Highlight and highlight products are really a difficult product for injection moldingenterprises, because they can't hide external defects, even the dust in the workshop will cause defects of different degrees, such as trachoma, pockmarks, contamination, etc., so the environment is also one of the key factors affecting such products.
The product surface white fog, from the visual point of view, it is white, so it is not obvious in white products, black highlight is the most obvious
According to the above theoretical basis, there is a certain gap between the plastic and the plastic in the blanking stage, which is brought into the barrel after being sheared by the screw. In the process of the screw shearing, the material will undergo physical changes. From glassy state to high elastic state, from high elastic state to viscous flow state, the process of this change may be only a few seconds to tens of seconds (according to the size of the machine or the product). In such a short time, it needs to change a complex process, and the injection defects will be produced immediately.
The space between the plastics is compressed to the inside of the melt to produce gas. If the gas cannot be discharged to the outside of the barrel during the plasticization, the existing gas will be wrapped in the melt and injected into the mold cavity. Whether the mold can be discharged smoothly depends on whether the exhaust of the mold is good or not, and the phenomenon of fogging or burning will occur.
Obviously, white fog is also a phenomenon of trapped gas. Many people engaged in injection molding technology mistakenly think that only coking is trapped gas, or if trapped gas occurs, they go to open the exhaust slot. This is unscientific. Burning is because trapped gas is too serious, and the gas is compressed under high pressure and high speed to produce local combustion. The combustion temperature can reach 600-800 ℃ in an instant, which belongs to trapped gas The highest level.
How can we make the best exhaust gas without white fog?
1. Mold
The exhaust is not completely solved by the mold. For the characteristics of PP material, the temperature range is very wide, and its flow performance is superior. If the exhaust slot of the mold is too large or the position is not right, it can not exhaust correctly, and it is easy to produce poor flash, so the correct exhaust is useful.
2. Process
It is very effective to master the correct skills in the actual work.
1) If the screw rotation speed is reduced, the melt temperature can be uniform, and the opportunity of entrained air is small. If the screw rotation speed is too fast, the opportunity of entrained air is more; the melt shear force by the screw is large, the friction heat causes uneven temperature of the melt, and the melt decomposes to produce gas body.
2) If the mold temperature is too low, the product surface is easy to freeze too early, and the slow filling can not be realized, which may lead to the 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 is, the slower the compression of the gas is, and the more favorable the discharge of the gas is.
4) The larger the clamping force is, the worse the exhaust effect is. The smaller the clamping force is, the better the exhaust effect is
