Charcoal forge wisdom

[grimm1966]

I'm looking for some charcoal forge wisdom on tending the fire and general fire pot setup.  I purchased a Centaur Forge fire pot years ago which is probably not the best for charcoal.  I'm going with charcoal because I live in Fairbanks proper and I don't think they (or my neighbors) will look kindly on burning coal.  Especially with the problems we have been having with air pollution.  At least with charcoal I can say it's just a glorified barbecue.

I built a stand for the fire pot and an attached mount for the blower.  My friend, who lives in Texas, was kind enough to send me up a blower that he rebuilt. I have attached an image of how I placed some fire brick around the fire pot to get some more depth.  I can always get some more bricks to build it up some more.  I'm guessing that I have about 6" of depth now.  Any advise about how these are placed would be great.  Mostly I want to work with some wrought iron rod that I have which is 5/8" in diameter.  I would also like to work with some plate, so getting as big of an area as I can would be a help as well.

So far I have been able to get up to welding heat, I lost about 1.5" of a pair of tongs that I was working on.    Some of the problems I have found is that when I was using the forge for about 4 hours last weekend the tuyere appeared to get clogged up with ash.  I wiggled the clinker breaker and poked at the coals and that fixed it.  I'm assuming that is something you need to do every now and then?

Back in the 80's I had an old Hay Budden anvil with a rivet forge that I did some forging with, but it's been a long while since I have done this, so any wisdom will be graciously received.  

Thanks, 

Jason

[Charles R. Stevens]

Thommas Powers is much better at getting charcoal and bottom blasts to play together than am I, but let's see what I can do to educate you. 

first off I would sorce full bricks insted of 1/2 bricks or some bank clay (if you shelter the forge) the 2" depth gain will help, as will placing two bricks on edge on top of the bearer bricks to form a trench. More effecency can be gained buy acualy nerowing your pot in one dimension, say going from 8X8 to 4X8, a couple pieces of 4" angle cut to fit would work. Now if you use clay you can ovoid buying more brick. 

Ash will build up, two things will help. Crank hard and bring up the fire fleas once in a wile and use soft wood or Adler/birch charcoal. The denser woods contain mor silica, so form more, denser ash, the lighter woods produce less and lighter ash that blows away easily.  

Biggest mistake made with charcoal is to much air, slow your role, as you can actually reduce the heat with more air than the fuel can use. 

[ThomasPowers]

The important thing is being able to put your workpiece into the reducing hot spot as horizontally as possible which usually means a taller fire is required---why Charles suggests  using taller bricks and restricting the firepot sides to make more of a trench to conserve fuel.

Yes you need to clean the fire as needed.  I have a shaker shovel made from rock shaker screen where I and scoop out the good stuff; put it to the side and then clean the firepot and dump the good stuff back in.  Charcoal will thrive on that where coal may go out on you trying that!

[Charles R. Stevens]

The compleatly modern blacksmith shows how to make a shaker shovel, tho he used it to acquire charcoal from the sent fire place fire it's the same idea, a small stall fork. 

[Glenn]

Making a charcoal shovel is simple, and the thing works !!

 

[Jasent]

One thing that has helped me not get clogged with ash is hit the air a little hard at first and blow the ash out. Makes a little bit of a mess but you learn to deal with all the ash

My fire pit is about 4" deep but I just pile it up higher 

[grimm1966]

Thanks guys,

That is a lot of help, now I need to construct a charcoal shovel.  @Charles R. Stevens I have that book and checked it out.   

I'm assuming that if you make the pile of charcoal larger, and pump the blower harder that you will have a larger heating area?

[Charles R. Stevens]

Charcoal realy likes a 6" hotspot, to go bigger you typically need multiple tuyere. Some folks make  a series of holes in a pipe to make a trench, others make a manifold and angle multiple tuyere in from the sides. As we can only effectively work about 6" befor running out of heat with hand tools, and moving the stock back and forth with lengthen the hot spot for longer bends and twists from the point of fuel effecency I would stay with an 8" bowl or a 8x4 trench with charcoal. Unlike coal fire spread is a real issue, and more fuel than can be supied air just burns up with out adding to your work. Second as hot air. Rises, you quickly reach a point of demenishing returns, you can acualy cool the coals buy inducing more air than can be burned. The reaction between hot carbon and O2 take time, this why a deeper fire for bottom blasts is so useful, with a side blast I takes a fraction of a second for the heated air to make that 90deg turn.  So just enugh air, let the stock soak so that it gets hot all the way to the core.  If you look at historical iron work, you can acualy see the 6" twists made in charcoal forges vs the longer twists made in coal and gas forges. 1" bar forges just fine in a side blast with a 7/8" I'd tuyere, it will forge fine in yours with a bit of tweaking. I have forged 18" 7/8" sucker rod into picket pins and 1 1/4" trailer leveler bars into splitting wedges with charcoal

First heat is an act of patience, not unlike perfectly roasting a marshmelo, second heat goes so much faster as you are only going from red to yellow or high orange 

[grimm1966]

Thanks Charles, that make complete sense.  I finally had some time today to do some more forging as it stopped raining.  Just when you get the system up and running, it rains and pours.    I narrowed the fire pot with some fire brick and it's working much better.   I think I wasn't turning the blower fast enough, now that I'm at about 60 turns a min. I'm getting up to welding heat reliably.  

I did some experiments with the wrought iron I have and some didn't do so well, others though worked out perfectly.   I will create a post on the experiments later, I'm still waiting for the last one to anneal.  

Jason

[grimm1966]

The weather finally cooperated so I have been able to get some more forging time in.   I have also been moving to a new job, that takes some time.  As I want to explore working with wrought iron and make some armour from it, if possible, I have been concentrating on making the wrought iron bar that I have thin.  

The first order of business was to make suitable tongs to grasping thin pieces.  As I'm just starting out I wanted to make it simple (I think)  and chose to make some viking style tongs.  This design works really well, I am very impressed, they can hold just about any shape and very securely.  If you notice that one of the reins is shorter than the other it's because I got it too hot and lost about 1.5".   They are a bit short, sometimes when I go to pull the iron from the forge it gets really hot.  They were made from 1/2" bar from Home Depot (A36?).  I'm probably going to make another pair that is longer and hopefully not burn the reins this time.  

One technique I wanted to try is a method used by old bucket makers in Italy where they forge out bucket blanks and then coat them with a clay slip, stack them, and forge the bundle at the same time.  The clay slip keeps the layers from forge welding and allows them to work on up to 7 buckets at the same time.  

To start with I forged down one of my 5/8" bars as thin as I could at welding heat.  It ended up about 1/8" to 3/16" thick by the time I was finished.  I then cut it in half and drilled holes on the ends so I could wire them together.  The bucket makers would wrap their bundles with a sacrificial sheet of iron to hold the layers together.  Now when I was doing this I did think to myself that the wire will just disintegrate at welding temps (it did).   But that didn't stop me   I covered the plates in the clay slip and wired it together.

[grimm1966]

Now the wire didn't hold up the the plates did come apart before I could forge the plates very much, but they did not weld, which was cool.  You could rivet the plates together but then I don't think you will be able to keep the rivet from welding to the plates and you would have to cut them apart.  My next idea was to just simply fold one of the plates over and try that.  So I folding the plate hot and kept the ends apart so I could coat it with the slip.  I then heated it up to welding heat and continued to forge it with a ball-peen hammer to aggressively move the metal.  This worked really well and I was able to get the metal down to about 16 gauge (1/16") and some parts thinner.  I must have had a bubble in the slip as a small part did start to weld and you can see from the picture.  I had to use a chisel to get the ends apart and the plate ended up breaking at the fold. Next time I'm going to open it up hot and see how that does.

This wrought is from the Globe grainery in Wisconsin and I have heard that it has a lot of phosphorus in it that makes it brittle.  I can see that in this example when I tried to open the plate cold. It's going to be interesting when I try to work the metal cold and see what I can make out of it. Lots of fun though.  

[Work With Nature]

On 8/17/2017 at 4:45 PM, Glenn said:

Making a charcoal shovel is simple, and the thing works !

Wow that is a great idea, Like the shovel I spose it is a great way to get out the dust before throwing on the charcoal. 

[grimm1966]

On my last forging session I wanted to test a couple of things, one of which is something I had seen the African smiths doing.  I noticed that they didn't bury the iron in the coals like most smiths do today.  They simply set the iron on top of the coals and tucked it in around the edges.  I tried this and it worked great and there are several advantages with this technique. 

First you use much less charcoal than you would otherwise, maybe up to half less, which is significant.  One of the reasons modern smiths like coal better than charcoal is it's ability to last longer.  I think this puts charcoal on a more equal footing with coal, almost, you still have to tend the fire a lot more with charcoal.  

The other advantage is that you can see exactly what temp the iron is, so no more having to pull the iron out to check to see if it's ready or not.  I was able to get up to welding heat with out issues.  

I was able to still heat the iron even when the level of coals was about 3 inches deep, but I noticed that the iron was getting more scale on it then when the fire was deeper.  So at that point the position of the iron was no longer in a reducing atmosphere.  Given this you need at the very least about 4 inches of coals to get to the reducing atmosphere.   I did about a 2 to 3 hour forging session and went through about 10 pounds of charcoal.  Before I was going through about 20 pounds or more.

I haven't tried to heat a bar like this yet, so I don't know how well it will work for it.  For plate like shapes it works great though.

[Jackdawg]

your forge looks great, and it sounds like your having fun.

With charcoal, I find as I mostly working on small stock, having the fire hot enough to heat the metal before it goes in, with minimal airflow while the stock is in the fire lets me get away with a much smaller fire.

You can heat metal on top of the fire with coal as you describe you are playing with for charcoal, it will just take a little longer to heat as you don't have the insulating properties of the material on top to help keep the heat in (it will be the same for charcoal). If you have a wind blowing, or if the weather is cold you may find this harder to do.

[grimm1966]

Thanks Jackdawg, 

I'm having so much fun it should be illegal.   That makes sense, it's no wonder that most medieval forges were inclosed.  I'm thinking I might be able to build a small overhang or enclosure with fire brick?  

[Charles R. Stevens]

One thing is getting it good and hot, with out burning it, it is akin to tosting a marshmallow. You can hand high yellow on the outside and high orange on the inside. As a wise smith told me, clean, flat, heat and pressure. Get 3 perfect and it will stick. My biggest problems starting it were not getting it evenly hot, not burning up on the outside and cold on the inside. The other problem was triying to smash heck out of it. A firm solid smack to stick it, not waking the unholy heck out of it. After you get it good and stuck, you need to heat it and weld it two more times.

[jlpservicesinc]

The largest reason for not using charcoal is because of the expense vs bagged coal and the longevity of it.. Now not so much a price difference as coal used to be cheap at 3.00 a bag vs 10.00 for charcoal.  In a perfect world it would be charcoal or coke and my preference is charcoal..  

ok, so lets establish a base point..   

A fire for forging using charcoal, soft coal, hard coal, coke, lignite, wood, or oil, or gas (propane, natural gas,etc etc) and all fire management for oxidizing, neutral or carbonizing is basically the same thing..     Fuel and air ratios..     Where this changes is as the air is introduced into the fuel  the fire goes through each of these phases..   in a gas or oil fired forge once up to temperature you can use a choke or fuel pressure to get some adjustment and then keep it there until you run out of fuel.. 

In a solid fuel forge these areas of the forge fire are transient (Oxidizing, neutral, carbonizing)  and simply based on how much air you put into the fire.. 

For charcoal a side blast forge is recommended for several important reasons..  1 of which is how the fire behaves and how the charcoal (dust, cinder, ash) actually insulates the fire above it which can translate into a smaller fire to get the same heat for a given section of metal..   With a solid fuel forge you are always anticipating or forecasting how much fuel you will need 2-5minutes from now and this is called fire management.. 

A bottom blast on the other hand doesn't offer this same insulating effect even if all the cinder, ash is allowed to settle on the bottom.. instead it just plugs up the grate.. 

The other factor that comes into play is with having side walls  with all the cinder, ash and dust it is very well insulated an the heat is concentrated into the work piece as it's reflected by the walls..  

A bottom blast was designed for coal and coke use which the materials themselves become the insulating wall so to speak which is forced in from the sides.. Charcoal on the other hand can just be dumped on and banked out..    

Enough about design..     But ideally if you are going to run charcoal,, move to a traditional designed side blast based on what you want to work on to get maximum BTU out of your fuel.. 

As to blast and what is going on in a solid full forge. It becomes understanding that you are in control of the blast.. The heart of the fire is where you do nearly all your heating as this is a Neutral zone and you won't have air attacking the steel as it's a Stoichiometric atmosphere.. (again changes with blast)

With this being said...  If you are understanding what is going on and you add enough air to reach this = neutral atmospere on top of the fire (like when using coke) the flame of the fire becomes a neutral atmospere and scaling is just about 0 and yes you can reach welding temperature but the heat is coming up from the bottom and it's only the flame and heated fuel directly under the metal that is neutral (the heart of the fire is oxidizing)
 

With charcoal while you can weld or heat or control the top of the fire and minimize fuel consumption It's all blast related..  A bottom blast will always use more charcoal then a side blast because of how the fuel burns differently and how much less charcoal needs air..  As you increase air volume you need a large fire (more fuel) to reach stoich..  

One other thing,,  When doing the plates like that with stacking using an oxidizing fire and clay coating will offer the best results.. And ideally you want to do it at just below welding temperature as the clay will act as a welding flux in a neutral environment..

To keep the plates the same thickness the heat has to be the same throughout the bunch and ideally you need more than 2 plates because they will not move at the same rate.. You will also need to have the correct hammer weight wise to effectually move the metal at the center of the bunch just as much as on the outside..  Ideally you are looking to slip the plates..  This skill set to be performed takes a lot of practice to pull it off.. Save the wrought iron and practice on 1/8's sheet until you can get all the sheets in the bundle to be the same thickness when done as there is more to it then just the clay..  

[Charles R. Stevens]

One misconception with coal and charcoal, pound for pound they contain the same amount of energy, it's when you compair cubic feet that things change.

i find I just put enugh charcoal over the top to his the stock.

last, if your burning up stock you are getting hot enugh, infact the more carbon the lower the welding temp.

[jlpservicesinc]

Its true..  The little dissertation I put together lacks a lot of the little details or big details depending on what you find to be important.. Thanks for pointing it out..   BTU's per pound is BTU's per pound and there are charts to look this information up..  5lbs of charcoal is a lot more volume wise than 5lbs or bituminous coal.. Again this is part of the main reason in how much air you put into the fire to reach a neutral zone..  or a stoichiometric air/fuel mixture.. 

By covering the material you are in essence creating an oven or blanket to help hold heat in..

 There is much information I left out as it would be a book.. Ideally working with someone in the know is the next stepping stone after videos and forums.. 
You don't always need to cover metal at the top of a fire is you are running a neutral fire higher up caused by running more air through a taller fire and this will move the heart of the fire upwards and outwards consuming more fuel.. 

interesting thread. 

 

[Charles R. Stevens]

Your answer was far from incomplete, infact it's better than my incoherent ramblings. 

[grimm1966]

Thanks guys, all good points.  Mea culpa.   I didn't want to imply that charcoal is better than coal/coke, I should have said that this technique increases charcoals usability.  

I have also started to keep a pile of charcoal to the side and let it catch fire so I have a supply of fresh coals to move onto the fire.  Which is a general practice for coal/coke I think. Weather permitting I'm hoping to do some more forging today.  I really need to get a pavilion, tent, or something to cover the forge and anvil so I can work whatever the weather is.  

[Charles R. Stevens]

I find that just using fresh charcoal to cover the work works fine, it provides insulation and shields my eyes from the heart of the fire.  A cover is important as ash and water are very carosive  

[grimm1966]

I cover the forge and anvil when I'm not using them with a tarp, but it's not big enough to use as a roof over them.  I'm going to have to save my shekels and get a pavilion or something more permanent. 

[jlpservicesinc]

1 hour ago, Charles R. Stevens said:

I find that just using fresh charcoal to cover the work works fine, it provides insulation and shields my eyes from the heart of the fire.  A cover is important as ash and water are very carosive  

+1   adding or banking on the side is not necessary unless you plan to do a larger section on the next heat..  IE after your current anvil and hammer forging time.. Charcoal will catch and be usable pretty much as soon as it's applied while you are taking your current heat.. 

The charcoal should be applied before the heat in preparation for the next forge operation..  " Fire management".. 

This will make the charcoal just about immediately available to heat the steel.. 

[jlpservicesinc]

Charcoal flares up (starts to burn) or extinguishes/ashes faster (not enough fuel) for a given fuel volume than soft coal.

lean fire manangement is what a lot of the asian and african smiths adhere to..  Reason being is they understand what they are forging and how to make the fire work for them (good fire managment skills) ..    

With charcoal because of how fast it can catch an produce heat vs soft or hard coal its nearly instant and so if you need a little more fuel to finish an operation you can just add it where using coal would be a big no, no..   With coals and coke the fire management goes up,  Coke not nearly as much as soft coal..