The basis for setting the speed segmentation must take into account the geometry of the mold, other flow restrictions and unstable factors. The speed setting must have a clear understanding of the injection molding process and material knowledge, otherwise, the product quality will be difficult to control. Because the melt flow rate is difficult to directly measure, it can be calculated indirectly by measuring the screw forward speed or cavity pressure (make sure that the check valve is not leaking).
Multi-stage injection
The following speed segmentation principles are recommended:
1) The surface velocity of the fluid should be constant.
2) Quick glue should be used to prevent the melt from freezing during the process.
3) The injection speed setting should take into account the rapid filling in the critical area (such as the runner) while slowing down the speed at the water inlet.
4) The injection speed should be guaranteed to stop immediately after filling to prevent over filling, flash lamp and residual stress in the cavity.
Material properties are very important because polymers may degrade due to different stresses. Increasing the molding temperature may lead to violent oxidation and degradation of the chemical structure, but at the same time, the high temperature reduces the viscosity of the material, reduces the shear stress, and reduces the degradation caused by shear. There is no doubt that the multi-stage injection speed is very helpful for the formation of heat-sensitive materials such as PC, POM, UPVC and their blends.
The geometry of the mold is also a decisive factor: thin-walled parts need a large injection speed; thick-walled parts need a slow-fast-slow speed curve to avoid defects; in order to ensure that the quality of the parts meets the standard, the injection speed should be set to ensure melting The body forward flow is unchanged. The melt flow rate is very important because it affects the orientation and surface state of the molecules in the part.
