Glenn

Does it matter how the metal gets hot?

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For years wood and charcoal were the fuel of choice for forging.  Then other fuels became available such as coal, coke, oil fired forges, gases such as acetylene, propane, etc, and electric induction heating, and etc. 

Disregard the shape of the forge and the question becomes does one type fuel heat the metal differently from the others?  What are the advantages of each type of fuel. 

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Heat is heat, beat is beat....if i could afford an induction machine, i would be all over it....I started using a charcoal forge, but found that propane was much easier, thus efficient. I would like to have a coal setup also, but due to logistics, have not done so yet. They all have their advantages and disadvantages.

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Heat is heat, but the manner of delivering it is different.

Gas forge heats up the whole piece, coal forge can be made to heat just the part you want. An oxy torch can be even more precise. 

I think induction and oil forges are more suited to industrial applications then the one man workshop. 

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Actually the small induction units are really nice for the small shop that can afford one.  I know of 2 smiths who have them around here. (One of the big selling points out here is that with an induction forge you can air condition your shop!)

I haven't seen a "small" oil forge yet; all of those I have seen were definitely industrial.

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I think the only difference is how clean the fuel is and how fast it heats steel. Induction is undoubtedly the cleanest and heats steel fastest. Next would be propane for clean but heats steel slower. Next on the clean scale would be charcoal and coal the dirtiest. They both will heat steel faster depending upon the air blast, more air more heat. But push comes to shove, it doesn't matter how you heat the steel, just hammer it and be happy.

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Induction coils can be customized to very precise small heats and much faster than a torch. 

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It does matter to some extent.  Oxy fuel heat sources can heat a piece so quickly that the outer "skin" can reach forging temps or even burn before the core is at working temperature.  This is especially true with bigger pieces.  Read up on soak times used in industry.  

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3 hours ago, arftist said:

should be constantly moving.

 

3 hours ago, Irondragon Forge & Clay said:

For heating with A/O a rose bud tip works best

Of course and indeed.  But to the original question of this thread, Oxy/fuel is not a great heat source for forging because the temperature of the flame can transfer energy into the surface of the steel faster than the steel's thermal transference can convey that heat to the center of the work piece. 

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Not to mention the price of oxygen and acetylene refill gas. But, it is torch work that lit the light bulb in my mind to old school blacksmithing potential. 

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I personally am a fan of soft coal or charcoal.. If I had to choose one and had unlimited supply.. It would be charcoal. 

Reasons are..  Any size fire can be built up in a short time frame..  The fire can be modified in any number of ways for different processes.  I get reheat times in under 30 seconds with 3/4" and under without being crazy on air input. 

The welding of metal is super easy and the heat is totally controllable. 

Where soft coal has one up on charcoal is the ability to create a hollow fire easily which can be used to good merit for exotic stuff like forge brazing,  heat treatment, welding while one piece is loose on top of the other bar.  etc. etc..  You can do the same with charcoal but it's tricky and you have to pick your sizes carefully.. 

For any production work, gas, oil are tops.. 

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My experience is with coking coal and coke. I've not used enough charcoal to have first hand experience. I'm comfortable with propane forged. My preference is coking coal.

Charcoal, as I understand burns fast and you need large quantities. It's expensive.

Propane is convenient. It too is expensive. It is limited by size. You can't get scrolls or other complex shapes into it. There is no or little temp control. When I see that dragons tongue and hear those burners roar,, all I see are dollar signe. Contrary to popular opinion, I do not believe there are any benefits using propane for production. I can pull a 8"-10" heat on 4- one inch bars and I can't outwork my forge using my 25# lil giant and my hand hammers. 

Using blacksmith coal or coke, I can heat any shape or size, heat treat great temp control. I believe if you are doing much forge work, coal/ coke is the best fuel and the cheapest. With 4" of coke under my iron and 2" on the top, I can maintain a neutral environment with ease. 

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Until there's a proper study and regulation of induction heating, yes, it does matter.

"Nevertheless, magnetic flux densities in excess of the action levels for peripheral nerve stimulation are reported for workers involved in welding, induction heating, transcranial magnetic stimulation, and magnetic resonance imaging (MRI). The corresponding health effects exposure limit values for the electric fields in the worker’s body can be exceeded for welding and MRI, but calculations for induction heating and transcranial magnetic stimulation are lacking."

The above is a quote from the linked to paper, by the US National Library of Medicine National Institutes of Health.

What's particularly disturbing about induction heating for blacksmithing, is the proximity of the person to the magnetic field and said field typically having absolutely zero magnetic shielding.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4305112/

Charcoal has always been my personal favorite, being more versatile in regards to being able to easily make a custom sized forge for different work if required, what with the low air pressure that is required as compared to coal or the less controllable and more complex gas forges.

Overall, seems to me that charcoal/coal forges are better for work that is highly variable in size and shape, such as custom fixtures or more scattered hobby work. Whereas gas forges seem to be better for predictably shaped repetitive work that's done by the dozens or hundreds.

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Well i don't know if this is totally accurate but i once heard that propane forges can slowly draw carbon out of high carbon steel. Whild coal, coke, and wood forges can slowly increase the carbon content. Don't take my word for it though, like i said im not totally sure. 

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Sorry that is untrue as generally you are scaling off the outer layers of the steel faster than carbon migration takes place. As for forge fuel; you can run any type of forge oxidizing or reducing---I can run my propane forge quite reducing or extremely oxidizing for instance; of course reducing in any type of forge means CO production.

You see a lot of these Urban Legends out there; like the folding and welding on japanese swords increases the carbon content. Unfortunately metallurgic testing has shown that the tamahagane from the tatara can start out at nearly 2%C and after all the folding and welding may end up at 0.5% C (What it does is to homogenize the carbon content and reduce inclusions in size and percentage).

The best way to maintain carbon content in a blade is SPEED which also correlates with fewer heats.  It's also a common problem for people that want to forge blades before learning the basics.  I've seen folks start with a high carbon steel and then abuse it so long it would not harden in water! In teaching at the University I see folks leave their blade in the forge and go visit the facilities, get a coke, check their phone,...They were warned!

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