adjusting blown forge atmosphere

[Scott Roush]

I built a vertical, forced air forge based on Karl's and am starting to wonder about atmosphere adjustment.  I'm getting ready to do some welding so I'd like some input on what to look for.  I'm getting a lot of scale.. way more than with my venturi and this might just be the nature of the beast. At this point, I only have an adjustable choke plate over the intake of the blower, but am starting to wonder if I should put a gate valve on there for more fine tuning.

What exactly am I looking for with the flame on these kind of forges?  Am I trying to get some blue in the flame that's exiting the mouth? That is how I did things with my venturi. But I'm having a harder time figuring this blown forge out...

[DANA HOLMAN]

Scott
I built mine pretty much the same way, buy from Kevin evans (rooster) I have a gate valve on mine and I have a blue flame no orange. I start mine out of the forge and then put it in the forge, and there is a blue flame that comes out about 5-6"
I would put a gate valve on, you will be happer
Dana

[kbaknife]

Scott, it's not all just air, but amount of air pressure, amount of fuel and fuel pressure.
Do you have your fuel not only regulate-able pressure wise, but also have the needle valve at the burner?
The amount of scale you have means to me that you simply have lots of heat/fuel/oxygen. That's not entirely bad. You really need heat to pattern weld.
But you can overdo it, too. I think Lin has some experience there.
You want a good "dragon's breath" of flame coming out the door.
That means that all of the oxygen was consumed in the combustion process INSIDE the forge, and the excess fuel is using the oxygen just OUTSIDE the door to finish burning.
First thing I would do is increase the amount of fuel so that ALL oxygen is consumed.
If you have excess oxygen in the forge, that hot oxygen will start looking for the next available fuel source to continue the combustion process, and that fuel source is your steel!
So, make sure you use up all the oxygen by adding plenty of fuel, and this is not necessarily done with the needle valve, but by increasing the pressure from the regulator at the end of your supply line.
Call me if you need to.

[Scott Roush]

Thanks Karl... that helps a lot. I always have flame coming out the door... but what color should the dragon's breath be?

I do have the needle valve in addition to the reg. So far I've only been changing the reg when going from forging to heat treating to welding....

[Lin Rhea]

Karl is right on the money. I will say that in my experience the steel will scale when it gets hot, but the atmosphere, whether it is reducing or not, determines at what temperature it starts to scale and how much it scales. I try to do like Karl says and adjust it to where it reaches as high a temp as possible before even starting to scale. My forge makes a roar when I got it right.

It seems to me that the fire "wants" the air and gas to be perfectly balanced and in the exact quanitites for that size and shape chamber to have burned to completion as it reaches the door of the forge. But, what we have to do to weld is to tweak the air down slightly from that or the gas up to keep a reducing atmosphere maintained. What do you think Karl?

[kbaknife]

You said it better than I did, Lin.
You also touched on a point - the size of the forge chamber.
Each of us have something that's going to be different - CFM of blower, chamber volume, etc.
I know that when I have too much air going in I get a "flutter" in the sound of combustion.
I either back down on the volume of air, or increase fuel pressure, or open up gas valve.
It's just a darned ballet. You're dancing with the forge.
You're also right in your wordage, Lin, better than I said it.
To sort of paraphrase what you said, you can get the steel to scale at lower or higher temps, depending on how you have the atmosphere adjusted.
it's a dance, like I said.
Scott, I've never paid much attention to the color of the dragon's breath, but I think the bluer it is, the higher the fuel percentage, and that's ok.
I'm at a point now that when I want to forge weld, I know how much pressure I want in my line, and how many turns to open my air gate and my fuel needle. As I get to the end of my welding cycle, I gradually reduce my line pressure and the temp visibly reduces in the forge without changing air/fuel settings - just pressure.
I've got two forges going now and have the 10" and 12" pipe to make two new ones.
I'm going to cut the 10" in 1/2 lengthwise and weld in 6" webs to turn into an oval, so I can have more horizontal length.
I'm sure when I do that, I will have a new learning process so I can figure out how to "dance" with my new partner.

[Scott Roush]

I love the image of you dancing around in your shop with your forges Karl.

Okay... sounds like I need to experiment a little more.

As to more horizontal length.. have you ever thought of something like a Fogg heat treat forge? I'm building one right now out of a 55 gallon drum.. just like his.  I'm gonna start doing swords soon so I will need it. But it will probably be real useful for my bigger bowies/camp knives.  I'm putting in a thermocouple....

[Lin Rhea]

Scott,
      I have zero experience with a drum forge like Don's. I saw him use his at Tannahill, but it was already lit when I got there. I would be interested in seeing a picture or two or , better yet a review, when you get it done. How are they to light? The big chamber might be tricky, I imagine.

[kbaknife]

Never thought of going that large.
I can heat treat any knife I want to build right now in my 12 inch, and that's with two layers of 1" wool. I've even seen swords heat treated in a vertical forge like we all have.
I want the extra length for forging my damascus billets as they get longer and be able to hammer/press more length in one heat.
Heat treating is not a problem in vertical forges.

[Lin Rhea]

It is true Karl, but I believe the logic behind it is that the drum forge can maintain a steady moderate heat throughout the length of the sword blade. I know that we can heat treat a sword in our forge, but I am thinking that Don developed the DF to reduce the risk of uneven heating. I really enjoyed seeing Don and his bunch working those swords. They heat treated about 10 sword blades that evening. He said that normally he would experience some failures, by that I mean cracks and breaks, but that night, none. When you get to see those guys doing their stuff, it is captivating. I satyed up past my bedtime to watch and that's saying something.

[kbaknife]

Well then I hope one of you builds one so we can all learn something.
I nominate Scott.
Any seconds?

[Scott Roush]

mine is mostly done... just need to cut some ports and such.

i plan to use the same blower/burner that i have for my vertical which i light outside the forge and slide in through a receiver tube.

will post when it's complete... as well as my drop point hunting sword. huh?

[kbaknife]

You'll need to calculate exactly where the inside edge of the wool is on both forges, because that's where the end of the burner will burn off, so it will always be only as long as the shortest forge liner.
But then again, you think of so many things at once I'me sure you've already considered that.

[Scott Roush]

I thought about it for the vertical... but not for the Fogg forge.  I have a piece of sacrificial pipe that burns off....  

Also... The Fogg forges only have 1" of wool inside of them. They are not supposed to hold too much heat.. at least that is what I read.  Apparently weed burners work just as well.. but since I have the blower I might as well use it.

Which brings up something else...

Did I see that you had some kind of quick disconnect for your burners???

[Jeremy]

Scott,

My other passion is HEMA and I've talked to some of the big names in US swordmaking about forge and blade design.  There are some excellent discussions regarding both (I highly recommend looking at the discussions regarding distal taper, cop and blade harmonics!) on the sword forum international bladesmith forums.

I have a few people looking for scrounged parts for a long vertical forge - of course shop time would helpful!

[Scott Roush]

Jeremy...  I will check that stuff out.  I'm still a little ways away from making a full size sword. I'm mostly making this forge because I have the drum and am interested in getting more even heats on my longer blades.  Right now my plan, regardless of how much of a longshot it is, is to forge a viking era short sword reproduction from the steel I HOPE to get from my smelt. Or use the iron from it for a laminated blade. Or use the cast iron from it to fry up some eggs.

Which is going good by the way. The preheats I've been doing in my furnace are very inspiring.

[kbaknife]

Originally posted by Scott Roush:

Which brings up something else...

Did I see that you had some kind of quick disconnect for your burners???

Just regular air line quick disconnect fittings. They're made to hold over 100 PSI and we're only running 4-7 pounds.
Here I have one with a dummy fitting in it to keep dirt out while I have the gas line connected to the other burner:
   

And here it is hooked up to the other one:
 

And here's the supply line:
 

[Scott Roush]

okay.. thanks. I need to be able to move my burner around for different things and need an easier way to disconnect.  I was just looking at high pressure disconnects online, but maybe I can find the lower pressure type locally....

[Wampus]

Ellis Knifeworks carries the quick disconnects combined with a shutoff valve.  Grainger tools has most of that type stuff too if you have a store near you.

  http://elliscustomknifeworks.hightemptools.com/valves.html  

Here's a pic of the assembly Ellis sells on my forge burner.

 

[kbaknife]

Scott, any hardware store or probably lumber yard that sells pneumatic nailers and such will have fittings.