Gas forge build advice

[Gerhard Gerber]

8 minutes ago, Matt Walker said:

Can you get your hands on a leaf blower. It'll probably be too much but some of the pressure could be vented for an air curtain. Fabricate a butterfly valve to control what goes into the forge.

https://www.amazon.com/Sun-Joe-SBJ597E-All-Purpose-Electric/dp/B01M3UK0VY/ref=sr_1_4?crid=3O13Y85XBXHE4&keywords=leaf+blower&qid=1693230640&sprefix=leaf+blowe%2Caps%2C567&sr=8-4

Thanks for that, we have a busted (switch) leaf blower lying around, definitely easier than the shop blower.

One problem, I was dreaming about a slightly quieter forge, leaf or shop blower.........blows that dream out of the water 

[Matt Walker]

I've had 2 shops, both had the blower for the coal forge mounted outside the shop. The air from a big blower was piped underground into the forge. I don't appreciate blower noise either. Never did it for my gas forges because they are noisy anyway, even atmospheric, just wear ear muffs. When I fired up my big gas forge I was going to be running the power hammer. I really enjoyed headphones connected to my iPod. Have a bluetooth set now. Listen to music or a podcast rather than blower whine.

[vlegski]

A ribbon burner doesn't need that big a fan to run efficiently. 

Mine is a 1/30 hp Dayton squirrel cage blower that'll fit in your hand with a water shut off value inline to adjust airflow. It's quiet enough to hold normal conversations. 

 

[Gerhard Gerber]

17 hours ago, Matt Walker said:

I've had 2 shops, both had the blower for the coal forge mounted outside the shop. The air from a big blower was piped underground into the forge. I don't appreciate blower noise either. Never did it for my gas forges because they are noisy anyway, even atmospheric, just wear ear muffs. When I fired up my big gas forge I was going to be running the power hammer. I really enjoyed headphones connected to my iPod. Have a bluetooth set now. Listen to music or a podcast rather than blower whine.

I have a big head, literally, taken to wearing my shooting hearing protection when busy with the angle grinder, but I can't stand it for too long, ditto for headphones and can't stand the in-ear jobbies.
I'm also slightly nervous about eliminating one sense and not hearing if something starts to go wrong.
 

 

16 hours ago, vlegski said:

A ribbon burner doesn't need that big a fan to run efficiently. 

Mine is a 1/30 hp Dayton squirrel cage blower that'll fit in your hand with a water shut off value inline to adjust airflow. It's quiet enough to hold normal conversations. 

 

When I read that I feel like like pulling out my hair, reminder of the two venturi burners I never got running despite all the advice from here.
I have a big ball valve just above the fan, tried choking the air and that certainly didn't work. 

[vlegski]

You indicated that you wanted a quite forge  and that i thought I was providing an valid option. 

Sorry if my input caused you distress and confusion. 

 

[Gerhard Gerber]

6 hours ago, vlegski said:

You indicated that you wanted a quite forge  and that i thought I was providing an valid option. 

Sorry if my input caused you distress and confusion. 

 

Please don't misunderstand, my frustration is not with you, your and everybody else's ideas and advice is very much appreciated.
I'm sitting with two forge projects that I have a lot of money invested in, one abandoned and now what seemed to be a success, setup that has and should work, but now doesn't.
Some local advice was also to lower the gas pressure to suite the fan, but during test burns outside the forge only half the burner lit up at lower pressure, it has a definite bias to the one side.

The spare leaf blower needs new bushes for the motor, so this weekend the shop blower will be cable tied to the setup for a test.
Going to a smaller diameter pipe for that section between the fan and gas nozzle will be relatively cheap, but I'm not sure it would help since that feeds into the large T-piece where the gas comes in, changing that means a complete rebuild.

[Gerhard Gerber]

Realized today high school physics is a long time ago, but I'm hoping halve the diameter = twice the pressure, got reducers and new pipe, going from 50mm to 25mm between the fan and the burner.
Working late so I'll have to wait till tomorrow afternoon to give it a test.

[Dan Hertzson]

Don't have time to look through the whole string, so I'll just add a couple of notes here:

1. Realize that by designing and constructing your own forges you will need to experiment to achieve acceptable performance.  Even a small change from a vetted design can have a big impact.
2. If you are trying to get more static pressure at the ribbon burner outlet, dropping the mixing chamber diameter is the wrong way to go.  A smaller diameter duct will lead to more static pressure loss due to friction, and consequently less pressure at the outlet.  Of course you are really looking to increase the flowrate of the air/gas mixture, but the pressure differential is what drives the flowrate.
3. If you have any kind of orifice (mig tip...) restricting the gas outlet into the mixing tube, get rid of it.  The connection size for the gas should be at least 1/4" diameter and possibly larger.  Mostly depends on the pressure you are using for propane.  This is also why indicating pressure for a forced air burner really isn't a good measure of how efficient your forge is.
4. Also, use a variable pressure regulator capable of at least 30 PSI outlet to meter your propane source.
5. If you still have trouble getting a neutral flame from your burner (and it is reducing), your system may be starved for air.  Before switching your blower, decrease the length of mixing tube and remove elbows in the line.  Short and smooth tubing will loose less pressure to friction and give you better flow.  Baffles will also greatly impede flow.
6. Flame retention at the burner outlet will improve as the forge gets hotter.  Tune your burner inside the forge.  Note that tuning may include either blocking off some burner outlets or drilling them out to larger diameter.  This can help balance the flame locations or help with stability.
7. Make sure all volatiles are completely burned off from the forge body and burner before firing the burner if possible.

[Gerhard Gerber]

Hi Dan

Thanks for taking the time.

1.  As I've found out......
2. I was maybe a bit unclear, my plan is to reduce to 25mm between the fan and mixing chamber which stays unchanged.
3. I find this a bit surprising, refer to #1, I'm using the same size mig tip as my friend with his working forge, but I'll keep this is mind for sure as its relatively easy to get rid of the MIG tip.
4.  Will post a pic of my regulator, at 200kPa its almost fully open.
5. Its much simpler as far as elbows etc are concerned than I planned initially, but there is a baffle in the burner.
6. Suspected as much due to my experience with my first forge, but I didn't want to get it too hot for the sake of the curing refractory, but running as it was that might take forever and a day.  The burner ran perfectly outside the forge, bit surprised by the result inside the forge.

[Gerhard Gerber]

[Dan Hertzson]

Hi,

 

Regulator should be good.  I would make the following changes if you still feel you have insufficient air:

1. Get rid of the mig tip in the gas train.  Those are really only useful for accelerating the gas stream to entrain air in a naturally aspirated burner and are not needed in a forced air burner.
2. Swap the blower and gas connections at the mixing TEE and don't reduce the duct size between the blower and burner outlet.  Both side inlet tee connections and smaller duct add to duct friction, which reduces the blower effective airflow.
3. If burner ran well, exactly as currently configured, outside the forge and is a problem inside it may be that the forge or burner block is still outgassing as it comes up to higher temperatures.  If you are still driving off steam from your refractory castings it can have a significant effect.  Try to slowly heat the chamber till you get up to a good forging temperature.  May take some hours.

Good luck.

[Gerhard Gerber]

Thanks @Dan Hertzson for all the advice, helped a lot on Saturday. 

I have no hair left on my left forearm and hand 

 

I tried the thinner tube, didn't work at all.

Removed a bend meant to tuck the blower under the shelve, went back to the shortest full size pipe with the tap and blower directly on to that.
In that configuration and going down to between 50 and 60kPa I got it to run for the first time.
Left it on for a while and then jerry-rigged fire bricks to block the back end and restrict the front, that's when the steam started coming out, so I shut it off.
Yesterday I wanted to run it a bit, must've done something stupid because I had a small explosion that shaved my arm, and when I got it lit it was make an ungodly pulsejet noise.  Figured out restricting the air stopped that, ran it for a while and then opened the air completely and the pulsejet noise was gone.
Chucked in a piece of mild steel, eventually got it red hot, but no more.

The only thing I haven't done is remove the MIG nozzle, but that's the next step.
But I have a question.
I was using very little gas, with the regulator at that setting my old forge wouldn't have run.
Thinking about what would happen if I remove the nozzle, I see a relatively low pressure system with a higher volume of gas, if my thinking correct?
If that could get me up to welding heat with the current blower that would be ideal, but I aided the fan a bit with a shop blower and much higher gas pressure (150-200kPa) and it would roar into life immediately.
 

[Alan Longmire]

7 hours ago, Gerhard Gerber said:

with the regulator at that setting

 

With a blown burner and no restriction in the gas line, your regulator probably won't read anything.  It's not gas pressure you need, it's gas volume.  The MIG tip is your enemy in that system.  Just dump gas straight out of the tube.  If you're worried that may be too much, i.e. if you don't trust your regulator to work at such low pressure, put a needle valve in the gas line about 10cm from where the line enters the mixing tube.  You can use that to tune the gas flow without messing up the mix.

 

One smith I knew didn't even use a regulator with his blown burners, just the tank valve and a needle valve.  That is a little extreme and certainly not safe, but it worked fine.  

[Pieter-Paul Derks]

In my blown burner the gas is pumped straight into a 1/4 inch tube connected at a right angle to the air line, no mig tis or anything. I have a needle valve in the line but I don't use it, between the regulator on the tank and a gate valve on the air I get all the control that I need. My forge is not a ribbon burner, just a straight pipe, dirt simple and works great.

 

 

[Gerhard Gerber]

Thank you, MIG  tip removal is next. I assume I don't need to worry about the thread where the MIG tip screwed in?
I couldn't find a needle valve in this country, not for love or money.
There are online shops that deliver in Namibia, would rather not support them, but I'm close.
 

[Dan Hertzson]

On 9/4/2023 at 2:51 AM, Gerhard Gerber said:

I aided the fan a bit with a shop blower and much higher gas pressure (150-200kPa) and it would roar into life immediately.

Sounds like you need more blower as well.  I saw that you removed some of the elbows, but did you switch the locations of the gas port and blower connection at the main TEE? 

[Gerhard Gerber]

48 minutes ago, Dan Hertzson said:

Sounds like you need more blower as well.  I saw that you removed some of the elbows, but did you switch the locations of the gas port and blower connection at the main TEE? 

Most likely, but I'll give it one more go without the nozzle.

I actually need a helping hand to manage the other monkey wrench to swop the air and gas feeds, no assistant this coming weekend.

Will try to make a plan because I get the logic, was watching the newest episode of Gold Rush Mine Rescue last night, and they increased the water pressure by removing a bunch of 90deg elbows.
I have enough gas, so give the air the straightest path.  I'm afraid if the blower is enough then, it'll be just barely 

[Matt Walker]

Good luck, but in my experience you need one elbow. With atmospheric laminar flow is good, everything needs to be smooth. But with a blown set up turbulence is your friend. Never had a ribbon burner, so not sure how much difference there compared to a pipe delivering the mixture. One would guess the block of holes would create a mixing effect. I think way back I tried a blown one with a straight pipe in and it didn't preform. Put an elbow in and life was good. Like Alan said if you just remove the mig tip you might be surprised. 

[Dan Hertzson]

He has both a burner block with holes and an upstream diffuser.  I've run multiport burners with no elbows upstream of the mixing point, but it does help to have a proper mixing chamber.  Turbulence can help with mixing, but a better option is to put the gas connection in perpendicular to flow from the fan and keep the fan inline (as I previously mentioned).  The final 45 deg elbow you have here should be no problem, but at least try switching the fan and gas ports on the Tee fitting.  If you keep your fan scroll down you will maximize its capacity.  Still not an optimal fan selection, but it will likely work a "normal sized" bladesmith's forge of between 300 and 500 cubic inches interior.

 

You also still need to bake off the steam from your refractory.  Run it at first with then doors open till it stops steaming, then close them down iteratively till you have a stable, fully developed, flame.

 

Then you need to learn to avoid pop-back when you turn things down from high to low fire.

[John N]

Nice looking build on the forge! I know nothing about ribbon burners, so cant comment on that aspect of the build.

 

I think I saw you had to put in a massive amount of refractory cement when you built it. (If I recalled that correctly), it will take a hellish amount of gas, and a long time to get to welding heat. On the bright side it will have an amazingly quick workpiece heat time once up to temp.

 

My main forge has about an inch of castable refactory, over a couple of inches of wool, and it takes about 30 mins to get to welding heat with the gas whacked up. Once hot its epic though.

[Gerhard Gerber]

@John N that is exactly what my blacksmith friend Mike said, his leftover 10kg of refractory went in my forge without making much of a dent.  He predicted I would need to take leave from work to get it up to welding heat.

It takes two burly men to move it, and said burly men have sore backs the next day 

All things I wish I knew at the start.

 

I have made peace with the fact I'll need to do this again, it's now purely a question of can I get any use out of this forge, and when I'll have the finances to tackle the next one.

[Gerhard Gerber]

Don't know anymore..... 

Swapped the blower and the gas input, removed the MIG nozzle. 

Almost set my porch roof on fire, massive flames coming out the side. 

No reading on the pressure gauge as predicted, regulator on the lowest setting didn't help, so I turned down the gas at the bottle, and as soon as the flames come under control it popped and went out. 

Tried several times turning down the gas as slowly as possible, same result. 

 

Re-installed the MIG nozzle and got it running, but at even lower gas pressure than with the previous config, any more gas and it flames out, stops "running" 

Didn't get video of the nozzle-less test became it was dangerous, neighbor wife called her husband, thought my place was on fire. 

Some videos of last and this weekend's tests:

 

 

 

[Dan Hertzson]

In the last video you appear to be getting decent flame out of your burner, but a little rich.  You have found the highest output you can get from the burner, but the forge may not tolerate it until it gets up to temperature.  Till you get there, to keep a stable flame, you may need to turn down both the gas and air a bit more.  Once the forge heats up the burn pattern will change as the flame front burns back faster to the block. 

 

You may still need to adjust the number and layout of your burner ports, as the diffuser does not appear to be effective at getting a full spread of flame (see earlier videos).  This last can be done by first blocking ports temporarily with ceramic blanket, and testing.  After flame pattern improves you can mortar closed any holes with high temperature refractory cement.  I would consider starting by blocking the holes closest to the pipe connection if you want a more spread flame, or on the perimeter if you want a more concentrated one. 

 

The real question is why isn't your forge getting hot with this much burner feeding it.  How long have you been leaving it running to see if it starts to get hot?  Is your forge fully cast, or a layer of ceramic blanket first?  What material did you use for casting (lightweight castable refractory or heavy)?  A lot of thermal mass could take a long while to get up to heat.

[Gerhard Gerber]

I'm confused @Dan Hertzson, last video's flame was the least impressive, but first time there was a hint of yellow.

 

Quote

You may still need to adjust the number and layout of your burner ports, as the diffuser does not appear to be effective at getting a full spread of flame 

Not possible, there were spots at the burner port where the refractory didn't get in and the insulation was showing, I filled those with refractory when I installed the burner, so I believe its in there forever now.
Your observations are correct, spread on the burner has only gotten worse from the first tests outside the forge and the 3 iterations of the plumbing while inside the forge.

Longest its run is about 30 minutes the first time, there was still a lot of moisture, and on the subsequent burns the refractory did start getting colour a bit quicker.
There's two layers of ceramic blanket with way too much refractory on top of that,  didn't know I was making a mistake there.  

I'm picking up a blower that started life in some car today after work, just a loner to test with, seems quite a bit stronger than my fan.

[John N]

It might all change once its up to a decent heat, 1000c or so - just got to keep pumping the BTU's into it until it gets there. 

 

Possibly like a nuclear reactor that forge, once its running, just leave it going - never shut it down. When its hot, it will only take buttons of gas to keep it hot