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Post by davisdesigns on Jan 27, 2016 21:36:14 GMT -8
I'm designing a rocket stove and would like to fab it entirely of steel, however i have read the temps found in the burn chamber and riser can quickly degrade the steel.
I have only seen pics/ images of light gauge chamber and riser liners that were made from stove pipe that have been catastrophically damaged.
I plan on using probably no less than 3/16" 0.1875" (4.7635mm) thick except for the very outer 'mass' 100# (25 gal) propane tank which is probably 12 ga. steel that will be capped with probably 1/2" 0.5" (25.4mm) steel plate.
Is there a issue with steel when used in thicknesses as mentioned? if their is can you provide links/ pictures not interested in hearsay, Thank You
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Post by satamax on Jan 27, 2016 22:27:52 GMT -8
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Post by davisdesigns on Jan 27, 2016 23:31:36 GMT -8
Thanks for your reply, i've seen that post and ignored it for a few reason; 1. They claim "You see this thing? It's hydraulic tubing About 6.5 or 7mm thick. More than 1/4" They fail to show adequate photos of the tubing/ pipe wall thickness. 2. I have been working with metal for decades now and to me it looks as if their insulation created a glass scale on the steel and is NOT the steel flaking. 3. the burn chamber kag/ tank appears to be aluminum? possibly SS, why would you use thin walled 0.1046" - 0.1345" chamber and attach a 6.5-7mm (0.255"- 0.275") riser and if aluminum how exactly was this done??? 4. I can clearly see the weld bead on the poorly designed 90 degree elbow and if that much scale was in fact the steel the weld bead scallops would be unrecognizable Wiki "Perlite softens when it reaches temperatures of 850–900 °C (1,560–1,650 °F). Water trapped in the structure of the material evaporates and escapes, and this causes the expansion of the material to 7–16 times its original volume. The expanded material is a brilliant white, due to the reflectivity of the trapped bubbles. Unexpanded ("raw") perlite has a bulk density around 1100 kg/m3 (1.1 g/cm3), while typical expanded perlite has a bulk density of about 30–150 kg/m3 (0.03-0.150 g/cm3).[1]" If one is concerned about steel why use Perlite ? I can only speculate as to why someone would post those photos and claim it as fact, what i see with many years experience is misunderstanding what they see or purposeful disinfo. If you read more on that site you will see a consistency to demonize metal and overlook the metals in their refractory cement...
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Post by satamax on Jan 28, 2016 1:11:13 GMT -8
Mate, my welds might be poor. But I have built this thing. The gas bottle is 3mm thick steel. I know they use higher grade of steel, not a XC38. It's a cyclonic rocket. I will get back to this type of construction one of thoses days, when I will have learnt more.
The tubing is about 10cm diameter inside. Coming from from the artificial snow system we have where I work in the winter. There's a column of water of about 500m. So, that's 50bars. You believe me or not. Well go on and build your thing out of all metal. If you think you can do better than thousand of metal tinkerers who have failed. Look on youtube, check the metal builds. And see if there's any follow ups. If you're into bragging rights. You would post follow ups every now and then. To say to people, oh, my "rocket stove" is soo great etc, wouldn't you?
They either don't heat because they're badly made, or fail after two or three months, and are deemed shit by the builders.
A properly made rocket has to be insulated to reach temperatures above dioxin forming temps. If it's not insulated, it might sound like a rocket, but won't be one.
By the way, what you see in my build is not perlite, but vermiculite.
And I tell you, that would make my life soo much simpler if I could use metal for the heat riser. Having a yellow, or even white riser, which would radiate enough to burn the latest traces of burnables in the gas stream would realy realy tickle my fancy.
Batch rockets are soo violent that they even eat refractories. I don't know where to turn next. Rigidized superwool and the likes? Or insulating firebricks.
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morticcio
Full Member
"The problem with internet quotes is that you can't always depend on their accuracy" - Aristotle
Posts: 371
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Post by morticcio on Jan 28, 2016 1:56:32 GMT -8
You can use steel if you want but it will have a limited lifespan - search for spalling on this forum. If you want a stove that can cope with the high temperatures then use the correct refractory materials.
Perlite is used as an insulator and on its own shouldn't be in contact with the 'hot face'. Mixing it with fireclay raises the temperatures it can take.
Usually firebrick or castable refractory 'liner' is in contact with the 'hot face' as they can cope with high temperatures and thermal cycling. If necessary an additional higher rated insulator (e.g. ceramic fibre blanket) can be placed between refractory liner and perlite.
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Post by pinhead on Jan 28, 2016 10:05:00 GMT -8
It's been tried and tried again.
The oxidizing flame of a properly-burning rocket stove produces a high temperature, high oxygen, low carbon environment in the burn chamber which simply destroys metal - there's no way around it. It's an oxidizing flame similar to that of an acetylene cutting torch.
If the stove is burning cold and rich (too much fuel and smoking) the metal will last. Once you get into true rocket territory METAL IS DOOMED.
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Post by davisdesigns on Jan 28, 2016 11:23:56 GMT -8
It's been tried and tried again. The oxidizing flame of a properly-burning rocket stove produces a high temperature, high oxygen, low carbon environment in the burn chamber which simply destroys metal - there's no way around it. It's an oxidizing flame similar to that of an acetylene cutting torch. If the stove is burning cold and rich (too much fuel and smoking) the metal will last. Once you get into true rocket territory METAL IS DOOMED. I have read this statement "METAL IS DOOMED" many times yet the only time I see catastrophic failure when thin gauge sheet metal i.e stovepipe is used. Do you have any evidence that 3/16" and thicker wall burn chamber is "doomed" with in 20 years or is this hearsay? I have personally seen refractory built stoves crack and fail in only a few uses, that's a gamble i don't want to take and i'm not skilled in its usage. However i do like the idea of pouring the refractory into a mould or around a plug and get some complex shapes that would be very difficult to do with steel. I do agree that proper mixed refractory will withstand higher temps but the opinions i have read about steel fauler appear to be coming from people that have more skills working that mud and mortar and not steel at least judging by their work with steel and comments such as the metal pipe sagging or collapsing upon itself when orange/ 1725 F sure i can see that happening with stove pipe but it doesn't happen with thick wall tubing/ pipe. It can be heated to white/ 2190 F and still retain its shape. Sure it can be deformed with a hammer but are you really going to be banging on the burn chamber and riser with a hammer ? Yes I agree that different mediums that are burnt and heating/ cooling cycle will cause the steel to oxidize but how much 0.001" a month, year, decade?
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Post by peterberg on Jan 28, 2016 13:18:31 GMT -8
Destroying a heavy gauge metal pipe like that is certainly no hearsay, In the thread "Small scale development" I described a 4"x 4" J-tube rocket made out of 1/8" mild steel duct, properly welded. I made a couple of those during that season in different guises. When insulated with loose vermiculite, the thing burned much hotter than without insulation. As a result of that, the steel at the bottom of the feed tube / beginning of the burn tunnel was destroyed because of heavy spalling in about 10 hard pushed test runs of about an hour each. Mind you this is about a tiny rocket, a larger one is much more violent. A temperature of 1200 C / 2190 F is easily obtainable. It won't melt, but it will corrode like mad, after cooling down I could get a handful of flakes out of it every time. So, 3/16" or thicker walled burn chamber in a properly built rocket is "doomed" within 20 years, yes, or more likely within the first month. Hope this a satisfying answer. When you don't want your steel rocket to fail, don't insulate it so it is able to shed lots of heat. It won't reach complete combustion routinely, but when you aren't interested in such a thing please go ahead.
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Post by pinhead on Jan 28, 2016 13:35:49 GMT -8
I have read this statement "METAL IS DOOMED" many times yet the only time I see catastrophic failure when thin gauge sheet metal i.e stovepipe is used. Do you have any evidence that 3/16" and thicker wall burn chamber is "doomed" with in 20 years or is this hearsay? I have personally seen refractory built stoves crack and fail in only a few uses, that's a gamble i don't want to take and i'm not skilled in its usage. However i do like the idea of pouring the refractory into a mould or around a plug and get some complex shapes that would be very difficult to do with steel. I do agree that proper mixed refractory will withstand higher temps but the opinions i have read about steel fauler appear to be coming from people that have more skills working that mud and mortar and not steel at least judging by their work with steel and comments such as the metal pipe sagging or collapsing upon itself when orange/ 1725 F sure i can see that happening with stove pipe but it doesn't happen with thick wall tubing/ pipe. It can be heated to white/ 2190 F and still retain its shape. Sure it can be deformed with a hammer but are you really going to be banging on the burn chamber and riser with a hammer ? Yes I agree that different mediums that are burnt and heating/ cooling cycle will cause the steel to oxidize but how much 0.001" a month, year, decade? I also ignored the "metal is doomed" crowd when I first started experimenting - with well-insulated 4 inch oilfield pipe in a J-tube configuration as an outdoor test. The pipe didn't sag, as I suspect it was supported slightly by the tightly-packed vermiculite around it. Looking down at the pipe after an hour of burning showed it glowing BRIGHT-yellow. After burning it daily for a few hours over the course of a little under a month, top of the burn tunnel had turned a dark gray color and was falling off in flakes. In one instance I bumped the "box" the contraption was in and the thing instantly started smoking back. I assumed the wood had shifted and needed to be moved to allow more air but no amount of fidgeting would re-initiate the draft. Once the fire was out I disassembled the rig and found the burn tunnel almost blocked by these "flakes" from the ceiling of the burn tunnel and the base of the riser. When I crushed them (fairly easily) they reminded me of slag from cutting with an acetylene torch. This was a four-inch J-tube with no P-channel, insulated with about 8 inches of loose vermiculite around the burn tunnel and about 3 inches around the riser. No heat extraction barrel, no bench - just burning on its own. It was extremely easy to start and initiate draft since the pipe had relatively low mass and heated quickly. Unfortunately, as has been said, it didn't last. My next iteration was a j-tube with a refractory core that lasted much longer under more intense conditions (a couple of years). When I replaced it with a 7" batch box I noticed that the refractory mix (refractory cement and vermiculite mix) had fared extremely well with little sign of damage. But go ahead and re-run the experiment; it'll be nice to have yet another person telling the noobs that "metal is doomed."
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Post by satamax on Jan 28, 2016 21:56:19 GMT -8
Davisdesigns, i never said it sagged under it's own weight when it was orange nor yellow. Most certainly white, because it is impossible to happen any other way. My welds are ugly, i know. It's lack of practice. Look at how uggly those are donkey32.proboards.com/post/18913/thread4mm rods, onto 1.5mm steel @140 amps. We call this north african welding over here. Do with whatever you find in the workshop. After hours of cursing, i did an aproximately gastight weld. And i should weld far better, my grandparents had a metalwork factory. And i did mechanic engineeriring at school. I vaguely know what metal is. But i don't do mig/mag nor tig, and don't brag about my welds. If it holds, it's plenty good enough. About your hypothetical all metal rocket. Go on, do it. But please publish all the photos and details of when it burns. So we can have a bit of a laugh.
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Post by davisdesigns on Jan 28, 2016 22:49:14 GMT -8
Davisdesigns, i never said it sagged under it's own weight when it was orange nor yellow. Most certainly white, because it is impossible to happen any other way. My welds are ugly, i know. It's lack of practice. Look at how uggly those are donkey32.proboards.com/post/18913/thread4mm rods, onto 1.5mm steel @140 amps. We call this north african welding over here. Do with whatever you find in the workshop. After hours of cursing, i did an aproximately gastight weld. And i should weld far better, my grandparents had a metalwork factory. And i did mechanic engineeriring at school. I vaguely know what metal is. But i don't do mig/mag nor tig, and don't brag about my welds. If it holds, it's plenty good enough. About your hypothetical all metal rocket. Go on, do it. But please publish all the photos and details of when it burns. So we can have a bit of a laugh. Look i don't know you or even know what you have built and wasn't looking down upon anyone that doesn't have a particular skill set as i clearly said i don't know much about refractor or mud. No need for you to be unpleasant "About your hypothetical all metal rocket. Go on, do it. But please publish all the photos and details of when it burns. So we can have a bit of a laugh. "
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Post by davisdesigns on Jan 28, 2016 23:57:23 GMT -8
I also ignored the "metal is doomed" crowd when I first started experimenting - with well-insulated 4 inch oilfield pipe in a J-tube configuration as an outdoor test. The pipe didn't sag, as I suspect it was supported slightly by the tightly-packed vermiculite around it. Looking down at the pipe after an hour of burning showed it glowing BRIGHT-yellow. After burning it daily for a few hours over the course of a little under a month, top of the burn tunnel had turned a dark gray color and was falling off in flakes. In one instance I bumped the "box" the contraption was in and the thing instantly started smoking back. I assumed the wood had shifted and needed to be moved to allow more air but no amount of fidgeting would re-initiate the draft. Once the fire was out I disassembled the rig and found the burn tunnel almost blocked by these "flakes" from the ceiling of the burn tunnel and the base of the riser. When I crushed them (fairly easily) they reminded me of slag from cutting with an acetylene torch. This was a four-inch J-tube with no P-channel, insulated with about 8 inches of loose vermiculite around the burn tunnel and about 3 inches around the riser. No heat extraction barrel, no bench - just burning on its own. It was extremely easy to start and initiate draft since the pipe had relatively low mass and heated quickly. Unfortunately, as has been said, it didn't last. My next iteration was a j-tube with a refractory core that lasted much longer under more intense conditions (a couple of years). When I replaced it with a 7" batch box I noticed that the refractory mix (refractory cement and vermiculite mix) had fared extremely well with little sign of damage. But go ahead and re-run the experiment; it'll be nice to have yet another person telling the noobs that "metal is doomed." Do you recall the wall thickness of the "oilfield pipe" That not a pipe i'm familiar with.. The failure in refractory cement i personally witnessed was the "batch box" design casted in halves and banded together by a 'non-noob' or was your reference to noob someone new to this forum in any rate the term 'noob' has been pretty played out about 10 years ago... Everyone is a noob to anything at one point and really comes off as snooty and some sort of idea that you are a better person for being a noobie prior to me...
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Post by satamax on Jan 29, 2016 0:47:02 GMT -8
Davisdesigns, i'm not being unpleasant. I'm just being myself, arogant and know it all The thing is, you were questioning my build. One of my first. Yep the welds are uggly, butt uggly. But it worked, nicely for a 4 incher. Untill it failed. Failure is explained at permies. You said you ignored my description of the failure. Well, fair play. But i'm not a liar, what gain would i have in steering people off metal builds, if they worked? When i say the elbow was like puff pastry on the inside, that's true. I had may be 2.5 inches of passage left. And having seen a fair bit of metal in my life, it shocked me that it could fail to that point. I knew that metal creep in building RSJ's can occur around 600C° But never thought metal could degrade that much that fast. If metal builds worked, i would be hohning my welding skills. Not steering people away from metal. Now, if you realy think you can do better. Make a real all metal rocket. Show us. I'm always willing to learn. Tho, don't brag before you've reached may be the 200 hours of burning. Don't say it's working wonderfully, if it's not insulated. I would even say; don't say it's working wonderfully, before you have tried a refractory and lots of insulation rocket.
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morticcio
Full Member
"The problem with internet quotes is that you can't always depend on their accuracy" - Aristotle
Posts: 371
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Post by morticcio on Jan 29, 2016 0:53:16 GMT -8
Putting comments about noobs, unpleasantness and bad welding to one side...
You asked the question; "Is there a(n) issue with steel when used in thicknesses as mentioned?".
The answer is; "The consensus on this forum is that there is an issue with steel no matter how thick it is. A metal burn chamber/riser will fail sooner rather than later."
Some hairline cracking in a castable or firebrick stove is acceptable. These usually disappear when the stove heats up. They can be repaired by smearing a refractory or clay slip over the cracks. If the cracks are major this could be down to numerous things - incorrect castable/water ratio, too much air in the castable, stove fired before the castable was completely dry, no room for expansion etc. I would advise using firebricks to start with!
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Post by peterberg on Jan 29, 2016 2:11:27 GMT -8
Gents! Please remember the number one rule on this forum is "be nice". I would be very grateful when everybody refrains from being obstinate from now on. Otherwise I have to weed out all the not nice stuff, work I don't like at all. Could we keep on topic, please?
Regarding refractories: I am using a new casted design of the batch box (devided into three parts) at the moment. Wall thickness 30 mm/1.18", 1200 C resistant continiously, specific weight 1.92 kg/liter or 120 lbs/cu ft. In daily use since beginning of October, no cracks uptil now. As soon as winter is over, I will report back about this. When there are still no cracks in there I will publish the SketchUp drawing. Actually, I was surprised it seems to hold because I just tried an old idea. That is, the top of the box will expand ahead of the rest so cracks appear in the bottom half.
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