ANOTHER %#!*@¢& Forge Attempt

DanF

DanF

Knifemaker / Craftsman / Service Provider
Joined
Apr 17, 2017
Messages
1,544
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Here's the victim, free to me, not large enough for a forge propane tank so I'll use new instead of old, rusted, and dangerous
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Getting started, going with the D shaped front opening, rear opening will be much smaller. Trying to think of a way to have front opening adjustable to accommodate a variety of sizes.
Right now, this is the plan:
3" high temp wool (1" each layer)
Rigidizer each layer
1/4" satanite
ITC 100 layer
Bubblelumina floor.
Two burner, forced air, planning for future PID install.
I'll try to post what is next in the build so maybe someone will see an issue and let me know before it becomes a problem for me.
Thanks,
 
Sounds good. 3" may be overkill, but will bring down chamber diameter. 2 blown burners IMO are excessive of that size forge - will necessitate two blowers unless you really want to mess around with flow rate metering (every time you change one variable (gas to a burner for instance) you will have to change the other 3 (air to both burners, gas to the other). Blown burners don't really have a max heat output other than air supply. A bigger blower = more heat output. I would design such that your flow pattern maintains a more constant temp throughout the forge and run it off one burner.
 
joedhiggins said:
Sounds good. 3" may be overkill, but will bring down chamber diameter. 2 blown burners IMO are excessive of that size forge - will necessitate two blowers unless you really want to mess around with flow rate metering (every time you change one variable (gas to a burner for instance) you will have to change the other 3 (air to both burners, gas to the other). Blown burners don't really have a max heat output other than air supply. A bigger blower = more heat output. I would design such that your flow pattern maintains a more constant temp throughout the forge and run it off one burner.
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Thanks, how successful would a one burner be with a PID control for HT? I think I read that a two burner with PID will give a more constant, stable temp for that purpose? A one burner would definitely be less expensive to build if it would/could hold within, say, a 3-5 degree temp variation? I'm all for saving some $$ if possible.
 
Just did one with an air tank. And ended up using 1in insowool. The 2nd layer just wouldn't fit in right.
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DanF said:
Thanks, how successful would a one burner be with a PID control for HT? I think I read that a two burner with PID will give a more constant, stable temp for that purpose? A one burner would definitely be less expensive to build if it would/could hold within, say, a 3-5 degree temp variation? I'm all for saving some $$ if possible.
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I have not built a PID controlled forge. I imagine that it would work somewhat poorly for precise temp control even with two burners. Maybe combined with a muffle it would have a small enough temperature gradient. I am assuming you want PID control for HTing. If this is the case, you can make an oven for a reasonable price. I am not in love with the idea of a dual purpose forge and HT option.

If I were to make a heat treating, PID controlled forge, I would do it in a vertical forge (almost like a foundry) with a permanent muffle installed and my TC inside the muffle. Basically a salt pot minus the salt.

I know some folks run PID forges for knifemaking, and I am sure there are good reasons other than HT, but I have yet to encounter them (I imagine certain high alloy/ss work or pattern welding SS would benefit). Just running a PID on a forge to HT carbon steel blades seems like a lot of work to save almost no money over an electric oven. After all, the solenoid valves for air and gas alone would be pricey. I know auto ignition isn't (necessarily) required in a PID forge, but you will never be able to get the temp low enough for something like a subcritical anneal without it. Any system I could think of to do that reliably would cost a bit of money to add. I guess you could also skimp on the solenoid for the air and just switch the gas, but then you probably exacerbate oxidation problems.

Don't mean to dump on a plan, and I could be wrong about this, so maybe someone who is smarter on the subject can weigh in.
 
One burner PID control works fine. I would venture a guess that most PID controlled setups are one burner. Multiple burners are only used on long forges.
 
valknut said:
Just did one with an air tank. And ended up using 1in insowool. The 2nd layer just wouldn't fit in right.
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Justin, what was the diameter of your tank alone?

J joedhiggins , from what I've read, they exist and can do a decent job. A muffle deletes the necessity to "pump" the blade, rather, let it sit and soak, say 10 minutes or so in a stable- temp muffle. In a perfect world my shop size would accommodate a forge and oven, but alas, I moved away from that mythical place long ago. :) Not a dump, I appreciate all suggestions.
 
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Joe,
A PID controlled forge keeps pretty good temp control with +/- 5 degrees being average.
It works far better with a blown burner for HT, which can run much lower than a venturi.

The info on setting a PID controlled burner up is in the Stickys.

Now, as to the amount of wool to use:
The thickness needs to be 1" minimum for a regular forge. More won't hurt anything.
The most important thing is the chamber size. If the tank is 12" wide and you put 1" wool inside you have about a 9" chamber. That is really wide. If you use 2" of wool, it is 7" which is goo if doing HT with a muffle pipe. 3" of wool would be a 5" chamber, which is good for forging, but tight for putting a muffle in for HT . So, either two layers or three would work. The chamber length on a propane tank forge ends up about 10" IIRC. With that, I would stay with 2" of wool.

Final note on PID control. If a small forge is well built and allowed to fully soak, a needle valve and a pyrometer will be fine for temperature control. Since a PID can be used as a readout with a TC, it is effectively a pyrometer. That is where I would start for most new makers. After learning to use and control the forge you can simply add the second needle valve and the solenoid to make it two stage PID controlled. When building any forge, put a port for a ceramic sheath in the forge as if it was a second burner port. That allows the TC to be placed in the sheath or slipped inside a muffle for HT. When the TC is in the sheath, plug the end with wads of kao-wool.
 
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Thanks for posting that Stacy, I had read that info a few months ago but could not remember where I'd read it.
Since I will be using a muffle, I may drop back to the 2 inches of wool, but will make that decision when I start putting the wool in place to see what I actually have.
I believe that I read that you want the forge chamber volume to be around 2.5-3 times the volume of the muffle. That's what I'm shooting for, if it sounds right.
 
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Front opening cut out to 6-1/4"x6-1/2". Once my wool arrives I'll be able to adjust the opening to accommodate its final size. Tomorrow I'll have to carefully measure and mark for the much smaller rear opening, but I will not cut that until I am sure where the final floor elevation will be.
 
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I had a piece of 2" angle I cut to use to stabilize the cylindrical shape, kinda "feet" as it were. From there I can decide later if I want the whole thing mounted on a pedestal tree that will support everything. I'll have to decide that after I get everything together to see if the blower, PID, etc would be suitable and stable mounted on a pedestal.
 
Just use a metal hf cart. Something like this
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*this isnt my set up someone posted it on FB and I thought it looked like a good idea*
 
I mount forges on HF carts. It works perfect.
The position of the gas valve and the direction of the forge are excellent in the photo above.

You can assemble the cart as per the instructions and have the top as a tray with a 3" lip, or flip the top over and have it flat and smooth like the photo shown. I like the tray top setup as it allows putting fire bricks in the top under the forge to keep things cooler. It also keeps stuff from rolling or falling off the top when moving the forge around. I like to raise the forge at least 3-4" above the cart top.

Use a pipe strap to bolt the burner manifold to the cart lip so everything stays solid. Controls and such can be put on a piece of sheet metal extending down from the cart top. If mounting the PID and other controls in a project box, just bolt the box to the bottom of cart top.
 
Thanks is a nice looking set up, thanks for posting it Justin! No use reinventing the wheel, I'll try to do something similar to that.

Question, will the flat shelf I have proposed have a negative effect on the burner flame swirl?
 
DanF said:
Thanks is a nice looking set up, thanks for posting it Justin! No use reinventing the wheel, I'll try to do something similar to that.

Question, will the flat shelf I have proposed have a negative effect on the burner flame swirl?
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Yeah, but not a huge one if the angle is right and the transition relatively smooth (the floor isn't built way too far up).
 
Have been reading much trying to understand as much as I can before I go forward. I just ordered $235 in wool and refractory stuff. 8# wool, 8# htz wool, satanite, ITC 100, and bubble alumina, building a decent forge ain't cheap!
I was reading that a rheostat is not so good for a blower, an air gate better, rheostat can burn out blower-- thoughts on that?

Now looking for a burner, TC, and PID.
 
Speed control on a blower works OK on shaded pole and universal motors (and DC), but it won't work at all on some motors. Also, as the blower slows down the cooling of the motor is less. This isn't normally an issue, but in something sitting next to a hot forge it may be. A gate valve is better than a choke plate in most circumstances.

I used to build speed control in blowers, but just us a gate valve now. There are a few circumstances where they are nice, but those are usually on a special use forge.
 
The pictured cart above is from my build. If you want to see more of what I did take a look at the video below. I agree with Stacey that the speed control on the blower motor is not necessary as the valve controls air flow just fine. I bought my burner assembly as a kit from HTT, but if I was building from scratch I would use a globe valve as they are designed for throttling and a gate valve is designed for shut off. Adding a by-pass with a solenoid valve controlled by the PID would be a great addition and while I've scrounged up the parts to do this I haven't gotten around to it and I've got where I can control the temp pretty good manually if I have a helper when I'm heat treating.

 
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