Proper lubrication of electric motor bearings determines 70–80% of its service life. According to statistics from the Elektromotors service center in Tashkent, more than half of the emergency failures of bearing units are not associated with wear of the steel itself, but with incorrectly selected grease, incorrect replenishment intervals, or a banal excess of plastic material in the shield cavity. In this article, engineers analyze which lubricants to use for asynchronous machines 0.55–315 kW, how to calculate the interval based on revolutions and bearing size, and how to avoid common mistakes during maintenance.
What lubricants are used for electric motors
For rolling bearings of industrial electric motors, greases with lithium, lithium complex or polyurea thickeners are used. The choice depends on the rotation speed, operating temperature of the unit and environmental conditions - in the workshops of Tashkent, where in summer the air temperature reaches +45 °C, the requirements for temperature stability are especially stringent.
- Litol-24 is a universal lithium lubricant for general industrial engines with frequencies up to 3000 rpm and unit temperatures up to +120 °C. Cheap, accessible, but when overheated above 130 °C it quickly liquefies and leaks.
- CIATIM-201 / CIATIM-221 - low-temperature lubricants for low-speed engines of crane and lifting equipment, operating range from −60 to +90 °C. Suitable for engines in open areas in winter.
- Mobil Polyrex EM is a polyurea lubricant specifically for electric motors: long service life, high stability up to +170 °C, low sparking. Standard for IE2/IE3 NEMA and IEC motors
- SKF LGHP 2 - premium polyurea grease for high-speed and high-temperature bearings, range from −40 to +150 °C, service life 2.5 times longer than lithium.
The fundamental mistake is to mix lubricants with different thickeners. Lithium + polyurea causes delamination and loss of the supporting film within 200–400 hours of operation.
How to choose a lubricant based on speed, temperature and load
The selection is made according to three parameters: speed factor n × dm (where n is rpm, dm is the average bearing diameter in mm), the operating temperature of the outer ring and the nature of the load (radial, axial, impact).
- For n × dm up to 300,000 - lithium greases are suitable (Litol-24, Shell Gadus S2).
- For n × dm from 300,000 to 500,000 - lithium complex (Mobilith SHC 100) or polyurea.
- For n × dm over 500,000 - only polyurea SKF LGHP 2 or Mobil Polyrex EM.
- The temperature of the node is above +110 °C - exclude Litol, switch to synthetics.
- Shock and vibration loads (cranes, crushers) - lubricants with EP (Extreme Pressure) additive.
For motors of crane mechanisms, vibration and reverses are taken into account separately - here you need a special product, the selection of which we write about in materials on repair of crane electric motors.
Table of lubrication intervals by speed and bearing size
The lubricant replenishment interval is calculated using a simplified SKF formula, but for most industrial machines the tabular values are sufficient. Below are practical intervals for engines in mode S1 (long-term) at a unit temperature of up to +70 °C.
| Bearing (internal d, mm) | 1500 rpm | 3000 rpm | 3600 rpm |
|---|---|---|---|
| 6206 (30 mm) | 18,000 h | 9,000 h | 7,000 h |
| 6210 (50 mm) | 14,000 h | 7,000 h | 5,500 h |
| 6312 (60 mm) | 11,000 h | 5,500 h | 4,000 h |
| 6316 (80 mm) | 8,000 h | 3,800 h | 2,800 h |
| 6320 (100 mm) | 5,500 h | 2,500 h | 1,800 h |
For every +15 °C above +70 °C the interval is halved. For dusty industries (cement, flour mills) the interval is also divided by 2.
Step-by-step lubrication procedure
- Clean the grease fitting from dust and old dried grease with a rag soaked in white spirit.
- On engines with a drain plug, open the drain hole at the bottom of the shield - this will allow old grease to escape and will not create excess pressure.
- Start the engine at idle speed and apply lubricant in small portions (10–15 g) with a syringe while the shaft is running. This distributes the material evenly across the raceways.
- The dose is calculated as G = 0.005 × D × B (grams), where D is the outer diameter of the bearing, B is the width. For 6312 this is about 12 g.
- After replenishing leave the drainage hole open for 20-30 minutes during operation - excess lubricant will come out on its own.
- Close the plug, wipe the assembly, record the date and brand of lubricant on the service card.
Typical errors and signs of improper lubrication
Over 12 years of operation, our service in Tashkent has recorded repeated personnel errors that reduce bearing life by 3–5 times.
- Excessive lubricant. The shield cavity is filled more than 50–60%. The bearing overheats by 20–30 °C, the lubricant foams and leaks onto the winding - then it almost always requires rewinding the motor winding.
- Lack of lubrication. Grinding, metallic squealing at high frequencies, an increase in the temperature of the outer ring above +85 °C, the appearance of tarnish on the rings during disassembly.
- Mixing of incompatible brands. Delamination, oil release, black marks on the shield.
- Lubrication through an uncleaned grease gun. Abrasive particles fall directly into the rolling zone - development of tracks in 500–800 hours.
- Ignoring tightness.Moisture and dust turn the lubricant into an abrasive paste.
If you notice vibration or heating, do not delay electric motor diagnostics: early lubricant replacement is 8-10 times cheaper bearing replacement.
When a service call is required
If the engine has operated beyond the design interval without maintenance, noise or strong vibration is observed - simply replacing the lubricant is not enough. In such cases, it is necessary to troubleshoot the unit, check the seats in the shields and, if necessary, replace the bearings themselves, followed by balancing the rotor.
Need help? Elektromotors engineers in Tashkent will select a lubricant for your engine fleet, draw up a maintenance schedule and perform service within 24 hours. Contact us via contact page - consultation on lubricant selection is free.