Forge Blower help...

[steve.h]

Evening all.
So I am trying to get my little forge running right. my current forge also doubles up as a fire pit for camping, its 40cm x 40cm and 12 cm deep, untill I have more funds this will have to do, I do intend to build a purpose built forge when funds allow. I have tried running it with my 2hp compressor, but even at full throttle the air delivery would only get my piece of 4mm an orange colour, bendable but I want to weld with it.

I have a 5" inline cenrifugal fan that does 225 M3 so that works out at 133 cfm, I read that if you reduce the pipe from the 5" to say 2" then this will increase the pressure of the airflow as well, So can anyone tell me if this is correct and also will I loose any cfm because of the reduction.

Would the 5" with reduction run my little forge hot enough to weld with (and my next forge of around 60cm X 90cm), so far I have only run it with wood, so burning down to charcoal and also adding some bagged charcoal to it. I do intend to buy a couple of sacks of coal, but not sure what to buy, do I use smokeless as this would help with keeping the smoke down and happy neighbours ??

I am loving what im doing so far but will be much happier when I feel like im going to melt stood infront of it.

Thanks for your input as ever.
Steve.H

 

[FranV8]

You would need the "fan curve" for the blower, it'll give you the relationship between volume flow and pressure drop.

What it needs is a plenum underneath the charcoal, into which the combustion air (from your blower) is blown, and then this air would permeate through the burning wood/charcoal. It's how it'd work on an industrial boiler too.

 

[rtbcomp]

I'd use coke. There are a lot of impurities in coal that could contaminate your steel.

 

[brightspark]

I'd use coke. There are a lot of impurities in coal that could contaminate your steel.

as said cokes a lot cleaner and hotter than coal. it can melt iron no problem with a blower

 

[gavuk]

Have a read....... here .........Steve ,Blackjack seems to have it covered

 

[Windy Miller]

I have made up a brake drum forge very similar to the disc one linked to above. The blower is an old hairdryer and the fuel is smokeless coal type stuff that I get at the garage. It works a treat and yes I do feel as if I'm going to melt when I stand near it! Proper coke would work better I think but the coal 'nuggets' that I use are good enough. Smaller chunks would be handy though, as would a better plenum chamber, but all in all it works surprisingly well.
It's a shame the OP is not closer to me as I will be getting it fired up this morning and he could have come over to see it in action!
I can post up some pics if anyone's interested?

 

[Jammy James]

I can post up some pics if anyone's interested?

Yes please i would be intrested to see it

James

 

[steve.h]

yes please, always interested in seeing what people are doing.

Steve.H

 

[chunkolini]

I have a neighbour who uses an old vaccuum cleaner to blow her forge, works a treat on a full sized forge, she has it sucking in clean air and no filter fitted, and has used it this way for years.

Chunko'.

 

[Drains]

Steve, following on from what Fran says

an increase in system pressure (eg smaller ducting), will decrease the cfm delivered. Some centrifugal fans are not designed to work well with much system pressure at all, the prime example being the "forward curved" type which you would find in, for instance, a car ventilation system.

Saying all that, your 5" fan will almost certainly work, in fact too well. You'll probably need to use a damper (a piece of something - metal, wood, a small child or dead cat) over part of the inlet to limit the cfm, or the fan will blow everything away.

"Blowers" are normally narrow, designed for pressure, not volume. "Fans" are wide, designed for volume. Hence forge blowers are narrow, and designed to push air through, no matter how much charcoal etc is in the way. They're also narrow as not much volume is needed, and more volume = more power, which would be a total pain on a hand powered blower.

 

[Windy Miller]

Well at last I have got around to uploading some pics!

First a view of the forge before I fired it up...



And then one of it burning...



The piece of steel you see heating up is about 25 X 6 flat bar.

Although the pice does not show it well, it was glowing a nice cherry red...



You will see from the first pic that there is a narrow grate in the base of the fire pot. This seems to work OK, but I am wanting to improve it somewhat. I find that the coals fall through the gaps after they break up into smaller chunks, and it becomes difficult to find a hot spot.

I am planning to fit a 6 or 8mm think circular plate in the base, sitting on a ring made from 10mm round bar. The plate would have 10mm holes drilled in a grid pattern to allow for the air flow. Do you guys think this would work better than the grate? Would I need a greater depth below the plate to act as a plenum chamber?

I would also like to extend the sides up a bit, as at the moment it is only about 50 mm deep. Also the use of 'real' coal or coke might be better, as I find that the large nugget things I have been using are too large, so it is quite tricky sometimes to 'bury' the steel in a real hot spot.

Generally speaking the forge works really well for what it is, but I would like to refine it a little to make it work REALLY well! Any suggestions?

 

[Hitch]

I got a fan/heater housing from a washer drier in me garage , wonder if that would do the business.

 

[julianthegypsy]

I run a centrifugal extractor fan on mine, but an old cylinder vacuum cleaner will work too. I use blacksmiths forge breeze, also known as beans, basically coke crushed into little nuggets. I have a flap valve which can be set to dump air to reduce the flow and sometimes put a bit of cardboard over the inlet to slow it down even more. On full bore it will fry inch bar if you don't pay attention.

 

[julianthegypsy]

Sorry, I just saw the photo. D'oh! Get a piece of plate and drill holes no more than six mm. six with one in the middle on about a two inch circle should do, then hook up your vacuum cleaner and have fun.

 

[Windy Miller]

Sorry, I just saw the photo. D'oh! Get a piece of plate and drill holes no more than six mm. six with one in the middle on about a two inch circle should do, then hook up your vacuum cleaner and have fun.

Blimey! I thought I would need masses of holes! Will that be enough?

 

[julianthegypsy]

Honestly, that will be plenty, any more and small bar will just disappear, you won't keep up with it! I'll try and find a photo of mine on full bore and bung it up when I can. I should add that mine is in regular professional use, and I use an oxy torch instead for doing odd fiddly bits. Somewhere on here there is a picture of a birdbath I made, the stem is a four foot piece of 20mm solid round bar, forged into a curve over the anvil and heated in my forge. And none of your "cherry red" either, bright yellow and way past scaling heat, I had to be careful not to burn it.

 

[pidgeon chit welder]

I seem to recall that during my apprenticeship in 1966 we used best welsh steam coal in the forge as it has one of the highest calorific contents around and made our own coke by rotating the burning fuel outer to inner as soon as it caught light and burnt off the yellow flame .
That way we had a variable heat source as needed .

 

[Windy Miller]

Well I took your advice Julian (well sort of!) and made a new base plate for the forge out of some 8mm plate. I forgot about the 6mm max bit and drilled 8mm holes, but it seems to work fine although it takes a bit longer to get it going now.

I wonder if I had a more powerful blower whether the 8mm holes would be more of a problem, but with a small hair dryer it seems OK so far, although I didnt have it going for too long as it was raining. Again!

The next mod I do will be to raise the sides a little, as I find that the coals keep rolling off the sides when I 'bury' the metal deep down in the hot spot. Maybe have a 3" or 4" high extension with a small (6"?) gap at the front to poke the workpiece through? Does that sound feasable?

 

[Stuggi]

I'd dish that plate a bit to create a pit around the ducks nest (the circle with holes in your forge). I'll take pics of mine when I get home, I have a quite big portable forge which can handle welding heat well when burning proper coal. The trick is to let the coal convert into coke before starting to weld, charcoal also works but it burns way too fast for my liking, and as I have access to a source of proper blacksmiths coal I wouldn't bother with charcoal. Look for a centrifugal type blower, it looks like a big version of the compressor side on a turbocharger.

 

[julianthegypsy]

Yep, if you can make a big dish to go round your bowl it would be great, and you can cut a piece away to let you shove bits in the side. If you hook a cylindrical vacuum cleaner to that and fill it with coke beans you will be rocking....
And forget all this nonsense about "cherry red" You want your piece bright yellow before you start belting it, and when it goes to dull red it goes straight back in the fire.