Oroshigane steel (3)....."Aristotle" again

The small “Aristotle” remelting furnace that I slapped together was suffering from one major deficiency….lack of air. The 50 cfm bathroom vent fan I used just doesn't have enough “oomph” to get this thing up to iron melting temps, though we gave a mighty effort. Secondly, because I didn't give the furnace time to dry out properly, the poor thing developed some pretty extensive cracks as the clay shrank.

Step 1) Suck it up and pull out the hated air mattress inflator, who's devilish shriek haunts me still. I swear, the damn thing makes my tooth fillings vibrate, but it does move the air.

Step 2) In hopes of getting one more use out of this little disposable design, I wrap the stack with baling wire, then apply more clay mix to the outer surface. A little extra mass will make the furnace both more sturdy and add a bit of additional thermal mass.

Let's fire it up!

You can't see what's happening to the metal inside the furnace of course, but the character of the flame can tell you something.

Here you see that the stack is full of burning charcoal. The flame is thin, red, and of low intensity; it's time to add the metal to be melted.

The idea here is to put the metal on top of the pile of burning charcoal, then keep adding more charcoal to the top as the pile burns down. The metal will slowly descend, hopefully to melt into a viscous pile at the bottom of the stack. The entire process should only take 15-20 minutes. This time, I am remelting old steel and cast iron blooms that I've made in another furnace, just playing and experimenting right now.

What I want to show here is the flame character.

As the iron and steel reaches melting temperature, the color of the flame shows more of an orange cast and there is a substantial increase in flame intensity. The air supply is unchanged from the first picture, but the flame is much “thicker” now.

As the melt progresses, the flame gets more yellow in hue.

Most of my melts have produced diffuse and airy blooms, probably due to my lack of a good, strong air supply. This time, I am running the burn for a longer period, just to see what I get at the end. Occasionally, the sound of the blower will change, indicating that tuyere is becoming clogged with slag (waste), molten metal or whatever. This design allows outside access to the tuyere, REALLY handy when you need to clear blockage. Just rod it out and keep going…..

In any event, after about 30 minutes, the tuyere keeps getting clogged and, because this furnace wasn't built to last, it has developed a fatal fracture. The flame has shifted firmly into the yellow spectrum.

Post mortem analysis showed that intense heat of the flame had eroded the area around the tuyere, so much so that the airway was blocked and the bloom stuck firmly in place. The intense, yellow flame shows that the air is blasting directly onto the metal itself and beginning to burn off carbon. If you are trying to lower the carbon content of cast iron, that's a good thing, but here…..not so much.

And what is the result?

An interesting bloom of mostly gray cast iron with a few tiny spots of steel, and lots of oxidized steel and slag, all mixed together into a big mess.

I quench the bloom in water, then spark test before smashing it into pieces.

Most of the bloom crumbles into garbage, but one small area from the side furthest from the air blast fractures in a way that shows the crystalline structure of steel. Well….at least a tiny bit of steel.

I'm still learning here, but what I think I see is some gray cast iron with a few larger white cast iron crystals. The lightest color, fine grain material sparks like medium carbon steel, but most of this mess appears to be slag, the melted remains of the furnace wall itself. The old furnace has been crushed, sifted, and put into a bucket to soak for a while, waiting to be reused. Clay is expensive here!

Still exploring, more is on the way…...