Bearing unit
A bearing unit ( 10, 10 ′) has a radially outer ring ( 31 ). The outer ring ( 31 ) is rotatable with respect to an axis of rotation (X) and is provided with a radially inner raceway ( 31 r ). A stationary radially inner ring ( 33 ) is provided with a radially outer raceway ( 33 r ). A row ( 132 ) of rolling bodies ( 32 ) is interposed between the radially outer ring ( 31 ) and the radially inner ring ( 33 ). Each rolling body ( 32 ) has three contact points (P 1 , P 2 , P 3 ) with the raceways ( 31 r, 33 r ) of the radially outer ring ( 31 ) and, respectively, the radially inner ring ( 33 ).
1 . A cutting machine comprising:
a bearing unit comprising:
a radially outer ring rotatable with respect to an axis of rotation and provided with a radially inner raceway;
a radially inner ring that is stationary and is provided with a radially outer raceway; and
a row of rolling bodies interposed between the radially outer ring and the radially inner ring, each rolling body having three contact points with the radially inner and outer raceways;
a cutting wire; and
a pulley connected to the radially outer ring of the bearing unit and coaxial with the axis of rotation of the bearing unit, the pulley in contact with the cutting wire and configured to guide the cutting wire as the pulley rotates about the axis of rotation.
2 . The cutting machine according to claim 1 , wherein:
each rolling body of the row of rolling bodies is arranged in dynamic contact with a first raceway of the radially inner and radially outer raceways, at a first, single, contact point, and
each rolling body of the row of rolling bodies is arranged in dynamic contact with a second raceway of the radially inner and radially outer raceways, at respective second and third contact points.
3 . The cutting machine according to claim 2 , wherein each rolling body of the row of rolling bodies has a respective center point of symmetry that is arranged on a plane of symmetry of the row of rolling bodies and is dynamically connected to the respective second contact point and the respective third contact point by means of second and third lines of action, respectively, that form, with the plane of symmetry, respective second and third angles that are equal to each other, each second and third angle having a value between 25° and 35°.
4 . The cutting machine according to claim 3 , wherein the second raceway comprises two annular portions separated from one another and mirrored with respect to the plane of symmetry.
5 . The cutting machine according to claim 4 , wherein the second raceway is a radially inner raceway, and is provided with a radially external circumferential groove configured to contain lubricating grease.
6 . The cutting machine according to claim 4 , wherein the second raceway is a radially outer raceway, and is provided with a radially inner circumferential groove configured to contain lubricating grease.
7 . The cutting machine according to claim 6 , wherein the ratio between the radius of curvature of the second raceway and the outer diameter of the balls ranges between 0.51 and 0.54.
8 . The cutting machine according to claim 3 , wherein each second and third angle have a value of 30°.
9 . The cutting machine according to claim 2 , wherein the second raceway is a radially inner raceway and is provided with a radially external circumferential groove configured to contain lubricating grease, the radially external circumferential groove disposed axially between the second and third contact points.
10 . The cutting machine according to claim 2 , wherein the second raceway is a radially outer raceway and is provided with a radially inner circumferential groove configured to contain lubricating grease, the radially inner circumferential groove disposed axially between the second and third contact points.