When injection molding PC materials, there are often problems such as bubbles scattered irregularly on the surface of the product or the bubble particles being fine and dense. How do we solve problems such as bubbles and blisters in PC injection molding?
Reasons for common PC injection molding processing problems:
1. Bubbles are scattered irregularly on the surface of the product, mostly caused by water vapor.
2. If the bubble particles are relatively fine and dense, they are mainly distributed around the gate of the product, forming ray-like or fan-shaped lines, which are mostly caused by air.
3. When there are many corners in the mold cavity, the difference in thickness is too large, or there are many inserts, or the gate position is inappropriate, the melt will flow into the mold cavity, stirring up the air in the mold to form eddy currents, and air streaks will form in certain parts. For example, in the switch and socket panels of molded electrical products, this situation often occurs because the sockets, interfaces and switches are all concentrated in one location. The solution to this defect is to modify the mold, strengthen mold exhaust, and optimize the gate position; on the other hand, reduce the mold filling rate, especially the injection rate in areas with air marks.
4. The main reason for the generation of decomposition gas is that the melt temperature is too high.
5 Another important reason is that the PC itself is of poor quality and easy to decompose. There is also the fact that PC is sensitive to chemicals and breaks down easily.
6 Solvent gas is mainly related to the quality of operations in production, such as unclean cleaning of the barrel, too much additives, etc.
Solution:
When the wall thickness of the product is large, the outer surface cools faster than the central part. As the cooling proceeds, the resin in the central part shrinks and expands toward the surface, causing the central part to be underfilled and creating vacuum bubbles.
1. The main solutions are:
a) According to the wall thickness, determine the reasonable gate and runner size. Generally, the gate height should be 50% to 60% of the wall thickness of the product.
b) Until the gate is sealed, a certain amount of additional injection material remains.
C) The injection time should be slightly longer than the gate sealing time.
d) Reduce the injection speed and increase the injection pressure,
e) Use materials with high melt viscosity grades.
2. The main solutions to bubbles caused by the generation of volatile gases are:
a) Carry out sufficient pre-drying.
b) Reduce the resin temperature to avoid the generation of decomposition gas.
3. Bubbles caused by poor fluidity can be solved by increasing the temperature of the resin and mold and increasing the injection speed.
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