Giving a new baffle material a try

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peakbagger

Minister of Fire
Hearth Supporter
Jul 11, 2008
8,904
Northern NH
My 30 year old Burnham Wood boiler has four 4" by 17" long 1/4" thick steel baffles that form a shelf that sits above the fire box and reflects heat back into the fire along with redirecting the hot gases to the front of the boiler before going above the baffle through a bank of vertical heat transfer tubes with the remains of turbulators. I have no idea what they originally used for baffles as it was a used and abused boiler when I got it for free. My guess is they were not standard A36 plate but over the years as they burned out I replaced them with A 36. I would get a few months before they started losing thickness and drooping to the point that the fell into the fire, meaning I would have to fish out red hot plates in order to load more wood in and see a further decrease in efficiency. I have them cut up by a local supplier and usually have two sets made up. They have no technical folks and are pretty limited on what they stock so no options of going with anything beefier from them.

I was out of spares and the ones I have are getting pretty thin so its a PITA. So I ordered up some 410 Stainless plate today. Not cheap but going to give it try. It definitely has a higher temperature rating and is also supposed to be corrosion resistant so maybe It will not thin out as quickly. I bought a piece from an online seller so I will need to cut it to size. I expect my angle grinder is going to be going through a fair share of cutting wheels.
 
So I ordered up some 410 Stainless plate today. Not cheap but going to give it try.
You'll see a big difference...that 410 will last a loooong time in that application.
 
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Had better for the price ;)
 
I got my plate yesterday and cranked up my angle grinder with zip wheels to cut it. I now have 3 out of the 4 baffles in 410 Stainless. Now I get to see how long they last.
 
I have had three hot boiler runs heating up my storage (my wood boiler is run off or full bore with no damper) with the new plates and they look like new, no sagging and the finish looks new. I am impressed so far. Maybe there are other less expensive options out there but 410 SS seems to work.

The old A 36 carbon steel plates would sag and have surface oxidation soon after installing, They sagged different amounts so there were big gaps where flames could go straight up.

Assuming no surprises I am thinking that this material may be a fix for the rear wall of a Tarm Solo from getting thin. My idea is just cut a plate of this stuff and set it in place in front of the wall.
 
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One last update, its definitely holding up, no signs of warping or drooping and the surface looks like new.
 
One last update, its definitely holding up, no signs of warping or drooping and the surface looks like new.
I wonder how thin you could go. Would adding any insulation on top improve anything?
 
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Not sure, I expect 3/16" would work. In my setup I would not have enough room for insulation on top. My guess is it may make it droop faster due the temperature difference on each side of the plates.

I was considering trying kaowool board but it also was too thick and would get hit on occasion when loading wood into the boiler. With the old steel plates they would droop down in the way of loading and they would get knocked loose and then I needed to fish out red hot plates

It really is a coal/wood boiler optimized for coal but the coal option in no longer in the cards as the rotary grate is toast, been that way since I got it. It is definitely a beefy piece of equipment that doesn't owe me anything (since I got it for free).

The thing I also have noticed is with the plates flat and tight together is I think I am getting better combustion, It is quite noticeable that I get a better coal bed. I wish I still had access to a combustion analyzer. It would be tempting to order some thinner gauge 410 and see how it works for turbulators but I expect it would not bend very well.

I am unsure if the folks who do the baffle mod on fishers have the same issue with baffle plates failing but this would definitely help.
 
Another update, not so good this time, One of the plates drooped down with significant curve and fell out of its track. It lines up with the hottest combustion point. The adjacent plates are starting to droop a bit but nothing like the center one. I think I coudl flip those two but the center one needs to be bent back or replaced. There is little or no surface deterioration or thickness loss on the bent one but unlike carbon steel, it is not bending back. I backed my Rav 4 Prime over it and it didnt budge. I will wait and try it with the Unimog SEE which is 14,000 pounds. I wonder if the plate is just going to crack rather than bend?

I do notice that my wood consumption has gone up and the time between filling the boiler has gone down with it out. It has reverted to a smoke dragon except it always runs at full throttle.
 
Boy, that is surprising.
I wonder if you could use ceramic fiber board there for baffles...like almost all the stoves do?
 
I do have some Kaowool in stock but it would get beat up loading wood into the boiler at the top of the loading door is not much lower than the shelf where the plates slide in. The other bigger issue is the shelf is wider than the door so a single piece of kaowool will not go in through the door.
 
Is kaowool a "board" ?
I know you can buy a product to put on ceramic insulation board to make it hard/rigid. Guy that built rocket mass stoves told me about it...
 
Yes its lightweight board. Fumed silica powder is used to seal the fibers and make it more rigid. I have both in stock. Unfortunately it still will not fit inside the doorin one sheet. ;(

The silica is also needed to keep the fiber from going into the air into the users lungs. It is is cause of silicosis.
 
The steel baffles didn't go in one piece either, right?
 
No the are 4" wide by 17" long so they can go in through the door and be rotated in place. I could cut the kaowool board into similar strips but it gets even weaker.
 
That's why I was thinking that the fiberboard coated with the "rigidizer" might be a better alternative here...still shocked that 409 SS didn't last, you must run some seriously high combustion temps!
 
The yield strength goes down to only 33 percent or so from 200 F to 1300 F.
So you're left with 1/3 of its strength at high temp wood fire combustion.

Is it possible to weld a 1/8" thick 1" wide strip on the back for additional strength? Just laying flat as I presume the exhaust flows over the top of the baffle?
 
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Btw, 409 is a ferritic steel, and austenitic steels generally do better mechanically at high temps.

I think the plate suffered from creep here.

Titanium it is :)

Or Inconel (beast to machine, but welding a strip of that (if welding is even possible for Inconel.... Bolting? ) on the steel might work.

Screenshot_20240317-211328.png
 
Austenitic stainless steels have a coefficient of thermal expansion 30-40% higher than ferritic stainless steels, which can pose issues with warping and distortion of the material in service due to uneven heating of the baffle.

Inconel can be welded (some alloys at least), but like welding stainless steels it requires encapsulation of the Heat Affected Zone (HAZ) in a shielding gas such as argon to prevent discoloration or "sugaring" (chromium carbide precipitation), generally this welding is outside the skillset of the average welder.

If you wanted to try 400 series (ferritic) again, I'd get a shop to bend a rib or 2 into it.

Alternatively you could get some kind of 300 series (austenitic) and get a rib bent into that.

I'd see what your local metal shop has in stock. I know I can get my hands on 304 and 316 locally.

1710730923727.png
 
I cant do much with the one that fell out but I did swap the other two that are starting to droop by facing them with the droop upwards. As long as I swap them out on occasion they will hopefully correct themselves.
using the Kaowool board is problematical as the gap between the bottom of the vertical tube sheet and the plates is about about an inch and half and the board is 1" thick. That means it would have to hand down into the fire box to keep the clearance and that means its going to get tagged on occasion when wood is put in the firebox.

It was a free boiler and around 40 years old so I cant complain.
 
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A new update, My experiment continues with some interesting results. I installed the two less curved strips back in the boiler with the curve facing up. The assumption was they would droop down and at some point I would need to flip them. So far they hane not drooped down and it actually gives me a bit more room to load wood in the boiler. The first strip is too curved to go back in. Its only 1/4" think and 4" wide but I backed up over it with my Rav 4 Prime and it didnt budge. My Unimog is still in its winter nap with snow piled around it but will give it try once its running and I have cord or wood in the back. That should be around 3000 pounds.

My guess is some unplanned heat treating has occurred. Next time I have the torch out I will probably try heating it to remove some but not all of the curve.
 
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A new update, My experiment continues with some interesting results. I installed the two less curved strips back in the boiler with the curve facing up. The assumption was they would droop down and at some point I would need to flip them. So far they hane not drooped down and it actually gives me a bit more room to load wood in the boiler. The first strip is too curved to go back in. Its only 1/4" think and 4" wide but I backed up over it with my Rav 4 Prime and it didnt budge. My Unimog is still in its winter nap with snow piled around it but will give it try once its running and I have cord or wood in the back. That should be around 3000 pounds.

My guess is some unplanned heat treating has occurred. Next time I have the torch out I will probably try heating it to remove some but not all of the curve.
You can also pre heat it in a nice big outdoor fire. You can increase the heat of outdoor fire by burying a metal pipe with 1 end by the bottom of the fire and a blower on the other end. Basically making a forge.