Experiments with getting the oil furnace to melt iron

Did you see in my video at 7:25 the close up of his oil burner nozzle? It seems to work really well. Here are two photos of my A6 I got from skamol they show how overheating iron in it also gives the crucible a hard time. That crucible has had only 13 iron melts. So there are three reasons why iron should not be overheated, 1. crucible will last longer 2. furnace refractory will last longer 3. overheated iron will seep into sand pores and also sinter sand so it will fuse to molding sand. The temperature that sand will sinter is lower than the melting point. Nearly every casting I poured with that A6 had a rough finish until I woke up to what was happening

 

Yes, the pouring temp of your iron may be dictated by the pattern you are pouring. Short chunky pieces will fill easily enough if at the low end of the spectrum and that will provide a nicer finish and be easier on fuel and equipment all around. But long complex patterns will have cold shuts or pour short if the rion is not hot enough.

The above pattern demands quite hot 2550 iron as the iron runs a long way and runs though pretty narrow channels. Since it is also a pour that maxes out my Super Salamander A25 crucible as is I do not have a lot of options for runners and gating. You can see just looking at the photo that the iron is hottest and the finish darkest/roughest near the gates with a nearly lustrous finish near the upper corners. And those corner areas will cold shut (I've had several!,if I try to pour iron that is not hot enough. Almost all of my patterns require iron in that temperature neighborhood aas almost all of them have thin sections and relatively long runs. I wish it were otherwise as it would save time, fuel, and wear and tear on equipment. Commercial foundries get around the surface finish issues by shot blasting the castings to make them look gorgeous. Shot blasting would be such a luxury.

Denis

 

I did see that nozzle, at first it looks like it's missing the outer part judging by the air swirl channels visible. That A6 has had a hard life with the glaze and graphite cooked out of the surface, even a crucible can burn if hot enough.

Even going from an A25 to an A16 with bronze, it has to be hotter and poured faster to allow for heat loss. I'm planning on experimenting with some kind of refractory mould wash sprayed on to improve iron finish, there's got to be recipes in the foundry manuals not to mention the zirconia based commercial mixes.

 

The test run with the A6 did work and I was able to cast 4 kilograms of iron successfully. Temps were very slow to get under way but at about the one hour mark the furnace seemed to be fully heated and ran nice and hot, reading over 1360 degrees C before the K type thermocouple melted again. Normally I get the flame to swirl 3/4 of a turn before exit but the larger air gap allowed at least three laps of the furnace before exiting judging by the flame tornado.

I ran it on a pure diesel, then some free dirty diesel and then a sump oil and diesel mix (which could have been mixed better: thick oil lumps). The smaller A6 crucible let me see the fuel spray in operation and it looks like the air intake is too close to the floor which causes fuel to pool on the floor during the initial startup until the refractory gets hot, this probably slows the heating to some extent. I'll have to angle the spray nozzle and air cone up away from the refractory and maybe preheat on gas instead of a diesel cold start. Fuel consumption was 14 litres per hour with 20 litres over 90 minutes from cold.

So consumption was lower, furnace was slower to heat but did get to a usable temp in the end.

 

I ran the furnace with the A6 crucible today and managed a semi successful iron pour with two good stove parts out of four. The thermocouple gave bad readings early in the piece, I think from not properly attaching the wires and inadvertently forming a second junction from the brass terminals I use to clamp the thermocouple extension wire to the thermocouple wire which fought the main junction. I fell back to the usual throttle settings and it all got up the temperature at the one hour mark which is about right considering how much dense castable refractory is in there. The unexpanded perlite I bought from a local processor worked as intended: it coagulates most of the iron slag into a sticky semi solid mass that can be easily removed with the skimmer a few minutes of run time after it's been added. The green sand has a bit of sea coal but not much now after being diluted with sand and bentonite and I rammed up four parts I think are off a railway caboose stove. The two legs cast fine but the small sliding fire door and the part with the round half circle cut outs are thin at less than 1/8"/ 3.2mm thick and didn't fill even with wire vents. I did accidentally get iron into the door's hole which partially blocked it before I had a chance to pour it. I'll have to cut wider and deeper runners for the next attempt although judging by the thin flashing and the iron traveling up the vent holes I think it was hot enough. I'll also try and tap the pattern castings into the sand to increase the thickness a bit too.

Edit: it was the mould with the two half round cutouts that copped the spilt iron, not the door as first mentioned.


Removal of the perlite / slag lump:




It was at this point I knew I'd f@$%ed up with molten iron down the wrong hole:


First iron leg after fettling along with the pattern original coated with white spray putty. You can see the masking tape covering the hole on the underside replicated in the new leg:


The two successful castings on top and the failed two below, the burnt sand came off with a wire brush, note the thin iron flashing on the bottom right corner. overall thickness is 2.6mm where it didn't flow.


Castings still in the flask with the bottom left casting getting the spilt iron.