|MadSci Network: Engineering|
I am going to describe the hand can opener. An electric can opener works in much the same way, except it is driven by an electric motor. Can openers work because cans have been somewhat standardized as far as the height of the lip at the edge, etc. If you want to see how long it took to invent a good can opener, visit the web site below. Inventor of can opener http://sciencenet.oit.net/database/Technology/9810/t00276d.html The opening process starts by applying a pressure to close the jaws of the opener around the top and bottom lip of the can. The serrated wheel grips the lower edge of the can lip and the upper jaw pierces the can lid just inside the lip. You can think of the opener as a large pair of pliers at this point, with a sharp point on one edge of the pliers. Once pierced, the handle of the opener is turned to drive the serrated wheel. As long as you hold the handle tight enough to overcome the force of the metal cutting action, the serrated wheel moves the cutter blade through the can top. This is not unlike a plow being pulled through a field. It takes a lot of force to hold the cutter down and pull it through the metal. A metal cutting lathe cuts metal in the same manner, dragging a sharp tool through the metal while it spins by at high speed. The cutting blade has to be stronger than the metal it is cutting so as to not wear out too fast. Metal cans are actually pretty thin and weak. You can practically cut them with a pair of scissors when they are just thin sheet metal laid out flat. There is usually enough leverage between the handle of the can opener and the cutting blade that hand pressure is enough to keep the blade in contact with the can and the serrated wheel moving. Sometimes, if the lip of the can is slightly higher than normal or the blade is dull, you have to really clamp down with your hands to keep the blade cutting. If the serrated wheel is worn, it might slip and not have enough frictional grip to drive the cutting blade forward. Electric can openers have the same piercing action and a motor to drive the wheel. The clamping action is released when a switch senses the top of the can falling away from the cutter.
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