Cracked and white injection defects

1、 What is cracked and white defects?

Cracking and white: cracking is a common defect of plastic products, including filiform crack, micro crack, top white, cracking and trauma caused by part sticking and runner sticking. It can be divided into demoulding cracking and application cracking according to the cracking time.

The main reason is due to stress and deformation (mainly residual stress, external stress and stress and deformation caused by external environment).

2、 How to improve?

1. Materials:

Properly use release agent, and pay attention to often eliminate aerosol and other substances attached to the mold surface;

Fully dry the materials before forming;

Pay attention to the selection of coatings and diluents that will not crack.

2. Forming process:

Avoid air entrainment due to poor feeding in plasticizing stage;

On the basis of increasing melt temperature and mold temperature and ensuring melt flow, the injection pressure should be reduced as much as possible;

Reduce the screw speed and injection speed, slow down the initial speed of melt passing through the gate, and adopt multi-stage injection molding;

Adjust the mold opening speed and pressure to avoid demoulding cracking caused by rapid strong pulling of products;

Avoid cracking due to welding marks and plastic degradation;

The internal stress is eliminated by annealing immediately after forming to reduce the generation of cracks.

If cracks have occurred on the surface of plastic parts, annealing can be considered to eliminate them. Annealing treatment can fully heat the plastic part for about 1 hour at a temperature about 5 ℃ lower than the thermal deformation temperature of the plastic part, and then cool it slowly. It is best to conduct annealing treatment immediately after forming the plastic part with cracks, which is conducive to eliminating cracks. However, there is residual stress in the crack, and the solvent in the coating can easily make the crack develop into a crack.