The effect of melt temperature on internal stresses can be explained by the stress relaxation phenomena. Polymer melts at higher temperatures require more time to cool and solidify, which consequently provides more time for stress relaxation. The longer the time available for stress relaxation, the smaller the residual stresses frozen in the molding. The lower viscosity of the melt due to the higher melt temperature also causes stress relaxation to occur more rapidly. The slightly higher internal stresses observed at lower injection speeds are due to the orientation of the melt. A higher injection speed equates to a higher flow rate, which reduces the level of orientation in the molding. A lower orientation results to lower internal stresses.
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