Moulding high temperature

Continuous casting is used for materials based on iron, aluminium, copper, steel and noble metals. The molten strand passes through a cooled mould, which produces a shell of solidified metal. The skin of the metal is in contact with the mould. High temperature lubricants perform the essential role of preventing the solidified metal from sticking in the mould, which could then allow the molten core to escape. 

The polymer is not easy to process and in injection moulding melt temperatures of 300°C are employed. In order to prevent excess embrittlement by shock cooling of the melt, mould temperatures as high as 150°C may be used. The polymer may also be compression moulded at temperatures of 250-260°C. 

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... 

The early 1980s saw considerable interest in a new form of silicone materials, namely the liquid silicone mbbers. These may be considered as a development from the addition-cured RTV silicone rubbers but with a better pot life and improved physical properties, including heat stability similar to that of conventional peroxide-cured elastomers. The ability to process such liquid raw materials leads to a number of economic benefits such as lower production costs, increased ouput and reduced capital investment compared with more conventional rubbers. Liquid silicone rubbers are low-viscosity materials which range from a flow consistency to a paste consistency. They are usually supplied as a two-pack system which requires simple blending before use. The materials cure rapidly above 110°C and when injection moulded at high temperatures (200-250°C) cure times as low as a few seconds are possible for small parts. Because of the rapid mould filling, scorch is rarely a problem and, furthermore, post-curing is usually unnecessary. 

Additives such as antioxidants and photostabilizers of low-molecular weight face two major problems (1) they may evaporate during high temperature moulding and extrusion process or (2) they may migrate to the surface of the plastic and get extracted. There are, in general, three ways of overcoming these problems. 

Support materials were prepared by blending the fine power as stated in the later part of this case study. PVA was used as the binder. The organic macromolecule was used to create sufficient pores in the material when bumed out after a solid strong support was formed. Drying was performed in a high-temperature furnace. The shape and thickness of the support were based on the mass of the material and the way it was moulded. 

These results at 20° C refer to low stress moulded parts made from Makrolon. The chemical resistance of this material may be affected by mechanical stresses and high temperatures. The polymer High Density 3... 

Salt baths can also be applied to mould cleaning. They are efficient in use but have the hazards associated with high temperature caustic chemicals. 

Poly(butylene terephthalate) (PBT) is a semicrystalline, thermoplastic polyester which is completely analogous to PET except that it has a longer, more flexible butylene chain linkage which imparts a rapid crystallization rate, thus making PBT well suited to injection moulding processes. This polyester is used widely for electrical and electronic components due to its high temperature resistance and good electrical properties (Chapter 8). 

ISO 4894-1 1997 Plastics - Styrene/acrylonitrile (SAN) moulding and extrusion materials -Part 1 Designation system and basis for specifications ISO 4894-2 1995 Plastics - Styrene/acrylonitrile (SAN) moulding and extrusion materials -Part 2 Preparation of test specimens and determination of properties ISO 19220 2004 Plastics piping systems for soil and waste discharge (low and high temperature) inside buildings - Styrene copolymer blends (SAN PVC)... 

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