Blown forge problem

Yes, the coarser stainless will work better than the tighter copper plated scrubbers.

I think your 3/4" pipe has too much gas velocity and thus the cool spot on the wall. 1" will be much better, and 1.25" is great for a large forge.

I think your idea of building a larger forge is good. Consider making it from a 16" to 20" section of 10" pipe. You don't even need ends on it, just stack firebricks as needed to make the front and back ports. This is becoming a more popular option as smiths are making different shaped objects than just small straight knives.
 
Thank you for confirming my thinking on the 3/4" pipe causing too much velocity. How long would be best for the 1" section of pipe? I'm thinking seriously about either cutting another hole in the existing forge body, or building the new forge using the 20 lb propane tank. If I were planning to do LOTS of forging then perhaps buying a section of 10" sch 40 pipe would be ok. I've got two bad shoulders so have to really limit my hammer work, so I think the propane tank would be just fine.

Stacy, didn't you say to put burner hole at the 9 O'clock position, about 1/3" of way from front, but angled toward the rear so the flame would hit about 1/3 from rear on opposite wall? Leaving the ends full size and open is a good idea as it makes lining the forge with insulation much easier. Weld a section of angle iron to bottom of each end to hold firebricks and to provide a shelf at front.

Thanks to all for ideas - got me wanting to just build a new forge. {g}

Ken H>
 
The trick is your gas velocity has to be faster then the flame propagation speed of a propane/air mixture. It is very easy to get carried away and get to big of a burner in a forge. You can tell it’s to big because your not able to adjust it down low enough without back firing up the burner tube. This is why a flare is shaped into the refractory so the air speed drops at that point and sticks the flame right there. How big is your forge chamber?
 
JT, I was thinking the flared end was for a Venturi burner, that a blown burner didn't require the flare? Comment?

Forge body is about 4" ID by 12" long. With the wall so close to where the flame comes out of burner tube I suspect is part of the problem. Originally I had about 6" ID, but added another layer of 1" to allow the forge to get hotter for forge welding. As small as the ID is, would the final section to 1" help much? 4" ID is pretty close for other wall.... I'd think anyway.

Remember folks, I am NOT an expert on forge burners - that's why I'm asking so many questions here.

Ken H>
 
For a forge that small, I would stick with the 3/4" pipe.

The "flare" JT and I talk about is in the refractory from the shell to the chamber. The burner itself should stop about 1/2" in from the shell. The flare is a bell shaped opening that rounds onto the chamber sides.

If you are going to do bigger projects, and forge damascus, I totally agree that a larger forge is a good idea. A propane tank will work, but the proportions require a lot of insulation to get a suitable chamber size. A section of any type of pipe between 8" and 10" diameter works very well. 16" is a good length to make most any normal knife. Pipe forges are easy to weld to, easy to line with Ins-wool, easy to apply the refractory, etc. Stacking firebricks is the simplest method of putting ends on it.

You can find some sort of cylinder in steel that will work for free or very little money. Most welding suppliers and gas refillers have old tanks they will give you or sell you for scrap metal price. A large steel compressed gas tank (Oxygen, helium, nitrogen, etc.) is about 8" ID. One tank will make several forges. If you don't have the ability, most any machine shop will cut it up. I have seen it done by hobbyists with a recip saw and a pack of metal cutting blades.
Propane places often have odd shape/size tanks they will give you. Have them remove the valve if it is still there. These are thinner than a compressed gas tank and will work fine. a 20# or 33.5# tank for a forklift arev just the right size.
 
Propane tanks, either 20# or 33.5# tank are just the right size. And I've got both of those scrape tanks on hand and plan to use one of those. These are about 12" OD, so 3" of insulation would make a nice 6" ID inside size. I can take the 33 lb tank, cut it to 16" length and use a 1"X12"X24" thermal blanket spec'd at an average work temp of 2300F to 2600F Withstands bursts to 3000F. That 12" wide will give 2" space on each end for coating with refractory cement (Spec'd as withstands working temperatures up to 3000-Degree F)
.

I found a 2 ft length of 2" pipe and some 1" pipe in my scrape pile to make new burner. 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 connecting at the 9 O'clock position, perhaps angle upwards a tad.

Looks like I just might have to build a new forge {g}
 
Thank you Stacy (and JT) for taking the time to provide advice and share knowledge on the project. I won't be able to build new forge for a few weeks, got a couple of slipjoints to finish and a set of steak knives, all which must be finished well before Christmas. I'll post a photo of finished project when I do finish. Might even have more questions, but I do think Stacy & JT (must not forget Jason) have done a good job of answering all questions.
 
If you have any questions your more then welcome to send me a message. Especially if your about to do something your unsure about. Better to ask then waste your time and money.
 
Thank you so much JT - I'll certainly keep your offer in mind You and Stacy are a couple of the main "go to" folks on the forum for sure.
 
JT, Stacy, since I've decided to build a new forge please allow me to ask ya'll 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 is planned 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, thank ya'll for all the help ya'll have provided.
Ken H>
 
Ken H> said:
JT, Stacy, since I've decided to build a new forge please allow me to ask ya'll 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 is planned 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, thank ya'll for all the help ya'll have provided.
Ken H>
Click to expand...
I don t think that you need that hard fire bricks inside . They will soak lot of heat so they will reduce efficiency and you will reach temperature slower..Fill everything with ceramic insulation and then that refractory cement .At least that is what I will do in my forge I work on...something like this ..simple
https://www.bladeforums.com/threads/gas-forge.1684684/
 
If it was me I would kinda go back to the drawing board on this. I would ditch the 3 layers of insulation. You only need 2” on the walls/floor. Plus 6” and especially 5” is really not enough for a good usable forge area. I mean it’s ok but if I was going to blow it I would go 8” not 6”. And I would not go to a 1-1/2” burner tube. That’s a big burner and you will not be able to get a stable burn low enough to do low temp stuff. All burners no matter the sizes need X velocity to burn property. To fast and it blows the flame out and to slow and it back fires up inside the burner. All your adding by going bigger is more BTUS. My tiny forge was made from a small air tank and it used a 1” burner and it would straight up melt steel. A 1” burner and put out a shit ton of heat. As for the floor I wound wrap with wool and cast over it with a cast able refractory to make a flat surface and coat the inside of every surface with the same refractory to make a nice solid shell. Hard fire bricks are not designed to insulate. Thy are designed to absorb heat and radiate that heat outwards into the steel enclosure (aka wood stove).
 
JTknives said:
Hard fire bricks are not designed to insulate. Thy are designed to absorb heat and radiate that heat outwards into the steel enclosure (aka wood stove).
Click to expand...
That makes sense - with both of ya'll saying the same thing. and the idea of a 1" burner tube makes really good sense also. I can do the smaller tube just fine. I've got pipe in the scrape bin for either size.

Thanks for chiming in with info.
 
First, If you haven't cut the tank down yet, consider making it 18". The size chamber you will get will be nice with a little more length. You may not need it today, but it may be nice later on. Also, it will allow the blades to be more in the middle during HT.

I agree with JT that 2" of refractory is fine. By the time the wool and refractory is done, you will be around 7". After pouring a flat floor, the chamber will be around 7X5".
The larger chamber will allow larger billets and odd shaped objects try working a large hawk in a 4" chamber). It also allows the blower to push more flame without a cold spot.
Be sure to arrange the seams on the lining so they are opposite each other. A third advantage of the slightly larger chamber is it is easier to install the lining and refractory.

Forget the hard firebricks. Use them for making a work shelf outside the front/back or as a hot table to set hot blades on fro cooling. Inside yo are far better with a floor of Kast-o-lite or bubble alumina.
Leave the forge a simple insulated cylinder. Get a dozen soft firebricks to stack at the front and back to make adjustable openings.
2" air manifold decreasing to 1.5" mixing manifold, reducing to a 1" burner will make a perfect burner for a forge your size.
 
Thanks Stacy - Looks like we've got 3 folks in total agreement what is best. That's the approach I'll take. 18" long? That's pretty big forge, and knowing how little I'll be using it wasn't considering anything that long. BUT - if ya'll are saying it will work just as good as the smaller size, then there doesn't seem to be any real downside to the larger forge body. A few lbs heavier for moving, but not that much. Looks like about 15 to 16" is max length I can cut and leave one end fully open for ease of lining.
 
If 15-16" is the max you can get, that is fine. I was just cautioning you not to make it too short. Also, if portability is your issue, the smaller length has some reason.

The main reason I said 18" was I was thinking that there was right at 18" clean tube on a 33.5# tank.
 
Instead of bricks to fill spase why not to use stone wool .It is cheap , good insulation and have high temp. resistance ?Then ceramic blanket and then cement ? Light and efficient ?
 
Stacy, I think I've mixed two different tanks in my mind. You said 33.5 lb forklift tank and I've got a 30 lb standard tank. I cut one end off right at the point to give max length with full size open end. That gives a total length of 17" to the very end. When I cut the other end it will provide a 7" to 8" opening providing a total length of 16".

And you're right, portability is VERY important to me - with bad back and shoulders I don't like to lift much weight when moving things around. As an "old man" I do have to be more careful than when I was younger. I even sold my 1800 goldwing this past summer. That was a BIG move for me, motorcycles have been my basic transportation for well over 50 yrs.
 
Natlek said:
Instead of bricks to fill spase why not to use stone wool .It is cheap , good insulation and have high temp. resistance ?Then ceramic blanket and then cement ? Light and efficient ?
Click to expand...
Natlek, I had to google "stone wool" to know what it is. Isn't that the same as rockwool that is used for insulation? If so, I've got LOTS of that stuff laying around in the attic. I never had any idea rockwool insulation could be used for insulation in a forge. Why do I not hear more about using rockwool for forge? Maybe not for total insulation, but at least for filling gaps in spaces.

I think I've got plenty of the ceramic fiber and will perhaps have some left over so don't think I'll need any. My idea on using brick for the bottom space wasn't to "fill space" so much as to provide a more durable bottom for the forge.

Comments Stacy?
 
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