Jun 23, 2020 Viewed: 39 Tag: injection  

How to solve the problem of shrinkage of injection parts in plastic products !

Shrinkage is also known as the depression in our mold injection industry, which is defined as partial collapse of the surface of the molded product (or the groove is recessed). Such poor molding is called shrinkage.


1. Plastic products

The ribs are too thick. When the ribs are thick, the ribs and the floor are also thick. Here, the plastic is concentrated. When cooling, the surrounding ribs and plates solidify first, but the junction of the ribs and plates remains liquid. The solidified plastic behind is cured first. The plastic shrinks, resulting in uneven glue, which can cause depressions or collapse.


The material temperature is not enough, or the molding parameters are not set correctly. Failure to reach the temperature of the material causes the molded product to shrink.


2, the mold


1 The mold temperature relative to the rib is too high

If the temperature of the mold surface relative to the rib is higher than its vicinity (generally it is true, because the melt melt is concentrated nearby, the heat load is large, and the mold temperature remains high), the condensation layer is thin and the rigidity is not enough. When the melt melt in the center solidifies, the residual Stress may pull the thinner layer inwards into depressions. The mold surface opposite to the ribs must be strengthened to reduce the temperature of the mold, so that the condensed layer is formed faster. When the condensed layer is thicker, the rigidity is greater and the depression is not easy to produce.

The mold temperature can be set from the value recommended by the material manufacturer. The reduction (or increment) of each adjustment can be 6 ℃, 10 shots. After the molding condition is stable, decide whether to further adjust according to the results.


3. The sprue and runner are too narrow or/and the gate is too small/the number of gates is incorrect or the location is not appropriate


If the sprue, runner or/and gate are too small, the flow resistance will increase. If the injection pressure is insufficient, the cavity cannot be filled, the melt density is small, and the probability of depressions is large.


4, injection molding machine


1. The material tube temperature is too high

2. The cooling time is too short

3. The pressure is not enough

4. Injection pressure is too low

5. Injection speed is too slow





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