Common problems and solutions of injection molding

In injection molding production, you will encounter the problem of fiber floating. Exposed fiber means that glass fiber is exposed on the surface of the product, and its appearance is rough and unacceptable. Analysis of possible reasons: When adding this filler, physical mixing is generally adopted, so only glass fibers are evenly dispersed in the plastic, but after the plastic is melted, this mixture will be separated in different degrees (depending on the proportion of glass fibers added, the length of glass fibers and the temperature of raw materials).

Why are glass fibers exposed?

When injecting glue, the flow of matter is different from that of liquid (liquid is Newtonian flow and plastic is non-Newtonian flow), but there is a saying that is more interesting and easier to understand. You should see that river. There are some branches and other sundries in the river, and some are often attached to the coastal banks. Because the flow speed of water on the river bank is slowed down by resistance, it is similar to the surface layer when filling. Therefore, in the injection molding of these branches, glass fibers are exposed, that is, floating fibers.

This is because the fluidity 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 both sides, so the best fluidity is definitely to run to the front, and the fluidity difference will stay on the surface of the mold (the same is true for the color difference between the bonding line and the last part when making raw materials such as PP, but the front end is generally waxy, and the separation from the toner is particularly obvious, because the color masterbatch is generally PE).

Generally speaking, the following methods can be adopted to reduce the proportion of floating fibers:

1. Increase the filling speed

After increasing the speed, although the speed of glass fiber and plastic is different, the ratio of this relative speed difference is smaller than that of high-speed glue injection, just like branches will never be left in the rapids of rivers.

2. Increase the mold temperature

This role is the biggest. The purpose of raising the mold temperature is to reduce the contact resistance between glass fiber and mold and make the speed difference between glass fiber and plastic as small as possible. And when the plastic flows, make the melting layer in the middle as thick as possible, and make the epidermis on both sides as thin as possible, just like a smooth river bank can't keep branches. RHCM uses this principle to realize the appearance without floating fiber.

3. Reduce the temperature of the screw metering section and reduce the amount of sol.

This is to minimize the possibility of glass fiber separation in plastic boxes. Generally speaking, it has the least influence on floating fiber, and has little influence in actual operation. But this can solve the burning problem well. This is because after adding glass fiber, the volume of glass fiber is much larger than that of plastic, which is easy to block the exhaust passage, so it is difficult to exhaust at the end, and glass fiber is easy to burn in high pressure and high oxygen environment!