Charcoal barbecue for heating metal

[JohnPW]

Numpty question:

I'm planning on using charcoal to heat steel for hardening, can you just put some charcoal on a suitable container or surface, eg a roasting tray, old frying pan or some bricks?

In other words, do I have to use a purpose made barbeque?

 

[NickWelford]

I believe you will need forced air with it. Coals (coke) would be better, but blow some air in with some kind of air blower.

 

[woodpig]

Depends on how hot you want to get the metal. You can easily melt steel with charcoal and an air source:

 

[wizard]

Charcoal of a good quality and a hair dryer will do the job and better than coke. i make my own charcoal both for the barbecue and my forge

 

[woodfarmer]

As above, most things will work. But, a brick type burning chamber will reflect heat into the burning chamber and can produce a hotter fire. It helps sometimes to let the items to heat and stay hot for a little while to help the surface carburise (a bit). I have to admit I tend to use an old pot bellied cast iron ex BBQ. But then I usually only use it for forging or stress relieving.

 

[rafezetter]

Depends on how hot you want to get the metal. You can easily melt steel with charcoal and an air source:

Just out of curiosity, is that a concrete V shaped furnace? I ask as I've wondered if concrete pavers could be used as a base for a brick forge - or even paves for the sides too - but I thought as they aren't fired like bricks they would shatter?

 

[Eric The Viking]

It looks like the inside of ridge tile to me, in which case I may experiment when the weather improves

For decades, I've got barbecues up to temp. quickly by starting with a propane (or MAPP) blowlamp and then using a hot air paint stripper. It has two big advantages over a hair dryer: the air is more directed, and the business end is supposed to be more heat proof.

My 30-year-old B+D one died recently. For some reason the mica sheets supporting the element fell apart, though both the motor and the element itself were fine. Boy that thing took some punishment - it didn't owe me anything, but I bet they're not made to that standard any more!

Anyway, being in urgent need (always happens on a week-end, dunnit?), I bought a Silverline one. It's much bigger, has a shorter cable and is less comfortable to hold, but it has two speeds and a temp control that can be turned right down. So it'll be handy. Also, the totally ridiculous 'knuckle protection' bit can probably be drilled for bolts to mount the thing to something fixed.

Has to be said, though, that it doesn't feel well made so I'm not expecting it to last long.

 

[Eric The Viking]

Which reminded me: I think the melting points of copper and of carbon steels are fairly close (1200 & 1400deg.C).

Does the team think one could get away with using copper piping to push air to the base of the fire in a ridge tile setup, or would the copper melt/oxidise away?

I have some coal-effect gas fires in the house. The newer ones use something like fibreglass to distribute the gas around the firetray, but the oldest one has pea gravel around a 10mm steel pipe with pinholes drilled at intervals. It wasted a lot of gas that burned badly at the back, so a while back I tried to bulk out the gravel at the back with some lengths of copper pipe.

I cleaned it before Christmas and retreived the pipe. The idea didn't work*, but the pipe survived pretty well - discoloured but not obviously eroded. I know it wasn't close to forge temperatures, but it made me wonder if it's possible.

 

[woodpig]

Just out of curiosity, is that a concrete V shaped furnace? I ask as I've wondered if concrete pavers could be used as a base for a brick forge - or even paves for the sides too - but I thought as they aren't fired like bricks they would shatter?

No, it's home made Refractory lining. Do a google for home made refractory and you'll find plenty of recipes. I think mine was: Bentonite (cat litter), Portland cement and Perlite. As a refractory it reflects the heat back making the most of the fuel you're using. In this case it was cast into moulds and then placed in a thin steel housing made from a bent steel shelf. A thick steel pipe with holes in it ran the length of the unit to provide an air blast from a hot air gun. I have some more pictures if you need them. Unit got scrapped sadly when I moved house but it worked very well.

 

[JohnPW]

Thanks for all the ideas.

Just out of curiosity, is that a concrete V shaped furnace? I ask as I've wondered if concrete pavers could be used as a base for a brick forge - or even paves for the sides too - but I thought as they aren't fired like bricks they would shatter?

No, it's home made Refractory lining. Do a google for home made refractory and you'll find plenty of recipes. I think mine was: Bentonite (cat litter), Portland cement and Perlite. As a refractory it reflects the heat back making the most of the fuel you're using. In this case it was cast into moulds and then placed in a thin steel housing made from a bent steel shelf. A thick steel pipe with holes in it ran the length of the unit to provide an air blast from a hot air gun. I have some more pictures if you need them. Unit got scrapped sadly when I moved house but it worked very well.

This looks like a similar set up but using "fire-proof bricks":
http://www.instructables.com/id/Folding ... /?ALLSTEPS

 

[woodpig]

I've not seen that instructable. I designed my around some unused steel shelving I had several years ago.

This is the basic steel structure.

And with the Refractory in place.

The hot air gun was only used as a blower, not as a heat source.

There are two types of Fire bricks, the old heavy ones and modern lightweight Refractory ones. The Refractory ones are very light and easily cut with a wood saw. If you can buy them locally that's good, I wouldn't expect them all to survive shipping though. It really is easy though to mix your own Refractory from one of the many recipes out there.

 

[woodpig]

EXIF says I took these pictures in 2008 so longer ago than I thought!

 

[dickm]

if you can find someone chucking out one of the old-fashioned big storage heaters, the bricks inside them are ideal for a simple hearth.

 

[JohnPW]

I was wondering about the use of a hair dryer to add air to the charcoal; can you just hold it over the charcoal so the air from the hair dryer just goes down on to it, or do you need to rig up a pipe to direct the air into the charcoal from underneath?

 

[Phil Pascoe]

if you can find someone chucking out one of the old-fashioned big storage heaters, the bricks inside them are ideal for a simple hearth.

I've never quite understood this thinking - surely bricks in a kiln or a forge are meant to reflect the heat back at the item being heated, whereas bricks in a storage heater are meant to absorb heat? The last thing you need when trying to heat something (especially with under powered gear gear, like most of us) is something absorbing heat. :?

 

[dickm]

Dunno about the theory, but storage heater bricks worked fine for me.
,

 

[Eric The Viking]

if you can find someone chucking out one of the old-fashioned big storage heaters, the bricks inside them are ideal for a simple hearth.

I've never quite understood this thinking - surely bricks in a kiln or a forge are meant to reflect the heat back at the item being heated, whereas bricks in a storage heater are meant to absorb heat? The last thing you need when trying to heat something (especially with under powered gear gear, like most of us) is something absorbing heat. :?

I think it's because, although they have high thermal mass, they conduct heat poorly. That's the reason they're in storage radiators: they get very hot inside, when the thing is heating up, and then 'leak' that heat out slowly over the rest of the day (at least, that's the theory).

So it's the poor conduction thing that's important in this case. As you say, they do in practice "reflect" heat back again (well, re-radiate it).

E.

 

[woodpig]

For a simple forge you can use either. Modern refractory bricks are quite fragile but will reflect more heat allowing you to get higher temperatures or use less fuel. The old hard bricks will probably last longer in an application like this though. When some folks build an enclosed forge they often line it with refractories but have a layer of hard bricks on the bottom for durability.

 

[sdjp]

Which reminded me: I think the melting points of copper and of carbon steels are fairly close (1200 & 1400deg.C).

Does the team think one could get away with using copper piping to push air to the base of the fire in a ridge tile setup, or would the copper melt/oxidise away?

Short answer: I'd go for mild steel over copper.

Although the melting points aren't too far apart, they are further than you recall: 1085 for pure copper, and 1585 for pure iron (carbon steels melt at a lower temperature; as with any solution).

There's more to than just melting point that for a tyure (air nozzle in a forge). In particular, at forge temperatures, the black iron oxide has a degree of self passivation; and iron that's just about to melt is a lot stronger and stiffer than copper that's just about to melt. It's fair to assume that whatever metal one uses will end up in the 'fully annealed' condition, over time. For copper, that's _soft_ - bend with fingertips sort of level, compared to iron.

Whilst it's not really a structural part, it doesn't take much imagination to foresee giving it a knock during the use of the forge, and that's the main thing I'd be concerned about with using copper there.

 

[Eric The Viking]

Thanks - points well taken.

I had some copper pipe knocking about, but can easily find steel instead, I expect.

E.