1、Blow MoldingBlow molding technology has been adapted from the glass industry for molding of hollow containers from thermoplastic materials. The most widely known blow molded objects are bottles, jars, cans, and containers of all types for the food, beverage, cosmetic, medical, pharmaceutical, and ho

2、me products industries. Among other blow molded objects are balls, toys, automobile fuel tanks, and car bumpers. These objects are hollow and thin walled. (Note: Some toys such as the head part of a child's doll, inexpensive kick balls, and huge 100 gallon polyethylene tanks may appear to be blo

3、w molded, but are actually made by a process called rotational molding.)Blow molding consists of three major stages: melting or plasticizing the resin, forming a parison or preform, and inflating the parison or preform in a blowing mold to produce an end product. In the first and second stages, plas

4、tic pellets are melted and mixed under heat and pressure to form a tube called a parison or preform. Either extrusion or injection molding is used to form the parison. In the blow molding process, the parison is extruded into a cold mold and inflated with hot air. When the molten plastic touches the

5、 sides of the cold mold, it cools and assumes the inside dimensions of the mold. As the preform is heated and while being inflated inside the cold mold, it is mechanically stretched along it vertical axis. Common problems in the blow molding process include production of irregular frosty surfaces an

6、d non-uniform wall thickness.These three industrial processes are not the only way to mold a plastic item. Processes such as calendering, casting, coating, laminating, compression molding, rotational molding, sheet forming, and vacuum forming may also be used. It is not the purpose of this module to go into descriptions of these processes but one must be aware that they exist. It is also not the purpose of this module to give an engineering description of the three described. The explanations are simplified to give the