Melting Polyurethane

Oh, yes, you did - sorry. Didn't notice that.




(use glue anyway)

dknguyen said:

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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I guess you didn't look closely at my drawing.

It turns out a clothing iron is a much better thing than a soldering iron. At least on mine, "Silk" temperature setting will melt the plastic without burning it, and pressing the tube end onto the iron will heat weld the lip of the inner and outer tubes to each other. BUt if you press to hard it spreads outwards.

I don't think you ever told us what you're building. Is it a new hair-thingy to make those charming pigtails?

Yes, that's exactly what it is.

I have some experience using PU.

PU is manufactured in two ways - outer diamer or inner diameter calibrated.

PU won't change it's original shape when heated. It melts at approximately 250 deg/C, which is quite usable making temperature sensors (TO92-package) water proof in a slightly widened PU-6 tube (outer diameter 5mm, inner diameter 4.0mm, TO92-package 4.25 - 4.35mm).

For a quick test you might heat an end of PU generously over a length of 1/2 inch using a cigarette lighter. Then press it (at least 10kg pressure) and allow cooling to room temperature. The "glued" PU can stand the same pressure (nominal 8bar) as the original tube.

Shaping PU must be done heating the material slowly (no torch or cigarette lighter) and using a cone for the desired inner diameter pressing it into the tube.

Dunking the end of the tube in boiling water (until it becomes "floppy") it can be increased in (inner)diameter from e.g. 4mm to 5mm without loosing much strength, since the outer diameter will increase as well, reducing wall thickness slightly. (normally 1mm).

Boncuk

Yeah, I tried the boiling water method before the iron and the tubing got larger...so large that it was no longer a friction fit sliding on the carbon tubes so I had to scratch that idea.

dknguyen said:

Yeah, I tried the boiling water method before the iron and the tubing got larger...so large that it was no longer a friction fit sliding on the carbon tubes so I had to scratch that idea.

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That's why I mentioned to heat it up slowly.