For Best Results, The Resin Must Be Conditioned, Stretched And Orientated

For best results, the resin must be conditioned, stretched and orientated just above the glass transition temperature. At this point the resin can be moved without fear of crystallisation. There are two stretch blow moulding techniques. In the one step method the parison production, stretching and blowing take place in the same machine. In the two step method the parison is produced separately from the stretching and blowing process. Although this process is the best in many ways, including upto 15% less material being used, it can have an impact on the clarity of the container and given we are producing presumably clear containers so the contents do not look dirty then extrusion blow moulding was selected.
Trouble Shooting.
Problem.
Suggested Solution.

Low Gloss.
Increase material and/or mould temperature. Improve mould venting. Increase air blowing rate.

Excessive cycle time.
Decrease material/mould temperature. Decrease part wall thickness. Increase material density. Increase melt index.

Low bottle weight.
Decrease material temperature. Increase extrusion speed. Decrease extrusion die temperature.

Rough Surface.
Decrease extrusion speed or Increase die temperature.

Parison curling.
Adjust and centre die; parison tends to curl towards thin area. Improve head uniformity. Clean the die head.

Wall thickness non-uniform.
Decrease material temperature. Increase extrusion speed. Lower the melt index of the resin. Increase the material density. Adjust and centre the die head.

Excessive shrinkage.
Increase material temperature. Decrease mould temperature. Increase air pressure. Decrease material temperature. Decrease material density.

Excessive thinning at the parting line.
Decrease wall thickness. Decrease the mould temperature. Increase the air pressure. Decrease material density and temperature.

Excessive Parison swelling.
Increase material and/or die temperature. Decrease the extrusion speed. Increase the melt index. Use a smaller die.

Doughnut formation.
Make sure the lower surface of the die is clean.

Warped product.
Cycle time too slow. Decrease mould and/or material temperature. Decrease part weight.

Variable bottle weight.
Increase the cooling on the extruder screw. Decrease the rate the extruder is operating at. Increase rear extruder temperature.

W. W. Bainbridge & B. Heise, in Design and Construction of Extrusion Blow Moulds, National Symposium Plastics Moulds/Dies, Society of Plastics Engineers, Palisades Section, Brookfield Centre, Conn. SPE Design RETEC 21.1, Oct. 1977
R. O. Ebewele, Polymer Science and Technology (London 2000)
Glossary of Plastic Bottle Terminology, Plastic Bottle Institute of the Society of the Plastics Industry (New York 1980)
M. Gordon, High Polymers (London 1963)
J. I.