jason0012

Damascus welding in induction forge

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I have recently been considering adding an induction forge to the shop in the near future and was a bit curious if one could be used for damascus welding and what sort of problems might arise. It would be primarily used for production forging in my shop which I know these are excellent for. I know welding flux chews through forge linings at an alarming rate, would it harm the copper coils? and would I need the entire billet covered in the coils, or could a simple loop get me up to an even heat? If need be I will stick to propane for welding.

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I've kinda been kicking that idea around.  The possibilities are there but there are limitations.  Once could, in theory build an induction autoclave.  That would be a completely oxygen free (argon filled) forge environment giving you the ability to do some interesting stuff. 

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Good Morning,

One of the side benefits of Induction Forges is the lack of scale or oxides. I haven't tried welding in mine, but the theory says it will work. The metal will get to welding temperature. There will be no problem if you are using a Hydraulic Press to weld. When heating a large section, it is peculiar that the center of the section is not as hot as the outer area, after/when heating you have to wait a few seconds for the center to get equally hot, from itself.

Neil

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You bet they'll work to weld but scale WILL form on the outside unless you protect it from the air. While I haven't gotten a chance to play with an induction forge I've talked to a few guys who use the things. Untill I came across a better solution to scaling I'd just flux the billet before heating it, stick it on with a spray of Pam or similar oil.

Building a glove box with an inert atmosphere would be fine for heating but you have to take it out sometime.

I'd LOVE to have one, heck I'd dig the ditch and plant the wire, get an electrician in and wire the shop properly!

Frosty The Lucky.

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Citizens,

Induction heaters heat from the surface in. They are not like microwave heaters that heat all the way through at the same time. The stronger the induction heater the deeper it heats form the surface inward. But the surface of the metal "transfers" the heat to the interior. That is why it is necessary to pause after initial heating to let that surface heat,  heat up the inside. In exceptional circumstances the surface could melt before the inside is at welding heat. Numerous parameters have to be taken into consideration to determine the electrical current, dimensions of the metal to be worked, timing and a whole lot of other factors.

SLAG.

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A microwave oven IS a induction heater and they heat the same way just at different frequencies. That's why you have to turn food in a microwave and why most have turntables in them now. Put a bowl of soup in the center and watch it, the outside boils first. It's also why you need to let food rest a minute before eating it. It's old school, (Amana Radar Range days) marketing puffery to say microwave ovens heat from the inside out, it just ain't so. Does anybody here remember the old Radar Range TV commercial with the housewife" in the 1950s dress, petty coats, etc. put a chicken in the Amana Radar Range, set the timer for 14 seconds, dance around the kitchen till it dings and remove a nicely browned chicken? 

The EM radiation in either device is stopped or impinged by the outer layers, preferably impinged so the EM radiation penetrates before shedding it's energy to the subject material. This is why putting metal in a microwave is a BAD thing, it stops the EM on contact and gets exciting. All the EM radiation is stopped so all the energy is shed in a very thin layer of highly conductive metal. The only way it can shed more energy than it can carry is returning it to electricity. The same thing happens in induction generators.

Okay, I'm starting to get out of my depth, I have a working handle on the stuff which really helps me find more in depth info if I needed it or  wished but I've talked enough. 

Frosty The Lucky.

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Frosty

You are right that both systems use electromagnetic induced heating. I misinterpreted some of the description in article in Wikipedia.

But it discusses at length surface heating differential of metal.

I quote,

... Induction heating is a non-contact process which uses the principle of electromagnetic induction to produce heat in a work piece. By placing a conductive material into a strong alternating magnetic field, electric current is made to flow in the material, thereby causing Joule heating. In magnetic materials, further heat is generated below the Curie point due to hysteresis losses. The generated current is predominantly in the surface layer, the depth of this layer being dictated by the frequency of the alternating field and the permeability of the material.

And it goes on thus,

The second major parameter to be considered is the output frequency of the power source. As the heat is predominantly generated in the surface of the component it is important to select a frequency which offers the deepest practical penetration depth into the material without running the risk of current cancellation.[5] It will be appreciated that as only the skin is being heated time will be required for the heat to penetrate to the center of the component and that if too much power is applied too quickly it is possible to melt the surface of the component whilst leaving the core cool.

I hope that clears up the subject and my confusion.

SLAG.

 

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To protect the coils you can use a ceramic liner, the magnetic fields will pass through it. Some coils are covered in high temp fabrics, it all depends on the application. The ones we had at work were 30kw units, and with the test coil which had a diameter big enough to fit a soup can I could take a piece of 1.25" round bar to yellow in around 15-20 seconds. 

Look up Ameritherm , they have a lot of useful information on their website.

To protect the coils you can use a ceramic liner, the magnetic fields will pass through it. Some coils are covered in high temp fabrics, it all depends on the application. The ones we had at work were 30kw units, and with the test coil which had a diameter big enough to fit a soup can I could take a piece of 1.25" round bar to yellow in around 15-20 seconds. 

Look up Ameritherm , they have a lot of useful information on their website.

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Thank you Slag, you not only know enough but are interested enough to read understand and put the science and terminology in lay terms with cites so we can read in more depth if we wish. You my friend are a lazy guy's dream. :lol:

Grant Sarver was making and selling induction forge units and another friend of mine took over after Grant passed though I don't k now if Gene is still selling them. The coils used on these are copper tubing and are protected with flowing water. I believe IIRC he had units that would operate on 40amp 240v circuit you'd need to contact Gene for the correct specs, etc.

I'd LOVE to be able to afford one the draw is almost zero unless you put something in the coils and then it's very economical. His small unit would melt 2" of 1.25" sq bar in just over a minute. Again, IIRC. They aren't commercial induction heaters, they're small shop and hobby shop units but I believe they'll scale them up considerably. IIRC they were marketing one that'd melt 2" of 1.25" sq stock in about 30? seconds.

You can bend up the tubing to do what you need, coils, wands, pancake coils, etc. Guys are heat treating blades or so I hear. Annealing non-ferrous metals, on and on. Like I say I'd LOVE one.

Frosty The Lucky.

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Frosty,

I must admit that I was a little mystified as to why steel, in an induction oven, heats on the outside and less so in the inside. Then the obvious hit me. Most folks' experience when using a microwave oven is for reheating tepid coffee, or last night's leftover Irish Stew. The latter two are essentially water based items.  (solvents or mixtures).

Water is a very interesting molecule. It is a polar solvent.

Let me explain. Water is chemically the compound of two hydrogen atoms and one oxygen atom. The molecule has a plus end and an opposite negative end. The positive pole is a hydrogen ion, (H+) and the negative pole is a hydroxyl ion (OH -). The alternating current of the microwave oven causes the electricity to alternate. (i.e. back and forth). This current is constantly changing polarity and the attendant magnetic field is flipping back and forth. That minute movement of all the molecules causes friction and the water molecules heat up together with all the other ingredients in the solution or mixture. The microwaves penetrate right through the coffee etc., and heat all the water molecules at the same time.

A piece of steel, behaves differently and the reaction is not as "efficient". Hence the differential heating of the outside of the metal and its interior.

Incidentally, Microwave heating was discovered by Mr. Percy Spencer a self taught expert on cavity magnetron tubes. (he helped the U.S. develop radar for the war effort. (W.W.2)). He had a chocolate bar melt in his pocket and the rest is history.

I hope that this piece helps clarify the phenomena for some of our i.f.i. citizens.

Frosty that was a wonderful compliment.

Thank you so much.

SLAG.

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SO- has anyone here actually used their induction forge to make Damascus from scratch through some finished knives? I thought I had read somewhere that Tom Ferry had done so, but now can't find anything about it...

TIA

Dave

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I haven't done pattern welding (or any welding) with my induction forge, but I'd like to comment on some of the things.

As has been mentioned, you will get scale in an induction forge. It's a byproduct of heating in an oxygen environment. It may be less than you get in a coal or propane forge, if your fire management is allowing a suboptimal mix. Mostly, it's low scale because it's consistent. There's no combustion using up fuel/oxygen which changes the chemistry of the air.

It does, indeed, heat from the outside in. But so does a coal fire or a propane forge. Induction has the ability to penetrate past the surface layer, depending on how you set the machine up, but for all practical purposes, it heats from the outside in. My forge is underpowered for 1" stock, but that's not really any different than trying to forge in any other forge that's too small. So the main difference here could be said to be that induction has a higher cost of entry per unit of thermal input.

My understanding is that there are coatings you can put on the coils to minimize the effects of flux. Rectorseal was the brand recommended by the gentleman at Mettleworks.

The main impediment I see which hasn't been mentioned is that induction heating really only works in a narrow range of distance from the workpiece to the coils. When you pattern weld, you start with a billet which is very fat and then gets drawn down very thin before becoming very fat again. This would mean you might have a difficult time designing coils to fit. Not unsolvable, but that would be a challenge to overcome.

On 4/2/2017 at 7:20 AM, jason0012 said:

 and would I need the entire billet covered in the coils, or could a simple loop get me up to an even heat? If need be I will stick to propane for welding. 

I missed this in my reply.

Coils will only heat where they "cover" the stock. There's probably some dispersion within the general range of inductance, but it's not major. So you would either need to have long coils, or move the piece evenly through a shorter one. There is a fairly complex interaction of the conductivity of the workpiece and the coils, the power, frequency, and other factors, so it's not something you can simply say "I'm going to add an additional loop" and have necessarily work right away. Doesn't mean it won't, or you can't, but its something you would have to work out.

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If you do a flat pancake coil part thickness is not an issue. You can also protect the coils from flux with any number of barriers that the magnetic field will pass through, some places uses fiberglass panels. A thin ceramic tile would probably work too an allow you to rest the part on the coil itself. I worked with a 30KW unit made by Ameritherm - great company to deal with.

As to scaling. When I made parts that I had to heat up with a torch and not use the oven I just gave them a coating of flux. The flux kept the oxygen off and thus no scale formed. You could do that with the billets too if they are scaling too much.

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