Choosing the Right Pillow Block Bearing

A pillow block bearing, often referred to as a bearing housing or plummer block, is a pedestal that provides support for a rotating shaft with compatible bearings like ball or roller bearings. For the purpose of this blog, we will be referring to this kind of bearing as a bearing housing or plummer block to avoid confusion among the other bearing types. Plummer blocks serve as housings that have a bearing placed into them. They are typically mounted on a surface parallel and offset to the axis of the shaft, and they contain a stationary outer ring and rotating inner ring. Mounting holes at the base of the plummer block allow for easy mounting and modification.

Additionally, these bearing housings are best suited for cleaner environments and are not meant to handle higher loads. While their application is fairly straightforward, it is important to know whether your system requires ball bearings or roller bearings. For this reason, this blog will outline how to choose the right bearing housing for your application.

In order to select the right pillow block bearing, you need to know whether your application would benefit from ball or roller bearings. Ball bearings use a ball as the rolling element between the stationary ring and rotating ring. They are designed with a housing, inner and outer rings, balls, and a ball separator. Moreover, they provide smooth, low friction in rotary applications. Unlike ball bearings, roller bearings have a roller as their rolling element. They are made up of a housing, inner and outer rings, rollers, and a cage or roller separator. Similar to ball bearings, roller bearings provide smooth, low friction movement in rotary applications. There are three main types of roller bearings that are typically used for plummer blocks.

The first is a tapered roller bearing which uses cone-shaped rollers that run on conical races. They have a great contact area, allowing them to carry higher radial and axial loads at low- to medium-speed levels. When paired with a plummer block, the thrust level of the tapered roller is only about 60% of the radial capacity.

Spherical roller bearings are self-aligning, double-row, combination radial and thrust bearings. Their rolling elements are crowned or spherically-shaped, and when paired with plummer blocks, have an incredible capacity for high loads and loads that require shock tolerance. Their one drawback is their limited speed capacity.

The last type of roller bearing often paired with plummer blocks is the cylindrical roller bearing. Cylindrical roller bearings are typically crowned or end-relieved for reduced-stress concentrations. They are made to withstand high radial capacities and moderate thrust loads. When paired with plummer blocks, they produce low friction and allow for high speeds.

Upon selecting which bearing works best with your pillow block bearing, there are a few design specifications to keep in mind. For one, it is important to consider the shaft diameter. When the shaft diameter is matched with the bore dimensions of the bearing unit, the plummer block can easily slide onto the shaft and into position. You must also consider the shaft height and shaft size as well as the maximum shaft speed and maximum load bearing capacity of your shaft for ease of operation. Moreover, the material your housing is made of is important due to the fact that the housing is responsible for protecting the bearings during operation as well as providing a mechanism to secure the bearings in place. The most common materials used for housings include aluminum, cast iron, pressed steel, stainless steel, and plastic.

Aluminum has a high load-carrying capacity, great endurance, and increased thermal conductivity. Cast iron has incredible resistance against corrosion, a high load-bearing capacity, and is the most common material used for pillow block bearings. Pressed steel can be used for lower load-bearing applications, and they make for an inexpensive alternative to the other materials. Stainless steel is ideal for applications that come in contact with corrosive materials or chemicals because of their high resistance factor and high pressure ratings. Lastly, there are various plastic materials such as nylon, PTFE, and acetal polymers commonly used for pillow block bearings, all of which provide great endurance and chemical resistance.