First furnace, what a good material to use for the floor?

Jason, you're stuck in a rut with the castable,he doesn't want to use it.
But, I totally agree with building too big on your first. A propane tank,wool/Satanite A6 is a great, easy to build, starter furnace.
With a 3/4" propane burner you'll get 10 to 12 melts out of a 20 pound tank.
Mine is definitely more efficient than my A10 furnace. Probably because of it's tighter bore.


FYI High Temp Tools has the following guidance on BA as a skim coat for fiber blanket.

Their guidance's are on the dry side when it comes to mixing. I've had better adhesion results with a very soupy mix with the Satanite. Apparently, the same with the BA.

 

I cant even imagine pouring a 60. That's a lot of metal. A small #10 holds a surprisingly amount of bronze. If ya drop a 10, ya call an ambulance. Drop a 60 and you call the morgue. Wheres Jeff to remind us with that grisly photo of what just a couple of drops look like on a foot?

 

You're probably right bonz, but iron?

 

It turns out I was wrong about what I thought was a 35+ year old dense castable furnace lining: it did get to 30 odd years in a sorry state with all kinds of slag deposits. It was relined about 5 years ago with some product specifically designed for repairing dense castable: I don't have the product name yet but it's white, comes in a block about 30 cm/12" cubed with the consistency of plasticine and after your lining has the slag chipped off and the surface roughened, this stuff is used to repair the lining. It can't be the usual cement based product as it comes already moistened and once applied, it needs to dry out and be fired to cure it.

That video of my last iron pour: I forgot to put a small refractory puck in the middle of my pouring ring so the pouring ring prevented my crucible lifter from opening without a struggle and a sizable splash of iron came out as I shook the lifter off: third/fourth degree burn stuff for sure.

 

I use a plastic-like refractory called blu-ram 3000F which was given to me by a friend. It is much as you describe as it comes pre moistened in slabs but is almost reminiscent of warm asphalt in its form and the way it behaves. It packs down hard and is as tough as any castable I've used once it's fired. It's made to be rammed into place so doing a skim coating wouldn't work to well. It makes great plinths and pucks. I've had the exact same miscue with the crucible ring. It was both frustrating and unnerving.

Pete

 

Thanks for the feedback on the pitfalls of over sizing. I will look into adding another inch of blanket and building up the floor on somthing cheap like sand or perlite. If I decide to expand I can rip out the extra layer and re hot face it.

Perhaps this is crazy talk, but has anyone done removable/installable inserts for quickly resizing to match various crucible sizes.

 

I don't think it is crazy talk at all. I have seen some home foundry guys reduce the internal diameter just by setting in well fit light (or low density) IFB’s.

I personally think a huge loss of efficiency comes from design restraints. If we could take the technology of a woodworking cyclones and spiral the flame, in conjunction with the crucible shape, you would have a home run!



I personally would rather run 20% more fuel and electricity then a design of this shape.

 

Yeah, THAT would be a royal pain to build. Fuel is cheap, burn it!

 

Usually you pick the size crucible and fuel you want to use and build around that.
Propane only requires enough space to burn that equals the space to get your tongs in to retrieve the crucible (1" or so).
Oil requires about 2" of space.
The tighter you keep the bore matched to these specs, the more efficient the furnace.
I bet a Satanite/wool sleeve could be made to be inserted in the bore to accomplish the change over.
You would probably have to use 1/2" wool to get the 1" difference because it will need to be coated both sides. Satanite once cured is a hard shell.
Let's theorize you build a cast iron rated, oil burning, BA coated wool furnace. Slide the sleeve in to do Al/Bronze melts with propane.

 

I think Alex was on the right track back at the start of post#13. The only thing that can't be relatively easily undone or modified is your tuyere height if you choose to change your floor height later, especially if you pour a castable hot face. Even if your bore diameter is a bit larger than needed (at this point) your going to have a furnace that's going to heat up pretty darned quickly. I'm glad I have the extra space down low for oil combustion, and keeping the heat down low can be a bit of a challenge. I'm thinking of adding an oversized disk to my plinth like Mark demonstrated elsewhere to aid in that, but that's another topic. So aside from finalizing your height dimension and tuyere position I wouldn't change a thing. From my experience as soon as I finished my last furnace at 10" bore I immediately wished it was 12.

If you build up your bottom with sand I'd use some kind of binder with it like fireclay so it's not fluid, and then coat it with satanite so it's not eroding and flying around in your furnace. If you don't want to commit to 50# of fireclay, pm me and I'll send you a pound. Satanite coated IFBs will do as plinths for now.
Picking up a mid sized crucible before finalizing your dimensions is a very good idea. Even if you'll be going bigger later you'll at least have a hands-on visual to make decisions. I started with a #10 budget graphite from Legend and it turned out to be a good choice for a few reasons. Note however that there are no real universal standards among brands and types as regards dimensions or capacities. The ones I'm referring to are spec'ed in kg of copper and don't have a spout. The ones shown in post #19 are spec'ed for brass and are a different shape and dimensions. These are important differences, so know your source and know what they're offering. The lifting/pouring tools you'll spend time and effort building won't be one size fits all, so it matters.

Pete

 

I don't think we've seen anything like that here. That sounds like it might be a job for moldable ceramic fiber similar to what Kelly uses for his pouring basin.

 

Kelly, I love your bace. I think if you could make an adjustable valve. It would be a great set up for LPG or NG. It would be a monster ribbon burner. You might have to add a blower.

 

Hi Kelly, my furnace arrangement is pretty similar and creates a toroidal chamber under the plinth with an air gap at the rim that allows the spinning flames to continue to spiral up the furnace unimpeded. I think the extra distance that flames travel in a spiral path increases the dwell time in the furnace so combustion heat has more time inside the chamber. At this point after three runs I still don't know if the results I get are from the cone air nozzle or from the refractory disc, so the next run will have to be without the refractory disc and with a similar charge of iron and with fuel consumption monitored. Assuming the flames still spin round the plinth and aid fuel vapourization and combustion, I'd hope it'll burn less fuel and heat faster.

 

Mark,

I will be very interested to see if there is a discernible difference in heating of the charge with and without the disc. If it makes a difference it would be good to know and would be a not too difficult a modification to make. Unless the difference is dramatic, it may take 3 to five melts each way to tell for sure.

I do not know what sort of fuel metering you are doing, but I can report that with respect to monitoring fuel flow I am very very happy with the pelton-wheel-style sensor I installed some months ago. I find it to be consistently accurate, sensitive (.01 L/minute increments), and very useful so that I know how much fuel is entering the mix at any given moment in addition to the running total of fuel burned. It helps me get my furnace tuned quickly and consistently from burn to burn. I would hate to be without it. Here is a thread I posted on it a while back.

http://forums.thehomefoundry.org/index.php? threads/measuring-instantaneous-and-total-fuel-flow-with-a-pelton-sensor-and-digital-readout.811/

I ran it this afternoon at .19L/min and melted 35 pounds to 2600F in 80 minutes from cold start to pour. I find that as little as .02 L/min makes a noticeable difference in efficiency with too little fuel not having enough heating power and too much causing incomplete burning prior to exhaust. Finding that sweet spot is easier for me by far with the meter. If do not know how rapid the fuel flow is, it is hard to know when you hit the sweet spot as it is possible to make the exhaust stream look right by increasing or decreasing the air flow despite the fact that the fuel flow rate may be too little or too much.

Denis

 

Hi Denis, I did read about the sensor with interest, at present all I can do is measure the volume before and after a run. The 8 mist nozzles are run at 50 PSI and a sample nozzle flowed at 3 litres per hour over three hours test at 50 PSI, so currently it can use up to 24 litres per hour and I think last time it was 21 litres for a 62 minute run cold to poured and 32 pounds weight. If I multiply your consumption, that equals 15.2 litres, 80 minutes and 35 pounds so the two furnaces are very roughly comparable as I'm burning fuel with less energy: 8-10% less.

Also apologies for the thread hijack too.

 

My apologies as well. I did not mean to compete in any way in the "rapid melt contest." That would be sort of pointless. My intent was to say that the meter helps me run my furnace efficiently and I hope that it might help others as well. And that is it.

It could also serve as a means of keeping one variable constant as comparisons are made between running setups of furnaces---with and without swirl-inducing discs for instance.

Denis

 

I agree you guys are hitting very similar numbers. Dennis, are you able to add more air with more fuel? If so or not,.... It might come down to thermal losses.

Have either of you measured the out side temperature of your furnace (outer diameter and lid just) before a pour? Then shut down, And maybe 1/2 and 1 hour afterwards (with the lid closed).

I think this would be interesting information if you have one of those simple laser infrared guns. Your ambient temperature and average wind speed would be helpful.

When I was designing my furnace, I was trying to keep thermal losses in mind like a Canadian home. Living in Canada -40°C to +35°C. Thermal losses create the biggest inefficiency gap. It is better to throw more insulation in your attic then to replace your furnace for a higher efficiency. I will be testing this when I catch up to you guys. For now, i’m just envious!