A thin hotface medium/low mass beer keg (drum size) furnace for melting Iron

Things that went right:

1. The iron was plenty hot at pour time.


Things that did not go exactly right:

1. It took a few minutes for me to figure out that I needed to choke down the leaf blower, but once I did, the Delavan siphon-nozzle burner worked well.
Edit:
The large lid opening did not put much back pressure on the blower.
When I made my new domed lid, the opening was much smaller, and so with the new lid I have been running the leaf blower on its lowest speed setting, and burning 3 gal/hr of diesel, and those are the settings that I use on all my iron pours now.

2. I did not have time to make my smaller lid to go over my large lid opening, so I had to run it with the large lid opening. Boy does that make for some heat coming out of the furnace in your general direction.
I had been told that I could not melt iron with a lid opening that large. (myth busted).

3. No time to mull the sand to make a proper mold, but this test was more for proof-of-concept of the new furnace anyway.

4. I used a cast iron motor housing for scrap, and did not clean the paint off of it.
As the pieces melted, slag formed on top the melt and started to bubble.
It was difficult to skim since the lid opening was large, but I was finally able to skim a 3/4" thick (about) cap of slag that was pretty stiff.
Once the slag was skimmed, presto, the magical liquid appeared. What a welcome site that was.
With a smaller lid opening, I would be able to skim the slag more frequently before it got so thick.

5. The crucible stuck to the plinth, even though I used two layers of cardboard (because I spilled slag down the side of the crucible and onto the plinth). Next time I will add some graphite to the top of the plinth to see if that helps. (Edit: The graphite is not necessary. Just don't spill slag down the side of the crucible).
Not really a problem, you just have to knock the plinth off and hope the bottom of the crucible does not come off with it.

6. I recorded the temperature of the four thermocouples vs time (one low on the furnace wall, and three spaced evenly above, with the top one about 2" down from the top of the refractory.
When the furnace reached maximum temperature, the walls of the refractory turned red hot, so the temperature readings were probably no longer relevant.
They were still reading when I looked before the pour, and so when I get more time I can play with fuel/air mixtures and see what the lowest fuel flow is that maintains the maximum temperature.
I was expecting the probes to burn up, but luckily they did not, nor did the probe wires.
Edit: After checking the probes the next day, they did indeed burn up completely.



S0 at this point I consider the test a success (a very hot success from the standpoint of standing next to the furnace wearing full leathers).
The iron was quite hot, it poured very easily, and the slag was not too difficult to skim, but I need a much longer skimming tool.
The furnace seemed to work well, but I will probably make a domed lid with a smaller hole in it. I need to add a trim flange around the top of the stainless shell to contain the top of the ceramic blanket.
I will upload the video and get a time-to-pour.
I can discharge the burner without compressed air, into a container and get a fuel flow.
I assume I used far more fuel than I needed to, but I was operating blind since I did not calibrate to 3 gal/hr before I started.

I did not bother with the ferrosilicon, and I did not try the limestone either.
I don't think I need limestone, but I will try it just to see what it does.

I have no doubt that I can repeat the success of this melt in the future, assuming I am masochistic enough to do so. (did I mention how hot it was standing around the furnace in leathers? sarcasm intended).

I understand the slag now, and know how and when to skim it.

 

Cool!

In a warped sort of way. Now you've got me thinking I can melt some iron.

I didn't understand skimming being more difficult through a larger opening. Was that because you were afraid of oxygen contamination of the pour? I'm thinking the oxygen won't find it's way in so that is all based on your combustion mix anyway, not flue opening.

Thanks for posting, I learned a lot like I can wait until cooler weather.

 

I had a clock going, and I jotted some notes about how the melt was progressing at a few points in time, but I am still uploading photos and videos.

I am sure that for the folks who do iron regularly, this thread will be a big collective yawn (rightly so), but for me, it was a personal lunar-like moment, ie: one giant leap for my personal ironkind.

I don't drink, but I did eat (4) candy bars while I sat out in the driveway, soaking it all in.
You have to die from something I guess. I have been a candy junkie for a while, but am trying to stop.

The furnace seemed to get hotter faster once I got the blower thing figured out.
It seemed noticeably faster to get the shell up to where it was red hot (that surprised me a bit, my big furnace does not turn red hot on the outside of the refractory).
I will check the video times to see if this is really true, but I think it will be faster once all things are setup, adjusted, and working correctly.
The refractory is pretty low in mass; less than two bags (I have the weight posted somewhere).

I am still surprised at how much more difficult it is to pour iron than it is to pour aluminum.
I can melt and pour aluminum in my pajamas and slippers (not really, I don't wear those, but if I did, I could).
The radiant heat from the opening in the furnace lid is intense, even with my large furnace that had a small lid opening.

Some of the things I learned tonight:

1. It does not take a lot of combustion air to melt iron. (the leaf blower runs on its lowest speed setting).
2. I don't think it takes that much fuel to melt iron either; perhaps 3 gal/hr. or a little less. (3 gal/hr is what I now use to melt iron).
3. I think I was forcing too much air and fuel into my big furnace, and probably cooling it in the process.
4. Its all about getting full combustion of the fuel in the furnace.
5. I always have had slag, whether I use clean iron or not. Oddly some say they do not have much or any slag, but I did observe porositymaster doing a lot of skimming (he does not use clean iron).
The iron I used tonight had paint on it, but no rust.

6. As the metal pieces melt, you get a lumpy mix of iron that is not fluid. As you continue to heat the melt, the melt gets slightly darker and starts to bubble.
The bubbling stuff is slag, not iron.
You have to skim off the slag.
If you just wait and let the melt heat longer, the bubbling gets a little more intense, but at some point it begins to get pretty solid, and if you don't skim it at this point it can get very hard and difficult to break through (I did this in a previous melt, and the slag was very hard, but had hot iron under it).

It is as you said long ago David "There is iron down there, you just have to dig down to it".
True statement, and if you skim frequently, you don't have to dig.

7. Melting iron is a waiting game, and not for the impatient. If you get impatient and start changing the air/oil settings, you may ruin a melt (been there, done that).
I can melt and pour 20 lbs of aluminum in under 30 minutes. I would anticipate at least a hour for iron, and sometimes more if all does not go exactly as planned.

8. Everything has to be right (3,000 F rated everything), and everything has to work exactly right (the burner), in order to melt iron. The radiant heat is significant. I recommend full leathers for sure. Edit: You need dark welding goggles that are UV/IR rated too.
You pour will only be as good as your gloves unless you have some good heat shields.


It was a bit unnerving to see the refractory shell get red hot on the outside (I could see it at the top where there was no ceramic blanket).
You get these feelings of doubt, like "is this sucker going to melt down, or what?", even though you know the Mizzou will take the heat.

Edit:
I need to make about three steel skimmers, since they tend to get hot quickly and begin to melt while you are using them. I used relatively thick steel for the skimmer, and that helped, but it still was beginning to overheat.

 

This furnace is not considerably smaller than the large one (I will check the volume, I could be wrong).

My larger furnace has inside dimensions of 15" dia, and 20" deep.

This lower-mass furnace has inside dimensions of 13" dia, and 14" deep.
This furnace will hold a #20 when using a flat lid, with almost 2" clearance around a #20.
I think with a domed lid, or extended lid, I could use a #30 or perhaps a little larger.

But for volume, if I did the math right, the high-mass furnace is 3,533 cu.in.,
and the lower-mass furnace is 1,857 cu.in.
So the big furnace has almost double the volume?
When I built the big furnace, I was under the impression bigger/heavier was better, and I anticipated doing routine iron pours of 70 lbs.
Smaller iron pours are much more manageable and not such a disaster when things go wrong.

 

I used a pretty tall plinth tonight, perhaps 4"-5".

For the large furnace, with a height of 20", that would put the crucible down pretty low, and in the cooler range of the furnace, especially using a #10.

The only real observable cool spot in the furnace tonight was right in front of the burner tube.

Edit:

I don't think furnace dimensions or furnace mass are really important, nor is the burner type very important (as long as it works correctly), and either oil or propane can be used.

What is really important is having some good leathers and boots, and knowing what you are doing, ie: what does slag look like, and when do you skim it.

Note that you need IR/UV-rated sunglasses (actually gas welding glasses, available at hardware stores) to protect the eyes, since the UV/IR is very intense, and you will have sunburn on the eyes without this item (been their and done that too).

 

Skimming was much more difficult through a larger opening because it roasted my gloved hand pretty quickly.
I ended up adding a few layers of slip-on flexible heat shields over my right glove to try and ward off some of the heat, but my arm was getting cooked too.
I have to assume I had far more than enough fuel flow, and that probably made things much hotter than they could have been if I had been using 3 gal/hr.

I know many have poured iron here, and ironsides and porositymaster make it look super easy (like aluminum pours), and maybe I am just a wimp, but I find iron pours to be quite difficult.
Maybe it will get easier when I get everything 100% setup and heat shielded.

There is a lot an anxiety when you don't know exactly what to expect, and when to expect it.
And during one of my iron pours a few years ago, I poured the excess iron into some ingot molds that I had preheated, but obviously not enough.
The moisture on the ingot molds caused the iron to pop, and it splattered on my leather jacket and some tiny little balls about 1/4 the size of BB's went into my gloves and onto my hands.
The result was 3rd degree burns in a fraction of a second (the skin just vaporized wherever hot iron touches it).
Iron is totally unforgiving if you splash it somewhere where it can get under your collar, on your head, in your shoes, etc.
With aluminum, you get a burn.
With iron you get vaporized if you are not careful, so just a word to the wise.
http://forums.thehomefoundry.org/index.php?threads/foundry-burns.203/#post-3171

 

The furnace tonight seemed to come up to a bright red temperature much faster than the big furnace ever did.
No doubt I was using an excessive amount of fuel tonight (I will check the exact flow rate tomorrow), but I tried all sorts of flow rates with the big furnace, including up to 10 gal/hr, and for all the successful iron melts I have had in the past (perhaps 3 total), it took a long time for the big furnace to get to the point where the metal started melting.

Scavenger uses a big heavy furnace, and his current furnace is much heavier than his previous one.
He notes that his melt times slowed down when the mass increased.

But I think there are a number of people who use high mass furnaces all the time for iron melts, and so it is not really a problem with high mass, it just takes a longer and uses more fuel.

 

Yes, I agree.
I guess I could try using a larger crucible to see just how much space is needed, but a #10 full of iron is difficult enough to handle, and a #30 is a handful and pretty much requires a crane and pouring cart.

But crucibles are tapered, and so the least amount of space is at the top of the crucible.
There is a lot more space below the top rim of the crucible.

 

Well basically I do all that because I don't have time to get out and do the actual footwork to figure it all out.
I get stuck in the office for 8 months to a year at a time when I can't do anything but work projects, and that is not very conducive to figuring out iron, or aluminum either for that matter.
But I do take breaks from work, and while at the computer I speculate and calculate to no end, since that is all I have time for.

I need to retire, but the wife says "no dice, you die in the chair working", and she means it.
She's a good wife though, so I can't replace her.

Edit:
With aluminum and 15 minute melt times, you can do a whole lot of experimenting in a days time.
My problem with iron has been that I have never been able to do more than one iron pour in a day, and I have not been able to do more than a few iron pours total over a several year period.
Just the nature of iron and the melt times.
When the melt times are off, it is even a slower process.

 

And helpful as ironsides and others have been, nobody has really done a very good write-up of how to do an iron pour (in my opinion).
Both ironsides and scavenger have written a ton about iron pours in general, and with ironsides my problems in particular, and with very detailed step-by-step procedures, and I can't express how grateful I am for that information, but I don't think it tells the complete story, especially if you have to deal with slag.
For example, if you are having problems with slag, some people just say they don't have problems with slag, and so you should not either.

I think you (David) came up with the best description about the slag on top, and the iron below it, and how you had to dig down.
But nobody seems to have heated iron to the point where the slag becomes hard, but that is indeed what happens. I think others know that you have to skim the slag before this point, and so it is never an issue with them. Knowing when to begin skimming can be a bit of a challenge with iron, and it is not like aluminum where you can easily skim at almost any time.

Edit:
It is tricky to describe what you see when the iron is melting.
I use a glass refrigerator shelf to look into the furnace and observe what the iron is doing and when (with UV/IR glasses).
The iron scrap gets hot on the ends first, and begins to drip down.
But for me, it is not quite like aluminum where you transition from a solid, to a mushy mass, and then into a nice low-viscosity fluid.
Iron is pretty high viscosity when it is melting, and as my iron melts down, it goes into a large mass that is pretty rugged on top, like the moon.
I pressed on the iron tonight right after it went down into the mass, and it was mushy, but still pretty firm, and I could not submerse the skimmer into it.

Eventually the mass begins to bubble on top, slowly at first, then faster, and this bubbling stuff is slag, and it needs to be skimmed off as you go from this point.
With aluminum, the slag is very distinct in both color and texture (generally dark and crusty), and the molten aluminum is very shiny and low viscosity.
With iron, everything is very bright red hot, even with UV/IR glasses (without UV/IR glasses, you simply go blind in short order), and the slag looks the same color as the molten metal (bright red). There is no distinct and observable molten iron/slag boundary. The molten metal may or may not be more fluid than the slag, depending upon how far along in the melt you are.

Leaving the slag in place, and just continuing the melt causes the slag to become stiffer, and if left long enough, it becomes quite hard, and you have to punch through it with the skimmer.

But the iron below the slag (if the burner was actually tuned correctly) is very hot, and if I had been skimming the slag off as I go, then chances are I would have been ready to pour much sooner. So this begs the question "How long does a melt really take" since I have obviously been sitting around looking at bubbling slag for what seems like forever when I probably could have skimmed and been ready for a pour.
Judging from the results of others, iron should melt in about an hour, else you are not doing something correctly.

The ferrosilicon I have added in the past causes the melt to become much more fluid, with red swirls and such.

I did not have time tonight to watch as the last small amount of slag melted back into the mix (as described by ironsides as about the time you reach pour temperature), but my pour was very fluid even without ferrosilicon.


One problem is getting the slag off the skimmer.
The slag tends to adhere to the skimmer, and that is another reason to have several skimmers on hand. Of course preheat the skimmer and anything else you stick into the melt.

I was able to get my melt skimmed tonight, and it was obvious by close observation that I had reached clean fluid iron, but it was a very hot affair, and I needed a much longer skimmer handle than I had, and perhaps a heat shield.
I use a 24" skimmer handle for aluminum skimming and never have a problem.
For cast iron, perhaps a 48" or longer skimmer handle.
The exhaust stream coming out the furnace lid hole is quite brutal during an iron pour, even with my old furnace.