Nichrome soldering question 1

[SACAN]

I am looking for input into what is the best/preffered method of soldering a nichrome resistance wire (18awg-30awg) to 18ga lead wire.

Currently we use a silver solder with a boron modified solder paste. For heat we use a small oxy-acet flame torch.

The nichrome is a resistance heating element that is encapsulated within a silicone/fiberglass blanket.

I have often seen element failures at the solder joint, and would like to look into the best way to make this connection of resistance wire to lead wire.

I think that the flame heating is possibly detrimental to the process, possibly oxidizing the resistance wire, and thus weakening it? Perhaps if there is any movement or shaking while the solder is bonding this can cause weakness? Also, after the connection is made the joint is then hammered down to thin it out as a thck joint will push through the element material causing a short.

Any thought? Can anyone reccomend a better process, tool, or material for this application?

 

[Timelord]

Had the same problem once. Went to spot welding the the nichrome to the leads. No more problems.

Timelord

 

[SACAN]

Did you need to tin the lead wires first?

Spot welding would work on our heavier resistance wire but I think it might be difficult with the 30g.

 

[Timelord]

I didn't tin anything, only cleaned the parts. I had a small capacitor discharge spot welder that worked great even on the smallest wires. I was able to use that spot welder to spot weld the individual wires in a copper window screen to a stainless frame. The dissimilar materials doesn't always make a pretty spotweld, but I was after electrical continuity, not mechanical strength. I have seen copper wires spotwelded to heating elements of a different materials in a lot of consumer goods like a electric frypan, toaster etc. and they are good mechanically strong joints. It may take some experimentation but it should work.

Timelord