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Old 10-13-2009, 11:15 AM
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Default Welding UHMW

Anyone here successfully weld UHMW plastic? At work we have approx 104 identical pieces of black UHMW that every now and then need to be replaced because the pins on the conveyor chain have jumped the machined path that the pins are supposed to follow. When they jump the intended groove, they take out a very large chunk of the UHMW (about 1/4" wide by 7 inches long). At this point we have no other option other than replacing them. The machined pieces are quite simple as far as the groove that is machined in them, and the mounting holes. If we had UHMW stock on hand we could make our own if management would purchase some shop equipment. Right now they are paying through the nose ordering them through the conveyor manufacturer.

I have saved about a dozen of the damaged pieces hoping to find a way to fix them. I was wondering if a kit similar to the plastic welding outfit from Harbor Freight (the $79.00 one) would work on this type of black UHMW, and if there are any plastic welding rods made for black UHMW. These UHMW pieces are slightly under 1" thick. Any information would be greatly appreciated..............thanks
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Old 10-13-2009, 12:02 PM
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Saw this:

WELDING
Because of its high melt viscosity, friction and butt welding are the only practical methods for joining Redco UHMW by welding. In butt welding, the cleaned joint faces are held under slight contact pressure against the heated tool at 200-220°C until a layer of about 4mm deep has become plastic on both sides. The two parts are pressed closely together under an axial pressure of 10-20 bar (depending on the material thickness) until cold. If the material is greater in thickness than 30mm, axial pressures of 50 bar and above are required, and in such cases presses or special welding machines are frequently used.
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Old 10-13-2009, 12:27 PM
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Thanks USMCPOP,

I guess I really do not understand what they are saying other than it appears that this is a finicky type of plastic, and is probably not going to be welded by the method most other types are. I wonder if there is a reason they use UHMW and not some other type of plastic for these conveyor guides. I may have to experiment with nylon or some other readily available type of plastic.........thanks again.
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Old 10-13-2009, 01:57 PM
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The only way I ever found to join was mechanical fasteners . I never found a glue or easy way to weld. Leon around factories UHMW is the most used for glides ,bumpers ,wear pads ,more than nylon or other plastics.Cheap readily available in many size logs.
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Old 10-13-2009, 03:08 PM
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Sounds to me like the UHMW just doesn't get really runny when you heat it, so it's harder to get it to bond together.

UHMW-PE has a lower co-efficient of friction and better abrasion resistance than HDPE (milk jugs) or LDPE.
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Old 10-13-2009, 05:23 PM
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I don't know if they use the same plastic, but I've seen engineers successfully weld on plastic child seats. Back when I was in the crash testing biz, we'd have different manufacturers engineers prototyping at our lab, and adding gussets and other pieces by welding them on. If I remember correctly, the set-up had your "gun" which heated the area to be welded, and it had a feeder attached that hooked up to an airline that would pulse and feed the plastic filler. Most of welding withstood 40+ MPH "crashes" with a 25 lb. dummy in the child seat, so you might be able to. Kinda wishing I'd paid more attention back then so I could give you a brand name/type of the welder.
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Old 10-13-2009, 06:08 PM
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Quote:
At this point we have no other option other than replacing them. The machined pieces are quite simple as far as the groove that is machined in them, and the mounting holes. If we had UHMW stock on hand we could make our own if management would purchase some shop equipment. Right now they are paying through the nose ordering them through the conveyor manufacturer.
If the expenditure is worthy in time and material due to these failures, it's time for your company to hire an engineer or contact a plastics supplier engineering dept. to have them spec the equipment necessary to do exactly what you need done.

And I'm positive that someone will have the equipment to make this happen on the shelf and in most cases have a tech deliver, set it up and train someone in your house on it's use.

This should be no different than contacting a welding company on a welding process such as Lincoln, when you need a process for welding Unobtainium etc.
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Old 10-13-2009, 06:12 PM
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From the Garland site.....
  1. Thermal Welding

    Can UHMW be thermal welded?

    Yes. It behaves much like regular HDPE. What temperatures and pressures are required? Minimum temperature 400°F. Minimum pressure of 300 psi recommended.

    What percentage of parent strength can be attained? 80%
  2. Ultrasonic Welding

    Can UHMW be ultrasonically welded?

    Yes. Again the process is much like regular HDPE. Thick sections of UHMW may be more difficult than HDPE because of lower modules. If plastic is softer, like UHMW, more attenuation of the ultrasonic energy occurs.
  3. Stress Relief - Annealing

    Most UHMW sheet, rod, bar and board stock have some stresses.

    Reason: When it is made it is cooled non-uniformly - the outside cools faster than the core.

    Typical question: Can I buy annealed stock? Yes, but it costs more.
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