Bearings – Rotary bearing – Antifriction bearing
Reexamination Certificate
1999-10-20
2001-03-13
Hannon, Thomas R. (Department: 3682)
Bearings
Rotary bearing
Antifriction bearing
Reexamination Certificate
active
06200038
ABSTRACT:
The present invention relates to the field of cages made of synthetic material which are intended for rigid ball-bearings.
The cages used in bearings are intended to constantly maintain a uniform circumferential spacing between the rolling bodies.
Cages made of synthetic material are produced by injection moulding a plastic, for example nylon-6,6, which may or may not be filled with reinforcing material such as glass fibre.
These cages consist of an annular ring with spherical slots open axially on one face of the ring and radially on both sides of the ring, each slot being extended axially by lips which extend in a direction which is axially away from the closed end of the slot.
A cage of this type is mounted by axial snap-fitting over the row of balls of the bearing, the said balls fitting into the slots with a very small amount of play. The enveloping spherical shape of the slots holds the cage axially over the row of balls and allows the cage to be centred with respect to the bearing races.
These cages are economical to manufacture, low in mass and do not suffer from corrosion problems. However, in certain applications entailing severe load and speed conditions, it has been found that these cages may exhibit premature failure, particularly breakage of the cage in the heel region.
Surprisingly, it has been found that these breakages were due to particularly high wear in the region of the interior edges of slots in the region of the lips lying in the direction of rotation of the bearing, under the effect of centrifugal force and the applied loads.
The interior edges of the slots are understood as meaning those edges of the slots which are located towards the axis of rotation of the bearing.
The bottom part of the slot is understood as meaning that part of the slot which is closest to the axis of rotation of the bearing.
It has thus been found that under certain speed and load conditions, the critical area of contact between balls and slots was located in the lower part of the slot, in the region of the lips in the direction of rotation of the bearing. So-called “edge” contacts between ball and slot occur in these critical regions, these contacts resulting from the bearing load and rotational speed conditions. The edge contacts occur at a sharp edge and therefore arise under conditions which are very bad both from the contact pressure point of view and from the local lubrication conditions point of view. Upon contact with the ball, the slot edge which is relatively flexible, will tend to deform. This deformation, combined with the high contact pressures, the friction generated by the rotation of the ball, and poor lubrication of the contact region, leads to premature slot wear.
The object of the present invention will be to overcome the drawbacks of this conventional cages and to propose a cage, the slot shape of which allows the ball-slot contact conditions to be improved by moving the region of contact away from the sharp edge.
The cage device according to the invention is of the type intended to hold balls in a bearing comprising at least one row of balls arranged between two raceways. The cage comprises a ring-shaped part axially adjacent to the balls and a number of slots in each of which a ball is arranged. A slot is formed by a concave surface, the slots being open axially on one face of the ring and radially on both sides of the ring, the said slots being separated by spacing parts extended on the opposite side to the ring by lips. The concave surface comprises a truncated-conical portion which meets a spherical portion.
In one embodiment of the invention, the truncated-conical portion is arranged along the interior edge of the slot and meets the spherical portion which occupies the rest of the concave surface, the conical portion closing up in the direction towards the axis of revolution of the cage. The spherical portion is arranged on the exterior edge of the cage. The region of ball-slot contact is thus moved away from the interior edges of the slot, thus avoiding the edge contacts at sharp corners between balls and slots, and this considerably improves the contact pressure characteristics in this area with, as a consequence, appreciably reduced cage wear. Furthermore, lubrication is thereby improved because of the conical shape at the base of the slot which offers the lubricant more space. A reservoir of lubricant which is entirely beneficial to the correct running of the bearing thus forms at the base of the slot. Compared with a conventional cage, the cage according to the invention maintains its ability to hold the balls in the slots of the cage both in the axial direction and in the radial direction.
In one embodiment of the invention, the truncated-conical portion meets the spherical portion tangentially.
In another embodiment of the invention, the truncated-conical portion meets the spherical portion along a secant, preferably forming a re-entrant angle or a hollow.
Advantageously, the angle &agr; of the truncated-conical portion is between 0 and &pgr;−2 arcsin (2×X/D
a
), D
a
being the diameter of the slot and X being equal to {square root over ((D
i
/2+L )
2
+L −Y
2
+L )} with Y=(D
i
2
+D
p
2
−D
a
2
)/(4×D
p
), D
i
being the diameter of the bore of the cage, D
p
being the diameter of the circle passing through the centres of the spherical portions of the slots.
The distance d between the base of the truncated cone and the centre of the spherical portion of the slot is between zero and D
p
/2−Y, D
p
being the diameter of the circle passing through the centres of the spherical portions of the slots, Y being equal to (D
i
2
+D
p
2
−D
a
2
)/(4×D
p
).
The diameter B of the base of the truncated cone is between 2×X and D
a
, D
a
being the diameter of the slot.
The present invention also relates to a ball-bearing comprising a cage as defined hereinabove.
The cage will thus offer resistance to wear because of the improved so-called “edge” contacts between the balls and the cage and because of the better lubrication, thereby reducing the risk of premature bearing failure through cage breakage.
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patent: 5906441 (1999-05-01), Seki
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patent: 2 306 582 (1997-05-01), None
Hannon Thomas R.
SKF France
Smith , Gambrell & Russell, LLP
LandOfFree
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