PID CONTROL FORGE ; Salt Pots; and more

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Stacy E. Apelt - Bladesmith

Stacy E. Apelt - Bladesmith

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Since this topic pops up about weekly, I thought I would make a permanent thread about it. I will sticky the thread.

Post any comments or links you have to related threads and articles. I'll add any that will help to the list.

BASIC INFO
A PID is a control device that learns from its operation. It turn itself on and off to try and reach a set temperature. As it does this it "learns" how long the temperature stays at the set point and how long the burner needs to be on to get it there. Slowly the PID tunes itself to the parameters of the forge and will hold the temp in a very close range.

The use of a PID can make a good forge into a great forge. The below articles are a collection of posts that have been made over the years on the subject.

Wiring Diagram for a PID controller 220VAC oven:
http://www.bladeforums.com/forums/s...eat-Treat-Oven-Wiring-Schematic-Future-Sticky

Info on wiring the coils and picking Kanthal size:
http://www.bladeforums.com/forums/showthread.php/1022992-Heat-Treat-Ovens-Some-Basics

This has most all the info you will need. Read all the way through the thread, as the info is spread about:
http://www.bladeforums.com/threads/pid-controlled-forge-heat-treat-oven-plans-wip.1385057/

Tempering oven build:
http://www.bladeforums.com/threads/pid-controlled-forge-heat-treat-oven-plans-wip.1385057/
Super clear wiring diagram - perfect for controlling a tempering oven: Postb #4 has the PDF
http://www.bladeforums.com/threads/pid-controlled-tempering-oven-diagram.1002319/

Auburn University paper that will make your head hurt:
http://www.eng.auburn.edu/users/jzw0001/chen4170/Chapter_8.pdf

More threads:
http://www.bladeforums.com/forums/showthread.php?t=523845
http://www.bladeforums.com/forums/showthread.php?t=704470&page=2
http://www.bladeforums.com/forums/showthread.php?t=635924
http://www.bladeforums.com/forums/showthread.php?p=7384923
http://auberins.com/index.php?main_page=product_info&products_id=40
http://www.bladeforums.com/forums/showthread.php/600318-PID-Controlled-Forge

SALT POT INFO - by Kevin Cashen

http://www.bladeforums.com/forums/threads/685750-All-About-Salt-Baths
 
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I highly recommend a blown burner. It is about as simple as it gets as far as building one. There is no orifice to position, adjust, etc. The flame can be easily balanced for atmosphere, and flame size with just a twist of a knob. Converting a blown forge to PID control later on is also very simple.

The biggest advantage of a blown burner is that it can run at virtually any temperature the gas supply will allow. It can run at a tiny flame that barely warms the chamber at .5PSI, up to a jet exhaust size flame that will melt your steel. A venturi burner has to run at a fairly high pressure to draw the air in. Most will start to sputter out at around 3-4PSI (1500-1600F, depends on your forge). HT soaks are a bit tricky with a venturi, but a piece of cake with a blown burner.

On building a forge:
1) Saving money isn't cost effective on the liner materials. Get 2" regular Kaowool or use 2 layers of 1" High-Z wool, satanite, and ITC-100. The 1" insulboard is good for forge ends and replaceable floors.

2) Get a proper regulator and a 10' hose. Use "quick-connect" propane fittings to hook it to the forge. That way, you can switch the tank to other forges or devices with ease. A 0-15PSI regulator and gauge is needed. 0-30PSI is also common.

3) If at all possible, use a blower that is made to power a forge. Most folks recommend a blower with 50-150 CFM, depending on the forge size and use. Forge blowers are longer lasting and have better static pressure than just any old squirrel cage blower. If you can't afford one now, that is OK, just use what you can get. You can always change the blower later on. Using a shop-vac or leaf blower is just plain crazy....get some sort of real blower.

4) The shell can be nearly anything from an old propane tank to a piece of stove pipe. Most folks use an 18" length piece of 10" pipe. Shoot for a chamber size of 4-6" diameter and 16" length for a good general use forge.

5) Make the forge "well made". Take your time and do all the steps fully. Short cuts or rushing things will make the forge not last as long or work as well.

6) If at all possible, put a floor in the forge of a shelf liner ( thin firebrick), or a refractory like bubble alumina or Mizzou. The floor is where the forge takes a beating....especially if you plan on welding in it.

7) Add a TC and ceramic sheath with a simple PID reading device to monitor the temp. This will cost about $50. It can later be changed to a PID controlled forge for around an extra $50-70.
8) Put on sturdy legs, or make a cradle for the forge. Nothing is worse than a forge that moves around in use.

9) Put the forge on a HF welder cart. That way the whole assembly ( including propane tank) can be rolled away when not needed. The tongs and other supplies will store on the shelves below the forge for easy access when needed. - http://www.harborfreight.com/welding-cart-90305.html


10) - Places like High Temp Tools and Refractory sell all the supplies needed to build a good forge - http://www.hightemptools.com/supplies-mainpage.html
Expect to spend $100-150 for building a GOOD forge. Adding temperature reading and control can run an extra $100 or so, but can be added later. I would build in the TC sheath when making the forge, though. A well built forge will last many, many years of heavy use, and can be easily sold if no longer needed.

TIP:
For doing HT in a forge, use a piece of 2" stainless pipe. This pipe is called a muffle. Put the blade in the pipe with just the end of the tang reachable by your tongs. Put the pipe in the middle of the forge. The flames will heat the pipe and the pipe will heat the blade. You will avoid overheating the edge or tip this way. When doing steels that require a soak time, like O-1 and 1095, this is about the only way to go when using a forge for HT.
 
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Some more forge building tips:
1) The burner should enter the chamber from the side at a tangent near the top. It should be angled about 15 degrees forward. It can be horizontal, or even slightly uphill toward the forge. It should not enter straight in the top pointing at the floor. I know you see a lot of those on ebay, but it is terrible knife forge engineering. The burner should make the flames swirl around the chamber walls, not make the floor hot in one place. Multiple burners should be spaced as needed, but should follow the rules for a single burner as far as angles and such. Try and mortar the burner flare into the wool and Satanite as smoothly as possible.
2) A burner flare makes the burner run better and last longer. Stainless is preferred for the flare.
3) The wool can be stiffened with Rigidizer. This makes it easier to apply the refractory coating, as well as stabilizing loose fibers.
4) The wool needs a covering of refractory. Never use it as is, or there will be tiny fibers blown out in the exhaust. Ever heard of mesothelioma?
Most folks use Satanite to coat the wool. Put on a 1/4" layer, let it dry well for a couple days. Try and make the interior as smooth as possible when applying the satanite.
When dry, fire at low for a while, let cool, and fire at medium. Repair any cracks, and when all is good, fire at full heat until the insides are glowing. Shut off and let cool.
5) The refractory will work better with a reflective coating on it. ITC-100 is one common type. Paint on a thin coat, let it dry, and fire it to cure. Sometimes a second coat is a good idea.
6) Avoid anything that resembles an angle or is rough as much as possible. The burner should be smooth inside, have no projections in the path of the fluids ( gas and air), and have smooth curves instead of 90 degree bends. All this isn't always possible, but think of the flow path of the air/gas and try to avoid any turbulence that you can.
7) A mixing chamber in a blown burner is a very good thing. It is merely a place the pipe gets bigger for about 4" and then gets smaller again. This creates a very well mixed gas/air blend to be burned in the chamber. The average manifold pipe is 1.5", so the mixing chamber is usually 3".
8) Front and back ports need to only be big enough to do the interior work ( satanite and ITC-100) and allow the blades you make to go in. The front port is usually about 3X4" and the back about 3X3". The back can be plugged with a fire brick when not needed. The ports should be flush with the chamber floor.
9) The blower motor should be lower than the burner. To prevent any gas from back pooling in the manifold during a power failure and then accidentally igniting by the motor sparks when the power comes back on install a master shut-off solenoid valve in the gas line. It should be a NC valve....power goes off - gas stops flowing.
10) While a forge needs to be well built, it can be over built. Unless you need them, whistles and bells aren't much more than trim. One good add-on is a sliding work rest. Weld two pieces of 1/2" ID pipe down the forge body sides. They should be at the position of the forge floor. Make a slide by putting two 24" pieces of round bar in them and setting a piece of 3"X1/4" steel across them. If the steel is roughly at the same height as the forge floor, clamp it on and weld it in place. This will make a 3" shelf at the port when it is pushed all the way in, and a bar/tong support when pulled out. I consider a slide like this the best thing since sliced bread. The pipe pieces can be welded to the legs if that is easier, and the shelf raised as needed. I think that you guys can figure out how to do that.

Safety Note:
Looking into a running forge can seriously damage your eyes. Sun glasses, or glasses made for glass work won't make it safe. Use a pair of glasses made for this job. Even with them, try and avoid starring into the forge for more than a few seconds at a time.


Stacy E.Apelt
 
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