Connection for tungsten heater

Question

This is my first post, so hello all :)

I have a tungsten wire thats wrapped around a crucible. I want to send ~20A through it in order to heat the crucible.

Now the tricky part. Since this is part of a delicate setup, I don't want to use solder or glue in order to minimize contamination through evaporation (this is a physics experiment). At the same time the setup has to fit inside a 10cmx10cmx5cm box.

Any ideas on components I could use to make these connections? Is using crocodile clips to connect the tungsten wires a completely stupid idea? :D

Answer 1

A simple pair of copper busbars (0.5 * 0.125) with a high pressure contact would appear to be all you need for each terminal. Separate your wires where they enter the busbar area and clamp each wire individually with a stainless steel screw and high pressure domed washer.

Separating the Tungsten wires may help in supporting your crucible.
If you are in a vacuum chamber you can connect your entry wire to one of the busbars, I doubt you need to do both at the low current you are using (20A).

Answer 2

Probably your best bet is welding, such as spot welding. That will involve only two materials- the copper wire and the tungsten. You can make the copper terminals large and with enough heat sinking that the vapor pressure of the copper is minimal.

Second choice would be to braze the joint, again if you keep it relatively cool the contamination might not be important. The solder used ("silver solder") is typically mostly silver but is alloyed with a bunch of other metals.

A third choice, if the tungsten wire is robust enough, might be to use screw terminals that are big enough and well heat sinked enough to keep them from heating much. Such as a ceramic insulated terminal block. Image from here.

In ceramic kilns a simple arrangement with a pair of washers and is used to clamp the heater wire (typically Kanthal alloy). Screw based methods need to be kept cool and they may eventually loosen up with cycling.

Answer 3

I do not know if tungsten wire is sufficiently strong, but I would use crimp connections. You don't mention the tungsten wire diameter, nor do you tell us what the operating current will be and thus we can't provide any detail.

In general, you can crimp pins or butt splices onto the resistance wire. You generally need to provide some heat-sinking on the connections to keep the connection temperature low enough that the crimp doesn't fail. Generally, just increasing the surface area of the connection is enough.

I am curious about your choice of tungsten wire - most common heating wire is Nichrome. Kanthal is often used in vape pens.