Blow molding Continuous tube process

Like the extrusion of metals, the extrusion of plastics involves the continuous forming of a shape by forcing softened plastic material through a die orifice that has approximately the geometric profile of the cross-section of the work. The extruded form is subsequently hardened by cooling. With the continuous extrusion process, such products as rods, tubes, and shapes of uniform cross-section can be economically produced. Extrusion to obtain a sleeve of the correct proportion almost always precedes the basic process of blow molding. 

Extrusion blow molding uses a section of hot extruded tubular material called a parison. This is extruded into an open mold, and compressed air or steam forces the walls of the parison to the sides of a cold mold. The process is commonly used to make bottles, industrial containers, medical items, technical parts, and toys. Blow molding has a low tool and die cost, and parts can be made very rapidly and in one piece. It also can be used to produce relatively complex shapes, although limited to hollow or tubular parts. The wall thickness is difQcult to control. Continuous tubing and film can be made in a manner similar to blow molding. 

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