What are wire race bearings?
A wire race bearing is a four point angular contact ball bearing. It consists of four wires which are formed into a circle to fit a housing groove machined into the inner and outer diameters of the relatively stationary and rotating parts. Into each of the wires is produced an accurately profiled groove which provides the bearing track upon which the balls run.
These balls are separated by a continuous cage band and thus the load is evenly carried. This cage band prevents any friction between the balls and aids lubrication. As it is the bearing elements that carry the load the role of the housing is merely to to hold the bearing assembly together. That is the choice of housing material does not affect the strength of the bearing. The housing can be made from steel, cast iron or aluminium alloys. The wire races are made from silicon chrome hardened and tempered wire with a minimum sectional hardness of 52 HRC.
The wires are supplied with a an accurate gap to allow for differential expansion (between the wires and the housings) over a wide temperature range typically 240 - 390 K. Owing to this gap the wires fit the housing exactly which eliminates machine tolerances.
The above picture shows a typical 3-part housing which is suitable to carry both radial and axial loads in nearly equal proportions. The cross section in this case is uniform and thus has a contact angle of 45 degrees. This angle can be reduced to form a rectangular cross section and thus change the load carrying characteristics for example to sustain more axial and less radial loads.
By altering the support housing design, we can produce a bearing more suited to carrying axial loads as shown below:
Alternatively, a double row of axial bearings can carry even higher axial loads, for example in indexing turntables.
Round Profile wires
In applications where the loads are low, round profile races can be installed as shown below: