Induction Melting Furnaces for The Hobbyist

Discussion in 'Furnaces and their construction' started by Al2O3, Dec 9, 2021.

  1. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I decided to start this thread to see if we might answer some questions about using commercially available induction heaters as hobby melting furnaces. Namely, my interest is, how realistic is it to have a single power supply to power an inductive melting furnace for melting a range of metals with melting temperatures up to say iron, or possibly steels, and moreover, are the import induction heaters suitable for such duty? For discussion, let’s say the 15kw units which are available for under $1000, because that appears to be about the maximum rating for 220 single phase powered systems, which I’m limited to and I suspect the same to be so for most hobbyists. This excludes RPC 3ph sources and large power transformers for higher voltage which would cost more than the power supply.

    Here are a couple of threads with related content and some answers.

    http://forums.thehomefoundry.org/in...n-isnt-just-nice-for-ferrous.1646/#post-37429

    http://forums.thehomefoundry.org/in...induction-tilt-furnace.1631/page-2#post-39620

    http://forums.thehomefoundry.org/index.php?threads/homemade-induction-melter.2046/

    1. How does operating frequency relate to intended use and applicability to melting different metals? Most of the “induction heaters” on the market are represented to be high frequency between 30khz-80khz. For magnetic metals, my understanding is this frequency range will concentrate the heating on the skin/outer diameter, which is nice for surface hardening, but not as nice for deeper penetration, ala melting. Lower frequency, perhaps 1khz to as much as 30khz, may be more preferrable but those seem scarcer and more expensive. Non-magnetic metals respond differently and a member in one of the threads above suggested the solution to such a system’s versatility in metal species is to rely on a conductive (graphite or clay graphite) crucible to be heated which will in turn promote melting non-magnetic metals. A conductive crucible would probably respond well to higher frequency power supplies since their shape is reasonably close to cylinders.
    2. How much metal can you melt with a given power level and how does the shape/size of the inductive coil and metal load affect this? Most of the inductive coils advertised with 15kw power level systems are small, say 60-75mm in diameter and maybe 4-5 coils. So what if you wanted to heat say an A10 size crucible? They are a little over 6” in diameter and 8” tall. At best, you’d have half as many coils for similar length copper tube. Will this just extend heating time or will this coupled with larger metal charges potentially overload the power supply too? Some reading indicates that for best efficiency and power transfer you want to minimize the gap between coil and heating load, but you can’t allow contact that would cause short.
    3. How much service power is required for a given kw rating and are the import units compatible with US single phase power? It was suggested in one of the previous threads that the advertised power rating is. Other than voltage, required input power is missing from almost every advertised system. I actually do have one supplier that indicated advertised power is “oscillating power” and not the continuous service supply power required and 15kw unit only required 7kw of supply power, so this is similar to what 3DTOPO mentioned in the linked thread, and that’s rather significant and certainly more practical. I’m already at 8kw on my resistive electric and would be happy at double that but “15kw” seems to be about the max “rating” offered for single phase power.
    4. Are the import units compatible with US power? It’s unclear. Most cite 220vac 50hz and have safety shut down features for voltage overflow above 245vac. US power is 240vac not 220vac and 245vac would not be unusual on occasion. So is the machine going to shut down frequently in over voltage on US power?
    5. I’ve asked at least six different offerors that claim to be the direct manufacturing sources if I could view a (English) manual. -No joy. The typical control panels have dials for heat and retain times. Most suggest a max of 90 seconds for heat time setting. Not sure about retain time. How does that work for melting?
    If I could melt an A10 full of any metal (say up to iron) on 8kw of 240vac 1ph power, I spend $900 and build a system….fairly easy decision.

    All input welcome, just trying to gather it all in one thread. If you have a different questions or understandings than I’ve stated above, please chime in.

    Best,
    Kelly
     
    metallab, Tobho Mott, Bldr J and 2 others like this.
  2. metallab

    metallab Silver

    Good idea, Kelly.

    I am also investigating and opened a topic on this earlier this year. My requirements are:
    * At least 1500 C inside crucible, so I can melt cast iron or (stainless) steel. For lower temps I can already use my Kanthal (resistance) furnace or propane for larger quantities.
    * May be rather small, 200ml crucible size (A2 ?) is enough.
    * Power rating 4kW / 220V is enough. For higher power I have to upgrade my home power to allow 3 phase and / or more amps. Now I have 230 V 35 A.
    * Overpower protection to prevent killing the MOSFETs. I suspect that the cheap (< $1000) furnaces on ebay / Amazon are not protected so can burn out.
     
  3. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Metallab, you may have posted this particular offering before, but I believe it has the protection features you cite.

    https://www.ebay.com/itm/255190497943?hash=item3b6a89fa97:g:PAwAAOSw2QZhUrgj

    I suspect, the power rating is similar to others meaning that the advertised power isn't actually the continuous input power level. It doesn't say but I suspect instead of the advertised 5.5kw, the service power require is half that or less, or for you, about 2.5amps @220vac. Based upon your description, this might be a pretty good fit for you as far as melting capacity. Their description is more fulsome than most and there were a couple of tidbits that caught my attention:

    "With dual air cooling and water cooling device, the packaged product can work for 30-40 minutes at a time."

    This is a little worrisome. Many of the 15kw machines are 100% duty cycle. The auction also says 15 liters/min of cooling water is required. That's pretty substantial.

    "Heating adopts medium frequency induction heating 10-320Hz"

    I suspect this is an error and the frequency range is actually 10khz-320khz. Even so 10khz could be very attractive for ferrous alloys below 30khz is not available on most of the inexpensive higher power units.

    3DTOPO, actually gave a very good explanation on operating frequency and melting various metals in the first thread I linked. With this thread, I'm just trying to gather everything together in one place.

    If you were going to exclusively melt iron and steels, I think you would want a power supply that operated in 1khz-10khz range and use a non-conductive crucible. That would transfer most of the energy directly and deeper into the ferrous melt, and you would achieve the fastest melt times and best efficiency.

    If you are a hobbyist, and want to be able to melt non-ferrous metals, you would need to use a clay/graphite crucible and the higher frequency (30khz-100khz) units would fairly effectively concentrate the energy transfer to the crucible. Then the heat of the crucible melts the charge. This would probably work for iron as well. This will not be as efficient as true inductive heat of the charge but you will have an electric furnace capable of melting metals up to iron.

    I'm very interested in the 15kw units available but they are really more comparable to my 8kw resistive electric, except, the initial melt only needs to heat the crucible not the entire furnace mass, and I would except better melt times. Also to get optimum efficiency, you need to minimize the gap between the inductive coil and crucible. This is more difficult to do with A-shaped crucibles and that's why induction furnace crucibles are typically cylindrical. It also means for optimum performance you use a dedicated crucible size. Problem is, I don't think the so-called 15kw units are enough power for my usual melts and that's the max available for 22vac single phase.

    There are a number of other nagging issues and getting answers for offers isn't happening. Most selling don't know anything about the machines and after six requests, I'm yet to have any of them send a manual. I am in contact with a mainland China manufacturer and hope to get some better info, and maybe a custom higher power single phase unit. We'll see. I already have two furnaces and can play the long game to get what I want/need.

    Best,
    Kelly
     
  4. metallab

    metallab Silver

    Indeed, I already have posted a link to this furnace, it appears to be very convenient. But I am still reluctant.
    The problem of the cylindical crucibles is that they are made from pure graphite which oxidize much quicker than the clay graphite ones, particularly at iron temperatures. And as you say, melting ferrous alloys at that high frequency might not reach the temperature of 1500 C and 15 liters (4 gallons) per minute is very much. I have seen on Youtube people using induction furnaces using a bucket of water for cooling and the water is just pumped around.

    EDIT: I found another interesting one.
    https://www.ebay.com/itm/124402230505
    Then I select the 3500W / 1kg / 220V model. When I can melt a few hundred grams of cast iron or steel it would be nice.
     
    Last edited: Dec 12, 2021
  5. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Yes, there are variants of that model and also similar models that have many discrepancies from one seller to the next. The ads/auctions are all lacking fundamental information. It would be nice to see some customers reviews or better yet, a manual.

    Morgan makes a line of cylindrical clay graphite induction furnace crucibles. I can post their offering if your interested.

    Best,
    Kelly
     
  6. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I did receive a reply on request for a manual. It's not especially enlightening but does provide a little better explanation of controls and indicates the inductive coil length is 5 feet. For those interested it can be downloaded here.

    https://ussolid.com/content/JFHFIH/JFHFIH01-15KW-Manual.pdf

    No particular allegiance to this supplier other than their responsiveness but I suspect it is similar in construction to other 15kw 1ph units from the myriad of mainland China sources. For US customers, they do claim to have in country stock and price includes shipping so is on par with off shore sources. The eBay link may not live for long. I also posted the importer's website. Search "Induction".

    https://www.ebay.com/itm/111988443045?mkevt=1&mkpid=0&emsid=e11051.m43.l1123&mkcid=7&ch=osgood&euid=c927d9dca8bd4ecdac8da9695ad072ef&bu=43193468527&osub=-1~1&crd=20211213005543&segname=11051&sojTags=ch=ch,bu=bu,osub=osub,crd=crd,segname=segname,chnl=mkcid

    https://ussolid.com/

    Best,
    Kelly
     
    DavidF likes this.
  7. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    These high frequency induction heating units are/were really designed for heating smaller pieces of steel and ferrous alloys. One of the potential problems with adapting them to melting is crucible size. The largest crucible I've seen them advertised with is 5kg (copper) which is a measly 3lbs of Aluminum......but a fairly efficient coil can be fitted.

    With the recommended coil length being 5 feet on the 15kw unit, it doesn't lend itself well to making a decent inductive coil for a crucible of any appreciable size because you can only get 1 or 2 loops of coil which isn't conducive to producing a strong field nor uniformly heating the crucible. I don't no how much the power factor suffers with additional coil length (one of the questions I've asked manufacturers, but concentrating the inductive heat in a narrow band of the crucible could cause crucible breakage. Incidentally, this issue doesn't change with power level because the frequency range is still the same, but you may have more power factor lee-way. Below, I've pasted excerpts from Morgan's Salamander Super (Clay Graphite Non-Ferrous & Ferrous) and Excell-Himelt (silicon-Carbide Non-Ferrous) line of crucibles. The start up procedure isn't very uplifting for anyone that was envisioning flipping a switch and having molten metal in a few minutes. That's a lot of babysitting. Also, haven't quite zeroed in on how you determine melt temp other than shut down and measure or experimentation. Maybe deviating is akin to running with scissors but read them and you'll see what I mean, but my resistive electric is truly flip the switch and walk away.

    Salamander Super

    Crucible Dimensions_Page_1.jpg Crucible Dimensions_Page_3.jpg

    Excell-Himelt

    Excell-Himelt First Use.jpg Excell-Himelt Installation.jpg MorganMMS-EXCEL-HIMELT-Crucibles_Page_3.jpg

    From the reading, the cylindrical crucibles aren't really intended for lift out use, but more so tilting furnaces, so you'd need to adapt a ladle to pour. It is also recommended that they only be charged 70% of brimful. Problem is the recommended installation procedure semi-permanently installs the crucible in your furnace so it isn't very conducive to crucible swaps for melting different metals.

    Most things point toward induction furnaces being configured for a particular melting duty. I'm still trying to determine how much compromise is required for a multi-purpose hobby melter.

    Best,
    Kelly
     
    Melterskelter likes this.
  8. metallab

    metallab Silver

    Thanks, Kelly Al2O3.
    When I read this, it is rather discouraging. Too much hassle I think. What Al2O3 says, not like flipping the switch of a Kanthal furnace, waiting 40 minutes (in my case) and pour the copper / bronze. I think it should be more mature for hobbyists.
    Commercial induction furnaces have usually a tilted setup and pour the metal out into a ladle or at least the crucible does not leave the furnace when hot.
     
  9. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Well, there is what the manufacturers recommend, and then there is what is commonly practiced. My guess is they can tolerate more aggressive heating if it is more uniform.

    I'm guessing some of those larger Morgan cylindrical crucibles are pricey so breaking one or having multiples for different metals becomes a bit of hindrance. I'm completely satisfied with my resistive electric for aluminum and sure I could do some bronze if wanted, so induction is really to add higher melt point metals. The notion of having an electric powered multi-metal hobby melter that you could dial to suit is appealing but not sure it's going to be that easy, practical, or possible but still investigating. It's possible I might find a smaller system for other metals useful but I already have two furnaces :rolleyes::rolleyes: and a stack of projects for my present foundry capabilities.

    Incidentally, per your previous remarks about graphite crucibles, even though they are consumed faster, I bet those pure graphite crucibles perform great in induction heating. If you could eliminate the free oxygen, like maybe with N2 or Argon purge, they might last a good long time, if it's worth the trouble. The small ones aren't very expensive.

    Best,
    Kelly
     
    Melterskelter likes this.
  10. Ironsides

    Ironsides Silver

  11. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I agree, it's not clear, but based on other similar auctions for apparently identical kit I believe it's 220vac 1ph. Also, it's not really 5.5kw, more like half that. All the import induction systems seem to rate the furnace by some sort of peak or resonant power level at the coil but they actually draw about half the "rated" power from the source, so I'm guessing 11-12amps @220vac. That's what I meant by the ads often omitting fundamental information.

    The same is the case for the so-called "15kw" (maybe all?) 220vac 1ph import units. They actually are 7kw so about 32amps @220vac. I figure they're are comparable to my 8kw restive electric which has no problem melting 20lbs of aluminum in an A20, but not sure of the "15kw" induction unit's ability to do same.

    Best,
    Kelly
     
  12. metallab

    metallab Silver

    This design would be nice.
    It is an induction furnace using a classic clay graphite crucible where when it is hot, the furnace body with the inductor coil is lifted and the crucible is initially left in its place, but when the furnace is lifted, taken out and the metal (copper in this case) is poured into the mold.

    (at 2:30 they start pouring)
     
  13. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I don't know if you've seen my resistive electric "lift off" furnace but that is exactly how it works. If I converted it to induction, I would likely keep the furnace body/coil stationary and drop or lift the base to expose the crucible. That way the coil doesn't need to have a flexible connection to the power supply.

    Best,
    Kelly
     
  14. mytwhyt

    mytwhyt Silver

    I've read all your threads, some several times. especial the lift off furnace. It's perfect for what you're doing in aluminum. The furnace makes pickup and pour quick and efficient. Would have liked to have seen more of the lift system. Picked up a lot from your threads on how to coat the foam and gate, and the rate the metal should advance into the foam,,
     
  15. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I had a very detailed thread over at AA. That's the dead link in my signature. I've started a revised cliff notes version and have had a few requests from my YouTube channel to do a walk around video. I have one somewhere if I can find it. I'll try to get to it in the near future.

    Best,
    Kelly
     
  16. Mach

    Mach Silver

  17. boroko

    boroko Copper

    Wow. Of course I admire your furnace, but until now, had only seen the walk-around and use. After reading that first page, I'm doubly impressed with the creativity you have in coming up with solutions and building it. I have been reading for weeks and sucking it all in. Thank you so much for sharing and inspiring.
     
  18. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    It was probably as much a means in creating reasons to exercise all the metal fab and sheet metal equipment in my shop. I've refined and added things here and thee over the years. It does consolidate my casting related equipment conserves valuable shop space, and is a joy to use. Ya-know what they say.....sometimes the journey is just as fun as the destination.

    I update the links in my signature for both furnaces.

    Best,
    Kelly
     
  19. boroko

    boroko Copper

    I understand the outlet for creative skills. I could build the part I want with a grinder and welder faster than I'm going to be able to do by getting into casting it, but the outlet of learning new skills is actually some of the reward.
     
    Tobho Mott likes this.
  20. Lou

    Lou Copper

    We have both a fixed connection with the lift up style and a tilt n' pour. We prefer the lift up. The only time the tilt n pour is nice is for casting stuff that freezes really quick where you have to cast under power to get it in the mold (platinum, in our case).

    For melting aluminum and presuming you're using a steel, graphite, or silicon carbide crucible...all of which get hot quite quickly-- you don't even need to have the crucible fully enveloped in the coil. When I melt a bunch of silver I'll have the top of a straight wall graphite crucible sticking 3-5" above the top of the coil. The crucible conducts enough that it melts.

    Our furnace is an Inductotherm VIP Powertrack furnace that we use for melting precious metals, mostly Pt and Pd. We have also melted Al, Si bronze, stainless steel, and some nickel and cobalt alloys.
    I have found that winding a coil that works is easy, but from what I've seen with melting stuff like platinum is that winding a coil that works well is difficult. Induction furnaces do really well at repeating the same task over and over again. This is if you are melting a metal without a crucible that acts as a good susceptor. In our case, Pt or Pd are melted in zirconia crucibles with alumina and zirconium oxide grog packed around the zirconia. It's double bagging and I highly recommend it if you're picking up a crucible of molten stainless. The radiant heat from that crucible is no joke and the double bagging adds a layer of safety/insurance/insulation that can't be overstated, despite the decreased capacity.

    I've actually owned one of those orange and yellow cheap-o Chinese made ones. Compared to a commercial furnace, they're mere toys and need a lot of help. I would rate their 15 kVa furnace at more like 3-5 kW of power.
     

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