Stretch blow molding preform blues 1

[walkingcube]

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...

Any ideas/suggestions?



Thanks!

 

[patprimmer]

What material are you using.

Regards
Pat
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[walkingcube]

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.

 

[patprimmer]

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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