Sealed Ball Bearing

SKF or any other maker of quality bearings can provide you with tables estimating the service life, taking into account such factors as rpm. weight load, ambient temperature and "service factor". You are far better off to build your device with an eye on quick servicing and replacement of bearings rather than a periodical replacement of a component that may not need it. I have sold bearings to a great variety of industrial users, and it has been my experience that frequent tinkering creates more down time than breakdowns ever do. If it ain't broke, don't fix it.

I assume that these are quite small motors (up to say 3 kW) as you should not be using sealed bearings in larger ones. I agree with guest that periodical - time based - maintenance is not a suitable strategy. On condition maintenance is far more economical. If these are small motors as suspected and you can not justify a condition monitoring programme then regular touch, feel and listen type monitoring will prevent most consequential damage. Your repair would then cost the same as a preventive time based repair but you will have a longer time between repairs.

If this could lead to major disruptions to a process then another strategy might be more appropriate.

ZZ- type bearings are being manufactured by so many known companies, like SKF you just quoted here. FAG is another one, and many more well known, you will find on the web - site through google or yahoo or wikipedia.

These bearings are Grease packed and sealed from both sides of bearings, hence one can use them, without any further provision of lubrication. If you know the working condition of these electric motors, you can assess the bearing B10-Life from their respective bearing catalogue, in term of Hours that bearing can safely run without any expected failure. As you said you want to be proactive and change the bearings before these fail, you may use such method as guideline.

BTW - when you do decide to change the bearings in a motor, do change all the bearings at a time, as a good practice, otherwise you will have some old as well as some new ones at a given time in a motor, which can defeat the purpose of changing the bearings in the first place. All the bearings in a given motor may not have same B10-life. Some will have higher and some lower life hours. You take the lower figure for deciding to change the bearings, as it is likely to fail first.

When assessing the bearing B10-life, one have to be familiar with the bearing details, more than just knowing the Bearing Numbers stamped on them, which are:- it's precision ( O , OO, OOO, in case of SKF bearings), it's Cage material, Lubrication to be used (in this case, it is Grease) etc. and the Bearing Loadings which can be a Resultant in case it's horizontally and vertically acting and speed in RPM and maximum working temperature at the motor. Good Luck.

ZZ is a shielded bearing not a sealed bearing. If you use a sealed bearing with rubber seals,under normal conditions, you can consider the bearing "lubed for life".

If the bearings are easily accessible, you can lubricate them with a small grease needle that can slip under the seal. You must be very careful not to damage the seal and not to allow any dirt into the bearing.

When I was working as a Plant Engineer we had a hand held device the would measure the roughness of the balls as they rotate. You had to know how many balls were in the bearing and set up an initial reading to compare. Worked real well.