Thin wall HDPE extrusion

[dans67]

I am trying to extrude a single lumen thin wall tube for medical application. I cant figure out how to maintain any type of tolerance. Is there anyone out there with experience in this area that could point me in the right direction? Thanks

 

[patprimmer]

Are you an extruder or a designer.

What is a lumen other than a unit to measure light output or intensity.

Twin wall HDPE is not exactly a new or novel process.

Regards
Pat
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[dans67]

I didnt say twin wall I said thin wall

 

[patprimmer]

OK

That has been around even longer.

And? are you a designer trying to specify tolerances or an extruder trying to maintain them?

Regards
Pat
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[dans67]

I am an extruder that is obviously having trouble with something. Do you take pleasure in trying to make others look stupid? I posted on here for advice, not to be criticized

 

[patprimmer]

I take pleasure in helping people who are prepared to frame a decent question and supply required information. It was not at all obvious that you where an extruder. I do not take pleasure in extracting information at great pains just to be able to help someone.

Tooth 1) What wall section.
Tooth 2) What dia tube.
Tooth 3) What MFI HDPE.
Tooth 4) What size extruder.
Tooth 5) What output are you running vs maximum for that extruder.
Tooth 6) Depending on what sort of drive and screw design of which I have no idea at the present so I don't even know what direction to take when asking questions are the amps steady and what is the compression ratio and length to diameter of the screw.
Tooth 8) Are any temperature zones over riding.
Tooth 9) What temperature is the water in the vacuum tank.

I give up

Regards
Pat
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[dans67]

Maybe I am misunderstanding your attitude. If so I apologize. Just seems very condescending.
Dimensions: .018" ID, .034" OD. Material is petrothene, I dont have the grade in front of me as I am at home now. Machine is a 1.25" 24:1 LD with a Zenith gear pump. I am not having any feeding or amperage problems. All heat zones are steady. I am only able to turn about 8 RPM on the screw because of the size of the tube. Water temp in tank is around 80F

 

[patprimmer]

I initially thought you where more than likely a designer or even a student and if a designer would have recommended you talk with your moulder.

Also I was irritated by yet again a prospect of having to ask 30 questions. It happens quite a bit and frankly gets tedious so I will cough to irritated rather than condescending.

OK that is a very thin small tube on a machine that is really much to big for the job. The gear pump is all that makes it possible I think. Even so you may get pulsations from the pump but at least hey will be small and regular. If you have an option for a smaller pump running faster that might help as would a pump with a greater number of smaller teeth.

Your residence time in the barrel must be extremely long, so I would keep the temperatures as low as possible for the back 70% or so of the barrel to avoid degradation, but don't overdo it or you will have inconsistent melt temperature and just as much trouble as if it was degraded. It might be wise to try to source material with extra processing aid/stabiliser added.
Sorry but it's a bit late to think clearly and I have a full day tomorrow. Do you know anyone who specialises in extruding drinking straws. They are bigger dia, but I expect will still tend toward similar problems and solutions.

Do you have a selection of screws to choose from. What does your raw materials man say.

Your torpedo and its adjustment and taper in the die will be very sensitive.

I am thinking you need more lik a a film blowing grade rather than an extrusion grade.

Regards
Pat
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[dans67]

I would love to be a student again! Unfortunately I have 15 years experience in extrusion and this one has me stumped. I have specialized in Nylon and Urethane so a thin wall HDPE is a curve ball at best for me. I know my machine is oversized but the output seems to be consistent due to the gear pump. I apologize for not providing enough data upfront. What hair I have left is quickly turning gray due to this project and I was just throwing out my basic problem in hopes of finding someone with some knowledge that could point me in the right direction. Do you know correct draw ratio for HDPE? The grade is Petrothene LM600700. Thanks for your help even though we got off to a rough start. I read your other posts and replies and I can see that you are knowledgeable in the field. Any advice would be greatly appreciated

 

[patprimmer]

I am more a moulder than an extruder but I have some experience in all conversion methods.

Your tube is almost a thickish blown film.

When making fibre, HDPE likes very high draw down ratios. 10:1 vs 6:1 for nylon seems to spring to mind, but don't trust me on that as it is a bit on the hazy side.

Spectra fibre is made by drawing down HDPE in very hot water, hence the term gel spun. It would be fairly easy to increase bath temperature and increase draw down I would think. Of course tube is harder to grab and stretch than is fibre. Hot water might really slow down your already low output and create melt consistency problems. I guess you cant draw by stages with multiple tanks.

Regards
Pat
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[patprimmer]

Oh

And I think you need a fractional MFI grade with no nucleating agent and possibly 3 to 5% Vinyl Acetate to allow more stretch and a bit less crystalisation.

Regards
Pat
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