Question

16 Freezing of polyethylene. Low-density crystalline polyethylene is injected into a cold steel mold at 25°C, forming a sheet that is 6 mm thick. The polymer is injected at 120°C, and center must cool below 50°C before the part can be ejected without distortion. Compute the residence time required for the part in the mold before ejection to meet this requirement. Assume that there is perfect thermal contact between the mold and the part. Property Polymer Steel Mold 37.5 Thermal conductivity (W/m K) Density (kg/m3) Specific heat (J/kg K) 0.26 920 7730 1670610

Answer 1

Biot No. hs Ksdid /2 Heisler chart イ2 0-26 SUfme O LD 6i Nou we howe Bt 0.086

Coc fournies No. 0.8 F 08 오 LET et ime eud oll be 42-6o Seconds