How to crimp to NiChrome spiral wire with glass fiber core 1

[RAndres]

I've got a requirement to crimp to a spiral heating wire. It's a NiChrome resistance heating element, which is wound as a spiral around a core of glass fibers. It's covered with a layer of foam rubber like insulation, and then with a woven fiberglass covering. My understanding is that NiChrome is usually crimped for connections. I want to crimp a section of normal wire to the ends of the heating element.

For testing, I've been pushing back the outer woven insulation, then cutting the foamy insulation with a stripper. That allows me to spin or "unthread" the foamy insulation from the spiral. The NiChrome spiral is pretty thin, something like 28-30 AWG, I've been putting it into a standard butt crimp barrel with the 16 AWG extension and crimping both together. Then I can push the woven insulation over the crimp. I'd like to find something quicker and easier to do, as well as something that gives a better strain relief. I'm not convinced having the inner flex/strength member in the crimp is a good idea.

Can anyone give me any tips on a better crimp method?

 

[itsmoked]

Not really. Crimping is the standard to NiChrome. The oddity I'm seeing is that normally one goes to the effort of keeping the crimps in free-air so the copper has a chance of staying below rapid oxidization temperatures. NiChrome is hard to solder. IIRC I saw my dad silver-braze some Nichrome once and it worked for a while.

I think you're doomed..

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Compositepro]

Fiberglass will crush and turn to powder if crimped too hard, but the fiberglass is the strength member when the cord is under tension. Tension on the nichrome coil will uncoil it. A spring clamp with some cushioning ought to be used to apply contact pressure to the nichrome over fiberglass. Contacting multiple turns of the coil will help prevent hot spots due to contact resistance. Since there is a rubber coating the heater is not intended to get very hot.

When I terminate nichrome wire I usually double-up the wire and twist it for a couple inches at the end, before crimping or clamping under a screw. This greatly reduces the heat generated near the terminal.

 

[RAndres]

Compositepro, constant tension spring clamping sounds like a good solution. If you have experience with any, can you point me toward an example connector like this?

 

[Compositepro]

I do not do it commercially but simply apply process engineering thinking to any problem. So I have no product recommendations.

A crimp plasticly deforms metal, so there will be some spring-back reducing contact pressure after crimp pressure is released. A screw clamp can have some spring to it like a flexible c-clamp. For solid nichrome wire clamping under a screw head works fine. For your cord a belleville washer or leaf spring should be used to maintain contact pressure as things move a few hundredths of an inch.

Placing a drop of epoxy or cyanoacrylate on the fiberglass cord where it will be clamped, and letting it harden before clamping will greatly improve the resistance to crushing.