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Stainless steel hood?


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I'm building a new coal forge and have a large part of a stainless steel drawer that is going to act as a hood. I know it's not the perfect shape but it seems to be about the best I could come up with for no cost.

I am a little concerned about the hood being stainless steel; will the stainless give off any sort of toxic gases at a high temperature or anything else hazardous I should know about? I'm not sure what grade of stainless it is.

Thanks, Wyatt

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No the stainless will be fine. Also it will be far enough to not get any extreme heat unless you built a wood or cardboard fire in there (which you probably wouldn't). Even at that stainless is fine. It's chrome plating and galvanizing that you want to keep out of the forge. For a stack, it won't get hot enough to burn the galvanizing so no worries there either. 

Is that 8" or 10" pipe? 10-12" is better for the stack. 

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As Daswulf said, the stainless will be fine.  The only real possible problem is some types of grain growth that can happen when certain grades of stainless sit for long periods between about 800F and 1200F...but at most that might cause a spontaneous crack near a weld or bend which is no big deal.

In theory, it'll have about twice the hot strength of carbon steel (though a little less cold strength) so there is some benefit if it happens to get stupid hot from the fire. If it's T304 (likely), it's good to about 1500 degrees without blinking. Above that it it'll degrade a hair but still shouldn't be a problem.

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Greetings Wyatt,

      I would rethink your hood design.  Some of your pictures the fire pot is positioned too close to your hood. Do some research on the correct size of the draft entrance. For sure get the 10 inch stack . Lots of info here on IFI . Just this ol boys suggestions. 

Forge on and make beautiful things 

Jim

 

 

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id suggest a 12" flue. 8 is small and 10 is doable. However, the least expensive 12" pipe is to use twp sections of that cheap single wall that you snap together. snap two together horizontally and you will have a 2' x12" section of cheap pipe. I believe this is close to the price of an 8" section.

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I'm sure 12" would be the best but I got quite of a bit of 10" for free from family so I'm going with that.

I also changed the design of the hood I'm going with, as Jim mention my hood design did not work at all. I went with a design very similar but with some small dimensional changes as the super sucker side draft. Should work much better. 

Thanks for all the great info, much appreciated

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10" flu has a cross sectional  area of 79.3 square inches.  That'd equate to a square opening of 8.9"  so it appears your changes are reasonable.  Because airflow isn't always as easy as the math says and you are modifying anyway, can that mod have a provision to adjust the opening a bit as you experiment with the forge running?  Might be easier to do it "temporarily adjustable" now and pin it down permanently later.  

Although I haven't worked with a super sucker like this, most seem to have the lower edge of the opening a couple of inches above the fire pit, unlike your photo.  With a temporary adjustable opening to tweak, you might also be able to get that to an optimal height for "sucking".

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51 minutes ago, Kozzy said:

10" flu has a cross sectional  area of 79.3 square inches.  That'd equate to a square opening of 8.9"  so it appears your changes are reasonable. 

That's the same math I did to come up with my final 8x9 opening. The adjustable opening probably would've been a good idea but it's a little late now... lol

And as for the bottom plate in the front, I didn't have it there originally so I could put stock all the way through the fire. I didn't want the hood to take up lots of forge space. However I did add one to it but left about a 2" gap in the middle for more versatility. 

The hood seems to work very well. The ducting system isn't complete yet so I just added 4 feet of 10" pipe to test it. I lit a small pile of leaves in the firepot and the smoke went sideways up the hood very nicely.

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Greetings Wyatt,

         Now your cookin. It would be best if you put a piece of cement board behind your forge so to cover the wood shelf . A chunk of hot coal on the shelf could be a big problem. Glad you are making progress and havin fun to boot. 

Forge on and make beautiful things 

Jim

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  • 1 year later...
On 1/3/2019 at 12:14 PM, Wyatt Kindler said:

I'll add a piece of insulation board behind it.

NO!!! :o Use concrete backer board on 1/2" stand offs, it's a good fire barrier and a 1/2" air gap will prevent heating the wall behind it. 

Frosty The Lucky.

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