windancer

Post pics of your ribbon burner forge where your gas inlet feed into the burner?

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I built a ribbon burner forge a couple years ago. I don't use it because of the explosions. They generally start after the first 45 to 60 minutes of use.

I posted the problem many places, did a ton of searches. I found a very few similar problems but none were ever resolved.

I have about $700 into the forge plus it takes up a lot of vaulable room. I currently use a smaller forge sitting on top of it.

This has been on my mind for the last couple years. The forge works beautifully and is way more than capable of forge weldingnas well as forge welding without flux. I would like to be able to use it :)

After using the forge for 45 minutes or an hour therer is a large VERY LOUD explosion in the forge- about the same as a .22 rifle going off in your ear. I have tried everything anyone thought might be causing it. When this happens it is extremely startling. So it has sat without even being light for ages now.

The only thing I can come up with is that maybe my gas post is too close to the burner inlet, and that maybe it needs to be furher away from the burner. I am wondering if this may be causing the problem. I may just add some more pipe and see if it stops the problem. I would not even be comfortable selling this geat forge to anyone the way it is. I am sure these explosions are very dangerous.

Any one here have experience with ribbon burners? How long is your pipe between the gas inlet and the burner? Pic would be a huge help to me!

Dave

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Maybe post a video of it happening if possible. What is the frequency of the explosion after the initial one?

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Good Morning Dave,

 

Talk to Ken Gerhardt or Ron Wailes. Their information is available through the NWBA membership list.

Both are very familiar with building Ribbon Burner Forges and they are accessable to you, so they can see what you have done different.

 

Neil

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Dave, what I think is probably happening is this:

 

On startup, everything is nice and cool. The gas/air mixture in your plenum is also nice and cool and the holes between the plenum and the forge chamber are similarly cool.

 

When you light the forge, things are still cool, but the hot face of the ribbon burner block starts to heat up. The back face is being cooled by the incoming fuel/air mixture. As the hot face gets hotter, the heat moves through the burner block and it gets hotter.

 

To work as intended, the speed at which the gas/air mixture moves through the holes in the burner block, needs to be faster than the speed the flame-front can move through the mixture.

 

As the temperature rises, the flame speed increases. Also, as the pressure rises, the flame speed increases. When you get a moving flame-front, it radiates heat ahead of itself, raising the temperature of the mixture ahead of it, and, because there is huge expansion during combustion, there is also a pressure wave ahead of the flamefront.

 

If it is relatively cool, the burner block "should" help to slow down the flame front by absorbing much of the radiated heat. This is most effective with small holes: it is pretty much the same principle as a flame arrester.

 

At some point (45 minutes to an hour in your case), the temperature of the block reaches the temperature at which the flame speed is higher than the mixture speed, the flame runs through one or more of the holes in the burner and reaches the plenum, where there is a big open space and the walls are far enough away not to absorb much of the radiated heat. The flame-front accelerates across the plenum until it runs out of fuel, but may reach the speed of sound as it travels. 

 

A supersonic flamefront is "detonation". A Subsonic flamefront is "deflagration".

 

Does it seem likely to you?

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I will not light the forge again until I redo the gas inlet. And were I to light it before that it would not be long enough for it to happen again!
The explosion is unburned gas igniting- and could well be enough to cause damage to the burner and unleash the gas through a break or crack.
I have no idea about the timing of subsequent occurances- I instantly turn it off.
I tried to talk with Ron at the last conference we both attended. His ONLY input was that I should buy one from him and throw away the one I bought from the ribbon burner place [can't think of their name right now].
Because I posted the full saga a couple years ago I am certain everyone was following my adventures.
What I would like is pictures of other ribbon burner forges that are working properly.

I only know that I am one of very few folks who have this problem :)
Since almost all the others are woring without the detonations, and the burner came from a company who specializes in burners, the things that may be different about mine is the setup- which is why I asked about pics.
I appreciate everyone trying to help and taking the time to think about this and post up a reply. I really do.
But I think that pictures of other setups are the only thing that may help.

Thanks,
Dave

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Dave, what kind of a blower are you using?  It needs to be one that will develop pressure.  Most common squirrel cage fans do not develop pressure.  If you are using a squirrel cage fan it may not be developing enough pressure to push the mixture through the burner correctly. I'm using one of the kind that Grant was selling and are now available at www.blacksmithsupply.com .  I have the larger one but I think that the smaller one will work fine. 

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Dave, can you post pics of your setup? I have struggled to find any with the search function.

 

The only things on the inlet side that I can think of that might help, would be to increase the mixture pressure in the plenum (which would increase the gas speed through the holes in the ribbon burner block), or to adjust the air:fuel ratio (maximum flamefront speed is usually somewhere around the stoichiometric mixture, so moving away from the stoichiometric tends to reduce the flame speed; of course it also affects the flame temperature, which reduces as the mixture gets further away from stoichiometric).

 

Air:fuel ratio adjustment "just" to prevent the explosions would obviously limit the operating air:fuel ratio range you could use. Much of the beauty of a blown system is the control it provides over the air:fuel ratio, so it would seem a shame to have to limit it.

 

Once the flame breaks through into the plenum, the only difference that any design changes upstream can make, will be to increase or decrease the volume of mixture that is available to explode. Having a bit less volume would be no bad thing, but it would seem preferable to address the cause of the problem first. I am pretty certain the cause lies somewhere in the forge and burner installation.

 

Obvious things to check would be that the forge flows freely enough to allow the burner to work unrestricted, and that the feed pressure is as per the burner manufacturers spec.

 

The pressure can usually be measured easily enough with a U-tube manometer (a length of clear tubing bent into a "U" shape and half-filled with water. Apply pressure (or suction) to one end and the water column will become lopsided. Measure the height difference between the water levels in each leg and you have the pressure in inches of water column. Colored water helps, and make sure the length of the U-tube is at least one-and-a-half times the maximum anticipated pressure, so it can't blow the water out.

 

Getting a handle on how well things are flowing in the forge itself is mainly about looking for anything that might restrict flow. There is no easy way that I know of to get good quantitative data.

 

I gather you are using the second-smallest of the Pine Ridge burners; presumably that's the GH190? It looks like it needs 7"-56" WC of pressure. Higher pressures will give higher speed through the burner ports and less chance of the explosions. What pressure are you actually getting?

 

How big is the forge? The GH 190 is recommended for "up to 1.5 cu ft" (about 2500 cu in) That seems pretty big to me.

 

My guess is that the burner would want a good 10"-plus between itself and the opposite wall to allow it to flow freely (there is a photo on the Pine Ridge website of a "miniburner top-mounted in a small forge" that seems to show the ceiling about 9" above the floor. Other photos on the site seem to show the burner recessed about 1" into the wall).

 

If you've built an unusually-shaped forge for specific work, this might be an issue.

 

Like I said, pics would be good.

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Good Morning,

 

I can't see anything about your forge in that video, other than the blower is down low and it is hard pipe up to the forge.

 

Where does your burner sit (top, bottom, side, angled, centered in the fire-box)? What is the diffuser plate like at the entry to the burner? What is the mixing chamber like, below the diffuser?

How many ports are there in the burner? Have you tried plugging some of the burner ports (maybe the ports furthest from the air inlet)?

What is the pressure you are running at? Have you tried adjusting the pressure up or down?

Where are you introducing the propane? Back far enough to allow the propane to mix with the air?

Are you using a fixed jet or just a section of pipe? Is the nozzle in the center of the pipe?

Have you tried spacing the burner back, out of the fire-box?

What are you using to control the air flow/pressure? Have you tried larger air pipe to the forge? Radius corners instead of a pipe elbow?

 

Like Tim said, something is allowing the fire to go back up into your mixing chamber. This normally is not enough air flow/pressure.

 

Neil

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I had the same problem a few years ago. It scared the crap out of me. Based upon my experiences with ribbon burners I see 2 problems.
First that blower is way inadequate. I tried about 5 different blowers on my forge and had mixed results. That type of blower does not put out the volume and pressure you need. Air volume is key to a good burn. I am using a moon bounce blower like for a kids yard moon bounce. Sounds crazy but it works awesome and corrected the blow back explosion problem. In a couple hundred hours since going to a moon bounce I've never had one explosion.

Secondly I think your pipe is way too short. You are right you need to extend the pipe and the gas inlet down lower to allow for a longer mix before hitting the burn chamber. I have my pine ridge LP390 mounted top instead of side like you have. But I don't think that's your problem.
Address those 2 things and I'll be amazed if you're not running beautifully. Don't give up on it. Ribbon burners are awesome.
Good luck and be safe.
Matt

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This is my current forge. Very large. 3 cubic foot burn chamber. 28" × 20" floor. The problem with the explosion I had on a smaller forge like yours and it corrected with the moon bounce blower.

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