Chapter 24, Cooling system equations

Cooling time Theoretically, cooling time is proportional to the square of the heaviest part wall thickness or the power of 1.6 for the largest runner diameter. That is: where the thermal diffusivity of polymer melt is defined as In other words, doubling the wall...

Chapter 25-1, Residual stress

A culprit in shrinkage and warpage problems Residual stress is a process-induced stress, frozen in a molded part. It can be either flow-induced or thermal-induced. Residual stresses affect a part similarly to externally applied stresses. If they are strong enough to...

Chapter 26-1,Shrinkage and warpage

Why do they occur? Shrinkage is inherent in the injection molding process. Shrinkage occurs because the density of polymer varies from the processing temperature to the ambient temperature (see Specific volume (pvT diagram)). During injection molding, the variation in...
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