This webinar recording focuses on:

• Motor assembly issues
• Electrical and mechanical inspection
• Static and run testing
• AC motors with ball, roller and sleeve bearings

Target audience: This webinar recording is most useful for service center mechanics, supervisors and engineers. The content will also be beneficial for machinists, managers and owners.

Chuck Yung
Especialista Sénior de Soporte Técnico de EASA

Cuando se rebabitan o se reemplazan cojinetes de deslizamiento, un paso importante durante el montaje consiste en verificar el contacto entre el cojinete y el muñón del eje que monta sobre el. El uso de cojinetes de deslizamiento auto alineables (también denominados esféricos o de ajuste esférico) hace que este paso sea casi innecesario. Aun así, los cojinetes de deslizamiento cilíndricos se deben inspeccionar para verificar que haya suficiente área de contacto.

Los cojinetes de deslizamiento, también conocidos como cojinetes de babbitt, de metal blanco o cojinetes lisos, han sido utilizados por más de 150 años. Para una explicación detallada sobre el diseño y funcionamiento de los cojinetes de deslizamiento solicite a EASA el documento de la convención del 2007: “Sleeve Bearing Repair Tips,” o el libro Mechanical Repair Fundamentals of Electric Motors, 2nd Edition.

Este es un artículo específico para verificar y corregir el patrón de desgaste al momento de instalar cojinetes nuevos en un motor eléctrico. Ajustar cojinetes no es difícil, solo se requiere algún conocimiento básico, Un parte interesante de la historia es el kit de herramientas suministrado con el antiguo automóvil Ford -Modelo A, que incluía un cuchillo para babbitt para rascar los cojinetes del cigüeñal. Imagine desmontar el motor de su auto en el camino, para retirar y ajustar los cojinetes de babbitt.

Tom Bishop, PE
Especialista Sénior de Soporte Técnico de EASA

La lubricación es requerida para reducir la fricción entre los elementos rodantes y las partes estáticas de los rodamientos. Al hacer esto, el lubricante también ayuda a prevenir incrementos de temperatura excesivos y a disipar parte del calor generado. En este artículo discutiremos algunas de las características y propiedades clave de los aceites y grasas lubricantes.

Tom Bishop, P.E.
EASA Senior Technical Support Specialist

This webinar recording reviews electric motor bearing grease and oil lubrication frequency and quantity, as well as procedures – and the steps to be sure to get all of this right. 

• Grease and oil lubrication frequency and quantities for ball and roller bearings
• Grease and oil lubrication procedures for ball and roller bearings
• Oil lubrication frequency and quantities for sleeve bearings
• Oil lubrication procedures for sleeve bearings

This recording is intended for mechanical technicians, field service technicians, shop supervisors and engineering staff.

Chuck Yung
EASA Senior Technical Support Specialist

Horizontal and vertical motors have uniquely different requirements for endplay, while sleeve bearing machines bring their own challenges. 

Topics covered in this recording include:

• Horizontal machines with rolling element bearings
  • Ball bearings
  • Roller bearings
  • Determining the required endplay
  • How to correctly measure endplay
• Sleeve bearing machines
  • End float requirements
  • Role of the coupling method in end float
  • Special methods to control end float

This presentation is intended for owner/managers, shop supervisors, machinists, service center technicians, and safety directors.

Chuck Yung
EASA Senior Technical Support Specialist

When sleeve bearings are rebabbitted or replaced, an important step during assembly is to check the contact between the sleeve bearing and the journal which rides in it. The use of self-aligning sleeve bearings (also called spherical or ball fit) renders this step almost unnecessary. Still, cylindrical sleeve bearings should be inspected to make sure the contact area is sufficient.   

Sleeve bearings, also known as babbitt bearings, plain bearings or white metal bearings, have been in use for over 150 years. For a detailed explanation of sleeve bearing design and operation, request the EASA 2007 Convention paper, “Sleeve Bearing Repair Tips,” or see Mechanical Repair Fundamentals of Electric Motors, 2nd Edition.  

This article is specific to checking and correcting the wear pattern when installing a new sleeve bearing in an electric motor. Fitting a sleeve bearing is not difficult; it just requires some basic knowledge. An interesting bit of history: the toolkit provided with the old Model A Ford automobile included a babbitt knife for scraping crankshaft bearings. Imagine dismantling your engine alongside the road to remove and fit the babbitt bearings.

En toda reparación mecánica, la capacidad para desmontar, reparar y volver a montar el motor de forma apropiada sin dañar innecesariamente ninguna de sus piezas es fundamental. Esto suena sencillo, sin embargo, durante el proceso de desarme se cometen demasiados errores costosos.

Si todos los motores entraran “como nuevos”, la tarea sería más simple, aunque esto no sería garantía de que el montaje del motor fuera adecuado.

Cuando un centro de servicio recibe un pago por reparar un equipo, quiere que este permanezca en funcionamiento, ya que, si el equipo falla dentro del período de garantía, deberá asumir el costo de volver a repararlo. Por lo que tiene sentido realizar la reparación correcta la primera vez.

Los procedimientos de reparación, así como los propios motores, son afectados por los cambios en la tecnología. Este libro intenta incluir las últimas tecnologías comprobadas. En muchos casos, los métodos de reparación tradicionales aún pueden ser la alternativa más práctica. Las opciones presentadas a lo largo de este libro están destinadas a ayudar a los técnicos a seleccionar el método de reparación correcto, reconociendo que la decisión final recae en el propietario del equipo.

Algunas veces los métodos de reparación pierden popularidad, no porque aparezcan métodos mejores sino debido a técnicas deficientes. Otros métodos de reparación son adecuados para algunas aplicaciones, pero no para otras. Es trabajo del reparador decidir cuál será el mejor método para cada caso.

Este libro se encuentra dividido en secciones para los componentes básicos del motor con métodos de reparación y consejos dispersos por todas partes. Donde resulte práctico, se discuten también las causas de fallo. Esto ayudará a los técnicos a seleccionar el método de reparación más apropiado para cada aplicación en particular. La información presentada se basa en publicaciones de EASA y en revistas técnicas y literatura suministrada por fabricantes de motores, proveedores y centros de servicio establecidos.

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Tabla de contenido

• Terminología del motor
• Aplicaciones del motor y encerramientos
• Procedimientos de inspección y prueba
• Consejos para desmontar motores
• Rodamientos
• Alojamientos de rodamientos, orificios de eje, sellos y ajustes
• Ejes
• Rotores
• Ensamble del motor
• Accesorios y cajas de conexiones del motor
• Dinámica del motor
• Vibración y geometría del motor
• Corrientes por el eje/rodamientos
• Consideraciones especiales para motores a prueba de explosión
• Fallos en las componentes mecánicas
• Reparaciones misceláneas

Esta obra contiene muchas sugerencias sobre el manejo apropiado de las diferentes partes de un motor para minimizar los daños durante el proceso de reparación. Sin embargo, es imposible desarrollar un listado que las incluya todas.

En cambio, el principio básico de tomarse el tiempo para usar la herramienta adecuada y por lo general el procedimiento apropiado guiará a los técnicos por el camino correcto.

Chuck Yung
EASA Senior Technical Support Specialist

There are applications where the end float inherent to a sleeve bearing machine is not desirable, and some means of limiting the axial movement is needed. This is usually accomplished by selecting an appropriate coupling and relying on the driven equipment to prevent axial movement of the motor shaft. 

The gear-hub style of coupling can be end-float limited by installing a “hockey-puck” spacer. The grid-style coupling can be limited by spacers inserted on both sides. 

Regardless of coupling style, unless the driven equipment has some internal means to limit end float, there are circumstances where some external means of preventing axial movement is needed.

Chuck Yung
Technical Support Specialist
Electrical Apparatus Service Association, Inc.
St. Louis, MO

This paper, authored by Chuck Yung, provides a comprehensive overview of recent innovations in mechanical repair procedures for rotating electrical equipment. It assumes the reader has a basic understanding of mechanical repair and aims to introduce new techniques that have evolved in response to industry changes. The paper covers various topics, including bearing housing repair, insulating housings, and balancing rotors, highlighting their interconnectedness.

One significant issue addressed is shaft currents, particularly those caused by VFD-fed motors. Traditional methods of insulating bearings are ineffective against these currents, necessitating new approaches such as ceramic bearings, grounding brushes, and insulating housings. The paper explains the difference between traditional shaft currents and those induced by VFDs, emphasizing the need for insulating both bearings to prevent current flow.

The paper also discusses rotor balancing, noting that ceramic coatings on bearing journals can be damaged during the process. It recommends supporting rotors on the nearest shaft fit to avoid damaging the ceramic material. Additionally, it introduces Nylon as a new material for insulating bearing housings, detailing its application and potential issues related to bearing failure and warranty concerns.

Insulating sleeve bearings presents unique challenges due to high temperatures involved in rebabbitting. The paper outlines various insulation materials and methods, including resin-impregnated fiberglass banding tape, 3M Scotchply, micarta bond, and epoxies. Each method's advantages and drawbacks are discussed, providing practical insights for service centers.

The importance of balancing rotors to tight limits is emphasized, as unbalance is a major component of vibration spectra. The paper explains the relationship between magnetic forces, air gap, and shaft deflection, highlighting the need for precise rotor balancing to prevent excessive vibration and potential damage. Special cases, such as balancing rotors with flywheels, are also covered, underscoring the importance of maintaining perpendicularity to the rotating axis.

In summary, Chuck Yung's paper offers valuable insights into mechanical repair techniques for rotating electrical equipment, addressing key issues such as shaft currents, rotor balancing, and bearing insulation. It provides practical recommendations for service centers to improve repair quality and efficiency.

Key Points Covered:

• Shaft currents and their impact on bearings
• Insulating methods for bearings and housings
• Rotor balancing techniques and challenges
• Insulating sleeve bearings with various materials
• Importance of precise rotor balancing to prevent vibration

Key Takeaways:

• VFD-fed motors require new insulation methods for bearings
• Ceramic coatings on bearing journals need careful handling during balancing
• Nylon is a promising material for insulating bearing housings
• Various insulation materials have specific advantages and drawbacks
• Precise rotor balancing is crucial to prevent excessive vibration and damage

This version of Principles of Medium & Large AC Motors manual is now available to address applicable IEC standards and practices. This 360-page manual was developed by industry experts in Europe along with EASA's engineering team. (The "original" version of this book based on NEMA standards remains available as a separate document.)

This manual includes drawings, photos and extensive text and documentation on AC motors, including how they work, information on enclosures, construction on components and applications. Many of the principles included apply to all AC motors, especially those with accessories that are associated with larger machines in the past (such as encoders, RTDs, thermostats, space heaters and vibration sensors).

While the manual covers horizontal and vertical squirrel-cage induction motors in the 37 to 3,700 kW (300 to 5,000 hp) range, low- and medium-voltage, most of the principles covered apply to other sizes as well. 

This valuable instructional/resource manual is available in printed and downloadable versions, and focuses primarily on IEC motors.

Sections in the manual include:
(Download the PDF below for the complete Tables of Contents)

• Motor nomenclature & definitions
• Motor enclosures
• Typical motor applications
• Safety & handling considerations
• Basic motor theory
• Motor standards
• Stators
• Squirrel cage rotors
• Shafts
• Bearings & lubrication
• Motor accessories & terminal boxes
• Test & inspection procedures
• Motor alignment, vibration & noise
• Storage procedures
• Synchronous machines

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PRINTED BOOK DOWNLOADABLE PDF

This book is also available focusing on NEMA Standards — in both English and Español.

NEMA - English NEMA - Español

Chuck Yung
Especialista Sénior de Soporte Técnico de EASA

Existen ocasiones en las que una aplicación requiere que un motor soporte una carga radial para la que los cojinetes de deslizamiento no son adecuados. En casos como bajas revoluciones, carcasas inusuales, etc., puede ser conveniente convertir el motor del cliente montado sobre cojinetes de deslizamiento envés de obtener un motor de repuesto con rodamientos de bolas / rodillos. Este artículo contiene procedimientos sugeridos y advertencias sobre problemas potenciales relacionados con dichas conversiones.

Primero, inspeccione las tapas del motor para asegurarse de que tengan la rigidez mecánica suficiente para soportar la carga y suprimir la vibración (vea la Figura 1). Si las tapas carecen de rigidez, puede que sea necesario utilizar tapas nuevas fabricadas con un material más grueso. En otros casos, se puede utilizar un inserto para reforzar la tapa existente.

By Chuck Yung
EASA Senior Technical Support Specialist

It’s fair to say that one’s outlook on life is colored by experience. A good example of this with sleeve bearing motors is the question, “What’s the proper clearance between a shaft and the sleeve bearing it rides in?” Chances are each of us has a rule of thumb for this, probably related to shaft diameter. Some of these may look familiar:

• One thousandth, plus 1 per in. of diameter
• Two thousandths, plus 1 per in. of diameter
• 0.0015 in. per in. of diameter
• 0.002 in. per in. of diameter

They can’t all be right, yet many of us may have used one of these rules (probably not the same one, either!) with great success. Which one, if any, is correct? The answer depends on the application.

READ THE FULL ARTICLE

Chuck Yung
EASA Technical Support Specialist

Member question: Can you settle a disagreement about the subject of sleeve bearing clearance? We have several contradictory guidelines, some of them from manufacturers. Which is best?

It is fair to say that our outlook on life is colored by experiences. In our industry, those experiences often are shaped by the customers we serve. A good example is this question about the proper clearance between a shaft and the sleeve bearing it rides in.

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.

Chuck Yung
EASA Senior Technical Support Specialist

There are times when an application calls for a motor to carry a radial load for which sleeve bearings are not suitable. In cases such as low rpm, unusual frames, etc., it may be desirable to convert a customer's existing sleeve bearing motor rather than obtaining a ball/roller replacement motor. This article contains suggested procedures as well as cautions about potential problems with such conversions.  

First, inspect the end brackets to ensure they are mechanically rigid enough to support the load and suppress vibration (see Figure 1). If the end brackets lack rigidity, it may be  necessary to use complete fabricated replacements using thicker material. In other cases, gusseting can be used to stiffen the existing bracket.