Forge question

K

KenH

Well-Known Member
Hello all, Looking for a bit of advice here from ya'll folks with LOTS of forge knowledge (Ed & others:)

Here is the forge with blower with stuff I had on hand for a quick 'n dirty setup for testing. This is the $78 blower from Amazon. The big pipe is 1-1/2" SS pipe with 2" PVC to connect bower to burner. The short section that goes into forge is 3/4" pipe. The end of 3/4" pipe is just flush with forge shell, not into insulation at all. The insulation has sort of a "bell" shape. This forge was originally built for a Venturi burner. I should mention there is no jet, only the 1/8" NPT nipple from gas hose to elbow at 90°.
Forge-Blower.jpg


The forge is running around 2 psig, with needle valve not full open. The blower is about half open, running on 120vac. At this point the forge has been running for perhaps 10 minutes max, and is settled in nicely around 2290F. If I close the blower inlet off fully and close needle valve a bit the forge will settle down around 1950F to 2000F range. My question is about the black spot in the forge. The black spot is where the flame hits from the burner. When I back the blower and gas flow off a bit to drop temp the black spot gets larger. Is this normal for a blown forge?


Oh, the video is mirrored from actual setup, not sure why it mirrored when I uploaded to youtube, but it did. I looked for a setting to flip back but didn't find one.

Thanks to all for any comments or suggestions
 
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Well, I'm no pro, but my understanding is that a cold spot directly under the burner happens due to unburnt fuel hitting that area.
 
That would be might thought also, but increasing air flow (or decreasing gas flow) drops the temp, and the burner has a stuttering sound then, not clean burning sound. I'm sure something is wrong with burner setup, I'm just not sure what it is.
Thanks for comment.
 
tkroenlein said:
cold spot directly under the burner happens due to unburnt fuel hitting that area.
Click to expand...
GOt a bit more info on another site, it seems that cold spot can be caused lack of mixing of air & gas. The idea is to move the gas inlet down to bottom so as the air/gas mixture flows the 90 will cause more mixing. Also perhaps a bit of coarse steel wool put in the 1-1/2" pipe to help with mixing. I'm also told my forge is on the small side for a blown forge, but maybe the extra mixing might make it work. I do have a 30 lb propane gas bottle I could build another forge, but I like the small size.
 
Just a thought...what if you made a smaller/restricted the burner? Seems to me it may not be a mix issue (since it's adjustable,) but a volume issue. Does that make sense?
 
I think the first step is to be sure the gas 'n air are mixing really good. At this point with the gas spraying direct into the 90 with the flow it could well not be mixing completely. I plan to move the gas inlet tomorrow, and more testing provided it's not too cold or rainy. Man, they're saying the high around here tomorrow is going to be in 40s and I don't do so well with cold weather {g}
 
I think that moving the gas injection nipple down farther on the plumbing is a good idea. Do you have a needle valve on the gas line for fine adjustments? Also a ball valve right up on the line so you can turn it off in a hurry is a good idea. I also find mine to be handy in lighting the forge burner. I turn on my bower first, open the valve on my tank, and then, with a burning torch held at the opening of the forge, I open the ball valve. As far as your forge being too small to be used with a blower, I'd say that my main forge is even smaller. Remember that you can only work 4"-5" of steel at a time. Use the choke on your blower and the needle valve on the gas line to adjust the heat in the forge.

Doug
 
Yes I do have a needle valve for fine adjustments and can easy put a ball valve for emergency shutoff. You just described the same way I lit this forge, turn blower on, then slowly open needle valve with hand propane torch held at opening of forge. I'm looking forward to tests after I move the gas inlet down, and maybe even some steel wool in pipe for mixing. Glad to hear your forge is smaller than my forge is - that's why I've built it small. I've got a larger 2 burner I purchased but don't much like it. It's square and burners point straight down from top. Not the best design at all, but I didn't know anything when I ordered it several years ago.

10°F? That's why I don't live that far north. I've spent most of my life South of I-10 along the Gulf Coast.

Ken H>
 
The two issues I see with that forge/burner.....

1. There are too many restrictions (turns/bends) in the burner piping. Each turn or bend creates restriction and slows velocity, which is necessary in a gas/propane forge. (each turn/bend/restriction reduces the effective CFM of the blower) What I have found works best is a pipe that fits the blower outlet, about 1' long, then a reducing 90 degree elbow into a 1 1/2" or 2" X 12"-18" that goes into the forge body. That reducer will increase velocity significantly over what the blower would produce with single sized pipe all the way through. A 90 degree elbow also causes the fuel/air mix to tumble more so then a lesser bend/angle, creating a better mix, and hence a better burn.

2. The location of the gas inlet. As it is, there is nothing to cause the fuel/air to "tumble" and mix. That, combined with the slowed velocity, is what's causing the "cold spot" where the flame impacts the interior of the forge. Moving the gas inlet closer to the blower..... and placing it at 90 degrees to the direction the pipe runs, will force the gas/air to mix not only as soon as it enters the burner pipe/tube, but will make the mix tumble as it make it's way past/through the angles in the pipe, and into the area where it ignites/burns.

Here's a pic to illustrate what I'm describing:

Weldingforgeblower.jpg


That is an older pic. I've since changed the length of the burner pipe that enters the forge body to 18"..... which increased the velocity, and improved the burn inside the forge. Pay particular attention to where and HOW the fuel inlet enters..... that alone creates more fuel/air mix......over a gas inlet that in inline with any of the piping.
 
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Ed, Thank you for your detailed reply. I did not realize air velocity was so important in a blown forge. I was thinking with the small body forge I have it would take less velocity than with a large forge. I see you don't have a gate valve to control air flow - do you have a variable speed on blower? OR, use just the plate over air inlet?

I know each additional 90° bend will add restriction to flow, but will also add turbulence to the air flow which should increase mixing of gas. Since that blower seems to blow more airflow than really needed for the small forge body I thought the flow would be enough. This test gave best burning with air inlet set about 50% to restrict air flow to burner so it seems the air flow is sufficient, but the air velocity might not be sufficient.

As I've said before, I do NOT have the experience to make solid decision and that's why I ask so many questions of folks on the forum.

Today I'll be moving the gas inlet down to bottom of 1-1/2" SS pipe, and stick a coarse brillo pad just past the gas inlet to increase air/gas mixing. I see you've got 1-1/2" pipe going direct into forge body, but this forge was built for a venturi burner and would require a good bit of work to make a larger inlet. I can do that if required, but I would like to take small easy steps before major surgery to weld a large inlet {g}. It may well be reducing the 1-1/2" pipe to 3/4" as it enters the forge body increases the air flow to such a speed it creates the cold spot. Hopefully moving the gas inlet down to improve mixing will help.

Again, thank you all for your help.
 
I do have speed control on the blower.....in the form of a ceiling fan speed controller. Just to be clear, is you use that type of speed controller, IT MUST BE A CEILING FAN SPEED CONTROLLER, AND NOT A LIGHT DIMMER. A light dimmer will burn the blower out in a heartbeat. Another BIG part of it is the needle valve.....that's really the "control system". :)

On my burner, because the gas inlet is 90 to the air flow, I have one source of turbulence/mix there.....and the another source at the 90 degree elbow. If you look closely, that elbow is a 2" to a 1 1/2" reducing elbow.....so it does two jobs....mix and increases velocity.

Looking closely at your setup.....that reduction just before going into the forge MIGHT be a problem source too..... my gut tells me that might be such a jump down in size that it's creating significant restriction......but that's just a possibility and what my gut is telling me. Were it me, I'd take that portion off, and see what the larger (is that exhaust pipe?) would give me if it goes directly into the forge.....although that galvanizing does concern me.

Finally, the way the burner enters the forge.....it really should be on more of a tangent.....
Flamepattern1.jpg



OK, all that being said..... I can tell you that IF you were to build a burning alike the one in the pic I posted...... it will work well in MOST forge bodies that are 6" to 12" ID......and lengths up to about 16".
 
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OK an update on the forge after moving the gas inlet to bottom of SS pipe...... AND learning more about tuning the burner {g}.

Ed, the pipe is 1-1/2" Sch 40 SS. I think before I'd try and rework this forge body to a larger inlet and tangent to forge body I'd just make another, and make sure the burner entered forge at the tangent you're talking about.

I'm running the gas around 2 psig as before and adjusting with needle valve. With forge running around 2300F and perhaps 80% blower speed the forge sounds good and no dark spot. If I turn blower up to 100% the dark spot appears (and temp falls). If I turn needle valve down to reduce gas flow the dark spot appears and temp falls. I then turn blower down to slower speed (to balance gas/air flow) and temp will stabilize around 2200F and dark spot goes away. It seems I just have to get blower speed 'n gas flow set correctly for clean burning and no dark spot. That's the "learning to tune".

Yesterday I played with gas flow and blower speed but could never get dark spot to go away, but today after I moved the gas inlet down to bottom of SS pipe I can adjust easy to have no dark spot. I think this is from better mixing of gas/air because the gas inlet is at bottom and 90° into air flow. Before you can see the gas inlet was with the air flow so was not getting the mixing required.

My temp indicator maxes out a bit over 2300 (2350?) so I didn't push it. 2300 is plenty for SS San Mai forging anyway. I think this burner would exceed 2400F easy. The big problem is the burner is putting the flame too much down and I have to be careful trying to hold billet over the side away from here flame hits the wall.

Thank ya'll for commenting and helping me learn about a blown forge burner. The temperature is still falling outside and down to 40F now and it's just too cold for an old man like me. I've got to start getting potted plants in from outside so they don't freeze tonight. 27F forecast!!! News is talking about dangerously cold weather tonight.

Ken H>
 
Ed, (or other folks) I just measured the ID of my forge and find it's smaller than I thought. It's only about 4" by 12" inside measurement. Since this puts the opposite wall so close to flame exit from burner, would mounting the burner at the 9 O'clock position about 1/3 from front, and angled backward so the flame would hit about 1/3" from rear help? That would give a longer flame travel before hitting opposite wall.
 
No. With a single burner, it's FAR more important to get the burner in at a tangent that forces the "swirling" of the flame pattern at 90 degrees to the forge's long axis. If you try to point the burner fore or aft, you will increase cold/hot spots, and more times then not, will have to deal with increased "Dragons breath" coming out the front/openings.
Also, it's much better to have too large a burner....that you can turn/adjust down, then it is a burner that isn't enough....that when you reach it's maximum output.....there's nothing else you can do, except build a bigger burner.
 
EdCaffreyMS said:
get the burner in at a tangent that forces the "swirling" of the flame pattern at 90 degrees to the forge's long axis.
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Ed, Thanks for the info. When you say "at a tangent that forces the swirling", do you mean burner pointing upwards? That's what it looks like in your post #12, burner coming in from side about 9 O'Clock and pointing upward slightly, but flowing across top of forge to other side forcing the flame to "swirl" downward along opposite wall. Do I understand correctly?

Next, I found a 2 ft piece of 2" Sch 40 pipe I could make a new burner with. I'm thinking about 12" long on blower end, then a 2" 90° elbow, then 8" or so of 2" pipe (or 1-1/2"?), then a reducer to 1" pipe section about 6" long to connect to forge body.

Looks like I just might have to build a new forge {g}
 
do you mean burner pointing upwards? That's what it looks like in your post #12, burner coming in from side about 9 O'Clock and pointing upward slightly, but flowing across top of forge to other side forcing the flame to "swirl" downward along opposite wall. Do I understand correctly?
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Yes Sir! Just image the flame coming out of the end of the burner in such a way that it is forced to follow the interior curvature of the forge...... that usually means at the 9 O'clock position, and pointed upward.

I found a 2 ft piece of 2" Sch 40 pipe I could make a new burner with. I'm thinking about 12" long on blower end, then a 2" 90° elbow, then 8" or so of 2" pipe (or 1-1/2"?), then a reducer to 1" pipe section about 6" long to connect to forge body.
Click to expand...

Referring to the part I in bold/underline to: Then into a 2' to 1 1/2" elbow. Then 1 1/2" of AT LEAST 12" long (otherwise you risk "backburn" once the forge is heated up....meaning the fuel/air will likely pre-ignite inside the burner tube.) I suspect you would not need a reducer and the 1" pipe, but there is no harm in trying, and if it doesn't meet your expectations, you can always remove the reducer and 1" pipe, and just use the 1 1/2" as the burner tube. If you do the reducer/1" pipe..... make the 1" pipe at least 4-6" long. Even IF the burner is oversize for the forge application...you have the ability to tune/turn it down. ;)
 
Ed, Thanks again for such prompt response. I think I'm getting a better handle on this now, and it looks like I'm planning on building a new forge.:)

I can do that just fine, use the 2" pipe to the elbow, then 1-1/2" pipe direct into forge. I can weld a sleeve of the 2" pipe to the forge body which should allow the 1-1/2" pipe to slip inside. The new forge will be larger than the existing venturi designed forge so the 1-1/2" burner tube might be ok.

And I've got a scraped 33 lb propane tank. These are about 12" OD, so 3" of insulation would make a nice 6" ID inside size. I can cut it to 16" length and use a 1"X12"X48" thermal blanket that is spec'd at an average work temp of 2300F to 2600F and withstands bursts to 3000F. That 12" width will give 2" space on each end for coating with refractory cement (Spec'd as withstands working temperatures up to 3000-Degree F).

Ed, thank you again for sharing your knowledge and experience with the rest of us folks.

Ken H>
 
Ed, since I've decided to build a new forge please allow me to ask you another question on lining the forge. To refresh I'm planning to use a 30 lb propane bottle cut to 14". I've got a couple of 1"X12"X24" ceramic insulation blankets rated at 2600F working temp, and the hard type firebricks. My thinking is to put 3 of the hard firebricks (1 on bottom, 2 side by side on top of bottom to fill space) with pieces of insulation filling the empty places with Refractory Cement (rated 3000F) in the bottom of forge body for the floor. Then the ceramic insulation circling rest of body. The ceramic insulation will be about 3" thick, with the firebrick providing 3" on bottom. This will give a 6" ID for the forge body. With the additional thickness of Refractory Cement I expect the total ID will be more in the 5" range.

My question is it a good idea to use the firebrick for the flooring of forge? OR, should the ceramic insulation be put all the way around?

The burner will be almost an exact copy of your burner shown above with 2" pipe for first portion, 90° elbow, then 1-1/2" section into the forge body, (around 12" each section). I'd been thinking 2" for all the pipe except for the last 6" into forge body and that would be 1", but based on your advice I'm going with 1-1/2" pipe from 90° elbow to forge body.

Plans for cutting the propane tank are to cut a 6" diameter hole in one end, then other end to be cut leaving full diameter of tank open. This will allow the front of forge body to have the metal covering to help protect end of insulation as I'm putting metal in and out. The rear will be full open to make for easier lining of forge. I plan a bracket on rear to hold firebricks to close that end, and slide apart if needed for long piece of metal.

Am I on track? Do I need to make any changes? I've not cut the propane tank yet, hope to do that next week.

Again, Thanks for all the help.
Ken H>
 
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As important as the temp rating on the ceramic fiber insulation, is the density...... #8 is the only one to use.

Personally, I would NOT put firebrick, or any other "hard" insulator anywhere other then the floor.... first, I would wrap ceramic fiber all the away around the interior, then cut it to a length so that the ends butt up against each other in the middle (long axis) of the "floor"....then use a firebrick "slip" (full length/half thickness) for the floor....seated atop the ceramic fiber. I also try to limit the use of refractory cement to a slurry..... thinned to down to latex paint type consistency , then brush over the fiber as if just "painting" it to hold the fibers tight.

"Hard" insulators such as firebrick, cured refractory cement, etc are heat robbers.....they do no reflect heat nearly as efficiently as straight ceramic fiber, use more fuel to heat up, more fuel to maintain heat, and are just poorer insulators then ceramic fiber. Now. that being said, if you were to place a large mass of steel, such as a big damascus billet in a ceramic fiber lined forge, the heat will dive down, and take a LONG time to re-heat....that's because it reflects versus holding heat like the "hard" insulators do. I'll use my welding forge as an example..... 3" of castable on the walls, 4" in the floor, and 4" in the "roof"...... from firing it up, to reaching 2350F.... 1-2 HOURS.... but once it reaches temp, I can place a 15lb (literally) in it, and have that billet to temp within 10-15 mins. With the same forge body lined with 1" ceramic fiber/ITC..... about 20 mins to 2350F. However.....I can place the same 15lb billet in it....and it be 45 mins or more to regain the temp. What I'm saying is that there are pros and cons to each...you just have to decide what is best for your uses/situation.....and go from there.

Why 3" of ceramic fiber?? Honestly, that is just a waste. Everybody has this notion/mindset that the thicker the ceramic fiber, the better....but that's just not true. I've done the testing...... 1" thick x #8 density ceramic fiber takes less time and fuel to reach heat, and less fuel to maintain then 2" or more....in fact, the thicker the ceramic fiber, the less efficient the forge. It's just the way the ceramic fiber is designed/engineered.
 
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