Injection molding is a method of producing shapes for industrial products. Products usually use rubber injection molding and plastic injection molding. Injection molding can also be divided into injection molding and die casting. Injection molding machine (referred to as injection machine or injection molding machine) is the main molding equipment for making thermoplastic or thermosetting materials into various shapes of plastic products using plastic molding molds. Injection molding is achieved by injection molding machines and molds.
Several 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 compounds, so the density of injection molded parts will increase with the increase of pressure. This characteristic is relatively obvious. When the density of plastic parts increases, its tensile strength will naturally increase, and vice versa.
However, when the density increases to the maximum value that PP itself can achieve, and then increasing the pressure, the tensile strength will not continue to increase, 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 a similar situation, but the apparent degree will be different
2) The hot oil injection molding of the mold can improve the strength of the steel parts and nylon parts
Nylon and POM materials are both crystalline plastics. The mold is injected with hot oil by a 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 slowing down of the cooling rate, the residual internal stress of the 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 accordingly.
It should be noted that the size of the nylon and POM parts injected with hot oil by the hot oil machine will be slightly different from that of the injection molded parts with water injection, and the nylon parts may be larger.
3) The glue melting speed is too fast, even if 180 ℃ injection molding will produce glue
Under normal circumstances, the pvc 90 degree material is injected at 180 ℃, and the temperature is sufficient, and there is generally no problem of raw rubber. However, it is often due to the reasons that the operator did not pay attention, or intentionally speed up the melting speed in order to speed up production, so that the speed of the screw retreat is quite fast. More than one-third of the position, the time for the PVC material to be heated and stirred is seriously insufficient, resulting in the problem of melt temperature and uneven mixing of raw rubber, making the strength and toughness of the injection molded parts quite poor.
Therefore, when injecting PVC material, be careful not to adjust the melt speed to more than 100 rpm. If it must be adjusted very quickly, remember to increase the temperature of the material by 5 to 10 °C, or appropriately increase the back pressure of the melt to match. cause heavy losses.
Regarding this issue, because most people do not care too much, it is specially raised here to remind you that you must pay attention during production, and remember to do a good job in inspection.
On the contrary, it should be noted that if the melting speed is too slow, even if it is 180-degree injection of PVC 90-degree material, it will cause the problem of glue burning, especially for transparent PVC, there will be many black spots and air lines on the injection molded parts.