PA66 has low viscosity, so it has good fluidity. This property can be used to process very thin components. Its viscosity is very sensitive to temperature changes. The shrinkage of PA66 is between 1% and 2%. Adding glass fiber additives can reduce the shrinkage to 0.2% to 1%. The difference in shrinkage in the process direction and the direction perpendicular to the process direction is large.
When producing nylon and glass fiber raw materials, it is easy to have poor surface appearance. Mainly scorching and exposed fibers, material flowers. The reason for the poor surface may be that when adding this type of filler, a physical mixing method is generally adopted, so only the glass fiber is evenly dispersed in the middle of the plastic, but after the plastic is melted, this mixture will have different degrees of separation (depending on the proportion of addition and the length of the glass fiber, and the temperature of the raw material also has a certain degree of influence).
When producing nylon and glass fiber injection molding, the flow of the material is similar to the flow of liquid. You should have seen that in the river, when there are some branches and other debris in the river, there are often some of this kind of debris attached to the river bank and staying along the shore. If it is in injection molding, it is the glass fiber exposed.
This is because the fluidity of glass fiber is much worse than that of plastic, and the flow of plastic in the mold is from the middle of the interlayer to the front, and the two sides turn outward, so the fluidity is definitely good. The flow will definitely go to the front, and the fluidity is not good. It stays on the surface of the mold. (The same is true when making PP and other raw materials. The color of the bonding line and the back part is different. It’s just that the front end is generally waxy and separated from the color powder, especially when adding masterbatch, because the masterbatch is generally made of PE as a carrier.) The fire retardant is adsorbed on the mold surface for the same reason)
The reason why nylon plus glass fiber is produced is because the glass fiber is clumped, which is mainly related to the price of raw materials.
Solving these problems has really made many customers rack their brains. For customers we have cooperated with, we have summarized three solutions based on our experience in solving the problem of glass fiber exposure. If there are any deficiencies, please correct me.
On the one hand: starting from the raw materials, PA viscosity should be as low as possible within the range allowed by mechanical properties, and short fiber should be used as much as possible for glass fiber. If it is PA66, you can consider adding some PA6 and recycled materials to increase fluidity. Personally, I think it is important to choose glass fiber.
On the second hand: starting from the process,
1. Appropriately increase the screw shear force;
2. Increase the injection speed, the screw speed can be adjusted to 70%-90%;
3. Increase the injection pressure;
4. The entire screw retracts 1-2MM to prevent gate floating fibers;
5. For complex parts, graded injection molding is adopted.
On the third hand: from the additives, if the first two methods cannot solve the problem, you can only consider starting with the additives.
At present, additives are used to solve the problem of floating fibers, mainly to enhance the fluidity of glass fibers and the bonding ability of glass fibers and resins. Some methods that are considered unconventional, such as using special dyes to dye glass fibers black (only applicable to PA black), make the surface very bright. Types of additives: siloxane ( silicone masterbatch and silicone powder ), modified amides and polymers (such as TAF, superdispersants, etc.), glass beads, compatibilizers, special black masterbatches (can dye glass fibers black). The anti-glass fiber exposure agent produced by the company can effectively solve these problems.
