Electric furnace + Varnished Copper Wire = Won't Melt

I've been using those commonly available 3kg electric furnaces, and they melt aluminum very well. They even melt copper wire very well... unless it's the more reddish copper wires which have that varnish coating over the copper.

When I put in a bunch of those red copper wires, the powdered black dross seems to all pile up at the very bottom of the crucible. I believe that this insulates the copper and prevents the copper from melting, especially since I can only take the PID to 1150C. So, I figure I start with as pure copper as possible - left over ingot pieces and raw copper wires. That melted very well. I added red copper wires to that and after 20+ minutes, it all froze inside instead of staying liquid - so, I think that the varnish still settled at the bottom. The copper in the crucible wasn't melted on the top, and poking it with a metal rod didn't compress or move the hard copper on top. I still added borax to the top but that didn't do much at all.

What is the best technique when melting these red varnished copper wires? Do I have to melt only a relative small amount of red copper wire at a time, pour, remove the dross at the bottom of the crucible, repeat until all the copper is made into tiny ingots, then melt all of those tiny pure copper ingots together? Or, do I need to add borax to the initial melted pure copper before adding the red copper wires?

Thanks in advance!

I hope your working under a fume hood or outdoors, the fumes from the insulation are very toxic.

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Originally Posted by alloy2

I hope your working under a fume hood or outdoors, the fumes from the insulation are very toxic.

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I'm in the garage with the door 1/4-1/3 of the way open, a fan turned on to blow the fumes towards the outside, and I wear a respirator mask (among other safety gear). That said, I'm not burning the wire insulation jacket off. All of the wires are stripped. Some wires have a varnish or an enamel "paint" on them, and those are the red copper wires I'm referring to (if you Google "red enamel copper wire", the first results should show what I mean by them.). Unless that's what you're referring to as insulation, since that varnish does seem to act as an insulator and produces fumes, too.

Also, I think I figured out why it doesn't melt. The red varnish on the copper wires (i.e. those from motors) collect at the bottom of the crucible, and turn black. It turns gooey and sticks to the bottom and lower sides, and stays adhered to the graphite crucible. Despite the high temperatures exceeding 1100C, the copper won't melt because that varnish seems to absorb most of the heat, and effectively acts as an insulator. That's my theory at least.
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When one of my copper buyers was describing why windings were now being downgraded below normal copper #2 he said it was because the enamel's glass transition (as opposed to melting) point created extra labor at furnaces. I have zero furnace experience myself so don't know what that means from a user perspective but glass transition contaminants without melting points are treated different than other contaminants that can be removed as slag. Dunno if that is useful at all. If not, enjoy the useless info!

Your electric furnace struggles to reach the melting temperature of copper any foreign material on the copper surface will reduce the heat reaching the copper in addition any heat escaping the crucible will lower the performance of your furnace.

The addition of a fluxing agent would be the first to melt once liquid becomes a wetting agent transferring heat to the melt also the flux would pick up any oxides absorbing them into the slag.

This list of flux's is the most commonly used, some like Borax are used alone or in combination with other ingredients to achieve different end goals.

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