Scale

[Leland Stone]

Howdy!

One of the most vexing problems I have when forging is the formation of scale. No matter how clean I wire brush my work as it comes out of the forge (I use coal exclusively), the newly-cleaned orange-hot steel instantly forms a new coat of scale.

I know this is inherent in forging; hot steel plus oxygen will always (and quickly) result in new iron oxide. Some of y'all may have some tips for reducing this scale, working around it, or otherwise NOT smashing it into one's workpiece.

Your comments are welcome, and thanks in advance. :)

Claymore

[GregDP]

Get it to anvil quickly and hit it faster than the scale can become a problem. Wire brushing is good, and necessary during slower task. But hammering is better. Scale becomes a bigger problem when we're at the anvil thinking not doing. At least that’s what I've found. ^_^ Material makes a big difference too. Stainless steels are also an option. Some hardly flake at all.
But I'd like to know any tips too. I wonder what the BlacksmithsJournal has to say.

[ciladog]

Just posted this in another thread.

There is a balance between the amount of fuel that is burning and the amount of air (or oxygen) that is needed to support the combustion. If the oxygen is not being consumed completely you produce scale on your iron because the excess O2 reacts with the hot metal.

Build a larger fire and place your work in a region of the fire where all the oxygen is being consumed.

[bigfootnampa]

Depending on the type of work I will use differing strategy... but commonly I do very little wire brushing. Scale is forming while you are brushing and you are losing heat too. Work quickly and strike hard and fast while you have the heat.
Keep good fire control... a slightly reducing fire helps significantly. For high quality work with expensive alloys you can use a light coat of spray flux such as "Fire Scoff" to protect the steel but for most of my work I find it overkill.

[bigfootnampa]

Do NOT OVERHEAT your steel!!! This is the biggest problem for most beginners. You can turn a WHOLE piece of steel into scale and ash in a hurry at white hot heats! The amount of work done per heat is, IMO, the second most important factor in minimizing scale problems.

[Alan Evans]

Some of y'all may have some tips for reducing this scale, working around it, or otherwise NOT smashing it into one's workpiece.

One can't do much about the generation of scale, apart from taking short heats (not long slow soaks) in a carburizing or reducing atmosphere as stated above.

You can minimize the visual and textural effects though which I guess is what you are asking.

The oxide is harder than the metal at orange heat but powders away at black heat.

You can refine your final surface texture by working the metal slightly cooler than you would when changing the section.

[WmHorus]

I minimize scale on my cable billets by spraying a small amount of water on the billet as I use the power hammer on it.

[GregDP]

Aye, the ol' wet hammer and anvil trick works, but I've rarely done that since it a rather large pop and splatter scared me away from the method. Try it at your own risk.

[Rich Hale]

Actually two years or more of forging will take care of this problem for the most part. That is if you put in alot of hours in the meantime

[Alan Evans]

Actually two years or more of forging will take care of this problem for the most part. That is if you put in alot of hours in the meantime

How? Please expand.

Personally I do not see it as a problem per se. It is just another option in the vocabulary of form and texture to be used as appropriate for the piece.

But please do expand on the 'two years' to take care of it, I am intrigued. Edited September 19, 2012 by blackersmith

[ThomasPowers]

With experience comes speed, the less time the piece is exposed to the air the less scale.

Like the old joke that experienced smiths use a special steel that stays hotter longer---actually the rapidity of our hammer blows keeps the steel hotter and we get more accomplished in a given time. It's not "bang, look, bang, look, bang"; but "BANG-BANG-BANG-BANG-BANG-BANG-BACK IN THE FORGE"

[Judson Yaggy]

Scale is a fact of life when blacksmithing. In general hammer first brush last otherwise you are just wasting heat. Blow or brush off the face of your anvil between heats, if excessive scale is still an issue find a way to adjust the oxygen getting to your work piece.

[rockstar.esq]

I tried the water on the anvil & hammer trick for a day. Greg and I agree, it's not for everyone.

I've learned that I was too stingy with my coal. Making a large well banked fire has reduced the scale tremendously. I find there's very little scale on the anvil after each heat now. It seems like some steels scale more than others. I've never tried stainless so I have no frame of reference.

[Rich Hale]

i would galdly 'splain that,,but Thomas did it better than I couild,,Thanks Thomas.....

[Larry H]

My 2 cents.........impatience causes scale by increasing air to accelerate the heating process, , , , slow down ! Everybody is always in a hurry these days, get in touch with your center, calm down, rest between heats while plotting your next move... and strike when the iron is hot ( like you haven't heard that before )

[son_of_bluegrass]

Often you need to slow down in order to go faster.

[Alan Evans]

i would galdly 'splain that,,but Thomas did it better than I couild,,Thanks Thomas.....

Neatly done, just as I thought I had put you on the spot!

Often you need to slow down in order to go faster.

And yet another cryptic comment! What is it about iron oxide that brings this out in blacksmiths I wonder?

Anthony Caro once said "There are only five important things to learn about sculpture. The first is scale, the second is scale, the third is......"

but I think he maay have meant a different sort of scale :)

[Ten Hammers]

Your own forge and your own fire building skills will be the thing that teaches you ( along with what Rich and Thomas have typed).

[son_of_bluegrass]

What is so cryptic about slowing down to go faster?

Not too long back on one of the science podcasts I listen to the episode was on how people who slow down, making deliberate moves and choices tend to get work done faster. Some of the show had to do with sports and how the best players tended to wait until the last moment (slowing down) to excel.

This can apply to smithing in two ways, I think.
One take your time when working to make deliberate and correct moves to get work done efficiently.
and two, don't try to force heat into the work piece too fast- all that does is heat the surface without penetrating to the center which will make the work harder and more work necessary.

Thus: slow down to go faster.

ron

[Alan Evans]

What is so cryptic about slowing down to go faster?

It is a perfect example of a cryptic comment...look it up! :) enigmatic, obscure and an apparent contradiction in terms, a masterly example.

Your perfectly straightforward explanation perfectly decryptified it, but you knew that didn't you:)

I have a couple of memorable experiences of the phenomena too. One was as a strapping 23 year old working with the then (as I perceived him) old man of 60 Alan Knight on the restoration of the Davies Brothers' gates for the National Trust Erddig House that constituted my main blacksmith training. We were working heat for heat on rolled snub scrolls and water leaves in wrought iron. First thing after I had lit the fire he would take a bar heat it work it , I would have my piece in the fire beside his and as soon as he'd finished try and reproduce exactly what he'd done, brilliant training! Trouble was after a few heats my piece was lagging and I was trying to copy what he had done two heats before! By the time we got to coffee break I had to work through with another 5 heats to catch up. I was absolutely knackered and running with sweat from the strength energy and speed of movement, he, the bastard, never broke a sweat or seemed to hurry!

One day I will act out the tale of my mate Jeremy who trained as a thatcher at the same time in the 70's. I witnessed him working with incredibly hasty movements... but he was moving across the roof much slower than his master who seemed so casual and slow in his!

In all seriousness and deference to the OP's question, the reason I did pick up on both your and Rich's comments was that they were not explicit responses to the practical question however true they may be.

Sadly some people will work for many years and not learn anything from experience. Being given some practical pointers to look for can help speed up the process. My favourite epigram "A wise man learns from his mistakes, a lucky man from the mistakes of others".

As a young smith making domestic fire tools and the like I used to hate scale on my work and invariably descaled and armour bright burnished all my work. My main consumable after coke was wire brushes. I even did it on architectural size work when I made the gates for Saint Paul's Cathedral, and for the hospital chapel in Guildford.

I think the main thing that experience teaches us about scale is to accept it rather than fight it. We alter our perception of it.

We can minimize its production by turning the air down in the furnace or keeping a large fire; we can remove it from the surface with scraper wire brush or the shock of water or by running the hammer down the arras' to flake it off. We can keep the anvil clean mid heat, we can work the metal at black heat to remove the marbled height differences and refine the surface.

Or we can celebrate it.

One of the delights about forged metal is that it records the process of its forming, scale beaten in to the surface at orange heat leaves a gorgeous pattern! I often use graphite powder in the top coat of paint to bring it out and enhance that hot-worked texture. On some projects in stainless steel the surface after electro polishing is magical.

Methinks I profess too much, I must go and make a punch! Edited September 22, 2012 by blackersmith

[Alan Evans]

and two, don't try to force heat into the work piece too fast- all that does is heat the surface without penetrating to the center which will make the work harder and more work necessary.

And another thing to clear up the apparent contradiction between your statement here and mine in post no. 6...

"One can't do much about the generation of scale, apart from taking short heats (not long slow soaks) in a carburizing or reducing atmosphere as stated above".

You are referring to a coal or coke fire I believe and I am talking about gas furnaces!

On bars over 75mm (3" square) I have had a build up of over 3mm (1/8") thickness scale if I have left the piece in the furnace too long!

[Dillon Sculpture]

On bars over 75mm (3" square) I have had a build up of over 3mm (1/8") thickness scale if I have left the piece in the furnace too long!

Yes please!

[Alan Evans]

Yes please!

:) suckers for big bars all!

[ThomasPowers]

Actually if your propane or NG forge is set reducing with a proper burner you should get no scaling at all even if you leave the piece in all day.

[Frank Turley]

I like all of this rambling. The ol' UCLA basketball coach, John Wooden, would say, "Be quick but don't hurry!" Finishing heats can be done at the low cherry to blood to dark red, and one will get a smoother finish that is easier to clean at ambient temperature.

I prefer not to scare people away from taking bright heats (lemon) when working mild steel. You do get thicker scale than at lower heats, but you want to move metal. A lemon yellow heat is optimal. I find that too many beginners and intermediates get the habit of trying everything at the cherry red heats, and that is not only time consuming, but it becomes hard work.