Using localized heat to fuse UHMWPE and others
Using localized heat to fuse UHMWPE and others
(OP)
Hey guys. I am a newcomer to this forum. I am trying to get fully cured or even B-stage ultra high molecular weight polyethylene to fuse to itself with the use of localized heat. I'm just wondering if there is a resource out there that goes over different thermal profiles used in post-process joining. I read over a few of the threads on plastic welding and other adhesive methods, but I haven't found anything definitive.





RE: Using localized heat to fuse UHMWPE and others
Don't let the name fool you, these guys do much more than ultrasonic plastic joining. We use a hot plate welding operation on our products and have a Branson machine.
RE: Using localized heat to fuse UHMWPE and others
RE: Using localized heat to fuse UHMWPE and others
RE: Using localized heat to fuse UHMWPE and others
RE: Using localized heat to fuse UHMWPE and others
If the joint geometry allows it, ultrasonic, vibration or spin welding (ie friction) will be the best ways to generate the heat.
PC-ABS will be easy. It can be solvent or friction welded. Respectable raw material suppliers will be able to provide volumes of information.
Regards
eng-tips, by professional engineers for professional engineers
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RE: Using localized heat to fuse UHMWPE and others
RE: Using localized heat to fuse UHMWPE and others
If I understand you last post, I read an applied pressure at the welding interface of 100 psi. once again, trial and error, but I would guess more like 500 psi or more might be required. Like I say, I GUESS. I have no first hand experience at this specific material.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Using localized heat to fuse UHMWPE and others
RE: Using localized heat to fuse UHMWPE and others
Bob Mileti
RE: Using localized heat to fuse UHMWPE and others
thanks for the input BTW.
RE: Using localized heat to fuse UHMWPE and others
Like any process the materials define what can and cannot be impulse welded. Impulse welding can be very efficient in thin ( .7mm thick or less )gauges or butt welding, but this may not fit your application. So my first question would be how thick are the 1cm X 1cm parts your looking to seal? There is also a bit of "black magic" in welding, since there are hundreds of formulations of UHMWPE, due to additives, such as colorants and processing agents, etc.
RE: Using localized heat to fuse UHMWPE and others
RE: Using localized heat to fuse UHMWPE and others
So here's the answer to your question as to how "impulse welding" works.
Impulse Welding uses a thin resistant wire or band, usually called a heating element, that heats up in a few hundreds of a a second to operating temperature. Once it reaches the desired temperature it holds it for , once again a desired time, then the energy is removed from the element to allow the sealed components to cool to a state that give you your weld. This is different that a heated die type tool, since the advantage is very quick seal times, and the ability to cool the process down before taking the pressure away. This ability to hold pressure is very important when sealing hard to seal materials, since you need to insure the two parts are properly knitted together before removing the pressure. Constant heat dies tend to pull the seal apart prior to the knitting of the 2 parts.
Pressure is important, but too much can cause "extrusion" of the material, therebye reducing the strenght (cross section) of the seal. So the "black magic" part is balancing the amount of pressure with the correct profile of temperature.
Something in the 40um thickness could be sealed in about 1 to 2 seconds and if all goes well can end up to be stronger than the material around it.
Now the next question is shape. Straight seals are the easiest but many shapes are also very doable. We've made sealing elements as small as a 12mm dia. ring seal, with and element width of .8mm wide to 10mm wide bands 4 meters long.
Hope that helps.
Bob
RE: Using localized heat to fuse UHMWPE and others
PE is a thermoplastic where adding some heat and maybe pressure will allow parts to fuse (actually due to interdiffusion and then entanglement of the long polymer chains). UHMWPE, although chemically similar to PE, has chains that are so long that it's impossible to make it flow / melt. That means a lot of heating / pressure and waiting will be needed to allow the extremely long chains to interdiffuse giving adhesion.
Therefore as mentioned you might use a thin piece of normal PE inbetween the UHMWPE to help or just look for a glue. Polyolefin glues exist I believe, for example from Loctite.
RE: Using localized heat to fuse UHMWPE and others
I am a bit perplexed about the changing dimensions of the part.
If it is UHMWPE, it will take a lot of pressure to get any real extrusion as the melt viscosity is very high.
The temperatures required will depend partly on molecular weight and thickness, but more on degree of crystallinity. I have welded metalocine LDPE at 90 deg C but needed 130 for MDPE. Even higher temperatures will be required for HDPE.
Molecular weight has nothing to do with density.
To my knowledge, UHMW and X linked PE are both normally LDPE.
If it is X linked, if you can weld it together then cure you should get an excellent bond.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Using localized heat to fuse UHMWPE and others
RE: Using localized heat to fuse UHMWPE and others
RE: Using localized heat to fuse UHMWPE and others
I determined the pressure by building a small prototype and testing before I built the full sized machine. The prototype had 2 square inches and a single air cylinder and a pressure regulator.
Metalocine LDPE will flow a lot easier than UHMWPE.
As I said earlier, a lot of guesswork involved, so some trial and error will be required.
Some sort of vibration or friction to generate the heat at the welding interface will be a lot better as the flow generated will mix the melted plastic where required.
If you use conducted heat, the welding interface will be the coolest spot and the material will flow everywhere but where required.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Using localized heat to fuse UHMWPE and others
RE: Using localized heat to fuse UHMWPE and others
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RE: Using localized heat to fuse UHMWPE and others