What role does injection mold play in injection molding
Apr 12, 2022
In the plastic injection mold, the hot runner is used in conjunction with the mold and plays a very important role in the injection molding process. For example, in the injection-molded production of ultra-thin parts (such as cell phone battery covers).
High-precision and high-quality products can be easily produced by using hot runners; for plastic injection molds with poor fluidity injection materials (such as LCP), the use of hot runners can significantly improve the fluidity of raw materials and ensure smooth injection molding production. ; For some large injection molding parts, such as automobile bumpers and door panels, TV back shells, air conditioner shells, etc., the use of hot runners makes very difficult injection molding relatively simple.
The tip of the hot runner tip is easily worn off by the glass fiber. After the tip is worn, there is too much cold glue in the gate area, and the injection pressure is not enough to flush out, and no glue will be produced. Therefore, the hot nozzles of many companies will not be able to produce glue after a few uses. If the nozzle tip is made of materials such as high-speed steel, the high-speed steel has poor thermal conductivity, and the temperature difference between the nozzle tip and the runner is too large, which will also produce cold material, which is also difficult to inject.
Plastic injection molds are filled at high speed. During high-speed filling, the shear rate is high, and the viscosity of the plastic decreases due to the effect of shear thinning, which reduces the overall flow resistance; the local viscous heating effect will also reduce the thickness of the cured layer. Therefore, during the flow control phase, the filling behavior often depends on the size of the volume to be filled. That is, in the flow control stage, due to high-speed filling, the shear thinning effect of the melt is often large, and the cooling effect of the thin wall is not obvious, so the effect of velocity prevails.
Generally speaking, the strength of the weld line produced by the plastic injection mold in the high temperature area is better, because the polymer chain has better mobility under high temperature conditions, and can penetrate each other and intertwined. In addition, the temperature of the two melts in the high temperature area is relatively close. , the thermal properties of the melt are almost the same, which increases the strength of the weld area; on the contrary, in the low temperature area, the weld strength is poor.
