Today's KNOWLEDGE Share : Shrinkage

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Today's KNOWLEDGE Share

Shrinkage – never-ending story?


When will the dimensions of a molded part finally become stable?

Answer: never!


Shrinkage is a continuous process! The only good news is that it follows a logarithmic curve. Whatever happens in the first 10 hours, the same amount will occur in the next 100, then in the next 1000, and so on.


At some point – and not very far down the line – daily temperature cycles or moisture uptake will have a greater effect on dimensions than shrinkage itself.


So, when should we measure shrinkage?

It depends on what we want to use the data for.


There are standards to guide us:

- DIN 16901:1982 (withdrawn)

- ASTM D955-21

- ISO 294-4:2018


Each defines a slightly different time window: 16, 24, or 48 hours after demolding (depending on the material and the standard).


When do you measure shrinkage, and why?

Do you use the concept of “technological shrinkage”?


source : Jozsef Gabor Kovacs

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