The Shop > Metal Stuff
Oil fired crucible furnace
MetalCaster:
Ironman makes it look easy.
Not only has he mastered iron, he has mastered green sand.
My sand too often is to wet, or too dry (I use oil-based sand), or something else goes wrong with the sand, and just about time I get the mould done and all the gates and risers cut, it all falls out of the flask half.
Some put a groove or two in the walls of the flask, but if your sand is right, you probably can use a bare inner wall.
Here are a few made locally.
I would try and make the tabs on either end cast integral to the unit (I think in the photos below they are screwed on).
I will have to review Ironman's tabs to see if they are cast on.
And the pins seem abnormally large in the photos below, but the flasks I have which use 1/4" carriage bolts on one side are prone to getting out of alignment.
In the future I will use 5/16" and larger bolts for the pins (different size either side).
I only have wood flasks at this point, but hope to make some metal flasks one day.
Metal ones last a lot longer than the wood ones.
Edit: Yep, ironman uses an integrally cast handle, as I suspected he would.
ironman:
vtsteam
For many years I used Morgan crucibles made in Australia and they were terrible! I used to call them candle wax crucibles because they would melt every time they were used. A friend told me about Vesuvius crucibles, so I bought one and it lasted four times longer melting iron than the morgan crucible. I got really lucky there and when I saw the morgan rep I said I would never buy his crucibles ever again. That being said I still have to buy the crucible pedestals from morgan because Vesuvius don't have small pedestals.
When I started to melt iron I used soft fire bricks as a pedestal and the same thing happened, it leaned over and touched the furnace wall. I then used hard fire brick and they cracked because of the weight of the iron in the crucible. I gave up on fire bricks and got the pedestals from morgan. They last as long as the crucible.
The top of the crucible to the exhaust vent is the hotest part of my furnace, so that is where the most wear and tear happens. Over time my crucibles get shorter because of this.
You must have micrometers in your eyes, every dimention with the molding box is correct except for the height (50 mm).
It is very hard to put into words how to gate castings because each one is different. I have a lot of experience and know what to do. Reading books without experience can lead to errors, you just have to make mistakes to learn. Good judgement comes doing as well as reading.
Pat
My early boxes had screw in handles but thought that cast in handles were less trouble to make.
vtsteam:
Thank you again Ironman for your advice and experience.
Putting two and two together, if you use less ramming force than I have, and use a cope of 1/2 the depth I have, the gas permeability of your cope must be a fraction of what mine is. I think I can see why you don't get blow holes, and don't need to vent cores.
You are (I think) using finer sand -- probably finer than I could have used without getting a lot of gas entrapment. Years in the past with aluminum, I tried very fine sand -- 140 mesh, but had blow hole problems that way. So I just used that fine stuff for facing sand. That's the reason I asked about the mesh of your facing sand.
Also, if you are using smaller diameter sprues and copes of 1/2 the depth compared to those I have used, then the amount of material tied up in sprues is possibly 1/3 what I have. This means, with a limited size crucible, that I would have more capacity to add a riser, possibly.
Speaking of crucible capacity, I have what were advertised as A-6 crucibles. I checked their capacity by weighing the amount of water they held on a gram scale, and it turns out they are A-4 crucibles of about .75 liter. Their designation is A for shape and the 6 is the number of kilograms of brass it will hold. Thus an A-6 will hold 13.2 pounds of brass in our weight system.
The Morgan crucibles, on the other hand, designate the A as shape, again, but the 6 designates the number of pounds of aluminum it holds. Since brass is about 3 times as dense as aluminum, that would translate to about 18 pounds of brass -- 1.2 liter -- or a substantial difference.
After carefully measuring my furnace and tongs, it looked like I could fit a true A-6 rather than the smaller A-6's I have and get nearly 50% more capacity. Unfortunately I hadn't seen your reply yet last night, so I ordered a Morgan Salamander A-6.
Oh well! I guess when all of these crucibles give up the ghost, (which may not be very long in the future) I'll finally get the right size and right brand.
A question about crucible treatment, Ironman:
Do you replace the crucible in the furnace after a pour to let it cool down slowly, or do you leave it in air to cool?
MetalCaster:
I have not had any problems with the Morgans, but there are different grades even within one manufacturer such as Morgan.
The rep told me that for non-ferrous work, the Morgan "Hi-Melt" was the most long-lasting, and this is a silicon carbide crucible.
The "Hi-melt" is rated 1000-1400 C (1830-2550 F).
For ferrous work, he recommended the "Salamander Super" which is rated 850-1600 C (1562-2912 F), and these are clay-graphite.
The brochure mentions that they can also be used for non-ferrous work.
Note in the photo below that both are labeled "Slamander", which is very misleading given the fact that one is only rated for 2550 F and non-ferrous work.
I think you would get good service from either of these two units if used with the respectively rated metals.
I have also heard reports of crucibles cracking if not placed back into the furnace to cool slowly.
I put mine back in the furnace just to keep them clean, dry and protected until they are cool and can be stored sealed in a plastic bag.
Morgan mentions many things that will damage a crucible such as heating them too fast when they are cold, causing uneven thermal expansion and cracking, improper loading, lifting and supporting from the wrong position, not keeping them dry, etc.
I think the silicon carbide units have to be fired at least once to seal the glaze before they are used to melt metal.
Morgan also mentions not letting the flames impinge directly onto the curcible.
vtsteam:
Thanks Pat, I had already looked at Morgan manufacturer's literature before ordering the crucible, a Super.
I would like to hear what Ironman does in his own shop, re. crucible care, since that is genuine long time practical experience that I trust.
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