Calculating Cooling Time…

I just received this question…

How do I estimate the cooling time? I located a chart referencing a proportionality constant of a polymer, is this the right way?

My Response
There are many helpful charts and factors, but these use too many assumptions and are just ways to avoid proper circulations.
Proper cooling time estimations contain the following considerations:
  1. Cooling time is is proportionate to the thickness squared
  2. Cooling time is inversely proportionate to the thermal diffusivity
  3. The temperature of the mold, melt, and part at ejection
One of the most common calculations are as follows:
tc = [(h^2)/(\alpha\,)(π^2)] ln |(4/π)[(Tm-Tw)/(Te-Tw)]|

h = wall thickness
\alpha\, = thermal diffusivity
Tm = melt temperature
Tw = mold wall temperature
Te = part temperature at ejection

If you perform a search on the internet, you can find automatic cooling time calculators which will quickly take all these factors in consideration once entered.
Additional Thoughts
Keep these factors in mind…
  • Always use your thickest portion of the part for these calculations
  • Assume your actual mold surface temperature will be higher than the temperature setting
  • Give yourself a 10-25% buffer based on the level of geometric complexity and amount of plastic shrinkage


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