This past weekend, I took my furnace out to an artist meetup and let attendees make small foam thingawhatevers for me to cast. It turned out to be over a dozen, which meant ganging up several in a sand bucket while the aluminum melted, pouring, and repeating several times. This also meant I was being a bit sloppy and not using pouring cups, which resulted in having several pools of metal fuse to my steel buckets. Any suggestions for preventing this from happening, other than making a bunch of pouring cups or just being more slow and methodical? I'm thinking of something like putting a thin layer of high temp grease around the bucket lip, or maybe cardboard around the edge, which would carbonize. BTW, the casting session was a total hit! The people there LOVED to be able to make something into a metal even though the results were pretty poor quality due to the increasingly hot casting sand and lack of a dip coat. Thanks! Edit: Oh, maybe parting dust? Edit2: Wow, that was a lot of really good advice. To summarize, the aluminum is bonding to the zinc surface of the galvanized bucket. There are lots of ways to prevent this: Alternately use flower pots or stainless steel cookware instead of galvanized steel buckets. Remove the zinc from the top edge of the buckets - maybe grinder with flap wheel. Wrap aluminum foil around the top edge or make a steel insert. Coat the top edge with oil and heat to produce a carbonized layer. There are also other coatings that will work, possibly including cheeze puffs. Take an extra couple of minutes to mound the sand up around the edge and use pouring cups.
I suppose the molten aluminum is no match for the zinc coating on the buckets. I have done the small tin cans with both ends cut out and Petrobond pouring cups with lost foam a few times. You could also pre-cast an inner rim of refractory cement to set in the bucket after compacting the patterns with sand. Your event looked warmer than ours, we were waiting for it to stop snowing to cast...
I do worry just a little bit about getting zinc fever when this happens, but I think the amount of metal fumes this produces would be very very small. Yup, beautiful weather, except for the rain all Saturday day and night, which let up just long enough to burn a big thing stuffed full of fireworks.
I could absolutely see aluminum adhering to the zinc. It won’t stick to bare steel at all though. Pete
Aha, solution #1 is to get rid of the galvanized surface around the rim. Any suggestions on the easiest way to do this? I'm kinda thinking flap wheel on my grinder.
Since I am cutting up a couple barrels/druns, I would make a 2" or 3" (50 or 75mm) band of that steel for the inside of the nice shiny bucket and bury it about 1" (25mm) deep in the sand. PS You could take Meteor's idea and implement it with cuttings from aluminum beverage cans, arranged either paint side in or paint side out, with a bent lip that wraps over the top of the bucket.
It probably won’t stick to the same spot more than once, but if it doesn’t touch the zinc in the first place then so much the better. I would probably try filling the pail leaving a 1/2” or so at the top, and as a last step before pouring, flick or otherwise build up sand around the edges of the pail to create a ridge (like a meniscus). Or, get a washtub with some sand in the bottom, set your pail in it, completely top off your pail, and let the overflow safely fall in the tub. (That would give a little better measure of safety anyway). In any event bring your pliers. By the way cheese puffs are said to work also. I haven’t tried it myself, but that could add to the fun. Pete
As has already been mentioned, it's because plated zinc bonds to steel and readily alloys with aluminum. There are coatings, mold washes, and more exotic stuff but if you wipe bare steel with a little oil and heat it, it will develop a brown/black oxide layer that isn't readily wetted by aluminum. But why would you put all that effort into remedying something you shouldn't be exposing yourself to in the first place? All the metal you pour should be going into your mold, not puddling on the surface. A pouring cup can be something as simple as a soup can with thend cut out with a can opener. A short section of muffler pipe can usually be reused because the aluminum shrinks enough to slip out when cold. Soup cans have ridges and have to be peeled/cut off. Best, Kelly
Get stainless cook pots. I pour the excess into stainless angles welded together to produce V bars that go right back in the crucible. No stick at all.
