Basics of Blow Molding

Blow Molding Parts

Blow Molding: Molding process in which air pressure is used to inflate soft plastic inside a mold cavity

  • Applications: One-piece hollow plastic parts with thin walls
  • Limited to thermoplastics
    Process: accomplished in two steps: (1) fabrication of a starting tube of molten plastic, called a parison (same as in glass-blowing); and (2) inflation of the tube to the desired final shape.
  • Two Types: Extrusion and Injection Blow Molding
  1. Extrusion Blow molding: (1) extrusion of parison; (2) parison is pinched 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.
  2. Injection Blow Molding: Starting parison is injection molded. 1) parison is injected molded around a blowing rod; (2) injection mold is opened and parison is transferred to a blow mold; (3) soft polymer is inflated to conform to the blow mold; and (4) blow mold is opened, and blown product is removed.