First, what is cracked steam white?
Cracking steam whitening: cracking is a common defect in plastic products, including filamentous crack, microcrack, top white, cracking and trauma caused by adhesive die and channel die of parts, which can be divided into demoulding cracking and applied cracking according to cracking time.
The main reason is caused by stress and deformation (mainly residual stress, external stress and stress and deformation caused by external environment).
2. How can it be improved?
1. With regard to materials:
Proper use of release agent, pay attention to often eliminate fog attached to the mold surface and other substances
Fully dry the material before molding and processing
Pay attention to the selection of coatings and diluents that will not crack.
2. Molding process:
Avoid getting involved in the air because of poor feed in the plasticizing stage
On the basis of increasing melt temperature and mold temperature to ensure melt flow, injection pressure should be reduced as much as possible.
Reduce screw speed and injection speed, slow down the speed of melt passing through gate, and adopt multistage injection molding.
Adjust the speed and pressure of die opening to avoid demoulding cracking caused by rapid tensile products
Avoid cracking everywhere due to weld marks and degradation of plastics
The internal stress is eliminated and the crack generation is reduced by annealing immediately after forming.
If cracks have already occurred on the surface of the plastic parts, the annealing method can be considered to eliminate them. The annealing treatment makes the plastic part fully heated for about 1 hour at a temperature about 5 ℃ lower than the hot deformation temperature of the plastic part, and then cools it slowly. It is best to anneal the cracked plastic part immediately after forming, which is beneficial to eliminate the cracking. However, there is residual stress in the crack, and the solvent in the coating can easily make the crack develop into a crack.
