As the weight of automobiles continues to advance, people are paying more attention to glass fiber reinforced modified plastics. Today we talked with everyone about how to ensure the effective length of glass fiber in the resin matrix from the equipment and process, first we must first understand the specific significance of the effective length of glass fiber modification.
The optimal length of glass fiber in the resin matrix
The length of the glass fiber in the resin matrix is too short to act as a filler and does not play an enhanced role (the same effect as the cheap CaCO3, which kills you). Too long, although the effect of the reinforcement is significant, it affects the glass. Fiber dispersion in the resin matrix, molding process performance and product performance.
Therefore, it is generally considered that the ideal length of the glass fiber in the thermoplastic tree matrix should be 5 times its critical length. The critical length is the minimum length necessary for a glass fiber in a given diameter of a fiber-reinforced thermoplastic to reach the stress value at which it breaks.
Because in glass fiber reinforced plastics, the length of glass fiber can only transmit the stress when it reaches a certain length, and it plays a role in reinforcing the material, otherwise it is high-grade CaCO3. However, it is not the same as a martial arts novel, "one inch long and one inch strong," but it has an optimal length. In addition, even if the optimum length is found, it cannot be 100% to ensure that the effective length of the glass fiber in the product is this value, because the processing equipment and the process have a great influence on the final effective length of the fiberglass, it is like, your Trousers have shrunk. So, next Xiaobian will give you a talk about how to ensure the effective length of glass fiber in equipment and process.
(1) screw configuration and barrel configuration
The overall goal of twin screw configuration design and barrel configuration for the preparation of glass fiber plastics is:
1 Prevent matrix resin from degrading and evenly disperse the glass fiber in the matrix resin;
2 to ensure that each fiber is maximally wetted by the polymer melt;
3 Shorten the fibers to the optimum length to ensure that the mixture achieves maximum reinforcement;
4 The volatiles in the extrusion process can be cleaned.
The groove introduced by the glass fiber should adopt a large lead, so that the polymer fills the screw groove to allow sufficient space to accommodate the glass fiber. In addition, in order to avoid that the inlet is blocked by the polymer, the short glass fiber is introduced using the thread original, and the long glass fiber can be introduced using at least one pair of kneading disc originals.
The design of the screw configuration downstream of the glass fiber inlet should be conducive to the change and homogenization of the glass fiber length. Long glass fiber is headless. After adding the screw, it must be cut into a certain length and mixed well with the melt. The mixing section should be composed of distributed mixed originals, or thin kneading discs and toothed mixed originals. The short glass fiber mainly depends on the polymer melt to wet and disperse the fiber, so the mixing section can be composed of a kneading block composed of a thin kneading disk or an original thread or an original toothed plate that is grooved on the screw thread.
High-viscosity polymers or high-glass-content (>40%) screw configurations provide a softer shear than low-viscosity polymer or low-fiber screw configurations, ensuring that glass fibers do not break excessively.
(2) Exhaust section settings
The twisted fibers in the long glass fiber are treated with a paraffin emulsifier impregnant, while the non-twist fibers are treated with a fortifier. At a certain temperature, after the glass fiber is mixed in the melt, the impregnant and the strengthening agent on the glass fiber are changed into a hair-drier component during the extrusion process, and an exhaust section needs to be provided for elimination. The exhaust section should be located downstream of the glass fiber inlet. At the exhaust port upstream of the exhaust port, a sealing screw should be installed to prevent particles from being pulled out by the vacuum pump, such as the reverse thread or the reverse kneading block.
(3) The final section of the screw (homogenization and build-up section)
In order to granulate the mixture extrusion die, a small lead should be used to transport the original thread in the forward direction to establish the extrusion pressure. Between the exhaust port and the final section of the screw, the toothed plate is sometimes set to homogenize the fibers to ensure even distribution of the glass.
(1) Join of glass fiber
Long glass fiber and short glass fiber are added in different ways.
1 Short glass fiber is generally added by a metering device, but when the length of the short glass fiber is greater than 6mm, a vibrating metering device can be used to add the polymer and the glass fiber premix together, otherwise the fiber and the resin will be separated. . In order to increase the output, side feeding devices can be added from the side feeding ports.
2 long glass fiber is relatively easy to add, no special feeding device is required, as long as the long glass fiber added to the twin screw feed port can be introduced.
(2) Where the glass fiber is added
Under normal circumstances, the polymer is added at the first (main) feed port. After it is melted, the glass fiber is added at the downstream feed port, ie, the subsequent feed is used. Because of the subsequent feeding, the glass fiber is added to the melted polymer. After the melt is mixed with the fiber, the fiber is wrapped to provide a lubricating and protecting effect, and the excessive breakage in the mixing process of the fiber and the resin is reduced, which is beneficial to the glass fiber. Dispersion and distribution in the melt.
to sum up
In the process of glass fiber modification, especially in long glass fiber modified plastics, there are many factors affecting the effective length of glass fiber. Some of the more critical factors are briefly analyzed above. Therefore, in the end, it is still necessary to feedback from the product's performance, and whether the process, equipment, and formulation are appropriate.