Analysis of the causes of bad floating fibers in injection molding and solutions

In injection molding production, have you encountered the problem of floating fiber, floating fiber refers to the glass fiber exposed to the surface of the product, relatively rough, the appearance is more difficult to accept, the possible causes of analysis: when adding such fillers, generally used physical mixing method, so only the glass fiber is uniformly dispersed in the middle of the plastic, but the plastic melting, the mixture will have different degrees of separation (depending on the addition ratio and the length of the glass fiber. (And the temperature of the raw material also has some influence.)
Why are the glass fibers exposed?
When shooting glue, the flow of the material is different from the flow of the liquid (liquid is a Newtonian flow, plastic is a non-Newtonian flow), but one of the arguments is more interesting and easy to understand. You should have seen the river, which has some branches and other debris in it, and there are often some of these river stays in coastal areas. This is because the flow of water on the river bank is slowed down due to the resistance, which is similar to the skin layer when injecting water. Therefore, these branches are molded in such a way that the glass fibers, or floating fibers, are exposed.
This is because the flow of glass fibers is much worse than plastic, and the flow of plastic in the mold is a fountain-like flow (fountain effect), which flows from the middle to the sides, so the best flow is running to the most. In the front, if the flow is not good, it will stay on the surface of the mold. (When making PP and other raw materials, the color of the bonding line and the color of the final part are the same. Usually at the forefront is the waxy, toner is separated, especially the color of additives. The most obvious, because the color masterbatch is usually made of PE, is the reason for making fireproofing agents on the surface of the fireproofing mold.
Generally speaking, the following methods can be used to reduce the proportion of floating fibers
1. Increase the filling speed
After increasing the speed, although the flow rate of glass fiber and plastic is different, the proportion of relative speed difference is small compared with high speed filling, just like a river does not leave branches in the rapid flow.
2. Increase the mold temperature
This effect is the greatest. Raising the mold temperature is to reduce the contact resistance between the glass fiber and the mold, so that the velocity difference between the glass fiber and the plastic is as small as possible. And to make the molten layer in the middle as thick as possible when the plastic flows, so that the skin on both sides is as thin as possible, so that the smooth river bank cannot retain the branches. RHCM uses this principle to achieve the appearance of floating fiber free.
3. lowering the temperature of the screw metering section and reducing the amount of solute
This is to minimize the possibility of glass fiber separation in plastic boxes. In general, the effect on floating fibers is very small and has little impact in practice. However, this can be a good solution to the burning problem. This is because after adding glass fiber, the volume of glass fiber is much larger than the volume of plastic, and it is easy to block the exhaust channel, so it is difficult to exhaust in the end, and the glass fiber is easy to burn in the high pressure and high oxygen body environment.