I need blown burner pro help please.

I was getting that he was asking about recirculating forge exhaust back into the system which I would think too hot and oxygen depleated... No?
 
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You don't want to re-burn your forge exhaust, that really produces CO in a hurry. You need to make an intake plenum in which the incoming air is heated by the forge shell, or indirectly by the exhaust.

Both fuel preheat (with liquid fuel) and blast preheat can improve efficiency and BTU output.
 
That is what I was trying to say Salem. Better at explaining it then I am. Plus I think the pics and descriptions I saw before were probably the same one you were talking about. That guy actually had a bunch of cool stuff, dont remember the site it was on though.
 
Salem Straub said:
You don't want to re-burn your forge exhaust, that really produces CO in a hurry. You need to make an intake plenum in which the incoming air is heated by the forge shell, or indirectly by the exhaust.

Both fuel preheat (with liquid fuel) and blast preheat can improve efficiency and BTU output.
Click to expand...

That's what I was pretty sure you (Salem) meant... I get the liquid fuel pre-heat (like a whisperlite camp stove) and your description of the manifold to heat up the air. My assumption would be, much like a direct injection newer car nice cold propane downstream in a fresh warm air channel equals nice efficient heat...
I am sure it is easier to balance, but I got a mental image much like Page mentioning the blower sneeze. A lot of things can cause that, cold engine on too big a cam causing the fuel to burn back into the intake stroke and back up the pipes, too hot and too lean causing detonation going back up the pipes... etc. Its that last one that had playing with hot air concerning me, but propane isn't quite as volitile as gas... so I may give that a shot. I pictured the flame front moving back into my plenum (if I still go ribbon burner) with those baffels and not making for a nice picture...
Thank you guys for contributing. The blown forges I have been exposed to here are either tinker manually to adjust or the pid controlled are all on or all off... I want as efficient a setup as I can get. My venturi has me filling 20# bottles like they are going out of style... Would like to make that trip a little less often. I think I have a pretty clear picture of how the rest of this is gonna build out. (Slowly...)
 
" My venturi has me filling 20# bottles like they are going out of style"

Get a 100# bottle.
 
I have 2 x 100# bottles... They feed the shop heater and my gas logs. The blown forge is gonna be hooked up on this system as what comes down to the shop is high pressure. My venturi is on a roller cart as I still had some shop reconstruction to do before I landed on a location for it, so it has the 20# under it.
Believe me... I love the big pigs a lot. They automatically switch over when one is empty and are out of the way.... Still doesn't make propane cheap ;)
 
Sorry to spur this mule again, but I am going to ditch the ribbon and go straight blown. Three or or four burners off of a common manifold (meaning a plenum feeds pressurized air from right next to the forge down about 6" of 1" pipe. Question is am I going to have to place an "injector" with a needle valve for each burner orifice, one needle valve for each injector, one needle valve for all injectors from a common rail in other words, or can I mix it in the plenum with one big injector?
I saw Fred is running individual needle valves at each burner, but my plenum and burners will look more like the custom sheetmetal intake manifolds on racing motors...
 
A blown burner with a manifold and four burners is a big forge. Only a rare few makers actually need or want one.

Each gas port ( there are no injectors in a blown forge) needs its own regulator needle valve. The gas to all of these can all be controlled by a single ball valve or solenoid. You tune each burner so they all run evenly together. Plan the air supply path in the manifold so the air is evenly distributed to the burners, too.

I believe you were making a forge for doing damascus. Most of these are best as a single burner vertical forge. A 1" burner and a good flare are all you will need to reach welding temps.

With all that, Multi-burners are only needed on long forges. I would not recommend anyone making their first blown forge with multi-burners, and even then only two burners will run a 24" forge just fine.

If I was to make a suggestion, I would suggest that you make a 10"X16" forge with 2" wool and a single 1" blown burner. If you ever reach a need for a bigger chamber to do large damascus billets or monster blades, you will have the experience to make the judgments needed in that build. By then you will have power hammers and presses, so the need will become self evident.
 
I concur! The big horizontal forge pictured, shows five ports; only three of them are active. Activating the other two adds nothing to the burn. A single burner vertical is a good place to start if you want to make damascus.

Fred
 
Thanks. I think I keep forgetting I am injecting my air supply so don't need multiples like atmospheric burners... Thanks.
I tend to use gas port/injector interchangeably. Comes from car stuff.. I tend to picture it like an intake manifold where air/fuel mixed in the plenum = carburated, fuel at each port = fuel injected... Sorry if that sounded confusing... :)
 
Yes, it is fuel injection.

1/4" piping for the gas and 1.5 to 2" air supply line from the blower. The gas enters the system in the 1.5"-2" line, then goes into the mixing chamber...a 4" piece of 3" pipe. from there it necks down to the burner tube. A flare on the burner makes it more efficient. Just like the air/gas system in a race car, it is all about higher and lower pressure areas. Avoid hard 90 degree bends.
 
Stacy, I hope I understand the question, one thing: I was told many times when building a blown forge that a 90 deg. bend downstream from where the propane dumps into the pipe is the best way to introduce some turbulence, that helps the somewhat reluctant propane mix well with the air. Are you saying that an enlarged section rather than a bend makes for better mixing?
Seems like you'd get better airflow without the bend, which is good, but I have more issues with too much air than too little.
Thanks for any light you can shed on that!
Andy
 
The gas should be introduced as far back as practical, and an elbow is a good way of getting a little mixing done.....
But, you have hit on the problem with allowing an elbow in the air line to introduce the turbulence to be the only thing to mix the fuel/air. Often the air flow is greatly restricted/reduced by the gate valve or choke plate. This negates the turbulence from an elbow, because there is plenty of room for the reduced air flow to go around the corner.

A proper mixing chamber is made with bell reducers to make for smooth pneumatic flow. 1.5" air line > 1.5"/3" bell reducer > 4" section of 3" pipe > 3"/1.5" bell reducer > 1" burner tube > flare.

Using a mixing chamber does several things. First, the pressure and velocity drops immediately as the air/gas flows into a larger space. This allows the mixture to combine better. The gas/air swirls a bit as it expands, and then compresses as it exits. The velocity and pressure increase again as it goes into the 1" burner tube, and then expands again as it goes out the flare entering into the forge chamber.

What I was talking about in avoiding sharp bends in the piping was to use street elbows, and to try and not have a bend right at the burner tube.
 
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Thanks for the explanation on the mixing chamber. I am going to be building a new blown forge and would like to make it work as well as possible. So, would this be a good configuration? Blower, gate valve, reducer-3" chamber-reducer, 45 elbow, 1" tube (how long?) then flare. Gas inlet right after the first reducer?

At a hammer in I saw a small forge that had the exhaust out the rear and a partial door that closed on the "work" end. The intake air past thru a pipe mounted so that the forge exhaust past around it and preheated the intake air. Claimed to be very efficient.
 
The gas inlet should be right after the gate valve.....entering the 1.5" - 2" pipe before the mixing chamber.
 
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