Detection of Faults in bearings based on load characteristics and fit

Detection of Faults in bearings based on load characteristics and fit

Loads applied to bearings can be classified as light loads, standard loads or heavy loads according to their magnitude, and as static loads, variable loads or impact loads according to their temporal variation. Furthermore, they can be categorised by direction as rotational loads

(also known as circumferential loads), static loads (also known as point loads) or directional loads.

Rotational loads, static loads or directional loads are not properties of the load itself as applied to a bearing, but rather load phenomena observed in relation to the individual rings of deep-groove ball bearings. When determining the fit between the inner and outer rings, one must first ascertain whether the load is rotational or static, and then decide whether to use an interference fit or a clearance fit.

a) Intrinsic noise: Raceway noise and various bearing and rolling friction noises (cylindrical roller bearings) are sounds inherent to rolling bearings. Raceway noise is produced by the elastic characteristics of the contact between the rolling elements and the raceway; when a deep groove ball bearing rotates, the rolling elements roll along the raceway, emitting a continuous, low-pitched sound; Abnormal rolling friction noises may produce unpleasant metallic grinding sounds such as ‘creaking’ or ‘squeaking’; such noises do not occur when the bearing is running smoothly. Therefore, this is not a cause for concern under normal conditions; attention should only be paid once the noise level increases.

b) Noise associated with bearing manufacture: This includes cage noise and chatter. Cage noise occurs primarily in ball bearings; when deep-groove ball bearings rotate, noise is generated due to the vibration of the cage and the impact between the cage and the rolling elements. This sound manifests as a periodic whine (in various types of bearings); it is a sound of a specific frequency caused by vibrations resulting from significant waviness on the raceway surface. This phenomenon is the most common issue, and we must pay close attention to it in future.

c) Noise caused by improper use: For all types of bearings, if the raceway surface or rolling element surface of a deep-groove ball bearing is damaged, indented or corroded, this will result in periodic noise and vibration. When dust enters the bearing during operation, it generates contamination noise. This noise is non-periodic but is also accompanied by vibration; its intensity is variable and it comes and goes intermittently.

To resolve this, the locking sleeve was removed and the fit between the shaft and the inner ring was readjusted; following bearing replacement, the clearance was set to 0.10 mm. After reinstallation and restarting the fan, both the bearing vibration levels and operating temperature returned to normal.

Excessively small internal bearing clearance or poor design and manufacturing precision of components are the primary causes of elevated operating temperatures in deep-groove ball bearings. To facilitate the installation of fan equipment; disassembly and maintenance, bearing housings with inner rings fitted into tapered bores via a locking sleeve are commonly adopted in the design; however, problems can easily arise due to negligence during the installation process, particularly regarding the adjustment of the appropriate clearance. If the internal bearing clearance is too small, the operating temperature rises rapidly; conversely, if the fit between the inner ring’s tapered bore and the locking sleeve is too loose, the bearing is prone to failure and burnout within a short period due to loosening at the mating surfaces.

As for large bearings, in order to avoid difficulties during installation and removal, a clearance fit is sometimes employed for the rings bearing the rotational load. In such cases, the shaft must be made of a hard material, its surface carefully machined, and sufficient lubricant applied to minimise damage caused by slippage.