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William Bronson
Post     Subject: 7" Batch box rebuild

I haven't looked at sheets of 18/8 ss , rather I looked for what hotel pans are made of because they are the cheapest source of stainless steel I know of.
I think a full size hotel pan is close to the right size for the ceiling of a 6" batch box.
If it could survive as hot face,  the shape is ideal for holding thermal mass or insulation, though either of these might lead to an early demise.
Edit: I think the shape might also help prevent warping, but...

I imagine this in the place of the cast iron roof.
Your post indicated that roof has  a 1.5" air gap as its only insulation, with only a sheet if steel on top of that.
I imagine this works  like a steel barrel, allowing the metal to radiate the heat rather than accumulate it, keeping it alive despite the hellish conditions.
If this is the case, backing the cast iron (or 18/8 stainless steel) with insulation or mass might be counter productive.

If I understand the batch box correctly, the box must be able to withstand heat and abrasion, but insulation of the box itself is optional.
The riser must be insulated and resist direct heat , but abrasion isn't much of an issue.
Your builds seem to be decoupling the insulative/refractory/ abrasion resistant properties where where it is useful to do so.
It makes me wonder if a batch box rocket with a completely stainless steel or cast iron burn chamber could work.
I think air gap insulation or would be needed, so the metal box wouldn't sap too much heat, thus stalling the reaction, but it might work.
Pure speculation of course, we haven't even see if the cast iron makes it!




thomas rubino
Post     Subject: 7" Batch box rebuild

Hi William;      No, I have not tried  18/8 ss.
I see it melts at apx 2500F  so it could take the box temps.
My experience with RA330 another high nickel metal is it took apx 10 minutes for it to warp.
Maybe a thick .25-.50" plate of 18/8 might hold flat.  Not sure about the price though, I'm thinking it might be cost-prohibitive.
Currently, I am using thick cast iron as a top and so far it has performed flawlessly!
I also am trying a 12"x24"x2" firebrick as the roof on my 6" batch in the studio, it also is performing flawlessly!

William Bronson
Post     Subject: 7" Batch box rebuild

Thomas,  have you ever tried 18/8 stainless steel as the roof of the chamber?
thomas rubino
Post     Subject: 7" Batch box rebuild

Hi David;
Yes, I think you misunderstood a few things.
I rebuilt the core because the ceramic fiberboard roof was falling apart and I wanted a new roof.
I rebuilt the core because my bricks were looking a bit shady.
I rebuilt the core to try dry stacking bricks and using all thread.
Ha Ha I rebuilt the core because I am a Rocket Scientist and we must experiment and learn new and different ways... sadly, not always a better way...
So, I rebuilt the core because I could!

Super wool is superior to ceramic fiber blanket, in that it is safe to handle without long sleeves and dust masks. No itching and not bad for your lungs.
After being heated to riser temperatures then Morgan becomes hazardous to breathe and dust masks are suggested.
My dry stack core has morgan wrapped around it.
I am a believer, in using Morgan wool and creating five-minute risers.

I hope this clarifies things for you David.

david higos
Post     Subject: 7" Batch box rebuild

Hi Thomas,

Why did you decide to rebuild it?

Does the superwool blanket have the same problems than the ceramic fabric blanket?

Dry stacking the bricks of the core...  How would you complete this combustion chamber without a ceramic blanket surrounding it? What would you use to surround and insulate this mortar-less chamber?

I guess you would rather not use the blanket 5 minute riser. If so, what materials would you use for a riser?

I hope I didn't misunderstand some of your posts.
thomas rubino
Post     Subject: 7" Batch box rebuild

Hey Phil;
I don't have a solid answer on that but...
My guess is that it is both, volume (as Peters sizes are very specific).
And the turbulence produced by the flat roof, a specific distance above the port.

Remember;   The objective is to create a super clean ultra hot burn.
Peter has the test equipment and has tried many variants of the design before publishing his current final numbers.
We can make anything burn, but without test equipment we can not know how clean a burn we are getting.
Phil Stevens
Post     Subject: 7" Batch box rebuild

Is it a volume thing or is it the turbulence induced by the flat surface? My intuition says that if it were a flat enough arch and the chamber volume remains constant, it might work. A compression arch wouldn't need any mortar.
thomas rubino
Post     Subject: 7" Batch box rebuild

HI Phil;
Part of Peters design on a batch, is a flat ceiling a certain distance above the top of the riser port.
An arch although looking cool would not function as intended.
Also refractory cement will not hold at batch temps... I tried...

Now an arched pizza oven.... oh yeah!
Phil Stevens
Post     Subject: 7" Batch box rebuild

I wonder if the extra effort in making an arch or vaulted roof for the box out of firebrick would pay off in durability. I'd be inclined to try either cutting angles and using a keystone, or a timbrel vault with splits mortared in place using refractory cement. The former would probably be easier as long as you had a diamond saw on hand.
thomas rubino
Post     Subject: 7" Batch box rebuild

Hi Fox;
That roof photo was abrasion from careless, in a hurry loading of wood.
Degradation of the board itself did not help but it was our loading that destroyed it.
As a fiddle playing excuse...  that batch is run all day from early am to 8-10pm all winter long.

The earlier photo showing the shop dragon roof has normal degradation wear.
7" batch is So much easier to load than a 6"

Fox James
Post     Subject: 7" Batch box rebuild

Thomas, that is a great rebuild and and a good call using dry stacked bricks.
That  very bad degrading on the ceramic fibre board, I think Matt must be right as I have been using the same ceramic board components for years and it is still in working condition although probably not for much longer.
Anyway I wont be using any Ceramic fibre anymore as all the latest info points toward it being a very dangerous  material to play with especially when disturbing used material! The airborne fibers can lie around for years and even once settled can be air bone again if disturbed!
thomas rubino
Post     Subject: 7" Batch box rebuild

Hi Gerry;
Yes, some quality international rocket scientist help can really make a big difference!
Without you, it would not be as quickly done or as nicely finished as it is!
Thank You!

The RA330 roof is defiantly going to be watched closely. I want/need to find a replacement for ceramic fiber board.
After using ceramic fiber board in several builds I have come to the conclusion that it just isn't holding up.
Any abrasion at all and it disintegrates.   Prier  to being heated it is wonderful stuff, safe, easy to cut  and form.
After being heated it becomes very fragile and easily damaged.
In its defense, Matt says that not all CFB is created equal and there is a big difference in quality.
Apparently you get what you pay for.
Personally no matter how much I spend on CFB, I seem to end up with the low quality stuff...
I won't be using or recommending it on any future builds.

RA330 products;
The RA330 secondary stubs have proven themselves to be the best secondary air riser that money can buy.
Matt Walker has been using a 4 sided 1/16" RA330 liner in his tiny cook stove ceramic board core for several years now, with good results.
I wanted to test the RA330 sheet metal as a single roof panel in a firebrick core, to replace the fragile ceramic board.
I have a second sheet of 1/8" RA330 on hand to be installed in my studio dragon asap.
The ceramic board roof on that stove is completely shot... it is very lucky to not have caved in on itself!

So sad we did not have time to rebuild that stove as well while my international  help was here...
He was so busy chopping firewood and gardening that the time just slipped by us...
Guess you will just need to return, to help with the upcoming rebuild on the 6" studio dragon...
I'll leave the light on for you...


Gerry Parent
Post     Subject: 7" Batch box rebuild

Great rebuild and upgrade Thomas!
Always nice to have a little iternational help now and again.
The RA330 ceiling in the firebox is going to be an interesting thing to monitor to see how it handles.
The threaded rods squeezing all the dry stacked bricks together and as support for the heavy door is a wonderful innovation.
Looks like your ready now for the upcoming winter with a dragon that’s ready to breathe some serious fire.
jordan barton
Post     Subject: 7" Batch box rebuild

Beautiful! Great job thomas. I like the 1/2" threaded rod thru the works.

Glad to hear it roared first try!

Want to come to my island and build me one? Wait I would need to find a place to put it in my tiny house..... hmmm
thomas rubino
Post     Subject: 7" Batch box rebuild

Hi all, after 2 seasons of hard burning the 7" batch in the shop (AKA The Shop Dragon) was in need of some attention.
With the help of a visiting rocket scientist from Canada we did a  complete teardown and rebuild on the core.

The firebox was completely removed.
An enlarged quick change secondary tube with an RA 330 stub was fabricated and installed.
30 brand new firebricks were used to create a no mortar dry stack core.

Matt Walker has been suggesting on stove chat, that any mortar used in the core is doomed to fail.
He recommends going dry stack.  
I built my black and white walker oven as a dry stack to try his idea out and it has worked perfectly!

My dragontech door got 4 ears welded on the sides.
Angle iron was used to create a pull point from the rear of the core.
1/2" all thread  gently squeeze's the entire core snug together.
A piece of  1/8" RA330 sheet metal was then used as a roof.

The inside of my 6 minute riser was still in usable shape, but the metal around the riser port was seriously spalled.
The Morgan super wool inside  was still in good shape.
Using a respirator I removed the  lower 24" section  of super wool  from the damaged pipe .
I easily peeled off the hardened layer of superwool and was able to use the remainder as filler around the bricks.
The upper  section was reused and a new piece of  Morgan  high temp Superwool was used as the lower.
I shortened the riser pipe, switching from a 6 minute riser design to a 5 minute riser design. (No side port)
A square riser base was built to hold my shortened 5 minute riser.
The entire core was wrapped with 1" thick , 8# High temp Morgan Super Wool.

Despite the warm temps and a stone cold  bell this new updated version took off and roared like a true dragon should!