Jump to content

Propane gas forge question


Recommended Posts

I am in the process of building my first propane gas forge. The question I have is it necessary to have extra vent to allow more oxygen into the forge? My forge is a square tube 8x8x12 horizontal forge. One end is welded close. The open end has a door on it with a 3x5 opening so that I can place my blades into the forge while it is running. The propane burner will be mounted on the right side 6" from the front of the forge, at a 45 degee angle.

Link to post
Share on other sites

I don't believe so. My forge is similar sizing, and the end is a sort of refractory circle thing with a hole in the center of it (one of these http://www.silversupplies.com/images/soldering/54116.jpgbut with a hole in the center), so really the only vent it has is an inch max diameter. I don't believe another vent is necessary, especially as the torch itself will draw a lot of the oxygen it needs to burn (venturi, blown, or just a standard plumber's torch or something).

 

However, having the end open, or at least a closeable door, will enable you to do longer blades in the future, especially if you're going to want to do even heating for heat treating.

Link to post
Share on other sites

Yes, you should have an opening in both the front and back to allow additional air to be drawn into the forge. The forge is depending on oxygen to burn the propane. If enough oxygen is not allowed to mix with the propane you will have unburned propane inside the forge looking for the needed oxygen. The only place to find this additional oxygen is out the front door. Of course a reducing (oxygen poor) flame is good if you are forge welding but during general forging this is just wasted propane. If you have the door in the back that can be closed down to allow for the control needed for an appropriate atmosphere in the forge.

 

Check out the attachments on my web site at the Forge Supplies page for how I like to build a forge.

 

Let me know if I can help you.

Link to post
Share on other sites

Number one I'm not a fan of square forges. Because it's harder to get good swirling of the burning gasses in them they have more of a problem with hot spots. What is the inside dimension of the forge? If it's 8X8X12" that's huge. My main forge, which is cast from a refractory, has a 4" diameter hole that is 7" deep. It has a rear port that can be blocked off but rarely is because it comes in too handy. With it I can austenize a blade that is over 12" and I can use it to avoid over heating the tip of the blade.

 

Doug

Link to post
Share on other sites

Also, when asking a question like this what type of burner you will be using is very important. Wayne's comments about fuel and gas mixing are accurate, but you really don't need an extra vent if you have a forced air (blown) burner and can control the air and gas volumes entering the forge. You may not need anything for the right sized venturi either.

Link to post
Share on other sites

Jerrod, I am not using a forced air burner on this forge. This is the burner I purchased. http://www.ebay.com/itm/U-S-made-Gas-burner-blacksmith-forge-raku-kiln-propane-foundry-150-000-BTU-/231758543576?hash=item35f5e2bad8:g:Lu4AAOSwzOxUXlEH Doug the diamensions are correct. The forge is 8"x8"x12". It will have 1" of insulation on the sides and 2" at the ends.

Link to post
Share on other sites

Just one more question about the size...is the 8x8x12 dimension before or after the insulation? If it is before then you are going to end up with 6x6 right? The reason I ask is that 1" if insulation is awfully thin. At a minimum I'd go 2". If your finished interior size is currently really 8x8 then I'd add another layer of insulation. You will be glad in the long run that you did. It will easily pay for itself in fuel efficiency and help you to attain higher heat with your burner.

 

On thing I have seen with venturi burners is that first you need enough opening so as to not create back pressure on the burner. The burning propane expands like 7:1 so you need an opening large enough to not limit that. The second thing is, in my experience, a venturi forge benefits from a rear opening even if back pressure is not a problem. It does not need to be as large as the front, but a small opening will help to even out the heat in the chamber.

Link to post
Share on other sites

A update to my forge project. There is now a 2" opening on the back side of the forge. It is treaded so I can cap it off if need be. The Support for the burner is also in place. It is also a 2". I checked with a distributor here in Tulsa about the insulation. They tell me the 1" insulation is good to 2300 degree. I can always add more. With the 1" insulation there will be a 6x6 work area in the forge. I plan on having a single insulated fire brick on the bottom of the forge to rest work piece on. I am contemplating buying a piece of 8" sch. 40 pipe and making a round forge to compare the two.

Link to post
Share on other sites

They tell me the 1" insulation is good to 2300 degree. I can always add more.

FYI, that just means it will survive up to that temperature, it doesn't say anything about the effectiveness of the insulation it will provide. I have about 1.5" in my forge and kind of wish I had more, but I didn't want to lose too much space in my pipe. If I ever need to build a whole new forge I'll probably go with a 10" diameter pipe and do at least 2" of insulation (giving a 6" internal diameter, minus the hard refractory coating I'd apply over that).

Link to post
Share on other sites

BTW, the burner you posted is not a forced air type, it's a venturi. A forced air system uses a fan. It's not a big deal, but it's good to get the terminology right, especially when asking questions. It saves some time sorting out good info from bad. You may not have enough burner for the size of the interior. Normally the ROT is one burner per 350 ci (when talking about venturi systems). You may end up wanting a second burner for this forge.

 

Just my .02

 

Geoff

Link to post
Share on other sites

Geoff, I never said I had a forced air burner. I knew I did not have a blower pushing air into the forge. However, your statement is still valid. Thank you. With everyones input I am changing my plans about insulation. There will be 2" of insulation on all sides of the forge. Thanks everyone for your input. Will post pictures when forge is complete.

Link to post
Share on other sites

Geoff, by reducing down to the 1.5 from the 2" inlet you may be causing a restriction and letting propane back up in the tube. I would try removing the reducer, or better yet, build a Ribbon Burner.

 

Let me know if I can help you.

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...