How to enhance plastic molding is a problem that is often discussed in the plastic molding industry. The effect of enhanced plastic molding undoubtedly has a very large jump in the cost of production and the qualification rate of finished products. However, many novice friends in the industry This problem is still quite distressed, so this chapter briefly introduces how to enhance the knowledge of plastic molding. The specific content is as follows:
First, in order to further improve the solidity and mechanical properties of thermoplastics. Glass fiber, talc, mica, calcium carbonate, kaolin, carbon fiber, etc. are often added to plastics as reinforcing materials. Resin is used as a matrix and a binder to form a new composite material, which is called reinforced plastic.
Secondly, due to the different types, lengths, and contents of plastic mixed glass fibers, their processability and physical properties are also different. The following mainly introduces thermosetting reinforced plastics for molding and thermoplastic reinforced plastics for injection.
Thermosetting reinforced plastic
Thermosetting reinforced plastics are composed of resins, reinforcing materials, and additives. Among them, the resin is used as a matrix and a binder, which requires good fluidity, suitable curing speed, few by-products, easy adjustment of viscosity and good compatibility, and needs to meet the requirements of plastic parts and molding. Reinforcement materials play a skeleton role, and there are many varieties and specifications, but glass fiber is commonly used, with a general dosage of 60% and a length of 15-20 mm. Auxiliaries include diluents to adjust viscosity (to improve the adhesion of glass fiber to resin), glass fiber surface treatment agents to adjust the state of the resin-fiber interface, to improve fluidity, reduce shrinkage, improve gloss and resistance Fillers and colorants for abrasive properties. Due to the selected resin, the specifications of the glass fiber (length, diameter, alkali-free or alkali-containing, count, number of strands, twisted or twisted), surface treatment agent, glass fiber and tallow blending process (premix method) Or the prepreg method, the plastic ratio and other properties will vary.
1. The fluidity of the fluidity-reinforcing material is worse than that of general compression molding materials. When the fluidity is too large, resin loss and glass fiber separation and accumulation are easy to occur. If it is too small, the molding pressure temperature will increase significantly. There are many factors affecting fluidity. To evaluate the fluidity of a certain material, a specific analysis must be made according to the composition. Factors affecting liquidity
2. Shrinkage-enhancing plastic The shrinkage of plastic is smaller than that of general compression plastic. It is mainly composed of heat shrinkage and chemical structure shrinkage. The factors that affect shrinkage are primarily plastics. Generally, phenolic resin is larger than epoxy, epoxy phenolic resin, unsaturated polyester, etc. Among them, unsaturated polyester material has the smallest shrinkage. Other factors that affect shrinkage are the shape and wall thickness of the plastic part. Thick walls shrink more, volatile matter content shrinks more, molding pressure is higher, and the amount of material is smaller, shrinkage is greater. Hot mold release shrinks more than cold mold release. , The shrinkage is insufficient when the curing is large, the shrinkage is small when the pressing time and the molding temperature are appropriate, and the curing surface is uniform. The shrinkage of different parts of the same plastic part is also different, especially for thin-walled plastic parts. Generally, the shrinkage rate is 0 to 0.3%, and the majority is 0.3% to 0.2%. The shrinkage is related to the mold structure. In short, various factors should be considered in determining the shrinkage rate.
3. Compression ratio The specific volume and compression ratio of the reinforced material are larger than that of ordinary plastics, and the premix is larger. Therefore, it is necessary to take a larger loading chamber when designing the mold, and it is also difficult to charge the mold. Premixing is more inconvenient, but the compression ratio can be significantly reduced if the preform process is used.
The above content is a systematic analysis of enhancing plastic molding knowledge. More information is available at http://ylscps.com
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