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lynnl
10-08-2002, 10:45 AM
Completed my charcoal furnace and fired it up to bake it out this weekend. Couldn't resist melting and pouring some scrap aluminum into ingots while I had a good fire going. That was even more fun than I'd imagined.

I have some questions maybe some of you who've been down this path could answer: I want to get one or two crucibles. Budget Castings Supply describes a 'Bilge' type and an 'A' type. Can someone enlighten me on the pro's and con's of the two types?
Also, from what I read, the silicon carbide is much sturdier than the clay graphite, but of course more expensive. I'm wondering just how fragile are those clay graphite crucibles? Are they likely to break with the slightest bump? Or would it take a pretty good jolt to break one?

Thrud
10-10-2002, 04:04 AM
lynnl:
You can make a good steel one for Aluminum for a lot less money. (I don't recommend it)

You have to look at the expensive crucibles for metals that melt at higher temps - Iron, Platinum, etc.. Safety should always be your first concern - do not cut corners!

ANY crucible can suddenly fail - that is why safety gear is so important.

[This message has been edited by Thrud (edited 10-10-2002).]

Alistair Hosie
10-10-2002, 08:00 AM
Lynnl
I have only done small castings all of which were centrifugal we used to cast platinum gold etc these carbon crucibles become more brittle when used as a little of the carbon flakes of in powder each time I have also used what appears to bea ceramic type which are safer.I would use metal if I were you its cheap and strong so if it gets a bit weary make a new one.
There is a good site on the web (if you contact me and I will look it up for you) were a guy addresses the kind of problems you have.
Listen to Dave you dont want this spilling or the crucible fracturing at the wrong time.Alistair

Al Messer
10-10-2002, 09:22 AM
www.backyardmetalcasting.com (http://www.backyardmetalcasting.com)

mikem
10-10-2002, 11:30 AM
Question for Thrud:
Why don't you recommend using steel for a crucible? What type do you like? Thanks--Mike.

Forrest Addy
10-10-2002, 12:23 PM
A certain amount of iron contaminates the alimunim melt.

Molten metals are in varying degrees to metal cucibles like hot chocolate is to marshmallows.

lynnl
10-10-2002, 12:59 PM
In view of the low-tech ("no-tech" really) nature of my foundry operations, a little contamination I'll just put up with. A contaminated casting's better'n no casting at all... (I realize that may not be true for critical applications.) The melt I made last weekend was in steel juice can. It was a one-shot deal, but there's no shortage of cans. That backyardcasting site had a neat steel pipe crucible w/lifting and tipping lugs welded on. I plan to make one of those as soon as I can find a suitable piece of pipe.

One idea I've had is to make a crucible of fireclay/sand mix, or maybe some of my leftover castable refractory, with a reinforcing mesh of steel wire embedded inside. Anyone have any thoughts on that?
Or possibly lining a steel container w/fireclay. Isn't that the way commercial foundries do their ladles?

chriss
10-11-2002, 01:19 AM
Get thee to a pottery supply store and purchase some "kiln wash".Basically, the stuff looks like coffee mate and its not expensive. Mix it with water to a creamy consistency and then paint it on the walls of your steel crucible. I find it helpful to pre-heat the crucible in the oven to @ 200F before painting the stuff on as it dries VERY quckly this way. I find I have to renew it fairly often but it does work and it really is an easy thing to do. I've done a ton of castings this way including building Gingery's lathe and dividing Head. The only other thing I would add is get some de-gassing briquetts for aluminum.

Happy melting,
Chris

lynnl
10-11-2002, 10:27 AM
Hey, thanks Chris, for that Kiln Wash tip. I hadn't heard of that. I'll try it. I've read about the degassing tablets, and intend to get some.

The ingots I poured were kind of rough on the sides and bottoms that contacted the sand. I don't mean just the sand grain imprints, but just a rough texture with some small voids and ridges. I was forced to rush the pour because it started to rain lightly. Don't know if my metal was not quite hot enough (still had some unmelted clumps in bottom of melt), or if that was due to the gas problem. Any thoughts or suggestions?

Lynn

[This message has been edited by lynnl (edited 10-11-2002).]