The difference between plastic Injection molding and blow molding

- Jun 25, 2020-

Injection molding, that is, thermoplastic injection molding, this method is to melt the plastic material and then inject it into the film cavity. Once the molten plastic enters the mold, it is cooled to a certain shape according to the cavity. The resulting shape is often the final product, and no further processing is required before installation or use as the final product. Many details, such as protrusions, ribs, and threads, can be formed in one step of injection molding. The injection molding machine has two basic components: an injection device and a mold clamping device for melting and feeding plastic into the mold. 

The role of the mold device is: 1. Make the mold closed under the injection pressure; 2. Take the product out of the injection device to melt the plastic before it is injected into the mold, and then control the pressure and speed to inject the melt into the mold. There are two designs of injection devices currently used: screw-type preplasticizers or two-stage devices, and reciprocating screws. The screw preplasticizer uses the preplasticized screw (first stage) to inject molten plastic into the injection rod (second stage). The advantages of the screw preplasticizer are constant melt quality, high pressure and high speed, and precise injection volume control (using mechanical thrust devices at both ends of the piston stroke). These advantages are required for transparent, thin-walled products and high production rates. The disadvantages include uneven residence time (causing material degradation), higher equipment costs and maintenance costs. The most commonly used reciprocating screw injection device does not require a plunger to melt and inject the plastic.

Blow molding: Also known as hollow blow molding, a rapidly developing plastic processing method. The tubular plastic parison obtained by extrusion or injection molding of thermoplastic resin is placed in a split mold while it is hot (or heated to a softened state). After the mold is closed, compressed air is passed into the parison to blow the plastic parison Swell and cling to the inner wall of the mold, after cooling and demolding, you can get a variety of hollow products. The manufacturing process of blown film is very similar to the blow molding of hollow products in principle, but it does not use a mold. From the perspective of the classification of plastic processing technology, the forming process of blown film is usually included in extrusion. The blow molding process was used to produce low-density polyethylene vials during the Second World War. In the late 1950s, with the birth of high-density polyethylene and the development of blow molding machines, blow molding technology has been widely used. The volume of hollow containers can reach thousands of liters, and some production has been controlled by computers. Plastics suitable for blow molding include polyethylene, polyvinyl chloride, polypropylene, polyester, etc. The resulting hollow containers are widely used as industrial packaging containers.

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