Tank forge.

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LeaderofthePack

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Aug 4, 2013
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Just had a few quick questions on building a forge. Looking to make one out of most likely a used air compressor tank, my only real questions are what size should I aim for for doing blades up to about 10" and what's a good refractory material for the walls( brick, clay wool, other). Thanks again for all the advice.
 
I made my forge from a 20# propane tank, and if I was going to do it again I would use a 30# cylinder
 
I used 2" kaowool and ITC100 thermal coating with a single fire place brick in the bottom, then I built my own blown burner that is more then big enough to heat the forge, I have never used naturally aspirated burners
 
Kaowool alone won't get hot enough- you'll need Durablanket and/or the ITC for the top layer on the inside.
 
Hope you don't mind me jumping in with a few more questions... I'm also about to start my forge build, so hopefully this helps us both!

This is my first post... Just recently finished my grinder build (which I'll post soon), and my first knife. Have two more half done, but decided the forge needs to happen first!

I have an old #20 propane bottle, and I'll likely weld in a 2" or 4" extension and mating flange so it can be relined easily.

My question is about burner design... I like Stacy's dual stage blown burner design, and plan to use a single burner with PID controller. (Very elegant design!) Firstly, what size is best for the gas plumbing? (Lines from the regulator to the solenoid valves, needle valves and burner). I'm suspecting 3/8" but it's hard to tell from images of various forges, and I haven't been able to find it documented anywhere.

I read that the orifice should be 1/16". Does this sound right?

I was thinking of using 2" plumbing from the blower, with a 2"-1 1/2" reduction at the burner end, mounted into a 2" holder on the forge body... Does this sound reasonable? Does the air gap between the burner mount on the forge body, and the burner need to be sealed?

Finally (for now), best location for the thermocouple insert? (I plan on using a ceramic sheath.). This seems to be a point that has many opinions, depending on application. This is my first forge, so I want it to be multi purpose. The PID controller and a muffle will help for HT, so a best all round location for the TC is good. I was thinking below and forward of the burner inlet, so the burner flame has circulated around the forge before it reaches the TC, and offset enough so it's not directly in the burner path? With a muffle inserted, this would put the TC behind the muffle relative to the heat circulation. Any suggestions? (I am thinking the burner would enter at the top side of the forge, horizontal, and tangential to the interior cavity, so the heat circulates around the inside of the forge.)

It's difficult without seeing various forge designs in action, to get the design principles right from piecing together a multitude of discussions etc, so any advice from those with real world experience would be wholeheartedly welcome!

Many thanks,

Tim.
 
Just a while back this topic came up, and some said that in a pid controlled forge, inside the muffle is the proper place for the TC

For my burner I used 2" pipe and welded a reducer in the end with a 1" hole, saved needing different size pipe

fuel delivery system was made from a 350.000 BTU roofing torch which was way way to big I removed the stock orifice and replaced it with a propane torch orifice drilled to 1/16
 
Thanks John,

I read that also, and agree, this would be ideal... but because I intend this one for multi purpose use, I didn't plan on leaving the muffle in full time. The only way I can imagine putting the TC inside the muffle, is to insert it from the bottom and drill an access hole in the bottom of the muffle?
 
http://www.bladeforums.com/forums/showthread.php/782574-PID-CONTROL-FORGE-Salt-Pots-and-more This has lots of info.

www.hightemptools.com has everything you need and lots of information.


The chamber should end up about 4-6" round. The length should be about 4" or so longer than the largest planned knives. That makes the average forge about 14-16" long.

Use 2" kaowool for the insulation, and a 1/4-1/2" coat of satanite over the wool. A final coat of ITC-100 will make the forge quite efficient. This all adds up to about 5" in refractory, so the average pipe/tank/tube used to make a forge would be around 10" diameter. 16" of 10" pipe works great.





I will give you all a few good time and money saving tips.
1) I see elaborate ends make with hinges, bolt, etc. The ends just need to be something insulating to close off the tube. I use 12"X12" squares of 1" insboard ( from HTT) for the ends. Cut into round shapes to fit the pipe and once the liner of kaowool/satanite is done ( leave about an inch or so of pipe unlined on each end), just mortar up the ends with satanite and slip in the insboard rounds. Square and flat forges can be completely lined with insboard ( The NC forges are made with it).

2) To close up a large back port or make the front port smaller, just stack some firebricks where they are needed. Don't close off a forge too much, though. The combustion gasses need plenty of opening to escape from.

3) Make the front and rear port bottom even with the forge chamber floor. This allows for smooth in and out movement of blades and work pieces.

4) Make a 6" or longer "hearth" of firebricks in front of your forge that is level with the front port. This makes blades and things easier to put in the forge and remove. The sides of the hearth are also a good place to set hot blades temporarily .
 
Thanks Stacy,

This is the link where I got most of my info, and there is a wealth of information there. Thanks for sharing so much experience!

I went back over it, and finally found a reference to using a 1/4" needle valve... The size of the gas plumbing was the one thing that had previously eluded me.

I'm looking forward to getting started on this project!

Tim.
 
Me too... Just scored a blower from an old ducted vacuum system my neighbor was tossing out... Pulled the blower off, wired it with a dimmer, and works like a dream. Fabricated a flange to accept 2" ABS pipe for the cold side feed. Also scored an old propane bottle from the same neighbor.
Modified Stacy's schematic a little to enable a programmable ramp/soak PID to control both the forge and a tempering oven. (I have an old toaster oven sitting around gathering dust.)

I'll post the schematic once I've finished the Visio drawing and proven the design.

Cheers.
 
Finished building the burner control and test fired last night! Too much air volume and not enough gas (regulator hasn't arrived yet, so used the one off the BBQ), but got it burning on both idle and heat settings. It needed to be set at the very lower limit of the blower speed, near the point it would cut out, so played with a makeshift baffle for the test. Making up a proper baffle plate this morning. (note the Asahi beer can baffle!)

Pretty happy with how the controller worker out. Pretty neat and compact. Just built for manual for now, and will rebuild with the PID once I get the forge body done and happy with the performance.



 
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Thanks Stacy, all of your information made it a lot easier.

Made up the baffle for the blower, but still seem to have too much air. Added a vane inside the tube to break up the air, but still not much better. It will fire with a lean flame, with the minimal amour of air flow, but as soon as I get the air flow a little higher, it blows out the flame. Had a nice even flame at one point when baffling the blower totally with the palm of my hand, but it was very touchy, and blew out easily.

The lean flame suggests it will take more air, but I suspect the problem is not enough gas pressure from the BBQ regulator for the size of the burner.

I think the only option now is to wait till the new regulator arrives in Thursday!



 
Just a quick update... the new regulator made a huge difference! added a 2" tee with a baffle plate to act as a waste gate, which makes it easy to light, and a 2" gate valve to regulate the air on the pressure side (the baffle on the air intake just wasn't cutting it). Much better control now, and I can run the fan at a higher speed so it doesn't sit right on the edge of the cutoff when fine tuning the speed control.

Ditched the propane bottle and opted for a HF 11 gal compressed air tank... same diameter as the propane tank, but squarer ends, and the biggest plus was that it was easier to cut 4" out of that that add 4" on to the propane tank to get the length I wanted! Cut a 1 1/2" strip to use as a mating flange, and welded and tapped 4 sets of tabs to connect the two parts, so it can be easily dismantled for relining.

Cutting the doors out today (just waiting for a reasonable time to disturb the neighbors!), then ready to line.

This has turned out to be the most fun project I've done in a long time!



 
That thing looks great, I like the idea of the flexible exhaust pipe ;0)

My burner was a little hard to keep lit when it was in the vice, But after it was in the forge it worked great, I think all it needed was a little back pressure
 
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