Shear Control Orientation Injection Molding
Shear Control Orientation Injection molding essentially applies a dynamic pressure to the melt through a gate, causing a vibrational shear flow of the polymer melt in the cavity, under which the molecular chains or fibers in different melt layers are produced. Orientation and freezing in the workpiece, thereby controlling the internal structure and microscopic morphology of the article, to achieve the purpose of controlling the mechanical properties and appearance quality of the product. The method of introducing vibration into the cavity has two types of auxiliary devices and screw vibration.
1. Auxiliary device vibration
Auxiliary device vibration is to install the vibration device between the mold and the nozzle of the injection molding machine. The injection phase is the same as the general injection molding. Usually, the melt passes through only one gate, the gate piston retreats to keep the flow path unobstructed, and the other piston The other flow path is cut off; after the cavity is filled, the two pressure-preserving pistons start to vibrate at the same frequency under the drive of a separate hydraulic system, but the phase difference is 1800.
Through the reciprocating motion of the two pistons, the vibration is transmitted to the cavity, and the melt in the cavity is cooled while generating a vibration shear flow. Experiments prove that this process can help eliminate common defects of products (such as shrinkage, cracks, surface subsidence, etc.) and improve the strength of weld lines. By using shear control orientation molding technology, by controlling the position and quantity of gates, molecules can be controlled. Or the orientation of the fibers gives a product that is stronger than conventional injection molded articles.
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.