MOULD HEATING

The main reason for extruding polystyrene is to prepare high-impact polystyrene sheet. Such sheet can be formed without difficulty by vacuum forming techniques. In principle the process consists of clamping the sheet above the mould, heating it so that it softens and becomes rubbery and then applying a vacuum to draw out the air between the mould and the sheet so that the sheet takes up the contours of the mould. 

In this method a mandrel is placed in the mould of an injection moulding machine, the mould heated, and thermoplastic forced in to flow round the mandrel and form a tube with a closed end mandrel and plastic then are removed and passed while still hot to the blowing mould, where air introduced through the mandrel blows the material to the shape required. 

Briefly, a measured amount of the thermosetting compound is placed in the cavity of a heated mould which is attached to the platens of an hydraulic press. The temperature of the mould may be (as an instance) 150°C. When the press is closed and heat and pressure applied the material flows and fills the cavity excess (known as flash ) escapes from the mould. Heat applied causes cross-linking and hardening of the material the moulding sets in the shape of the cavity and after a pre-determined time (perhaps three minutes) can be removed. Pre-heating the material (to, say, 70°C) can be employed as a method of shortening cycle times. 

Carbon fibre-reinforced polymer composites mould heating process... 

Hot Press Moulding—Heated matched dies are loaded with thermosetting compound and pressed together until cured. 

To inhibit mould without using additives, the wrapped rye bread may be exposed to microwaves or to dry heat. Acetic acid produced by bread cultures is an effective inhibitor of mould. Heat treatment amplifies this effect. 

Vacuum Forming. A sheet of material is placed over a porous mould, heated if necessary, and the air between the sheet and the mould is pumped out through the mould, forcing the sheet to conform to its shape. A variety of rigid shapes are made from ceramic fibre blankets... 

The tips of nozzles and the ends of heating elements are particularly susceptible to mechanical damage. Mould heating as for start-up (from a soft start) generally enables the nozzles to be removed easily and the manifold to be dismantled. It is recommended that ... 

Flexible PVC, calendered, extruded or injection moulded Heat stability up to 200°C Non migratory, non chalking light stability depending on application Cadmium pigments, red and yellow toners Azo-condensation Polycyclics Lead pigments Phthalocyanines Bis-arylamides Isoindolinones Iron oxide Dioxazin Special monoazos... 

The mould heating oven may be heated by direct gas flame, hot air, infra red, molten salts or fuel oil. The moulds are usually cooled by water immersion or sprays, and occasionally by cold air. Cooling is not critical but one must be aware of the effect of rapid cooling on the relative crystallinity of polymers. 

PSU/PES continues to find new applications in consumer products. For example, in 2002, Solvay announced that Keurig Premium Coffee Systems patented Coffee House Taste by the Cup brewing system was using injection moulded, heat- and residue-resistant hot water delivery components made from UDEL PSU resins. 

The mould heating and the curing time influence the last phase of heat supply. Only a small amount of heat is fed to the melt in order to form the part and to complete the forming process. 

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