Twisting a profile tube

[BExtrude]

I am trying to twist a dog bone shaped cross-section tube with a OD major axis of 2.6mm and an ID of 1.0 mm. After twisting it is shaped like a twizzler. I need uniform twisting and heat to set it at the twisted shape. Has anyone heard of using a revolving mold to do this?

 

[MikeHalloran]

You mean like in an extruder with a revolving head?

Oh. Wait. Are you proposing to twist something that's already been extruded straight? Grip a length, heat, twist, cool, cut off the ends, repeat. Automate the process for consistency.

A 'mold' to slide along the stuff? With zero twist at entry, and a fixed twist at its exit end? With the heat/twist/cool cycle going on within it? First problem is that heating plastic is a slow process, so the translation speed would be not more than a few mm per minute.



Mike Halloran
Pembroke Pines, FL, USA

 

[BExtrude]

I have been using the heat, twist, cool method but I would like to automate it making it more consistent and less operator dependent.

 

[patprimmer]

You do not need to twist the die face. That would twist the melt, not the profile.

Mike nailed it.

If you have the ability and commercial justification to modify the extrusion line, you need to modify your downstream equipment or calibrator so that teh twist is applied as the extrudate cools.

A steel plate with the shape cut into it that is rotated mechanically at a speed tied to extruder output speed could be designed. It might need several stages or might need the head to run underwater.

Regards
Pat
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[nornrich]

BExtrude,

I worked on a project that was a twisted tube bird feeder. The cross section was circular, so it sounds a little easier to handle then your cross section. We were extruding a tube that had three internal segments and we wanted the segments to twist. What we ended up doing was angling the puller belts counter to each other. This made the tube twist. Don't know if this could be used to apply to your application.

Rich....

Richard Nornhold, PE

http://www.personna.com