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Causes of black spots in plastic injection molding

by:Vowin Rapid Prototyping     2023-02-09
Plastic products have relatively high requirements on appearance. Generally, the surface of the product must be complete without any pits and hollows. At the same time, the color of the surface should be relatively bright, and there should be no other variegated colors, such as black spots. For plastic products, black spots are often encountered in the process of injection molding. There are many factors that cause black spots, such as problems with the raw materials of the product itself, or some other problems that occur during the processing. It can also cause dark spots. What are the specific reasons? The engineers of Wo Neng Precision will sort it out for you. Let’s look at it in detail.





The reason why there are too many black spots in the process of plastic injection molding


1. The quality of the raw material itself is poor, and there are too many black spots;


2. Partial overheating of the screw leads to aggravated carbonization of the material, and the carbonized product is brought into the material strip, resulting in too many feeding points;


3. The local shearing of the screw is too strong, resulting in aggravated carbonization of the material, and the carbonized product is brought into the material strip, resulting in too many feeding points;


4. Too much head pressure (including clogging, too many filters, too low temperature of the head, etc.), too much reflow material, aggravated carbonization of the material, and the carbonized material is brought into the material strip, resulting in too many feeding points;


5. The service life of the machine is long, the gap between the screw and the barrel increases, and the carbonization on the wall of the barrel increases. As the extrusion time goes by, it is gradually brought into the material strip, resulting in too many feeding points;


6. If the natural exhaust port and the vacuum exhaust port are not cleaned for a long time, the accumulated carbonized matter will increase, and then it will be brought into the strip by continuous extrusion in the subsequent period, resulting in too many feed points;


7. The external environment or artificially caused other impurities to mix in, resulting in more black spots;


8. The die (including the discharge port and internal dead corners) is not cleaned cleanly, resulting in too many black spots;


9. The discharge port is not smooth enough (for example, some shallow grooves and potholes, etc.), and the material may accumulate for a long time. As the extrusion time goes by, it will be gradually carbonized and then brought into the material strip, resulting in more black spots;


10. Part of the original screw thread is damaged (dead corners are formed by lack of corners, wear, etc.), resulting in aggravated carbonization of the material at the dead corners. In the subsequent continuous extrusion process, it is gradually taken out to the material strip, resulting in more black spots;


11. The natural exhaust and vacuum exhaust are not smooth, causing carbonization of the material in the screw, resulting in more black spots.
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