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Linear burner, scrapheap edition


G-son

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Spring is here, so now it's time to try a burner build. First out is a linear burner, mostly for handheld use (that's the plan anyway). I intend to build it mostly of stuff I already have, the first picture (if they show up in the correct order this time) shows the lawnmower handles that the tubing is cannibalized from - they're both 22mm/7/8" outside diameter, but the more expensive mower had 2mm thick metal, while the cheaper ones were 1mm (0.080 & 0.040"), making the inside diameter 18 and 20mm. I'm using a 0,6mm MIG jet, and since so called ½" pipe (actually 15,75mm inside diameter, almost 5/8") supposedly is a bit too small for that jet, I'm hoping 18 or 20mm will be correct. I was aiming for 10x id in length, the 20mm tube is exactly that, the 18mm is closer to 9,25x id, I couldn't get a longer straight piece from that scrap.

The cone templates were calculated using http://craig-russell.co.uk/demos/cone_calculator/ (remembering taking metal thickness into account when feeding in the numbers)
Dimensions used were big end 3x tube diameter, and length 4x. Other sizes can easily be made, and since I've soldered them in place I can just apply heat to remove these, should I want to.

Templates were transfered to thin sheet metal, and that was shaped using a rubber mallet and the first steady thing of suitable diameter I could find - the seat post on an old bicycle. Once they were roughly the correct shape I silver soldered the joint, after that I spent some more time getting it round.

Final step for today was silver soldering the cones to the tubes. Now we're waiting for another warm day with dry weather, no more progress until then.

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To begin with, nice work so far. 

Forget ten diameters; you want nine diameters for the length of your mixing tube. Why; because longer mixing tube lengths smooth out the flame by slowing the incoming gas/mixture through friction. Nothing's for nothing, and the price you'll pay is a weaker flame. You already have a slightly weakened flame, do to the MIG tip being a couple of thousandths over ideal diameter, for a half-inch burner size, so don't add to that with a longer mixing tube than needed.

How do you plan to mount your gas tube and gas jet to the funnel? And are you building a standard linear burner or a Vortex burner? If a standard burner, I would suggest mounting the gas tube in a steel or half-hard brass tube, which is mounted within your burner's cone via three 1/2" to 3/4" wide sheet metal curved vanes, set at a 30-degree angle, just like the impeller blades used on axial computer fans. Instead of curving the vanes, you could cut them out from a tin can.

So, why go to the trouble? While not anywhere near as strong a swirl as provided by the right fan, three such curved  vanes will double the effectiness of your funnel.

If you have a rotary tool, you could cut the end and a short section of wall from cans just larger that your cones to serve as caps, cut out three sides of the areas for vanes between the the the wall and a central area used for a central lamp nut (to be silver brazed over a central hole), and bend the cut outlines down to become rib-vanes; this will allow you to cut metal discs mounted on lamp nuts for air chokes, which will be needed to seal the burner against the chimney effect.

23 hours ago, Frozenforge said:

This will be an interesting build.

Yes, it will. It may also be very encouraging to sheet metal enthusiasts. I think a lot more people will be working with sheet metal as time goes by; it is a natural skill to be coming on strong in a high tech age:)

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On 4/14/2018 at 2:34 PM, Frozenforge said:

This will be an interesting build.

Thankyou! I hope it will be a functional burner too! ;)

On 4/15/2018 at 1:31 PM, Mikey98118 said:

To begin with, nice work so far. 

Thankyou!

Longer mixing tube has been suggested for a calmer flame in handheld burners (i.e, burners not used in forges etc.), and since that's the kind of use I'm planning first I thought I'd start with a bit extra length. Once it's completed and tested I can easily shorten it, adding length is a bit more complicated (quite doable, but requires more work than simply cutting the end off).
So called ½" pipe is actually 15,75mm, I've gone up to 18 & 20mm to better match the 0,6mm MIG tip. Do you think the MIG tip still is a bit big for that?

I'm building a standard linear burner. 
My current plan for mounting the gas tube etc. is to make a clamp that grips around the mixing tube, and bend a piece of flat bar back around the funnel, there's a crude drawing in the attached picture. This construction would allow me to move the mixing tube/funnel closer or further away from the gas jet, just by loosening the clamp. It would also allow me to change between the 18mm and 20mm tube (or another, if I need to make more to find the right size) on a single gas jet/tube etc. assembly, so i don't have to make two diffrent sets of "gas assembly mounts". To me, this is a prototype build, I'm trying to keep it simple while still being able to easily swap out pieces. 

I do however like your suggestion of turning vanes in the funnel very much, I have been thinking quite a bit about diffrent ways to help the air rotating down into the funnel and vanes should be both simple and effective. I will certainly try vanes, in one form or another. Also thinking about multi-step cones, i.e. starting with a short shallow angle cone on the mixing tube, then putting a short steeper angle cone on that, and possibly more stages. Aerodynamics 101, avoid large changes of direction as it will result in turbulence. A multi stage cone can go from large starting diameter to a shallow angle mixing tube entry without being very long... but that kind of experiments lies far down the road.

I still haven't figured out how I'll make the air choke, but since this burner isn't going into a forge (I don't have one) I don't think the chimney effect would be a problem for now. Ideally, I'd like to end up with a burner that runs a neutral frame w/o restricting the air flow into it - my logic being that any time you have to intentionally restrict flow you're wasting energy, energy that could have been put to use in a better designed burner running wide open. That's part of the reason I'm trying two mixing tube diameters (and can try more), I'd like the basic design to get as close to neutral as possible running wide open, and only adjust by choking as little as possible if I have to. I might run out of patience for redesigns further down the road, but that's the intention right now. 


Sheet metal has one very big advantage. With a little bit of knowlege and a few basic hand tools, you can make almost anything out of it. Remember, most of the cars from the 1920s and earlier were not stamped like modern day production, they were shaped using hammers, mallets, blocks of wood, and other rather basic tools. If people can create curvy body panels that way, something like a funnel (that only requires the metal to bend one way, not stretch or shrink) should be within anyones grasp if they just want to give it a try. 

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Without being subject to chimney effects, a linear burner has no need for an air choke.

By using a short bit of tubing, with an inside diameter just larger than the gas tube, to hold the inner edges of the three vanes, you will be able to move the gas assembly back and forth between both burners. I am assuming you have already read the Burners 101 thread, and need no help figuring out the details of gas assemblies; including the whys and wherefores of maintaining the gas jet centered and parallel the mixing tube axis and at the proper distance from its entrance?

BTW it just kills me that you didn't post this juicy little item in that thread :D

3 hours ago, G-son said:

Sheet metal has one very big advantage. With a little bit of knowlege and a few basic hand tools, you can make almost anything out of it.

And those same tools help electronic techs and computer geeks build perfect cases for their gear.

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Great! So, no air choke now. That makes life easier.

I do like that version of gas assembly holder, but I have not been able to find suitable small tubing yet. I'll dig through the scrapheap some more, if I find something good I might go your route, otherwise it'll be the clamp style - or something completely different, if some piece of scrap jumps put at me and gives me another idea. There's bound to be some compromizes when any build is based on materials you have, rather than the materials you want. 

I have indeed read the Burners 101 from start to finish (a couple of months ago so I might have forgotten some bits) and asked a number of things a few months back. Showed how to make sheet metal cones there back then.
How to build and properly aim the gas assembly with what I've got has been on my mind for a while. I don't have a clear picture of it yet, but I'll get there.

I did think about putting this build in that thread, but I decided it would be better off in it's own thread. This build may take a while, and in your thread there would be probably 30 other discussions mixed in between it, it's hard to follow something when it gets spread out like that - and that's the downside of that thread, there's huge amounts of great info in there but it has become spread out and mixed with some not so relevant stuff - all important to the people that posted it, but perhaps not to everyone who reads the entire thread. Once this burner is done (successfully, I hope) it might be a good idea to make one post about the build in burners 101, showing the basic steps through the build and with a link here for those who want to read it all in detail, but for now the slow build is probably better off here.

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Great! Or you could start a new thread about sheet metal in burner and forge construction, making it easy for people to look at and contribute to; I think the topic is important; in any case, I don't want what you are doing to eventually get shuffled off to obscurity.

 

Frosty and others have repeatedly advised people how easily forges can be constructed of sheet metal. Two or three guys have posted photos of their sheet metal fabrications on IFI, and this important technique keeps being ignored; I think people assume that anything new to them must be hard to deal with. Sheet metal work as something new and frightening; what a side state of affairs that is!

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  • 1 year later...

I hit a few problems a year ago and put this project on the shelf, I didn't have the materials I wanted and couldn't think of a good method to get the tip centered using what I had available at the time. I've realized if I'm waiting for perfection I'm never getting it done, so I'm at it again, with slightly lower standards - better to get a working prototype done and learn something from that, than having a pile of unfinished parts on the shelf.

This is my creation from today. A 0.6mm MIG tip with a tapered down tip and filed down thread (done with a drill and a file) to fit in the end of a 6mm copper brake line. Soldered that to the brake line (easy to heat and remove, if I need to).
On the other end there is what used to be a camping stove, that attaches to a disposable gas canister. I removed the burner, drilled a bigger hole through the jet, drilled a recess that the brake line dips into and silver soldered them together. 

I know the gas in those disposable canisters isn't propane and I'm sure they can't deliver enough gas to feed a burner like this at full throttle for long, probably not even in a water bath, but this is the stuff I have here and now, so I'm using it. I might just learn that it doesn't work, or that it works great with the gas turned down far enough. 

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Well, only one funnel on each size of mixing tube, don't know which one matches the mig tip size best yet. But yes, that's where' it's going. 

Anything specific that makes you think it won't work, or is everything about it wrong?

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How are you going to mount the mig tip to the mixing tube? You are aware the jet should only be just inside the intake cone, not inside the mixing tube. Yes? That would have all that copper tubing sticking out of the intake end and copper's too soft to support the weight. Well, that or sticking all the way through and sticking out the flame nozzle end. Neither is workable. 

Have you looked at any of the proven linear burner plans available? Try a web search for "Ron Reil, burner", Ron's has been around for some time and is well proven.

Frosty The Lucky.

 

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Yes, I am aware the tip goes just before the beginning of the mixing tube. I intend to put the copper tube through some kind of clamp to lock the tip in position, and the clamp attached to the funnel edges probably.
I used a long piece of copper tube because I want some distance between the burner and the gas canister, should make it easier to keep the canister in a water bath at the same time as the burner is in a usable location. The copper tube is indeed too soft to take the weight of canister/burner, but adding two or three steel rods is a simple matter once everything is in the appropriate location (and the copper tube has been bent ~45 degrees, unless I change my mind before I get there). If I find the tube is too long it's a simple matter of heating the soldered or brazed end to take it apart and cut to whatever length seems appropriate at the time.

I have looked at the proven designs. They require materials I don't have and don't know where to buy around here, so I'm experimenting with what I've got instead. 

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I understand trying to get parts and pieces I may think common other places in the world ad look forward to seeing what you come up with. Please give me a shout if you run into problems, I'll be happy to lend what help I can.

Frosty The Lucky.

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Seems like a good plan to me. Just make a way to mount the jet tip so you can center it in the funnel and adjust its axial position. The air induction isn’t as sensitive to axial position as I expected. 

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Well, it's alive! Silver soldered a few more pieces together today to hold the gas tube/tip in the 18mm mixing tube, and cobbled together a nozzle without remembering anything about what length or diameter, so it became about 27mm diameter, started at 1" length but it couldn't take much gas then, increased to about 1½" and got what you see in the pictures and video.

As suspected, gas supply from disposable canisters is an issue. Works fine with the flame turned down, but at wide open pressure drops in minutes. Water bath should help a bit at least.

In the picture with three flames, the two left ones is with the burner turned down to the smallest stable flame, and the right flame is turned up "high" (as high as it went with little gas left and no water bath, far from the actual max under better conditions).
The video goes from low to high and back to low. At around 9 seconds the flame seems to "lift off" from the burner, a very clear and sudden change in the flame right at that setting. 

Now I'm about to read up on nozzles, as that might be something I should try changing.
 

 

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I’m interested to hear a flame analysis  from someone who knows. The video makes the flame look rich to me, but better at high pressures. Have you optimized the axial position of the gas jet? It may be that you are a bit close to the mouth of the funnel. Hard to see from the picture. I slid the jet back and forth while running to get a sense of where it worked best. 

I like your mechanical arrangement, thank you for sharing. 

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Looks pretty good from here. Are you sure you can't find a conversion fitting to run this on a propane tank? To my eye the little sputter when you were running the pressure up was a little slosh sending liquid to the burner. You're drawing gas fast enough to make it boil and that can send liquid to the burner as well.

If you can use a decent size tank say 10 kg. or so you won't get liquid propane splashing to the outlet. 

Frosty The Lucky.

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I do want a large tank as it would be much better (and cheaper in the long run), and now that I know I've got a useable burner it's beginning to make sense to get one. For now I'll run it like this while I try different adjustments and modifications, and unless I've built more burners by the time I get a big tank & regulator I can just cut the copper tube and attach the hose to it. If I get a few more things I can build a small forge for it too, and from there the sky is the limit. :)

Nice to hear that it looks good. Not bad for the first test of my first burner, with a build cost somewhere around $5. Half of that is the copper tube. :lol:

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Yup, I mean the flame retention nozzle; it's called that for a very good reason. Part of the reason is that it can help create the need for its function; which is exactly what your burner needs. The last flame photo (on the right) isn't half bad, but you will still want just a little more heat than that, and you can get it by inducing more air through the use of a more radical nozzle. You might as well get on with that, because a sheet metal flam nozzle will last very fast at thoghs higher flame temperatures your burner needs to do effective work, anyway.

"...because a sheet metal flame nozzle will last very fast at those..."

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The burner could handle quite a bit more gas (all I could supply) without going out since I moved the nozzle out about ½" (all photos/video are from after that move), so I intend to se what an even longer nozzle does. Increasing the diameter would be relatively easy and interesting too. Although I'm not sure what makes a nozzle "radical".
Yeah, I know mild steel sheet metal won't last long there, but for quick and dirty prototypes it's nice. Once you know the size you really want it's worth putting a bit more work into something that lasts longer.

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