Why are the vertical sides of tin cans* ribbed rather than smooth? Surely it can’t be to make them easier to hold, because they are inevitably covered with a paper or plastic label; also, pull-tab beverage cans and glass and plastic bottles have no such ribbing but no one complains that they’re too difficult to hold. Is the ribbing some incidental side-effect of the manufacturing process, or does it have some intended purpose?
*Yes, I realize that today most “tin cans” are made of aluminum; I’m using the word in its colloquial sense to refer to the thick, cylindrical cans which require a separate can opener and are commonly used to preserve soup and vegetables. Think Andy Warhol or string telephones.
[QUOTE=psychonaut]
Why are the vertical sides of tin cans* ribbed rather than smooth? Surely it can’t be to make them easier to hold, because they are inevitably covered with a paper or plastic label; also, pull-tab beverage cans and glass and plastic bottles have no such ribbing but no one complains that they’re too difficult to hold. Is the ribbing some incidental side-effect of the manufacturing process, or does it have some intended purpose?
*Yes, I realize that today most “tin cans” are made of aluminum; I’m using the word in its colloquial sense to refer to the thick, cylindrical cans which require a separate can opener and are commonly used to preserve soup and vegetables. Think Andy Warhol or string telephones.
[/QUOTE]
No, they’re made of steel; the tin coating is still used. The ribs (actually called “beads”) are there for strength/reinforcement, though they also help the label to stay on.
IANAPhysicist, but I don’t understand how ribbing in that plane would add to strength. I imagine that the most force that cans are going to have to endure is when stacked, so along the y-axis. In this case, wouldn’t it make more sense to have the ribs longitudinally?
The stresses the can sees during transportation and storage are minuscule compared to those imparted on the can during the manufacture process. That’s when the strength of the can is needed.
[QUOTE=wiki]
Part of the tube that forms the wall is bent, almost at its end, turning outward through 90 degrees, and then bent further, toward the middle of the tube, until it is parallel to the rest of the tube, a total bend of 180 degrees. The outer edge of the flat piece is bent against this toward the middle of the tubular wall, until parallel with the wall, turning inward through 90 degrees. The edge of bent portion is bent further through another 90 degrees, inward now toward the axis of the tube and parallel to the main portion of the flat piece, making a total bend of 180 degrees. It is bent far enough inward that its circular edge is now slightly smaller in diameter than the edge of the tube. Bending it yet further, until it is parallel with the tube’s axis, gives it a total bend of 270 degrees.
[/QUOTE]
[QUOTE=Nametag]
No, they’re made of steel; the tin coating is still used. The ribs (actually called “beads”) are there for strength/reinforcement, though they also help the label to stay on.
[/QUOTE]
[QUOTE=wiki]
No cans presently in wide use are composed primarily or wholly of tin; that term rather reflects the near-exclusive use in cans, until the last half of the 20th century, of tinplate steel, which combined the physical strength and relatively low price of steel with the resistance to corrosion of tin.
Use of aluminium in cans began in the 1960s. Aluminum is less costly than tin-plated steel but offers the same resistance to corrosion in addition to greater malleability, resulting in ease of manufacture; this gave rise to the two-piece can, where all but the top of the can is simply stamped out of a single piece of aluminum, rather than laboriously constructed from two pieces of steel. Often the top is tin-plated steel and the rest of the can aluminum.
[/QUOTE]
[QUOTE=Nametag]
The ribs (actually called “beads”) are there for strength/reinforcement, though they also help the label to stay on.
[/QUOTE]
So why aren’t beverage cans ribbed (or beaded, if you prefer)? Soup isn’t that much heavier than pop, and yet soup cans are thick and beaded whereas pop cans are thin and smooth.
During the manufacturing process, the cans are sealed, then heated so that the contents are cooked and sterlilised - I expect the ribs offer a little bit of flexibility to cope with thermal expansion of the contents, but in that case, the question really should be; why are some cans not ribbed? - excluding soft drinks cans, there are some cans of soup/beans/vegetables that aren’t ribbed.
[QUOTE=Mangetout]
During the manufacturing process, the cans are sealed, then heated so that the contents are cooked and sterlilised - I expect the ribs offer a little bit of flexibility to cope with thermal expansion of the contents, but in that case, the question really should be; why are some cans not ribbed? - excluding soft drinks cans, there are some cans of soup/beans/vegetables that aren’t ribbed.
[/QUOTE]
Wait a minute, don’t sealed tin cans explode or at least deform when heated? You know, the ol’ baked-beans-in-the-campfire routine?
[QUOTE=Shamozzle]
Wait a minute, don’t sealed tin cans explode or at least deform when heated? You know, the ol’ baked-beans-in-the-campfire routine?
[/QUOTE]
When heated in an uncontrolled way like that, quite possibly, yes.
[QUOTE=Shamozzle]
Wait a minute, don’t sealed tin cans explode or at least deform when heated? You know, the ol’ baked-beans-in-the-campfire routine?
[/QUOTE]
Mrs M’s banoffee pie recipe entails boiling unopened cans of condensed milk in a saucepan. No explosions to date (but one saucepan ruined when she decided a little nap would be just the thing while it was on the stove :smack: ).
I think they heat them inside pressurised ovens to prevent them exploding, but it’s always going to be tricky balancing the pressures inside and outside the can exactly - having ribbed cans would (I think) allow a bit more flexibility in either direction - if the oven pressure is higher than the can pressure then it can squeeze down a bit, and vice versa.
Note: I don’t know for sure that this really is why the cans have ribs, it just seems the most plausible explanation.
They used to heat the filled cans before the top was appled, then, w/ the can still hot, they seal the top on, thus creating a slight vacuum as the contents cooled. Just as is done in home canning. The vacuum prevents spoilage for quite a length of time. I suspect they still do it the same, but I’m not positve. The cans are probably more subject to denting, and possible loss of integrity and the vacuum, in the side wall, thus the ribbing offers some added strength in the side wall to help avoid this.
[QUOTE=Mangetout]
I think they heat them inside pressurised ovens to prevent them exploding, but it’s always going to be tricky balancing the pressures inside and outside the can exactly - <snip>
[/QUOTE]
In canning, it’s not the least bit tricky to balance the pressures. You simply put a bit of water in the pressure cooker. Since the volume remains constant, and the temperature change is the same for both the insides and the outsides, the relative pressures should stay the same.
[QUOTE=Mangetout]
During the manufacturing process, the cans are sealed, then heated so that the contents are cooked and sterlilised - I expect the ribs offer a little bit of flexibility to cope with thermal expansion of the contents, but in that case, the question really should be; why are some cans not ribbed? - excluding soft drinks cans, there are some cans of soup/beans/vegetables that aren’t ribbed.
[/QUOTE]
Aluminum soft drink cans are extruded, and the thin gage aluminum is much easier to work than the thicker aluminum or steel, which is cold rolled, IIFC.
[QUOTE=Santo Rugger]
In canning, it’s not the least bit tricky to balance the pressures. You simply put a bit of water in the pressure cooker. Since the volume remains constant, and the temperature change is the same for both the insides and the outsides, the relative pressures should stay the same.
[/quote]
That doesn’t sound right - heat takes time to be transferred to the contents of the can - by definition, the heating device must be hotter than the cans, during the heating phase. The pressure could probably be balanced artificially though.
I realise that. I was talking about steel cans - I’ve seen plain steel cans containing similar foodstuffs to the ribbed ones.
[QUOTE=psychonaut]
Surely it can’t be to make them easier to hold…
[/QUOTE]
Just a thought but could the ribs be used in the manufacturing process for machinery to pick them up or for the ribs be used to guide a particularly ribbed can down a particular path?