion equipment is chilled to prevent melting of the components due to the heat generated by the friction of compression. 

Figure 88. Extrusion equipment, (a) Excenter drive extrusion press, (b) screw extruder, (c) vacuum screw extruder...

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