coal erupting from forge

[TheIronTree]

HI folks,

 

This is probably a newb question, but I've noticed that on my home made forge I can be happily blowing air in waiting for the steel to get hot and bang a load of red hot coals get spewn out of the fire pot luckily away from me most of the time.

 

I'm using small anthracite coal and mixing in coke from the last burn, I've got a clinker breaker which to an extent works. The pot is a truck brake drum cut down to about 5-6" about 16" wide with a clay pot that tapers to about 6" square where the air inlet is, also have noticed that the grate (cast iron drain cover) has melted badly the last time I used the forge.

 

For a while all is good till I get down to using only coke then I randomly get eruptions, the air isn't too much as it's barely blowing in.

 

Anyone shed some light on what I'm doing wrong?

 

Going to clean it out tomorrow after she's cooled overnight. Been on for two days, was making some tight 100mm (4") scrolls in 16mm round and square (9/16"??). And today was bending 50*8mm flat (2"x5/16"?) The hard way to a 13" I/d at 180 degrees.

 

Dan

[the iron dwarf]

you should try 50mm handrail section the hard way with a 40mm inside radius, that causes a few odd words to be said.

 

as to your eruptions, are you getting a clinker in there blocking it a bit

[L Smith]

Yea coke tends to get lighter in weight as it burns. Try putting more coal or coal with it I bought 500# of coke once about the size of potatoes coulden't believe how light individual peices were!

[Everything Mac]

I seem to be getting the same thing with coke if it is at all moist. Could that be your issue?

All the best
Andy

[Dan C]

Anthracite can pop as well if it has moisture trapped inside.

[John B]

If your grate is melting, then I would suspect the fuel,

 

It may seem a silly question but what does the clinker look like and form as? The reason I ask is because if it is forming into quite a solid lump. this will deflect the heat back down into the grate (causing it to burn), and still heat above as the air escapes around the edge of the clinker allowing  the fire to heat metal above,

 

It could also cause eruptions as it breaks down as Dave the Dwarf suggests.

 

What size anthracite are you using? Personally it's a fuel I steer clear of for various reasons, the clinker/residues being the main one.

[Glenn]

Look to see that the ash does now accumulate and fill the air tube. Ash below and fire above will place the grate in a position where it is NOT cooled by moving air, and will burn out.

 

As others have suggested, I would think trapped moisture is causing the fuel to fracture.

[Frosty]

Another thought occurs to me when you say the blower isn't moving much air or off. If it's not moving enough air to prevent combustion gasses from settling into the tuyere it cay ignite and detonate when you give it a little more air. things like CO are still flammable and can do exciting things.

 

If you get exhaust gas detonation it can just be a little poof, a huff that lifts coals from the fire a little bit, up to a bang that throws burning embers tens of feet around the shop.

 

Frosty The Lucky.

[TheIronTree]

Hi folks,

 

The ash has never got to the point of blocking the inlet as there is at least 6" of 80mm square tube (all I had at the time!) Air inlet is 60mm pipe with a flange to fit my blower onto. 

 

The coal I used because I thought anthracite was better for some reason, it was free tbh as my coal man gave me it to try, might try some

bituminous if he has any as I can't get coke easily anywhere local.

 

Yes the clunker is rock hard, almost glass like and hasn't got any bigger than half a gold ball size so far, that's from like a full days running (only used a 15l bucket of coal during the day).

 

The blower is definitely blowing air through enough to push any gasses up I would say, only gets limited if I think it's going to blow bits out, you can see it starting with a few yellow embers spitting then it just lets go!

 

Haven't cleared it out yet as I've had other work to do so I don't know what state the second grate I put in yesterday afternoon is in but from the sudden drop of fuel down the inlet with a slight poke this morning I'd say it's shot.

 

Dan

[TheIronTree]

GGot time to clean her out this eve, as suspected the grate was toast, weirdly only above the air inlet (tuyere?) The frame as such round the outside was intact to an extent, I'm just wondering if because the inlet comes up into the pot and then there is about 1.5" all around before the clay starts if that's causing problems? Also noticed lots of black coal/coke near the inlet where the stuff above has the grey/white/brown?

 

Dan

[Frosty]

Okay, my next thought is: lose the cast iron floor drain grate. Cast iron has a much lower melting temp than mild steel, a simple row of 12mm round stock with about 8-12 mm space between makes a fine air grate. (I'm just winging it with the mm so adjust to reality for me okay?)

 

The casters at the iron pour typically pour Cast iron at 2,000f so it melts a bit cooler than that. Mild steel typically melts around 2,700f, the higher the carbon content the lower the melting temp. Mild steel will be much more durable for the air grate unless it's designed to be a cast iron air grate.

 

I'm thinking the sparklers you're seeing aren't coals but sparks from the cast iron burning. If I'm correct, that is why the air grate would be more damaged above the air inlet where there is more combustion air at a lower velocity. Turbulence directly above the air supply pipe will cause a lot more linger time around the air grate so it won't cool it like across the way. If that makes sense, if not you can model it with smoke blown into a clear plastic model.

 

Frosty The Lucky.