extrusion blow molding
Extrusion Blow Molding is the simplest type of blow molding. A hot tube of plastic material is dropped from an extruder and captured in a water cooled mold. Once the molds are closed, air is injected through the top or the neck of the container; just as if one were blowing up a balloon. When the hot plastic material is blown up and touches the walls of the mold the material "freezes" and the container now maintains its rigid shape.
Extrusion Blow molding allows for a wide variety of container shapes, sizes and neck openings, as well as the production of handle-ware. Some extrusion machines can produce 300 to 350 bottles per hour. Extrusion blown containers can also have their gram weights adjusted through an extremely wide range, Extrusion blow molds are generally much less expensive than injection blow molds and can be produced in a much shorter period of time. Advantages of extrusion blow molding include a high rate of production, low tooling cost, and a vast majority of machine manufactures. Some disadvantages usually include a high scrap rate, a limited control over wall thickness, and some difficulty of trimming away excess plastic.
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Extrusion blow molding: (1) extrusion of parison; (2) parison is pinches at the top and sealed at the bottom around a metal blow pin as the two halves of the mold come together; (3) the tube is inflated so that it takes the shape of the mold cavity; and (4) mold is opened to remove the solidified part.
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