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In the injection molding industry, the plastic shell has a certain shrinkage after molding, which can be demonstrated from the following four aspects: molding process, plastic shell structure, mold structure, and plastic properties.

1. Effects of Molding Process on Shrinkage of Plastic Shell
(1) The molding temperature is constant. When the injection pressure increases, the shrinkage decreases;

(2) Keep-up pressure increases, while the shrinkage decreases;

(3) Increased melt temperature and reduced shrinkage;

(4) The mold temperature is high and the shrinkage increases;

(5) The holding time is long and the shrinkage decreases, but the shrinkage is not affected after the gate is closed;

(6) Long cooling time and reduced shrinkage;

(7) The injection speed is high, the shrinkage is slightly increased, but the impact is relatively small;

(8) When molding, the shrinkage is large and it turns to small when it is done. The late shrinkage begins to grow two days later and stabilizes around a week. Plunger injection machine has a large molding shrinkage.

2. Effects of Plastic Structure on Shrinkage of Plastic Shell
(1) The shrinkage of thick-walled plastic parts is higher than that of thin-walled plastic parts (but the shrinkage of most thin-walled 1 mm plastic parts are larger than that of 2 mm parts, which is due to the increase of melt resistance in the die cavity);

(2) The shrinkage of the plastic part with an insert is smaller than that without the insert;

(3) The shrinkage of plastic parts with complex shapes is smaller than that of simple shapes;

(4) The shrinkage of plastic parts in the height direction is generally smaller than that in the horizontal direction;

(5) The shrinkage of slender plastic parts is small in the length;

(6) The shrinkage of size in the length of the plastic parts is smaller than that of size in the thickness;

(7) Large shrinkage of inner hole and small shrinkage of shape.

3. Effects of Mold Structure on Shrinkage of Plastic Shell
(1) Large gate size and reduced shrinkage;

(2) The shrinkage of the vertical gate decreases while the shrinkage of the parallel gate increases;

(3) The shrinkage of plastic shell being close to the gate is smaller than that of away from the gate;

(4) The shrinkage of plastic parts with mould limits is small, and the shrinkage of plastic parts without limits is large.

4. Effects of Plastic Properties on Shrinkage of Plastic Shell
(1) The shrinkage of crystalline plastics is greater than that of amorphous plastics;

(2) Plastic with good fluidity has a small shrinkage;

(3) When filling material is added into plastics, the shrinkage of molding decreases obviously

(4)The molding shrinkage is also different for the same plastics in different batches.

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