Stainless Steel Woodstove ?

[StihlHead]

Someone posted about building a copper wood burning stove on another metallurgy forum, and the consensus was that copper is just way too expensive and it gets too soft at the required temps for secondaries to burn (it becomes plastic). Also from a design perspective, copper is just too good a heat conductor to allow temps to reach the needed temps for secondary combustion to occur and the plastic/deformity issue would not really be an issue. So in the case of designing EPA type wood stoves, copper seems to not be the choice in materials with the added requirement for a firebox material with a lower heat transfer rate to allow temperatures to get high enough to burn wood cleaner.

Reverse-intuition strikes again when it comes to EPA stoves. Lower heat transfer metal allows for higher temps in the firebox to burn cleaner and more efficiently. Doh!

 

[Hass]

How about Aluminum?
Easily welded. Great conductivity, 95% of people in the world would believe it's stainless on first look. (and probably many looks thereafter)

Kidding...
They use regular carbon/mild steel for a reason

 

[StihlHead]

No good... Al has a really low melting point @ 1200 F. One overfire and you would have a raging inferno. But it would be nice to be able to make a stove out of beer and coke cans!

 

[MasterMech]

dune,
Sounds like you are familiar with copper welding ?
Done a bit of TIG myself but not copper so......what type
of shielding gas is required ?
Helium ?
rn

I occasionally do some TIG work on copper sheeting at work. Argon is the universal gas of choice for TIG. Does anyone still use Helium? That's old school and how TIG welding was orginally know as Heli-Arc welding. You definetley need some serious current. Like 200+ amps while working with 1/8" material. That means a liquid cooled TIG torch too. Usually need to pre-heat all but the smallest pieces and it helps to have a graphite plate or something else that is a thermal insulator (but will tolerate extreme heat) to place under the work. It is not a fun process. The torch angle and arc length are very critical. Too much heat will boil and oxidize the copper and too little will never get a stable pool to work with. Your filler rods should be super clean. With TIG gloves, the heat is so intense that even gripping the back of the torch as far away from the arc as possible, I have to stop every minute or so to cool down my hands. That's a bummer cause once you get the process rolling, the last thing you want to do is interupt it and start again.

It's such a nasty metal to weld I would exhaust every alternative means before setting on welding a joint.

 

[Dune]

Helium is not old school at all for certain applications.
Aluminum always welds better/easier with helium.
Copper and high copper content alloys benefit even more from the use of helium.
Using helium to tig is essentialy the same as having 30% more amperage at your power source, without having the torch have to carry the extra current.
200 amps for 1/8" copper is so marginal that it does explain a lot of your issues, especialy with copper. Is it a transformer power source as well (such as a synchrowave), adding to the agony?
My main welder is a 425 amp inverter, which is equivelent to 550 amp transformer.
Even my little 200 amp gas cooled inverter puts a 250 amp synchrowave to shame, and easily welds 1/2 inch or thicker, with pre-heat.

 

[Crane Stoves]

Stainless is nearly identical in density as mild steel so weight is not an issue. Cost definitely is, stainless is about 3.5 times higher than mild steel.

Also stainless has about 1/3 lower thermal conductivity than mild steel. Probably not ideal for a stove.

Stainless is very good for internal stove parts, the baffles I made for my stove are made out of 1/4 stainless. The first one I made was made from 1/4 diamond plate and it warped badly.
The stainless steel is holding up just fine.

this member answered this perfectly, the main reason stainless is not used is because it does conduct heat well and would need to be thin sheet metal stainless like used on the old Petit Godin's, stainless is also very expensive to buy and even more expensive to work with (requires heliarc / tig welding, cant be drilled effectively, etc). even if you had free stainless available its not wise to use it to build a heating stove (a cooking stove maybe were you dont want to conduct heat to the outer parts of the stove to burn your hands when frying an egg might be OK to do) LOL hope that explains it.... GL

 

[Dune]

this member answered this perfectly, the main reason stainless is not used is because it does conduct heat well and would need to be thin sheet metal stainless like used on the old Petit Godin's, stainless is also very expensive to buy and even more expensive to work with (requires heliarc / tig welding, cant be drilled effectively, etc). even if you had free stainless available its not wise to use it to build a heating stove (a cooking stove maybe were you dont want to conduct heat to the outer parts of the stove to burn your hands when frying an egg might be OK to do) LOL hope that explains it.... GL

I agree with your post for the most part, but for clarity; yes stainless is harder to drill, but is certainly doable.
As for welding, I chose stick, MIG or TIG depending upon the size of the job (MIG for large jobs) thickness of the metal (stick stainless is easy and produces beautiful welds on thicker metal) or the perceived quality, thin metal, or out of position weld ( TIG is best for out of position or thin metal).

 

[Crane Stoves]

make no mistake.... welding stainless is an art and requires some degree of skill (trying to stick or mig a stainless stove would most likely buckle the material) and ive never heard of a machine for homeowners that could effectively weld stainless, you can stick cast iron too but that does not mean it can be done for safe long term use in a stove that heats your home. drilling stainless can be done if you have a Bridgeport in your backyard.... if not, you will just loose all your hair and enter a sych ward at the local hospital LOL. no sir...stainless steel should not be used as a project stove to heat your home! any Stove Company or Stove Manufacturer like myself will say the same thing...

 

[Dune]

make no mistake.... welding stainless is an art and requires some degree of skill (trying to stick or mig a stainless stove would most likely buckle the material) and ive never heard of a machine for homeowners that could effectively weld stainless, you can stick cast iron too but that does not mean it can be done for safe long term use in a stove that heats your home. drilling stainless can be done if you have a Bridgeport in your backyard.... if not, you will just loose all your hair and enter a sych ward at the local hospital LOL. no sir...stainless steel should not be used as a project stove to heat your home! any Stove Company or Stove Manufacturer like myself will say the same thing...

Like I said, I agree with most of your post.
Not saying to make stoves out of stainless.
As to the welding lessons though, you are barking up the wrong tree. I make everything and anything out of stainless steel
I MIG, TIG or stick, depending, as I said.
The welding process chosen does not determine warpage, total heat input versus metal thickness does, but there are ways to aleviate that, such as heat sinks. Contrary to your opinion though, TIG inputs MORE heat than either MIG or stick.
I don't keep my Bridgeport outside, it would get too rusty, but regardless, stainless steel drills perfectly well with a sharp bit, and correct speed and feed rate. No, it is not easy for beginers or the inexperienced.
As to the cast iron, I have been repairing cast iron for over 30 years and have burned many a box of sticks doing so, and repaired uncounted stove parts. Stick is the prefered method of welding cast iron whether you realise it or not.

 

[Crane Stoves]

agree with you dune... but ill stand by thoughts that your a pro metal fabricator (and most people are not). Stick is preferred for welding cast iron but unless your very good folks will whined up with a puddle of ugly spatter and cast iron that has been compromised around the area of the joint (10 times more brittle then cast iron already is).... i damb sure wouldn't want to overfire a welded cast iron home heating stove (at least on any structurally important parts like the combustion chamber) YIIIKES! but it is good that pro's like you exist to help the rest of do things that simply shouldn't be done by a novice <333

 

[kettensäge]

Someone posted about building a copper wood burning stove on another metallurgy forum, and the consensus was that copper is just way too expensive and it gets too soft at the required temps for secondaries to burn (it becomes plastic). Also from a design perspective, copper is just too good a heat conductor to allow temps to reach the needed temps for secondary combustion to occur and the plastic/deformity issue would not really be an issue. So in the case of designing EPA type wood stoves, copper seems to not be the choice in materials with the added requirement for a firebox material with a lower heat transfer rate to allow temperatures to get high enough to burn wood cleaner.

Reverse-intuition strikes again when it comes to EPA stoves. Lower heat transfer metal allows for higher temps in the firebox to burn cleaner and more efficiently. Doh!

Interesting thread.
I suppose you could build a plate steel stove and have it copper or nickel plated.
Not that I would do it, but I guess that way you can have the look and thermal performance without all the headaches?

 

[MasterMech]

... ive never heard of a machine for homeowners that could effectively weld stainless,...

Funny, I've got quite a few items around work that were glued together with a Millermatic 140 (110V). I imagine any small 140amp MIG would do equally well. Machine is good up to 1/8" stainless.

 

[Crane Stoves]

Funny, I've got quite a few items around work that were glued together with a Millermatic 140 (110V). I imagine any small 140amp MIG would do equally well. Machine is good up to 1/8" stainless.

Yea i do like the new 110 machines from Lincoln and Miller, ive never tryed stainless with them but i guess id attempt it if i had reason since i had to sell my trailblazer.... Im not sure i would trust any welds on stainless that were not tig welded though but thats just me (im sure someone skilled could use several methods) just in my day Tig was always the proper way to weld stainless.

 

[MasterMech]

Tig is fantastic on stainless (especially thin stainless) because you have zero spatter and much more control over the heat. You can make some very pretty welds with the Tig torch. Thin stainless also requires tricks like back-purging from time to time to prevent the weld from oxidizing and that usually goes along with the TIG process. But where looks/spatter don't matter and/or access is tough, I rock the MIG all the time. Helluva lot faster and if it's set right, the welds are every bit as strong.

 

[Dune]

Spatter can be eliminated when MIG welding stainless by using one of several tri-mix gases. Argon-CO2 mix is going to cause excessive splatter (and other problems) when MIGing stainless steel. Most manufactured S.S. items are robot MIG welded.

TIG can do miracles to stainless, but stick actualy works very well too, for thicker metal. Stick stainless' main limitation is out of position.
It doesn't want to go up hill at all. Some people have developed a method of welding vertical with stick, but I don't trust it for structure.
It seems more like a series of large overlapping tacks than a true 100% fusion weld. I will often whip out a TIG torch just to weld the verticle portion of an assembly which can''t be rotated into the flat position.

The use of aluminum or copper heats sinks in contact with the metal to be welded can reduce distortion greatly, some shops going as far as having thick aluminum bench tops. Patience is your best friend when dealing with very thin stainless.

 

[Lindane]

Anyone ever heard of one being made from stainless steel ? Would the reason for them not to be available be weight and cost ? Any other thoughts on the matter ?
Also any possible way someone could post a picture of the internal part of a PAPA BEAR FISHER ? so as the plate can be seen ( plate that the gas has to travel under thru the fire to get out the exhaust...hoping I stated hat correctly

 

[Lindane]

Tig is fantastic on stainless (especially thin stainless) because you have zero spatter and much more control over the heat. You can make some very pretty welds with the Tig torch. Thin stainless also requires tricks like back-purging from time to time to prevent the weld from oxidizing and that usually goes along with the TIG process. But where looks/spatter don't matter and/or access is tough, I rock the MIG all the time. Helluva lot faster and if it's set right, the welds are every bit as strong.

 

[Lindane]

my husband made me one out of mild steel if that is the same and I love it
[QUOTE="jeepin1121, post: 81957]

 

[bholler]

my husband made me one out of mild steel if that is the same and I love it
[QUOTE="jeepin1121, post: 81957View attachment 227523

The clearances to combustibles and the floor protection are both lacking greatly. Your install looks very unsafe

 

[SSExperiment]

I made a 304 SS stove out of 3/8" plate that I purchased as scrap. (Old filter press plates) It was cut with a plasma cutter and a LOT of grinding, stick welded mostly with 1/8" 309-16 rods. (about 20 lbs)

Being so thick, the warping was minimal, but small parts pretty much require preheating to prevent serious cool-down movement. It has a full width baffle leaving a 2" transfer area to the upper chamber, firebrick floor and a cast refractory door and door-side wall.

Two intake ports feed the fire directly, two feed pipes that go through the bottom of the fire and dump just in front of and below the window. Stove pipe is 10' of SS, 6" .190 wall tube.

It is about 18" x 20" deep by 24" tall. How does it work? It lights easy and drafts extremely well. The window blackens immediately but clears as it heats up. It heats up quickly. The reflectivity of the interior surfaces combined with the refractory make for great burns, immediate action when refueling.

BUT:

I knew that SS "holds" heat, moves more with heat, and in general behaves differently than mild steel. Watching the stove turn a golden straw color, I realize that it's cresting 700F.. with a dull red circle forming below the window.

You'd think it would feel painfully hot, but it doesn't. Run hand past the window and it's intense, not so much past the steel. Hot, but not overly intense.

The surface is ground with flap discs, just to shape it and knock down welds. Turns out the emissivity of any polished metal is super low... a couple hard mineral deposits on top from the first fire actually feel hotter despite being the same temp.

For fun, putting a 2x8 solid mild steel unfinished block on top, going to see how it feels. Then look at roughing up or oxidizing the surface- have had interesting results adding oxide layers to SS by putting pieces in coals overnight. Also, the secondary air is hard to tune, may have too much volume and a cooling effect.

This will be a sauna stove, btw. So, can it be done? Sure. Would I do it again? Not sure. Fun experiment but easily takes 3-4 times as long for a garage fabricator. Once I figure out how to get a little more radiation from it, maybe I'll be sold.

Also- it convects wonderfully, being 18" off of the floor. Very strong laminar flow follows the profile of the angled top until they meet and rise with considerable force.

 

[SSExperiment]

I made a 304 SS stove out of 3/8" plate that I purchased as scrap. (Old filter press plates) It was cut with a plasma cutter and a LOT of grinding, stick welded mostly with 1/8" 309-16 rods. (about 20 lbs)

Being so thick, the warping was minimal, but small parts pretty much require preheating to prevent serious cool-down movement. It has a full width baffle leaving a 2" transfer area to the upper chamber, firebrick floor and a cast refractory door and door-side wall.

Two intake ports feed the fire directly, two feed pipes that go through the bottom of the fire and dump just in front of and below the window. Stove pipe is 10' of SS, 6" .190 wall tube.

It is about 18" x 20" deep by 24" tall. How does it work? It lights easy and drafts extremely well. The window blackens immediately but clears as it heats up. It heats up quickly. The reflectivity of the interior surfaces combined with the refractory make for great burns, immediate action when refueling.

BUT:

I knew that SS "holds" heat, moves more with heat, and in general behaves differently than mild steel. Watching the stove turn a golden straw color, I realize that it's cresting 700F.. with a dull red circle forming below the window.

You'd think it would feel painfully hot, but it doesn't. Run hand past the window and it's intense, not so much past the steel. Hot, but not overly intense.

The surface is ground with flap discs, just to shape it and knock down welds. Turns out the emissivity of any polished metal is super low... a couple hard mineral deposits on top from the first fire actually feel hotter despite being the same temp.

For fun, putting a 2x8 solid mild steel unfinished block on top, going to see how it feels. Then look at roughing up or oxidizing the surface- have had interesting results adding oxide layers to SS by putting pieces in coals overnight. Also, the secondary air is hard to tune, may have too much volume and a cooling effect.

This will be a sauna stove, btw. So, can it be done? Sure. Would I do it again? Not sure. Fun experiment but easily takes 3-4 times as long for a garage fabricator. Once I figure out how to get a little more radiation from it, maybe I'll be sold.

Also- it convects wonderfully, being 18" off of the floor. Very strong laminar flow follows the profile of the angled top until they meet and rise with considerable force.

Update: stove burns hot inside, definitely puts off heat better than before when it was shiny/new. Generally have to close intake and pipe dampers quite a bit, or it burns through fuel too quickly. Overall, functional and should be durable, but does NOT put out (radiate) the same amount of heat per fuel load as a mild steel stove. I will not build a SS stove again, even with free material. And absolutely not if the material is less than 3/8” thick. The only real benefit, besides durability in my opinion, is the SS stovepipe keeps itself clean due to decent burns and the amount of expansion/contraction per cycle- loosens and flakes off any creosote. Fun experiment but the consumption/output is getting a little old now that the novelty has worn off.

As further proof of the lack of radiant heat: added 15 gallon water tank and a 6” x 9” water jacket. With the same fuel charge as before, the sauna reaches the same temp and the water is also hot. (The top 1/3 at least) So the heat conducts well to the water jacket area, instead of going up the chimney.

 

[snobuilder]

Update: stove burns hot inside, definitely puts off heat better than before when it was shiny/new. Generally have to close intake and pipe dampers quite a bit, or it burns through fuel too quickly. Overall, functional and should be durable, but does NOT put out (radiate) the same amount of heat per fuel load as a mild steel stove. I will not build a SS stove again, even with free material. And absolutely not if the material is less than 3/8” thick. The only real benefit, besides durability in my opinion, is the SS stovepipe keeps itself clean due to decent burns and the amount of expansion/contraction per cycle- loosens and flakes off any creosote. Fun experiment but the consumption/output is getting a little old now that the novelty has worn off.

As further proof of the lack of radiant heat: added 15 gallon water tank and a 6” x 9” water jacket. With the same fuel charge as before, the sauna reaches the same temp and the water is also hot. (The top 1/3 at least) So the heat conducts well to the water jacket area, instead of going up the chimney.

pic or it didn't happen....LOL

 

[SSExperiment]

pic or it didn't happen....LOl

Pic is above, here’s a firebox pic- ashy creosote on left is at the water jacket, and you can see the window square.