Blow molding process is a commonly used plastic processing method, but also the rapid development of plastic molding method, the process by air pressure to mold hot melt billet blow into hollow products. Blow molding mold only negative mold (concave mold), compared with injection molding, blow molding has lower equipment cost, strong adaptability, good molding characteristics, can produce products with complex fluctuating curves.
First, the material requirements of blow molding process
If the melt index of the hollow blow molding material is 0.04 ~ 1.12, then it is a high-quality raw material, and the commonly used materials are polyethylene, polyvinyl chloride, polyamide, cellulose acetate and polyacetal resin, etc., of which polyethylene is used more.
Second, the type of blow molding process
There are four types of blow molding process, namely injection blow molding, extrusion blow molding, stretch blow molding and blow film molding.
Injection blow molding
Injection blow molding is mainly used for the processing of the billet supported by the metal core, and its advantages are as follows: there will be no waste generated during the processing; The wall thickness of the product and the dispersion of the material can be controlled; High molding precision, smooth surface; Small batch production is possible.
The disadvantage of injection blow molding is that the cost of molding equipment is high and it is not suitable for larger blow molding products.
Extrusion blow molding
Extrusion blow molding is to first use the extrusion method to make a bottom of the plastic billet, and then move the billet to the blow mold to make hollow products, mainly for the processing of unsupported billets.
The advantages of extrusion blow molding are as follows: high production efficiency; Low equipment cost; Wide selection of molds and machinery. Its disadvantage is that the scrap rate is high; Poor recycling and utilization of waste materials; The thickness control of the product and the dispersion of the raw material are limited; Trimming operation must be carried out after forming.
Stretch blow molding
There are two processing methods of stretch blow molding, one is extrusion a stretch a blow molding, the other is injection a stretch a blow molding, can process biaxial orientation products, can greatly reduce production costs, improve product performance. The product made by this molding method has the characteristics of high transparency, strong impact resistance, high surface hardness and good rigidity.
Blow molding film method
The blow molding film method is to squeeze the plastic into a tube by extrusion method, and then blow air into the tube to make it expand continuously to a certain size, and then fold and wind it into a double-layer flat film after the tube cools. Blow molding film method is widely used in the production of polyethylene, polyvinyl chloride, polyamide and other films.
