When producing transparent plastic parts, it often happens that the injection molding takes more than ten hours, or even a few days, and the black spots cannot be removed. Not only waste a lot of production time, but also waste a lot of the company’s raw materials.
Therefore, how to prevent the problem of many black spots is a very meaningful thing. Some of the precautions and precautions listed below will be very helpful in preventing black spots.
1, When arranging production, it should be noted that the injection molding machine that will arrange the production of transparent plastic parts or light-colored plastic parts cannot be recently injected with easily burnt raw materials such as POM and PVC. It is best not to produce dark or black injection parts.
At the same time, try to use high-quality or newer injection molding machines to produce transparent plastic parts. If the screw and check ring of the injection molding machine have been worn more, it is easy to cause black spots due to scorching.
Therefore, in order to prevent black spots more effectively, it is best to select several newer and better quality injection molding machines to produce transparent plastic parts, and separate hard plastic transparent materials such as PC and transparent ABS from transparent PVC materials. It’s important to use the machine and not share it.
2, The less secondary recycled materials (commonly known as “gating materials”), the better. Of course, it is best to produce all raw materials. In order to save raw materials, it is usually necessary to reuse some secondary recycled materials. Therefore, the secondary recycled materials must be kept clean, free from black spots and oil marks.
Because the powder components in the secondary recycled materials are easily scorched, causing many black spots, the powder must be sieved before production. The performance of transparent PVC is most obvious in this respect, so the secondary recycled materials of these two materials must be screened more cleanly. In order to prevent the secondary recycled materials from causing stains during storage, transportation and beating, it is best to use the operation method of immediately recycling the secondary recycled materials by machine-side beating.
3, When heating up, it is better to adopt the method of heating up step by step. This can prevent scorching caused by local overheating in the heating tube, especially raw materials that are easy to scorch, such as PVC materials.
When producing transparent PVC materials, the temperature should be adjusted to about 110 ℃, and the temperature should be kept for a few minutes after the temperature rises enough, and then the temperature should be adjusted to the injection molding production temperature. Once the injection temperature is reached, it must be produced immediately, otherwise a large number of black spots will be generated over time.
4, A stable production cycle must be maintained, and it can not be stopped for a long time, and it can be switched on and off. Some scorching materials will cause a lot of black spots even if they are stopped for a few minutes. When it needs to be temporarily shut down, the temperature should be lowered by 30 to 50 ° C first, and then stopped after a few minutes of production. PVC materials also need to be washed immediately, otherwise there will be endless troubles.
5, Never use a large machine to produce small molds, which is also an important reason for more black spots. Because the injection volume is relatively small, the melt stays in the heating cylinder for too long, and it is inevitable that the scorching problem will occur. In particular, raw materials that are easily burnt can hardly be produced.
6, Be careful not to adjust the temperature too high. The temperature of the front, middle, and rear heating cylinders should also be reduced step by step, and the temperature of the middle and rear furnaces should be lower, which is very good for preventing scorching and causing black spots.
7, The quality of toner is very important. If it is difficult to dissolve evenly, it will cause a lot of toner spots, and it is difficult to eliminate. Sometimes the raw materials need to be pre-plasticized in advance to eliminate the problem.
8, The injection cycle is too long, and the raw materials that are easy to scorch, such as PVC materials, are prone to black spots.
The above-mentioned measures and precautions for transparent plastic parts to prevent black spots also have a certain effect on light-colored plastic parts, and the black point of light-colored plastic parts will be better controlled than transparent plastic parts.
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