Not hot enough

Today I fired up my makeshift forge for the first time.
It's basically a repurposed old bbq, and a small hairdryer for blowing air through the holes.
It was not a big success. I succeeded in flattening the piece I was working on, but imo it was not hot enough. My pieces only got to be slightly red-ish.

The steel had to be hammered very hard in order to get it to do something.
Any suggestions for improving it in order to make it get higher temperatures?
Or is this bad enough that I have to scrap it and make something better?

Attachment 79422

Hey Bruno,
great work and you're almost there. i would consider enclosing the top. maybe just some fire bricks stacked - one on each side and a couple across the top supported by them as a roof.this should keep the heat in more. {just an idea} You really don't want to shape the steel too much if it is not hot enough as you will face cracking and damage the steel structure.
Hope that helps or inspires a better idea to do it on the cheap for you.
Regards
Adam

Thanks. Now I only have to figure out where to get firebricks and firecement. :)
Apart from making forging easier, it should also make it easier not to hammer dents into the surface of my anvil.
My anvil is an old one, made by a blacksmith for taking along to horse shows etc.
He made it himself. It is nice enough for what I do, but it was made for hammering iron, not steel. So it does not have the surface hardness of a proper anvil.

Companies that sell refractory cement for kilns will most likely have the items you want. There are different grades of fire bricks, you just need the low temp version ( cost Less).

I have actually done this before and know that this can work. I was just using a fire pit but the old bbq is great!

1. I might be mistaken but it looks like the ashes you have in there are from firewood. Use charcoal since the entire piece of it burns at once and will be hotter.

2. More airflow might be needed. I was using a shop vacuum and had the hose hooked up to the side that blows the air out. I used the handy mans secret weapon (duct tape) to attach it to a piece of pipe so I would not melt the hose. Then I stuck the pipe into the fire pit.

Doing this I was able to get metal a nice bright red. I used this method to harden a throwing knife of mine and it is still straight.

Hope this works for you or at least gets you closer to your goal.

Bruno,

The big question is what are you using for fuel? If you are using wood it won't get hot enough and the ash will block the air flow. I would suggest using raw charcoal not I repeat not briquettes. Briquettes have clay binders and other additives not conducive to forging. In the US Walmart carries raw charcoal it in 5 and 20lb bags. Some sellers call it natural charcoal. Charcoal needs a fairly deep fire 6" at least.

The hair dryer should be enough for the air supply-maybe drill out the holes bigger. Make you fire smaller. Can't tell from the pictures but if there are holes in the entire bottom of the BBQ then that is the main problem. You are diffusing the air over too large of an area. A razor blank doesn't need a very big fire.

Cheap kitty litter (bentonite clay) mixed with wood ashes and some straw will make a decent refractory. May crack some but just repair with more of the mixture. You may have to soak it for a while to get it to soften to a moldable clay. Place it around the out side of your BBQ and form a rectangle about 4-5 inches wide by 8 inches long by 6 or so inches deep. This will seal off the holes you don't need. Drill out holes still showing.

Putting a top on it will help but most charcoal and coal forge are open. Fuel, airflow and fire containment are the big factors.

The holes were only in the middle 6 inches or so.
I used wood charcoal, but not enough I guess. Not 6" thick anyways. And it was cheap stuff with bigger and smaller lumps, and the bigger ones were probbaly part wood inside still.

Do I understand correctly that you advise to put the insulation mix on the outside?
And I guess that I need to fill the entire bowl with charcoal then, 6" deep?

EDIT: Is it correct that red hot is the correct point for forging?
And while forging the metal loses heat. At what point do I need to put it back in the fire? As soon as it is no longer red?

Quote:

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Originally Posted by Bruno

The holes were only in the middle 6 inches or so.



Do I understand correctly that you advise to put the insulation mix on the outside?
And I guess that I need to fill the entire bowl with charcoal then, 6" deep?

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No.
Sorry, didn't explain very well. Meant the outside of the inside:confused:
Place the insulation mix on the inside of the bowl. The rectangle I described is a cavity centered over the air holes. You want to concentrate your fire over the air flow. So if you built a box say out of Styrofoam 5 " wide x 8" long By 6 " tall you would put it over the air holes and fill in your refractory/kitty litter around it. When the refractory dried you would pull out (probably have to break it up to get it out) your box and Voila there is your fire pit.

Quote:

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EDIT: Is it correct that red hot is the correct point for forging?
And while forging the metal loses heat. At what point do I need to put it back in the fire? As soon as it is no longer red?

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With most steels you want to forge at a dark to maybe bright orange heat. When the steel cools to a dark red reheat.

Thanks. And then when I use it, I fill the entire cavity with charcoal?

Quote:

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Originally Posted by Bruno

Thanks. And then when I use it, I fill the entire cavity with charcoal?

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Yep, maybe even mound it up a bit as well. Also, make sure that no air leaks between the hair dryer and the holes. The pile of charcoal will create some resistance to the air flow. The air will seek the path of least resistance so if there are any leaks they will let the air escape.

As you can see from the remains of the fire in the first picture, the hardwood charcoal is going to create a lot of ash and small pieces. You will have to clean them out periodically.

Today I bought refractory cement (which is suprisingly pricey) which I will use to mix with ashes and kitty litter to make the lining and cavity of my forge. I don't have straw handy, but I am going to try to use glass wool instead. it doesn't burn either, and should be reasonably good to hold everything together.

I'll take pictures along the way.

Consider this as a fire containment problem. You want to keep the heat in one place to get work done with it.

For this type of forge, burning charcoal or coal, an open fire simply radiates working heat into the environment and the hot gases and burning products randomly exhaust into the atmosphere. If you can build a bottom and some walls around that spot, of a fire resistant material like refractory (cement, brick, clay) then that material will absorb the heat and reflect the radiant heat back into the workpiece. A refractory bottom prevents heat lost to conduction through the bottom of the forge (in this case the sheet metal of the BBQ).

If you can contain the heat and fire products in a more confined place, the heat will concentrate and for that local spot will generate far more heat to work with. This also allows the smith to heat only a controlled portion of the work rather than the whole piece, but it also means that hot spot can be very hot and will burn the material if care is not exercised. The learning curve there can be expensive if using expensive materials. You're still on the low end where you are working up to the right amount of heat. :)

The smith can modify the shape of the walls for bigger or smaller work pieces by using bricks, or even simply a bigger pile of fuel. Sometimes though, the fire will expand into a fuel pile and then the fine small point burn you want is lost. Walls of some sort can be helpful in that way and also not burn as much fuel in an uncontrolled way. And, a drip can can be used to sprinkle water over the parts of the fire where you don't want burning and keep the hot spot smaller.

Further, piling fuel over the top of the hot spot to forms a sort of box to trap some of the hot product from escaping and acts as an informal layer of insulation. Most coal/charcoal fires requiring refueling frequently so a complete box is difficult to manage if you plan to work for several hours, so the natural limit of this type of forge is a bowl or a walled trench so more fuel can be easily added as the fire burns.

Charcoal is a very clean fuel, coal is not, so this method of forge building also allows the fire to burn away the contaminants in coal like sulfur, dirt and water (a process called coking) as the bottom of the top layer burns. With coal it is possible to bake this top layer into a hard shell of material as it cokes and it can function as a roof of sorts if you can figure out how to stuff more fuel into the bottom of the pit. But that's for more advanced pyromaniacs.

Gas forges, or the other varieties of non solid fuel forges, do the same thing in principle. They are generally either a box or tube of refractory and the burning products simply heat the refractory and that radiates heat back into the work. A big open tube is not very efficient at heat containment, so often the ends of the tube will be blocked or restricted to delay the exit of the burn and allow that heat to warm up the refractory. Less wasted fuel, less wasted time and money. These fires are less likely to burn steel because of the radiant heat principle. Their atmospheres are better controlled so there is less scaling/oxidizing of the steel being worked.

In summary, a stout bottom of refractory to keep the BBQ from burning through and whatever shape you want for a fire above that. Control the heat lost and keep it contained and you solve the problem.

I hope this makes sense.

Perfectly.

Tomorrow I'll be shopping so I hope to be able to start transforming my old BBQ.
As it happens, on monday I have a holiday because someone is making the floor of the bathroom.
With any luck I'll be able to make a decent airflow solution as well.

Good times.

Last week I improved my forge.

The ingredients:
- a bucket of ash
- bucket of water
- refractory cement
- kitty litter
- 1 lovely assistant (she always wants to help in the workshop)

http://onikudaki.be/gallery2/d/52-1/...8040212f991cf6

This is the top view. I made is a bit longer than necessary for razors. That way I can also make kitchen knives. The pit is 6 inches deep, and the walls are a couple of inches thick. The bottom is also 3 inches thick. The square in the middle is where the diffusor plate fits.

The mixture is about 3 parts kitty litter, 2 parts ash, 1 part cement. It is very sticky stuff to work with. With my second bucket of gunk, I figured out to add water to the litter first, because it absorbs like mad, and if dry it makes the mixture almost impossible to mix with water.

http://onikudaki.be/gallery2/d/55-1/...8040212f991cf6

The air holes are in the front of the pedestal I am going to attach a 4 inch fitting for air piping. The other end of that will be atached to a big fan.

http://onikudaki.be/gallery2/d/57-1/...8040212f991cf6

Nice Bruno!

Last weekend I fired it up for the first time. I did not have proper charcoal, so I used cocos briquettes. My main goal was to see whether the temperatures would be reachable. The first 15 minutes were pure joy, since the steel got to orange yellow temperatures. After 15 minutes or so, suddenly the briquettes collapsed and filled the entire firepit with black brown dust that smothered the fire.

That sucked. But as I said, I knew before that it was not ideal. At least the forge fullfills its purpose without a problem. The air supply was still a cheapo hair dryer. I am working on building a controllable air supply. Today I bought 75 pounds of charcoal. I could tell this was out of the ordinary so I explained what I needed it for. I asked whether I could get it in winter (I had all that was left), and he said that if I needed it, he could order more. He told me that it would sell sooner or later, and having it in stock during the winter was not a real problem

http://onikudaki.be/gallery2/d/59-1/...3159c9b83112cf

And here is the blank I tested on. The part that will become the tang is still the original size. The blade is the shape I hammered out of the blank. Not bad. This took me 15 minutes. It's not perfect of course. But for a first try it could have been worse. And compared to when I worked on the kitchen knife, I did not have to pound the hammer so hard to get the steel to budge :)

http://onikudaki.be/gallery2/d/61-1/...3159c9b83112cf

Briquettes produce too much ash with all the glue and other junk in the composite. Hardwood charcoal is the stuff you need. I have found that some restaurant suppliers will have it. If the fire is hot enough, nearly all the charcoal will be reduced, there is very little ash. Making charcoal is not difficult if you can't find the right stuff to buy.