Four point contact bearings are single row angular contact bearings having a slight change in the construction compared to the angular contact bearing. This type of bearing normally tends to have contact at four points i.e. two in the outer race and two in the inner race.
The four point contact bearing has some advantages over the other kinds of the bearings in the following aspects.
- It requires lesser space in the axial direction than the double row configurations.
- They have the capability to carry axial thrust loads in both the directions and a small amount of radial load.
The bearing consists of the following in its construction.
- Solid outer rings of single construction
- Split inner rings
- The ball and the cage assemblies made of brass or polyamide cages.
- The split inner ring tends to accommodate a large compliment of balls. The inner races are normally matched for that particular bearing alone.
- The cage assembly is normally integrally assembled with the outer race.
- The normal contact angle for the rolling elements and the cages is 35 degrees.
- The bearings are suitable for working with minimum angular misalignments either in the housing bores or due to shaft deflections.
- Due to the presence of split inner races, the bearings are not available in sealed or shielded condition.
- The bearing must have a minimum axial load in order to work with low friction. In case of a low axial load, care should be taken to ensure the preloading of the bearing.
- For cases where the four point bearing is used only as a thrust bearing, a large radial clearance must be provided in the housing for the outer race. This prevents the bearing from being subjected to any radial load.
The four point contact bearing is available in two variants. They are
- Four Point Contact bearings without retaining slots.
- Four Point Contact bearings with retaining slots. The retaining slot is provided in order to prevent the outer race from rotation, when the bearing is used as a pure thrust bearing.
The bearing is normally specified with series starting as QJ2 and QJ3 for four point bearing without retaining slots. For bearings with retaining slots they are specified as QJ2 – N2 and QJ3 – N2.