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Johnson gas forge
- Thread starter ajg17d
- Start date
http://www.google.com/search?q=john...%2Fwww.ebay.com%2Fbhp%2Fforge-furnace;130;225
I guess I dont know how to post pictures on here...
its a Johnson gas appliance co. 142 with no blower... (need to figure that out)
Natural gas
can it be used as a forge or just as a heat treat furnace? The info I can find about it says it is a heat treat furnace. It says 180000 btu / hrs 1350 to 2350 temperature range I guess I dont know what I have
about all I am sure of is it is HEAVY!
I guess I dont know how to post pictures on here...
its a Johnson gas appliance co. 142 with no blower... (need to figure that out)
Natural gas
can it be used as a forge or just as a heat treat furnace? The info I can find about it says it is a heat treat furnace. It says 180000 btu / hrs 1350 to 2350 temperature range I guess I dont know what I have
about all I am sure of is it is HEAVY!
Last edited:
Stacy E. Apelt - Bladesmith
ilmarinen - MODERATOR
Moderator
Knifemaker / Craftsman / Service Provider
- Joined
- Aug 20, 2004
- Messages
- 37,786
That salvaged scrap HT oven does not look like a good deal for more than $20.
Johnsons are good industrial HT furnaces. They aren't forges. They are not small/light, nor are they portable.... and they are not small shop user friendly. Most homes don't have the industrial gas pressure needed to run one. Check the label for operating pressure. The blower needs to be the proper size, to. If it is dirt cheap, you can just re-build it for propane, and add a blower. Frankly, it is almost as easy to build a PID controlled forge and have both forging and HT capacity that doesn't weight 300 pounds.
Johnsons are good industrial HT furnaces. They aren't forges. They are not small/light, nor are they portable.... and they are not small shop user friendly. Most homes don't have the industrial gas pressure needed to run one. Check the label for operating pressure. The blower needs to be the proper size, to. If it is dirt cheap, you can just re-build it for propane, and add a blower. Frankly, it is almost as easy to build a PID controlled forge and have both forging and HT capacity that doesn't weight 300 pounds.
How would I go about converting to propane I got it free so no big deal if its not worth it. I would guess new orifices to start. Would you happen to know about a good tutorial for the pid forge (no clue what it is but I am committed to make some type of forge, will be looking into it as soon as I send this message. Thanks for the help you have already given me.
Stacy E. Apelt - Bladesmith
ilmarinen - MODERATOR
Moderator
Knifemaker / Craftsman / Service Provider
- Joined
- Aug 20, 2004
- Messages
- 37,786
The stickys have a whole segment on PID controlled forges and ovens.
To convert that oven to propane, first you need to know what type burner you have. If it is a venturi burner, it has no blower and the air is drawn by the venturi of the gas jet. The air chokes affect the amount of draw and the combustion. The orifice size creates the draw. Natural gas has a larger orifice than propane does. The orifice will most likely need to be changed. You would want something around an .030-.035" " orifice. A photo of the burner would tell me if it is venturi. Before tearing it apart, try and determine the orifice size. If it isn't a lot off, the forge may run OK on propane with a little adjustment of the air chokes. It won't hurt to try it and see ( assuming it is venturi)
If it is a blown oven, you will have to add a proper size blower. Also you need an air valve and/or blower choke to regulate the air flow. If the entire manifold is missing, then you need to make that, too. Depending on what is still there, it may be easier to build a complete new burner. In a blown burner, the gas is directly mixed into the air flow in the manifold with no orifice. Any gas inlet pipe or tube size over 1/8" ( 1/4" is standard) will work. The gas flow is regulated by a needle valve.
In a simple PID control, a digital device called a PID reads the temperature in the forge and compares it to the temperature programmed. If the forge is lower , it opens the gas valve. If it is higher, it shuts it off. This requires a pilot flame for a safe operation. Control is a bit irregular because the flame is either full on or completely off.
In the two-stage PID I designed, the flame switches from a pre-set HIGH to a pre-set LOW instead of ON and OFF. No need for a pilot and very close temperature regulation. It costs less that $10 more to have this much more accurate control.
To convert that oven to propane, first you need to know what type burner you have. If it is a venturi burner, it has no blower and the air is drawn by the venturi of the gas jet. The air chokes affect the amount of draw and the combustion. The orifice size creates the draw. Natural gas has a larger orifice than propane does. The orifice will most likely need to be changed. You would want something around an .030-.035" " orifice. A photo of the burner would tell me if it is venturi. Before tearing it apart, try and determine the orifice size. If it isn't a lot off, the forge may run OK on propane with a little adjustment of the air chokes. It won't hurt to try it and see ( assuming it is venturi)
If it is a blown oven, you will have to add a proper size blower. Also you need an air valve and/or blower choke to regulate the air flow. If the entire manifold is missing, then you need to make that, too. Depending on what is still there, it may be easier to build a complete new burner. In a blown burner, the gas is directly mixed into the air flow in the manifold with no orifice. Any gas inlet pipe or tube size over 1/8" ( 1/4" is standard) will work. The gas flow is regulated by a needle valve.
In a simple PID control, a digital device called a PID reads the temperature in the forge and compares it to the temperature programmed. If the forge is lower , it opens the gas valve. If it is higher, it shuts it off. This requires a pilot flame for a safe operation. Control is a bit irregular because the flame is either full on or completely off.
In the two-stage PID I designed, the flame switches from a pre-set HIGH to a pre-set LOW instead of ON and OFF. No need for a pilot and very close temperature regulation. It costs less that $10 more to have this much more accurate control.
That is a pretty big forge. I believe the sticky can be found in this thread, http://www.bladeforums.com/forums/s...reads-All-The-Good-Info-You-Want-In-One-Place. Are you thinking of building a forge to fit inside of your Johnson forge?