Views: 56 Author: Site Editor Publish Time: 2021-03-17 Origin: Site
In order to meet the development needs of automotive lightweight, automotive materials have gradually developed from the traditional single metal materials to the "multi-material" direction. The so-called "multi-materialization" refers to the combined use of multiple materials in the automobile manufacturing process. For example, the body frame and shell, in addition to the original steel materials, also combine lightweight materials such as aluminum, magnesium, and glass fiber reinforced composite materials. According to the performance requirements of different positions, a variety of materials can be appropriately combined and selected to achieve a greater lightweight effect while achieving excellent performance. Long glass fiber reinforced thermoplastic material is a new type of automotive material emerging under the trend of "multi-materialization".
Long fiber reinforced thermoplastics (LFT) refers to the glass fiber reinforced plastic particles obtained from long, continuous glass fibers that are fully infiltrated by resin through a special process and then cut into specific sizes. Usually the length of glass fiber is 10 to 25 mm. Long glass fiber reinforced PP material is cheap and has excellent performance no less than that of reinforced engineering plastics, thus showing high cost-effective advantages and good prospects.
LFT material manufacturing process
The traditional glass fiber reinforcement technology is to melt and mix the glass fiber tow directly with the resin base material in the twin screw extruder. Under the action of the frictional shear between the screw and the barrel, the glass fiber bundle is shredded, and the short glass fiber reinforced material is obtained. The length of most of the glass fibers in the final product is lower than the critical length of reinforcement, and the reinforcement ability of glass fibers is not fully utilized.
Different from the preparation of short fiber reinforced materials, long glass fiber reinforced thermoplastic materials are made of long, continuous glass fibers, which are fully infiltrated by resin through a special process, and then cut into specific sizes to obtain glass fiber reinforced rubber particles. When the length of the glass fiber exceeds the critical length Lc, the LFT material shows the performance advantages of high strength and good heat resistance, and can replace the short fiber reinforced thermoplastic composite material.
LFT material performance characteristics
(1) Excellent mechanical properties
Products made of long glass fiber reinforced materials have glass fibers forming a three-dimensional three-dimensional network structure, which can withstand greater stress and load, and effectively absorb energy, so that the composite material can achieve more excellent mechanical properties. The following figure shows the mechanical properties of different fiber-reinforced composite materials:
It can be seen from the above figure that the addition of glass fiber can effectively improve the mechanical properties of the material, and the long glass fiber reinforced composite material is significantly better than the short fiber reinforced material reinforced with the same glass fiber content in tensile modulus and notched impact. . Under the same glass fiber content and under the same force, the PP material reinforced by long glass fiber only has toughness and whitening, while the PP material reinforced by short fiber has brittle fracture.
(2) Degree of warpage
The addition of long glass fiber can significantly reduce the molding shrinkage rate of the matrix resin, but sometimes the glass fiber is prone to uneven orientation in the matrix, causing problems such as large differences in the shrinkage rate between the melt flow direction and the vertical direction, which ultimately leads to the warpage of the part. Therefore it is deformed and cannot be assembled (as shown in Figure 5). The solution is to greatly improve the uniformity of fiber orientation during the injection molding process by improving the interface bonding force between the fiber and the matrix, and reduce the warping deformation of the material.
(3) Product appearance
Due to the addition of glass fibers, the distribution of glass fibers in the resin matrix is difficult to control, resulting in floating fibers on the surface of the product, which affects the appearance of the product. Through a special process, a better control of the glass fiber in the composite material is achieved, so that the surface of the product is smooth and free of floating fibers.
LFT material application
At present, auto parts and spare parts are the first area of LFT application, accounting for more than 80% of LFT production, and there is a tendency to continue to increase. In hybrid and electric vehicle components, engine compartment areas and other structural material applications, LFT materials can be used to manufacture highly integrated components, thereby reducing weight and cost. When used as materials for engine peripherals, LFT materials can achieve high retention of mechanical properties under long-term heat-resistant conditions. When used as automotive interior materials, they have the characteristics of low VOC and low emission. The following are application examples of LFT materials: