Several injection molding processes that affect the strength of injection parts:
1) Increasing injection pressure can improve the tensile strength of PP injection parts
PP material is relatively elastic compared with other hard rubber materials, 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 conversely, it will decrease.
However, when the density increases to the maximum that PP itself can achieve, and then the pressure increases, the tensile strength will not continue to increase, but will increase the residual internal stress of the injection parts, making the injection parts brittle, so it should be enough.
The same is true for other sources, though to a different degree.
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2) Hot oil injection molding can improve the strength of steel parts and nylon parts
Nylon and POM materials are both crystalline plastics. The mold is injected with hot oil by hot oil machine, which can slow down the cooling speed of the injection parts and improve the crystallinity of plastics. At the same time, due to the slowing down of the cooling rate, the residual internal stress of the injection parts is also reduced. Therefore, the impact resistance and tensile strength of nylon and POM parts injected with hot oil by hot oil machine will be correspondingly improved.
It should be noted that the size of the nylon and POM parts injected with hot oil will be somewhat different from that of the water injection parts, and the nylon parts may be larger.
3) The melting speed is too fast, even if 180℃ injection molding will produce plastic
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Under normal circumstances, the pvc90 degree material is injected at 180 ° C, and the temperature is sufficient, and there is generally no rubber problem. However, it is often due to reasons that do not attract the attention of the operator, or in order to speed up production and intentionally accelerate the melting speed, making the speed of the screw retreat is quite fast, such as only two or three seconds, the screw will retreat to the maximum melting amount of more than half of the position, PVC material is heated and stirred seriously insufficient time, resulting in the melting temperature and uneven mixing of raw glue problems. The strength and toughness of the injection parts will become quite poor.
Therefore, when injection molding PVC material, be sure not to adjust the melt speed to more than 100 RPM. If it must be adjusted quite quickly, it is necessary to remember to increase the material temperature by 5 to 10 ° C, or appropriately increase the melt back pressure to match, and pay attention to frequently check whether there is a raw glue problem, otherwise it is very likely to cause significant losses.
On this issue, because the average person will not care too much, so it is especially proposed here 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 melting speed is too slow, even if the material is 180 degrees of injection PVC90 degrees, it will cause the problem of burning glue, especially transparent PVC, and there will be many black spots and gas lines in the injection parts.
