Melting furnace recommendation for silver
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kurtak
Well-known member
Per the bold print - if you are melting metal (brass. copper, silver, gold) that often you are better served getting a gas/propane fired furnace
Those electric furnaces just don't hold up before the heat elements burn out & you have to replace the elements &/or furnace
You will never need to replace a propane furnace - on the other hand you will end up replacing those electric furnaces regularly if you are melting metal regularly
If you are a handy kind of guy you can even build your own propane furnace - there is LOTS of info here on the forum about that
When I first started doing this (something like 15 years ago) I went through 3 electric furnaces (in short order) before I bought my first propane furnace (takes a #4 crucible) I have melted many, Many, MANY kilos of silver in it & it is still working fine
I also have a second propane furnace that takes a #40 crucible for smelting
Do yourself a favor & invest in a propane fired furnace - or if you are a handy guy build your own
Everything you need to know about propane fired furnaces is post on this forum --- use the forum search function
You can start by searching my postings using "furnace" as a search word & my name (kurtak) as the author --- that will lead you to much more info posted by others
Kurt
Fantastic, thank you for sharing your knowledge, so I do not make the same mistake and buy 3 forges... My only issue is I live in a HOA with a bunch of retiaries who love to complain. I am afraid a propane furnace would freak them out and I would have to deal with that. DO you have any experience with induction coil melters?
Living in an HOA could be problematic. Ensure that what you are doing conforms to the rules of the HOA or there could be enormous financial implications. Even if you are adhering to all federal, state, and local government regulations, the HOA has its own rules.
Time for more coffee.
Time for more coffee.
I am the token redneck in our community, so when the transfer from builder to HOA happened, I got on the board as the VP, that way I could intercept all the nasty letters about me.
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Anybody ever figure out why the elements in electrics are so unreliable? I am wondering if excess CO2 carborizes the element to where a slight bump will break the wire. Anyone know for sure?
goldscraphobby
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How about repurpose your cheap Chinese (Italian) furnace, remove the elements, drill a hole in the side and one for air and stick a mapp gas torch through the hole. Almost the same footprint and could cover the tank so it not exposed
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Am willing to bet it's CO2. I used a ceramics kiln for a while. Bought the ceramics kiln same time as another party bought one, same make and model. Mine went on the fritz after 3 uses at lower temps., theirs is still in use 3 years later, firing once a week.
Cryogaijin
Active member
I disagree. Electricity is vastly cheaper than propane presently, especially if your propane furnace isn't getting peak efficiency. (by definition, an electric furnace has to get pretty darn close to ideal efficiency. Will explain at the bottom of the post) I presently use a castmaster electric furnace, and their 5kg propane furnace. (I've also tried a couple cheaper electric furnaces, gotten insulation burnthroughs, and let out the magic blue smoke. This made me laugh and laugh, as I'm an EE and had anticipated this likelihood, and mitigated against it causing any problems.)
I get about 30 copper melts per heating element. (Castmaster sells their replacement heating elements on Amazong for $100) the 3kg graphite crucibles I mostly use get aboot 15 pours before they start making me nervous by how thin they are. This could EASILY be increased by not opening the forge up as often as I do. . . but I like watching the melt if I can.) So if you add in the cost of the heating element and crucibles, you end up around 5ish dollars per melt. (I pay below 8c per Kilowatt hour, and 2kg of copper takes about an hour to melt, so 12c per melt in electricity)
On the propane side, I'm a LOT less comfortable. (EE like I said. . .) I'm presently getting 4 or 5 copper melts, max, per tank. (Not sure why it is so low, but. . .) Clay-graphite crucibles seem to last me about 10-15 pours. The borax to glaze them is non-trivial as well, but lets just call that 50c per melt. So we're talking $5ish in propane per melt, plus the cost of consumables, so say $6.50.
Now I'll readily admit that I'm VERY new to all of this, and my propane setup could likely be improved dramatically by someone with more experience than I. But for ME, for what I'm doing, my electric furnace makes sense more often than the propane one does.
Once I get into sandcasting that may change.
I also like that the electric furnace can absolutely melt things that like to burst into flames when exposed to oxygen. Don't draft the melting chamber too much, and you can absolutely make magnesium-aluminum alloys. They are a bit hard to pour, however. . .
(On the topic of efficiency: Converting electricity to heat is by nature 100% efficient. Electric devices waste product IS heat, so you're literally maxed out there. You do get losses because the heat is not perfectly concentrated on the metal you want to melt; but that is true of a propane furnace as well. And with an electric furnace you don't have to worry about convection out the top anywhere near as much. (Small vent hole with kaowool insulation.) So in the end electric furnaces are by nature more efficient. . . if this matters to you. Now if I were getting 10 copper melts per propane tank vs 4-5 things would be dramatically different, but I'm not, so. . .)
I would invest in better heating element wire
and run it far below the current limit, which is recommended.Issuing CO2 as the thing ruining the wires, I would say it could be, but oxygen is certainly much more harsh to heated metal. There are more speciallized alloys for heating elements, than NiCr or FeCr alloys. They contain few % of aluminium, which will burn firstly, creating protective layer of aluminium oxide on top of the wire, protecting it from further burning.
In laboratory practice, with good insulated wire without moving and vibrations (transferring the furnance, anyhow disturbing it - protective coating dross off and wire burn quicker) they last practically forever. When you are looking for temperatures of 1200°C, wire must get to even higher temperature, so seek the elements capable of going past 1450-1500 °C. They aren´t cheap, but work for ages.
Mounting of the wire is also very important. Best, it would be hanging in the air without touching the walls of furnance. Otherwise as it heat up, it elongate and slightly move, scraping its surface against the wall - drossing off even more oxide coating. Opening/closing the furnance, element switching on/off, rapid cooling etc...
The biggest thing I do to kill my elements is incinerate in my furnace. Once you switch to a reducing atmosphere, that oxidizing layer gets reduced back to elemental metal....then reforms when it's oxidizing again. Do that a few times and the wire gets thinner, then finally burns out.
Cryogaijin
Active member
If I ever run into the issue that I can't get a castmaster replacement, I will roll my own. Already have the wire ordered. The issue is that the element and heating chamber are integral on this (and most units like it). Thus far I'm pretty satisfied, though I am slowly upgrading the systems as I use it. (soldering the wires together rather than using tension connectors improved longevity instantly. . .)I would invest in better heating element wire
Mainly, its easy to calculate estimated length of wire for the furnance based on the resistivity and power rating for length of the wire. I go on 60-70% when assembling something like this. Just have the required power and design the length and diameter of the wire used to achieve that number.
Also bear in mind that very good insulation could result in overheating of the wire (in some places) and limit its life expectancy. Sometimes I run the furnance empty with additional thermocouple very close to heating spiral just to approximately measure the temperature on the wire, and then adjusted the power input/length of spiral - not to overcome the acceptable operating temperature value.
Also bear in mind that very good insulation could result in overheating of the wire (in some places) and limit its life expectancy. Sometimes I run the furnance empty with additional thermocouple very close to heating spiral just to approximately measure the temperature on the wire, and then adjusted the power input/length of spiral - not to overcome the acceptable operating temperature value.
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The biggest cost, in my opinion, with the electric furnaces, is the cost in labor to make the necessary repairs. I didn't see that factored in to the electric cost per melt. Also the inconvenience factor when the electric goes down. I prefer electric, but when all is considered, I much prefer gas for its reliability and ease.
Electric has better temp regulation, economy (quality heating element), you can use graphite crucibles much more economically than in the gas powered.
But yes, gas furnance is much more easy to maintain and run.
But yes, gas furnance is much more easy to maintain and run.
Cryogaijin
Active member
Desoldering and resoldering the leads takes fairly minimal time and effort. Removing all the screws is a pain. The insulation is pretty well shaped to let the element in and out, so I'm not really sure what you mean by "Cost in labor to make repairs" About the same amount of time as it takes for me to drive to get a propane refill?
