Views:151 Author:Vera Publish Time: 2019-02-21 Origin:Site
The mechanical properties of nylon can be improved by adding glass fiber, toughening agent and other fillers. But in the process of glass fiber reinforced nylon injection molding, floating fiber often appears. Floating fiber is also known as exposed fiber, that is, glass fiber exposed in the product surface, relatively rough. Due to the exposure of glass fibers, the application of such products is limited and is mainly applied to high-strength structural members. And All appearance parts made of fiber adding material are matte or etched (for example, electric tool), because ordinary fiber material is difficult to achieve bright appearance.
Cause of formation
There are many reasons for floating fiber formation, and the main reasons are the following three:
Poor compatibility between glass fiber and nylon
Because the plastic melt is subjected to the friction and shear forces of screw, nozzle, runner and gate during the flow process, it will cause the difference of local viscosity, at the same time, it will destroy the interface layer of glass fiber surface. The smaller the melt viscosity, the more serious the damage of interface layer is. The bond between glass fiber and resin is smaller, when the adhesion is small to a certain extent, glass fiber will get rid of the bond of resin matrix and gradually accumulate and expose to the surface.
Density difference between Glass Fiber and Base resin
In the process of plastic melt flow, glass fiber and resin have different flowability and different mass density, so they have the tendency of separation. Glass fiber floats to the surface and resin sinks to the inside, thus forming the phenomenon of glass fiber exsertion.
When the nylon melt is injected into the mold, it will form a "fountain" effect, that is, the glass fiber will flow from the inside to the outside and contact with the surface of the mold. Because of the low temperature of the mold surface, the glass fiber with light mass and quick condensation will be frozen instantly. If not fully surrounded by the melt in time, it will be exposed to form a "floating fiber."
Therefore, the formation of the “floating fiber” phenomenon is related not only to the composition and characteristics of the plastic material, but also to the molding process, and has a large complexity and uncertainty.
Improvement the compatibility of glass fiber and nylon
Add some compatibility, dispersant and lubricant additives, such as silane coupling agent, maleic anhydride graft compatibilizer, fatty acid lubricant and some domestic or imported anti-glass-fiber exposure agents to the molding materials.
These additives can improve the compatibility between glass fiber and resin, increase the homogeneity of dispersed phase, increase the interfacial bond strength, reduce the separation of glass fiber and resin, and improve the phenomenon of glass fiber exposure. It is shown that the compatibility of the modified material glass fiber in the matrix is obviously improved by the addition of the compatilizer in the matrix.
Improvement of moulding process conditions
1. Increasing the filling speed
After increasing the velocity, the velocity of glass fiber and plastic is different, but the ratio of relative velocity difference is smaller than that of high speed projectile.
2. Raise mold temperature
This effect is the largest. Raise mold temperature, is to reduce glass fiber and mold contact resistance, so that glass fiber and plastic speed difference as small as possible.
Make the melt layer as thick as possible and the skin on both sides as thin as possible, just as smooth banks cannot hold on to branches. RHCM technology (high-speed high-temperature molding technology) is the use of this principle to achieve the appearance of non-floating fiber.
3. Reduce the temperature of screw metering section, reduce the amount of sol
It's about keeping plastic from glass as much as possible. Generally speaking, it has the least effect on floating fiber, but it has little effect in actual operation. However, this can be a good solution to coke burning. This is because the glass fiber can easily block the exhaust passage, so it is difficult to exhaust in the end, and the glass fiber is easy to burn in high pressure and high oxygen gas environment.
Improvement of the mould
The surface of the product can be made of sub-smooth or etched surface, reducing the visual reaction of glass fiber exposure.