2. Screw vibration
The working principle of the screw vibration is to provide the injection oil cylinder with the pulsating oil pressure, so that the injection screw reciprocates to realize the vibration, the vibration generated by the injection screw acts on the melt, and the vibration is transmitted to the cavity through the polymer body, thereby The melt in the cavity creates vibrations that can continue to be closed to the mold. This type of device is relatively simple and can be implemented by using the control system of the injection molding machine or by modifying the hydraulic and electrical control systems of the injection molding machine.
Shear Control Orientation After the polymer melt is injected into the cavity during the injection molding process, a solidified layer begins to appear in the cavity. Due to the highest velocity gradient near the solidified layer, the melt here is subjected to intense shearing and the degree of orientation is greatest. The velocity gradient near the center layer is small, the shearing effect is small, and the degree of orientation is also small. The vibration is introduced during the pressure holding process, so that the polymer melt in the cavity is cooled while being subjected to vibration shearing, and the orientation caused by the vibration shearing forms an orientation layer of a certain thickness due to the cooling action of the mold.
Compared with no vibration, the thickness of the orientation layer produced by the vibration shear flow is much larger than that of the ordinary injection, which is why the mechanical properties of the product can be improved by introducing vibration shear flow into the cavity. In addition, due to the periodic compression pressurization and pressure relief expansion generated by the vibration, a large shear internal heat can be generated in the thin-walled portion, and the cooling of the portions can be delayed, so that the shrinkage of the thick-walled portion can be sufficiently obtained from the gate. The supplement is effective in preventing defects such as shrinkage cavities and depressions.