Bearing lubrication is the cornerstone of ensuring optimal motor performance. Proper lubrication serves to reduce wear by maintaining separation between rolling surfaces, dissipating friction-induced heat, safeguarding against contaminants, averting corrosion, and securing rolling elements during assembly. Astonishingly, over 50% of bearing failures can be attributed to inadequate lubrication. This highlights the significance of delving into the insights provided in the remainder of this article.
Available Lubricant Varieties
Greases available today comprise base oils (mineral or synthetic), thickeners (such as polyurea, lithium), and assorted additives (anti-oxidants, rust inhibitors, anti-foaming agents, etc.). Regardless of operating conditions, grease degrades over time due to factors like oxidation, oil bleeding, mechanical stress, and evaporation. Consequently, for most bearings, eventual regreasing is necessary. Prominent lubricant categories include:
- Lithium Soap Based Grease: Boasting excellent heat and water resistance, along with mechanical stability.
- Calcium Soap Based Grease: Exhibiting superior water resistance, yet somewhat lower heat resistance.
- Sodium Soap Based Grease: Excelling in heat resistance, though somewhat less in water resistance.
- Non Soap Based Grease: Showcasing remarkable heat resistance.
- Polyurea Grease: A preferred choice for electric motor bearings due to high-temperature performance, inherent anti-oxidative properties, and robust shear stability. Especially effective in sealed bearings.
- Oil: Different oil additives may not be compatible. Adhering to the manufacturer-recommended oil for each relubrication is advised. If a change is necessary, consult the manufacturer for compatibility.
Proper Relubrication Steps
Executing bearing relubrication demands adherence to eight straightforward steps:
- Ensure the motor is running or recently turned off while still hot (under operational conditions, grease viscosity decreases).
- Confirm the grease gun contains the suitable lubricant for the targeted bearings.
- Clean the fill and drain fitting surroundings to prevent contaminant introduction.
- Remove the drain fitting to enable excess grease escape.
- Leave the drain plug out throughout the regreasing process.
- While the motor runs at operating temperature, gradually add the recommended grease quantity or monitor until it reaches the relief tube.
- Upon substantial purging of excess grease, reinstall the drain plug and clean any surplus around the drain.
- Post-installation, establish a baseline for motor noise and vibration. Regularly assess these measurements; significant changes warrant bearing lubrication inspection.
(Note: Filling bearings with grease should be one of the final steps in bearing replacement to ensure minimal contamination.)
Determining Proper Lubricant Quantity
For the most accurate measurements, consult your motor manufacturer’s guidelines. If unavailable, gradually pump grease until clean grease emerges from the discharge port. Avoid rapid pumping, as it could force grease through bearing seals and into the motor cavity.
Optimal Relubrication Timing
Motor manufacturer recommendations should guide when, how much, and which type of grease to employ. Many grease manufacturers rely on a complex mathematical equation for scheduling:
Frequency (hours) = (Bearing diameter in mm × F bearing type × F temperature) / F contamination
These factors incorporate bearing type, operating temperature, and contamination level. If math isn’t your forte, a personalized schedule based on motor knowledge and records can be formulated for practicality.
Shielded and Sealed Bearings
Single shielded bearings necessitate regreasing according to manufacturer instructions. However, double shielded bearings usually adhere to the “Lubricated for Life” principle and do not require regreasing. Sealed bearings are fitting for high-contamination settings. They are typically designated for lower-speed motors and boast an anticipated life span of three years under the “Lubricated for Life” category, obviating the need for regreasing.
