THEORETICAL BACKGROUND BLOW MOLDING

Blow Molding (BM) process makes it possible to manufacture molded products economically, in unlimited quantities, with virtually no finishing required. The basic process of blow molding involves a softened thermoplastic hollow form which is inflated against the cooled surface of a closed mold. The expanded plastic form solidifies into a hollow product. Blow molded components are now seen all over the markets and industries for traditional materials, particularly in liquid packaging applications. The last few decades saw the introduction of polyethylene (PE) squeeze bottles for washing liquids, polyvinyl chloride (PVC) for cooking oil and fruits squash bottles, and polyethylene terephthalate (PET) for carbonated beverage bottles. Nowadays, it is also used for the production of toys, automobile parts, accessories and many engineering components. Blow Molding Process is intended also for manufacturing of most automotive parts and accessories. Below are some of the car plastics parts that are being produced by blow molding process. The use of plastics parts make our car more light weight and helps our car run faster. Extrusion Blow Molding Machine Parts and Functions • Extruder Motor—Drives the screw in the barrel to rotate and push the melted material into the die head. • Gearbox—Reduces the speed of the extruder motor into a required speed enough to push the material into the die head. • Hopper—A feed reservoir into which the material is loaded. • Extruder—A part of the machine that accepts solid resin material, conveys it in a surrounding barrel by means of a rotating screw, melts the material by means of heaters, and pumps it under pressure into the die head. • Cooling Fans—Cools down the barrel during machine shut down to prevent the material from degradation. • Heating Bands—Device attached on the barrel and the die head used to melt the solid material at a required set temperature. • Die Head—Used to form the melted resin into a parison and also used for adjusting the characteristics of molten resin to create a stable parison. • Die & Pin—Used to align the flow of parison to get a good and centered parison. • Hot Cutter—Cuts the parison after the mold is closed for the blowing process. • Blow Pin—Used to blow compressed air into the parison to inflate it after the mold has been closed and form the desired design of the mold. • Mold—A hollow form or a cavity into which a molten plastic material, called parison, is introduced to give the shape of the required component. • Deflasher—Used to cut the excess material on the bottle which is called a flash material (top and bottom). • Post Cooling—A part of the machine that is used to cool down the inside of the bottle, to lessen the cooling time required inside the mold. • Article Discharge—A part of the machine used to take the bottle out.

Higher Institute for Plastics Fabrication
WORKBOOK for Extrusion Blow Molding
Practical Course
Prepared by
Extrusion Blow Molding Department