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Injection mold heating and cooling

When any substance is heated its internal energy increases as the result distance between atoms increases it move away from its equilibrium position. But atoms have tendency to come to equilibrium position because this is a stable position. So when the source of energy (heat) is removed mean cooling is start atoms try to contract and will try to reach its stable position. But to reach this position atom should have sufficient minimum energy .This energy is dependent on temperature.

As we know that heating and cooling also depend upon temperature difference between source and body. If this difference is high faster will heating or cooling rate.

So when heated plastic material is injected in the injection mold. In mold its cooling started now atom try to contract toward its equilibrium position. Plastic part shrink on the core and take the dimension of the core as core is solid enough it can not compress it. Heated plastic material losses its thermal energy through injection mold and water circulating in it.

When cooling time will be more material will lose its heat faster because metal (injection mold has high thermal conductivity (Ability to transfer heat) as compared to air. So when we remove component after long cooling time material lost most of its heat inside the injection mold and material atom will not have sufficient minimum energy so they can not contract further. This is why dimension is stable due to high cooling time.

When the cooling time is less, plastic material lost its heat less inside the injection mold. And also outside the injection mold component cooling rate is slow as compared inside the injection mold because air thermal conductivity less as compared to metal. Now material atom has high thermal energy and for more time. So now atom will have more tendency to contract and have more ability to come back to its equilibrium position. (Also shrinking time on core is less). This is how when cooling time is less chances of dimension disturbances increases.

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