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Melting Polyurethane

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dknguyen

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NewAge Industries - Superthane® Polyurethane Tubing

I have some small diameter surgical tubing that fits perfectly into larger diameter surgical tubing. But they don't always fit so well that they won't slide out under some force. I want it to stay put and I don't want to have to add glue then slide them into each other because that's messy and causes other problems. I was wanting to slide the tubing into each other and then apply some heat to get them slightly gummy (not liquify them) so that when they cool the two inserts sort of stick together, but not so gummy that they lose their shape as tubes.

Does polyurethane get gummy when heated? Does it even melt and solidfy like a thermoplastic? Any toxicity of slightly melted polyurethane) because burning does)? Is the gumminess a very small or large temperature range?

I read that it softens at 135C and melts to a gummy state at 180C. I want it slightly gummy (sticky) but still hold it's shape. I'm not sure if softening just means softer, or if it means soft and sticky but still holds it's shape.

It doesn't have to be a "weld" it just has to make them fit together slightly better so they can't slide out under a bit of force. If I could, I would actually much prefer to just put my soldering iron on low heat and run it along the mouth of the tube so that the ends "gummy" or "melt" into each other. That would be sufficient. But of course...toxic fumes if it burns instead of gummies up. Not to mention it would ruin the tip, but I have a beater iron.

EDIT: Seems my beater iron's minimum temperature is 250C, not anywhere near 135C-180C that is needed.
 
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dknguyen

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I haven't tried any tests yet because one of the things I learned is to apply heat to polyurethane lest you start burning it. If I try them it'd probably be tommorrow...outside...by tapping my iron all over some tube and seeing what happens. But that's a good point If I can get the outside tube to just shrink, even by 0.25mm, that would be enough. 0.25mm might be too much actually.
 
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timsvb

New Member
I'd try with an electric heatgun, the type used for stripping paint and also used on heatshrink tube. Have had to do similar things myself in the past. Try heating the larger tube first till it's at the required temp and "stickiness", then slide the smaller tube (unheated) in to see if it bonds adequately. If not, then keep experimenting until you get it right, or have to cave in and purchase a proprietory adhesive.
Well ventilated area most important!:)
PS. sometimes when the tubes are still warm, a kind of barb like join can be attained by crimping or closing off slightly with a wrap of wire or similar process.
Enjoy
 
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smanches

New Member
Polyurethane won't rebond after it's cured. And it takes some VERY nasty s**t to dissolve it. Sorry, that's all the info I have. Worked in a plant for a time but didn't learn that much. Although I cleaned enough parts.

Although that tubing is soft enough that it still might stick (mix together) at the seams.
 

tcmtech

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I doubt this will work in your application but I occasionally have to attach hard plastics of dissimilar materials together some times when repairing plastic bodied water pumps or plastic tank fittings and I often use a simple friction welding method. I just hold one stationary and the spin the other one with a drill at high speed with a bit of force and they heat up and mix and then weld themselves together.
 

timsvb

New Member
I doubt this will work in your application but I occasionally have to attach hard plastics of dissimilar materials together some times when repairing plastic bodied water pumps or plastic tank fittings and I often use a simple friction welding method. I just hold one stationary and the spin the other one with a drill at high speed with a bit of force and they heat up and mix and then weld themselves together.
I'll have to remember that one. Sounds like a plan.
 

tcmtech

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It works very well! I just shape one part slightly convex and the other slightly concave so they dont walk around while spinning. I haven't found two plastics that wouldn't take hold of each other so far either.
To do it all you need is to make the right adapters so the drill can hold onto the one piece.

An old plumber taught it to me. It was his cure all fix for mismatched plastics that dont have reasonable gluing compatibility.
 

duffy

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Are you trying to connect tubing? They sells T's and fittings for these things at auto supply and hardware stores.
 

dknguyen

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These are being used as flexible couplings to connect carbon fiber rods together. But in order to connect two rods of two different diameters, you need to have an insert of smaller diameter tubing into the larger diameter tubing so you have different ID at both ends.
 
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Rolf

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These are being used as flexible couplings to connect carbon fiber rods together. But in order to connect two rods of two different diameters, you need to have an insert of smaller diameter tubing into the larger diameter tubing so you have different ID at both ends.
When I see the word coupling I usually think of rotating shafts and torque. If you have torque how are you going to keep the rod from slipping in coupling? Clamps or pins comes to mind and why couldn't they serve two purposes?
 

dknguyen

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They're behaving more like hinged joints, not torque joints. I just need to stop the sleeves from slipping out of each other.
 
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duffy

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Have you looked at kite connectors?
Goodwinds - Catalog

These look rigid, but many of them are made of flexible rubber. They are designed to couple carbon fiber rods.
 

dknguyen

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I'm not sure that would make a very big difference. I'm not terribly worried about the rods sliding out. Their OD fits perfectly into the ID of the sleeves. I'm more worried about the sleeves sliding out from each other because the small sleeve's OD and the large sleeve's ID can be nearly slip fits.
 
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duffy

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How about glue? There's polyurethane glue, like "Excel", might work.
 

dknguyen

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In the OP, I think I mentioned I didn't want to use glue if I didn't have to because it might get a bit messy with the way everything is put together. The manual says to just use regular CA.
 
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