Chuck Yung
Technical Support Specialist
Electrical Apparatus Service Association
St. Louis, MO
The paper "Sleeve Bearing Repair Tips" by Chuck Yung, presented at the EASA Convention 2007, provides a comprehensive guide to understanding, repairing, and maintaining sleeve bearings in electric motors. Sleeve bearings, also known as babbitt bearings, plain bearings, or white metal bearings, are used in large motors where rolling-element bearings cannot achieve the desired bearing life. This paper explains the principles of sleeve bearings, factors influencing their design, and practical tips for repair and maintenance.
Sleeve bearings are typically made of tin- or lead-based babbitt and are machined slightly larger than the shaft. They are lubricated by a continuous film of oil, which minimizes surface wear and cools the parts. The major factors influencing sleeve bearing design include the weight to be supported, peripheral speed of the shaft journal, viscosity of the lubricant, and operating temperature. Designers aim to keep sleeve bearing load pressure around 45 psi, compared to higher pressures in internal combustion engines.
Proper clearance between the shaft and bearing is crucial for stable shaft position. Insufficient clearance results in excessive heat due to friction, while excessive clearance can lead to unwanted movement and vibration. The optimal clearance is governed by factors such as shaft orientation (horizontal or vertical), weight, peripheral speed, length-to-diameter ratio, oil viscosity, and load. Horizontal machines typically require more clearance than vertical machines due to shaft deflection and other factors.
Labyrinth seals are important for retaining oil and preventing leaks. The closer the clearance between the shaft and labyrinth seal, the better the seal. However, running contact between the shaft and labyrinth can cause damage and high vibration levels. The paper provides guidelines for labyrinth seal clearance, emphasizing that it should be slightly more than the bearing clearance.
Lubrication is key to sleeve bearing life, with oil rings or forced-oil systems providing continuous oil flow to the bearing. Oil viscosity can affect the stiffness of the shaft/bearing assembly, and the recommended oils should be used unless modifications are made in consultation with the OEM or customer.
Fitting a new sleeve bearing involves establishing a wear pattern by spinning the rotor with the bearing journal dry or lightly oiled. The objective is to achieve a minimum of 60% contact centered in the bottom half of the bearing, with no contact at the corners or top. The paper advises against using lapping compound for fitting, as it can embed in the babbitt and wear the shaft journal.
During the test run, monitoring bearing temperature and vibration is crucial, especially for 2-pole machines with higher surface speeds. The paper recommends using a vibration analyzer to detect early signs of bearing friction and prevent damage. End float and magnetic center should be clearly marked during the final test run, and total end float should be documented.
The paper concludes with general guidelines for sleeve bearing clearance, emphasizing that different applications require different clearances. It advises contacting the manufacturer or EASA Technical Support for help with unusual sleeve bearings.
Key Points Covered:
- Principles and design factors of sleeve bearings
- Importance of proper clearance between shaft and bearing
- Guidelines for labyrinth seal clearance
- Lubrication methods and oil viscosity considerations
- Fitting procedures for new sleeve bearings
- Monitoring bearing temperature and vibration during test runs
- End float and magnetic center considerations
Key Takeaways:
- Sleeve bearings require careful design and maintenance to ensure proper function.
- Proper clearance is crucial to prevent excessive heat and unwanted movement.
- Labyrinth seals play a key role in retaining oil and preventing leaks.
- Continuous lubrication is essential for sleeve bearing life.
- Fitting procedures should avoid using lapping compound to prevent wear.
- Monitoring bearing temperature and vibration can prevent damage during test runs.
- Different applications require different sleeve bearing clearances, and expert advice should be sought for unusual cases.
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