How to Solve the Phenomenon of "Floating Fiber" in Glass Fiber Reinforced Nylon
Adding glass fiber and toughening agent to nylon can significantly increase the mechanical properties of the material. But in the process of glass fiber reinforced nylon injection moulding, the phenomenon of "floating fibers" often occurs. Floating fibers are also called dew fibers, that is, glass fibers dew on the surface of the product, which is rough. Due to the exposure of glass fibers, the application of this kind of products is limited, mainly used in high strength structural parts. And all the appearance parts made of fibre-added materials are matt or etched surfaces (such as electric tools), because ordinary fibre-added materials are difficult to achieve a bright appearance.
There are many reasons for the formation of floating fibers. The main reasons are as follows:
(1) poor compatibility between glass fibre and nylon
Because plastic melt is subjected to friction and shear force of screw, nozzle, runner and gate in the process of flowing, it will cause difference of local viscosity. At the same time, it will destroy the interfacial layer of glass fiber surface. The smaller the melt viscosity is, the more serious the interfacial layer is damaged, and the smaller the bonding force between glass fiber and resin is. When the bonding force is small to a certain extent, glass fiber will get rid of the bond of resin matrix. Gradually accumulated to the surface and exposed.
(2) Specific gravity difference between fiberglass and matrix
In the process of plastic melt flowing, because of the difference of flowability and mass density between glass fiber and resin, the two tends to be separated. Glass fiber floats to the surface and resin sinks inward, thus forming the phenomenon of glass fiber exposed.
(3) Fountain effect
When nylon melt is injected into the mould, the "fountain" effect will be formed, that is, the glass fibers will flow from the inside to the outside and contact with the cavity surface. Because of the low temperature of the mould surface, the glass fibers with light and fast condensation quality will be frozen instantaneously. If they cannot be fully surrounded by the melt in time, they will expose and form "floating fibers".
Therefore, the formation of "float fiber" phenomenon is not only related to the composition and characteristics of plastic materials, but also to the forming process, which has greater complexity and uncertainty.
Solution of Glass Fiber Reinforced Nylon "Floating Fiber"
In actual production, there are various measures to improve the phenomenon of "floating fibers":
(1) Improving the Compatibility between Glass Fiber and Nylon
Additives such as compatibility, dispersant and lubricant, including silane coupling agent, maleic anhydride graft compatibilizer, fatty acid lubricant and some home-made or imported anti-Glass fiber exposing agent, are added to the moulding material to improve the compatibility between glass fiber and resin, improve the uniformity of dispersed phase, increase the interfacial bond strength and reduce the separation of glass fiber and resin. Thus, the phenomenon of glass fiber exposure can be improved. For example, the compatibility of the modified glass fibers in the matrix was significantly improved when compatibilizers were added to the matrix.
(2) Improving the Forming Process Conditions
A. Increasing filling speed
After increasing the velocity, the relative velocity difference between fiberglass and plastics is smaller than that of high-speed jets, although the velocity difference between fiberglass and plastics is different.
B. Increasing die temperature
This function is the biggest, increase the temperature of the mould, is to reduce the contact resistance between the glass fiber and the mould, so that the speed difference between the glass fiber and the plastic is as small as possible. And let the melting layer in the middle of the plastic flow as thick as possible, and the epidermis on both sides as thin as possible, as if the smooth river bank could not retain the branches. RHCM uses this principle to achieve appearance without floating fibers.
C. Reduce the temperature of screw measuring section and the amount of sol
This is to minimize the possibility of separating plastic and glass fibers. Generally speaking, it has the smallest impact on float fibers and has little effect in practical operation. However, this can be a good solution to burning. This is because after adding fiberglass, it is easy to block the exhaust passage, so it is difficult to exhaust in the end, and fiberglass is easy to burn in high pressure and high oxygen gas environment.
(3) Mold aspect
The surface of the product is deliberately made into a matt surface or etched surface to reduce the visual response of glass fiber exposure.