Bearing internal clearance is defined as the total distance through which one bearing ring can be moved relative to the other in the radial direction (radial internal clearance) or in the axial direction (axial internal clearance).
Bearing tolerances include dimensional tolerance and rotary tolerance or dimensional accuracy and running accuracy, are regulated by ISO or JIS standards (rolling bearing tolerances) etc. For dimensional accuracy, these standards prescribe the tolerances necessary when installing bearings on shafts or in housings. Running accuracy is defined as the allowable limits for bearing run-out during operation.
In addition to the basic requirements on a bearing like load capacity, speed limit and life time; low noise and vibration is becoming more and more important in most applicatons. Vibrations in bearings are caused by time varying forces in bearings. The contact forces move around the bearing, giving rise to perfect bearing vibrations in the outer ring. It is wellknown that excecssive vibrations can cause premature failure and costly maintenance, often including unplanned downtime and loss of production. High vibration levels also increase energy consumption. High noise levels, in turn, result in apoorer life environment for personnel and family. Therefore, to find out the roof causes of noise & vibration and prevent potential from the beginning is critical to perfect performance of the bearings.
Because of high, repetitive stress to the rolling contact areas, fatigue phenomenon will occur to the bearing material after a duration of operation. Loading stress ultimately dislodges a surface section and the bearing fails. To delay the advent of material fatigue, bearing ring and rolling element materials should have the following properties:
● High level of hardness
● High rolling contact fatigue resistance
● Good wear resistance
● Dimensional stability
● Good mechanical strength
Lubricating grease consists of a mineral or synthetic oil combined with a thickener. The thickeners are usually metallic soaps. However, other thickeners, e.g. polyurea can be used for superior performance in certain areas, i.e. high temperature applications. Additives can also be included to enhance certain properties of the grease. The consistency of the grease depends largely on the type and concentration of the thickener used and on the operating temperature of the application. When selecting a grease, the consistency, operating temperature range, viscosity of the base oil, rust inhibiting properties and the load carrying ability are the most important factors to be considered.