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Stretch blow molding preform blues

Stretch blow molding preform blues

Stretch blow molding preform blues

(OP)
Hi folks!

I'm running into this problem that I'm having issues wrapping my head around, and I hope that someone will have some ideas to inspire me.

I was wondering if anyone has faced a problem where the preform used in SBM blows up 1/2 way during the stretching/inflation process. Tried reducing the pressure, then it won't blow. Temperature doesn't seem to do much as the preform doesn't want to thin out as it ought to. I think I'm missing something...ponder

Any ideas/suggestions?



Thanks!

RE: Stretch blow molding preform blues

(OP)
I'm using PA12. The weird thing is that I've done it before for a part at 25mm diameter. Our customer now wants a different model at 29mm, which so far has been eluding us.

RE: Stretch blow molding preform blues

Nylon 12 often incorporates some plasticiser.

Check the grade data for relative viscosity, plasticiser content, nucleating agents and lubricant. You need a blow moulding grade not an injection grade.

One critical data point will be elongation at break. You need a grade that gives it as high as possible.

Another critical point is moisture content. The material must be dry when moulded and I expect the preforms should be dry when stretched. While this is not as critical as it is for polyesters or lower numbered nylons like 6 or 6.6 it still can be a problem if neglected   

Regards
Pat
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