As the lighter weight of automobiles continues to advance, people are paying more attention to glass fiber-reinforced modified plastics. Today we will talk with you about how to ensure the effective length of glass fiber in the resin matrix from the equipment and process. First of all, we first To 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 it does not play an enhanced role (the same effect as the cheap CaCO3, which will kill you). Too long, although the effect of the reinforcement is significant, it affects the glass. Fiber dispersion in the resin matrix, forming processability and product performance.
Therefore, it is generally believed that the ideal length of a glass fiber in a thermoplastic tree matrix should be 5 times its critical length, which is the stress at which the glass fiber withstands the glass fiber in a given diameter of the fiber-reinforced thermoformer The minimum length required.
Because in the glass fiber reinforced plastic, fiberglass length only reaches a certain length in order to transfer stress, play a role in enhancing the material, otherwise it is high-grade CaCO3, but not like the martial arts novel 'an inch long, one inch strong', but there is a In addition, even if the optimal length is found, it can not be 100% guaranteed that the effective length of glass fiber in the product is that value because the processing equipment and processes have a great influence on the final effective length of the glass fiber. For example, your pants have shrunk, so Xiaobian then talk to you about how to ensure the effective length of fiberglass on equipment and workmanship.
Equipment factors
(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 the 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 of the glass fiber should adopt a large lead, so that the polymer fills the screw groove, to flow out enough space to accommodate the glass fiber. In addition, in order to avoid the plugging of the inlet by the polymer, the short glass fiber is introduced with the thread original, long Fiberglass can be imported using at least one pair of kneading discs.
The design of the screw configuration downstream of the glass fiber inlet should be conducive to the change and homogenization of the length of the glass fiber. The long glass fiber is of no head. After the screw is added, it must be cut into a certain length and mix well with the melt. The mixing section should consist of Distribution of mixed original composition, or thin kneading disk, tooth-shaped hybrid original. Short glass fiber, mainly by the polymer melt fiber soaked and dispersed, so the mixing section may have a thin kneading plate consisting of kneading block or screw The original grooved thread or the original tooth plate element.
High viscosity polymers or high glass content (> 40%) screw configurations provide a softer shear force than low viscosity polymer or low fiberglass screw configurations to ensure the glass is not excessively broken.
(2) Exhaust section settings
Twisted fibers in long glass fibers are treated with a paraffin wax emulsifying impregnant and untwisted fibers are treated with a toughening agent. After a certain temperature, after the glass fibers are melt-mixed, the impregnating agent on the glass fibers and Reinforcing agent in the extrusion process by the high temperature will become a component, the need to set the exhaust section to be excluded.Exhaust section should be located downstream of the fiberglass inlet, upstream of the exhaust section near the exhaust port should be set Sealing screw original to prevent the role of the vacuum pump particles were withdrawn, such as the reverse thread original or reverse kneading block.
(3) the last section of the screw (homogenization and build pressure section)
In order to extrude the mixture into a die, a small lead forward feed screw thread should be used to establish the extrusion pressure. Between the exhaust port and the last section of the screw, a toothed plate element is sometimes provided, To ensure uniform distribution of glass fiber.
Technological factors
(1) glass fiber added
Long glass fiber and short glass fiber to join using different methods.
① short glass fiber metering devices generally join, but when the chopped glass fiber length greater than 6mm is, you can use vibration metering feeding device, polymer and glass fiber premix together, or it will cause the fiber and resin separation In order to increase the output, the side feeding device can be used to add the side feeding port.
② long glass fiber easier to join, do not need special feeding device, as long as the hanging glass fiber into the twin screw feeding port can be.
(2) the location of glass fiber added
Under normal circumstances, the polymer is added to the first (main) feed port, to be melted, and then the glass fiber feed port in the downstream to join, that is, the follow-up feed because of subsequent feeding, glass is added to the molten polymerization In the material, after the melt and the fiber are mixed, the fiber is wrapped to play a lubricating and protecting role, thereby reducing excessive breaking of the fiber and the resin during mixing, which is beneficial to the dispersion and distribution of the glass fiber in the melt.
to sum up
In the glass fiber modification, especially the long glass fiber modified plastic process, the effective length of the fiber length of many factors, the above simple analysis of some of the more critical factors.So, ultimately, the final performance of the product from the feedback, technology, Equipment and formula is appropriate.