What is the difference between a blow molding process and an injection molding process?

- Oct 21, 2019-

The blow molding products are all hollow; because of the injection molding port, the molded product will have a small and unnecessary part, and there will be a process to cut it off, but if you look carefully, you can still find it;


Injection molding is a method in which a thermoplastic or thermosetting molding compound is first uniformly plasticized in a heating cylinder and then pushed by a plunger or moving screw into a cavity of a closed mold.


Injection molding is suitable for almost all thermoplastics. In recent years, injection molding has also been successfully used to form certain thermoset plastics. The molding cycle of injection molding is short, and the quality of molded products can range from several grams to several tens of kilograms, and moldings with complicated shapes and precise dimensions, with metal or non-metal inserts can be formed at one time. Therefore, the method is highly adaptable and has high production efficiency.


Blow molding: A method in which a hot parison closed in a mold is inflated into a hollow article by gas pressure, or a tubular parison is inflated into a tubular film. This method is mainly used in the manufacture of various packaging containers and tubular membranes.


Any melt blown material with a melt index of 0.04~1.12 is a good hollow blow molding material, such as polyethylene, polyvinyl chloride, polypropylene, polystyrene, thermoplastic polyester, polycarbonate, polyamide, cellulose acetate and poly Acetal resin or the like, in which polyethylene is most used.


Injection Blow Molding: The plastic is first made into a bottomed parison by injection molding, and then the parison is moved into a blow mold to be blown into a hollow product.


Extrusion blow molding: The plastic is first made into a bottomed parison by extrusion, and then the parison is moved into a blow mold to be blown into a hollow product.


Stretch blow molding: Stretch blow molding is a blow molding of biaxially oriented stretching by first stretching the form longitudinally and then inflating with compressed air to achieve transverse stretching. Stretch blow molding can greatly improve the transparency, impact strength, surface hardness and rigidity of the product, and is suitable for blow molding of polypropylene and polyethylene terephthalate.


Blown film method: A method of forming a thermoplastic film. The plastic is first extruded into a tube by extrusion, and then continuously expanded to a tubular film of a certain size by air blown into the tube, and then folded and wound into a double-layer flat film after cooling.