# Ridges on tin cans?October 26, 2004 1:17 PM   Subscribe

Why are tin cans (ie soup cans, milk cans, bean cans, etc) ridged?
posted by ashbury to Food & Drink (12 answers total)

Very clever, keswick. I always thought the ridges were pragmatically implemented: to create less of a vacuum, so that the food-stuff slides out of the can quicker and with less fuss. This really only applies to foods that are flush with the can or solid...like condensed soup, jellied cranberry, etc.
posted by naxosaxur at 1:56 PM on October 26, 2004

I thought it would be grip.
posted by Hackworth at 2:15 PM on October 26, 2004

As I understand, introducing something like corrugations to the geometry of the can strengthens it by stopping the shape from failing uniformly in response to pressure or stress.

If you think of a perfect cylinder, any force that you applied to it in one spot would transmitted pretty uniformly across the surface. When you introduce some kind of irregularity into the surface of the can, then it doesn't get stressed smoothly. From any given point, some areas are going to start to bend, but other areas are likely to be situated in such a way that they actually resist the stress, or distribute it more widely. That doesn't mean you can't crush the can, of course, but it means that the shape is much more likely to retain its basic shape.

I also believe it's pretty important for these variations to be relatively uniform--you obviously can't just beat the crap out of a cylindrical can and expect it to be stronger. But if you introduce graduated, consistent variations into the shape, then external stresses can be reliably distributed through out a wider area, and the shape is basically stronger.

Of course, that could all be a load of crap.
posted by LairBob at 2:17 PM on October 26, 2004

The corrugations are for strength. Here's a simple experiment to demonstrate: fold a piece of paper about fifteen times, alternating what side you fold to: VVVVVVVVVVV. Now put the edge of the paper on a table (so the corrugations are vertical). You can place a small book on top of the sheet of paper, and it will be supported--Eureka! without the corrugations, the paper obviously would not have been able to stand on edge and support the book.

In the same way, a soup can's corrugations keep it from folding up flat when you press on the sides.
posted by notsnot at 3:13 PM on October 26, 2004

The strength angle makes sence to me if you're directing the stress perpendicular to both directions of angled material. But it makes less sense coming in from the outside surface:

VVVVVVVVVVVVVVVVVVVV

^
force |

or even the top:

force --> VVVVVVVV
posted by weston at 4:04 PM on October 26, 2004

By the by, in the demonstration of cylindrical strength category, make a cylinder out of a piece of printer/copier paper by taping the short ends together in the middle with a small piece of tape (like 2 - 3 cm). The resulting cylinder is typically strong enough to hold a collegiate dictionary, but a light poke in the side will bring is down. Similarly an aluminium soda/beer can will hold a person who weighs up to 180 pounds, but again, a light poke will destroy it instantly.
posted by plinth at 4:18 PM on October 26, 2004

Which leads me to my next question: why don't aluminum cans have ridges? Pop and beer cans are so much easier to crush so you'd expect these precious commodities to be protected as well wouldn't you?
posted by ashbury at 5:12 PM on October 26, 2004

Ok, so I cheated in my explanation. However, try this: hold the folded paper in both hands, with the folds running cross-wise. Try to bend the paper into the corrugated can shape. well-nigh impossible, eh? That's how the corrugations strengthen against side-loads.

As for axial (stand-on-soda-can) strength, think of a can with severe corrugations - 1/2 " in and out, diametral variance from 3 to 4". To accordian-crush the can, the inner diameter would have to get smaller and the outer diameter, bigger.

/ \
\ /
/ \
\ / normal, ID=3, OD=4

note the actual pleats are diagonals, which might be as long as 1/2 * sqrt(2)=.707.

_ _
_ _ crushed, the ID and OD have to vary by not 1/2 on each side, but .707!

Of course, this is all outta my ass.
posted by notsnot at 5:25 PM on October 26, 2004

For the most part, aluminum is recycled, so crushability is a *good* thing after product use. Since, prior to use, beer and soda are under pressure, and the pressure increases the effective strength of the cans, there is not such a need fr stronger cans.
posted by notsnot at 5:28 PM on October 26, 2004

I always thought the ridges were pragmatically implemented: to create less of a vacuum...

In which case they'd run vertically, not horizontally...
posted by five fresh fish at 8:45 PM on October 26, 2004

There is a brand of beer in Canada that has vertical ridges on the cans. The cans are lighter but more vertically crush resistant. (Engineering students are often bored.)
posted by Mitheral at 7:52 AM on October 27, 2004

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