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Is it necessary to use a special screw and barrel?

Update:09 Nov 2018
Summary:

1) Each plastic has an ideal plasticizing processing te […]

1) Each plastic has an ideal plasticizing processing temperature range, and the barrel processing temperature should be controlled to be close to this temperature range. When the granular plastic enters the barrel from the hopper, it will first reach the feeding section, and dry friction will inevitably appear in the feeding section. When these plastics are insufficiently heated,
When the melting is uneven, it is easy to cause an increase in the wear of the inner wall of the cylinder and the surface of the screw. Similarly, in the compression section and the homogenization section, if the molten state of the plastic is disordered, the wear is increased.
2) The speed should be adjusted properly. Some plastics are supplemented with reinforcing agents such as fiberglass, minerals or other fillers. These materials tend to have a much greater frictional force on metallic materials than molten plastics. When molding these plastics, if you use high speed, you are improving the plastic.
At the same time as the shearing force, the reinforcement will correspondingly produce more shredded fibers, and the shredded fibers contain sharp ends, which greatly increase the wear force. When the inorganic minerals slide at high speed on the metal surface, the scraping effect is not small. Therefore, the speed should not be adjusted too high.
3) Remove debris from plastics. In general, the original purchased fresh plastic does not have any sundries, but after transportation, weighing, drying, color mixing, especially adding recycled materials, it is possible to mix debris. Small as metal scraps, as big as a heating ring nut paper clip, even
A series of warehouse keys have been mixed into the barrel, which is self-evident (the barrel is also damaged at the same time), so magnet holders must be installed, strict management and monitoring .
4) The moisture contained in the plastic has a certain influence on the wear of the screw surface. If the plastic does not completely remove the moisture before the injection, the residual moisture enters the compression section of the screw, and the high-pressure pressure "steam particles" melted in the molten plastic are formed, and the screw is advanced along with the injection process. From the section to the head of the screw, these "steam particles" are relieved and expanded during the course of the shot, like a fine impurity of hard particles, which causes friction damage to the wall surface. In addition, for certain types of plastics, at high temperatures and pressures, moisture may become a catalyst for cracking the plastic, producing harmful impurities that can attack the metal surface. Therefore, the drying work before plastic injection molding is not only directly related to the quality of the parts, but also affects the working life of the screw.