how to determine the size of a burner?

[MikeAlmogy]

Hi all.

This is my first post so please do not roust me too much.

My name is Mike. I'm from Israel. I'm a beginner blacksmith.

I have built my own coal forge, gas forge and power hammer. 

My question is regarding my gas forge.

Like i said, i built a gas forge, 2 3/4 atmospheric burners. It worked nice (not great) but i had 2 issues. first one, i did not manage to get over 1080 degree C. The second is that the design was not optimal to what i need. I built it deep but low and narrow. Great for long objects but not so much for many items together.

My new design is (interior) 18cm high, 30cm deep and 39cm wide and if i got it right, it is 21060 cubic cm which is about 1285 cubic inch. way way bigger for my two 3/4 burners.

 So my question is, what are my options?

For start. i'm going to try and reduce the volume by adding a second layer of breaks on the side, which will reduce the volume to 14580 cubic cm (890 cubic inch). But i'm not 100% comfortable with this solution.

What size of burners do i need in order to achieve welding temp ? 1"? which size of nozzle? (I'm using a gas equipment, not mig nozzles, now i got 0.8mm hole). 

Maybe a blower is better solution? 

Right now the forge does not go higher then 750 degree C and when i increase the gas pressure (i started at 0.2-0.3 bar and moved up to 0.7) the burners turn themselves off. 

Advice will be most appreciated.  

Thanks and sorry if this question was already been answered. I tried the search but English is not my native tongue  and reading all the posts is hard for me.

Referring me to the right article or post will be most welcome.

 

Thanks,

Mike.

[ThomasPowers]

Mike how much water does it take to fill a 10 liter bucket?---Of course the bucket has holes in it and we are not telling you how many or how large.  This is the same question as asking how large/many burners it takes to heat a forge to welding temps without giving information on how the forge is built and insulated.

[MikeAlmogy]

I wrote that it is 39cm wide, 30 deep and 18cm high.

The isolation is heat resisting breaks on the bottom and the left and right sides. The front, back and top are isolation wool. front and back 3 cm wide, top 6 cm wide (2 layers).

I'm not talking about isolation. assume that the isolation is fine. I'm talking about volume. I have room to only 2 burners. Now either i downsize my dimensions or i enlarge my burners ((via bigger size of tubing or by adding a blower).

 

Thanks,

Mike

[Latticino]

Pictures will help.  Especially closeups of your burner design, forge configuration, door system...

You may not be aware, but there are many folks who prefer to forge weld in coal forges due to their capacity for localized high heat.  A well designed gas forge is typically better for general stock heating.  They are also quite good at the generalized heating needed for forge welding of stock that needs generalized heat, like pattern welded billets.

Your larger forge is extremely large, likely more than you need as a beginner, unless you plan on going into production.  If that is the case you will likely need a different forge design than a typical hobbyist smith.  Fortunately you have a world renowned production blacksmith in Israel.  I suggest you go see Uri Hoffi and ask his direct advise.

I would say that your forge liner is not thick enough.  I typically recommend at least 2" thickness of refractory insulation wool on all sides.  you don't give us information on the type of heat resisting bricks you are using either.  If they are the dense type of hard brick (which I assume you are using) they are a large thermal mass that will take a enormous amount of time to heat up.  If there is a thermal pathway to the forge exterior it will also bleed heat.  Your idea of adding more hard bricks to the forge interior will most likely not help and may make things worse.  Better doors and insulation will likely help more, larger burner ports for larger burners should be easy for a smith who has built three forges to accomplish as well.

For the same size burner opening a blower assisted burner can be designed to put out more heat than a naturally aspirated/ventauri type.  However you need to have the correct regulators and tanks (if using propane) to handle the greater gas flow as well.  Blown burners will also need additional safety equipment as well as a different design.

I'm not sure how these posts will help you as they are written in the same English as the existing posts on the site that cover gas forge design that you say you can't reference.  I suggest you go see Uri, by all accounts he is an excellent teacher and engineer and if approached correctly may be able to set you straight.

[MikeAlmogy]

Uri is my teacher. I will go see him but it will take some time. Small country but with twin little boys i do not have a lots of time.

I did read some posts, this is how i got to know this forum.

Anyway, my main problem is that the heat does not go over 750 degree C and that the burners shut off when i increase the gas pressure. I have a adjustable gas regulator.

 

Thanks,

Mike

[Frosty]

Welcome aboard Mike, glad to have you. My first piece of advice being: If you're close enough talk to Uri Hofi.

You're making a number of normal mistakes, nothing new we all did and I still make some of them. I'm famous for making my forges too large. 

First, lose the assumption your insulation (Isolation) is good. The brick has an insulation value of an equal thickness of lime stone. It's also a tremendous heat sink and WILL require significant time and fuel to heat. Not forgetting the heat being conducted through and radiated to the outside. 

The current consensus is, two layers of 1" (2.5cm), 8lb ceramic wool blanket. I use the name Kaowool for convenience but any equivalent brand will be fine. Rigidize it with a fumed silica and water solution for two significant good reasons: 1, it makes it stiffer and structurally more sound. 2, it encapsulates the ceramic fibers making them much less a breathing hazard.

The inner liner or flame face should be approx 1/2" of a water set, high alumina hard refractory rated to 3,000f. There are many methods of applying it from making forms and casting to, plastering it on like adobe over mud bricks. The purpose of the refractory layer is two fold: 1, It's armor, hot ceramic blanket is about as strong as cotton balls, a layer of hard refractory protects it AND reduces how much heat the blanket has to withstand. 2, A high alumina refractory is not subject to being dissolved by welding fluxes. Just a sprinkle of a borax based welding flux will dissolve HOT ceramic blanket like hot water on cotton candy. It will also dissolve typical fire brick about like cold water on a sugar cube.

I don't know what castable refractories are available in Israel so I have to leave you on your own on that one. Look for something similar to the American product "Kast-O-Lite 30" It has a number of advantages for a hot face in a forge and maybe Wayne Coe can ship you some, I don't know.

The floor needs to be a BIT tougher than the walls and roof but don't get carried away. I've been having good luck with the same construction as the walls and roof but making the hard refractory a LITTLE thicker, say 3/4".

The last construction technique is a Kiln Wash. It's not really necessary if you have a good flame face refractory However the right kind can increase the efficiency of the forge significantly and had a nearly diamond hard and almost inert layer of armor. ITC-100 is the most commonly known name for Kiln Wash in the blacksmith community in this country but it's not the cheapest nor best IMNHO. What you want is a Zirconium Silicate or zirconium phosphate containing kiln wash. Apply it in thin coats of about latex paint consistency allow it to dry before applying a second. Talk to ceramics suppliers or shops it's used in pottery kilns to prevent glazes from sticking and increase efficiency of the kiln. 

Do you have a product line that will require that large a forge? If so then some tweaking and larger or more burners is a must.

Next Mistake: Why do you think you can't move or add burners? You have tools, you could even patch and grind the welds smooth in deleted burner ports if cosmetics matter. I'm impressed you got plumbing cross burners to burn that well, not really good but not bad either. Check out the Illustrated T burner instructions on Iforge for a simpler and more efficient easy to build burner. Again, you may have to adapt to plumbing fittings available in Israel. If you'd like a higher efficiency but more technically demanding to build burner check out Mike Porter's burner.

The Illustrated T instructions lay out how many burners are required per volume with caveats about shape. A 1,200 cu/in chamber is going to need four well tuned 3/4" burners, probably six or more if you have to use plumbing crosses for the burner. It's just a matter of arithmetic, crosses don't have larger diameter side so they can't intake as  much air. Meaning you just can NOT feed it as much fuel. Less fuel and air means less heat output. It's arithmetic. A T as shown uses a 1" x 3/4" T, it's air intake is double what's available with a cross. 2x the air lets you use 2x the fuel. It's why I can get away with using a 0.035" mig contact tip while most everybody else is struggling with a 0.030" jet.

I only converted SAE measurements to Metric once for my convenience, you have conversion software as available to you as I have. We're going to run into problems with terminology, parts availability, etc. I may be more used to it but it's there. We just have to deal right? If you don't understand whit I mean just ask me. If I don't understand you I'll ask for clarification. That's all it is, we have to speak a common language, we call it a trade jargon over here, so we can communicate clearly. Right?

Frosty The Lucky.

[Frank Turley]

I won't be much help with your gas forge size. However, several years ago, I had Uri Hofi and his then striker, Tsur Sadan,  demonstrate for my students for 1 1/2 days. Since that time, Tsur has opened his own smithy. If you could contact him, you would have a wealth of information at hand. Tsur is personable and open and has been presenter of workshops in the U, S.

Besides, he told me that his name in Hebrew translates as "Rock Anvil." If that is true, then I am envious.

[Latticino]

Didn't see the pictures when I responded earlier, now that I see them I have the following to add/enhance Frosty's typical excellent response:

1. Forge floor, at least appears to be made of full thickness hard fire brick with no insulation below it.  With that surface area and minimal insulation I'm surprised you get even the minimal heat you currently have.  You must eliminate thermal breaks to the exterior of the forge (insulate between the inner forge skin and any path the outside).  Lose the fire brick and line forge per Frosty's direction.  The rules of thumb for burner quantity/size/capacity verses forge volume are for WELL INSULATED FORGE CHAMBERS.
2. You forge door is huge and looks like it provides a thermal path via the door frame to the outside even when closed.  When you get the insulating castable material Frosty recommends, consider casting a door as well and make sure there is a good layer of insulation between the forge interior and any metal.  You might also want to make a small opening in the door for both exhaust of combustion gases required for the type of burner you are using and for working smaller pieces.  If you use the back door you seem to have be careful regarding the propane hose location.  Also consider a different door operating system that won't have that hot door radiating heat towards the operator every time it was opened.  Ideally during operation your forge door is closed or only slightly ajar most of the time.
3. How long was the forge running before you said it would not get to the desired temperature?  Was the door open or closed?  With that much door opening and thermal mass you are going to have trouble getting up to heat unless you are burning tons of propane.  Forge will be very inefficient, not what you want as a beginner.  If you are a student of Uri's try to take advantage of his engineering knowledge.
4. Burners: On the plus side you seem to be achieving a nice stable flame in the photos.  On the other hand:  your flares appear to be slightly inside your forge, and your flares and mixing tubes appear to be made out of galvanized pipe.  This is a recipe for disaster and needs to be addressed immediately (if assembled in stainless steel ignore this).  Also the burner on the right looks to have a lower flame output.  It appears from the photo that the orifice may not be well aligned on that one.
5. I hope the method you are using for holding your burners in place is temporary.  If the forge ever gets up to temperature that system may fail with unexpected consequences.
6. Please seal your refractory blanket better.  As someone who now lives with reduced lung function due to years of working with unsealed refractory blanket insulation heating chambers I can tell you it is worth it to be more careful.  If not for yourself, for your family.

[MikeAlmogy]

Hi all. and thank you very much :-)

My forge "design" and burners supposed to be a copy of Uri forge that i saw and worked on in his shop. However, i might got the dimensions wrong, I did not took measurements of his forge. The idea, as i see it, for the opening in the front is that you do not need to open the whole door, unless you need to insert a really big piece. the front is also the exhaust.

Just to remind you guys, i had a former forge that did not even had a door and it reached 1080 degree C. Same dimensions except that the former one was little bit lower. same isolation and same burners. i simply made it higher and with the door on the wider side then the narrow side.  

The burners are of Uri design and material. Except that on his he got a piece of stainless steel as the flare and i used a galvanized pipe flare that i saw on a thread here. I did used to have a piece of stainless steel on the bottom and i might changed it back to it (funny story about that).

I even buy the isolation components from the same shop he does (and surprisingly it is very close to my workshop, relatively speaking). my isolation is up to 1500-1700 degree. Giving that i want my top heat to reach maximum of 1250 degree C i think i'm good. I do use ceramic wool blanket. It is 30mm thick. On the top i use 2 layers, on the front and back, one layer. 

I red what you all wrote and i accept it. i need to improve the isolation and design but my question remains, assuming that i want only 2 burners, what are my options?

My goal is to have a large enough forge to put 8-12 bars of round 16mm diameter 25cm long pieces. I want to make tools. 

 

Thanks,

Mike

[MikeAlmogy]

Ok some more input.

I managed to get up to 1020 degree Celsius. but with 1.5 bar. not acceptable:-(.

The forge losses lots of heat. i need to build a smaller and better one. Im a little upset but that the cost of learning. Compare to my 4x4 hobby, this is nothing :-D.

I changed the burners to have a strait 1" stainless steel with nice thick wall.

I also downsized the interior by adding more breaks but to be honest, on second thought im not sure that it was a good idea. it takes the breaks more time to get hot then air i think. 

It took me more then an hour to reach 1000 degrees. not acceptable but like i said, learning phase.  

My most concern about the burners was answered so now i just need to have a better frame and isolation to the forge. also a better door mechanism. I do not want to use breaks as door.

Btw, i keep forgeting to write this, im not using propane. im using butane gas. we do not have propane as regular store gas. i do not know what are the difference between the two.

Thanks and i will keep you posted on results.

Mike

[Latticino]

Going to add this and then I'm done with this thread:

1. Pressure used of your fuel source is more related to the orifice size than anything else.  If you are attempting to compare with performance of someone else's burner using only pressure, it needs to be both the same size orifice, the same general configuration of burner design, and the same fuel.  For example I easily reach 2,400 degrees in my forge (as indicated by a type K pyrometer) with residential natural gas at 7 inches WG of pressure (0.0174 bar), but I have a blown burner, variable orifice, industrial ventauri mixer and a 1 inch gas supply line.  1.5 bar does not seem out of line for a butane NA forge with mediocre INSULATION.
2. A forge optimized for production work is different from one for hobby work.  For the former you don't really care how long it takes to get completely up to temperature as long as it holds temperature in a stable fashion, particularly when there is a large amount of stock mass moving in and out of it regularly.  Good production forges will have much more thermal mass in their construction than hobby forges for that reason (both will still want to be fuel efficient, but that is more a matter of correct insulation and door design).  You most likely don't have the capability to use 8-12 pieces of 1/2 inch stock all at once, or even within one heat cycle.  That needs the tooling, equipment and experience that Uri has.  Depending on what kind of tools you are planning on making, if the stock is medium/high carbon steel, keeping at elevated temperatures for extended periods will both scale away the stock and decarb the surface.  While you are learning I, along with the others here who are attempting to assist you, recommend a much smaller forge.
3. Based on a 5 minute Google search (which presumably you could have done yourself) butane burns at a slightly higher temperature than propane (max temp 3615 vs. 3595), but needs more air in the mix for combustion (almost 50% more).  That means your burner design must be a lot different to be optimized for butane.  The flame speed from a given burner outlet will be different as well.  Our typical rules of thumb and experience with burners will not necessarily apply.  I wouldn't comment further on your burner design any more than I would on a diesel fired forge burner, other than to say that I would be very concerned about the burner tip getting so hot and the potential for a dangerous situation for ignition in the mixing tube if you get up to temperature, shut down then restart before the unit has completely cooled off.
4. It looks from the photos that you have a mixture of lightweight insulating BRICKS and heavy hard fire bricks in your forge.  While both will take longer than blanket to heat up, the heavy bricks will provide very little insulation at all.  As I stated before, to have a well insulated forge you need to have insulation surrounding the entire chamber that you are heating, especially the floor if you have your burners pointed at it.
5. I find your forge design and location near stored combustible materials to be dangerous.  I strongly suggest you get the entire setup inspected by whatever passes for a code official in Israel.  Barring that I would be sure to have a chemical fire extinguisher on hand, install an emergency shutoff valve in a spot you can get to several feet away from the forge and never leave it unattended while it is firing.

Good luck with your journey into blacksmithing.

8 hours ago, MikeAlmogy said:

The burners are of Uri design and material. Except that on his he got a piece of stainless steel as the flare and i used a galvanized pipe flare that i saw on a thread here. I did

One last thing.  I can't imagine anyone on this site suggesting using a piece of galvanized pipe as a flare.  Perhaps you mean black steel pipe?  The galvanizing is a zinc coating that will burn off at forging temperatures releasing a dangerous gas.

[JHCC]

37 minutes ago, Latticino said:

9 hours ago, MikeAlmogy said:

The burners are of Uri design and material. Except that on his he got a piece of stainless steel as the flare and i used a galvanized pipe flare that i saw on a thread here. I did used to have a piece of stainless steel on the bottom and i might changed it back to it (funny story about that).

One last thing.  I can't imagine anyone on this site suggesting using a piece of galvanized pipe as a flare.  Perhaps you mean black steel pipe?  The galvanizing is a zinc coating that will burn off at forging temperatures releasing a dangerous gas.

There was a thread a month or two ago by someone who built a Frosty T-burner from galvanized pipe, and was immediately warned of its dangers. @MikeAlmogy might be thinking of that post -- and this is a very good reminder that the discussion on an IFI post is often just as valuable as the OP!

[MikeAlmogy]

I made a mistake. it was not galvanized steel. my fault. anyway i removed the galvanized flare and replaced it with stainless steel one.

about the idolation i use.

i use two type of bricks. ceramic  brick and they supposed to be very good quality. not the best but definitely not the worst. i think that they give better isolation then blanket but they are much more expensive and less durable. the floor bricks are heat resisting bricks that has more durability then the ceramic ones. on my new forge i will use a ceramic blanket and on top of it those bricks as floor.

 i can try and get the commercial name if it is any interest for you.

 

Mike

[MikeAlmogy]

Hello. It been a while since i logged into this forum.

Here are my current forges. (And yes, i have a kwool without refractory layer. will be address on the next rebuild)

Both of those forges works great. I'm really happy about them. Soon i will build my third one and a smelting furnace :-)

 

BTW, i removed the flip doors. I'm using a isolation break at the moment. easier to handle and safer i think.

[Irondragon Forge ClayWorks]

You really need to read this thread about the dangers of unprotected insulating blankets.

 

[MikeAlmogy]

You are right.

I decry the importance of it and i'm sorry for that.

I need to "re-configure" my small furnace and when i do that i will use a isolation cement or coat the blanket. Not sure what kind of material to use for the coating. Cement?

 

Thanks,

Mike  

[MikeAlmogy]

just to wrap it up, here are my two gas forges at the moment. one with ceramic fiber blanket soaked with rigidizer (i do not like the outcome so i ordered  rutland dry mix patch. saw on their website that it can hold up to 1500ºC). The bigger one is made of isolation bricks and refractory cement. the top is not connected to the floor so i can play with it as needed.

[Mikey98118]

On 7/5/2017 at 7:21 AM, MikeAlmogy said:

Right now the forge does not go higher then 750 degree C and when i increase the gas pressure (i started at 0.2-0.3 bar and moved up to 0.7) the burners turn themselves off. 

Okay, two bars are about 30 PSI gauge pressure, so .7 to 1 bar more means your burner blows out at about 45 PSI; that doesn't say much for their stability in this forge. On the other hand, fan-blown ribbon burners provide positive pressure; they are also a better design for larger forges. I suggest that this path solves both of your problems while providing the most frugal design for fuel use. Your forge is too large to use off-site anyway, so such fan-blown burners present no downside.

[MikeAlmogy]

4 hours ago, Mikey98118 said:

Okay, two bars are about 30 PSI gauge pressure, so .7 to 1 bar more means your burner blows out at about 45 PSI; that doesn't say much for their stability in this forge. On the other hand, fan-blown ribbon burners provide positive pressure; they are also a better design for larger forges. I suggest that this path solves both of your problems while providing the most frugal design for fuel use. Your forge is too large to use off-site anyway, so such fan-blown burners present no downside.

Thank you but you answered the original question which was referring to a different (original) forge. The two forges i posted on January 5 are my current forges and they work extremely well. In fact i managed to melt some material i put on the smaller forge (got distracted). 

Ribbon burner is on my to-do list. Now i'm playing with a small (1/2") fan blown burner i built for a smelting furnace. (very small one). 

 

Thanks,

Mike

[Mikey98118]

I love small; all my favorite cars were and are small; the wife and house are too. Anyone who follows my writing knows that I get excited about small burners in small forges. But sometimes we just gotta look up from our obsessions and admit that the other guy's dog is pretty cool too. Ribbon burners aren't my thing, but they are still magic.

[MikeAlmogy]

I do not argue with that. It is in the to-do list. 

[ThomasPowers]

MikeAlmogy, what kind of ore are you smelting?  (or planning to smelt?)

[MikeAlmogy]

bronze, aluminium, copper, brass.

I wish i could smelt steel but not sure if i have the resources for that. My dream is to cast my own anvil :-) but 120KG of smelting steel is no joke. Not sure that there is a big enough smelting plant in Israel for that. 

[the iron dwarf]

you have bronze and brass ore in israel?

in most parts of the world it is only possible to make these metals from alloys of copper and zinc or tin not directly from ore.

aluminium can also be a problem to smelt with just gas as a lot of electricity is required as well

[MikeAlmogy]

we have but it is not cheep. i'm not planning on smelting tons of that. so i will see.