The use of double alloy screw barrel, these points shou […]
The use of double alloy screw barrel, these points should be paid attention to:
1. The debris in the plastic should be inspected.
Generally speaking, there is no debris in the fresh plastic purchased originally, but after transportation, weighing, drying, color mixing, especially adding recycled materials, it may be mixed with debris. It is as small as metal scraps, as large as heating coil nuts, paper clips, and even a bunch of warehouse keys. It has been mixed into the double alloy screw barrel. This damage to the screw of the injection molding machine is self-evident (barrel Of course, it will be damaged at the same time), so it is necessary to install a magnet holder and strictly manage and monitor the feeding.
2. The speed should be adjusted properly.
Because some plastics are added with reinforcing agents, such as glass fiber, minerals or other fillers. The friction of these substances on metal materials is often much greater than that of molten plastics. When injection molding these plastics, if they are made with a high rotation speed, it will increase the shearing force to the plastics, and at the same time, the reinforcement will produce more shredded fibers. The shredded fibers contain sharp ends, which will cause abrasion. The strength is greatly increased. When inorganic minerals slide at high speed on the metal surface, their scraping effect is not small. Therefore, the speed should not be adjusted too high.
3. Each plastic has an ideal plasticizing processing temperature range. The processing temperature of the barrel should be controlled to make it close to this temperature range.
Granular plastic enters the bi-alloy screw barrel from the hopper. It will first reach the feeding section. Dry friction will inevitably occur in the feeding section. When these plastics are not heated enough and melted unevenly, it is easy to cause increased wear on the inner wall of the barrel and the surface of the screw. . Similarly, in the compression section and the homogenization section, if the molten state of the plastic is disordered and uneven, it will also cause increased wear.
4. The water content in the plastic has a certain effect on the wear of the screw surface.
If the plastic is not completely drained of water before injection, when the remaining water enters the screw compression section, it will form "steam particles" with high temperature and pressure that are previously melted and mixed in the molten plastic. From the chemical section to the screw head, these "steam particles" relieve pressure and expand during the injection process, just like tiny impurity hard particles, which have frictional damage to the wall.
In addition, for certain types of plastics, under high temperature and high pressure, moisture may become a catalyst that promotes the cracking of the plastic, producing harmful impurities that can corrode the metal surface. Therefore, the drying work before plastic injection molding not only directly affects the quality of the parts, but also affects the working life of the screw.