A question on forced air propane forges

bikermikearchery

bikermikearchery

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Jan 18, 2007
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After a real long delay I finally got around to trying to run my new forced air propane forge. The forge is a 8 1/2" x 18" tube lined with K-wool and saintanite. The gas mix chamber is from D Ellis. The blower is salvaged from a wood stove of unknown origin and unknown CFM.
My first try with this blower setup, Running at about 3 1/2 to 4 pounds of gas pressure, and the air gate wide opened I was only getting about 1600 f. when I tried to increase the gas it back popped through the blower.:eek:

1. Is the back popping from not enough air flow/CFM?

2. Can I get more heat by going to a higher CFM blower?

3. Any recommendation for how many CFM the blower should be able to put out?

Semper Fidelus
Mike



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The short answer is that you need a much more powerful blower.
The inside dims of my forge are 10 x 12 roughly and I use a blower that will run up to 110cfm @ 6" of water. (a commonly reference for the pressure)
Wide open I can run mine up to 2800 and maybe a bit more. Its hot enough that it hurts to look at it even for a second.
I would say you need at least as powerful blower as mine and maybe a bit more considering the length of your forge.
110cfm at 0 sp means nothing to you, you will need one that works that cfm at pressure.
The bad news is that these blowers are not cheap, expect to pay at least $200 and that is a really good deal, more likely is $300-$500.
The good news is that you may never have to replace it, these things run nearly forever. I run mine nearly evry day for 8-16 hours 4-6 days a week and my last one lasted 15 years.
Del
 
Edit...I jsut realized thats "highjacking", I'll ask elsewhere. Sorry
 
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My automobile blower seems to work well; I got it for $2.00 at a yard sale, 'course I added the coffee can shell and ABS tubing outlet and plywood.

it can bee seen working here: http://www.youtube.com/watch?v=KKjy9fnL4YY

P.S. I use a 6 amp battery charger that I also got at a yard sale to power it, For Heat treating I only need to use the 6 volt setting but forging heat requires 12 Volts.
 
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Mike are you using a small propane bottle,if so it may be freezing up on you,that will cause the popping.A 100 # tank is much better,you can set in a bucket of water that will help-are you using a high pressure regulator--regards Butch
 
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Thanks Del for the explanation on the CFM@pressure and the short answer.
The inside of the forge is about 5 1/5" x 18" total volume is quite close to your set up, and it was actually heating up quite evenly. So that was good. I just need more heat.

Butch Yes its a small bottle, Regulator was from Darrel Ellis also. I haven't had a problem with this regulator when running a venturi burner.
 
I dont know the Cfm of my blower but, I recycled a 3600 RPM motor/blower from an old oil furnace and built my owm plenum chamber for it. I control the air flow with a simple gate valve. I start my forge with a moderate air flow and set the gas pressure at 1 1/2- 2lbs to start. as the forge heats up I increase the airflow and reuce the gas pressure. At full temp my air is wide open and the gas is at about 3/4 lbs. I get more than enough heat to weld.
 
i was told thata 60 cfm is the minimum that you want to go. i am running a 60 and i can see where more air would be better.

good luck

jake
 
bikermikearchery said:
Thanks Del for the explanation on the CFM@pressure and the short answer.
The inside of the forge is about 5 1/5" x 18" total volume is quite close to your set up, and it was actually heating up quite evenly. So that was good. I just need more heat.

Butch Yes its a small bottle, Regulator was from Darrel Ellis also. I haven't had a problem with this regulator when running a venturi burner.
Click to expand...


You will want to move up to a larger tank, although I don't think that is the immediate problem. I run mine off a 500gallon tank.
Del
 
60CFM is the minimum that will efficiently run a forge. 100-120CFM is a good size for most all forges. You will need to be able to control the air volume and pressure with a gate valve and/or choke plate. A speed control also works good on the blower. Not all blower units are good for forges. You want one that delivers the air at a steady pressure. Many cheap blowers are rated at higher volume than they actually deliver, because they are made to deliver the air at no resistance. Forge blowers have to pump the air through a pipe. That is one reason not to use too small a pipe size for a blown burner. 2" air pipe, and 1" burner pipe is a good combo.

Stacy
 
I don't know alot about forges (yet). These are relatively cheap, and for their size they put out volume and deliver static (pressure).

Inline fans if you scroll down you will see a performance curve. Use that to select your fan, flow goes down as static goes up, so the static pressure your fan will be working against will need to be known before, else you WAG it.

A picture of the fan, and size of the wheel and rpm would help a guess as to your current fans capability.
 
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ron,
Those are duct fans for 4" to 12" ductwork. They are not the same as forge blowers.
Stacy
 
bladsmth said:
ron,
Those are duct fans for 4" to 12" ductwork. They are not the same as forge blowers.
Stacy
Click to expand...

Yes, I am pretty sure most forges are PSC squirel cage blowers not much bigger than 6" diameter wheels, many in about the 2-4 inch diameter range. (just a guess). and the fans are on the clean side of the combustion chamber, not the dirty side, so any fan would actually do if the operating conditions were agreeable.

Someone mentioned very high static pressures, which squirel cages typically never attain. So i went to a stronger fan type.
 
Ron,
Whil at first glance those blowers may look good, even the most powerful of them would be insuficient for the size and type of forges we are discussing.
Mine runs on a 1HP motor, if you start looking at many of the blowers you will see that most are fractional HP and most are small fractions, like 1/20.
The largest of the fans listed only draws 3 amps at 120v. Don't remember my conversions, but that seems a little small.
Del
 
delbert ealy said:
Ron,
Whil at first glance those blowers may look good, even the most powerful of them would be insuficient for the size and type of forges we are discussing.
Mine runs on a 1HP motor, if you start looking at many of the blowers you will see that most are fractional HP and most are small fractions, like 1/20.
The largest of the fans listed only draws 3 amps at 120v. Don't remember my conversions, but that seems a little small.
Del
Click to expand...

Does anyone have a good reference, so i can educate myself? something related to forge construction, even if its only a chapter of one reference.
 
ron,
The blowers used to power a full sized forge can indeed be a big unit. Here is a good quality ,variable speed unit used to power a full sized coal forge:
http://www.centaurforge.com/115-volt-PB-50vs-Blower-Variable-Speed/productinfo/PB50VS/

Now, why would anyone spend $400 on one of those if a $20 blower and a light dimmer rheostat will work???........well, those big units are made to deliver air volume at a steady rate. Many smaller blower types will deliver plenty of air at full speed and no resistance, but choke it down, or slow it down, and the air volume plummets to nil. The shape and size of the vanes on the blower have a lot to do with it. Speed and HP are the other factors.

For a smaller forge, a simpler blower will work. One of these:
http://www.centaurforge.com/115-volt-Dayton-Blower/productinfo/115VBLOWER/
will do the job. Add a $30 speed control, and it will give good service on most smaller propane forges.
When welding temps are needed, you will need a 150CFM or better blower with the right type of vanes. As a guideline a blower should have larger vanes than the simple cooling fans, and a larger motor. I would say 1/5-1/6HP and up will work in most cases. One saying is, "If it is quiet, it is the wrong type of blower." While that is not an exactly true statement, it is based on the fact that most small cooling blowers have small and low angle vanes to deliver a smooth and quieter air flow. Blowers made to force air have larger vanes at a higher attack angle and will this make a lot more noise as the slice the air.

Now, how do most folks get around this dilemma? They use a fairly large CFM squirrel cage blower, and use a gate valve in the 2" air line going to the burner. If the air line is reasonably short, there isn't much pressure drop, and the valve will allow metered delivery of air. The more it is opened, the more air it delivers. Using a choke plate on the blower's intake will allow the blower to be reduced in air pressure. This is all some folks use to regulate the air flow, while others use a combination of a choke plate and a gate valve. A 1/4HP blower with these air controls will be able to deliver any amount of air desired to the forge. This will allow the forge to run at 1200F or 2400F....and still have a balanced atmosphere.

Stacy
 
Both of my gas forges use 140 cfm pole blowers.

In choosing a blower for any forge it is better to error on the side of to much volume and not falling into the trap of purchasing, too little a unit that has no possibility of producing the required air flow. Its one of the variables in building a forge that affects not only the amount of heat one can produce in the forge, but also in delivering the atmosphere. needed during different forging operations.

Fred
 
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