Introduction of three injection molding processes affecting the strength of injection molded parts
Injection molding machine (injection molding machine or injection molding machine for short) is the main molding equipment that makes thermoplastic or thermosetting materials into plastic products of various shapes using plastic molding molds. Injection molding is realized through injection molding machines and molds.
Here are some injection molding processes that affect the strength of injection molded parts:
1) Increasing the injection pressure can improve the tensile strength of PP injection molded 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, and vice versa.
However, when the density is increased to the maximum value that PP itself can reach, the tensile strength will not continue to increase if the pressure is increased, but will increase the residual internal stress of the injection molded parts, making the injection molded parts brittle, so it should be stopped.
Other materials have similar situations, but the obvious degree will be different.
Oil injection molding can improve the strength of Saigang parts and nylon parts
Nylon and POM materials are crystalline plastics. The mold is injected with hot oil transported by the hot oil machine, which can slow down the cooling rate of the injection molded parts and improve the crystallinity of the plastic. At the same time, due to the slow cooling rate, the residual internal stress of the injection molded parts is also reduced. Therefore, impact resistance and tensile strength of the nylon and POM parts injected with the hot oil engine heat transfer oil will be improved accordingly.
It should be noted that the dimensions of nylon and POM parts molded with hot oil transported by hot oil machine are somewhat different from those molded with water transported, and the nylon parts may be larger.
3) Melting speed is too fast, even if 180 ℃ is used for injection molding, the glue will be raw
Generally, the 90 degree PVC material is injected at 180 ℃, and the temperature is enough, so the problem of raw rubber generally does not occur. However, it is often due to reasons that do not attract the attention of the operator, or to intentionally accelerate the speed of glue melting in order to speed up production, so that the screw retreats very quickly. For example, it takes only two or three seconds for the screw to retreat to more than half of the maximum amount of glue melting. The time for PVC material to be heated and stirred is seriously insufficient, resulting in the problem of uneven glue melting temperature and raw rubber mixing, The strength and toughness of the injection molded parts will become quite poor.
Therefore, when injecting PVC materials, you must be careful not to arbitrarily adjust the speed of the melt adhesive to more than 100 rpm. If it must be adjusted very quickly, remember to raise the material temperature by 5 to 10 ℃, or increase the back pressure of the melt adhesive appropriately to cooperate. At the same time, pay attention to frequently check whether there is a problem with raw rubber, otherwise it is very likely to cause significant losses.
As most people don’t care too much about this problem, here is a special reminder to pay attention to it during production 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 PVC 90 degree material is injected at 180 degrees, it will also cause the burning problem. Especially for transparent PVC, there will be many black spots and air wrinkles on the injection molded parts.
