tempering cast iron woodstove

[Cord-n-8R]

I hope this is the right section for this post.

I have a cast iron Dutchwest airtight woodstove from the mid-80's. There were some internal parts (baffles & grates) that were deteriorating badly and needed replacing. I just recently was able to locate replacements and the recent warm spell we had gave me the oppurtunity to let the stove go out, give it a cleaning and install the new parts.

I remember reading somewhere that cast iron should be cured or 'tempered' by having several smaller fires before you begin full firing.

Can anyone explain what this should accomplish and 'exactly' what the proper procedure should be?

I know what tempering means and assume that it should prevent the warping/cracking that caused the parts needing to be replaced. I'm just not sure what the proper procedure should be. How hot should the first few fires be and what should the duration of each one be? I started a small fire last night, threw in a couple 2" sticks which burned for 1/2 hour or so with the door open and let it go out. How many of these smaller fires should it take to properly temper the cast iron?.... should they be progressively larger and longer?.... and should I let the stove cool 'completely' for a day or so before lighting the next small fire?

The weather's returning to normal around here and I'm anxious to start stokin' the fire again. 

   
   

[WH_Conley]

I may have been doing it wrong, wouldn't be the first time, but I have never heard of tempering cast. Always started using anything cast just like I would be using it the rest of it's, or my, life. Kinda got me interested in this theory now.

[Gary_C]

I think you are confusing seasoning of cast iron cookware and tempering of steel. As far as I know, and can remember, there is no such thing as tempering of cast iron.

But I am curious as to what you know about tempering. Just what do you believe is meant by tempering and what does it do to the steel?

[SwampDonkey]

I can't imagine anyone manufacturing and selling a stove that I can't go ahead and build a regular fire in. I wouldn't tell the insurance company or let word get out to the fire marshal. ;D

[SPIKER]

there are cases where the stove is new and is painted, in those cases it was/is common for several small fires to be built and or let heat very slowly to help cure the stove and prevent a hard burn of the coating at first. help it set.  but that being said I have not heard about this requirement for un-painted cast. (unless coated in oil in which case the cast smokes like crazy when heated, hotter the first fire the more it smokes small fires burn it off slowly and makes less overall smoke...

mark

[Cord-n-8R]

Well, I guess what I remember reading may have had to do with curing the stove when it was new to help 'set' the painted surfaces and burn off any oils or impurities without creating too much smoke but what I believe tempering means is to reduce the brittleness of hardened, or heat-treated, steel or other metal by reheating it to the proper temp. and then cooling it without quenching, thereby increasing the elasticity or 'ductility' .

Gary_C, I know what is meant by 'seasoning' cast iron cookware and am not confusing these process'.

After doing a Google search of 'tempering' and finding that my definition is pretty accurate, and tempering can be done to reduce cracking and warping, I've decided to just go ahead and burn several smaller fires, increasing the intensity and duration of each one.... I figure it can't hurt and if it prevents the parts from warping and cracking again,,, great! I s'pose it's possible that the deterioration of the parts may have been caused by overfiring but I'm usually pretty careful about that.

Anyway, thanks for your input, it may just have stimulated me to do more research the subject.       

[beenthere]

Cord-n-8R
Is it possible that the curing/tempering needed is done to the cast parts at the end of the casting process, prior to being assembled into a stove? Seems that would be the best time to do whatever would be needed.

[Cord-n-8R]

You would hope... but then again, you would hope that auto makers could make a 100 mpg car that lasts 250,000 miles. 

[Cord-n-8R]

Beenthere, My point is manufacturers may not always have the consumers best interest at heart... maybe they want you to hafta keep purchasing replacement parts.

I notice your kinda in my neck of the woods... are you a logger?... forester?

[beenthere]

Yup, I'm some of both. Mostly a hobby sort of player. 

I'm thinking a stove with early warp in the castings will go back to the dealer real fast. My present boiler has a cast iron door, and I don't recall babying it when I first fired it up, and it is fine after 20+ years. So am thinking it must have been seasoned/tempered/cured or whatever before put on the stove.
Have another Vermont Castings Defiant, and don't recall having to do anything special with it....except know that the oils from mfg. would stink the place up at first. It did, but have not had any warping problems to my knowledge.

I like that 100 mpg car.... ;D

[LeeB]

Don't nobody quote me, but it seems like I remeber reading someting about tempering cast iron in one of the old Foxfire books. However I got CRS real bad these days so I might just be dreaming.

[MrMoo]

Cord,
You are doing the right thing. Cast iron stoves do need to be tempered. The manual that came with my Vermont Casting Defiant Encore said that a series (4-5) of small fires need to be done to break in the cast iron. They said to build a fire up to about 200 degrees and let it go out and then let the stove completely cool down. The following fires should all get some what hotter until the last gets up to about 400 degrees. After that a normal heating fire can be built.
Keep warm

[Tom]

The wood stove I installed in the house in 1973 had the same instructions as given by Mr. Moo.
I don't remember the instructions saying why to do it though.

[Tom]

Swamp Donkey sent me a link to Vermont Castings   where there is a Manual in PDF.  Don't load it if you don't have a fast connection.  It's big-g-g.


Conditioning Your Stove
Cast iron is extremely strong, but it can be broken with
a sharp blow from a hammer or from the thermal shock
of rapid and extreme temperature change.
The cast plates expand and contract with changes in
temperature. When you first begin using your Encore,
minimize thermal stress by allowing the plates to adjust
gradually during three or four initial break-in fires.

So, I guess the proper word is conditioning and reason to condition is to relieve stresses in the metal. 

[Cord-n-8R]

The stove is 20+ yrs. old and this is the first time I had to replace any parts... and they were a grate inside the firebox and the baffle under the catalytic combustor, so they are probably subject to more intense heat. Consolidated Dutchwest was actually part of, or bought by Vermont Castings so your references are fitting. So it stands to reason that tempering to reduce brittleness makes sense.

Today I'm doing the fifth burn and will probably just keep it burning now since I normally just burn a medium fire with the stovepipe temp between 400-500 deg., unless it's really cold out and I need to run it hotter.

Thanks for the replies, I think other peoples input just helps to stimulate the brain cells.   

[tyb525]

I beleive catalytic converter is ceramic, so it should be ok. The grates don't do alot structurally, so they should be okay. My dad actually made new grates for ours, and they are solid, so it holds the coals longer which is nice, but the ashes can still be shaken down. The ash that ends up in the pan is pretty fine, so you know you aren't wasting good coals.