What is the difference between blow molding and injection molding?

- Feb 21, 2019-

Blow molding products are hollow;Injection molding because there is injection molding mouth, so the molding of the product will be a small part of the fast do not want, youdao process will cut it, but if carefully observed or can be found;


Injection molding (injection molding) is a method in which the thermoplastic or thermosetting molding plastics are uniformly plasticized in the heating cylinder and then pushed into the closed mold cavity by the plunger or moving screw. 


Injection molding is suitable for almost all thermoplastics.In recent years, injection molding has also been successfully used to form certain thermosetting plastics.Injection molding molding cycle is short (a few seconds to a few minutes), the quality of the molding products can be from a few grams to dozens of kilograms, a molding complex shape, precise size, with metal or non-metal insert molding products.Therefore, this method has strong adaptability and high production efficiency.


Blow molding.By means of gas pressure, the hot billet closed in the mold is blown into a hollow product, or the tube billet is blown into a tube film without a mold.The method is mainly used in the manufacture of various packaging containers and tubular membranes.All melt index of 0.04~1.12 are relatively good blow molding materials, such as polyethylene, polyvinyl chloride, polypropylene, polystyrene, thermoplastic polyester, polycarbonate, polyamide, cellulose acetate and polyacetal resin, among which polyethylene is the most widely used.


(1) injection blow molding.The injection molding method is used to first make plastic into a bottom-type billet, and then the billet is moved into a blow molding mold to blow hollow products.


(2) extrusion blow molding.The extrusion method is used to first make plastic into a bottom-type billet, and then move the billet into a blow molding mold to blow hollow products.


(3) stretch blow molding.Stretch blow molding is a kind of biaxial directional stretch blow molding, the method is the first will also carry out longitudinal stretch, and then use compressed air blowing to reach transverse stretch.Stretch blow molding can greatly improve the transparency, impact strength, surface hardness and rigidity of products. It is suitable for the blow molding of polypropylene and polyethylene terephthalate (PETP).


(4) blowing film method.A method for forming thermoplastic films.By means of extrusion method, the plastic is first extruded into a tube, and then continuously expanded to a certain size with the help of air blowing into the tube, and then folded and wound into a double-layer flat film after cooling.