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Several Injection Molding Technological Parameters Affecting the Strength of Injection Molding Parts
- Jan 17, 2019 -

1. Increasing injection pressure can improve the tensile strength of PP injection parts.

PP is more elastic than other hard rubber, so the density of injection parts will increase with the increase of pressure, which is relatively obvious. When the density of plastic parts increases, its tensile strength will naturally increase, and vice versa will decrease.

However, when the density increases to the maximum value that PP itself can reach, the tensile strength will not continue to increase with the increase of pressure. On the contrary, it will increase the residual internal stress of the injection parts and make the injection parts brittle, so it should be stopped. Others are expected to have similar situations, but to varying degrees.

2. Mould heat transfer oil injection can improve the strength of steel and nylon parts

Nylon and POM are crystalline plastics. The cooling rate of the injection parts can be slowed down and the crystallinity of the plastics can be improved by injection moulding with hot oil conveyor. At the same time, due to the slowdown of cooling rate, the residual internal stress of injection parts is also reduced. Therefore, the impact resistance and tensile strength of nylon and POM parts injected with hot oil will be improved accordingly. It should be noted that the size of nylon and POM parts injected with hot oil from hot oil engine will be different from that of water injection moulded parts, and the nylon parts may be larger than that of water injection moulded parts.

3. The melt speed is too fast, even if it is injected at 180 C, it will be raw.

Usually, PVC 90 degree material is injected at 180 C, the temperature is enough, and there is no problem of raw rubber in general. However, it is often due to the fact that the operator does not pay attention to it or intentionally speeds up the melt speed in order to speed up production, which makes the screw retreat quite fast. For example, in only two or three seconds, the screw retreats to the position of more than half of the maximum melt volume. The time for heating and stirring PVC materials is seriously insufficient, resulting in the problem of uneven melt temperature and mixing of raw rubber. The strength and toughness of the injection parts will become quite poor.

Therefore, in the injection of PVC materials, we must pay attention not to casually adjust the speed of the melt to more than 100 rpm. If you have to adjust it fairly quickly, you should remember to raise the temperature of the material by 5 to 10 C, or increase the backpressure of the melt glue appropriately to cooperate. At the same time, you should also pay attention to check whether there is any problem of raw glue. Otherwise, it is likely to cause significant losses. On this issue, because ordinary people do not care too much, so here is a special point to remind the production must pay attention to, and remember to do a good job of inspection. On the contrary, it should also be noted that if the melt speed is too slow, even if it is 180 degrees for injection molding of PVC 90 degrees, it will cause the problem of burning glue, especially transparent PVC, there will be many black spots and air marks on the injection parts.