Patent ID: 7430933

Claim:
A seal for a ball screw with a ball screw shaft, a ball screw nut and a number of balls accommodated between the ball screw shaft and the ball screw nut, in which the ball screw shaft has an outer peripheral surface on which a ball rolling groove is formed and the ball screw nut has an inner peripheral surface on which a ball rolling groove corresponding to the ball rolling groove of the screw shaft is formed, said seal for the ball screw being disposed at each of both end portions of the ball screw nut and comprising: a foreign material removing member having a hole of a shape corresponding to a sectional shape of the ball screw shaft taken perpendicularly to an axis thereof to prevent foreign material from invading from an outside of the ball screw nut to an inside thereof; and a seal member having a hole of a shape corresponding to the sectional shape of the ball screw shaft taken perpendicularly to the axis thereof to retain lubricant existing inside the ball screw nut, said foreign material removing member and said seal member being mounted to the ball screw shaft while being overlapped to each other, wherein inner peripheral portions of the foreign material removing member contact the outer peripheral surface of the ball screw shaft and the ball rolling groove thereof and the seal member contacts the outer peripheral surface of the ball screw shaft and the ball rolling groove thereof, said foreign material removing member being disposed outside the seal member in the axial direction of the ball screw nut, wherein said foreign material removing member is provided, at an inner peripheral surface thereof, with a protruded portion in the form of spiral projection which contacts the ball rolling groove of the screw shaft and a foreign material removing opening formed so as to extend from an end face of the foreign material removing member directed outward in the axial direction of the nut to a middle portion thereof for scraping and discharging the foreign material outside the nut, wherein said foreign material removing member has an axial thickness that is larger than the axial thickness of said seal member.