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Induction heater...

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boscoe

Member
So I want an induction heater to braze some aluminium with these 'magic' welding rods I got the other day. Basically the story goes like this. I buy some welding rods that are supposed to weld aluminium at 380 degrees C through a chemical reaction I think raising the temp further to 600 odd where you apply the welding rod. And it works fantastically on small bits of aluminium it's far stronger than the aluminium itself the problem is I want to weld bits of aluminium 10mm thick and 80mm wide up to 100mm long and I under estimated how long it would tak to heat with a blow torch, well in my cold shed it just dosen't get up to 380C. So I was watching some youtube vids and this guy made an induction heater and was near melting steel, I followed a link he provided to build a 2KW one with water-cooling resonant RLC circuits with 400V caps and such but I don't want all that to heat up a little bit of alu. I also saw a little heater pulling 3A at 24V getting steel cherry red so I was thinking could I just make a signal gen at a fair frequency of 50-60KHz run it through an audio amp like the pass labs F5 which has great HF response and capable of driving 1ohm loads at 10A! Then just hook that up to my coil? I should get about 100W or so? Which is all I need. I end up with a coil with a big ass field generated around it at 50KHz why do I need anything else? I only want to pre heat the alu to get the heat inside it then use the torch to do the welding.

So if have got this far thanks for reading and do you think this will work?
 

Sceadwian

Banned
What's powering your torch? I bought a 50 dollar mapp/oxy pencil torch at Home Depot that will hit almost 3,000 C

Not for production work but if that low cost approach helps then you would scale up by going to a moderately priced oxy/acetylene torch from a welding store.

With aluminum though it's not so much the temperature it's the oxygen, Aluminum is an EXTREMELY reactive metal, typically the only way to properly weld it is using an inert gas arc welder.

Typically best results for aluminum are done with TIG welders.

Can you post link to these 'magic' welding rods? There's something going on here that doesn't have anything to do with aluminum welding.
 

dr peppers

New Member
Hmm, I dont wanna be a killjoy but I dont think thats gonna work, induction heaters rely on the heated material being magnetic, ally isnt so probably wouldnt heat up, or maybe just a tiny amount due to the impurities.

I have a chinese wsm200 tig welder that I got off ebay for 150 quid, it will produce pulsed dc and welds ally really well, if your ally is really thin or oxidised or contains impurities then you'll need a true ac tig set which are pricey.

I have a nifty circuit for making an induction heater around 200 watts just using 4 or 5 electronic components, heres the link, part 2 is the one that I tried, part 3 on gets complicated,

https://webpages.charter.net/dawill/tmoranwms/Elec_IndHeat2.html

Using an audio amp isnt a good idea, you need higher frequencies than most amps will produce, and there are some designs that will but most will not work into a low impedance load without going unstable and blowing to bits.
 
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Sceadwian

Banned
You can heat non magnetic metals in an induction heater if the frequency is right, any metal object magnetic or not will have eddy currents flow in the presence of an ac magnetic field. Magnetic objects just heat faster and at a lower frequency because they heat from magnetic hysterisis.
 

dr peppers

New Member
Ok then I'm corrected.

If the object to be heated acted as a shorted turn in a transformer then that makes sense.
 

boscoe

Member
What's powering your torch? I bought a 50 dollar mapp/oxy pencil torch at Home Depot that will hit almost 3,000 C

Not for production work but if that low cost approach helps then you would scale up by going to a moderately priced oxy/acetylene torch from a welding store.

With aluminum though it's not so much the temperature it's the oxygen, Aluminum is an EXTREMELY reactive metal, typically the only way to properly weld it is using an inert gas arc welder.

Typically best results for aluminum are done with TIG welders.

Can you post link to these 'magic' welding rods? There's something going on here that doesn't have anything to do with aluminum welding.

https://www.techno-weld.co.uk/home.html

I using a butane propane mix as you can use 'dirty' flames like oxy-acetylene. I'm not too bothered about buying more equipment as I'm not too bothered, I just suggested this project becuase I have a good 90% of the kit to make it.

Hmm, I dont wanna be a killjoy but I dont think thats gonna work, induction heaters rely on the heated material being magnetic, ally isnt so probably wouldnt heat up, or maybe just a tiny amount due to the impurities.

I have a chinese wsm200 tig welder that I got off ebay for 150 quid, it will produce pulsed dc and welds ally really well, if your ally is really thin or oxidised or contains impurities then you'll need a true ac tig set which are pricey.

I have a nifty circuit for making an induction heater around 200 watts just using 4 or 5 electronic components, heres the link, part 2 is the one that I tried, part 3 on gets complicated,

https://webpages.charter.net/dawill/tmoranwms/Elec_IndHeat2.html

Using an audio amp isnt a good idea, you need higher frequencies than most amps will produce, and there are some designs that will but most will not work into a low impedance load without going unstable and blowing to bits.

Thanks for the link will be having a read through that. The Pass Labs F5 audio amplifier is good up to 1MHz I think and 10A into a 1ohm load is possible.
 

Sceadwian

Banned
I using a butane propane mix as you can use 'dirty' flames like oxy-acetylene. I'm not too bothered about buying more equipment as I'm not too bothered, I just suggested this project becuase I have a good 90% of the kit to make it.
Acetylene when mixed with oxygen burns clean, what you're refering to as 'dirty' is the acetylne burning in ambient air, not enough oxygen.

No straight fuel mixture will give you good results with ambient air you have to use pure oxygen with the fuel. Oxy/anything will work okay for many things, aluminum is not one of them, even trace oxygen makes the metal useless, it has to be done in an inert gas envelope

I read the link you posted, that's nothing more than aluminum brazing, it's not welding at all.

The only way to truly weld aluminum is to use a MIG/TIG
 
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dr peppers

New Member
A true ac tig can be adjusted to produce a uneven waveform, when the welding current polarity is reversed this has the effect of cleaning the weld area (junk tends to get pulled to the cathode from memory, maybe its the anode), professional rigs I've repaired have a 'clean' adjustment on them.

Miging ally is a professionals task, its well hard to do and tends to only work well on pure ally (and you need a spool gun to prevent birds nests), tig is the more common method, tig is also good on thin steel or where you want really good control of where you want the weld.
 
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tcmtech

Banned
Most Helpful Member
You are confusing heat temperature with quantity of energy being transfered or produced.

How hot something is is not the same as how much energy it is holding.

If your large pieces of aluminum have 100 times the mass of the small ones they will need 100 times as much thermal energy put into them to get to the same temperature.
 

dr peppers

New Member
Thats sort of what I was thinking, I just made a mess of explaining it.

I found tig not to warp plate steel as much as you can heat a localised area without heating up half the plate causing it to bananna.
 
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