Lubrication Systems and Grease
Bearing lubrication closed bearings
Smaller electric motors sizes are fitted with closed bearings (2Z) lubricated for life. These bearings must be replaced at the end of the service life (see Table 2). High temperature grease (i.e. 85°C) bearings are recommended for the replacement. The service life of these bearings is considerably longer than standard ball bearings with standard grease (70°C). Smaller sizes of rotor nl® electric motors are supplied with 2Z bearings with a WT (85°C) grease as standard. These are special bearings supplied by SKF with a temperature range of -40°C to +160°C and a service life higher than the average lithium complex greases. It is recommended replacing 2Z bearings every 4 years to prevent contamination as a result of ambient humidity and air pollution.
The rotor nl® electric motors that have been fitted with open bearings, are supplied with a lithium based grease as standard. Grease types based on lithium with mineral base oil can be used for re-lubrication. Good quality high temperature grease should be the preferred choice. If an electric motor is fitted with a special bearing and/or special grease (upon request), the bearing/grease information would be specified on the rating plate as well as the re-lubrication period. Re-lubrication must be done accordingly.
Open bearings with grease in bearing housing
Open bearings are used for larger electric motors sizes that have been fitted with ball bearings. The grease is based on lithium with mineral oil. These bearings can be re-lubricated many times. The old grease is collected in the used grease chamber of the bearing cap. Re-lubrication must take place whilst the electric motor is operating. The fact that the grease nipple and the grease canal may be both completely empty before the first re-lubrication must be taken into consideration. Certain degree of counter-pressure is felt through the grease gun during the re-lubrication indicating the amount of grease that have been applied during re-lubrication The used grease chamber needs removing and cleaning after a number of re-lubrications, where appropriate, at the same time with the replacement of the bearings. If bearings are subject to light load and have a long residual life left, they probably only need cleaning, used grease needs removing, bearings and bearing caps need partially refilling with grease (grease filling: bearings 50% and bearing caps 30% of the free space). Ex-e and Ex-n electric motors with open bearings and a used grease chamber are supplied without a lubrication nipple.
Open bearings with used grease discharge
If the electric motors are equipped with an automatic used grease discharge, unlimited re-lubrication is possible. The automatic used grease discharge works on an oscillating wheel principle that discharges the surplus grease to the used grease chamber. Closed used grease chambers must be open during re-lubrication and for one hour after the re-lubrication whilst the motor is operating to ensure that the surplus grease can be discharged.
The re-lubrication period depends mainly on the rotating speed, the shaft load, ambient factors and the electric motor installation. Re-lubrication must be carried out in accordance with the recommendations of the bearing and grease supplier. General guidelines can be found in the re-lubrication table. The values specified are for general guidance only and apply for horizontal motors with bearings temperature 70°C (for normal load and ambient temperature). The re-lubrication period must be halved for vertical electric motors. The re-lubrication period must be halved for every run when the temperature was 15°C above the bearing nominal temperature. Longer re-lubrication period is sometimes recommended if motors run at low temperatures; any re-lubrication period must not be longer than two times the recommended re-lubrication period. The re-lubrication period must be shortened when heavy or fluctuating shaft loads are applied.