0
\$\begingroup\$

This is only peripherally an electrical engineering question, but there are no other engineering forums on stack, so forgive me.

I am designing a homebrew device to melt low-temperature metals (like tin). I have a coil of heating wire. I am going to use an Arduino and a relay to turn the power on and off, and I have a thermocouple and a temperature sensor for thermostat control. The electrical side seems fairly simple.

The issue is that this wire is uncoated, as are all the others I can find. Since I want to wrap it around a metal container to heat it, I need a thin layer of insulation to prevent shorting the wire, while maintaining the best heat conductivity possible.

I found some ceramic insulators, but I'm not thrilled:

For one thing, I would need a lot of those. They are thicker, and have an air gap inside. Ideally, each insulator should be as small and thin as possible. A coated heating wire would be ideal. A coating would be great. I would like to wind the heater coil around a metal cylinder, possibly a can. I would love to coat the can with thin layer of clay, but I'm fairly sure thermal shock will rip it apart after one or two heating cycles. I would like the insulator to be able to tolerate at least 600°F, possibly 800°F. The can should be good until at least 1200°F from what we've seen so far putting them in hot wood fires.

I'm also interested in anyone's solution for regulating heat at the top and bottom as well. I was planning on a double-walled cylinder, with a bigger (insulated) outer cylinder, but I should probably heat the bottom as well. For the top, all I could think of was creating some kind of double-walled glass cover, but it would have to be able to take a lot of thermal stress, maybe the inside layer (or both layers) pyrex?

Ideas? Suggestions for parts/materials?

\$\endgroup\$

closed as off-topic by Scott Seidman, PeterJ, Daniel Grillo, Ricardo, Keelan Aug 10 '15 at 10:36

  • This question does not appear to be about electronics design within the scope defined in the help center.
If this question can be reworded to fit the rules in the help center, please edit the question.

  • 1
    \$\begingroup\$ For insulating the wires, and thermally insulating the crucible, glass fibre as tubing or cloth should be good to 1000 F. It might burn off the glue on first use. Quartz glass, if you can find it, is good to 2000 F or more. \$\endgroup\$ – tomnexus Aug 6 '15 at 4:44
  • \$\begingroup\$ It's not listed at the bottom of stackexchange, I didn't think to try. What I'm worried about is current shunting from the heating coil into the metal container, effectively bypassing the heater. Spacing the wire is not the problem. \$\endgroup\$ – Dov Aug 6 '15 at 4:45
  • \$\begingroup\$ @tomnexus, that sounds great! \$\endgroup\$ – Dov Aug 6 '15 at 5:38
  • 3
    \$\begingroup\$ I'm voting to close this question as off-topic because this is largely a materials engineering and mechanical engineering question. \$\endgroup\$ – Scott Seidman Aug 6 '15 at 10:57
  • 1
    \$\begingroup\$ This is one of the issues that I deal with. There is no need to migrate it to get a good answer. \$\endgroup\$ – W5VO Aug 6 '15 at 14:03
2
\$\begingroup\$

You can buy roving-woven thin glass fiber matting very easily and cheaply these days just about everywhere, if you wrap that tightly around the metal can, then hold it in place by wrapping the resistive wire tightly around it you will have a crude-ish set up that will sort of work.

The glass fiber will insulate to a degree, so you will want to fill it with a low-viscosity (ceramic) clay, that will penetrate the fiber and create better contact. This is probably the best balance between doable and good contact, AFAIK.

You can roll any number of thermocouples under the glass matting, provided they are in some way insulated, if they aren't you should put them between a small overlap at the edge of your matting cylinder.

\$\endgroup\$

Not the answer you're looking for? Browse other questions tagged or ask your own question.