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:
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:
https://www.aliexpress.com/item/100...00023065162260!sea&curPageLogUid=ul3vXpzelE58
https://www.aliexpress.com/item/100...00020179271366!sea&curPageLogUid=YjB6Yj031PF0(interesting video in the product description showing various applications other than melting metals)
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:
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:
https://www.aliexpress.com/item/100...00023065162260!sea&curPageLogUid=ul3vXpzelE58
https://www.aliexpress.com/item/100...00020179271366!sea&curPageLogUid=YjB6Yj031PF0(interesting video in the product description showing various applications other than melting metals)
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