In Reply to: pet posted by Rajendra Jadhav on 10/10/00 at 12:26 PM:
PET is a semicrystalline material, and like all semicrystallines, can be affected greatly by processing conditions. In the case of injection molding, one can influence the crystallinity by changing mold temperature.
Simply put, a hotter mold will allow the material to cool at a slower rate. As the material cools more slowly, the molecules are given more time to migrate/move and arrange themselves into a more efficient crystalline structure. A cold tool, conversely, will 'quench' the material, cooling it very quickly. This quick cooling does not give the molecules sufficient time to arrange themselves efficiently.
The result is that hotter tools increase crystallinity, while cold tools decrease it.
More crystallinity generally results in:
1. More shrinkage
2. Increased strength
3. Better chemical resistance
Hope this helps.