(1) Defect characteristics
The main manifestation of white spots on plastic product is that there is a significant whitening phenomenon on the surface of Plastic Products during the plastic manufacturing process, i.e., the appearance of frost-like fine cracks.
(2) Causes of defects and elimination methods
White spots, also known as white spots on the top. The main reason for the appearance of white spots is that the force is too large at the white spot, and the chemical resistance and mechanical properties of the plastic parts at the white spot are greatly weakened. The specific analysis is as follows.
1) Injection mold
(1) If the surface of the mold cavity is rough, it will increase the demolding resistance and cause white spots. Therefore, the surface roughness of the mold cavity should be reduced.
(2) If the ejector pin of the injection molding manufacturer is placed on the weak part of the plastic part, it will aggravate the occurrence of white spots. Therefore, the ejector should be placed on the thick wall.
(3) If the demolding angle of the mold produced by the plastic supplier is too small, it will increase the demolding resistance of the plastic part, and the force applied to the plastic part during ejection will also increase, which is easy to cause white spots. Therefore, the demolding angle should be appropriately increased.
(4) In order to improve the strength of the ejection part, it can be strengthened locally, which can be strengthened from the structure and wall thickness.
(5) If the contact surface between the ejector pin and the plastic part of the Injection Molding Manufacturer is too small, the local stress of the plastic part is large, which will cause white spots. Therefore, the cross-sectional area of the end of the push rod should be appropriately increased.
(6) For plastic parts with core, demolding is more difficult and white spots are also easy to occur. Therefore, it is necessary to release the vacuum state between the core and the plastic part, such as installing an air valve in the core to release the vacuum, which is a good method.
2) Plastic molding process
(1) If the temperature difference between the melt and the mold is too large, the residual stress in the plastic part will increase, and it is easy to appear white spots when subjected to local force. Therefore, the melt temperature should be reduced and the temperature difference between the melt and the mold should be reduced.
(2) If the cooling time is too short, the stress in the plastic part cannot be fully balanced, and when the local force is too large, white spots will appear. Therefore, the cooling time should be appropriately extended.
(3) If the injection pressure is too high, the residual stress in the plastic part will also be large, which will cause white spots. Therefore, the injection pressure should be appropriately reduced.
(4) If the holding pressure is too high, the stress in the plastic part will be large, and when it is subjected to a large ejector force, it is easy to cause white spots. Therefore, the holding pressure should be appropriately reduced.
(5) If the holding time is too long, it is also easy to produce residual stress and white spots. Therefore, the holding time should be shortened.