Views: 2 Author: Site Editor Publish Time: 2023-07-19 Origin: Site
During the injection molding process, there is a certain gap between the plastic and the plastic in the unloading stage, and it is brought into the barrel after the screw shear. During the screw shear process, the material will undergo physical changes, from the glass state to the high elastic state, from the high elastic state to the viscous flow state, the change process may only be a few seconds - tens of seconds, in such a short time to transform a complex process. Injection defects also occur;
If the gas is not discharged to the outside of the cylinder during plasticization, the existing gas is wrapped into the molten material and injected into the mold cavity, and whether the mold can be successfully discharged depends on whether the exhaust of the mold is good, then the phenomenon of fogging trapped gas or burning.
Exhaust is not completely by the mold to solve, for PP material characteristics, the temperature range is very wide, its flow performance is superior, if the mold exhaust groove opened too large or the wrong position, can not be correctly exhaust, but also easy to produce bad flash, so the correct exhaust is useful.
In terms of process:
Mastering the correct adjustment skills is very effective in practical work.
1) If the screw rotation speed is reduced, the temperature of the molten material can be uniform, and the chance of the entrain air is small, such as the screw rotation speed is too fast, the chance of the entrain air is more; The molten material is subjected to the large shear force of the screw, the friction heat generation leads to the temperature of the molten material is not uniform, and the molten material decomposes to produce gas.
2) Increasing the mold temperature can benefit high pressure and slow filling to gain time. If the mold temperature is too low, the product surface is easy to freeze prematurely, and slow filling cannot be realized, which may lead to lack of glue.
3) Reduce the injection speed, the faster the speed, the faster the gas compression, the higher the temperature. The slower the speed, the slower the gas compression, the more conducive to gas discharge.
4) clamping force, the greater the clamping force, the worse the exhaust effect on the surface of the cavity, the smaller the clamping force, the better the exhaust effect on the surface of the cavity.
Obviously, the white fog is also a phenomenon of trapped gas, many people engaged in injection molding technology mistakenly believe that only burning is trapped gas, or trapped gas to open the exhaust tank, which is unscientific, burning because the trapped gas is too serious, the gas is compressed under high pressure, high speed state can not release the local combustion, combustion temperature can instantly reach 600-800℃.