Ball screw with alternately disposed steel balls and ceramic balls
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United States of America Patent
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-
Dec 31, 2002
Grant Date -
N/A
app pub date -
Jul 30, 2001
filing date -
Jul 30, 2001
priority date (Note) -
Expired
status (Latency Note)
Importance
Abstract
A ball screw comprising a screw shaft 1 made of steel and having a thread groove 6 on outer peripheral surface, a ball nut 2 made of steel and having a thread groove 7 opposing the thread groove 6 on inner peripheral surface, a return tube 3 attached on the ball nut 2, and a plurality of balls inserted between the two thread grooves 6 and 7 and in the return tube 3. As the balls, steel balls 4 made of bearing steel and ceramic balls 5 made of silicon nitride are disposed alternately at a given ratio. Diameter Dc of the ceramic ball 5 is set to a value smaller than diameter Ds of the steel ball 4 so that contact stress acted on contact surfaces of the ceramic ball 5 and the two thread grooves 6 and 7 will be equal to contact stress acted on contact surfaces of the steel ball 4 and the two thread grooves 6 and 7.
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