The injection molding process and the blow molding process are also plastic production processes. Careful observation will reveal that the two have obvious differences in principle and have their own advantages. So, what are the advantages and disadvantages of injection molding process and blow molding process?
Injection molding is the parison is completed in the injection mold, and blow molding is the parison is completed in the blow mold. Generally, blow-molded products are hollow. Because injection molding has an injection port, a small part of the molded product will be cut off.
1. Injection molding process
Advantages: The wall thickness distribution of the parison in the injection molding process can be precisely controlled by the injection mold, so that the wall thickness of the obtained container is more uniform, and the thinning phenomenon that is easy to occur in the corner part of the general blow molded product is avoided. The parisons made by injection can all enter the blow mold for inflation molding, which reduces the waste of molding materials and saves the trimming man-hours of the product.
Disadvantages: injection molding and blow molding must use two sets of molds and a hollow core mold with a valve, and the cost of injection molds and core molds are relatively high; the temperature of the injection parison is higher, and the high temperature parison is blown in the injection mold After expansion, a longer cooling setting time is required, which prolongs the entire molding cycle of the product and reduces production efficiency; the internal stress of the injection molding parison is relatively large, and when the mold is changed, it is easy to be unevenly cooled, thereby increasing the blow molding of polyolefin plastics. There is a danger of stress cracking in the container. Each product must use two sets of molds, injection parison mold and inflation molding mold. The injection parison mold must be able to withstand high pressure, the positioning tolerance level of the two molds is relatively high, the cost of the mold is increased, the shape and size of the production container are limited, and it is not suitable to produce a container with a handle.
2. Blow molding process
Advantages: The cost of blow molding machinery, especially blow molds, is low. When forming similar products, the cost of blow molding machinery is about 1/3-1/2 of that of injection machinery, and the production cost of products is also low. In blow molding, the parison is formed under a lower pressure through the die and inflated at a low pressure, most of which is 0.2-1.0mpa, so the residual stress of the product is small, and it is resistant to stretching, impact, bending and environment. This strain has higher performance and better performance. In injection molding, the melt has to pass through the mold runner and gate under a high pressure of 15-140mpa, which will cause uneven stress distribution. The relative molecular mass of blow molding grade plastics, such as pe, is much higher than that of injection grade plastics. The wall thickness of the product is uniform, no post-modification processing is required, the product has no seams, and there is less waste.
Disadvantages: The design requirements of the blow mold should be equipped with an exhaust groove, and the bottom should be concave. The mold body should be corrosion-resistant carbon tool steel and ordinary alloy steel. Tube blank temperature and blow molding temperature. If the temperature is too high, the melt viscosity is low and it is easy to deform, causing the tube blank to appear uneven in thickness during transfer. Too low temperature products often have more internal stress, which is prone to deformation and stress cracking during use.
3. Comparison of injection molding process and blow molding process
At present, injection molding is suitable for almost all thermoplastics. In recent years, injection molding has also been successfully used to mold certain thermosetting plastics. The molding cycle of injection molding is short, and the quality of molded products can range from a few grams to tens of kilograms. It can form molded products with complex shapes, accurate dimensions, and metal or non-metal inserts at one time. The method has strong adaptability and high production efficiency.
Blow molding is widely used. It is a method to inflate the hot parison closed in the mold into a hollow product by means of gas pressure, or to inflate the tube parison into a tube film without a mold. This method is mainly used for the manufacture of various packaging containers and tubular films. As long as the melt index is 0.04~1.12, they are relatively excellent hollow blow molding materials, such as polyethylene, polyvinyl chloride, polypropylene, polystyrene, thermoplastic polyester, polycarbonate, polyamide, cellulose acetate and Polyacetal resin, etc., of which polyethylene is used more often.
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