Thread: Not hot enough

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)



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.



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.

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



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

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.