Induction Heating (for heat treating small pieces) ?

[Bart Slarty]

This just popped into my head. I was remembering segments of the TV show 'How It's Made', where they used electrical heating coils to quickly heat parts for the quenching stage. This approach appeals to me because of the speed, which would hopefully minimize oxidation (of 4130, which I am not using with tool wrap).

I know absolutely nothing about such devices/systems, or where to look, so I'm hoping I can get a nudge or two in the right direction from this forum. Most of the pieces I cook are 6" x 4" or less, and I would be happy with that size capacity, or even smaller.

TIA,
Dar

 

[Ries]

they are, like everything else, on ebay. Blacksmiths have been using them a lot lately, for heating pieces to forge, but also for heat treating. amperage and time of heat is adjustable, so you can get pretty precise with practice. Here is one, but there are lots. A grand to fifteen hundred from China. Old school american industrial ones exist, $40,000 and up new.

High Frequency Induction Heater 15 KW Welding Furnace 30-100 KHz 220V 2200 â | eBay

1 x 15 KW High Frequency Induction Heater Furnace. Welding and Polishing Machine. High frequency induction heater furnace. 15KW High Frequency Induction Heater Furnace 30-100KHz Heating Tool Stable 110V.

www.ebay.com

 

[Hightemp]

A couple of things:

• The great part about induction heating is that you can tune it to just heat the surface if you want
• You'll need a special coil for most parts to get the correct heating profile
• You can't just set a temperature - you'll have to verify using a different technique

In general, probably not great for your use case.

 

[john.k]

I bought an induction heating plant from the Telephone company.......must have taken up 500sq ft of floorspace ,and it had glass thermionic valves in it.......Also bought one from Crane Copper ....it could melt 5 ton of brass ,the HF power was transmitted thru copper water pipes with water flowing inside .....and there was 50 lbs of big silver contacts in the lekky system,before you even started on the copper.

 

[chipss]

I designed and sold induction equipment for years. Things to consider based on a couple points raised here:
Induction due to cost is a production tool.
It uses a lot of electrical power unless you are using small 1000-2000 watt units.

The output frequency of the machine determines how deep into the metal the heating effect is. RF radio frequency say 400 kHz penetrates steel only .035 deep. The rest of the heating to the core is just soak time. A lower frequency machine say 10 kHz output heats steel .100 deep.

Power density and you do the math:
For case hardening you need around 15kW per square inch. In other words, heat the skin fast to 1550-1650F then quench it. Using 400 kHz you'll have a nice .040 deep case. 10 kHz you'll have a nice .100 deep case with a soft core.

For mass heating you need lower power density say 3-8 kW per square inch to allow soak time. This for thru hardening, forging, brazing etc.

The little 1-2 kW units on ebay are cheap and fun to play with but practicality is limited.

Ask away and I'll pitch in with answers.

 

[Hightemp]

they are, like everything else, on ebay. Blacksmiths have been using them a lot lately, for heating pieces to forge, but also for heat treating. amperage and time of heat is adjustable, so you can get pretty precise with practice. Here is one, but there are lots. A grand to fifteen hundred from China. Old school american industrial ones exist, $40,000 and up new.

High Frequency Induction Heater 15 KW Welding Furnace 30-100 KHz 220V 2200 â | eBay

1 x 15 KW High Frequency Induction Heater Furnace. Welding and Polishing Machine. High frequency induction heater furnace. 15KW High Frequency Induction Heater Furnace 30-100KHz Heating Tool Stable 110V.

www.ebay.com

Ries, we bought one of these a couple of years ago to try out for some experimentation (didn't want to spend 5 figures since it was a proof-of-concept). I'm not an electrician nor electrical engineer, but someone who is took a look at it before we set it up and basically said it looked like a death trap. We returned it and found a used system on ebay which he was comfortable with. I don't remember the specific concerns.

 

[chipss]

The ebay units from Wuhania do work. But,, they often have a limited tuning range based on the output transformer ratios and the tank circuit capacitors. Therefore you have to be good at calculating inductance and then making a coil to suit the application. Or trial and error at making coils and watch the metering so you don't blow it up. Coils are relatively cheap to make for these little machines as they're just water cooled copper tubing. The real problem is when the machine soon goes tits up there is no service or parts availability. So unless you're good at board level diagnosis and repairs you're just staring at a dead box of sparky things.

Oyeah water cooling...
You need a recirculating water cooling pump station. Distilled water only going through the machine and coil, not deionized. Nope, don't use well or city water, too many minerals and too cold. Condensation in the machine will create shorts.
The internal devices are temperature limited and usually 100F is the top limit or pop go the SCR's, Mosfets or IGBT's. $$$

The stuff I sold ranged from 1 kW to 6 megawatts.

 

[Ries]

Ries, we bought one of these a couple of years ago to try out for some experimentation (didn't want to spend 5 figures since it was a proof-of-concept). I'm not an electrician nor electrical engineer, but someone who is took a look at it before we set it up and basically said it looked like a death trap. We returned it and found a used system on ebay which he was comfortable with. I don't remember the specific concerns.

I know a couple of dozen blacksmiths who use these daily. None are dead yet. Of course, these are people who work with power hammers with 250lb hammer heads that can hit 100 times a minute...
I have been meaning to buy one for a while, myself.
My buddy Andy, who makes blacksmiths tongs commercially, uses one all the time, and he still feels fine.
I know several shops who have been using these for fifteen years or more.
I suppose it depends if you are OSHA inspected regularly, and the diligence of your employees, but they are commonly used for forging and heating in small shops across america, with no deaths I have heard of.
My friend Grant started importing them from China over 20 years ago, and sold dozens to blacksmiths and knifemakers across the USA.
Safety is, obviously, a personal decision, but I find a radial arm saw much scarier, myself.

 

[Bart Slarty]

As expected, I'm not going to be able to dive in and change my process quickly or easily. It does sound like there's potential for what I'm doing (thin plates from .040"-.15" thick, mostly 6" x 4" or smaller).

Thanks for all the replies, which we're actually more than I was hoping for. I appreciate it. I have some thinking and learning to do ---->

"Bart"

 

[chipss]

Heating the whole plate? Just use an oven.
Heating an edge you need Radio frequency for the thin material. 400kHz.

If the operating frequency is too low you get what's called current cancellation. Remember that 400-450kHz penetrates steel .035.

 

[dian]

induction austenizing is beneficial, because you can achieve smaller grain size (they dont have time to grow). however keep in mind: temps are different (higher), holding time is different (shorter), weird things happen to permeability (→currie) and specific heat while the material heats up. you have to know what your doing or have the system set up by the vendor for a specific task. it would take an awfull lot of experimenting to get the process right in a production environment and current consumption might be prohibitive. if you just want to heat up a nail in 2 seconds and bend it its fun.

 

[michiganbuck]

We used induction coils to braze TCT cutters.
You would hold a scriber or the like on the carbide and when it would slide/float, move out and back
as you took your foot off the switch, about a half minute each.
Something like this video.