What Is a Spherical Bearing?
Spherical bearings are bearings in which the inner and outer rings are in spherical contact.
They are mainly used for oscillating, tilting, and low-speed rotational motion. Spherical bearings are spherical and can support large radial loads and axial loads in both directions at the same time.
There are two main types: lubricating type, which requires lubrication of the spherical surface of the sliding portion in contact with the bearing, and non-lubricating type, which does not. They excel in wear resistance and are used in joints of industrial and construction machinery and other locations where large loads are applied.
The lubrication-free type is maintenance-free and is best suited for applications where oil is not required, such as in food processing machinery, or parts of machinery that cannot be lubricated.
Applications of Spherical Bearings
Oilless spherical bearings have excellent resistance to wear and are capable of carrying large loads. Examples of applications include industrial machinery and construction equipment.
Oilless spherical bearings have low creep deformation when supporting compressed loads and have excellent resistance to wear. In addition, they do not require lubrication and do not require maintenance.
Oilless spherical bearings are suitable for supporting axial loads in one direction and are used in areas where oil is used, such as in food products, and in locations where lubrication maintenance is difficult.
Principle of Spherical Bearings
1. Oil-Supplied Bearings
Spherical bearings are generally made of high-carbon chromium bearing steel for both the inner and outer rings, and the sliding surfaces are treated with a phosphate coating. In addition, many are covered with a dry coating of molybdenum disulfide. These bearings operate at low torque and have a large load capacity with excellent wear resistance.
The sliding portion between the inner and outer rings is characterized by spherical contact and the absence of the grooves necessary to incorporate the inner ring, which allows for a large load capacity and can be used where impact or alternating loads are applied. If the sliding surfaces where the inner ring and outer ring contact each other are poorly lubricated, heat generation and other problems can occur.
2. Oilless Spherical Bearings
An example of an oilless spherical bearing is a combination of a special PTFE liner reinforced with copper alloy adhered to the sliding surface of the outer ring and hard chrome plating on the sliding surface of the inner ring. High lubricity is added to the sliding surface itself.
Even without lubrication, large loads can be supported by applying a process such as adhering to a material with excellent resistance to wear.
Other Information on Spherical Bearings
1. How to Fix Spherical Bearings
When using spherical bearings, the housing in which the spherical bearing is mounted and the shaft that is inserted into the spherical bearing are dimensionally toleranced according to the application. Care must also be taken to ensure that the housing has sufficient wall thickness to prevent deformation due to load.
When mounting in a housing, only the outer ring should be pushed in so that no force is applied to the inner ring. It is also important to push only the inner ring into the shaft as well so that no force is applied to the outer ring. Poor mounting may result in uneven loading due to deformation of the bearing, resulting in shortened service life and rattling.
There are four different conditions of use when determining the dimensional tolerances of the housing and shaft of a spherical bearing: inner ring rotating load, outer ring rotating load, normal load, and heavy load.
Dimensional Tolerances for Oilless Type
For the inner ring rotating load, the recommended tolerance for the shaft under normal load is k6, and for heavy load is m6. For both housings, H7 is recommended for steel and J7 for light alloys.
For the outer ring rotating load, the dimensional tolerance of the shaft is h6 for both normal and heavy loads, and the housing is k7 for steel and m7 for light alloy for normal loads; for heavy loads, m7 for steel and no light alloy is specified.
Dimensional Tolerance for Oil-Filled Type
There are slight differences in dimensional tolerances for oil-feeding types, so it is necessary to check the manufacturer’s technical data before determining dimensional tolerances.
2. Examples of Spherical Bearing Applications
Spherical bearings are used in a wide range of applications, with the most common use being in large equipment. In the use of shaft couplings, a shaft is connected with a coupling having two spherical bearings. This allows the eccentricity and misalignment of the two shafts to be absorbed.
An example of use in heavy construction equipment such as power shovels is the rod ends of hydraulic cylinders used in each joint. Other applications include coupling parts of cranes and suspension parts of trucks, which are often used under heavy loads with vibration and shock.