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Old 08-24-2010, 06:11 PM
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Default Upright Drum Smoker-Kamado Hybrid

All,

So, I am here looking for info on refractories. I know there are a bunch of custom bbq forums out there, but I am interested in taking a bit of a different route than what is talked about in those. This seems to be THE place to talk about refractories.

Let me first explain what I am thinking about doing. I want to make a hybrid of a traditional upright drum smoke and a kamado.

What I am thinking about is a 30 gallon carbon steel drum inside of a 55 gallon. I was thinking I would line the 30 gallon with "some kind" of refractory and fill the void between the two drums with some kind of insulation. I will bond the lids together with insulation in between and also have a layer of refractory on the underside of the smaller lid. I would like the two lids to come on and off as one piece. The bottom third of the inside barrel I would like to have a thinker layer of refractory as that is where the firebox will be. The firebox BTW will be expanded metal, so thus will flow plenty of air. I will have a piper coming through near the bottom that passes through both durmas as well as the refractory with probalby a ball valve as a damper on the outside.

This is a take on some other ideas I have seen but I am taking things a bit further. What do you all think?

So, here are some questions:

For the insulating layer between the two drums could I simply use loose perlite or vermiculite or does it really need to be bonded with some kind of cement? Which do you think is better?

I know kamados are made out of castable refractory, does anyone know if it is insulating or dense castable?

In general does anyone have any thoughts as to what type of refractories and mortars I want to use to line the inside, keeping in mind it will be bound to carbon steel? Also, how thick does it need to be? I was thinking possibly as little as 1/2" as I will have a separate insulating layer on the outside. As I mentioned, the lower are would be thicker. I was thinking some kind of castable or mortar for the full liner and firebrick for the thicker lower portion.

Thoughts? How thick? What type of refractory? Is there something that will hold itself in place over this much vertical or do I need an inner tube mold? Will anything bond well with the outer carbon steel?

I am going to use a forced ventilation system to be able to maintain very prcise temperatures. Looking at a product called BBQ Guru for this peice.

Thanks ahead of time for any coments...
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Old 08-26-2010, 07:41 AM
Il Pizzaiolo
 
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Location: So. Orange County, CA. USA
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Default Re: Upright Drum Smoker-Kamado Hybrid

I have a little Kamado grill and it had a great part in starting my journey to my Pompeii oven. My little Kamado is made of fired dense clay. I think the newer versions, the Big Green Egg, are made with a castable refractory. Dense, yes they are. This style of grill is heavy and it shares the idea of stored heat. I’m not really clear why you think you want to use 2 metal drums, as a containment you could use a single outer metal drum and then line it with insulation and at the innermost chamber use a castable or mortared firebrick. I think you want a significant amount of thermal mass, I don’t think you’d get your desired result from less than 1 or 2 inches of inner liner. I think what you might find that’s close to what you envision is an Indian Tandoor. These little guys tend to be used at high temps, like our Pizza ovens. Are you thinking about lower temps, below 350F?
As for the BBQ Guru, I’ve looked at this too and thought that some modification to schedule the oven startup and allow some sort of heat profile to be programmed might be interesting, but since a pig can be done in the WFO at lower temps, I think my time is better served elseware. The getting the oven started at a set time, without actually being there isn’t tough with a timer and electric charcoal starter.
Keep the dialog coming and you’ll get all the info you desire.


Sorry I should have been more awake when I responded to the thread. Are you looking to keep things at low temps only?


Chris

Last edited by SCChris; 08-26-2010 at 08:54 AM.
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  #3  
Old 08-26-2010, 08:32 AM
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Default Re: Upright Drum Smoker-Kamado Hybrid

I don't understand why you need refractory material in this application, except for the firebox. Don't smokers run at a low enough temperature that it wouldn't bother the steel drum at all?

One thing I can say is that slathering a half inch of any kind of mud on the inside of a smooth steel drum is not going to be a success, particularly if it's subjected to thermal shock or expansion.

On the other hand, it may be that I don't understand what you're trying to do at all. Perhaps a sketch would be helpful?
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Old 08-26-2010, 10:24 AM
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Default Re: Upright Drum Smoker-Kamado Hybrid

What is the end result/use you are looking for? With the firebox offset outside the drum(s) I would think you would have to have an awefully hot fire going to allow for any substaintial heat to build up in the inner drum.

Using the Big Drum Smoker (BDS) and its clone the Ugly Drum Smoker (UDS) the fire box is below with a heat deflector. This seems to keep fairly accurate temps using holes in the bottom around the fire to open and close as needed to increase or decrease temps. I have seen on cold nights guys wrapping them in welders blankets and maintain the same temps.

Are you looking for portability? It is going to get real heavy real fast using cements and mortars.

Be interesting to see what you come up with. Keep us in the loop.
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Old 08-26-2010, 11:13 AM
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Default Re: Upright Drum Smoker-Kamado Hybrid

All,


Thanks a ton for the replies. After speaking with a local expert on refractories I think I may me changing my game plan a bit. I don't think I am going to go with a castable at all. First I think the castable is just going to be too complicated and too expensive to really get done right for this application and second heat will penetrate to the drum and especially if I am looing to insulate the from the outside there will proably be too much expansion to the drum. With rods running through both the drum and the refractory there is going to be too much chance of cracking the inner liner. Even if I didn't insulate I think you are right I may still have expansion problems. I also agree, that I don't want the weight to get too out of controll. I am planning on putting in casters, but still want to keep it reasonable.

This is a UDS design, so no offset firebox.

As to the reasons for wanting both refractory and/or additional insulation, I am interested in reducing fuel consumption and maintaining extremely even cooking temperatures and I believe that in concert with the electronicly controlled forced induction and the refractory and insulating layers I can acomplish this.

I would also like the option to use this as a fairly hight temp grill. I will have to see how feasible that ends up being as the upper gate will be a fair distance from the firebox but I thik the refractory will help with that. I would love to be able to do some serious seering with it, but that is really just a nice to have feature, primary purose is for low and slow.

Not looking to make money with it, which is is another reason I want to keep cost within reason.

So here is what si am thinking now. I think I am still going to go with the drum within a drum design with loose perlite between the two. That should help greatly with insultation and I won't have to wory about shifting and cracking. I am thinking about just simply using firebicks probably just in the lower third. A layer on the botom and a ring around the lower third. Not sure if I even need to bother with mortaring them or not. Might just go with a cylendar of expand metal to help keep them pushed to the sides.

I would still go with a pipe and ball valve as the damper.

Thoughts on the new design? You think I should just go with the bottom portion for the firebick. It will obviously keep the weight down and I would think it would be plenty to help stabalize the temperatures. The perlite on the outside would do the rest I would think. My hope is that the outer durm should remain touchable (at least for the low temp cooks).

As to the heat deflector the primarly option I have seen is simple plate carbon steel, but I was also thinking I might just be able to use a pizza stone. Thoughts?

I had another idea today. I am thinking about above the fire box and below the deflector putting in a #6 (a little bigger than 6 inches diameter) Cast Iron "clean-out" ferrule with a brass cap that would pass horizontally through both both drums. I thought that would be a neet way to add wood chips if needed. I would make a chip loader from 6 inch vent duct with the ends seeled and a chunk cut out from the lenght on one side so that I could put chips in, slide through the ferrule and just spin it to drop the cips on the fire box.

I know this is probaly all hard to picture. I will try to sketch something, but my drawing skill a somewhat lacking. Need to see if I can find my compass.


Again, thanks for all the replies. Great discussion so far. I look for to further dialog.

Chris
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Old 08-26-2010, 12:17 PM
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Default Re: Upright Drum Smoker-Kamado Hybrid

I think if you could build a basket out of expanded metal you could line it with firebricks around and on the bottom. Maybe put another piece of expanded metal around the inside to keep them from toppeling. The firbricks in the basket will give you some retained heat as well as stabelizing heat. Make some handles for the basket that you can secure some stainless Steel chains from to facilitate lifting and dropping the basket. This will solve for 2 issues, the high searing and grilling as you could tie off the chains with the basket in the up position and you could also load more wood and charcoal if needed.

The drum inside the drum with loose insulation would be better and lighter as it would alow for inner drum expansion. I also think you will have a cool outer drum. However remember that any metal leading out from the firebox will take heat with it and cause a hot spot on the outer drum.

A pizza stone will crack after awhile with so much heat, if you can find something more durable I would go that route.

I have toyed with getting a guru for several of my cookers, but (and don't take this the wrong way) I found proper fire management is all I need for any of my cookers. With your insulation idea and firebrick basket you are going to loaded for bear when it comes to fuel conservation and heat retention. Give it a go without the guru for awhile.
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Old 08-26-2010, 01:29 PM
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Default Re: Upright Drum Smoker-Kamado Hybrid

Oh man. Great idea on the moveable refracroty firebox. I dig it. I probably could also just sit it on the defuser if I want to avoid the chains. I suspect stainless stell chains can't be too cheap.

I hear you on the heat from the metal that passes through. Not sure if there are any alternatives though. Probably just paint those with some red high temp paint to remind me not to be stupid. I am open to ideas. I had thought about using clay pipe for the iner section then epoxying the metal furhter out, but I doube it will really avoid that much heat and it would definetly complicate the assembly.

So, as to the difuser, you think some plate carbon stell is still my best bet?

BTW, I did look into a stainless ssteel 30 gallon drum but it is like $400 vs $40. If properly seasoned with a shortening and some nice high temps, all of the carbon steel and cast iron should get a nice protective carbon coating.

The part I am still concerned about is the pipe coming in the bottom as the damper. I was thinking black iron, which is just steel pipe that has protective paint. I assume all that paint should burn off during seasoning so hopfully won't release any contaminaits during cooking later on, but I am to entirley sure. I think the other option could be brass or bronze on the protions that come in to the inner drum. Obviously stainless is an option again, but want to watch costs. The other portion I am conerned about is in regard to the ball valve. I know a similar design has been done before but I am not sure about the valve failing under the temperature transfer through the pipe. There are several materials to choose from for this as well. Maybe I'll pose that one if one of the general bbq forums. Thoughts?

I will say I found a nice product that should help and might even block a little of the heat. I found a ceramic inpregnated high-temp, food-grade, thread tape that will both help seel the thread as well as stopp the threads from seizing. It is like 15 bucks a roll, so not too bad.

Here is a link in case anyone ever has need for such a product:

Sealant Tape, Ceramic, 1/2 x 600 In - Pipe Sealant Tape - Thread and Gasket Sealants - Adhesives, Sealants, & Tape : Grainger Industrial Supply



One last question, does anyone know a source for round heavy guage stainless grill grids. Either off the shelf or custom. Probablly need around 18 inches in diameter.


Thanks again,
Chris
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Old 08-26-2010, 03:24 PM
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Default Re: Upright Drum Smoker-Kamado Hybrid

Hey Chris,
A few years ago I observed a custom installation at the local Orange County fair where a vendor had lined a clamshell smoker with refractory, firebrick splits to be exact. These splits were butted up against each other in a grid but I could not tell how they were attached to the steel smoker. A fire was burning away on one end of this 12-13' long pit. A few months ago I tried to do the same thing and lined my 30" offset smoker with as much firebrick as I could fit inside and was surprised at the results. Using my firebox, it took forever to heat up my pit (I was using lump oak charcoal) and it occurred to me all that heat went into the firebricks. The net result was twice as much fuel needed than a normal burn. I am now convinced the way to conserve fuel is to insulate the outside of the pit with a ceramic insulation 'jacket' and maybe a firebrick or two inside. This is for pulled-pork and brisket smoked ideally at 212F until internal meat temp plateaus at 160 (where collagen starts to break down) and then the internal pit temp remains constant until the meat reaches 190F. I'm not sure a refractory liner will be efficient in a smaller pit unless the fire is built directly inside.
John
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Old 08-26-2010, 04:16 PM
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Default Re: Upright Drum Smoker-Kamado Hybrid

I think the worst enemies of UDS's are cold outside temps and windy conditions, therefore, insulation would be a great benefit, in addition to retaining heat within the drum. I am not sure that adding thermal mass would make much difference here, in fact it will require more fuel to bring the drum up to operating temp.
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Old 08-26-2010, 04:22 PM
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Default Re: Upright Drum Smoker-Kamado Hybrid

"For the insulating layer between the two drums could I simply use loose perlite or vermiculite or does it really need to be bonded with some kind of cement? Which do you think is better?"

Mix it with cement. Something like an 8:1 mix. Then it will still be in place when your steel drums rust out.
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