Do you really want to use an aluminum pot?

[David2011]

Recently I posted a link to a guy building a 74' sailboat and smelting 17,000 pounds of lead for the ballast. Today I was watching another of his videos where they were pouring relatively small amounts of lead into small areas of the keels (twin keeled boat). They were pouring from their big pot into a 15 gallon or so aluminum crawfish pot to get the lead from the big pot to the desired location. No, they were not filling the smaller pot. Have a look at the dent they got in the pot. The builder commented that the aluminum was distorting at about the temperature of the molten lead. The dark area shows the fill level of the pot.


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[country gent]

At molten lead temps aluminum losses a lot of strength. adding to this is using it as a transport pot the bottom is unsupported so more area to give away. Another thing may be unlike us how close is he monitoring his melts temp. going from 700* up to 850* would really accelerate this. Ill bet hes running hot to offset carry time and heat loss

[sniper]

Aluminum loses its "solidus" and becomes increasingly weak at about lead melting temperatures. Makes me shudder, to think of the amount of casting I did with an aluminum pot before I found that out! I quit immediately! I wonder how many new casters aren't aware of that? The guys at RCBS, Lee and Lyman must know something, making and selling cast iron or steel pots, ya think?:smile:

[kevin c]

So those same companies' aluminum ingot molds don't fail mainly as a matter of lower temperature, limited weight and duration of exposure? No weakening over time?

[lightman]

So those same companies' aluminum ingot molds don't fail mainly as a matter of lower temperature, limited weight and duration of exposure? No weakening over time?

Thats an interesting question. Mold temps when casting are a few hundred degrees lower than melting temps so this should not be a problem. Theres a lot of concentrated heat on the bottom of a smelting pot.

Thinking along the same lines, I used to use an aluminum Dutch oven back in my camping and floating days. For the weight savings. I'm thinking about it sitting on a grate full of hot oil. I expect the temps were well below the dangerous level.

[country gent]

When pouring and casting ingots its amazing the temp drop over the pour. Most moulds while running 700*-750* lead at a medium pace may only get to 350*-400*. Another help to the ingot moulds is while aluminum they are a cast aluminum which helps dissipate heat along with the design The gaps between ingots helps heat to dissipate quickly. Another is the much lower mass of the ingots being poured.

That aluminum pot poured with 20-40 lbs of molten material will heat much more just do to the mass of he material its holding. THen with no fins or grooves for heat disiption its going to really heat up

[Conditor22]

aluminum pot got too hot
https://i.imgur.com/TO8DDf2.jpg

https://i.imgur.com/455hfsA.jpg

IF you keep the temperature down they can work in a pinch, I used the above pot for several years before I let it get too hot. Got lead all over the burner and board I had underneath.

[jsizemore]

I hope no one got hurt!

[kevin c]

Nothing like an actual real life example, there, Grmps. And thanks to lightman and country gent on why aluminum ingot molds don't fail. Makes sense to me and reduces a worry on my part.

[EDG]

The ingot molds are small. They only hold one lb of lead per cavity - no big deal.
Aluminum melts at 1100° F.
An air-only propane torch will burn at around 1,995 °C (3,623 °F), less if heat loss to the surroundings is taken into account. Yeah the lead is only 750°F but the actual gas flame is much hotter.


So those same companies' aluminum ingot molds don't fail mainly as a matter of lower temperature, limited weight and duration of exposure? No weakening over time?

[mdi]

Another thought about ingot molds. The ones I remember seeing were about 3/16"-1/4" thick and aluminum cooking pots are much thinner. This along with the lower temp/time make the molds safe. The aluminum normally doesn't change color when it gets hot and usually will just "dissolve"/fall apart with no warning...

[tazman]

Way back at the beginning of my casting experience, I was using a torch to accelerate the melting process while using an aluminum pan. I held the torch in one spot a bit too long and opened a hole in the side of the pan.
Fortunately, the lead had not all melted yet and I was able to get all of it out without dropping some of it on the floor or myself.
Now I use a small stainless steel pot for smelting. I only work with small batches at a time. It takes longer but I have the time.

[country gent]

While aluminum melts at 1100* it starts to weaken around 650*-700*. Molten steel is moved in big steel pots but they are lined with a fire lay to insulate the steel pots. Heat is a big factor in fatigue type failures. A well supported base may allow you to get away with it for awhile but its a question of when not if it will fail. I had a cast iron pot fail on me one cool morning. My fault I didn't give it enough pre heat time opened the burner up to high to soon and expansion cracked it. A good steel pot is the best bet for smelting casting.

[David2011]

A bit off topic; that reminds me of a horrible fatigue failure at a steel mill in the Houston area when I was a kid. A lift hook on one of those big steel pots failed while they were moving a load of molten steel, dumping it onto the floor of the mill. Several people were injured terribly and some died.

[Catshooter]

I've been teaching my grandson to ask himself, "What could go wrong?" I don't think the sail boat man is asking himself that.


Cat

[Ozark mike]

If you ever welded aluminum with o/a you would know aluminum has a tendency to just fall away when melted now add several lbs of melted lead sounds like 3rd degree burns or worse to me. I use a half gallon stainless bowl for my contraption