Apologies in advance, I fear I'm about to ask a dumb question but I want to make sure I have this right. I'm working away with my small propane forge and having fun. I'm still not confident about how oxidizing / reducing my forge atmosphere is. I've read that:

1. I can learn things from the rate of scaling of metal in the forge
2. I should be looking at the dragon's breath

For #1: Rate of scaling

When we talk about scale do we mean the thicker black flakes that get left behind on my anvil? Or the thin black coating (not soot)? Or both? I believe we mean both.

When we say that a reducing atmosphere will not create scale on metal - how can I even tell? When the metal is hot in the forge, the scale is also hot, so at high temperature how do I tell if scale is building up? Then of course, once I remove the hot metal from the forge it'll scale in the open atmosphere as it cools - so I guess I don't really know how to conduct this test at all.

For #2: Dragon's Breath

I think I am making some progress here, but would like to double check a fact:

Here is my forge running almost fully choked. The work piece in it has borax on it. I believe this is a good reducing atmosphere suitable for welding:

(More photos here: http://imgur.com/a/P9vf6)

Can anyone let me know if I am right? I believe I need to get the temperature hotter (turn the forge up) but that I'm not too far off. Am I?

I'd like to get a photo of what I think is neutral and what I think is lean - but I ran out of propane and time, so that'll have to wait for a bit.

You can see the "cold" end of the work piece is, to my eye, very heavily scaled - but that piece had been through probably 15-20 forge heats, and quenched in water several times too - so that doesn't seem like an unreasonable amount of scale. Is it? 

Here is a video of the forge take around the same time as the photo:

 

Thanks in advance for any advice offered.

Suggest you partially block off the front of the forge. Think bricks.

That way you reduce the amount of heat escaping but can still work through the smaller opening.  The blocking device should be removable if needed.

4 minutes ago, Glenn said:

Suggest you partially block off the front of the forge. Think bricks.

That way you reduce the amount of heat escaping but can still work through the smaller opening.  The blocking device should be removable if needed.

Yes, for sure. In fact, I'm expecting to get the bricks today for this very purpose. I also intend to cut back the kaowool "hood" I built in so that I can better place the bricks without forcing all the hot exhaust down onto my table.

Glenn is spot on. I will go further and suggest that you don't have an actual problem; just an incomplete forge. We occasionally discuss the problem of too much back pressures against burners, caused by closing down a forge's exhaust passage overmuch. There would be just as much consternation over too little back pressure if more people left exhaust ports very large. Fortunately,y you are already planning the needed change to complete your forge in style.

19 minutes ago, Mikey98118 said:

Glenn is spot on. I will go further and suggest that you don't have an actual problem; just an incomplete forge. We occasionally discuss the problem of too much back pressures against burners, caused by closing down a forge's exhaust passage overmuch. There would be just as much consternation over too little back pressure if more people left exhaust ports very large. Fortunately,y you are already planning the needed change to complete your forge in style.

So now I'm excited to make that change!

...BUT: In the photos and video, am I correct in my belief that the forge environment is reducing? And how do I go about judging that based on the scale buildup (i.e., if I can't see the scale when it's hot, and taking it out of the forge guarantees scale buildup, how do I know whether I'm reducing or oxidizing?) 

Haven't we talked about this already Andy?

It's been discussed repeatedly scale WILL form on hot steel in open air. PERIOD.

A forge with a neutral or reducing atmosphere: gas, coal, charcoal, electric, etc. can NOT form scale there is NO oxygen to oxidize anything. To check, shine up a thin piece of steel and put it in your forge hot and running. If the surface appears clean till it's the same temperature as the forge it is NOT scaling up.

If you're getting soot your choke is closed WAY too far.

Trying to judge air fuel ratio by dragon's breath color with borax in the forge is like trying to tune your guitar in the front row of a rock concert.

Have you noticed the recent discussion of the huge orange exhaust plume from my NARB forge? I know how to tune burners by look and sound and those burners are near perfect but the forge is generating orange flames in the exhaust a good 12" high. The general consensus resulting from some deductive logic is the orange is the product of the calcium component in the castable refractory.

Perhaps before trying to weld in your forge you wait till you have all the parts and learn how to tune it. Getting in a rush is a fast track to making mistakes more permanent. About the settings on your choke. By all indications your forge is running rich, orange dragon's breath, WHY close the choke more? A LITTLE rich is a good thing when required but a LOT rich is DANGEROUS in the extreme.

So in short, finish your forge, tune the burner, use the shiny steel coupon method if you used Kast-O-Lite refractory. Once you have it tuned lock the choke! Do NOT move it again, it's where it should be!

AFTER you have it complete and tuned is a good time to try welding. Just remember ANY time hot steel meets open air it WILL form scale. Yes the black flaky stuff on your anvil.

Frosty The Lucky.

2 hours ago, Frosty said:

By all indications your forge is running rich, orange dragon's breath

Ah ok - I'm trying to get a frame of reference so that I can tune it. I thought I knew what rich looked like, but wanted to confirm that I wasn't totally off base.

So now I'm pretty sure I can recognize rich. Once I have a chance to run the forge again, with the brick doors/baffles, I'll try to get to neutral and get a photo of that.

Does temperature affect the atmosphere? I feel like 5-10 minutes is enough for the burn to steady out. Should I be letting it run longer before I bother trying to tune?

Thanks for the explanation on the steel coupon scale test. Again, I don't have a frame of reference and I had assumed that the scale wouldn't begin to form until the metal was already incandescent (at which point, I believe, I wouldn't be able to see it). So now I understand that, if I'm oxidizing, I would see it scale even before it gets to those temps.

Steel oxidizes on contact with oxygen be it orange rust in the winter arctic or the spark raging stream of a cutting torch. Scale is formed at a higher temperature than red rust say starting around low orange.

Sorry if I was snappy, not your fault.

Frosty The Lucky.

 

  "... am I correct in my belief that the forge environment is reducing?"

It could be a little reducing, and still get that hot, with yellow (not blue) fire coming out of the exhaust; very little. Lets change the question to "should I reduce my gas pressure"? Yes, you surely should; your photo is merely showing much too much of a good thing

Ok - so I finally got back to the forge. I bricked up the back and most of the front and saw what I thought was a nice improvement. I can now easily forge mild steel with the regulator set almost as low as it can go (1-2 psi at @10C). So that's great!

I went and tried a forge weld again. Took three attempts, but I got it. I think the first two attempts were just not hot enough. I "cranked up" the forge to around 6psi which got the steel into a yellow/white colour (as judged in the sun by my eye) and it just worked. You could tell with the first two setting blows that it was together. Very encouraging. Photos below (gallery is here if the embedded photos don't work http://imgur.com/a/iUKxn)

3rd attempt, I waited for the weld area to uniformly get up to that lemon yellow colour.

...likely not the prettiest weld. I forgot to wire-brush the sides as I was doing this.

 

Ground away about 1/2 a mm - you can still see the line between them. I presume that is scale and oxidization? Does that bind the two pieces at all?

 

Ground away about a full mm now in the center, and the steel there is fully welded. Hard to tell in the photo, but the line is gone and the metal appears solid and uniform. Super cool!

Thanks everyone for the help!

You could go an improving forge and burner performance just about forever, but It seems to be doing just dang fine! Congratulations

I give you a hearty thumbs up on your forge, well done.

Your weld is set but needs a couple more welding heats to be fully welded. The sharp line between the sides is not an inclusion or such, it's not completely welded. Warm it enough flux will melt on it, brush it, flux it bring it to welding heat let it soak a bit and make more setting blows. Repeat, then refine.

Frosty The Lucky.