forge questions.

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vikingGoalie

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Aug 20, 2019
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So I've built a pretty decent sized forge, imo, it's got a 18 inch long inner chamber, is a ribbon burner, pid controlled.
I'm super happy with it.

Propane consumption, I've tested this by filing my propane tank doing a session and refilling it.

So I did a 3hr forge welding session where it was at just over 2200 for most of that time. I did this twice, first time I used 2 gallons of propane, second time 1.9. So call it 2.
So I'm using 2 gallons per 3 hours. That doesn't seem bad to me and I'm ok with that. However, I have no frame reference on how that compares to other similarly sized ribbon burner forges.

Also my only annoyance, and it is a small one, is that I can get up to 2200 in about 15 minutes, the first time I put any significan amount of steel in there it will plummet in temperature like 500+ degrees. and it will take a good 10 minutes before it's back to 2200.
I believe this is because all of the refractory hasn't full absorbed the heat yet (but not 100% on that) but seems that way. Because subequently I can later on in that same session throw in some cold billets and it doesn't effect the temperature that much.

Just an oddity but also, pretty new to this all so just asking if that seems normal.

Lastly, I'm running off a 40lb tank, I notice about 2-3 hours in it'll start to freeze up. I'm going to throw it in a tub of water next time.
A bbq sized small tank takes about 30m-45m and it'll start freezing.
Should I really be sourcing a 100lb tank sooner then later to get around this?
 
You’re correct on the refractory not being heat soaked and dumping temperature when you put anything in it.
A 100lb tank is worth it’s weight in gold, they don’t freeze up, maybe it will when it’s almost empty but that’s not very often. IMO BBQ tanks are almost worthless when it comes to a bigger forge.
 
As Nick said - Get a 100# tank.

Let the forge soak at around 2000 for 15-20 minutes if you are welding.

You didn't tell us about your refractory, but for a large welding forge you want 2" of kaowool ( preferably High-Z) and at least 1/2" of refractory coating. 1" isn't too thick.
 
Stacy E. Apelt - Bladesmith said:
As Nick said - Get a 100# tank.

Let the forge soak at around 2000 for 15-20 minutes if you are welding.

You didn't tell us about your refractory, but for a large welding forge you want 2" of kaowool ( preferably High-Z) and at least 1/2" of refractory coating. 1" isn't too thick.
Click to expand...
https://imgur.com/a/KiMzkyQ
So I have 2" of kao then decent amount of kastolite. Yea I need to mount the control box, but I'm debating putting this on a different base first
 
Nice build.

Your heat dump issue is caused by two things:
1 - the volume of the chamber is rather large. Not much you can do about that.
2 - the door exposes the full chamber opening. This is the biggest problem, and the easiest to fix.
Just inside the sliding door, make a soft firebrick closure that closes off the top portion of the opening and only leaves the amount of opening you need to insert the billets. Just cut and fit them so it leaves the desired opening. No need to make them permanent, as you will replace and modify them often.. If you look at images and videos of peoples forges ( see the Larrin/Devin video just out) you will see pieces of old firebrick closures laying all over the forge area.
If you want to be fancy, you can cast a removable D-shape opening reducer in Kast-o-lite.
 
You can also pick up a 2nd 40# tank and use a manifold to run them together, so it's drawing half from each tank. I don't have a truck and some places won't refill a 100# tank if it's not transported vertically. I can put the 40# vertically in my car. Not sure I could life a 100# up and into the car? 100# would be nice, but the 40's are easier for my currently. I gotta look for a used on on FB marketplace!

I run a small forced air burner (basically a mini ribbon, but with a 2" diameter or so round nozzle with stainless tubes welded inside to create several flame jets) and get 4 hours at least before it starts icing up usually. Most of my forging sessions are 2-4 hours, so it's rarely an issue with a full tank, but it may ice up towards the end if the tank is less than half full. The forge itself is from an old bbq propane tank, so about 12" deep and 7" diameter inside roughly, 2" kaowool and around 1/2" Satanite.
Nozzle.jpg


I welded up some 1.5" x 1.5" angle iron to some steel to the forge frame top and bottom to make little trays for fire brick doors:

q bert1.jpg

hard fire bricks make good doors and are easy to slide back and forth. 2" x 2" angle would probably work as well and not need the metal spacer for clearance for the thin, hard fire bricks.

Forge hotter.jpg
 
I agree with Stacy, looks like a nice build, for the most part.
Another option for the doors would be to rotate them 90 degrees so they open from the bottom up. Shouldn't be too hard to modify your build for that. (I'd put the handles on the bottom)
What are you calling 'up to 2000'? I'm assuming you're referring to the thermocouple reading? How much of the castable is up to the same color?
When you say decent amount of kastolite, what do you mean? How thick are the walls in total with the 2" kaowool?

I learned about forge building from one of the founding members of the NWBA and my first introduction to blacksmithing was forging a 90# anvil for a medieval village outside of Seattle.
I learned early on that when forging larger pieces of steel, you can never, within reason, have too much thermal mass. My first forge that I used for 14 years was a 22" pipe with 2-1/2" of castable. It took 30-45 minutes to get to a full heat, but I could put multiple 2 x 6 x 6 billets in without any significant drop in temp.
I used to think the 2-1/2" was a bit overkill, so my second (current) forge for larger stuff is 2" of kaowool with 1" castable. I have only had this one about a year, and have not used it much, but I'm wondering if 1" doesn't provide quite enough thermal mass to prevent a drop in temp with large loads.
 
It varies a little bit the kastolite is about 2 inches thick in most spots over the kao. I have about 40-45lbs of kastolite in this, not including the ribbon burner.
As far as up to temp, yes I'm going off the thermocouple reading. As far as uniform color, the forge definitely changes as all that refractory soaks up the heat. I was just surprised how much of a drop it is (500 degrees) and takes a good 10 minutes to recover .
That was with throwing these in
https://imgur.com/a/zP4JCuH
 
Well, there is your other problem. That amount of mass will have to be raised to the forge temperature before it rebounds. That takes time.
 
Stacy E. Apelt - Bladesmith said:
That amount of mass will have to be raised to the forge temperature before it rebounds. That takes time.
Click to expand...
But on the flip side, once the refractory is up to forge temp, you can put large chunks in without any significant drop in temp and/or turn the propane way down. Forges like this are great for longer forging sessions, not so much for short ones. This is why we have 3 forges in our shop.
The induction forge gets used 80% of the time, it's great for quick forging sessions and one-offs. Prep time is as long as it takes to plug it in and change coils.
The small propane forge gets used 19% of the time, it's good for working on multiple pieces and smaller forgings. Prep time is about 5 minutes for the forge to get hot enough to put in a piece of steel.
The large one gets used rarely, it takes 30-45 minutes to get to heat, but once there we can put in large chunks of steel and/or turn the propane down to ~2# of pressure to maintain forging temps for multiple hour sessions.
 
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