In the injection molding production, have you encountered the problem of floating fiber, the exposed fiber is the glass fiber exposed on the surface of the product, it is rough, the appearance is more difficult to accept, the possible cause analysis: when adding such filler, it is generally The physical mixing method is adopted, so only the glass fiber is uniformly dispersed in the middle of the plastic, but after the plastic is melted, the mixture will be separated to different degrees (depending on the ratio of addition and the length of the glass fiber, and the temperature of the raw material is also certain. influences)
Why is glass fiber exposed?
When the glue is shot, the flow of the material is different from the flow of the liquid (the liquid is Newtonian flow, the plastic is non-Newtonian flow), but one of the arguments is more interesting and easy to understand. Everyone should have seen the river, there are some branches and other debris in the river, and there are often some such rivers along the coast to stay. Because the flow rate of water on the river bank slows down due to resistance, this is similar to the skin layer at the time of filling. Therefore, these branches are in the injection molding, that is, the glass fiber is exposed, that is, the floating fiber.
This is because the flow of glass fiber is much worse than that of plastic, and the flow of plastic in the mold is a fountain flow (fountain effect), which flows from the middle to the sides, so the best fluidity is to run to the most. In front, if the fluidity is not good, it will stay on the surface of the mold. (The same is true for the color of the bonding line and the final part when making PP and other raw materials. It is usually waxy at the forefront, and the toner is separated, especially the additive color. The most obvious, because the color masterbatch is generally made of PE as a carrier, and it is also the reason to do the fireproofing agent on the surface of the fireproof mold.
Generally, the following method can be used to reduce the proportion of floating fiber:
1. Increase the filling speed
After increasing the speed, although the flow rate of glass fiber and plastic is different, the ratio of the relative speed difference is small compared with the high-speed injection glue, just as the river will never leave branches in the rapids.
2. Increase the mold temperature
This effect is the biggest. Increasing the mold temperature is to reduce the contact resistance between the glass fiber and the mold, so that the speed difference between the glass fiber and the plastic is as small as possible. And let the middle molten layer when the plastic flows as thick as possible, so that the skin layers on both sides are as thin as possible, so that the smooth river bank can not retain the branches. RHCM is using this principle to achieve the appearance of no floating fiber.
3. Reduce the temperature of the screw metering section and reduce the amount of sol
This is to minimize the possibility of separating the glass fiber of the plastic box. Generally speaking, the impact on the floating fiber is minimal, and the effect is not significant in actual operation. However, this can be a good solution to burnt. This is because after adding the glass fiber, the volume of the glass fiber is much larger than that of the plastic, so it is easy to block the exhaust passage, so it is difficult to exhaust at the end, and the glass fiber is easy to burn in a high-pressure high-oxygen gas environment. of!
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