How to solve the floating fiber in injection molding?(Two)

How to solve the floating fiber(two)?

 

Floating fiber is also called exposed fiber. In the production of raw materials with glass fiber is most likely to appear is the surface appearance of bad, mainly for burnt, exposed fiber and material flower.And this is the most important, the most difficult to solve is the exposed fiber. The so-called exposed fiber is the glass fiber exposed on the surface of the product, relatively rough, the appearance is more difficult to accept. White glass fiber in the plastic melt mold flow process exposed to the exterior, to be condensed after molding in the plastic surface to form a radial white traces, when the plastic parts for the black will be due to the increase in the color difference and more obvious.

 

In the previous article, we talked about improving the compatibility of nylon materials with glass fibers and improving the feeding parameters of injection molds to improve the floating fiber phenomenon. This article will also talk about some other ways to improve:

3. Optimization of injection molding process conditions

The development of appropriate molding process conditions, to improve the "floating fiber" phenomenon is critical. Injection molding process elements of glass fiber reinforced plastic products have different effects, the following basic rules can be followed to introduce.

1) Temperature

The first is the barrel temperature. Because of the glass fiber reinforced plastics melt index than non-reinforced plastics lower than 30% to 70%, poorer fluidity, so the barrel temperature should be higher than the general situation 10 ~ 30 ℃. Increase the barrel temperature, the melt viscosity can be reduced to improve fluidity, to avoid filling and welding bad, and is conducive to increase the dispersion of glass fiber and reduce the orientation, to obtain a lower surface roughness of the product. But the barrel temperature is not the higher, the better, the temperature is too high will increase the nylon polymer oxidation and degradation of the tendency, slight color changes will occur, and when the seriousness of the coking black.

In setting the barrel temperature, should make the charging section temperature is slightly higher than the conventional requirements, slightly lower than the compression section can be, in order to take advantage of the preheating effect, reduce the screw on the fiberglass produced by the shear effect, reduce the difference in local viscosity and the damage to the surface of the fiberglass, to ensure that fiberglass and resin bonding strength between the PA66 + 33% GF melting temperature of 275 ~ 280 ° C, the highest temperature does not exceed 300 ° C, the barrel temperature can be set at this level, the temperature can be increased in this area, the temperature of the polymer is not higher than good, the barrel temperature can be set at this level. The maximum temperature should not exceed 300℃, and its barrel temperature can be selected within this range.

Next is the mold temperature. The temperature difference between the mold and the melt should not be too large, to prevent the melt from filling the glass fiber cold in the surface sludge, the formation of "floating fiber", so the need to use a higher mold temperature, which is to improve the performance of the melt mold filling, increase the strength of the fusion trace, to improve the surface finish of the product, to reduce the orientation and deformation is also beneficial. But the higher the mold temperature, the longer the cooling time, the longer the molding cycle, reduced productivity, and molding shrinkage increases, so it is not the higher, the better. Mold temperature settings, but also consider the resin varieties, mold structure, glass fiber content, etc., in the complex cavity, high glass fiber content, filling the mold difficulties, mold temperature should be increased appropriately. For the material of PA66 + 33% GF automobile handle cover, we choose the mold temperature of 110 ℃.

2) Pressure

Injection pressure has a great impact on the molding of glass fiber reinforced plastics, higher injection pressure is conducive to filling, improve the dispersion of glass fiber, reduce product shrinkage, but will increase the shear stress and orientation, easy to cause warping and deformation, demolding difficulties, and even lead to the problem of overflow edge, therefore, to improve the phenomenon of "floating fibers" need to be slightly higher than the non-reinforced plastics, based on the injection pressure, according to the specifications of the mold temperature. Therefore, to improve the "floating fiber" phenomenon, it is necessary to slightly higher than the non-reinforced plastics on the basis of injection pressure, according to the specific circumstances of the appropriate increase. In addition to the choice of injection pressure and product thickness, gate size and other factors, but also with the glass fiber content and form, the higher the general glass fiber content, the longer the length of the glass fiber, the greater the injection pressure should be.

3) The size of the screw back pressure for the uniform dispersion of glass fiber in the melt, the fluidity of the melt, the density of the melt, the appearance of the product quality and mechanical and physical properties have an important impact, usually using a slightly higher back pressure is more favorable to help improve the "floating fiber" phenomenon. But too high back pressure will produce a large shear effect on the long fiber, so that the melt is easy to degrade due to overheating, resulting in discoloration and poor mechanical properties. Therefore, the back pressure is set slightly higher than the non-reinforced plastics.

4) Injection speed, using faster injection speed, can improve the "floating fiber" phenomenon. Increase the injection speed, so that the glass fiber reinforced plastic quickly filled with mold cavity, glass fiber along the flow direction for rapid axial movement, is conducive to increasing the dispersion of glass fiber, reduce the orientation, improve the strength of the fusion mark and the apparent finish of the product, but we must pay attention to avoid the injection speed is too fast, in the mouth of the nozzle or gate at the occurrence of the phenomenon of "jet", the formation of serpentine defects, affecting the appearance of the plastic parts.

5)Screw speed
Glass fiber reinforced plastic plasticization, screw speed should not be too high, to avoid excessive friction shear force on the glass fiber damage, damage to the glass fiber surface interface state, reduce the adhesive strength between the glass fiber and resin, exacerbate the phenomenon of "floating fiber", especially when the glass fiber is longer, due to the fracture of part of the glass fiber and the phenomenon of uneven lengths, resulting in the molded parts The strength of each place is not equal, and the mechanical properties of the products are not stable.

Through the above analysis, it can be seen that the use of high material temperature, high mold temperature, high pressure, high speed, low screw speed injection, to improve the "floating fiber" phenomenon is more favorable.