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I know this is a stupid question, and it shows how much of a newbee I am. But when I was reading the thread about no flux welding, I could follow most of the conversation. Except one thing, what does a "reducing" mean.

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As in reducing flame? Clarify a bit...

To become old and wise... You first have to survive being young and foolish! ;) Ikisu.blogsot.com. Email; milesikisu@gmail.com mobile: +27784653651

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Mtodd, actually I think this is a great question for beginners to understand. You will come across that term a lot in a number of different situations. To put it simply, the term "reducing" is usually used to describe an atmosphere inside a forge, kiln, oven, etc. that will not cause the metal to oxidize and form scale or rust.

 

A fire can have one of three atmospheres:

  1. Oxidizing: more oxygen than fuel (Carbon)
  2. Neutral: just enough oxygen and fuel that both are entirely consumed
  3. Or Reducing: more fuel, and hence more carbon, than oxygen

However, it's a little more complicated than that. It is actually a chemistry term that comes from oxidation-reduction reactions (or redox reactions). Rust and scale are forms of "oxidation," the opposite of which is "reduction." Wikipedia defines the two this way:

  • Oxidation is the loss of electrons or an increase in oxidation state by a molecule, atom, or ion
  • Reduction is the gain of electrons or a decrease in oxidation state by a molecule, atom, or ion.

Iron (Fe) in its elemental state has 2 or 3 electrons that are at a high energy level and want to react with other elements. Oxygen on the other hand has 6 and only needs 2 more to make it stable. Thus, common rust occurs when iron gives it's two electrons to oxygen in the following reaction: 4Fe + 3O2 → 2Fe2O3.

If iron rusts this way far enough you get a mass of iron ore called Hematite (Fe2O3).

 

I won't bother fully describing the reduction of iron ore, as I believe this site, http://www.chemguide.co.uk/inorganic/extraction/iron.html, covers it very well. But to sum it up the excess of carbon causes CO, or carbon monoxide, to form. The CO and Carbon in the furnace react with the hematite to produce pure iron and CO2.

In the case of a forge it is good to have a reducing atmosphere because the steel will ideally not oxidize and grow scale while it is in the forge. Once a piece is pulled out into the open air, however, scale will grow which is the reason for flux. But in the case of a nicely stacked billet flux may inhibit welding more than the fire scale that grows between the layers. I've never welded without flux, but the discussions here and elsewhere make me want to try. An oxidizing atmosphere, will actually cause scale and rust to form more quickly than naturally in air. A neutral flame is hard, if not impossible to achieve in a forge hence a reducing flame. It is possible to carburize (add carbon to) a piece of steel in a reducing atmosphere, but typically you have to really try to accomplish that feet and even then the higher Carbon layer is only on the surface, unless the steel actually melts (which is often the goal of hearth melting wrought iron or mild steel).

 

I hope this helps without being too confusing. Let me know if anything is unclear (or just plain wrong :) ).

~Josh S.

"It is the glory of God to conceal a thing: but the honour of kings is to search out a matter." Proverbs 25:2 (KJV)

bezalelblades.blogspot.com

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That's a nice explanation, Josh. To achieve the reducing environment is why most of us adjust the gas in the forge to where we get approximately 6" of flame coming out of the opening. Hence the term "Dragon's Breath". This is a good indicator of having more fuel than oxygen in the forge.

 

Using a fuel like coal or coke is a whole different case and I'll leave that to others to explain how it can be done.

 

I've been experimenting quite a bit this winter with no flux welding and find that it's a viable way of welding but does require being a little more careful about providing the right environment for it to work correctly. The addition of a flux like borax makes the process a little more forgiving.

 

Gary

Gary

 

ABS,CKCA,ABKA,KGA

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I think I am getting the idea. That in reducing the coal until most if not all the moisture and impurities have been burned off and what remains is coke. When there is no more smoke and the fire is burning clean with only blue flame. Does that sound right?

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mtodd, reducing coal to coke makes for a cleaner fire, but a clean fire can still be oxidizing, so this is not the meaning of "reducing" in this context.

Like Joshua Snead said, a reducing fire is one where there is an abundance of fuel so it doesn't try to make fuel of your workpiece instead, the result of such an event would be non-weldable scale (iron oxide). Instead the fire is "pushing" the reaction in the other direction (in this case very slightly)

 

Any flame that burns sooty, like a candle with too much wick, basically contains within it a small reducing atmosphere. Let's leave it at that mental image however, since too much soot would also inhibit welding. A reducing atmosphere based on CO-gas instead of soot is the clean and proper way to go about such welding work. Coke (factory made, or coked coal in the forge) and charcoal makes this CO gas rather than soot.

 

(One can fine tune a gas forge to be reducing without soot getting in the way of a weld, but as a rule volatiles such as tars and oils in coal, other oils and natural gases will soot. (gases to a varying degree, often quite little) Coke and charcoal will not.)

Edited by Steffen Dahlberg
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Well there for a minute I had a flashback to Chemistry class and the what the heck did you say feeling but, I hung in there and I think I actually got what you all were trying to say.

 

In short the flame you are using whether it is coal sourced or whether it gas sourced, the flame needs to be as perfect as possible on the mix of air and/or source, to eliminate all the containment's from the flame itself, effecting the steel! In other-words you must control the oxygen in a given environment or the steels quality can and will be effected!

 

Or then again I may have lost a thing or two in trying to reduce this down to a "redneck definition" !!!!

Edited by C Craft

C Craft Customs ~~~ With every custom knife I build I try to accomplish three things. I want that knife to look so good you just have to pick it up, feel so good in your hand you can't wait to try it, and once you use it, you never want to put it down ! If I capture those three factors in each knife I build, I am assured the knife will become a piece that is used and treasured by its owner! ~~~ C Craft

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First of all coal needs to be burned to coke before being used for forging. That is done when the smith lets the coal fire burn until the smoke decreases. No one actually forges with coal or at least they shouldn't be. If the steel is put right into the smoking coal it can pick up sulfur which will increase it'w brittleness. Also, once coal is reduced to coke in the fire pot, also called a duck's nest, fresh coal is put around the fire on the tray to reduce down to coke while the central fire burns. Or you can just start out with blacksmiths coke.

 

The other reduction that we worry about is the atmosphere of our forge. For a solid fuel forge, like a coal forge, the fire just above the air inlet is oxidizing, somewhere in the middle is the neutral zone, and the oxidizing layer is found somewhere near the top of the fire.

 

My understanding is that steel will not pick up much carbon in a forge. One of the ways it was done way back when was to seal iron or low carbon steel in a crucible with a carbon source and heat it at high temperatures less than the melting temperature to produce blister steel.

 

Doug

HELP...I'm a twenty year old trapped in the body of an old man!!!

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Wow, thanks you guys. A lot of good stuff. I think I am getting a better idea now. So basically I need to have a big clean fire that is big enough to bring the work to weld temp. Big enough that I can keep the work in the neutral layer and away from the oxidizing layers of the fire.

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Wow, thanks you guys. A lot of good stuff. I think I am getting a better idea now. So basically I need to have a big clean fire that is big enough to bring the work to weld temp. Big enough that I can keep the work in the neutral layer and away from the oxidizing layers of the fire.

 

That's correct, you really want to keep the piece towards the top of the fire. It can be tricky to adjust the temp in a coal forge to get the right atmosphere but you will learn with experience. How far up it needs to be depends on the depth of your firepot and your air flow. Do you have an electric blower, or hand crank? Electric is nice because the amount of air will not fluctuate, but it will use more fuel unless you turn the air off after every heat.

 

One sure sign that you have too much air is if your work sparks while in the forge. In that case the steel is burning and rapidly oxidizing. (It may spark a little as you pull it out into open air though.)

"It is the glory of God to conceal a thing: but the honour of kings is to search out a matter." Proverbs 25:2 (KJV)

bezalelblades.blogspot.com

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Joshua,

I have an electric blower. Its sort of redneck version though. I hooked a shopvac up to the tuyere and wired a dimmer switch that one would plug into a table lamp to adjust the brightness, basically functioning as a rheostat. So I can adjust the air pretty well. As for the sparking, I do tend to try to get the work as close to that heat as possible. From what I read in Jim Hrisoulas book The Complete Bladesmith he said that's what one should look for when forge welding. I know he also said that high carbon steel welds a slightly lower temp, but I get nervous I'm not getting the steel hot enough to weld. I don't know, like you said I will just have to learn from experience. Thanks again for your time and input, it really means a lot to me.

Matt

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I think that blower will work just fine. Jim Hrisoulas is a great bladesmith! His work is far beyond my current level. He's been in the business for a very long time and no doubt learned to forge weld from blacksmiths who often use sparking as an indicator. Blacksmiths do not typically worry themselves about carbon content and heat treating. He has a great deal of experience and control over his methods, unlike most beginners.

 

I happen to disagree with Jim on that point because you are literally burning carbon out of the metal and can risk totally destroying a piece of steel. A good number of the ABS Master Smiths and Journeymen that teach here at Haywood will immediately cut off a piece of steel if it sparks, if not throw away the blade entirely. Furthermore, it is not difficult to reach that yellow-white temp needed for welding without burning the steel. Like you said, it just takes a bigger fire. In case this helps, here is a diagram of the forge I use with it's various atmospheres at a general forging temp.

 

Coal Forge Atmospheres.jpg

 

As the air flow increases the oxidizing layer comes closer to the top, but generally if I keep the work above the firepot it will not spark, even at a white heat.

 

And your welcome, the chemistry bit was a good review for me. It's easy to forget that stuff. (Now I just need a refresher on calculus... maybe later :P .)

"It is the glory of God to conceal a thing: but the honour of kings is to search out a matter." Proverbs 25:2 (KJV)

bezalelblades.blogspot.com

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You only need a fire that will heat the section of the work that you can work with your hammer when it comes to forging. For heat treating you my need a fire closer to the size of the work but even there you can work the piece back and forth in the fire to heat it evenly. It depends on what you can make work.

 

Doug

HELP...I'm a twenty year old trapped in the body of an old man!!!

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