Burners required

[Irentei]

Hey. im trying to set up a gas forge and have begun making burners. The burner's main pipe has an inner diameter of 1" 
the gas tank has an outer diameter of 102 cm while ive measured the inside room to be 14 cm square in the opening on each end with a depth of 54 cm i think this translate to the inside being 645.15 cubic inches.

will 2 burners be overkill or sufficient for this size of forge ?

also how much will the length of the main pipe affect the burn? and how necessary is the nozzle at the end ?

im completely new at this so all feedback is appriciated :) 

thanks in advance

[Irondragon Forge ClayWorks]

Welcome to IFI... I suggest reading this thread to get the best out of the forum. https://www.iforgeiron.com/topic/53873-read-this-first/

The expert's on gas forges will be along shortly to advise you. Myself with a forge that large, I would go with 3 burners if I planned to do any welding in it. Is the 645 ci before or after insulating and refractory?

[Another FrankenBurner]

It is obvious that you have not researched burners at all.  I am not criticizing, simply stating what I read.  Propane burners while sometimes seemingly simple are scientifically complicated.  I am no expert on any of this stuff but have spent time researching and built a handful of successful burners.  If you want to do the research and development on your own burner, that is fine, but know that that is exactly what you would be doing.  If you just want burners that will work properly without the fuss of inventing your own, research a known to work design and build it to the specs of that design. 

The burner you have started is a linear burner.  Ron Reil's burners are of the linear design and the ones I hear about the most.  You ask how much the length of the main pipe affects the burn, the answer is a lot.  All of the well working designs explicitly state the length of what most call the mix tube.  In the case of your reducers, they look to be a lot smaller then they should be in order to induce enough air.  I know that on the 3/4 inch burners, I have heard at least 2.5 inches.  If you were to go with that same ratio, you would need a reducer from 3 inch to the 1 inch, though I don't know this to be true as I have never built a 1 inch burner or researched them.  You ask how necessary the nozzle at the end is, that depends on how you are using the burner and making the forge.

The easiest known burner that I know of is the Frosty T burner.  The other known to work designs I can think of off the top of my head are the Mikey burner and the Reil burner.  To give an idea on the research and development portion of a burner, the Frosty T burner consists of a threaded fitting, a length of pipe, a tee fitting, a brass fitting, and a mig tip and Frosty once stated he worked on the design for years to get it refined to the point it is today.

I will speak mostly in metric as that is what you stated measurements in.  If your openings are 14 cm then your diameter is not 102 cm.  I assume you are meaning circumference?  Which would be a diameter of approx. 32.5 cm.  If you were to fill the tank with insulation to the point you had exactly the box you dimension (14 X 14 X 54), I come up with the same cubic inch volume.  However, if you go with the two inches of ceramic blanket and a half inch of kast o lite 30 this would open that volume up to 1015 cubic inches.  If my math is right.  Quite an increase and quite a large forge which is generally not encouraged especially to newer smiths.  

Usually the thought process is to build a forge big enough to be able to accept any project that we can come up with.  The problem with this thinking is that forge will eat lots of fuel to warm and if most of your work does not require a forge that big, you are wasting so much fuel that you end up building a smaller forge and the big beast collects dust.  Whereas if you start small and find that you built too small, you build a second forge for the big project and still use the smaller forge for the small projects.  I have built a Freon tank forge which has an internal volume closer to 150 cubic inches and it has met my needs so far.  I don't make bearded axes or large scroll work though.  I have since made an even smaller forge for when I work the small stuff and have plans to make a larger diameter forge but not very long.  You stated the length at 54 cm which is quite long.  Something I read on these forums which holds true for me is that you can only work about 6 inches (15 cm) before the metal cools, unless you are using a power hammer.  If you are constantly heating metal that you are not working, you are scaling your metal for no reason.  

I am not trying to discourage you at all.  If you want to build a large forge and invent your own burner, go for it.  Many do.  A few succeed.  Though, there are some examples on this forum where they get a large forge working correctly only to realize how much propane it actually uses and build a smaller one.

If you want to go ahead, the standard thought on 3/4 burners is 350 cu.in. of properly insulated forge volume to forge weld.  I do not know what they are for 1 inch burners.  You would need 3 of the 3/4 burners for the 1015 cu.in. so I suspect 2 of the 1 inch burners would do well if properly built but I don't know for sure.  

If you still want the big forge but don't want the fuss of the burners, I recommend the Frosty T burner.  Easy to make and it works.

I'm sure the experts will be along to correct any of this information that might be incorrect.  Hopefully something in here is helpful.

[Mikey98118]

I think Curtis put things pretty well, and you would do well to follow his advice; he is rapidly turning into an expert.

[VainEnd84]

Just one small clarification on what AnotherCurtis said, the reducer does not induce the air flow but rather increases the volume of induced air, the flow of the gas jet is what creates the pressure difference that induces the air flow.

I suppose you could think of the reducers like a lens, focusing the air flow from a large area to a smaller one, just as a lens can focus light into a smaller point.

[Mikey98118]

I think reducer shape and size has a lot to do with sufficient spin in the incoming air.

[VainEnd84]

That too, though I can not for the life of me remember how/why a funnel causes vortex formation.

[Mikey98118]

I have been thinking about it for five years and I can't bring up a mental picture of how either. Just memorize the rules of the "what" of vortical flow and forget trying to visualize the how.

[Frosty]

Cool, you guys are saving me a LOT of typing. Nicely said Curtis, I only have a couple particulars to add.

Burners are built on ratios with the throat diameter being the departure dimension. The throat is the narrowest point in the transition from intake port(s) and mixing tube. With plumbing parts  this is the end of the pipe nipple that screws into the bell reducer, T or whatever. 

BTU output is directly related to the ID of the mixing tube. Eg. a 1" burner tube is 2x the area of a 3/4" tube and will heat 2x the volume of forge. Eg. A 3/4" burner will bring a 350 cu/in forge to welding temp where a 1" burner will bring 700 cu/in to welding temperature. This is assuming the burners are properly built and well tuned and the forge is reasonably well insulated and not loaded up with large thermal mass. 

If your forge is 1,000 cu/in then two 1" burners is a nice amount of too much, you can always turn the propane pressure down. However, if your forge is long compared to width then three 3/4" burners will make a more evenly heated forge and will be enough to bring it to welding temp.

Tube length should be 8-9x the ID of the throat, 9 seems to work best in general. Making the tubes much longer lowers the ability to induce intake air but the trade off is more thorough mixing. There is leeway but not a LOT. between 8 & 9 consistently works best.

Irentei: Your mixing tubes look way too long but that might just be the pic on my screen. 

I don't have a ratio for intake size but I find a 25% increase in the diameter in the T burner works well. For example: 3/4" x 1" T or 1/2" x 3/4" T. and so on, this ratio seems to work well. Another Curtis' example of a 2.5" bell reducer working well on a 3/4" linear burner is a ratio of, . . . Dang IT I had to hunt down my TI calculator! Okay, a 2.5" dia bell reducer is 4.91 square inches. Put it on a 3/4" tube and the ratio is: 11.11 : 1. Don't gripe I'm rounding up. So if you're following this ratio a 1" tube would want a 1" x 8" bell reducer. See why I haven't messed with a rule of thumb for intake size? 

The ratio using a 1" x 3/" T = 1.6:1 and it works nicely.

Okay, that's as far s I'mm going to get into the particulars now, I've laid them out in the illustrated T burner instruction (or whatever I called it) thread along with detailed construction information.

Mike: Stop wondering why a cone or bell reducer induces a vortex in the tube. I've been kicking ideas for simple vortex inducing structures I could build into a spun Wasp burner when you mentioned cones inducing them. So then I thought about the obvious for a little while and it slapped me on the forehead. It's the conservation of angular momentum And it accelerates as the diameter of the vortex is reduced by the cone.

Go ahead Mike slap yourself on the forehead, I did.

This is another good reason to build the intake port the most advantageous shape eg. Trumpet (air foil) shape. Hmmmm?

I have to go now, I have a doc apt and we lost Buffy the missing cat so I have to take care of her remains. She's our one family member who didn't survive the quake. She spent  5 days hiding and whether she was injured or just didn't eat or drink too long and her internal organs shut down, she didn't make it. She crossed the rainbow bridge after 9:00 pm last night.

Sorry for getting all maudlin and sappy on you but she was a great cat, we rescued her 9 years ago and she was a full grown adult then. I have to stop or I'll just go on, I love that old cat and it'll be tough saying good bye, I'll talk to her on the car ride.

Be well guys, live like this is your last day and dance like nobody's watching!

See, I'm getting all sappy.

Frosty The Lucky.

 

[Mikey98118]

2 hours ago, Frosty said:

Tube length should be 8-9x the ID of the throat, 9 seems to work best in general. Making the tubes much longer lowers the ability to induce intake air but the trade off is more thorough mixing. There is leeway but not a LOT. between 8 & 9 consistently works best.

Yes that is true, and like any rule of thumb, it has conceptions. However, people who just want to get on with forge building are wise to stay within guidelines; ex[experimentation can be fun but will take most people for out of their way.

[NelsonR]

I think everyone else has covered much more than I could on the topic of the burners. The only thing I would add is that this may not be the right forge build to start with for a couple reasons. I'm obviously not entirely sure what your end setup will be, but it almost certainly will be the hummer of gas forges. I am assuming that you will either A: simply be lining it with Kaowool or some other ceramic blanket or B: be lining it with a ceramic blanket and then pouring castable refractory to fill the rest. Either setup will require a lot of propane to run, as the first leaves you with with a massive amount of airspace to heat, and the second will take a long time and a lot of propane to heat up, as castable refractory acts as much more of a heat sink than soft refractories, such as ceramic blankets and some brick. That is not to say that a forge this size doesn't have its place, but it's an expensive forge to learn on. I in no way want to discourage you from chasing your ambitions, but I would suggest a smaller forge to start out . Even one half the size as the setup you are working on now should be sufficient for the first year or so of forging (maybe less, depending on how often you plan on forging stuff) and it will save you a small fortune (perhaps a slight exaggeration) on propane. In the end, though, the only decision that matters is your's, and your willingness to live with it,

 

Best of luck,

Nelson

[Mikey98118]

A large shell doesn't need to become an equally large forge; it can instead provide extra room for insulation and/or room enough to sift from the obvious tunnel shape to an oval or dome shaped forge, depnding on whether added room in only two dimensions is wanted, or extra height is also desirable.

[NelsonR]

6 minutes ago, Mikey98118 said:

A large shell doesn't need to become an equally large forge; it can instead provide extra room for insulation and/or room enough to sift from the obvious tunnel shape to an oval or dome shaped forge, depnding on whether added room in only two dimensions is wanted, or extra height is also desirable.

This is true. As long as that's the case, there shouldn't be a problem. Unfortunately I have seen a lot of less than optimal forge builds, so I generally am wary of such large designs for first time forges.

[ThomasPowers]

And many times way too large for incorrect reasons: both in gas and solid fuel forges with the "I want to make swords" crowd who didn't research enough first to find out that you only want to heat what you can work in a single time at the anvil as heating the rest: is money thrown away, leads to grain growth and weakening of the metal, leads to decarburization and leads to scale losses.

[NelsonR]

The first forge I ever built, years ago, was an 11" deep coal forge. I figures that since I eventually wanted to go on to forge welding for some of my future projects this would help to ensure that the steel reached high enough temps for a successful weld. Instead it just took a long time to get all the coke burning, and once it got up to heat and would burn through any steel I put in it within just a minute or two. Luckily the mistake was not too costly as I later re-purposed it into a (rather fuel-inefficient) brass foundry, but it helps to teach that bigger isn't always better in blacksmithing.