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K. Wilczyński, A. Tyszkiewicz


Calculation of the cooling time of plastics materials in the injection moulding process


Polimery 1995, No 2, 109


DOI: dx.doi.org/10.14314/polimery.1995.109

Summary

The cooling of injection moulded pieces (their shape being approximated to a plate) in the mould was discussed and differences in cooling of amorphous and crystalline materials were pointed out. The possibilities of analytical and numerical calculations given by the Fourier equation were characterized and a numerical solution (by the finite differences method) of the problem of calculating the cooling time of plastics materials was presented. Basing on this solution, a computer program was elaborated for the calculation of temperature in consecutive layers of a moulded piece of crystalline or amorphous material in the function of the cooling time. This program was used for a computer simulation of the effect of injection moulding parameters (moulded piece thickness, mould temperature, injection moulding temperature) on the course of material cooling in the mould. Either polystyrene (PS) or low-density polyethylene (PE-LD) was used. It was possible in this way to establish the minimum cooling time of the moulding piece necessary to attain the assumed temperature of its removal from the mould. Corresponding analytical calculations were also carried out. In the case of an amorphous material (PS), differences in the results of analytical and numerical calculations are negligible, whereas in the case of a crystalline material (PE-LD) they are essential. It is suggested, therefore, to apply numerical solution in the case of crystalline materials.


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