DRIVES , MOTORS & GEARS DEEP GROOVE BALL BEARINGS
NSK
NSK bearings adapted to meet servomotor demands
Available from NSK is a range of deep groove ball bearings adapted to the specific requirements of servomotors . Thanks to the development of special greases and a highly effective , low-friction seal , NSK solutions overcome the limitations of conventional electric motor bearings when used in servomotor applications .
For rolling bearings , servomotors present a challenge . With their frequent start , stop and reversing operations – as well as tiny corrective movements prompted by the sensor system – the typical motion profile of servomotors places bearings under intense stress . Furthermore , the frequent reversing and associated micro-vibration cause the lubricant film between the rolling element and running surface to be wiped away ( without the opportunity for afterflow re-lubrication ) to a greater extent than would be the case with continuous rotating bearings used in conventional electric motors .
Potential consequences include the generation of local micro-friction points on the raceways . This friction is caused when the lubricant film is insufficient and metal-tometal contact occurs between the raceway and ball .
To surmount these issues , NSK has developed a special grease known as EA7 . Compared with conventional greases , EA7 offers improved lubricating properties when subject to micro-vibrations . The grease also helps to ensure that the bearings operate with low frictional torque and correspondingly minimal power loss . In practice , the use of EA7 lubricated bearings in servomotor applications leads to longer operating life and the doubling of service intervals .
Another factor that increases the service life of servomotors is cleanliness during operation . If the bearing grease releases particles ( such as metal or sulphur ) that migrate to surrounding components , the encoder may become dirty . Over time , this contamination will render the motor incapable of detecting precise position . A further consequence of escaping lubricant
Servomotors present specific challenges that can compromise conventional electric motor bearings
can be slippage during braking , which again might promote inaccurate positioning .
To provide a solution to the contamination issue , NSK has developed another grease for servomotor applications , called LGU . Compared with lithium soap grease , LGU emits around 90 % less sulphur and metal particles , thus contributing to the long-term cleanliness of the bearing environment . The result : service intervals are extended by a factor of 1.5 .
NSK has developed special greases and seals for its range of servomotor-specific deep groove ball bearings
Companies building or integrating servomotors can choose whichever grease is most suitable . EA7 extends the service life of deep groove ball bearings when subjected to the micro movements typical of servomotors , while LGU minimises the release of particles on to surrounding components , preventing imprecise positioning . These two high-performance greases are available as an option for the deep groove ball bearing series that NSK has developed for use in servomotors .
A further feature of these bearings is NSK ’ s DW seal , which offers a combination of exceptionally good sealing and low frictional torque . With DW seals , the company ’ s designers have developed an effective solution to the conflicting requirements of reliable sealing and energy-efficient bearing operation .
The range of deep groove ball bearings for servomotors is described in a new catalogue entitled ‘ Bearings for Electric Motors ’, which is available in print or as a PDF download at : www . nsk-literature . com / en / industrial-motor-bearings www . nskeurope . com
Issue 47 PECM 47