A pillow block bearing is a type of bearing that is housed within a cast-iron mounting bracket that doubles as the outer housing for the bearing. Typically manufactured from a gray cast iron, the pillow block bearing housing has provisions to allow the housing to be bolted down snugly. The inner bearing component of the pillow block bearing is commonly a soft metal material, such as white metal, while the outer housing can be a split or single housing. Primarily designed for low-torque, minimal-load situations, this bearing is also designed to be used in clean environments within an industrial setting.
While the term is often used interchangeably in certain parts of the world, a pillow block bearing and a plummer block bearing are not the same device. Unlike the pillow block bearing, the plummer block does not contain an inner bearing. The plummer block is a bearing housing that is designed to operate under higher loads and in corrosive, industrial settings. One common feature of both bearing housings is that the housing is designed to be bolted to a stable surface through the use of cast-in bolt mounting holes on the base of the body assembly.
Used to support a spinning shaft, the pillow block bearing provides a stable and secure housing for the often expensive bearing. Special seals, placed at the entrance and exit of the bearing housing, protect the bearing from contaminants, such as dirt and dust. A split housing is often used to promote easier bearing changes as well as much easier shaft maintenance, while an unsplit, or one-piece, housing is also used in some applications. In some applications, the unsplit style of pillow block bearing is used in areas that offer less access and lower shaft speeds. This is commonly due to the less frequent requirement for maintenance with a slower turning shaft bearing.
By using a pillow block bearing on a spinning shaft, the duty cycle of the shaft is greatly increased. The bearings prevent the shaft from distorting and wobbling while turning, thereby damaging any connective unions and weakening the very structure of the steel shaft. While the modern pillow block bearing uses a replaceable soft metal bearing shell inside of a cast iron or cast steel bearing housing, early versions of the device occasionally used a poured bearing inside of the housing. These types of bearings were often short-life bearings and required frequent service.