How to improve the screw life of injection molding machines
Read: 2274 Release time: 2014/10/30 13:39:56
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The following explains the causes of screw wear and the methods to reduce wear:
(1) Each plastic has an ideal plasticizing processing temperature range. The processing temperature of the barrel should be controlled to be close to this temperature range. The granular plastic enters the barrel from the hopper, and will first reach the feeding section, and then the feeding section. Dry friction will inevitably occur. When these plastics are insufficiently heated and unevenly melted, it is easy to cause increased wear on the inner wall of the barrel and the surface of the screw. Similarly, in the compression and homogenization section, if the plastic melt state is uneven , Will also cause increased wear.
(2) The speed should be properly adjusted. Because some plastics are fueled with reinforcing agents, such as fiberglass, minerals or other fillers. These materials are often much more abrasive than molten plastics. In the injection molding of these plastics, if a high rotational speed is used, while the shear force on the plastic is increased, the reinforcing agent will also generate more shredded fibers correspondingly. The shredded fibers contain sharp ends, so that The abrasion force is greatly increased. When the non-polar minerals glide on the metal surface at high speed, its scraping effect is also quite a lot. Therefore, the speed should not be adjusted too high.
(3) Detect debris in plastic. Generally speaking, the original purchased first plastic does not have any debris, but after transportation, weighing, drying, color mixing, especially adding recycled materials, it may be mixed with debris. As small as metal shavings, as large as a hot loop nut paper clip, and even a string of warehouse keys, there are precedents that have been mixed into the barrel. This damages the screw is beyond words (the barrel is also damaged at the same time), so , Must be strictly managed and monitored.
(4) The water content in the plastic has a certain effect on the wear of the screw surface. If the plastic does not completely remove the moisture before injection, when the remaining moisture enters the compression section of the screw, it will become a "steam particle" with high temperature and pressure melted in the molten plastic. With the advancement of the screw in the injection process, the Up to the head of the screw, these "steam particles" expand and release pressure during the injection process, like hard particles of fine impurities, which cause friction and damage to the wall surface.
In addition, for certain types of plastics, under high temperature and pressure, moisture may become a catalyst that promotes the cracking of plastics, generating harmful impurities that can erode the metal surface. Therefore, the drying work before plastic injection not only has a direct relationship with the quality of the part, but also affects the working life of the screw. As mentioned earlier, in order to extend the working life of the screw, flame hardening and nitriding are usually used. However, due to the widespread use of filled plastics and reinforced (glass-reinforced) plastics, and the individual plastics are corrosive or highly abrasive, the life of these processed screws is still too short. In recent years, some new High-tech processing methods have greatly improved the situation.
The brief introduction is as follows: using plasma transfer method, hard materials such as nickel and cobalt alloys are injected into the plasma arc in powder form, and then melted and coated on the surface of the screw, which becomes a metallographic bonding state, which is more than ordinary spraying. More solid. Ion nitridation is used to replace gas nitridation, which causes nitrogen to chemically interact with the metal on the screw to form a thin but uniform, hard and more coating. Because the cost of ion nitriding is relatively cheap, and its wear life is 2 ~ 3 times that of common hardening tools, it is often used for smaller diameter screws. In addition, there is an ion-insertion treatment method, the resulting screw has higher hardness and longer life.