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Post by domino on Sept 10, 2013 2:44:42 GMT -8
Hi all,
Just joined up today so I can get my rocket stove project off the ground. I've done some reading and watched lots of video and now I would like to make my own rocket stove to take camping, fishing etc.....
The materials I have to use are some 6" chimney flu (for the case) and some 3" s/steel tube to make the rocket elbow. I would like to try to utilise the J shaped magazine also.
The plan is to make up some disc top and bottom and then fill the case with vermiculite.
Now all I need to work out is how long the tubes need to be? Is there a formula to follow?
Thanks
Domino
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Post by Donkey on Sept 10, 2013 6:19:21 GMT -8
Welcome, domino..
The general rule for J-tube rockets is that the feed should be 1/3 or less the height of the heat riser AND the burn tunnel (horizontal bits) less than half of the heat riser. In other words, both should be as short as possible and still be practical to use.
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Post by domino on Sept 10, 2013 8:54:23 GMT -8
Excellent thanks,
I plan to get the first 1 cut and welded tomorrow night. I will keep the feed tube and burn tube as short as the chop saw will allow. What would you recommend for the height of it, is there an ideal ratio between inlet/exhaust?
Thanks.
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Post by Donkey on Sept 10, 2013 10:24:48 GMT -8
Nah.. As tall as is practical.
Oh, if you use metal, and you build it well, the metal WILL burn out.
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Post by domino on Sept 11, 2013 11:25:58 GMT -8
Nah.. As tall as is practical. Oh, if you use metal, and you build it well, the metal WILL burn out. Spot on, thanks. It's 304 stainless steel, left over from an exhaust build. Will that still burn out over time? I've got the burner made and it works ok, gets going quite quick and makes the right 'rocket' noise. I think the magazine and horizontal tube should be shorter but I'm limited by the chop saw I have to use and working with short scraps. |
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Post by Donkey on Sept 11, 2013 15:06:47 GMT -8
Cool..
I can't answer the question about the stainless..
Recently I serviced a sauna rocket (it's on the boards here somewhere), I had to replace the barrel which had burned through the top. To my surprise, the stainless steel piece that I'd used for the inside of the heat riser was still intact. It showed no sign of damage.
I can't say what gauge it was, I didn't pay attention.. Got it out of the dump to use as usual, expected it to be sacrificial, so I slapped it in and forgot about it.
Chances are that you'll be fine.
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Post by domino on Sept 11, 2013 22:55:12 GMT -8
Awesome! I can see how mild steel wouldn't last very long but hopefully high quality 304 and above will survive for many years. I have a rocket based(ish) chimenia that uses a S/S beer barrel for the main body and all the rest is S/S too. We've been using it for 5 years now and at least once each summer it's cherry red top to bottom!! It's still going strong with no signs of failure  |
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Post by trucky on Sept 12, 2013 9:46:23 GMT -8
Does anyone know where one could find higher quality stainless steel? Like 310 or 330? Is it possible to find enough for a build without spending $100+ ordering a sheet?
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Post by satamax on Sept 12, 2013 11:17:52 GMT -8
Industrial salvage. What big industry do you have around. Milk or cheese factories come to mind.
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Post by trucky on Sept 13, 2013 9:03:38 GMT -8
Awesome! I can see how mild steel wouldn't last very long but hopefully high quality 304 and above will survive for many years. I have a rocket based(ish) chimenia that uses a S/S beer barrel for the main body and all the rest is S/S too. We've been using it for 5 years now and at least once each summer it's cherry red top to bottom!! It's still going strong with no signs of failure According to Azom.com, 304 has... "Good oxidation resistance in intermittent service to 870°C and in continuous service to 925°C. Continuous use of 304 in the 425-860°C range is not recommended if subsequent aqueous corrosion resistance is important. Grade 304L is more resistant to carbide precipitation and can be heated into the above temperature range. Grade 304H has higher strength at elevated temperatures so is often used for structural and pressure-containing applications at temperatures above about 500°C and up to about 800°C. 304H will become sensitised in the temperature range of 425-860°C; this is not a problem for high temperature applications, but will result in reduced aqueous corrosion resistance."
It mentions that "Grade 310 is generally used at temperatures starting from about 800 or 900°C - above the temperatures at which 304H and 321 are effective." Since "Grade 304 is the standard "18/8" stainless...[and] the most versatile and most widely used stainless steel..." I would imagine it's what's been burning out on people. Maybe your chinemia isn't getting as hot as a rocket stove could?  |
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Post by domino on Sept 14, 2013 3:24:49 GMT -8
According to Azom.com, 304 has... "Good oxidation resistance in intermittent service to 870°C and in continuous service to 925°C. Continuous use of 304 in the 425-860°C range is not recommended if subsequent aqueous corrosion resistance is important. Grade 304L is more resistant to carbide precipitation and can be heated into the above temperature range. Grade 304H has higher strength at elevated temperatures so is often used for structural and pressure-containing applications at temperatures above about 500°C and up to about 800°C. 304H will become sensitised in the temperature range of 425-860°C; this is not a problem for high temperature applications, but will result in reduced aqueous corrosion resistance."
It mentions that "Grade 310 is generally used at temperatures starting from about 800 or 900°C - above the temperatures at which 304H and 321 are effective." Since "Grade 304 is the standard "18/8" stainless...[and] the most versatile and most widely used stainless steel..." I would imagine it's what's been burning out on people. Maybe your chinemia isn't getting as hot as a rocket stove could? Correct, it wont have a constant temp anywhere near as high as genuine rocket burner and that is most likely why its still going. It has turned a dark bronze colour now but no signs of rust. The main body is 316 S/S (a beer barrel) and that section of it has changed very little over the years. I look forward to using and testing my new prototype which I plan to build in 304 as a proper rocket stove with an insulated burntube. |
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