What are factors that affect plastic shrinkage?

Time：2025-12-26 10:20:33 / Popularity： / Source：

For previous reading, please refer to What are factors that affect plastic shrinkage?.

2 Impact of molding process on shrinkage rate of plastic products

(1) As molding temperature remains unchanged, injection pressure increases and shrinkage decreases;
(2) Keep pressure increasing and shrinkage rate reduced;
(3) As melt temperature increases, shrinkage decreases;
(4) Mold temperature is high and shrinkage rate increases;
(5) Shrinkage rate decreases when pressure holding time is long, but shrinkage rate is not affected after gate is closed;
(6) Cooling time in mold is long and shrinkage rate is reduced;
(7) Injection speed is high, shrinkage rate tends to increase slightly, and impact is small;
(8) Molding shrinkage is large and post-shrinkage is small; post-shrinkage is large in the first two days and stable for about a week.
(1) Barrel temperature: When barrel temperature is higher, pressure transmission is better and shrinkage force is reduced. However, when using a small gate, shrinkage rate is still large because gate solidifies early. For plastic parts with thick walls, even if barrel temperature is high, shrinkage rate is still large.
(2) Filling: In molding conditions, minimize filling to keep size of plastic part stable. However, if feed is insufficient, pressure cannot be maintained and shrinkage rate will increase.
(3) Injection pressure: Injection pressure is a factor that has a greater influence on shrinkage rate, especially holding pressure after filling. Under normal circumstances, when pressure is high, shrinkage rate is small due to high density of material.
(4) Injection speed: Injection speed has little impact on shrinkage rate. However, for thin-walled plastic parts or very small gates, and when reinforced materials are used, shrinkage rate will be smaller if injection speed is accelerated.
Mold temperature: Generally, shrinkage rate is larger when mold temperature is higher. However, for thin-walled plastic parts, when mold temperature is high, flow resistance of melt is small, and shrinkage rate is smaller.
(5) Molding cycle: Molding cycle has no direct relationship with shrinkage rate. However, it should be noted that when molding cycle is accelerated, mold temperature, melt temperature, etc. will inevitably change, thus affecting change in shrinkage rate.
(6) Mold temperature: The higher mold temperature, the greater shrinkage rate.

What are factors that affect plastic shrinkage

3 Influence of plastic part structure on product shrinkage

(1) Shrinkage rate of thick-walled plastic parts is greater than that of thin-walled plastic parts (but most plastic 1mm thin-walled parts have a greater shrinkage rate than 2mm, which is due to increased resistance of melt in mold cavity);
(2) Shrinkage rate of plastic parts with inserts is smaller than without inserts;
(3) Shrinkage rate of plastic parts with complex shapes is smaller than that with simple shapes;
(4) Shrinkage rate in height direction of plastic parts is generally smaller than in horizontal direction;
(5) Shrinkage rate of slender plastic parts in length direction is small;
(6) Shrinkage rate of length direction of plastic part is smaller than that of thickness direction;
(7) Inner hole shrinkage is large and outer shrinkage is small.

4 Influence of mold structure on shrinkage rate of plastic products

(1) Gate size is large and shrinkage rate is reduced;
(2) Shrinkage rate in direction perpendicular to gate decreases, and shrinkage rate in direction parallel to gate increases;
(3) Shrinkage rate far away from gate is smaller than that near gate;
(4) Shrinkage rate of plastic part with mold restrictions is small, and shrinkage rate of unrestricted plastic part is large.

5 Influence of plastic properties on shrinkage rate of products

(1) Shrinkage rate of crystalline plastic is greater than that of amorphous plastic;
(2) Plastics with good fluidity and small molding shrinkage;
(3) When fillers are added to the plastic, molding shrinkage rate is significantly reduced;
(4) Different batches of same plastic have different molding shrinkage rates.

Gud Mould Industry Co., Ltd