Blow molding is a manufacturing technique that uses thermoplastic materials (be it polymer or resin) and shapes them into molten tubes. These tubes are then inserted inside a mold cavity and inflated. The inflating portion of the tube takes the shape of the cavity inside the mold. Once the tube has filled up the entire cavity, it is cooled down and extracted out of the mold.
Blow molding generally makes hollow parts which are made out of thermoplastic materials. One of the most common examples of blow molded products is bottles. Some other examples of blow molded parts include industrial containers, garden and other household items, medical containers and supplies, hood-related parts for automobiles, and interior components of electronic appliances.
Types of Blow Molding
Blow molding processes are categorized on the basis of how the hollow tube is formed, the size of the tube, and the nature of movement (stationary, shuttling, linear or rotatory) between the tube and the mold. Based on these parameters there are three kinds of blow molding.
Extrusion Blow Molding – In EBM the polymer or resin is melted, and the molten material is extruded in the form of a tube. The two separate halves of the mold are cooled and closed-in over the tube. Compressed air is then pumped through this extruded tube either through a needle or a pin. The part of the tube-encased by the mold begins to inflate acquiring the shape of the interiors of the mold over time. Once the polymer has taken shape, it is cooled and extracted out of the mold. EBM has two methods of extrusion known as continuous and intermittent. Some examples of continuous intrusion are rotatory wheel machine and continuous extrusion machines. Intermittent extrusion involves reciprocating screw or an accumulator head.
Injection Blow Molding- instead of closing the tube with the mold, in IBM the material is injected into the mold and onto a core within the cavity. The tube is then rotated on the core which results in the blowing of the tube. Once enough of the material has settled around the cavity from the core rod, the mold is cooled down for the material to harden and retain shape. The process is divided into three steps: injection, blowing, and extraction. All the three steps are carried out by a single integrated system in an automated fashion. Some common examples of IBM parts are bottles, medical components and cosmetic packages among others
Injection Stretch Blow Molding- ISBM is similar to ISB in most steps. Here the polymer tube is injected into the mold cavity. The mold is then processed for blowing. However, in ISBM, the tube is not only stretched radially but along the length as well. Some common polymers used in ISBM are PET and PP. These polymers demonstrate an improvement in their material properties when stretched. The stretching also results in better strength and barrier-forming properties while reducing the overall weights of the components. ISBM gives much higher quality results when compared with EBM or IBM.
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