With a graphite crucible, induction melts non-ferrous metals like butter. This was my first little 15kW induction generator: That video is not sped up at all. From a cold start, that little machine could melt 8kg of copper and poured within 25 minutes. Total cost in electricity was 30.4ยข In my propane furnace, would probably take about an hour and cost like $10-$15? That induction generator cost me $1200 delivered and the furnace is nothing more than a copper coil with a tad of ceramic blanket. I've been casting since 1988 and induction really is the magical melting machine. Much amaze.
Very interesting. I saw your intro thread mentioned your new rig as 36kw. What was the jump in purchase $ to 36kw? 3DTOPO, there's a lot of information and misinformation out there about induction melting at the hobby and small scale level and about the import hardware. As someone who is using them I was wondering if you could comment, maybe expanding upon your remarks here: http://forums.thehomefoundry.org/in...-36kw-induction-tilt-furnace.1631/#post-37013 What is the frequency range and what sensitivity does it have to the metal and crucible size with non-ferrous metals. Is the machine sensitive to the charge size? What input power is required? Power level aside, some of the import machines advertise some pretty strange and impractical input voltage/current combinations. Any guidance/restrictions on adapting custom induction coils? Any hazards regarding proximity to field? Inquiring minds and casters want to know! Best, Kelly
Thanks! The 36kw machine, customized with single-phase transformer, with tilt furnace, a couple MgO crucibles and freight all came to $4k. Freight alone was $1k - not bad for two large wooden crates weighing hundreds of pounds to arrive from China. If you have 3-phase, you can get a 40kw induction generator for $1,900 + $300 shipping. Just search for "induction furnace" on eBay. Short answer: frequency doesn't matter using a conductive crucible such as a graphite. Long answer: The frequency determines how deep the induced current can penetrate a given load. The lower the frequency, the deeper the skin depth. The deeper the skin depth, the more heating from resistance. So, imagine if you will a hollow pipe sitting vertically in the work coil. While the pipe is a complete O, the "skin" is the cross-section of the pipe itself (which is maximum resistance and maximum heating). But if you add a slit along the length of the pipe (making a C), the "skin" is no thicker than the cross section of the pipe wall - and so it can't heat much from resistance anymore. That is why low frequency machines are best for melting ferrous metals. But with a graphite crucible, it is just like a complete pipe and the "skin" is the cross-section of the crucible. That means it heats up fast and easily - even with high frequency machines. In other words, if you are using a conductive crucible (such as graphite), you don't have to be concerned with the machines's frequency. And to melt non-ferrous metal, a graphite crucible is pretty much a requirement regardless of the frequency of the machine. The reason is copper and aluminum, etc. have much less resistance than steel, and are not magnetic so they can not be heated from the alternating magnetic fields. That is, ferrous metals heat from two ways: (1) alternating magnetic fields until it reaches the currie point - pretty much the same as bending back and forth the metal at the frequency of the machine, and (2) resistance which hass much more resistance compared to non-ferrous metals. Non-ferrous metals are only heated in one way: (1) resistance which is quite low with aluminum and lower yet with copper. So that means the only practical way to melt non-ferrous metals is to use a conductive crucible. And in-fact, with a conductive crucible you can melt glass, quartz and granite! I'm not sure I understand the question, but the larger the charge, the less dense the energy will be. So a 15kW machine can easily melt 20 pounds of copper, it would struggle to melt 40 pounds and at some point it would become impossible to melt at all. For 15kW machines both 110V and 220V single-phase seems to be the standard. Anything larger and 3-phase seems to be the standard. Note that the actual power needed is less than what the machine claims. For instance, a 15kW machine only needs a 7.5kw breaker. I think it's because they consider it to be 15kw because that is how much power is in the work coil in resonance. The coil is limited to maximum length which should be stated somewhere in the machine's documentation. All else being equal, the lower the frequency, the longer the work coil could be. You can go longer than recommended but the Power Factor will suffer. The 15kW machine allowed a pretty short length, but the 36kW machine allows for much longer work coils. The 15kW machine's power was cut nearly in half trying to use a flexible cable attached to the work coil, but the 36kW machine doesn't mind one at all. You do need to keep the cables running the work coil distanced about a foot away from the machine (don't ask me how I know!!!). I understand that it could be a problem for someone with a pacemaker. You probbaly don't want to wear a loaded gun when working in close proximity to the machine. Awesome! Please let me know if you have any questions or would like any clarification!
Thanks for that, very helpful. That was the question. My understanding was they hit a wall and it's not just extended melting time. Maybe it's just the cheapies on Alibaba but I also understood that it could cause destruction if there was not a constant current control features. 15kw serviced by 110v would be 136 amps! Do they tolerate 3-phase from RPCs? The manufactured phase (wild leg) is a different voltage to ground. I have an RPC but it's only 7.5kw. I actually have 3-phase in my residential neighborhood because there is a community well and the pump house is 3-phase. It's about 250 yards from my shop, but doubt the power company would make the connection let alone foot the bill. I have a dedicated 200 amp service in my shop and bet they would up it for a very modest connection fee, but would still be 240 single phase. ...and why is this? Do you recall the max coil length? I have to admit, this is one aspect that had me very sheepish about the import units. The equipment looks like something that you'd see in a server room, not sitting next to a foundry furnace. Trying to imagine how the equipment with LEDs, touch pads, etc, would fair with even a brief view of a radiating 3000F crucible. Also scratching my head about how to make a tipper furnace without flexible cable. The power source tips too? What happens as the coil diameter increases compared to the crucible diameter? Just thinking about keeping the coil cool. Are you closed circuit liquid cooling I presume? What thickness of ceramic wool separates the coil and crucible and does the wool really withstand close proximity to crucible at iron temps? I'm envisioning a lift off furnace like my current rig that just exposes the crucible for snatch and pour. Sorry for all the Qs. Best, Kelly
And I'm envisioning using a bottom tap crucible positioned directly over the flask (under vacuum) in an inert atmosphere in the melt chamber.
Cheers! Well you would hit a wall using propane or oil too. If you have a 200,000 BTU burner, your not going to be melting 500 pounds of copper. As for the machines they are quite smart and robust in my experience. Impressive machines for the money - rated for 100% use. Generally, you want not just enough power to melt something, but far more power to melt it quickly and efficiently. Actualy it would be half that as I had pointed out. I ran my 15kw machine on a 40-amp 240v breaker. New machine is on a 75-amp 240v breaker. I personally wouldn't even consider it 110v because I have 220v. If I didn't, I suppose I would look at it differently. I don't have any experience with that so I don't know. I could only suggest contacting the manufacture. I've had good sales and support experiences despite the language barrier. In my experience the power company is quite interested in new 3-phase power installations. It's like asking for 3 straws for a big gulp instead of 1 and they are in the business of filling the cup. There is a second phase wire that also stops short, maybe about 500 yards of here. The power company said they could run me a new wire and install a 2-phase to 3-phase transformer. But he said I would be limited to 35kw and getting a single-phase transformer in my 36kw machine was simpler and less expensive. If they could deliver 65kw+ I would have gone that route in a minute. He said that wire itself is quite cheap. If all the poles that are needed in, it wouldn't cost much. He said I would probably have to pay for some new guy wires which weren't terribly priced either. As I stated I suspect its because they consider the power in resonance. Why is it in resonance? Because the coil uses alternating current at high frequencies. But I guess you would have to ask the manufacturer - just was giving a heads up. Sorry I don't - but for the 15kw machine it was only a couple loops around a 8kg crucible with room for insulation. I would suggest looking at the manual for any machine you are seriously considering. I'm not sure how else they would make the controller look? It is really a computer that controls some serious hardware. You do get what you pay for. The machines that are split in two (called AB) - a transformer and controller - cost more but are a bit better built than the single combo unit. And the bigger and more expensive the machine the more impressive the hardware. The 15kw machines are really built for mass use heat treatment. If you buy a 65kw you will see a huge difference in hardware. One can be consider a consumer machine and the other a professional machine. In terms of radiant energy, it's not a big deal pulling out a white hot 4kg crucible. Bigger than that and it really needs to stay shielded in the furnace or things a couple feet away will instantly start smoldering. That's what I did - but it kind of sucked. Here's what I had - it even had two garage door springs. The power factor decreases. Provided you have sufficient water, in theory it would be possible to dip the coil in molten steel - not that I recommend doing that! The trade-off is use lose a little power factory to have something insulated - which seems to more than make up for the decreased power (still plenty of juice going in there!). Yup - it was too easy using my water main, but the cost in water cost far more than electricity to run. So I had a little cooling pond built with a copper coil in it which exchanges the heat. It depends - can be done without any ceramic blanket. If there is room for the crucible I'm running than I like an inch but even a quarter of an inch is a lot more insulation than none - that stuff is pretty amazing. If you get the 2600F blanket its fine at copper, brass, and iron temps. Melting steel will deteriorate it, but lasts well enough for at least a melt. Usually what I do know is between the blanket and crucible I use high-purity alumina hollow spheres. They are rated to 3600F and take the worst of the heat away from the blanket. Neato setup. Should be fine for about everything, but I would not recommend steel over 4kg that way. It's all good. I came to a forum to discuss this kind of thing.
Mooohahhhaha Not a bad way to do things really. I had thought of it, but I just don't like the idea of using a crucible with the hole at the bottom full of molten steel.
I should mention that I wouldn't recommend running more than a 4kg crucible for steel on a 15kw machine anyways. I've done it in a 8kg crucible but it really is a bit of a struggle for that machine. So I was able to just barely melt steel in an 8kg crucible, and not with the flexible cable. After pulling out an 8KG incandescent crucible I decided I would not be doing that again! Had I been content with melting everything else like butter in an 8KG crucible and not insisted on being able to safely pour 8KG or more of steel (eg tilt-able), I would have been content with the machine. But so much happier with the bigger machine. If I had 3-phase I would have got a 65kW machine for about the same price and as much as I love the new one, that does sound dreamy!
Sort of what I figured and a bit on the smallish side for my desires but an electric melting furnace for any metal through iron (or more) is very attractive. An A10 which would be closer to 13kg of iron brim full would be more desirable, at least for me. Was looking at the 20-25kw offerings but single phase choices get slim. Best, Kelly
A 15kw machine could probably just pull off a 10kg crucible for everything except steel and above. It's gonna be a bit slower though. Note that for induction you generally want a cylinder opposed to an A or Bilge since usually the coil is a fixed radius, but A crucibles will work. When I looked anything over 15kw was non-existent for single phase - nice there are some options it sounds like. It literally took me months to find someone willing to swap in a 2-phase transformer. I'm happy to share the vendor if anyone asks, but it is through Alibaba. I would do business with them again.
Hmmm, I'm set up for about 50KVA in my shed so I'd be able to power a 40KW induction furnace. It would be nice to be able to melt an A20 size crucible.
When I was looking I did see some people trying to pass off 20kw models that were actually 15kw models. So I would recommend asking specifically how many amps and volts does the unit require to check if it works out. Lucky! The machines actually use half the power of what they name them (my explanation is in this thread), so you could actually run closer to a 100kw. That said, 40kw should let you use a 20KG crucible, but I would probably get a 50kw or 60kw machine. I've learned that once you get a taste of how amazing it works, you'll want more. Also, more power means more versatile and just easier to melt, well, anything!
