Extruding HDPE thin wall tube

[aksim]

Having 20y experience in making small dia tubes of various materials using "free extrusion" technique. Recently met a challange: to make a HDPE tube 6mm OD, 5mm ID on 38mm (1.5") extruder with flex PVC screw. Though screw seems to handle the material, thin wall collapses in cold water bath. Air pressure inside doesn't help. The tube doesn't have to be perfect round. Would a hot water bath precooling help or any other tricks available? Thanks!

 

[Compositepro]

Extrude the tubing and draw over a mandrel that has tiny holes for cooling water or air.

 

[Pud]

I assume you're using a fractional MFI grade of HDPE?

Politicians like to panic, they need activity. It is their substitute for achievement.

 

[aksim]

That could be one possible solution, but some questions arise. Basically the die air pin should be long enough to reach the water overflow hole on cooling bath. Running plastic tube then seals the pin from water. What if tube breaks down for some reason and water flows into a die head. A huge mess follows. Besides, the solidification area of the melt will extend to a certain length over the air pin, which will probably slow down the line speed.

 

[aksim]

Used Exxon Mobile HYA 600 and 800, MFI 190C/2,16kg - 0,3 and 0,7. Temps from 150C (300F) to 205C (400F).