You are walking the plant floor and it's just one of those days. Nothing seems to be going right. And then, your nemesis, that same ol' machine, goes down again. As usual, the bearings failed. "Why me?," you ask, "They must be bad bearings. We can't afford the down time every time this happens. I'm getting tired of this." So, you call your bearing supplier and ask for a solution to your problem.
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The supplier tells you quite emphatically that the bearings are not poor quality. However, you also learn that they could be the wrong type for the application and that you will need to analyze the required bearing functions and performance demands. The supplier starts the problem-solving sequence by collecting the following data:
- the machine's function and construction
- bearing dimension limitations
- bearing mounting location (point)
- bearing life span
- bearing load (direction and magnitude)
- bearing running capacity
- vibration and shock load
- bearing speed
- bearing temperature (ambient and that generated by internal friction)
- friction and torque
- environment (corrosion, lubrication cleanliness of the environment etc.)
- allowable misalignment for inner and outer rings
- requirements for mounting and dismounting
Shaft assemblies generally require two bearings to support and locate the shaft both radially and axially relative to the stationary housing. These two bearings are called fixed and floating bearings. The fixed bearing withstands both radial and axial loads and locates or aligns the shaft axially in relation to the housing. Being axially free, the floating bearing relieves stress caused by thermally-induced expansion and contraction of the shaft. It can also allow for misalignment caused by fitting errors.
Bearings that support axial loads in both directions are most suitable for use as fixed bearings. In floating bearings, the axial displacement can take place in the raceway — cylindrical roller bearings — or along the fitting surfaces — deep groove ball bearings. There is also the cross location arrangement in which two angular contact ball bearings act as fixing and non-fixing bearings simultaneously, each bearing guiding and supporting the shaft in an axial direction only. This arrangement is used mainly in comparatively short shaft applications.
Because they are designed for the widest possible use, the specifications for rolling bearings are standardized. However, to meet the diversity of applications required, you can select a bearing of non-standard design. To do so you will need such specifications as the dimensional and running tolerance, internal clearance, and preload, bearing material, heat treatment, and cage design and material.
If bearings are to function as expected, you must select and implement appropriate methods of installation and handling — fitting methods, lubrication methods, sealing methods, shaft and housing construction, and dimensions.
Deep groove ball bearings
This type of bearing is arguably the most popular. Its application and assembly is rather simple when compared to other types. The Conrad design limits the number of rolling elements. These bearings are available with or without seals and shields. They also available with grease for maintenance-free applications. A wider cartridge design is also available that allows more room inside the bearing for addition grease.
Deep groove ball bearings are suitable for radial, axial, or combination loads. They provide very quiet operation, need minimal lubrication, and operate at relatively high speeds with less friction than roller bearings. On the other hand, their load capacity is less that of roller bearings. Debris contamination could be a concern since the point contact of the rolling elements in ball bearings is more sensitive to dirt than are roller bearings. Deep groove ball bearings are typically used in electric motors, pulley, and gearboxes.
Angular contact bearings
Select this bearing over deep groove ball bearings when the axial load is higher. Their radial capacity can be higher since their construction allows for more rolling elements as compared to the Conrad bearings. This type of bearing is not available with integral enclosures. Single-row bearings, with or without radial load, accept thrust in only one direction. They can be assembled in tandem with another bearing — DB or DF configurations — to allow thrust in both directions (see two-row angular contact bearings). They are typically used in hydraulic pumps and machine tools.