Washing Machine Wave Wheel Plastic Mould

Plastic material and mold shrinkage rate

1. Plastic raw material shrinkage

This refers to the characteristic that a plastic part dimensionally shrinks after being taken out of the mold.

2. Plastic molding shrinkage

Molding shrinkage refers to the shrinkage of a plastic part that is related to the thermal expansion & contraction properties of the plastic itself, the mold structure, and the molding process conditions.

The level of molding shrinkage: the actual shrinkage of a plastic part can be expressed as S_A, i.e.:

In the formula, a = part dimensions under molding temperature conditions;

                            b = part dimensions under room temperature conditions.

It is not possible to measure part dimensions under molding temperature conditions, so cavity size under room temperature conditions is used:

In the formula, c = cavity size under room temperature conditions;

                           S_c = calculated shrinkage rate of the plastic part.

When S_c is known, cavity size can be calculated by using S_c, i.e.:

3. The principle of selection of shrinkage rate

* For plastics with a small range of shrinkage rate, the intermediate value can be taken on basis of the shrinkage range. This value is referred to as the average shrinkage rate.

* For plastics with a wide range of shrinkage rates, the shrinkage should be determined according to the shape of the part, in particular the wall thickness of the product. Choose the upper limit (large value) for thick walls, and the lower limit (small value) for thin walls.

* The shrinkage rate of each part of a product is different from one another, so it should be selected according to the actual situation.

4. The shrinkage rate of common plastic material

ABS: 0.5%

PC: 0.5-0.7%

POM: 2.0-2.5%

PVC: 1.0-2.5%

PS: 0.3-0.6%

PBT: 0.2-1.4%

HDPE: 1.2-2.5%

TPE: 1.0-2.0%

LDPE: 1.5-3.6%

PC/ABS: 05-0.7%

GPPS: 0.3-0.6%

HIPS: 0.4-0.7%

AS: 0.4-0.7 %

PA6: 1.0-1.5%

PEEK: 1.2%

PPS: 1%

PPO: 0.5-0.9%

PE: 1.2-1.28%

PA66+GF30: 0.3-0.7%