Heating time

[RhysKawka]

So ive built my first charcoal forge with a controlled air flow with a 1200w hair dryer. And i was just wondering, at an estimate how hot you think this forge could be getting at? And also with this estimate how long it would take for a railroad spike to reach cherry red colour?

[Charles R. Stevens]

Properly built your charcoal forge can burn up steel, be patient heating steel, it can take 10-15 min to heat up a peice of 3/4 or 7/8" stock to a good orange heat. The second heat won't take but 2-3 min.  

[ThomasPowers]

Rhys; what's the time it takes to get my vehicle from 0 to 100kph?  It runs on gasoline.  If you find it difficult to give an exact answer as you need to know a *LOT* more details; well that's what we find with your question too.

Charcoal was used for smelting, forge welding, melting steel for over 1000 years before the first use of coal in smithing.  So if your forge is not getting hot it's probably a design issue and you have not provided a picture or a very detailed description of it to us and then ask detailed questions about it.  Please provide more data!

[SmoothBore]

For the sake of general information and enlightenment .....

The "1200w" rating of your hair dryer, is in reference to the heat it imparts into the air stream, ... and is only superficially related to the volume of air it provides.

( There is probably an advanced, and highly esoteric formula, that could inform us about the volume of ambient air, needed to dissipate the hair dryers heat output, without exceeding a temperature deemed "safe" by the insurance Underwriters Laboratory. But nobody really cares about that. )

What matters, is that the air volume produced by the fan in the hair dryer, is sufficient to adequately oxidize the fuel.

I would GUESS that this is true, ... but for all I know, your Forge might accommodate 10 cubic feet of charcoal, ... rather than the more typical  .25 cubic foot.

A properly oxidized charcoal fire, will easily exceed 3000F

 

It's also important to differentiate between "lump" charcoal, ... and Henry Fords pressed "briquettes".

Lump charcoal tends to burn faster, and therefore hotter, than an equal amount of charcoal briquettes.

It's my understanding, that among those who fire their Forges with charcoal, the lump variety is much preferred.

 

.

 

[RhysKawka]

Im currently using lumpwood, and i have a firebrick construction of 2ft by 1.5ft roughly. I know its not entirely accurate but ive done a quick test and its taken me 12mins and 36 seconds to get a small cast steel wrench cherry red. Any idea on the temperatures i might be getting?

[Charles R. Stevens]

Hot enugh to burn up the wrench. 

Are we talking bottom blast or side blast? How big is your tuyere, what style of tuyere, depth ect. Forges are like lady's, they are all beautiful, but they all have their perticulars.

[ThomasPowers]

What colour do you mean by "cherry red"?  Colour perception is extremely dependent on person and environment

Here is a chart in C:

 

[RhysKawka]

Okay so i have a side blast forge, its a 3inch diameter iron pipe about 2.5ft long. And the colour (in low light) was round about light red

[Buzzkill]

1 hour ago, RhysKawka said:

Im currently using lumpwood, and i have a firebrick construction of 2ft by 1.5ft roughly. I know its not entirely accurate but ive done a quick test and its taken me 12mins and 36 seconds to get a small cast steel wrench cherry red. Any idea on the temperatures i might be getting?

Is that 12 minutes 36 seconds from the time you lit the forge, or the measured time after you felt the forge was up to temperature and added the wrench?  That seems like a long time if it's the second option and a wrench which I will assume was 3/8 or less thick and probably less than 3/4 inch wide in the shaft part. However, even that doesn't give you a good idea of the maximum temperature you are reaching with your fire unless you left in there much longer and it never ended up higher in the color spectrum.  If you have your fire pot constructed correctly and you have fuel for your fire, the determining factor on the temperature you will achieve is the air flow.  Either way too much or too little air can make your fire cooler.  In between that, more air = hotter fire.

[Frosty]

3" is WAY too large for the blast, 3/4"-1" will concentrate the heat in a fire ball, I like to call the heart of the fire but that isn't catching on. Oh well.

What's the shape of your fire, round, trench, etc.? It makes a difference, though side blasts typically work very well in a trench they work just fine in a bowl shaped "pot". On the occasions I've used charcoal it's been in the field so rammed mineral earth made my table and fire pot. Sometimes a steady breeze a piece of pipe and some sheet metal was my blower air source. Bricks on stood edge makes a good general trench if stacked in parallel rows. 4.5" x 4.5" x 9" is a good working size. Not perfect forget perfect good enough is excellently good enough.

Fuel feeds the fire but air make it hot. You need to localize the air for two main reasons: first to concentrate the heat in one controlled zone. Secondly to conserve fuel a 3" dia. blast might as well be a wind on a pile of fuel, it'll blow over the outside rather than through the fuel.

Place the tuyere pipe about an inch off the floor of your fire "pot" blowing across the deck. Pile your fuel about 4-5" deep directly in front of the tuyere, cover the end even.

Even a blow drier provides way more air than a forge needs for most small scale uses, a RR spike is small scale. Forget the heat switch on the blow drier it's a waste of electricity to a forge fire. Place the output of the blower so you can direct it away from the air supply pipe, you won't need nearly that much air most of the time. Too much air can literally blow the heat away from your work while oxidizing it, these are B-A-D things, don't do it.

Another aspect of air blowing through or past too far or quickly is fuel size. The chemical reaction of oxidization (fire) only happens where fuel and oxy come in contact. Large lumps of fuel have a relatively smaller surface area to volume ratio than smaller. This means air can only contact the surface and passes on the oxy unconsumed. Break up your charcoal to walnut  or smaller size, peanut size is a good bottom limit. With the increased surface to volume ratio the reaction is faster and more concentrated. This consumes the oxy quickly the fire is literally hotter and the remaining charcoal in the pile insulates the heart keeping it hotter.

You bury your work in the fuel pile in the heart. Too close to the air blast and unconsumed oxy will attack your steel, scaling, even burning it. Placed above the oxidizing zone your work is in the hottest part of the fire and out of the oxy. Above the heart is above the HOT zone but is a good place to preheat work, etc.

Remember, small bits of fuel, moderate air blast, place your work in the sweet spot, heart, fire ball, whatever you wish to call it. Most importantly keep an eye on your steels but do NOT stare at the fire, IR will damage your eyes. No UV from this kind of fire but the IR is dangerous. Anyway, keep an eye on your steels and have your moves planned BEFORE you take your work out of the fire. You have literally seconds to do your forging so know what you're going to do, have your tools arrayed and in hand when you pull your steel then take it directly to the anvil, vise, etc. We all need to take a look at what we've done and plan our moves just do it BEFORE you put it in the fire.

Frosty The Lucky.