My first attempt at melting silver with my DIY induction heater rig had too little power to even get a glow, but with a higher voltage power supply, I'm now able to get yellow hot, or at least very bright red hot. Looks to be about as hot as when melting with a flame, but it's just not quite there. The silver doesn't melt. [youtube]http://www.youtube.com/watch?v=QLphNgNQoJQ[/youtube] (It looks white because of the high IR sensitivity of the camera) This was consuming about 430 watts. The next step is to increase the power further, but cooling and insulation need to be improved first. Ultimately, I want to be able to melt around a kilo at a time, but that's a fair way off. I'll need 1000 watts or more for that, and the whole system will have to be redesigned to do it. But some initial progress has been made, and I wanted to share with those that may appreciate it!
Some progress made:- The revised power supply delivered only a modest power increase. The biggest single improvement was insulation around the crucible, which keeps the heat in, and reduces burn-away of the crucible. Silver melted, but was not fluid enough to pour. Curiously though, gold did melt enough to pour (65% Au with Cu), as seen in this crappy video. Maybe the alloy has a lower MP than silver, or silver is too good a conductor and does not heat up as well in an IH. [youtube]http://www.youtube.com/watch?v=UFzkAX89qko[/youtube] The melted silver (screwed up image sizes) The poured gold
On the au it's like some oxidation? You need some flux like borax to take away some of the impurities (this is not refining) and some pickle ie acid to burn of the oxides. I use this http://jewellerssupplies.com.au/borax-flux-powder-250gm-p-2085.html They also have pickle 500gm for $14 you just need to email them. Quite cheap and I like the easy containers they come in, plus I am just walking distance away.
Thanks for the responses, though the point of the exercise is not to produce clean looking metal, but to develop a design for an induction furnace that can melt a kilo of silver. The videos are to show the progress of that to anyone interested. (Is there? Or shouldn't I bother?) The crap look on the result is due to oxidation of the 30% copper in the alloy. Here's what it looks like after a clean in hot sulphuric acid (slightly better). But it will look like the sample on the right (99.95% Au) after I refine it. Also, although borax produces a nice surface finish by absorbing base metal oxides, it's mainly a flux, and while needed for silica crucibles, should not be used with graphite crucibles. It's not needed, and gunges them up.
The crucibles in the videos are graphite... Not sure what you mean, but sounds interesting. Though I'm sure graphite is what I should use. In fact, what I'm trying to do is *precisely* what this guy has done:- [youtube]http://www.youtube.com/watch?v=jhUd_aH7OxA[/youtube] I have that larger type of crucible, but my current rig can only get a faint red glow out of it. So for now, I'm only using the small 40x40mm graphite cylindrical crucibles.
Huh? What do you mean by "reverse coils"? How could you ever not need a crucible? The (heat) insulation around the crucible is also electrical insulation, so no problem there...?
Neat. Does it operate at 50hz or did you build a HF power supply for it yourself? Because from what I've read the key to getting induction furnaces hot with small loads is higher frequencies but because of the current required that causes problems with the switching transistors and capacitors.
You will need two induction coils, one is oppose winding the other. Then this will create magnetic field which will hold the materials in mid air. Melting without the crucible. Do your own search, you find them. Tips
