General information about bearings
The load capacity
The main function of a bearing is to transfer the load between a stationary part of a machine (usually the housing) and a rotating part of a machine (usually the shaft) with minimum friction.
The load capacity can be caused by:
- the mass of the machine or its parts;
- the mass of the product to be moved;
- power transmission.
For a rolling element bearing, these loads must be transferred between the inner ring and the outer ring of the bearing by means of rolling elements
The lifespan and proper functioning of bearings depends on a number of determining factors:
- the cleanliness, which therefore determines the quality of the bearing steel;
- the right amount of lubricant;
- the use and good seals of bearings;
- dimensional accuracy;
- load capacity;
- radial, internal clearance in the bearing;
- packing and storage in the warehouse.
However, other external factors also play a major role:
- the choice of bearing type and bearing arrangement;
- a clean working environment;
- correct mounting and dismounting of the bearings with special tools;
- precision machined shafts and housings;
- the right choice of shaft and housing fits;
- operating temperature;
- aftercare and maintenance;
- strong pollution from the outside and other operating conditions.
A bearing generally consists of three parts:
- two rings containing bearing raceways, one ring is attached to the stationary structural part and the other ring to the moving structural part;
- rolling parts such as balls, rollers and needles for the movability of the rings relative to each other with minimum friction;
- a cage, for guiding and keeping the rolling parts separated.
Rolling bearings can be divided into two large groups:
- ball bearings, theoretically with point contact between balls and raceway;
- roller bearings, with in theory a line contact between rollers and raceway, which are mostly used for higher loads.
The most commonly used bearing in the world is the single row deep groove ball bearing in all kinds of sizes and variants.
Bearings are produced in many different types and sizes, which means that there are many designs that all have their own characteristics and properties. There are seven types of bearings that are most commonly used worldwide:
- single row and double row deep groove ball bearings;
- single row and double row angular contact ball bearings;
- double row self-aligning ball bearings;
- cylindrical roller bearings;
- tapered roller bearings;
- double row spherical roller bearings;
- axial ball bearings, also called thrust bearings.
The choice of the type of bearing is determined by, among other things:
- the installation space;
- the size and arrangement of the bearing load;
- the speeds;
- the fixed dimensions in the construction;
- the shaft size.
Each bearing is identified by a code. Its characteristics are determined by an ISO standard. The ISO (International Standard Organization) is tasked with developing and coordinating standards with the aim of international interchangeability of products. Strict application of this by the bearing manufacturers ensures full interchangeability of bearings – regardless of brand – with the same type number.