eFunda: Introduction to Extrusion Blow Molding
engineering fundamentals Introduction to Extrusion Blow Molding
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Extrusion Blow Molding
Extrusion blow molding is the oldest, simplest, and most common type of blow molding. Common gallon or larger size gas tanks and water tanks are often manufactured using extrusion blow molding. Its procedures are:
1. A hot hollow tube of thermoplastic material is dropped from an extruder. This tube is usually called parison.
2. The parison is then captured in the closed chamber of a divided mold which seals one end of the parison and leaves the other end open.
3. Compressed air is injected through the open end of the parison. The parison is expanded like an inflated balloon.
4. Compressed air continues to blow in until the parison reaches the wall of the mold. The hollow parison now conforms to the shape of the mold cavity.
5. The molded plastic stays in the mold until it cools and hardens. Once released from the mold, further handlings such as rimming and trimming can be performed.
Pros and Cons of Extrusion Blow Molding
Pros
  • Simple
  • Low costs
  • Fast to setup to begin production
  • Allows a wide variety of container shapes
  • Can produce large size containers
Cons
  • Production speed is slower than other newer blow molding methods.
  • Not suitable for precision parts. Wall thickness is difficult to control.
  • Limited to hollow parts.

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