Induction Heating | Practical Machinist

Actually, while it used to be that the cheapest induction heating units started at over 20 grand, this is no longer true.
My friend Grant Sarver, who is an industrial blacksmith and manufacturer, has started importing an inverter induction heating unit, about the size of a small inverter tig welder, that is quite controllable, and usable for heat treating, forging, and so on.

While not cheap, at about $, it is an order of magnitude cheaper than the older models that used to be all that were available.
He has a Boeing Surplus Unit, for instance, that he paid something like $700 for, that Boeing paid well over $50,000 for when new.
So his new imports are quite a bargain.

I know several blacksmiths and knifemakers here in the Northwest who have bought them, and they are quite happy with them. I am saving up for one myself, as for certain production forging jobs, they are really sweet- 1" square to yellow heat in a few seconds, with localised heat that is very controllable.

They are mostly using them to get metal to forging temps, rather than precise heat treating, but the machine is controllable enough that it should be possible to heat treat with it.
For some alloys, you might need to make an inert atmospheric chamber for it- not exactly cheap, but again not insurmountable.
I know another guy, who makes mokeme-gane, which is a technique of laminating dissimilar metals, and he has an electric furnace that uses argon to replace the oxygen, and it is not terribly complicated or expensive.

Here is a link to Grant's induction heaters- they draw about 50 amps, similar to a Miller inverter welder.

http://www.blacksmithsdepot.com/Templates/cart_templates/cart-detail.php?theLocation=/Resources/Products/Forges_and_Parts/OC_Induction_Forge/OC_Induction_Forge_Basic_Kit&where=&PHP SESSID=de26ce9aa9d4da568d4b8bbe Grant just uses a $500 tig torch radiator- it plugs right in 110, is small and pretty quiet, and parts are available at any welding supply store. Since the technology is all worked out, to function in dirty fab shop situations, they are pretty bulletproof, and no fussy plumbing.

I am not sure about the magnetisation question- kaynes (thats the blacksmithing depot link I posted), and ask em.
My guess is that since you are generally heating it above magnetic, to cherry red or hotter, it wouldnt be a problem, but I dont know for sure.

The great thing about Grant's unit is that it is designed for a small shop- its easy to change the timing, the amps, and so on. A lot of the old huge industrial units are much more single purpose.

I have seen him demo it, and its truly amazing- 1/2" square to cherry red is just a few seconds. 3/4" square to a sparkling, yellow forge welding heat in 45 seconds or so.
He has his hooked up to a foot pedal to initiate the cycle, so you insert the work piece in the coil, hit the pedal, and the preprogrammed cycle brings it up to the heat you want, then shuts off. Pull it out, and do whatever you need to it- Grant is using it in production forging to make things like blacksmith tongs- he has made 30,000 pairs in the last ten years or so.
Repeat as needed.

He custom winds new coils from 1/4" copper tube, around pieces of scrap pipe or steel, by hand, in a few minutes, brazes on fittings, and goes to town. Here's Wikiopedia's description on how they work. http://en.wikipedia.org/wiki/Induction_furnace What I personally still don't understand is how they are still cheaper to run then then a fuel fired furnace. Even if you can get the whole electric system to be rather efficient you still need to buy the electricity. The electricity is almost always produced in the power plant, that tends to be burning fossil fuel, or is at least selling power at rates competitive with those burning fossil fuel. That said due to the way thermodynamics work out, the fossil fired power plants tend to be often no greater than 40% as they put out a lot of waste heat. Then there are efficiency losses all the way down the line till that electricity enters your machine. On the other hand if you locally burn the fossil fuel at your plant you get far greater efficiency. Indeed it seems virtually every other industrial heating application is done by fuel and not electricity. Thus I have always wondered why it is so common, unless it is just so much easier to control the heat. Does anyone know the efficiencies of a fuel fired furnace?

Adam I dont have much experience with heat treating- but for forging, the reason people like these machines instead of propane forges are several.

Are they cheaper? Well, it depends how much work you are doing. When I fire up my propane forge, which is a bit bigger, and more sophisticated than the one Forrest linked to, it takes about 10 minutes to get up to heat. Then, depending on the size of the piece of metal I am heating, it might be as short as two or three minutes, or it might be as long as ten, before I can forge the piece. So my forge is running for a long time, heating up the whole shop, burning propane and making noise, for a little bit of heating. In many blacksmiths shops, these forges run 8 hours a day. Its much easier to just leave em on, and pay the gas bill, then to wait for heatup every time.

Meanwhile, the inverter powered induction heater is quick, and is only on when its actually heating the piece. If I am running 3/4" round stainless bars, which I often do, the inverter might be consuming electricity 1/10 of the time the forge would be running, or even less. So on a strict amount of heat per minute basis, the propane forge might be cheaper- but as actually used, it usually comes out to be more expensive, plus the constant heat and noise tends to wear you down.

The inverter is quiet and elegant, and applies just enough power to do the job, exactly for the amount of seconds needed.

The other thing is that when using a gas forge to heat metal, you get a lot of heat where you dont want it- the whole bar gets hot. With the induction heater, it can be yellow hot for 3", and then a foot away, cool enough to pickup without gloves on.

When heating a building, there isnt really "waste" heat- its all going to the building. When heating a 2" long piece of steel, you want the heat exactly where you want it, and nowhere else.
So these things may not be cheaper- but they are so much more controllable and elegant that everybody I know who has used one wants one.

Induction brazing has been an idea that has been kicking around in my head for the past few months.

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What is induction brazing?

The metal parts to be brazed are placed in the induction coil, and an alternating current is passed through the coil. This creates an oscillating magnetic field within the coil, which generates eddy currents in the metal parts. These eddy currents heat up the joints which melts the brazing alloy.

Potential benefits

• faster
• safer
• less heat on the tube
• precision heating
  • you could program the heating sequence (time and temperature profile)
• cheaper (?)
  • oxy-acetylene setup is ~$400 + gas refills + upkeep
• environmentally friendly (?)

Vision:

• Induction coil heats up a braze-on in seconds
• heat is controlled by a programmable sequence
  • pre heat > melt > post heat
• heat two bosses at once
• parts rest in a fixture
• a silver-braze washer applies the exact amount of solder
• flip a switch, done!
• Cost <$200

Some rough research:

• given that the copper is radiating bright orange, those pipes must be getting up to c
• Silver braze melts at ~650c
• people in the makerworld successfully make their own:
  • How to make Mini Induction Heater - Hackster.io
  • https://www.instructables.com/DIY-Powerful-Induction-Heater/
  • Building a 3kW Induction Heater ll Complete Build Guide - YouTube
  • DIY induction heater that can BOIL STEEL - YouTube
• There is a range of off-the-shelf products from $30 sketchy DIY units to $10k industrial units
  

Risks/unknowns:

• is the heating too localized?
• does quick heating effect the mechanical properties of steel?
• compatibility with stainless steel?

Questions:

• Would this be a useful tool?
• Does anyone know if this has been done before in framebuilding?
• Does anyone have any experience with induction brazing?

I am not an expert in electrical engineering (especially AC circuits) nor brazing. I would love to get some feedback from the community before I put my time and money (and test my landlord’s risk tolerance) on the line!

Super cool thought! The ideal would be to get some sort of closed-loop control working, probably easiest with a non-contact thermometer of some kind. You could probably get an off-the-shelf soldering oven reflow controller to do a basic PID loop for temp control.

imo even if it took a while, the ability to “set and forget” would be useful for doing other tasks while waiting for it to complete.

Great suggestion. This guy on youtube purged with CO2:

I wonder if you could create a little argon dam to eliminate the need for flux and cleanup:

I’m not sure how much argon you would need, and how the price of argon compares with the time cost of fluxing and cleaning. Maybe purging the tube itself is enough?

Additional resources:
NPK-12-11-18 Water Soluble Mixture Fertilizer
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Good idea. What do we name it? Braze-o-matic? Brazebot?

All the top tube to seat tube connections on Chicago made Schwinn varsitys were induction brazed on a asse3mbly line. There was a preform of silver dropped in.
I’ve messed around with induction heating for forged parts, and cyclefab here in seattle uses it for a special propane heating attachment they make for an industrial customer.
It would be super fast and clean, but the coil shape is specific to the part you are heating. This is because the magnetic field strength is:

6.1.1 Magnetic field strength, magnetic induction and flux

The magnetic field strength H , generated by a flow of charged particles, is defined according to

(6.1)I=∮CH⋅dl

where I is the current passing through a closed contour C (Fig. 6.1A). The quantities H (A/m) and d l (m) are vectors. For each configuration of conductors carrying an electric current the field strength in any point of the surrounding space can be calculated by solving the integral equation (6.1). A current I through a long, straight wire produces a magnetic field with strength H = I /2 πr at a distance r from the wire. So the field strength is inversely proportional to the distance from the wire.
TL:DR
the coils need to shaped to the part and very close.
I think it would be awesome for fork crowns or bottom bracket shells were they have a lot of mass and are slow to heat up.
For H2O bosses, I can put them on as fast as needed with the gasfluxer and no paste flux.
Hahn Rossman

Thanks @Bucko, that is a great resource. It looks like they are using of those industrial units to great success. I bet that would have more than enough power to braze a BB joint. Once I educate myself more and do some experiments, ill try reaching out to them for their expertise!

Update to this thread: I went ahead and ordered this guy from amazon: link

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