21 Jun 07 10:42, DAVID WILLIAMS wrote to Roy Witt:

 DW> -> Essentially all beverage containers in the United States are
 DW> manufactured -> from aluminum, whereas beverage cans made in Europe
 DW> and Asia are -> approximately 55 percent steel, and 45 percent
 DW> aluminum alloy.

 DW> I know that Sapporo beer, from Japan, comes in aluminum cans.
 DW> Actually, they're often large screw-cap bottles, which can be
 DW> resealed, but they're still aluminum.

Bottles, kinda like brake fluid cans?

 DW> Do you mean that 55% of European cans are steel, or that somehow the
 DW> steel and aluminum are used together in the same can?

I don't know of any way to chemically or physically meld steel with
aluminum, however, I'm no expert in that field. I do have extensive
experience in working with both, however.

 DW> When I fed my cats last night, I noticed that the can looked like
 DW> aluminum. I tried the magnet test, and sure enough there was no
 DW> attraction. Other types of cat food comes in steel cans, though. The
 DW> aluminum cans must have thicker walls than the ones of aluminum
 DW> beverage cans. They're quite rigid, even with no internal pressure.

I also have a cat and if you look at the cat food can closely, you'll see
that it has features in it that will make it hard to twist or mutilate
that can like you would a beverage can. i.e. on the bottom, there are
ridges stamped into the can near the edges where the side wall meets the
bottom. The edge is rolled over and forms a stiff ridge that defies any
efforts to bend it. Also, the verticle walls of the can are very short and
the top of the can has a stamped ring around it to help stiffen the top.
Of course, once the can is opened, it becomes more pliable.

 DW> I still think the effect of pressure, making a very thin-walled can
 DW> effectively rigid, must enter into the economic calculations. It
 DW> reminds me of some early space rockets, which would virtually
 DW> collapse under their own weight, except for the pressure of the fuel
 DW> in them keeping the metal stretched tight.

The wall thickness is due to the process of drawing the aluminum blank.
The blank starts out as a flat sheet, cut into several pieces and ends up
as a bunch of cans. The drawing process stretches the material in some
places, but doesn't affect others.

What keeps the can from collapsing is the tapered form at the top and
bottom. Also, as you say, the pressure inside keeps the walls under
tension, until the pressure is relieved. But it's the fact that liquid
can't be compressed that makes the can rigid. Once there is an exit place
for liquid to flow, it will no longer stop the can from collapsing.

                R\%/itt


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