three injection processes affecting the strength of injection molded parts

Three injection processes affecting the strength of injection molded parts

injection machine is the main molding equipment which makes thermoplastics or thermosetting materials into various shapes of plastic products by using plastic molding mold. Injection molding is realized by injection molding machine and mold.

So, here are some injection processes that affect the strength of injection molded parts:
1) Increasing injection pressure can improve the tensile strength of PP injection parts
PP material is more elastic than other hard rubber materials, so the density of injection molded 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, otherwise it will decrease.
However, when the density is increased to the maximum value that PP can reach, the tensile strength will not continue to increase when the pressure is increased, but the residual internal stress of the injection part will be increased, making the injection part brittle, so it should be enough.
Other materials have similar situation, but the obvious degree will be different.
2) Hot 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. At the same time, due to the slow down of cooling rate, the residual internal stress of injection molded parts is also reduced. Therefore, the impact resistance and tensile strength of nylon and POM parts injected with hot oil will be improved correspondingly.
It should be noted that the size of nylon and POM parts injected by hot oil engine is slightly different from that of injection parts injected by water engine, and nylon parts may be larger.
3) The speed of melting is too fast, even if the injection temperature is 180 ℃, the rubber will be raw
In general, the 90 degree PVC material is injected at 180 ℃, the temperature is enough, and there is no problem of raw rubber. However, it is often due to the reason that the operator did not pay attention to it, or in order to speed up the production, the speed of the screw backward is very fast. For example, it takes only two or three seconds for the screw to return to the position where the maximum amount of glue is more than one-half. The time when PVC material is heated and stirred is seriously insufficient, resulting in the problem of uneven glue temperature and mixing The strength and toughness of injection molded parts will become quite poor.
Therefore, when injection molding PVC material, please pay attention not to adjust the melt speed to more than 100 rpm. If you have to adjust it very fast, you should remember to raise the temperature of the material by 5 to 10 ℃, or increase the back pressure of the melt glue properly to match. At the same time, you should always check whether there is a problem of raw glue, otherwise it is likely to cause significant losses.
As for this problem, ordinary people don't care too much, so it is proposed here to remind us that we must pay attention to it during production and remember to do a good job in inspection.
On the contrary, it should also be noted that if the melt speed is too slow, even if the material with a pvc90 degree is injected at a 180 degree angle, it will also cause the problem of burning. Especially for transparent PVC, there will be many black spots and air marks on the injection parts.