Factors Affecting The Plastic Shrinkage
1. Effect of molding process on shrinkage of plastic products
(1) The molding temperature is constant, the injection pressure is increased, and the shrinkage rate is decreased;
(2) keep the pressure increased and the shrinkage rate decreases;
(3) The melt temperature is increased and the shrinkage rate is decreased;
(4) The mold temperature is high and the shrinkage rate is increased;
(5) The holding time is long and the shrinkage rate is reduced, but the shrinkage rate is not affected after the gate is closed;
(6) The in-mold cooling time is long and the shrinkage rate is reduced;
(7) The injection speed is high, the shrinkage rate tends to increase slightly, and the influence is small;
(8) The molding shrinkage is large, and the rear shrinkage is small. The post-contraction is large at the beginning of two days and is stable for a week or so. The plunger type injection molding machine has a large shrinkage rate.
2. Influence of mold structure on shrinkage of plastic products
(1) The gate size is large and the shrinkage rate is reduced;
(2) The vertical gate direction shrinkage rate is reduced, and the parallel gate direction shrinkage rate is increased;
(3) The shrinkage rate away from the gate is smaller than that of the near gate;
(4) The shrinkage rate of the plastic part having the mold restriction is small, and the shrinkage rate of the unrestricted plastic part is large.
3. The effect of plastic structure on the shrinkage of products
(1) Thick-walled plastic parts have higher shrinkage than thin-walled plastic parts (but most plastic 1mm thin-walled parts have a larger shrinkage than 2mm, which is due to the increased resistance of the melt in the cavity);
(2) The shrinkage ratio of the insert with the insert on the plastic part is smaller than that without the insert;
(3) The shape of the plastic part is complicated, and the shrinkage rate is simpler than that of the simple shape;
(4) The height direction of the plastic part is generally smaller than the horizontal direction;
(5) The shrinkage rate of the elongated plastic part in the longitudinal direction is small;
(6) The dimension in the longitudinal direction of the plastic part is smaller than the shrinkage ratio in the thickness direction dimension;
(7) The inner hole shrinkage rate is large, and the shape shrinkage rate is small.
4. Effect of plastic properties on shrinkage of products
(1) The shrinkage rate of crystalline plastics is greater than that of amorphous plastics;
(2) Plastics with good fluidity, low molding shrinkage;
(3) Adding filler to the plastic, the molding shrinkage rate is significantly reduced;
(4) The same plastics in different batches have different molding shrinkage rates.