Cooling plastic

Hot Colors, Cool Plastics 2004. Proceedings of a SPE Retec conference held Marco Island, FI., 20th.-21st. Sept.2004. 

Retec 2001. Hot Colors, Cool Plastics. Conference proceedings. 

Flashless mortar-type smokeless proplnt with calorific value 900—llOOcal/g is made from NC (12.2-13-4% N) 50-8, NG 12-44, cooling plasticizer 2—10, (0aNOC2H4)2N(NO2) 0—35%, small amt of stabilizer, small amt desensitizer and small amt inorganic salt to aid ignition. Thickness depends on burning time desired. Example of one compn used NC(13.25% N)... 

On cooling, plastic materials tend to contract or shrink considerably more than other materials such as metals, ceramics and glass. For example, a copper pipe will shrink by 0.01% if the temperature is reduced by 10°C. Under the same conditions, a high-density polyethylene pipe would shrink by 0.07%, and polypropylene and hard PVC pipes by 0.04%. In addition, surfaces of plastic materials cool before their cores. Such a situation leads to the initial contraction of plastic materials at surfaces, before significant change in dimension occurs in the bulk. The skins of moulded plastics tend to be stiffer than the bulk, so are more prone to degradation by mechanical action, e.g. flexing. 

On cooling, plastics tend to contract or shrink more than other materials found in museum collections including metals, ceramics and glass, and to... 

At the final filling stage, the melt flow is nearly static and the pressure buUds up to pack the mold cavity. In order to prevent overpacting or to iron out surface wrinkles and sinks caused by contraction of the cooling plastic, many machines have a secondary system to increase [Pg.258]

During the cooling of the component, the heat is drawn from it by the mould. The amount of heat involved depends on the component weight, the type of plastic (specific heat content), the ejection temperature, and the cycle frequency. The mould passes this heat to the environment (by heat conduction to the machine and by radiation or convection to the ambient air), if no special temperature control system is connected up. The higher the mould temperature, the greater the amount of heat released to the environment. So, when the machine starts up, the mould initially heats up to the temperature at which the amount of heat supplied by the solidifying and cooling plastic can be released to the environment. 

The injection, holding/packing pressure, cooling, plasticization and cycle times. 

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