Roller bearing components

1 RINGS

The inner and outer metal rings can move relative to each other. In the case of the ball bearing shown, the relative movement is circular, with the inner and outer rings rotating in concentric circles. If the inner ring is fixed on a shaft and the outer ring connected to a wheel, the wheel can turn with low resistance. The pressure (load) on the rings induced by the rolling elements can create wear and fatigue in the ring material, and for this reason, the steel is hardened and contains around 1% carbon and 1,5% chromium. Therefore, care must be taken when installing bearings where interference fits are specified, as excessive force can easily crack the brittle rings.

2 ROLLING ELEMENTS

Sliding friction between two metal surfaces is dramatically reduced when rolling elements are introduced, as depicted in diagram 2. This is the basic principle of a roller bearing employing rolling elements to achieve the same. These elements can be divided into two categories: ball or cylindrical. The main difference lies in the contact area as balls make point contact on the surface while cylinders result in line contact (diagram 3). With the increase in load (pressure), the point contact of the ball becomes elliptical and the line contact of the cylinder turns rectangular. The larger contact area of the cylinder enables these bearings to carry higher loads but its maximum rotational speed is lower than the equivalent-size ball bearing. Most roller bearings use steel rolling elements but ceramic (silicon nitride) options are becoming popular as they offer even less friction and are more durable in certain applications. These bearings are referred to as hybrid bearings.

3 CAGE

The main purpose of the bearing cage is to separate the rolling elements evenly around a bearing. This reduces friction and heat build-up while guiding the elements along the optimal path between the rings. In bearings where the outer or inner ring can be removed during installation, it helps to retain the elements and prevent them from getting lost. The cage also allows lubricant to enter the bearing. Common materials used for producing cages include metal and polymers.

4 SEALS

The purpose of a bearing seal is to hold the lubricant inside the bearing while keeping contaminants out. There are both non-contact and contact seals. These contact seals make positive contact on the moving surface of either the inner and outer ring, adding to the friction, but is able to keep moisture out and prolong service life in harsh environments.

Ceramic bearings are becoming more popular as they offer even less friction and are more durable