The blow molding process is a commonly used plastic processing method and a rapidly developing plastic molding method. This process uses air pressure to inflate the hot-melt parison in the mold into a hollow product. Compared with injection molding, blow molding has the characteristics of lower equipment cost, strong adaptability, good molding ability, and can produce products with complex undulating curves.

1. Material requirements for blow molding process

If the melt index of the hollow blow molding material is 0.04 to 1.12, then it is a high-quality raw material. Commonly used materials are polyethylene, polyvinyl chloride, polyamide, cellulose acetate and polyacetal resin, among which polyethylene applied more.

Second, the type of blow molding process

There are four kinds of blow molding processes, namely injection blow molding, extrusion blow molding, stretch blow molding and blown film method.

Injection blow molding

Injection blow molding is mainly used for the processing of parisons supported by metal cores. 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 make plastic into a bottomed parison by extrusion, and then move the parison to a blow mold to make a hollow product, which is mainly used for unsupported parison processing.

The advantages of extrusion blow molding are as follows: high production efficiency; low equipment cost; wide selection of molds and machinery. The disadvantage is that the scrap rate is high; the recycling and utilization of waste are poor; the thickness control of the product and the dispersibility of the raw materials are limited; the trimming operation must be carried out after molding.

stretch blow molding

Stretch blow molding has two processing methods, one is extrusion-stretch-blow molding, the other is injection-stretch-blow molding, which can process biaxially oriented products, which can greatly reduce production costs. Improve product performance. The products made by this molding method have the characteristics of high transparency, strong impact resistance, high surface hardness and good rigidity.

Blown film method

The blown film method is to extrude plastic into a tube by extrusion method, and then blow air into the tube to continuously expand it to a certain size. After the tube is cooled, it is folded and rolled into a double-layer flat film. The blown film method is widely used, and is often used to make films such as polyethylene, polyvinyl chloride, and polyamide.