Presumably you read a lot of news and articles on car lightweight, long fiberglass PP and nylon yellows, and who launched a new fiberglass products. The stereotyped emphasis on "why? How to use? Where?" To no one mentioned the most primitive things - how to prepare these materials? Xiaobian read just think "the body is hollowed out" in the car To use those parts of plastic, but also how hyped to talk about?
1、The optimal length of glass fiber in the resin matrix
Glass fiber in the resin matrix length is too short, only played the role of filler, can not afford to enhance the role (like a few hundred dollars a ton of CaCO3 the same effect, the loss of you); too long, although the enhanced effect Significant, but affect the dispersion of glass fiber in the resin matrix, forming processability and product performance.
Therefore, it is generally believed that the ideal length of glass fiber in the thermoplastic matrix should be 5 times its critical length. The critical length is the minimum length necessary for the glass fiber under stress in a given diameter of the fiber reinforced thermoplastic to reach the value of its stress at break. Popular is that you go to the mall to buy pants, trousers tube length is generally not just good to the ankle, but grow a few centimeters, to prevent shrinking overnight into a pants is a concept. As the saying goes "no more than pre-less."
Figure long / short glass fiber modified PP performance comparison
Because in the glass fiber reinforced plastic, fiberglass length only reaches a certain length to transfer stress, play a role in enhancing the material, otherwise it is high-grade CaCO3. But it is not the same as a martial arts novel "one inch long, one inch strong", but there is a best length. 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 the value because the processing equipment and process have a great influence on the final effective length of the glass fiber. For example, your Pants shrink. So, then Xiaobian talk to you about how to ensure the effective length of fiberglass on equipment and technology.
2、Factors that affect the effective length of glass fiber in plastics
1、 equipment factors
(1) screw configuration and barrel configuration
The general objectives of twin-screw configuration design and barrel configuration for preparing glass fiber plastic are: (1) to prevent the matrix resin from degrading and to make the glass fiber uniformly dispersed in the matrix resin; (2) to ensure that each fiber is maximally melted by the polymer Degree of wetting; ③ the fiber cut to the best length, to ensure that the mixture to achieve maximum enhancement effect; ④ extrusion process of volatile emissions can be drained.
⑴ glass fiber added to the screw configuration: glass fiber added to the groove should be used for large lead, the polymer filled with screw groove to flow out enough space to accommodate glass fiber. In addition, in order to avoid the port being blocked by the polymer, the short glass fiber is introduced with a thread original, and the long glass can be introduced with at least one pair of kneading disc original.
⑵ glass fiber cut off and dispersed:
① glass fiber inlet downstream of the screw configuration design should be conducive to changes in the length of glass fiber and homogenization. The long glass fiber is endless. After the screw is added, it must be cut into a certain length and mix well with the melt. The mixing section should be composed of distributed and mixed original pieces or thin kneading discs and toothed mixed original pieces.
② 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 grooved in the spiral groove on the original thread or toothed plate composition.
(3) high viscosity polymer or high glass content (> 40%) screw configuration than low viscosity polymer or glass fiber content of the screw configuration provides a softer shear to ensure that the glass will not be over-broken .
(2) exhaust section settings
Because some of the glass is pretreated, such as long fiberglass twisting fibers are treated with a paraffin wax emulsifying impregnant, and untwisted fibers are treated with a toughening agent. At a certain temperature, after the glass fiber is melt-mixed, the impregnating agent and the reinforcing agent on the glass fiber become the constituent components after being subjected to the high temperature during the extrusion process, and the exhaust section needs to be disposed of to be excluded. Exhaust section should be located downstream of the fiberglass inlet, upstream of the exhaust section near the exhaust port, the sealing screw should be set to prevent the vacuum pump under the action of the particles were withdrawn, such as the reverse thread or reverse kneading blocks.
(3) the last section of the screw (homogenization and build pressure section)
In order to extrude the mixture into the die, a small lead forward feed thread should be used to establish the extrusion pressure. In the exhaust port and the last section of the screw, and sometimes to set the toothed plate original, the fiber homogenization, to ensure uniform fiberglass distribution.
2, process 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 added by side feeding opening.
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 in the first (main) feeding port, to be melted, and then add the glass fiber feed port downstream, which uses the follow-up feed. Because follow-up feeding, glass fiber is added to the molten polymer, the melt and fiber mixed, the fiber wrap, play a role in lubrication and protection, reducing fiber and resin over-mixing process is conducive to fiberglass Dispersion and distribution in the melt.