The demand for a silent electric motor, that is, one that operates with very little noise and vibration, was the main application that led engineers to develop and commercialize low-noise ball bearings. As a result, the manufacturing equipment industry has coined the term electric motor quality (EMQ) to identify this special class of low-noise bearings.
Today, a wide range of applications require the use of EMQ bearings.
Where does the noise come from?
Noise in a rotating bearing is the audible component of vibration and a function of rotational speed. The greater the vibration, the shorter the bearing's service life; Furthermore, excessive vibrations can damage the engine or machinery.
Vibration is caused by several factors, including: rough or damaged raceway and ball surfaces, inadequate geometric tolerances (roundness, concentricity, eccentricity and/or parallelism), contamination, inadequate lubrication, incorrect radial clearance and shaft and shaft adjustments . housing.
How we reduce noise
An EMQ bearing is produced by superfinishing the bearing contact surfaces to a mirror finish, which ensures very smooth rotation. Equally important is maintaining tight control of the geometric tolerances of the bearing components.
Particle contamination in a bearing increases the noise level; however, engineers can prevent this by using seals to keep out contaminants and taking care to only use “clean” lubricants that have been filtered to remove large solid particles. It is also essential to specify the correct radial clearance: it must be as close to zero as possible, without causing the bearing to lock during rotation. If the radial clearance is too loose, excessive vibration will occur and cause noise.
As with any type of bearing, the service life of EMQ bearings also depends on external factors. Extreme care must be taken during handling and assembly as impact forces resulting from a bearing being dropped or impacted during installation can create small dents in the races, called brinelling . Brinelling creates excessive vibration during rotation, which ultimately leads to bearing failure.
Shaft and housing roundness can also contribute to noise, especially in smaller, thin-section bearings. Poor roundness can distort bearing rings during installation, preventing smooth rotation and generating noise.
EMQ bearing manufacturers typically perform a 100% noise inspection on bearings using special equipment called an Anderon Gauge (or similar tool). This device measures the vibration speed (displacement x frequency) of a rotating bearing in Anderon units (equivalent to 7.5 microns per second) in three frequency ranges: low, medium and high. The higher the vibration speed, the louder the bearing.
Finally, it is important to highlight the fact that EMQ standards are not uniform among bearing manufacturers, except those located in China, where a national standard exists. Despite this lack of uniformity, however, you can be assured that a manufacturer's EMQ assessment (based on sufficient empirical evidence) indicates that the bearing is suitable for use in electric motors.
