There are some important factors that have impact on the shrinkage of rotomolding products.
1. Impact of rotomolding technique.
(1) When the temperature is same, while the pressure is increasing then the shrinkage is decreasing.
(2) When the melt temperature is increasing, the shrinkage will be reduced.
(3) When the temperature of mold is rising, the shrinkage is increasing at the same time.
(4) If the dwell time is long then the shrinkage will be reduced, but the seal has no effect on the shrinkage.
(5) When the mold cooling time is long then the shrinkage will be declined.
(6) When the injection speed is high, the shrinkage has inclination to increase but has little impact.
2. Impact of product’s structure.
(1) The thicker rotomolding product will have larger shrinkage.
(2) The products with inserts have larger shrinkage than those without inserts.
(3) The products with complicated shapes have larger shrinkage.
(4) If the inner hole has larger shrinkage then the appearance has lower shrinkage.
3. Impact of molds.
(1) The larger running gate is, the lower shrinkage is.
(2) If the shrinkage of vertical running gate is decreasing, then the shrinkage of parallel running gate is increasing.
(3) The shrinkage near the running gate is larger than far away it.
(4) If the rotomolding product has the mold limitations, then the shrinkage will be reduced, or it will be increased.
4. Impact of nature of rotomolding product.
(1) Crystalline rotomolding products have larger shrinkage than amorphous one.
(2) The better flowability of material, the lower of the shrinkage.
(3) If the mold is added filler, then the shrinkage will be decreased significantly.
(4) Different quantities with same material also have various degrees of shrinkage.
