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Blacksmithing and Metallurgy

Cheap induction forging, Maybe?


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  #1  
Old 02-04-2017, 12:18:20 PM
Pete Spaco Pete Spaco is offline
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Default Cheap induction forging, Maybe?

Lately I have been trying to get a $35 Chinese 1000 Watt 12 volt to 48 volt (DC) induction heater working well enough the heat a 1/2 square bar to forging temperature.
It's this one:
http://www.banggood.com/Low-ZVS-12-4...l?rmmds=search

I am not sure that this little thing is gonna have enough power, but I am learning a lot in the process.
If you are interested, I have a webpage and (currently) 3 youtube videos about it.
Webpage:
http://spaco.org/Blacksmithing/ZVSIn...eaterNotes.htm

Youtube:
https://www.youtube.com/playlist?lis...3pELWdxCM3XH4I

Pete Stanaitis
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Old 02-04-2017, 01:57:16 PM
I like oldstuff I like oldstuff is offline
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Default Re: Cheap induction forging, Maybe?

Pete, I'm a induction guy having been involved designing and selling units from 500 watts to 7 megawatts.

Firstly we'll assume the unit is working.
As there is no metering that shows voltage on the coil it's difficult to know what's going on.

Every unit has it's "tuning range" where it will couple to the coil and the load.
As it's designed it seems to be a high voltage output as it's designed with only a tank circuit consisting of the big black tank capacitors and the coil.
Note that whatever coil was provided with the unit likely has the correct number of turns to suit it.

Now to mess with the tuning and to suit your part, let's build a new heating coil and see if that helps. Make one with the same number of turns smaller in diameter to suit your part. Make it about 3/8" larger in inside diameter than your part. Making the smaller coil helps with "coupling distance" and may help load the power supply better. Or maybe the power supply won't tune into it. Only one way to tell as there's likely no supporting data for the machine to determine the right pico henries or inductance range needed. Another thing to trial and error is to temporarily short out a turn or two (make them touch together) to see if it likes that induction range better. *You can go through a lot of copper tubing trying to optimize the coil design!

Basic coil theory:
More turns =higher voltage of the output
Less turns = lower voltage of the output

This is all well and good, but with no monitoring meters on the unit it's a crap shoot as to where the supply is running as far as output volts, current and frequency.

On commercial machines you take one or more of the tank caps out of the circuit to get the frequency up, adjust taps on an output transformer etc. But at this point, leave the caps all in.

If you want, send me a PM with name and address and I'll mail you a book on induction equipment theory and operation. It's written in the early 60's slide rule era, but is still the holy grail of induction basic knowledge.
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Old 02-04-2017, 07:56:45 PM
Pete Spaco Pete Spaco is offline
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Default Re: Cheap induction forging, Maybe?

Thanks for your input, "I like oldstuff".
I am doing most of those things. I haven't looked at my videos lately, but I thought that I was calling out the current draw on a regular basis.
I have not been reading voltage across the work coil because I thought the current would be a better indicator, realizing that fewer turns would probably give me lower voltage anyway.
Interestingly, the coil diameter on 3 of the 4 units that I bought were of different diameters; ID's:
1 1/2" (~ 120KHz)
1 3/4" (~113 KHz)
2" (87Khz)
And I did wind a 1" coil, all of the same number of turns. (147 KHz)
And they did behave pretty much as you suggested. Except that the 1" coil doesn't want to oscillate in some situations.
I even made a 2 turn coil. But I don't think it won't oscillate at all. When I hit the power switch, current goes well above the 25 amps that I am comfortable with. More testing to do on that, though.
I just today doubled the bank of capacitors and got the Fres down to about 61 KHz with the 2" coil. But, because those added caps are a few inches from the other bank, I have some current sharing issues to deal with.

Test a little, think a lot, repeat.

Pete Stanaitis
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Old 02-05-2017, 12:07:47 AM
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Default Re: Cheap induction forging, Maybe?

Quote:
Originally Posted by Pete Spaco View Post
I just today doubled the bank of capacitors and got the Fres down to about 61 KHz with the 2" coil. But, because those added caps are a few inches from the other bank, I have some current sharing issues to deal with.
As your output is down near line frequency you are getting what is called current cancellation in the workload. 61 hZ is waaaay too low to see any induction heating in the small stuff you're working with as the induced current travels right through the part and is cancelled by the other (reverse polarity) side of the sine wave. 60 hZ is for parts a foot in diameter and larger! *For small parts try getting the freq higher. Actually as high as the little unit can give you without popping the transistors.

your 2 turn coil has too much inductance and would require a transformer with suitable turns ratio to tune to and drive that coil.
Remember that you're essentially tuning a radio transmitter that uses the antenna as the heating coil. But with little data on your unit you have no way to determine it's limits or sweet spot.

For general heating you may want to consider the equivalent of 3-6 kW per square inch of workload.
for case hardening the power density has to be upped bigtime in the area of 10 - 15 kW per sq inch. Obviously nothing that your little units can provide.
To attain that sort of current density you'll have to reduce the workload size considerably. Then you're back into the current cancellation situation.

Here's a primer for your perusal.
http://www.asminternational.org/docu...a-38b8fab3a160

Last edited by I like oldstuff; 02-05-2017 at 12:25:23 AM.
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Old 02-05-2017, 01:49:32 AM
Vanman Vanman is offline
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Default Re: Cheap induction forging, Maybe?

So, these induction heater power supplies are little more than a resonant LC circuit? I had never realized that. I always envisioned them as being driven by a high power, high frequency inverter.

I would think, when heating metals with a high magnetic permeability like iron and steel, that the resonant frequency would be changed dramatically?
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Old 02-05-2017, 06:59:16 AM
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Default Re: Cheap induction forging, Maybe?

Does reaching the Curie temperature have a big (limiting) effect on the heating?
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Old 02-05-2017, 10:25:38 AM
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Default Re: Cheap induction forging, Maybe?

^ yes once you hit 1425F and steel loses it's magnetic properties it just takes more power to keep going higher.

---------- Post added at 08:25:38 AM ---------- Previous post was at 08:11:09 AM ----------

Quote:
Originally Posted by Vanman View Post
So, these induction heater power supplies are little more than a resonant LC circuit? I had never realized that. I always envisioned them as being driven by a high power, high frequency inverter.

I would think, when heating metals with a high magnetic permeability like iron and steel, that the resonant frequency would be changed dramatically?
They don't need the rectifier in his little units as they're driven by batteries. Formal sold state induction supplies are either constant current or constant voltage output and are an inverter.
Usually 220 or 480V 3 phase to dc then pumped up to whatever freq output and voltage is needed via the mosfets or IGBT's. Maybe scr's but those are becoming an obsolete device in favor of the more efficient transistors. A couple isolation transformers and chokes protect the discreet components, help with 3/5/9/13 harmonics etc. Then the tank circuit with big caps a transformer etc.

Last edited by I like oldstuff; 02-05-2017 at 10:41:07 AM.
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Old 02-05-2017, 10:59:26 AM
Pete Spaco Pete Spaco is offline
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Default Re: Cheap induction forging, Maybe?

Just to address a few comments from the last few posts/questions:

I like oldstuff:
The frequency is Kilo Hertz, not Hz. Not close to line frequency.

vanman:
The resonant frequency of my devices drops by about 10% between "idling" and inserting a 1/2" square mild steel bar into the work coil. Not true for copper, lead or tin, which hardly effect the current or frequency at all.

The "high power" question:
All depends on the size of system. I am currently driving my little board with 3 car batteries. At work, we had a 25Kw 3phase system back in the 1960's that looked like something from a Frankenstein movie. For instance, I had a 5KW unit from Westinghouse at one time. I am pretty sure it was the same box and with most of the same parts as a small AM radio station transmitter, with a few output differences. Vacuum tubes. 10,000 volts. 4 feet cubed. I think it drew about 50 amps from a single phase 240 line. Very inefficient.

Elden DuRand:
Yes, reaching the curie point does make a big difference. A mild steel workpiece that draws about 22 amps when I start heating it, shows a drop in current to 16 amps when it hits that point.

As mentioned, this $30 board doesn't come with a power supply at all.
You have to find your own. I recently bought a 48 volt 26 amp power supply which I intend to connect once I get up the guts to do it.
That kind of power supply can cost anywhere between a couple hundred dollars and over a thousand, depending on features. And that one will only supply 1KW!

There are a few (Blacksmith Supply) companies here in the USA who are reselling 5Kw to 15KW induction heaters that run in the 30KHz to 80KHz range (which is where I'd like to be). The guys I know who are actually using them to do real work have been paying about $3500 for 5KW unit. But I did a little googling yesterday and found some 15KW units for as little as $700!
Don't get the idea that I am endorsing those Chinese 15KW unit for $700. And for most of us, I don't even know where we'd get the power to run it, if it did actually work.

Pete Stanaitis
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Old 02-05-2017, 12:13:28 PM
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Default Re: Cheap induction forging, Maybe?

Oops seems I can't read... You did say khz...
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Old 02-05-2017, 09:59:04 PM
t6299fm t6299fm is offline
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Default Re: Cheap induction forging, Maybe?

Hi,
Were you associated with the company Inducto"? I have a cool little induction furnace made by them that is rated at 50 pounds of iron. It has a 50 HP motor generator. Do you know anything about these? I need a power factor meter for it. I run it on water power with my OLD 1929 Leffel/Westinghouse Hydro generator.
Forbes
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Old 02-05-2017, 10:34:41 PM
Vanman Vanman is offline
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Default Re: Cheap induction forging, Maybe?

Oh, I'd very much enjoy seeing some photos of all of that equipment. And nameplates too.
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Old 04-27-2017, 06:40:42 PM
Pete Spaco Pete Spaco is offline
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Default Re: Cheap induction forging, Maybe?

Just a quick update:
I have now been running this little system on 48 volts for as long as 15 to 20 minutes at a time, drawing about 20 amperes and it is working pretty well.
There are now 11 videos instead of the 3 that I mentioned earlier. Again the playlist is at:
https://www.youtube.com/playlist?lis...3pELWdxCM3XH4I

And I have updated the webpage a lot too:
https://www.spaco.org/Blacksmithing/...eaterNotes.htm

It is interesting to see that only about 25% of my youtube traffic for these videos is from the USA. And 4 of them are in my top ten! The darn things must be pretty popular.

I have now gotten 10 ounces of steel up to 1200 degrees C.

Pete Stanaitis
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Old 04-27-2017, 11:50:08 PM
SoTexRattler SoTexRattler is offline
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Default Re: Cheap induction forging, Maybe?

Have you tried heating any Stainless Steel in the work coil?

I made several hi-Q Ham Radio mobile Loading coils for 160meters (1.8-2Mhz) and I had 3/8"NF SS studs in the top and bottom plexiglas coil ends. They got noticeably hot when doing a key-down test at 100watts output.

I had always heard SS was deemed too lossy for use in a strong RF magnetic field so I went back to steel.
Steel didn't warm up as much as SS did.

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Old 04-30-2017, 09:19:27 PM
Pete Spaco Pete Spaco is offline
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Default Re: Cheap induction forging, Maybe?

No, I haven't tried heating any stainless steel. But from your observation, it sounds like I should give it a try.

Pete Stanaitis
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Old 05-01-2017, 01:02:01 AM
SoTexRattler SoTexRattler is offline
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Default Re: Cheap induction forging, Maybe?

BTW, I saw a 2500W heater assembly by the same company but their included coil was a flat pancake coil..??? Maybe it was for inductive stove tops.

But 2.5kw would be just right for what you are trying to do with a solenoid coil.
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Old 01-03-2019, 01:00:18 AM
Pete Spaco Pete Spaco is offline
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Default Re: Cheap induction forging, Maybe?

Time goes by-----
I recently bought the bigger brother to the 1000 watt heater that I discussed here earlier.
This one is rated at 1800 watts. I shoulda looked a bit closer because there's also a 2500 watt version, but once I get the kinks out of this one, it'll be easy to move up to the 2500 watt version.
Aliexpress was the source for this one and they sell a "Combo 2" which comes with the Driver board with two fans on it, a little water pump with hose, a 48 volt 50 amp power supply, a DC circuit breaker and a ceramic insulated graphite crucible.
The "Chinglish" is a particular problem with these units since the marketing department, the design group and the document preparation group weren't paying much attention to eachother. But I DO think they have a solid design, considering all that.
So I am taking it slow and haven't actually applied power to the whole system yet, while bullet proofing the setup method for myself and for others.
And, from the experience I got from the popularity and contacts I got about the 1000 watt unit, I decided to put up some helpful cautionary info for folks now going to these slightly larger units.
If you are curious, my first setup video (in the description you get a link to new webpages about them) is here:
https://youtu.be/PHKNaDTl1JY

As usual, I welcome comments,
Pete Stanaitis
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