Induction furnances from Aliexpress/China

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orvi

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Due to some requests about what to look for and what precisely was my experience with these, I will post some info + links here.
These machines are sold from various vendors on Aliexpress, originate in China, and I am quite pleased with their performance vs. price ratio.
We are talking about these:
1674589536155.png 1674589662830.png
There is plethora of variations in specs, but casings are looking the same, typology also, electronics inside are very similar and these are probably manufactured in some larger factory, and then redistributed to all different vendors. Most "pronounced" is VEVOR.

From this "series" 15 to 25kW rated are single box machines, from 30kW and higher, main transformer is separated from the "motherbox", as it would become extremely heavy and impractical. This is great, great advantage, as you can separate these two parts and better protect the main unit from heat damage and accidental spills/spattering of molten things.
I have personal experience with 15kW and 35kW machine. All in all, for what you pay, it serves you very well. At least, in my case. Some people who also posses these mainly didn´t happen to have issues with them.

As with all Chinese products, once it is "rated" for 15kW, it means that at 15kW it can easily go south in few dozen minutes. From personal experience, most of the time, "rated" values in Chinese terms are something we know as "absolute maximum ratings" :) Apart from that, there isn´t that much to be espetially aware of, just general things.

These furnances are produced primarily as heaters for various metal parts - fitting ball bearings, O-rings, soldering pipes to the coolers, bending steel bars etc... So it comes with some interesting timing features, which are unfortunately of no great value for just melting stuff :)

It has it´s own breaker in the back, main ON/OFF switch, then green/red button for start/stop current flow through the coil, and left knob for adjusting the power of the machine, which is displayed on the display in the front panel. Usually, machine comes with pre-made coil. But with some skills, you would be able to bend your own coil from appropriate sized copper pipe, hammering the both ends to enlarge their circumference and after purchasing few rubber O-rings and proper nuts, you can create variety of heating coils for different crucibles and chores.

Machine has built-in flow meter, which will start beeping, if flow of cooling water through the machine stops. This is best checked before doing anything, just to be sure it is working - ensuring your safety.

It is advisable to attach amp-meter or watt-meter to the input power line to monitor the real current used - as machine cannot detect "true load". As various objects (small/large, graphite/copper/gold/silver/iron etc...) have different electromagnetic properties, they will take various ammount of electromagnetic flux. So, small crucible in big coil will take only low flux, heating very slowly. If you use correct size of the coil, which match the diameter of crucible, you can transfer the flux of energy much more efficiently, heating small size crucible to bright orange heat in several seconds. That is why the amp-meter is handy to measure approximately how much power is going to the thing you are heating.

They call them high frequency machines, but truth is, melting metal powders is cumbersome, and you need some sort of solid metal plug/heel to begin the melt with (if you are using ceramic/clay/silica/magnesia crucibles). With graphite, you conveniently heat the crucible first, then metal start to melt, it itself catch induction and speed up the rest of the melt as you add more powder. And this is extremely convenient - as whole melts of kilos of like silver take 10-30 minutes, depending on what power you can deliver to the crucible. Induction also somewhat stir the metal melt, altough I advise also to mix with graphite rod as well.

Once you upgrade from propane or nat. gas to induction, rarely you want to go back to the gas :) There is significant overlap between use of oxy/fuel torch and small scale induction melting, but once you pass certain ammount of material, induction wins most of the times. Electric furnances has it´s own advantages (like precisely monitored temperature - perfect for cupelling), but they are slow to heat and transfer of heat is indirect.

Pros:
-good price vs. performance ratio
-nice features
-does the job
-not one specific chore only - you can adjust it for many applications, metalworking, tempering or annealing steel, soldering pipes, even use it as heater for evaporations where you throw piece of graphite into the big beaker and place it on top of the coil (dangerous, but very effective) etc.
-speed up the processes
-shorter heating period and good insulation prolong the life of graphite crucibles due to minimized burning
-basically allow efficient use of graphite crucibles, opposed to gas furnances

Cons:
-VEVOR add to their products one year guarantee, but if something broke inside or you fry it, you will probably never get refunded or given help, and resorted to repair on yor own
-it is somehow underrated speaking of main power transformer, and some types can lack overheating shut-down (speaking of transformer, mainboard has it´s own overheating shutdown circuits). It does not literally burn, but somehow sometimes manage to crack the ferrite core (if you go very high power for long time, many times in row without proper time to cool) and render machine practically useless, if you aren´t able to dismantle it, glue it together and reassemble.
-15-25kW machines are powered by single phase 220V (or 110V) mainly. So in order to squeeze good power from it, you will need quite high power socket in your house/place to plug it in. Otherwise it will shut your breaker all the time. 35kW and more are usually 3-phase, so most of the times no issue there.
-15kW type machines has connections for the coil leading directly from the fron panel. This is somewhat not the best design, regarding that in front of main electronics and knobs, you have your bubbling 1300°C crucible :) I advise to DIY some reflective sheet metal cover, which will prevent excessive heating of the main panel from radiating heat.

Price tag for 15kW machines is currently around 800euros, with some deals maybe slightly lower. 30-35kW types go higher, at 2500-3000eur. If you are going full on refining, this is piece of machinery that you will find extremely helpful. It will quickly pay for itself.

So this is my experience, and experiences may vary from user to user.

Some links below:

(interesting video in the product description showing various applications other than melting metals)
 
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Gwar

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Great thread ! I have always wanted to try one of these out with a vacuum of sorts to see if it would be possible to produce silver bars of a better looking quality, using crystals or fine shot, the hold back is that as stated, if something goes wrong, one is down and out with little or no recourse.. G
 

orvi

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Great thread ! I have always wanted to try one of these out with a vacuum of sorts to see if it would be possible to produce silver bars of a better looking quality, using crystals or fine shot, the hold back is that as stated, if something goes wrong, one is down and out with little or no recourse.. G
I think you would be able to somehow DIY vacuum melting attachment to this low-tech furnance, but I am not sure if I would dive into it. This can be very dangerous if not done properly.

Altough, 800euros/USD is not "unaffordable" pricing, making some room for another expenses. I cannot give opinions on vacuum furnances used for casting, as I only saw one in person in my life. Never touched this thing, neither worked with it. But for sure, it must be cool :)

With pure silver, you may be able to melt pure silver crystals/shot inside one of the graphite molds with lid. You can also make flat coil (shaped like old electric stove heating elements), cover with one layer of mineral wool, then place "loaded" graphite mold, insulate well with mineral wool and crank it up :)

Graphite burns, as any sort of carbon... So mold won´t hold forever - but it will mostly burn on the outside.
I can see this very real to be perfected - of course, without vacuum. As silver is melted inside closed graphite mold, not that much oxygen survive inside, so sprouting would be minimal, if any.
 

snoman701

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I've got a "15 kw". Mind you at 240 volts on a 30 amp breaker, my calculations P = I * V say that that is only 7.5 kw in, but it works.

I have a coil that I wrapped. I get decent coupling on a "silicon carbide" crucible from amazon, and can melt about 10 oz of pure gold as long as I put a cover on it. A pound of silver is very doable.

I can't get it to couple with a standard graphite crucible of the same size as the silicon carbide.

For large steel, I have to start out by coupling a small piece, then get it hot past it's magnetic point, and slowly introduce the steel into the coil.

For the price point, it works. It makes money. The day it stops working, it stops working.
 

stoneware

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I've had my dual station induction furnace for 8 years, then last year it quit working.

The circuit board with the 7 caps one of the soldered tabs let go taking the copper with it. Easy repair, but decided to contact the vendor.

The new circuit board $55.00 US, a revised version has a much better design than the older one. Not yet installed.

Top image is of the slave, coils are liquid cooled.

I beleive the 15kw furnace is the largest avaialable in single phase any above would be 3 phase.

1.jpg

2.jpg

3.jpg

4.jpg
 
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stoneware

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If you have the single station furnace and want to give the crucible some distance, flexible cooling lines.

These electrically conductive lines are what they use for the tilting crucible or when using a wand.

line.png
 

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orvi

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I've got a "15 kw". Mind you at 240 volts on a 30 amp breaker, my calculations P = I * V say that that is only 7.5 kw in, but it works.

I have a coil that I wrapped. I get decent coupling on a "silicon carbide" crucible from amazon, and can melt about 10 oz of pure gold as long as I put a cover on it. A pound of silver is very doable.

I can't get it to couple with a standard graphite crucible of the same size as the silicon carbide.

For large steel, I have to start out by coupling a small piece, then get it hot past it's magnetic point, and slowly introduce the steel into the coil.

For the price point, it works. It makes money. The day it stops working, it stops working.
Yeah, that is true - this one goes to around 7-9kW, depending on type of material being heated.
I never had a problem catching induction to various types of graphite, even graphite rod catch induction inside the crucible. Good to know this can happen with cheap stuff... Maybe some altered frequency of the machine rendering graphite invisible for the induction.
 

snoman701

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It's not invisible, small pieces of graphite definitely work....the crucible is just too big for the coil. If the coil was bigger, it would max out the current. It does the same thing as a big chunk of steel. I tried to heat it in stages, but couldn't feed the crucible into the coil slow enough...and it just wasn't realistic.

So this works for heating small amounts quickly. Beyond that, not so much.

I'd really like something with a bigger crucible. While it will heat 10 oz of gold reasonably well, it won't do 10 oz of sponge. You simply can't pack the sponge tightly enough into the crucible.
 

Yggdrasil

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It's not invisible, small pieces of graphite definitely work....the crucible is just too big for the coil. If the coil was bigger, it would max out the current. It does the same thing as a big chunk of steel. I tried to heat it in stages, but couldn't feed the crucible into the coil slow enough...and it just wasn't realistic.

So this works for heating small amounts quickly. Beyond that, not so much.

I'd really like something with a bigger crucible. While it will heat 10 oz of gold reasonably well, it won't do 10 oz of sponge. You simply can't pack the sponge tightly enough into the crucible.
It is game between frequencies, size and current.
The smaller the piece the higher frequency is required to create the eddy current inside the pieces. This can be overcome by using a heel or compressing the powder so much that it conducts between themselfes and thus appear as a larger chunk.
The current creates the magnetic field which induces the eddy current inside each piece. The stronger the field the higher eddy current.

The design of the machine dictates the amount of impedance/length the coil can have.
The “normal” 100kHz 15KW machine has a limit of 1,5meter for the coil.
At least mine have.

There are massive amounts of reading material regarding coil designs out there.

Edit spelling
 

orvi

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It's not invisible, small pieces of graphite definitely work....the crucible is just too big for the coil. If the coil was bigger, it would max out the current. It does the same thing as a big chunk of steel. I tried to heat it in stages, but couldn't feed the crucible into the coil slow enough...and it just wasn't realistic.

So this works for heating small amounts quickly. Beyond that, not so much.

I'd really like something with a bigger crucible. While it will heat 10 oz of gold reasonably well, it won't do 10 oz of sponge. You simply can't pack the sponge tightly enough into the crucible.
I can relate to the "tuning" issue - when you need to squeeze the best of the machine. That is why we have like one full box of different coils (DIY of course), mainly different diameter coils, then flat coil for heating beakers and silica dishes with different stuff/cupellation on magnesia boat/hollowed magnesia brick/portland cement etc...

Most of the times, we have one "general" coil of larger diameter to fit most of smaller and also medium sized crucibles. But when you need to do bigger jobs, or adjust for crucible when speed and efficiency is needed (quick bulk sample processing), we switch to the best matching coil. As we bore some specific diameter crucibles from graphite, we have it all nicely standardized and flexible. 3-4 minutes and coil is switched. Not much of an issue :)

Making some new DIY shaped coils is relatively easy, and with appropriate nuts, steel pin to enlarge the inner diameter, few O-rings, hammer, pliers and vice you can get it done relatively easily. Then check for the tightness of the seal, and you are good to go. There are some limitations regarding length of the coil - as Yggdrasil pointed out. Usually, quite OK manual comes with the machine (mine is in english, they improve slowly, not only chinese :D ), also with some tips to ease the work and how to tune it.
 

billgold

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I think you would be able to somehow DIY vacuum melting attachment to this low-tech furnance, but I am not sure if I would dive into it. This can be very dangerous if not done properly.

Altough, 800euros/USD is not "unaffordable" pricing, making some room for another expenses. I cannot give opinions on vacuum furnances used for casting, as I only saw one in person in my life. Never touched this thing, neither worked with it. But for sure, it must be cool :)

With pure silver, you may be able to melt pure silver crystals/shot inside one of the graphite molds with lid. You can also make flat coil (shaped like old electric stove heating elements), cover with one layer of mineral wool, then place "loaded" graphite mold, insulate well with mineral wool and crank it up :)

Graphite burns, as any sort of carbon... So mold won´t hold forever - but it will mostly burn on the outside.
I can see this very real to be perfected - of course, without vacuum. As silver is melted inside closed graphite mold, not that much oxygen survive inside, so sprouting would be minimal, if any.
Rather than a vacuum furnace, unless you wanted the degassing capability that would provide, you could create a fairly airtight box and feed nitrogen gas from a tank to purge out oxygen and other gases. Or even better would be helium.
 

billgold

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It's not invisible, small pieces of graphite definitely work....the crucible is just too big for the coil. If the coil was bigger, it would max out the current. It does the same thing as a big chunk of steel. I tried to heat it in stages, but couldn't feed the crucible into the coil slow enough...and it just wasn't realistic.

So this works for heating small amounts quickly. Beyond that, not so much.

I'd really like something with a bigger crucible. While it will heat 10 oz of gold reasonably well, it won't do 10 oz of sponge. You simply can't pack the sponge tightly enough into the crucible.
Can you just start with the power turned down and then crank it up slowly?
 

FrugalRefiner

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Rather than a vacuum furnace, unless you wanted the degassing capability that would provide, you could create a fairly airtight box and feed nitrogen gas from a tank to purge out oxygen and other gases. Or even better would be helium.
Considering the shortage of helium, I think that would be a terrible waste. I believe argon or CO2 would probably be better choices.

Dave
 
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