Looking for specific input on camping stove design

[trucky]

*Or, if I just missed the threads with the information I'm looking for, kindly let me know which ones to read through!

Hi All,

I've combed through this site this afternoon, but have had trouble figuring some things out.

I'll be living in the back of my pickup truck for the next year, and would like a rocket stove (in dimensions similar to, perhaps a little bigger than, the one included at the bottom of this post) to be my means of cooking. Problem is, all the cheap/portable DIY designs outlined on youtue or elsewhere have the intake, burning chamber and chimney in some sort of steel (stove pipe, soup cans, etc), which, as folks here have pointed out, inevitably burns through. So, my questions are:

1. Would a higher grade stainless work? 310 or 330? Or would that merely prolong its death? In this paper (linked to in another thread), the author writes, "The 310 stainless may be somewhat difficult to obtain. Damon ordered a 24 gauge sheet from the East coast. It was not cheap: around $300 for a 4 x 10 sheet, which will produce approximately 15-1/2 elbows for stoves." I would gladly spend $20+ for the price of a stove-worth of 310 stainless steel if I could somehow find it. Ideas? According to Azom.com, 310, 330, and 321 would potentially work: On 310: "Good resistance to oxidation in intermittent service in air at temperatures up to 1040°C and 1150°C in continuous service. Good resistance to thermal fatigue and cyclic heating. " On 321: "Good oxidation resistance in intermittent service to 900°C and in continuous service to 925°C. These grades perform well in the 425-900°C range, and particularly where subsequent aqueous corrosive conditions are present. 321H has higher hot strength, and is particularly suitable for high temperature structural applications."...And 330 is even more heat tolerant than those two, apparently. So, now I just need help locating some!

2. I spoke to someone at Silverfire.us about their "Survivor" model camping stove, but the guy on the phone wouldn't tell me the grade of metal used inside. All he said was "the refractory alloy we use doesn't have a comparable rating to stainless steel," but he wouldn't divulge more than that. Is suitable "refractory alloy" obtainable, and without a bulk order? What should I look for?

3. Two years ago, user Hpmer responded to a newbie (like me!) that, for a basic emergency stove, "...for the vermiculite/perlite, I'd suggest you mix that well with clay soil or clay slip as the stove pipe will burn out and any loose insulation will flood into the burn area. I've had success with a mix of clay:ash in a 1:2 ratio. Makes a light weight "brick-like" material once it is fired. Finally, I've had good success using a 4" horizontal feeder tube connected to a 6" heat riser. The larger riser seems to contribute to a cleaner burn. I've used 6" institutional food cans."

Given the approximate dimensions of the stove in the image at bottom, would a 3'' thick clay/ash cylinder, acting as both combustion chamber and insulation, last more than a few months without cracking/crumbling? Would a thinner or thicker wall resist degradation better than 3"? Is there some kind of glaze that can be applied to the interior to make it more robust?

4. In a different thread three years back, Moderator Peterberg suggested using refractory cement:  "The filling in refractory castable is made of ground porcelain or firebrick, depending on the temperatures it can withstand. The kind I am using is designed for maximum temperatures of 2190 Fahrenheit. It is a relatively light material with a specific weight of 1.9 instead of the 2.5 to 3.0 for normal concrete. As such, it is a medium insulating concrete. Artists sometimes use it for casting statues, because of the rapid strength development. Professional heater masons do make castings in almost every stove. Checking whether one of them is willing to sell you a bag..."

Would a cast cylinder of refractory cement work well? Should I add perlite or clay pellets to it?


Those are my questions. Thanks for any input you can give!

(Obviously the one I make won't be as spiffy as this one [though at $500 it oughta be spiffy!], but it's what I'm shooting for.)
ticflickr.com/5003/5352674801_2c16453740_z.jpg

[hpmer]

If you're willing to spend some money, you can buy small tubs of furnace cement at Home Depot and buy a bag of perlite off their website. Mixing the two together would give you a pretty durable and light cookstove.

I'd still build it around metal cans used as forms to make the build easier, and would build it twice as high as the one you pictured to help burn more of the smoke.

I was going for "dirt cheap" and so used clay from the yard and ashes for my builds. They work great and as long as you don't bang them around the mix holds together really well. It ends up firing hard much like bricks if you burn them hot enough and long enough. The outside can is important for protection.

Careful though, these stoves get a bit addictive and you'll probably end up building a few before you're through.

[trucky]

Thanks for the reply, Hpmer! And what of the problem you (or was it someone else?) mentioned about the rear wall crumbling as sticks are inserted into the combustion chamber? Is that why you suggest keeping and replacing metal cans in the chamber?

Thanks again!

Trucky

[hpmer]

Well, with a horizontal feed, you're going to be continually poking the rear wall and since mine is simple clay/ash it can take a beating. So I usually take a can and cut both top and bottom off, flatten it out and place it against the back wall. The sticks then bump up against it rather than the rear wall. It will burn up over time so it's a sacrificial piece, but it's a lot easier getting another can than trying to repair that back wall.

I now much prefer the vertical feed for these cook stoves. Complicates the build somewhat but the fuel feeds itself with gravity, and I seem to get a cleaner burn due to better mixing of oxygen.

By the way, the quickest and easiest way to join the metals cans for me has been a crimping tool used in the AC trade for joining ductwork, and ductwork can be used instead of the cans for both inner and outer parts of the build. Your refractory mix goes in between, the inner will burn out and the outer serves as the housing.

Finally, I've started using floor underlayment for the inner form which for me is now square, and easier to patch if necessary using a flat tool (trowel, flat piece of wood, etc.)

[trucky]

A vertical feed, you say? I'm imagining the feed in the above picture, only at 45 degrees. Is that right? Or do you mean a feed that's truly 90 degrees vertical? I have trouble picturing that. Is there a thread somewhere here which shows what you're describing?

[Donkey]

Sept 15, 2013 6:12:37 GMT -8 trucky said:

Is there a thread somewhere here which shows what you're describing?

Pretty much all over the boards, mate.. Not at 45%, but straight vertical.
There's a real sweetie on this thread
Not the ONLY way to do it. Look around.

[hpmer]

Looks like a "J". The short side is the feed tube, the bottom the burn tunnel, and the high side is the heat riser.

Like in your picture, the pot goes at the top of the riser.

3:1 is a good ratio for riser:feed tube height. Provides more space to fully burn the smoke.