Tuesday, November 24, 2009

Ball Bearings

Cheap steel was key to allowing the routine design of parts that rolled against one another

If the utility of an invention were somehow derived from the genius of its inventor, it would be pardonable that so many sources trace the idea for the ball bearing to a 1497 drawing by Leonardo da Vinci. But good ideas, like useful evolutionary traits, tend to emerge more than once, in diverse times and places, and the idea of arranging for parts to roll against one another instead of sliding or slipping is very old indeed. The Egyptians already had the basic idea when they moved great blocks of stone on cylindrical rollers. Similar ideas occurred to the builders of Stonehenge as early as 1800 B.C. and to the craftsmen who constructed the cylindrical-shaped bearings on the wheel hubs of wagons around 100 B.C. (On these wagons the axle turned with the wheels, so the bearings enabled the axle to roll against the wagon chassis.)

The first design for a ball bearing that would support the axle of a carriage did not appear until 1794, in a patent filed by a Welsh ironmaster named Philip Vaughan. Ball bearings between the wheel and the axle enabled the axle to remain fixed to the carriage chassis. But cast iron ball bearings were brittle and tended to crack under stress. It took the invention of the Bessemer process for making inexpensive steel, plus the invention of the bicycle, to fix the ball bearing permanently in the minds of engineers everywhere. Jules-Pierre Suriray, a Parisian bicycle mechanic, patented his steel ball-bearing design in 1869, and in that same year a bicycle outfitted with Suriray’s ball bearings won an international cycling race. The demand for ball bearings—on automobiles, tanks or guidance systems—has pushed manufacturers ever closer to the ideal of shaping a perfect sphere. No turning wheel will survive for long on its axle without ball bearings machined to a tolerance of less than a thousandth, or even a 10-thousandth, of an inch. Many sources claim that the most perfect spheres occur in the bearings of computer hard drives, but in fact that honor goes to the ping pong–size spheres of fused quartz that serve as gyroscopic bearings for the satellite Gravity Probe B. Its gyroscopes are 30 million times more accurate than any other gyroscope ever built.

Source of Information : Scientific American September 2009

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