Reader’s question: “Why are some food containers ribbed and others are not?”
Thank you for this question. My first job as an engineer was for Continental Can Co. during the summer of my junior year in college. My project was to speed up beer can production from nine cans/second to ten cans/second. This was when we had “man cans” which were nearly impossible to crush with one hand to impress the ladies and required a ‘church key’ (i.e.: can opener) to access the beverage. These cans were made of tin coated steel sheets which were first lithographed with the proper label. Then the approximately 4’ x 4’ sheets were slit to can size, rolled and edge crimped. Then the seams were soldered as they passed over a molten bath of lead. Next, a prepared bottom was roll crimped to the cylinder and then spray lacquered inside to prevent the contents from contacting the container.
When I surveyed my wife’s pantry recently, I discovered that all the metal cans were nearly continuously crimped from top to bottom. Small aluminum cans with crimped tops and bottoms were un-ribbed, while ‘normal’ height cans, which had been made by extrusion processes, were un-ribbed and very thin walled. They all seemed to be meant to hold contents with specific properties.
I am certain that in all cases the ribbing is meant to add structural strength/rigidity to the can. Money can be saved without sacrificing performance if we add ribs to the can sidewall to compensate for using thinner, less expensive material.
When was the last time you knowingly picked up a dented can at the grocery? Forget the small dents. Consider how strong a can must be to be stacked eight feet high and then loaded by a forklift two or three palettes high for commercial transport.
There are more factors in play here than just presenting a customer with a dent-free can of peaches. The thin-walled smooth aluminum cans with no ribs are mostly all meant to hold carbonated beverages. The beverage itself with its full liquid and pressure-creating properties adds greatly to the structural strength and rigidity of the container. Compare the heft and feel of a can of beer to a can of green tea. Or apple juice. Enough said. What happens when you remove the top of say, tonic water? Once it is open, you can barely manage to pour out the contents without the bottle collapsing in on itself.
All the same principles apply to plastic containers which might not display small ridges but consist of larger smooth curved surfaces to provide strength and rigidity. To demonstrate this, take a drive down a rough dirt road, first in a square boxy Jeep JK, and then take the same ride in a curvaceous modern SUV. The shakes and rattles are greatly reduced by the curvaceous body design.
I look forward to hearing more questions from PRT readers. Any questions and comments may be submitted via email directly to: askengineerprt@gmail.com Responses will be given directly to the submitter or will be published in subsequent issues of the PRT.