by garrett pritchyk bryant richardson and mike scesa n.
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Blow Molding

Blow Molding

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Blow Molding

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  1. By Garrett Pritchyk, Bryant Richardson, and Mike Scesa Blow Molding

  2. What is blow molding? • Polymer process that creates hollow plastic parts • This process begins with melting down the plastic that is to be blow molded in to a parison • Parison - in blow molding, the hollow tube of plastic melt extruded from the die head, and expanded within the mold cavity by air pressure to produce the molded part. • Hot air blown into the parison forces it against the mold walls where it is then cooled • Mainly limited to processing of thermoplastics • Most plastic bottles are processed this way • There are three main types of blow molding

  3. History of Blow Molding • Process of blow molding originated from blowing of glass then adapted to polymers • Evidence of Egyptians and Babylonians using blow molding for plastics • Enoch Ferngren and William Koptike are the people credited for the process of blow molding • Sold the first blow molding machine to Hartford Empire Company in 1937 • “In the United States soft drink industry the amount of plastic containers went from zero in 1977 to ten Billion in 1999.” (

  4. Which shapes can be blow molded?

  5. Blow Molding • Medium Tooling Cost (relative) • Medium Equipment Cost (relative) • Low Labor Intensity • Batch size can range from 500 - 50,000,000 units

  6. Types of blow molding Extrusion blow molding Injection blow molding Stretch blow molding

  7. Extrusion Blow Molding(EBM) Begins with a parison/ pre-form and is then placed into an enclosed cooled metal mold Then air is blown into this mold to shape the material to the desired shape Once it is cooled the part is ejected from the mold Can be made continuously or intermittently

  8. EBM

  9. Continuous Extrusion Blow Molding Shuttle Machinery Rotary Blow molding -Very Important in making bottles for food storage -Used for making containers that need up to six layers -Used for medical containers -Blowpins are forced into the molds to calibrate the parts while forcing air into the molds • -Used to make large quantities of product • Size of mold can range from small bottles up to 30 liter drums • Multiple molds and parisons

  10. Intermittent Extrusion Blow Molding Reciprocating Screw Machinery Accumulator Head Machinery -Uses hydraulic pressure to blow the mold -Used for making HDPE dairy containers and five gallon PC water cooler containers -Up to 8-head machines for output of multiple containers -An internal plunger uses hydraulic pressure to blow the mold -Can make products with up to 7 different layers of materials -Used to make gasonline containers, playground equiptment, and other large containers


  12. What’s made by EBM • Dairy containers (HDPE) • Water Cooler Containers (PC) • Medical Containers • Gasoline tanks • Playground Equipment • Shampoo bottles • Pipes • Hoses • Industrial parts and drums

  13. Injection Blow Molding • Polymer melt is supplied to mold halves from injection molding machine • Pre-form injection molded over a mandrel and transferred to the blowing die • Air is injected under pressure through the mandrel blowing the polymer against the mold walls where it cools and freezes as with extrusion blow molding

  14. Factors Critical to Injection Blow Molding • Shear & temperature dependent viscosity • Temperature-dependent tensile strength on the pin • Tensile elongation during inflation • Crystallization kinetics on the core pin • Crystallization kinetics during blowing and cooling

  15. Injection Blow Molding cont. • Gives much better control over finished component weight and wall thickness than extrusion blow-molding • better precision in the unblown, injection molded neck areas, lending itself to screw closures, etc. • Solid handles can be molded in

  16. Stretch Blow Molding • Injection molded preformed top • IR heaters raise the pre-form above the glass transition temperature • Core rod stretches polymer to the bottom of the mold • High pressure air expands the polymer to the walls of the mold

  17. SBM • Single stage • Pre-form and blow molding process happen in the same machine • Convent for small batch production • Two stage • Pre-form is made in one machine • Blow molding occurs in another • Faster production for large batches

  18. SBM Advantages/Disadvantages • Low tool and die cost • Fast production rate • Molds complex parts • Stretching results in strain hardening • Reduces product weight by 10% when compared to similar methods • Limited to hollow parts • Wall thickness is hard to control

  19. SBM Machine

  20. SBM Diagrams

  21. Blow Molding Patents and Research • Lear Corp. & Fremont Plastic Molds • Ribbed parts are formed using specialized core rod with ribs • Increases friction for non-slip covers • Bayer Polymers • Flexible thermoplastics are blow molded over metallic inserts in the die • Creates a hard and soft layer • Hybrid seats and cross-beams

  22. Blow Molding Patents and Research cont.

  23. Limitations of Blow Molding • Thermoplastics • PET • PC • HDPE • LDPE • PP • ABS • some PVC • Limited levels of reinforcement for composite materials • Thickness should be as uniform as possible to avoid distortion

  24. References • CES EduPack 2008 software, Granta Design Limited, Cambridge, UK, 2008. • • •

  25. Questions?