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I Forge Iron

Mokume in a kiln?


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You bet. I have done quite a bit of cooper/brass, in one. 

 Way more consistent, and repeatable billets than in a forge.  I clamp it and pack it inside a stainless container with charcoal. Cook at 850c for 1 to 2 hours.  Remove from heat and reduce thickness by 50% to consolidate the welds. Follow up heats in a forge to shape as desired.

The main thing to think about and prep for ahead of time is how you are going to make that initial consolidation. I make my clamp so it fits in my press. If no press is handy make clamp to fit a nice big vice. They work well for the initial squish though 50% reduction may not be feasible in one heat. So follow up heats with a forge and hammer instead.  

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Tlmg, I keep seeing people using clamps, but has anyone used a weight?  This would work more in a forge, or a kiln that you could run something through the top for the weight.  Then run it through the heating cycle. When it hits temp the weight would push the layers together forming the bond.  If someone was doing a lot of it a fixture could be made, and an indicator could even be used to know when it has squished. If I understand it correctly, the items are on the verge of liquid on the surface when joined.

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1 hour ago, BIGGUNDOCTOR said:

 If I understand it correctly, the items are on the verge of liquid on the surface when joined.

What I am describing is actually a solid phase weld. There is so much more control in a kiln you can do a better job keeping things from melting ( and thus blurring the boundaries.) so you get a much higher quality product.  A weight applied while heating would just soak up the heat, slowing you down. Clamps are easy and there is a side effect most people don't think about, which is that Copper expands more than steel when you heat it so your clamp effectively gets tighter when you heat it. Some people take this idea to extremes by using extra low expansion metals as the bolts of the clamp. 

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Mokume is diffusion welding just like a forge weld. The secret is to get the metals in contact: close enough, hot enough or for long enough. Get any one "enough" and the metals will first exchange electrons, then nuclei becoming one piece. 

Getting the stock clean enough, think mirror polish and solvent clean is one method of getting the metal molecules close enough together to exchange atoms. Clamping it is another way to get the atoms close enough together. Heat gets Brownian motion excited enough atoms start jumping the boundary. 

Clamps, polished and heat speeds the process nicely and a kiln gives you exquisite control. 

Tristan knows his stuff, I've only done it enough times to know how it works, not be good at it.

Frosty The Lucky.

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