Measurement of structure-borne sound of rolling element bearings in machines and plants for evaluation of condition
|Publication Date:||1 April 2013|
|ICS Code (Rolling bearings):||21.100.20|
|ICS Code (Noise emitted by machines and equipment):||17.140.20|
Rolling element bearings are highly loaded components in machines which, if faults or damages occur in the bearing, could result in premature failure of the machine and expensive consequential damage. The diagnostic techniques which form the subject of this guideline aim at detecting at any early stage those states of the rolling element bearings which could result in functional problems up to and including failure of the rolling element bearing before it comes to the end of its planned life time duration.
This guideline is concerned with rolling element bearings not only for rotating components in driving and driven machines but also for power transmission elements in machine sets and power units. It applies primarily to rolling element bearing applications in stationary plants and to those causes of damage which occur during normal operation. As regards rolling element bearing applications in vehicles and mobile installations, there can occur additional effects from vibration and structure-borne sound entering from the outside. This guideline will not deal with these effects nor with measurements taken at test rigs for examining rolling element bearings. Detailed information about the latter may be found in DIN 5426-1 and DIN ISO 15 242-1 and DIN ISO 15 242-2. The measurement procedures they described call for the rolling element bearings to be loaded and clamped under defined conditions. The test arrangement, measurement conditions and the way transducers are connected are defined requirements and do not correspond to the requirements applicable to in machine assembled rolling element bearings.
This guideline supplements the usual vibration measurements of machines with those methods which are described in the DIN ISO 10816 Series of Standards and which cover the state of the entire machine and its components in the frequency range extending up to around 1 kHz. In its informative Annex E, DIN ISO 10816-1 recommends that measurements of structure-borne sound also be taken in order to monitor and diagnose the condition of the rolling element bearings. Such measurements should be taken, appraised and evaluated on the basis of the present guideline. Structure-borne sound measurements of this kind are taken not only during acceptance measurements following the assembly and installation of machines and power units but also before or after repair work. The rolling element bearing diagnostics described here covers the structure-borne sound generated during rolling, frictional and shock-related events in the various components of the rolling element bearing and which extends into and above the frequency range of 20 kHz.
This guideline applies to rolling element bearings running at speeds higher than 120 revolutions per minute. It applies to single- and multiple-row ball, rolling element and self-aligning roller bearings. Special practical experiences are necessary for measurement and evaluation in the case of needle-roller bearings on account of the low structure-borne sound level.
Applications with bearings running at slower speeds (very low speed engines) will require additional, more extended measurement procedures and special practical experience which cannot be covered here.
Basically in what follows a distinction will be drawn in diagnostics between simple and complex rolling element bearings. An overview of features of this classification shows Annex C. This can relate not only to the constructional design but also to vibration excitation and structure-borne sound excitation. Simple rolling element bearing systems are found in rotors with low eccentricity running in two bearings. There are no energy-intensive additional sources of structure-borne sound either close to the bearing which is to be monitored or at the rotor. Examples of simple rolling element bearing systems include those in fans and blowers with a low level of structureborne sound, in electric motors, in pumps, and in conveyor pulleys.
In the case of complex rolling element bearing systems, either on the rotating shaft or integrated in the housing there are additional and dominating sources of structure-borne sound outside the rolling element bearing. Bearing systems with three or more bearing positions can be included here. Complex excitations of structure-borne sound occur furthermore in machines with connected components running translatorily or eccentrically, in shock and friction partners, and when high eccentricities obtain. Examples include reciprocating machines, gear trains, screw compressors and friction rollers.