induction hardening how does it work

M

M Wadel

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Sep 11, 2005
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well does anybody know? are there any benefits for knives using these kind of machines? are these machines large and/or expensive? is it possible to build these machines by yourself like a furnace?
 
I have been reading up on induction heaters. I have a friend that is a machinist for Boeing and he uses several for tool and die making. From what I have read it would be a great high tech forge, fast heat, consistant and no propane to run out. The down side is the expense. He uses induction heaters to heat treat tools and says they work great. A 3/4" dia. mill bit goes from room temp to orange in less then 15 seconds. Your arm would never get a break if you used one for forging.

PS: I am new to these forums but some of you know me from the other forums. It is always great to chat with as many bladesmiths as possible.
 
Certainly to buy an induction heater would be expensive and of course it takes lots of electric power to run.There really isn't any benefit for knives.
 
interesting 15 seconds heheh well thats fast.

how many kilowatts does an inductionhardening machine consume? im reading up right now on inductionheting, if i got it all right its a basicly an electromagnet of some sort (well it could be way more advanced than that i suppose). so this is combinations of large coppercoils and iron cores or??
 
There is a copper coil which surrounds the core which is what you're heating .I've made steel with induction heating .The alternating current through the coil excites the atoms and heats the metal.Basic adjustments are power and frequency.
 
Induction heating, as far as I know doesn't use 60HZ power to operate, well at least not on tool steel. I can't quote you the correct frequency but I believe it is in the KHZ range. This requires a frequency generator and amplifier with enough power to heat the metal. There is generally cooling fluid of some variety flowing through the induction coil to keep it from getting to hot. This adds one more layer of technology to the mix.

Jim A.
 
They use microwave frequencies (Ghz) and the copper coil has water pumped through it for cooling. The newer solid state units are more efficient then the older tube units. However you can buy the tube units fairly cheap now. Some of the smaller ones run on 110vt 60Hz. There are cook stoves now that use induction heating that are pretty neat.
 
Davies and Simpson's Induction Heating Handbook (McGraw Hill, ISDN 07 084515 8) goes into a lot of detail on how induction heaters work and how to tweak them for specific applications.

I've been plunking away at one as a "back burner" project for over a year now. I just blew up some mosfets yesterday, in fact. It's not as easy as a charcoal forge, but I believe it is do-able.

An induction heater is a transformer. The workpiece is the transformer secondary. It's a shorted secondary. Lots of current flows and the workpiece gets hot fast.

Frequency needs to be inversely proportional to the square root of thickness. For knives, you need a minimum of 1 to 3 MHz. Not easy, but do-able. You also need a good "power density." That means you need lots of kilowatts per unit area. You can reliably get about 1.5 or 2 kilowatts out of an American wall outlet, so treating small areas of the blade at a time is more feasable than trying to zap the whole blade at once.

I'll try to keep folk posted on how things go once I've replaced my mosfets.:o

Some good websites on the subject:

HWG Inductoheat

LectroTherm

and ASTM

I've made steel with induction heating
Click to expand...
Hey Mete... a littel birdie told me you melted the HEATER before you melted the STEEL!:D
 
It actually worked very well. This of course was a big commercial unit , not homemade. The only excitement was when some insulation broke down and created a very large arc which lite up the whole place !!!
 
Induction heating is really neat to watch. I had a small unit that would bring 30 lb of steel to 3000f in 6 min. The water cooled coil ran at 1300 volts DC at 3000 HZ. Biggest problem with fast machines is the power requirements. Mine used 126 amps of 480 3 phase and mine was one of the smallest machines then available. Not something a knife maker would use but it was sure fun to run.:D
 
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