Problem with leakage of welded Nylon components
Problem with leakage of welded Nylon components
(OP)
I am currently trying to establish the root cause of some leakage problems that we are experiencing with welded plastic components. I have been working on this part for the last year, and am really at a stand still now. The part is a small canister (approx. 3" diameter)that must not leak after welding, and be able to withstand pressure up to 300 psi. When I initially was assigned to this project, the burst pressure was the major defect that we saw. I had wild variation in the burst pressure and leakage was manageable (1% max). All the parts are 100%leak tested (bubble emission @ 80 psi), so we were o.k. there. I have changed the material to a prime Dupont Zytel 70G33LBK031, to try to correct the burst strength issue, and have had excellent results. Burst pressures since the change have not fallen below 450 psi, and are much, much more consistent. Part appearance is greatly improved, but I am now seeing huge leakage rates at times (up to 60%). It seems to be lot specific, as one lot that we just finished was .25% failure due to leak, and the previous was 45%. I have made multiple visits to the molder, but still cannot find the root cause of the problem. Now for the question....I would like to have some recommendations for testing (laboratory)that could give me some better information. We have tried some labs in the past, but we really didn't get anything we could use (other than "you need to do more testing...that will be $$$$$"). The parts are ultrasonically welded, and I am quite confident it is a material issue. What specific test could be performed on these parts?, and who can do it?
Any ideas or reccomendations would be greatly appreciated..
Any ideas or reccomendations would be greatly appreciated..





RE: Problem with leakage of welded Nylon components
Are the parts dried prior to welding?
Due to the glass fill additional weld area may be required versus the previous material.
RE: Problem with leakage of welded Nylon components
RE: Problem with leakage of welded Nylon components
Thanks for the help.
RE: Problem with leakage of welded Nylon components
See section 11
RE: Problem with leakage of welded Nylon components
Again, thanks to all.
RE: Problem with leakage of welded Nylon components
Fiberglass and carbon fibers are often used for making pressure vessels but almost always require a liner to prevent leaks.
I suggest you locate a leak and look at it under a microscope. 100 to 200 power would be adequte for this. It is often amazing what you can see when you actually look.
RE: Problem with leakage of welded Nylon components
Regards
Pat
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RE: Problem with leakage of welded Nylon components
The previous material was Entec Hylon (basically carpet scraps). It was 33% glass filled nylon 6/6.I went thru the whole process of drying, etc.. but the variation of the materials was just too great to get any consistent results. The change to Dupont was extermely benificial, as the burst strength is solved as far a we are concerned. I just cant get the leakage figured out. I have samples of good and bad parts (welded and unwelded), but I cannot cut/section magnify, etc. I really need a resource for this, and am trying to get to Dupont to get some help.
We recently went to an outside lab, but it feels like we were taken, and management has lost its taste for more testing form those guys.
Do you (or anyone have a number or contact at Dupont? When I tried to contact them, I got shifted around quite a bit.
RE: Problem with leakage of welded Nylon components
It sounds like you purchase enough material to get some quick help.
Have you tried any Vydyne materials?
I'm very close to them, physically, and maybe able to get some help.
What does the welder supplier say?
My numbers for the old Technical Support Center are no longer valid. I believe that they have broken this group up by divisions.
RE: Problem with leakage of welded Nylon components
I have mentioned before in posts the general lack of support from DuPont - unless you use a zillion tonnes per annum - others have found different.
The best support we have had is from EMS Chemie. The materials are much better for processing and nothing is too much trouble. (We are a very small user too!)
I would suggest that you try and contact your local EMS agent - you may be surprised.
(I have no commercial interest in EMS - just a user)
We are in the UK, but have heard the same from other sources.
Q: Why 6.6? Your comment about carpets would suggest PA 6 as (afaik), PA 6.6 is not used for yarn, but I see that it is PA6.6?
Cheers
Harry
www.tynevalleyplastics.co.uk
RE: Problem with leakage of welded Nylon components
If the supplier is using good clean carpet croppings and using a good quality glass, it should be fairly consistent.
Big variations in nylon mouldings are normally to do with moulding wet granules or NOT CONDITIONING before testing.
I also agree with Pud re DuPont service, if they identify you as a key or strategic account the service will be absolutely first grade, however if you are not on that list, they won't even return calls. Your best bet is to arrange throug your moulder to approach the rep for the DuPont material. If they can't help, find a supplier who can. There are lots of suppliers of nylons around ranging from the big multinationals like DuPont and BASF to local specialist compounders.
Regards
Pat
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RE: Problem with leakage of welded Nylon components
Oops! Forgot BASF - they are quite good too!
H
www.tynevalleyplastics.co.uk
RE: Problem with leakage of welded Nylon components
RE: Problem with leakage of welded Nylon components
I actually used Vydene as a feedstock when I was running the compounding plant a year or so ago. It was good resin. They had no agent in Aus, so we got no service, but then again we did not need it.
Regards
Pat
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RE: Problem with leakage of welded Nylon components
RE: Problem with leakage of welded Nylon components
It sounds like you have a good connection with Solutia.
If you don't mind I will contact you via a private forum.
Regards
Pat
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RE: Problem with leakage of welded Nylon components
The welding supplier was not much help. I attended one of their training sessions where I met many other people with the exact same problem. The welding suppliers response to polymer questions was "try plastics web".
Is there any testing that can be done on the leaking parts that would give me any insight as to the cause of the leak?
I know that it is a void in the weld, but other than that, i am stuck for the cause.
I will try to contact other suppliers to get opinions for other materials.
Again, much thanks for the help.
RE: Problem with leakage of welded Nylon components
RE: Problem with leakage of welded Nylon components
I don't just mean obvious sources. For example, if the cleaning lady sprays furniture polish you'll get silicone everywhere. Deodordants and hair conditioner are other sources.
Chris DeArmitt
RE: Problem with leakage of welded Nylon components
Even though operators are not supposed to use any silicone around the die heads it can and will be used if the operator has any problems.
The mention of furniture polish brings up an incident where car polish was the culprit at a local molding company had when parts went for further processing
RE: Problem with leakage of welded Nylon components
Thanks again for the advice.
RE: Problem with leakage of welded Nylon components
Due to the new information that the leak occurs at a bubble or void in the weld, I am more inclined to think it is moisture in the nylon when welded or a lack of resin at the weld joint due to higher glass fibre levels. Tensile strength significantly improving while weld strength significantly drops fits well with more glass and/or higher molecular weight (tougher but poorer low) base resin.
I have seen so called vibration welding do better than so called ultrasonic welding in 35% G 6.6 (the combined water tank and chassis for a steam iron).
They are both friction via vibration at the surface to be welded type welds, but the frequency and amplitude are different.
Regards
Pat
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