The use of double alloy screw barrels should pay atten […]
The use of double alloy screw barrels should pay attention to these points:
1. The sundries in the plastic should be removed.
Generally speaking, the fresh plastic purchased from the original factory does not have any debris, but after transportation, weighing, drying, color mixing, especially adding recycled materials, there is a possibility of mixing debris. It has been as small as metal dust, as large as a heating ring nut paper clip, or even a series of warehouse keys, mixed into the double alloy screw barrel. It has happened to the screw barrel of the injection molding machine. Of course, it will also be damaged at the same time), so a magnet holder must be installed to strictly manage and monitor the feeding.
2. The rotation speed should be adjusted properly.
Because some plastics are added with reinforcement, 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 the high speed is used, the shear force on the plastic will be increased, and the reinforcement will produce correspondingly more shredded fibers. The shredded fibers contain sharp ends, which cause wear The force is greatly increased. When inorganic minerals glide on the metal surface at high speed, 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 barrel processing temperature should be controlled to make it close to this temperature range.
When the granular plastic enters the double 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 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 section and the homogenization section, if the molten state of the plastic is disordered, it will also cause increased wear.
4. The moisture contained in the plastic has a certain effect on the wear of the screw surface.
If the plastic does not remove all the water before injection molding, when the residual water enters the screw compression section, it will form "steam particles" with high temperature and pressure that are melted and mixed in the molten plastic before the injection process. From the chemical section to the head of the screw, these "steam particles" are relieved and expanded during the injection process, just like tiny hard particles of impurities, which produce 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, producing harmful impurities that can attack the metal surface. Therefore, the drying work before plastic injection not only has a direct relationship with the quality of the parts, but also affects the working life of the screw.