I had an odd thing happen today. As I was closing down shop, I put a piece of metal in the fire to anneal it. It was an old rod from an oil pump. I brought it up to temperature and covered it with coke. Just as I unplugged the fan, it popped and threw coke against the wall.
Now the question: What happened?

Probably a build up of flammable gasses in the tuyere after turning off the air in the presence of an ember.

It's more common to get little gas explosions when you give it it's first air after taking a break like to forge something but it happens on shut down occasionally too.

The term "little" explosion is relative. There's a really good reason you usually see a bellows above the forge, it kept flammable gasses from filling it and making an explosive mixture. An explosion that size can do serious damage and injury not to mention blowing burning coals all over the smithy. In most cases though the only volume filled with gasses is a few cubic inches of tuyere so it's usually just an annoyance.

Of course you may have a Gremlin living under you forge who likes poking the fire out of the pot.

Frosty

I like the gremlin idea best. Even with the gate shut, there is a small brrrze that should keep gas out of the tuyere.

Had one pop back on me and the bellows forge cart, at the historic site, once. Scares the bejeebers out of ya!!!! Now I prop the ash dump open, when I take a break.

We had a bellows let go at the Ft Vancouver site in days gone by -

It was mounted above the forge and when it went, it blew out one side of the bellows, ripped it loose from one side of the mount (some stout lag-bolts came out) and blew apart the relief mechanism that was supposed to act as the weak point to keep that exact kind of explosion from happening. Real lucky no one was hurt.

Folks said they heard it go from across the site about 300ft away.
Those ol' gas gremlins can be nasty little fellas when they want to!

I over oiled my blower one time and it backfired, almost wet myself, and another time a rock slipped in with the coal went off and spewed debris wide and far, always have clean shorts handy in this business I always say.... well if I was clever enough I would always say that!

Good tip on the ash dump. I run charcoal so I don't see it too often but I have has flames coming out of the blower opening one time.

your fire goblin wasnt happy with you that day, thats what it boils down to.

Any idea how the gasses went UP into the bellows? I'd always heard they're heavier than air.

And YES, I'd forgotten to mention propping the ash dump open, though exploding coal gas will open it and dump the ash automatically.

Frosty

Jerry, it most definitely cleaned out the ash dump!! When the forge cart was built, they built the bellows even with the bottom of the fire pot. :(

Edited September 14, 200916 yr by CurlyGeorge
Forgot something.

Sounds familiar. I had a similar thread a while ago called Only One Eyebrow. It sure gets exciting at times :)

Jerry, it most definitely cleaned out the ash dump!! When the forge cart was built, they built the bellows even with the bottom of the fire pot.

Ah, that isn't uphill enough for sure. Usually they were mounted overhead.

On the other hand you could advertise it as fire pot speed cleaning for when you're in a hurry for a good clean welding fire.

If it happens at a demo tell people you're demonstrating a blacksmith's wedding tradition. It's a blacksmith bride's bouquet toss for ladies with calloused hands.

Frosty

shop - Blacksmith Photo Gallery
My forge has the bellows under the forge and I have never had a single incident so blaiming it on location may not be the answer. My guess would be to look to your valve between the two bellows. This is where the draw needs to be sealed against.
Gobbler

Quote from rmcpb: I had a similar thread awhile ago called Only One Eyebrow.

Hmmmm............... Maybe that's where the rest of my hair went!!!!! :D

The "pop" could have been caused from something as simple as a piece of foreign mat'l mixed into the coal/coke, that when heated caused it to break apart/explode. I have had this happen before during use - but not to the point of blowing coal/coke out of the firepot. This doesn't happen often but once in awhile. - JK

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Any idea how the gasses went UP into the bellows? I'd always heard they're heavier than air.


Frosty

if they were warmer than the air they would rise...and on the opening stroke of the bellows it may suck it up

Edited September 14, 200916 yr by fat pete

On a double lunged bellows the top chamber is the only one that is supposed to be connected to the forge and it doesn't have an opening stroke---it gets force fed from the lower chamber. If you are getting any back draw with it you need to check the valve in the middle board to make sure it's making a good seal.

With paired single action bellows you need to alternate the stroke carefully to avoid draw back; unless they have a very good check valve, (the ones Theophilus described in 1120 do not have a check valve; even though the bellows he describes for an organ had a check valve. So we infer that it was known but possible not used for metallurgical process bellows)

Edited September 14, 200916 yr by ThomasPowers

What Thomas describes is exactly what happened at FT Vancouver.

The bellows (double chambered) was mounted about 6' above the forge but the drawback pulled it into the top chamber when it ignited. Result: Big-Badda-Boom!