View Full Version : INDUCTION HEATING from a welder?

12-30-2010, 10:41 AM

anyone into it? try it? used it?

i spent 3 years making carbide tools, got quite good with them. coils, jigs, getting zapped...amazing what 15 Kw will do to 1" bar! only an oxy cutter is more impressive!

so, im reading here and there, and seeing a method for hardening crankshafts etc, was to heat with a flame to red as you lower into oil water whaterver to quench it...fairly standard procedure. and i couldnt help but wonder if anyone has tried with induction? at home?

im thinking just a simple cheap stick, 110 amp, rectified to DC, then chopped via FET or whatever into a high frequency, 10 KHz or so... water coolings fairly easy... neat plumbing please! and heating coils are eassssy to make...

ill have to brush up on it, cant recall if current or voltage was more important. i know the old units used to use in excess of 1000volts.... a stick welder usually only does 50 or so...

:wee: my project then? :wee:

it would be ever so handy for some jobs.... like soldering and brazing and even sometimes welding...shrink fitting, case hardening...


and yeah...still trying to decide where this thread really belongs....

12-30-2010, 12:28 PM
Induction heating is one of those technologies that are quite simple in the basics, but in practice not so easy to implement.

I have a 100 kw induction furnace, and making coils to get an accurate match can be quite hit and miss. More of an art than a science. Dead easy to get a poor match with little energy transfer. My system 'rings' the coils to measure their frequency of resonance, then sets itself to oscillate at that frequency. Simple enough, except that the charge alters the frequency, so really it needs to constantly adjust as more is added to the crucible.

Mine works at about 3Khz and circulates a scary number of amps (thousands) though 3/4" copper pipe coils with glycol solution pumped though for cooling. I use a 15Kw chiller to cool the glycol.

There is a yahoo group discussing induction heating called Electro_cast

Electro_cast : Messages : 549-578 of 578 (http://groups.yahoo.com/group/Electro_cast/messages)

12-30-2010, 06:54 PM
thanks for the link, some chasing there...

100 kw is freakin huge! would have required its own mains supply and some bickering with the power company as to whether they had the capacity or not...

im all too familiar with the "easy basics, hard implementation"

unfortunately due more to peoples stupidity, ignorance and plain stubborness.

the unit i used, i was basically given charge of was 15kw, brand spanking new. i read the manual. noted things such as MIN water temp and MAX water temp. MIN/ MAX water PRESSURE.

so what did we have?

a $50 grand unit. a $25 grand chiller. and then the old guy was given the task of sourcing a pump. not me. the old guy. his attitude was "read the book when it breaks"

he returns with a plastic pond pump with roughly a metre of head.

cough cough ahem, i raise a stink, ignored, forced to set it up anyway. (and what the ^%$$ do we need distilled water in it? just use the tap!)

this continued for 3 more pumps, as i was ignored again and again... too small, cast iron, you name it... and forking out 3 grand each time to fly the technician in to "commision" the unit...

they then went and forked out on a grundfos(?) for one of the mills.... and luckily, used the old pump on the inductor. stainless. 250 kpa or summink... i was also allowed to throw out the 1/2 pipe and plumb up with 50MM hi pressure PVC.... instead of using 3 reducers on each junction...

AT LAST! i could use pipe under 1/4 inch for the coils!

then there was, yes...matching coils.

the simplest analogy ive thought of for the dummies is;
you have two cups.
the machine is one, the work is the other.
your pouring water(energy)from one to the other.
you want both cups to be of equal size. otherwise the water that overflows is just being wasted... you either have to remove it or replace it.

and yep, dont bother calculating anything! the machine having "auto-tuning" and "coil taps" does the main work for you... most of our stuff was fairly basic, and small. like 1/2" bar type things. then the larger items, 6*18*12"slabs of steel, brazing diamonds to one edge. this took slightly more work to make, a lot of time to heat, and required setting the tap switch to different positions as the job heated up... the problem with it being so "artsy", you cant easily explain why youre doing it.

ok, as the steel heats up its permeability is reduced, reducing the induction/impedance of the coil, which then alters the frequency of the tank circuit that requires the changing of the tap to re-match the impedances. then when it reaches the curie point, all hell breaks loose and it may as well be aluminium in there...

yes, peoples eyes glaze... whats impedance? reactance? if you aint got a background in it, go read and leave me alone to do my job!

what did get me was you could make two seemingly identical coils. one would work fine, one wouldnt. just trip a fault. which seemed to require setting a jumper on the control panel to reverse the phase.

then trying to make a tiny 3 turn pancake coil from 3/32 pipe... ran into pressure issues again.... multi million dollar job and theres no investment on the brazing side of it...which was meant to be our side of it.

i then got sick of the old guy and quit.

was then asked to come back for a day to braze up some more of the diamond slabs. with a torch. cus the old guy had blown up the inductor...

i do miss using it as a rail gun occasionally :p

alright, sorry, this is more of a whinge than anything now...

best to get off me butt and have a go than sit here typing and..wondering :p

12-30-2010, 07:21 PM
Have you seen this thread? All fifteen pages dedicated to building an induction furnace and probably one of the longest running, intermittently active threads on the Zone.


12-30-2010, 07:33 PM
i did a search before i wrote this thread.... so obviously i havent seen that thread! grrrr!

thanks :)

12-30-2010, 09:09 PM
......100 kw is freakin huge! would have required its own mains supply and some bickering with the power company as to whether they had the capacity or not...

Back in 1969 I ran one this size in a research center near Montreal, Canada. Long before solid state electronic stuff it had a hulking great motor/high frequency generator unit and a cabinet full of big capacitors that were switched in and out to keep the power factor acceptable. The thing could melt 500 lbs of pure copper in minutes plus the field leakage brought the steel mezzanine floor it was installed on up to a very high temperature around the crucible. Not to mention cooking the wire reinforced hydraulic lines for the crucible tipping system. That was fun, a rain of hot oil from a burst hose landing on a crucible full of molten copper.

I only worked there six months, I valued my health too much to stay longer.