Recommendation? Blown Air Forge???

J

Jamie G Lupole

Joined
Jun 21, 2019
Messages
8
Hello All,
I've been doing some research on a recent build and can't quite find the answer(s) I need.
My current blown forge build is horizontal with blower at the side angled slightly down and forward from just above center line. with a 3" gas inlet/burner tube and with a variable speed squirrel cage blower. It is round, 24 inch long and a 7in interior work dimension, with 4inch of kaowool for insulation. Front and back can be fully or partially closed up with secured fire bricks. I am using a 50gal tank with multiple safety shutoffs/valves. Much of this this design was based of my old vertical forge.

My problems/questions:

1.) Is my 3" gas inlet/burner tube too big? It blows a good flame (and the jet engine sound is cool), but I seem to struggle to get it to hold and sometimes get to welding temps. Which doesn't seem possible to me. Should I build a smaller burner/inlet tube? Maybe down to 1.5in? Should it be 1.5" for the whole blower tube to nozzle end/tip? or just 1.5" at the nozzle tip, is that ok?

2.) Is my forge chamber too big? 24"x7" with 4" all round insulation. Again, doesn't seem to be from my previous research. I can somewhat shorten the chamber length. with a homemade refractory plug put to the back.

3.) Regulators, I have one that restricts it to 20psi but it tends to make the burn flutter more, so I don't really use it. I can also adjust gas flow thru the various valves and air flow. I seem to get a very nice adjustable flame this way, but still struggle with temp control and just blow thru my propane supply (lots of adjusting gas pressure flow and air flow here). Should I change out the regulator to an adjustable one?

4.) 50gal Tank, is that too small for that size forge? I get tank freeze after a couple of hours and can never get the last 1/4 of propane used because pressure drops too low for a good feed. I have a 100gal tank but there are a lot of new regulations associated with its use and will need to be moved from the perfect area to and inconvenient area to make the use of the 100gal. tank worthwhile doing. (still got tank freeze w/100gal just took longer)

5.) Suggestion here (after all quirks are worked out): Is it worthwhile to add a PID control set-up? as I don't HT any stainless or D2. I send those out when needed.

All this is to get consistent forge welding temps, but as is, this and my 2 burner atmospheric forge can handle any of my general forging and heat-treating needs.

If you need more info just ask, Thanks ahead of time for any input and info.

Jamie
dba: KUMA Knives
 
What size is the burner itself?
I do know that the openings for the forge have to be big enough for the burner. In other words, closing up the forge to try to make it hotter doesn't work if it's closed too much for the burner size.

I'm assuming you are talking about 100# tanks and not 100 gallons. I've got a similar sized forge with my ribbon burner and have never had my 100# tank (about 22 gal) freeze up on me, even in the winter in the PNW even when I lived in the foothills of Mt Rainier in WA.
 
Man I’d like to see some pics and possibly a video.
As Weo mentioned I believe you are stating gallons and meaning pound when referring to your tank size.
Are you saying a 3 inch diameter burner entering your forge? That is huge, 1 1/2” is probably on the large side of normal.
You said using a 20psi regulator but what psi are you actually running? I rarely go over 7psi on my blown forge usually 4-5.
 
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Yep, I meant pounds not gallons, (brain fart).
And after a pm elsewhere, I think I "reversed" designed my burner. Currently, my blower goes straight into the burner tube to a reduced nozzle end. I was wrongly thinking compressing/forcing the gas mixture together (maybe I was trying to make a jet engine! Haha!). I'm going to change that to 1-1/4 or 1in??? burner pipe with a flared end and hybrid ported ribbon burner end and add an elbow or two in the air feed improving the air mixture and to the gas line, a needle valve with gage instead of a set regulator. Unless someone can suggest a good adjustable regulator. As I understand the tank freeze was happening because of the amount of propane blowing thru what I essentially built was a combination blown/atmospheric burner in overdrive wasting a lot of propane. This should solve most of what I need. I'll see how that works out. By explanation that should make a more efficient burner overall, correcting most of my issues. Hopefully.
I guess what worked for my vertical forge didn't translate to a horizontal design.
At least my forethought of making my forge design changeable will pay off.
 
One thing you really want in a forced air forge, really good air/gas mixing. Inject the gas as close to blower as possible, then at least 12" (maybe even 14" better?) the 3" mixing pipe should be reduced to 1-1/4" or so for the final length. This will increase the air flow speed.

A photo showing how the forge is built will certainly help. Good luck
 
Ken H> said:
One thing you really want in a forced air forge, really good air/gas mixing. . .
Click to expand...
Some ribbon burners also have a 'mixing chamber' with baffles in it to encourage mixing.
 
No matter which forge I'm running the gas pressure is the same, 5 PSI. Less or more and the forge will start giving problems. I run well head gas, but gas is gas. I place the needle valves in the line as close to the burner as I can get them. I've tried different locations but this works best.
Post us a picture if you can. Regards, Fred
 
Fred.Rowe said:
No matter which forge I'm running the gas pressure is the same, 5 PSI. Less or more and the forge will start giving problems.
Click to expand...
Gas pressure depends on jet size - "IF" running a jet. It seems that most blown forges don't use a jet, but rely on an 1/8" NPT or so nipple to inject gas into the air flow which uses a low gas pressure. I and a few other folks do use a jet in the end of that 1/8" nipple and use higher pressure which causes the gas to spray into the air flow in hopes of better mixing.

I think Atlas Forge uses a jet on their blown forge, but don't quote me on that.
 
A blown forge has no jet. The gas is not injected.
Most people use a 1/4" needle valve at the point of entry into the burner. The valve is attached to the side port of a Tee with the air flow down the direct axis. It is as simple as that. The size and heat of the flame is controlled by the air gate valve and/or fan speed, and the gas needle valve. 5 PSI is more than enough to run a blown burner. Closing the needle valve is how you determine how much gas you get.
 
Stacy, I was under the impression that Atlas forge used a jet on their blown florge? I'm "pretty sure" I've seen where he commented on using a jet. I've been using a jet on my blown forge - that allows me to adjust the flame from 5 psi range rather than over a 1 to 2 psi range. Either way works just fine as the needle valve does the actual metering of the gas.

Atlas Forge - perhaps you'd chime in and set the record straight, jet or no jet in your blown forge.
 
24x7 is a big forge!! Most people recommend 2" thick wool and then refractory, did you go with the 4" to reduce the ID down to 7"?

This is what my gas setup looks like for the blown/forced air forge:
K0X3tvd.jpg


3/8" male flare to 1/4 NPT adapter to connect into the propane line, 1/4" NPT 6" nipple to a 1/4" needle valve into another 6" 1/4" NPT nipple and into a 3/4 to 1/4 NPT reducer into the 1 1/2" elbow. 1 1/2" tubing from the gate valve going to the blower and a 6" 1 1/2" nipple coupled to a 5" 1 1/2" nipple which will be filled with sections of SS tubing welded inside as a defuser (not shown).

Local guy is helping me build up my first forge and this is how he does it. He used some other diameter piping for the propane portion because he had other stuff on handle and used other adapters (I think he used 3/8" and 1/2" nipples in the propane area?), but I decided to go this route for less connections/adapters (less leakage points). Propane tank with 2 layers of 1" Koawood and going to have fire brick doors front and back. I got to see his forge and it was up to temp in 5-7 minutes running ~1 PSI propane out of the regulator from the tank. The forge body itself will have a piece of pipe welded to it as the port for the burner at around the 9 o' clock position; this way I can light the burner outside of the forge, put in and adjust. When shutting down, I can remove the burner completely so it doesn't sit in the forge while it cools down. He also built a forge for a couple other local smith (including a local forge group with a few FiF winners in their ranks!) of the same design and they forge weld with it.

I looked at the Graham Forge from Atlas and from what I could see from the pics, it looks like a propane fitting (3/8" Male flare) that is welded to the burner tube, but I don't know the diameter of the orifice of the male flare where it goes into the tube?
 
Charles at Atlas uses his regular venturi burner with a small blower. It is a little different than the standard blown burner. More like an air assisted venturi burner. I don't know if he makes the jet hole a bit larger. Hopefully he will chime in.
 
When Taz mentioned the 3/8" flare fitting on the Graham blown burner I had to go look. Yep, it's a 3/8" flare fitting and the regulator and hose seems to be only the regulator and hose with no needle valve or jet. I'm "almost" sure I remember Charles talking when I was building my blown forge (Thanks Stacy for all the help) there was a discussion about what size jet (if any) to use for a blown forge. I'm "almost" sure Charles said he used a jet with a blown forge - that was 2 (3?) yrs ago. As mentioned before I use a jet so I can adjust the PSI in the 5 to 10 psi range rather than the 2 to 4 psi range with an 1/8" nipple (or 1/4" nipple).

I sure hope Charles will chime in and correct me if he never mentioned using a jet with blown burners.

Ken H>
 
Another reaso Charles uses a jet on his blown burner is that the burner tube is very short and has limited mixing space and ability.The jet makes the gas move faster and gets a combination of venturi and blown effects. While I admire Charles' ingenuity, it is not the blueprint to build a blown burner.

Here is a tutorial on building a blown burner I wrote a while back:
He had asked about my reference to a "chamber" in the burner.

It is a good idea to have a "bulge" in the burner as a mixing chamber. This is where the gas and air mix to more fully burn in the chamber. It adds a lot to the forge efficiency. You just use a larger piece of pipe and two "bell reducer" adapters. If the burner is 1" pipe, then a 3" piece of 3" pipe is the mixing chamber. Thus, you use two 1" to 3" bell reducer adapters to make the burner go from 1" to 3" to 1" again, and then out into the forge chamber. The bell reducers are standard fittings at plumping supply and hardware stores. Here is a link to what I am talking about. Use the sizes available in your area. The chamber can be any size at least twice the burner pipe size. 2.5 or 3" works great.
http://catalog.industrialpipega.com/viewitems/black-malleable-sch-40-80-fittings/bell-reducers-2

The burner pipe size for a medium size forge could be 1" or 1.25". That mostly depends on what use it will see. If doing regular forging and HT, 1" is plenty. If welding damascus, 1.25 would be great (but the 1" will still do fine). 1" is what I would suggest, unless you plan on making a larger forge in the future, or doing lots of welding. ( The whole burner can be moved from forge to forge for many years of use.) The length of the pipe pieces used to make the burner isn't terribly important as long as it has about an 8" long pipe as the burner tube going to the forge.

If I was to make up a shopping list for building a top notch 1" burner for a 5-6" chamber by 14-16" long forge it would be (starting from the blower):
Blower - 100-150CFM range, preferably variable speed. A fan/light controller will often work as a speed control. DC blowers are super if you find one.
2" floor flange. You need some sort of flange or other fitting so the blower can connect to the burner piping.**
2" closed nipple to connect flange to next item.
2" gate valve. A gate valve is placed here to adjust the blast from the blower. If using a speed control, the valve may not be needed, but a ball valve is still a good idea.****
4" piece 2" pipe.
2" by 1" bell reducer
1" closed nipple.
1" street elbow ( ell) ****
1" tee with a 1"X1/4" reducer bushing in the side port. This is where the gas valve is placed. A 1/4" needle valve is used to control the gas flow. The gas line connects here. Using "quick connect" gas fittings on the gas hose is a really good idea. HTT&R has them, as well as most everything else needed to make a great burner.
3" piece of 1" pipe
1" by 3" bell reducer
3" piece of 3" pipe
1" by 3" bell reducer
8" piece of 1" stainless steel pipe. This is the burner tube to enter the forge. Stainless pipe is recommended here, everything else can be black iron. Buy a spare of this pipe, as it will need replacing eventually.


** A plain piping floor flange is a good looking and easy way to mount the blower to the burner piping. Just make some sort of "O" ring or rubber gasket and bolt them together. There are many other ways to do it, too. Use whatever seems simplest for you. Try and match the pipe size coming from the blower with the blower outlet size to some degree. All that matters is that the pipe out of the blower should be larger than the burner pipe by at least twice the size. 2", 2.5", or 3" pipe usually works right, depending on the blower used. Maintain that diameter until the elbow.
Here is what a floor flange looks like:
http://shopping.search.yahoo.com/se...8x?p=pipe+floor+flange&trbkt=VIP226&fr=mcafee

****If everything was kept linear, the whole burner would be a good 36" long. That will work fine, but takes up a lot of room and is a balance issue. Placing an "ell" in the setup right before the "tee" not only shortens the length of the assembly, but places the blower in a hanging down position below the forge which keeps hot gases from flowing up into the blower when the forge is shut off. A good practice is to always shut off the gate/ball valve when shutting down the forge.
Make a bracket or brace of some sort to support the burner arm and blower, as just hanging it from the forge is pretty unstable. If building the forge on a rolling cart, weld this brace to the cart.
In many setups, the floor flange, gate valve, and first length of pipe before the tee are PVC pipe fittings. Since this part of the burner should always be cool, that works fine. However, iron piping will never crack or break on you." Penny wise, pound foolish" applies here.
Also, it might seem easier to just use the tee to do the job the street ell is doing, but a street ell fitted on the end of the tee makes a much smoother path for the air stream. The gas entering the air stream from the side of the tee also increases mixing. Again, the couple extra dollars spent here is well invested if you want the max from your burner.

A burner certainly can be built cheaper and simpler, but the burner is like the engine on a car. Why build a classy hot rod and then put a Yugo engine in it. Money spent on a good burner will be money well spent. A properly built burner can last a lifetime. You might change the blower, and certainly will change the burner tube at the forge end, but everything between them can last forever....so build it like a tank.

High Temp Tools & Refractory has the parts as a kit and other forge building supplies.
 
Thanks all, I believe I achieved what I needed. I will post pics as soon as I can of the updated burners. Inefficiency definitely was because of the poor fuel/air mixture.
 
Stacy E. Apelt - Bladesmith said:
A blown forge has no jet. The gas is not injected.
Most people use a 1/4" needle valve at the point of entry into the burner. The valve is attached to the side port of a Tee with the air flow down the direct axis. It is as simple as that. The size and heat of the flame is controlled by the air gate valve and/or fan speed, and the gas needle valve. 5 PSI is more than enough to run a blown burner. Closing the needle valve is how you determine how much gas you get.
Click to expand...
Ken is correct, I use a jet on all my blown forges. There is no venturi effect in my blown burner, it is purely blown. The jet orifice is .042" with a custom flare fitting TIG welded over it. It is a short mixing tube, and the perpendicular jet mixes it very rapidly. It lets me control the gas with a regulator instead of a needle valve. It also allows me to limit the amount of gas to the size of the blower, which is 120k BTU, for safety reasons. I could use a bigger orifice(or lack thereof), but my products are aimed at beginners who might otherwise give it way too much gas and blow themselves up. Then again, I'm one of the only forge makers to use DC blowers instead of the Dayton 178 CFM. I like the ease of control and ability to run off a 12v battery if at a site with no electricity. A simple PWM controller to regulate the speed of the fan, instead of the gate valve.

Just an example, I am building a custom vertical forge for a friend. It needed a much larger 225k BTU burner, so I used a 40 CFM fan and a .062" orifice/jet. This allows me to know that when the regulator and fan are both at max, the burner will run fine.

Hundreds, if not thousands, of knifemakers have built blown burners with the design that Stacy recommends, and there is absolutely nothing wrong with it. When building 1000 burners at a time, you can have custom parts made that aren't available from the hardware store that greatly reduce the complexity.

Here's a quick lighting video we did a couple years ago, showing the simplicity and small size of a working blown burner.
 
Ken H> said:
Gas pressure depends on jet size - "IF" running a jet. It seems that most blown forges don't use a jet, but rely on an 1/8" NPT or so nipple to inject gas into the air flow which uses a low gas pressure. I and a few other folks do use a jet in the end of that 1/8" nipple and use higher pressure which causes the gas to spray into the air flow in hopes of better mixing.

I think Atlas Forge uses a jet on their blown forge, but don't quote me on that.
Click to expand...
I had not considered that. Thanks for the post Fred
 
Charles, thanks for chiming in. I agree with you after using both a needle valve, then switching to a jet with no need for needle valve. A blown forge with jet is simpler and cheaper to build, and sure doesn't need that big blower.
 
Karl B. Andersen said:
See if these help:


Click to expand...
Karl, let me know next time and I'll bring some materials over that would make casting much easier. Also, I'm not fond of buying partial amounts of castable. When I split up a bag, I pour the entire bag in a barrel and mix it thoroughly (while dry) then bag it up. Otherwise, you don't usually get a consistent mix of the ingredients since they tend to settle in the bag. Top scoops will be lighter materials, and the bottom will be mostly alumina. Neither mix and cure like they should.

Very nice videos, and good job on a solid forge build.
 
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