Chuck Yung 
EASA Technical Support Specialist 

While shaft currents are not a new problem (papers on the subject date back prior to 1930), what is “new” is our understanding of how to solve the problem. Shaft currents have been described as shaft voltages, circulat­ing currents, bearing currents and circulating voltages. This article will refer to the phenomenon as “shaft currents” because it is the current that causes the damage.

When a conductor is passed through a magnetic field, voltage is induced into the conductor. 

It is not the voltage that damages a bearing, but rather the current. (Fuses fail because the current is too high, not the voltage.) We don’t have a practical way to measure the current through the shaft, so we measure the magnitude of the voltage instead. 

This presentation introduces you to ANSI's new shaft alignment standard. Topics covered include:

• A discussion of alignment Quality grades, AL 1.2, AL 2.2, AL 4.5
• Shaft alignment tolerances
• Issues affecting measurements
• Conditions affecting alignment stability

Target audience: This presentation benefits service center technicians and supervisors looking to improve shaft alignment knowledge and skills. 

Electric motor repair report form to collect basic motor, bearing, shaft, coupling information.

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

Occasionally an end user wants to take a motor designed for horizontal mounting and use it in a vertical position. In this article, we will address some of the key mechanical factors that should be considered when applying a horizontal ball bearing motor in a vertical mounting position. Figure 1 illustrates a horizontal motor in a vertical shaft down position.

These key factors include:

• Axial thrust load capacity of bearing supporting rotor weight
• Rotor weight
• Weight of output shaft attachments
• Axial thrust from direct connected driven equipment
• Bearing lubrication paths
• Bearing lubricant retention
• Shaft up or shaft down orientation
• Ingress protection
• Locking axial thrust bearing

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

De vez en cuando un usuario final quiere utilizar un motor diseñado para montaje horizontal en posición vertical. En este artículo, trataremos algunos factores mecánicos clave que deben ser considerados cuando se utiliza un motor horizontal con rodamientos de bolas en una aplicación en la que trabaja en montaje vertical. La Figura 1 ilustra un motor horizontal en posición vertical con el eje hacia abajo.

Los factores clave incluyen:

• Capacidad de carga axial del rodamiento que soporta el peso del rotor.
• Peso del rotor
• Peso de los elementos acoplados al eje de salida
• Empuje axial de los equipos de impulsión acoplados directamente
• Trayectorias de lubricación de los rodamientos
• Retención del lubricante de los rodamientos
• Orientación del eje: Hacia abajo o hacia arriba
• Protección contra ingreso
• Fijación axial del rodamiento de empuje

Tom Bishop
Technical Support Specialist
Electrical Apparatus Service Association
St. Louis, MO

The paper "Dealing with Shaft and Bearing Currents" by Tom Bishop, presented at the EASA Convention 2007, addresses the critical issues related to shaft and bearing currents in electric motors and generators. It begins by explaining the symptoms of bearing currents, which often manifest as audible noise from the bearings, indicating advanced stages of failure. Visual inspection of failed bearings may reveal fluting of the races, frosting of the balls or rollers, and a dull grey or dark "smoky" finish on the bearing surfaces.

The paper categorizes current damage into three types: electric pitting, fluting, and micro-cratering. Electric pitting is characterized by single crater damage, typically seen in DC applications like railway traction motors. Fluting appears as multiple lines across the bearing races, caused by mechanical resonance vibration. Micro-cratering, the most common type of damage in motors powered by variable frequency drives (VFDs), results in a dull surface with molten pit marks.

Bishop explains that shaft voltage becomes problematic when it leads to bearing current, which can discharge through the lubricant film on the bearings, causing damage. He describes methods for determining if damaging current levels are present, such as measuring the voltage from the shaft to the motor frame. If the shaft to frame voltage exceeds certain thresholds, it indicates potentially harmful bearing currents.

The paper identifies several causes of damaging currents, including magnetic dissymmetry, electrostatic discharges, and capacitive coupling between the stator windings and rotor. Magnetic dissymmetry is often associated with larger motors that have segmented laminations, leading to asymmetric flux and circulating currents. Electrostatic discharges can occur in applications like belt drives and fans, while capacitive coupling is common in motors supplied by VFDs.

Bishop outlines various solutions to eliminate or control shaft and bearing currents. These include insulating bearings, using shaft grounding brushes, and installing filters or reactors between the drive and motor. Insulating bearings can be achieved through methods such as insulated housings, insulated bearing journals, and ceramic rolling elements. Shaft grounding brushes provide a low resistance path to divert current away from the bearings. Filters and reactors help reduce the magnitude of bearing currents by modifying the VFD output waveform.

The paper also discusses the importance of grounding and the use of stranded, low-impedance ground cables to establish a dedicated common ground path between the motor and drive. Proper grounding helps minimize the common mode voltage and reduce the risk of damaging bearing currents.

In conclusion, Bishop emphasizes the need for condition monitoring to detect early signs of bearing current damage. Techniques such as vibration analysis, lubricant analysis, and microscopic analysis can help identify and address issues before they lead to complete bearing failure.

Key Points Covered:

• Symptoms of bearing currents and types of current damage
• Methods for determining if damaging current levels are present
• Causes of damaging currents: magnetic dissymmetry, electrostatic discharges, capacitive coupling
• Solutions to eliminate or control shaft and bearing currents: insulating bearings, shaft grounding brushes, filters, reactors
• Importance of grounding and using stranded, low-impedance ground cables
• Condition monitoring techniques: vibration analysis, lubricant analysis, microscopic analysis

Key Takeaways:

• Bearing currents can cause significant damage to motor bearings, often indicated by audible noise and visual signs like fluting and frosting.
• Determining the presence of damaging currents involves measuring shaft to frame voltage and identifying thresholds.
• Various causes of damaging currents include magnetic dissymmetry, electrostatic discharges, and capacitive coupling.
• Effective solutions include insulating bearings, using shaft grounding brushes, and installing filters or reactors.
• Proper grounding and the use of stranded ground cables are crucial for minimizing common mode voltage.
• Condition monitoring techniques help detect early signs of bearing current damage and prevent complete bearing failure.

Cyndi Nyberg 
Former EASA Technical Support Specialist

There are a number of ways that the shaft of an electric motor can become magnetized in service. The most likely culprit is electric current through the motor and shaft, either from internal dissymmetry, welding or from a variable frequency drive. It can also be caused by electrical faults in the system, or even a lightning strike. 

We of course know that shaft voltages and the associated currents can cause bearings to fail. A typical ball bearing failure from shaft currents is shown in Figure 1. when a shaft is magnetized, it can further lead to bearing failures, unless something is done to elimi­nate the residual magnetism. The first reason for bearing failures is that the residual magnetism can cause shaft currents, which can quickly lead to bearing failures. But in addition, a magnetized shaft will attract bits of metal to the bearings. This reduces bearing life because it damages the bearing surfaces. 

The magnetism in the shaft may be strong enough that a screwdriver that sticks to the shaft. In fact, this is the most simple test to check for a magnetized shaft. 

Steve Skenzick
HPS Electrical Apparatus Sales & Service

En mi centro de servicio hemos visto problemas en ejes previamente reparados que fueron metalizados. En estos casos recibimos motores para revisión. Después de la inspección y de medir los ajustes de los rodamientos en el eje, encontramos algo que simplemente no se “sentía” bien. Podríamos decir por la apariencia que los ejes habían sido reparados antes de la revisión actual.

REVISED September 2022!

The EASA Technical Manual, containing more than 900 pages of information specific to electric motor service centers, is available FREE to EASA members as downloadable PDFs of the entire manual or individual sections. The printed version is also available for purchase. Each of the 13 sections features a detailed table of contents.

VIEW, DOWNLOAD OR PURCHASE

DESCRIPTION
Filled with practical information, this 118-page handbook (3.5" x 6", 9cm x 15cm) makes a great “give-away” item for your customers and potential customers! Buy this great resource as is OR custom brand your company logo and information on the cover to turn it into a great marketing piece for your salespeople!

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TABLE OF CONTENTS

MOTOR DATA–ELECTRICAL
Standard Terminal Markings and Connections
DC Motors and Generators (NEMA & IEC Nomenclature)
Field Polarities of DC Machines
General Speed-Torque Characteristics
Full-Load Efficiencies of Energy Efficient Motors
Full-Load Efficiencies of NEMA Premium™ Efficient Motors
Effect of Voltage Variation on Motor Characteristics
Power Supply and Motor Voltages
Effect of Voltage Unbalance on Motor Performance
Starting Characteristics of Squirrel Cage Induction Motors
Allowable Starts and Starting Intervals

MOTOR DATA–MECHANICAL
Suffixes to NEMA Frames
NEMA Frame Assignments–Three-Phase Motors
NEMA Frame Dimensions–AC Machines
IEC Mounting Dimensions–Foot-Mounted AC and DC Machines
IEC Shaft Extension, Key And Keyseat Dimensions–Continuous Duty AC Motors (Inches)
NEMA Shaft Extension And Keyseat
Dimensions–Foot-Mounted DC Machines (Inches)
NEMA Frame Dimensions–Foot-Mounted DC Machines (Inches)
NEMA Frame Dimensions–AC Machines (mm)
IEC Mounting Dimensions–Foot-Mounted AC and DC Machines (mm)
IEC Shaft Extension, Key and Keyseat Dimensions–Continuous Duty AC Motors (mm)
NEMA Shaft Extension and Keyseat Dimensions–Foot-Mounted DC Machines (mm)
NEMA Frame Dimensions–Foot-Mounted DC Machines (mm)

MOTOR CONTROLS
Power Factor Improvement of Induction Motor Loads
Capacitor kVAR Rating for Power-Factor Improvement
Full-Load Currents–Motors
Maximum Locked-Rotor Currents–Three-Phase Motors
NEMA Code Letters for AC Motors
Starter Enclosures
NEMA Size Starters for Three-Phase Motors
NEMA Size Starters for Single-Phase Motors
Derating Factors for Conductors in a Conduit
Allowable Ampacities of Insulated Conductors
Motor Protection Devices–Maximum Rating or Setting

TRANSFORMERS
Full-Load Currents for Three-Phase Transformers
Full-Load Currents for Single-Phase Transformers
Transformer Connections

MISCELLANEOUS
Temperature Classification of Insulation Systems
Resistance Temperature Detectors.
Thermocouple Junction Types
Dimensions, Weight and Resistance: Solid Round Copper Wire (AWG and Metric)
Square Bare Copper Wire (AWG)
Insulation Resistance and Polarization Index Tests
Properties of Metals and Alloys

USEFUL FORMULAS AND CONVERSIONS
Temperature Correction of Winding Resistance
Temperature Correction of Insulation Resistance.
Formulas for Electric Motors and Electrical Circuits.
Motor Application Formulas
Centrifugal Application Formulas
Temperature Conversion Chart
Conversion Factors
Fractions of an Inch–Decimal and Metric Equivalents

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

Service centers routinely check the shaft extension runout of motors and generators. When there are issues associated with them, or when applicable, the coplanarity of the mounting feet and the amount of end foat of horizontal sleeve bearing motors and generators are checked. A common point about all three of these dimensions is that they are checked with the machine assembled; that is, no disassembly is required. There are many other mechanical tolerances associated with motors and generators, such as bearing fits. However, the focus of this article will be the three tolerances just mentioned. Rather than referring to both electric motors and generators, for brevity the term “machine” will be used.

Topics covered include:

• Shaft extension runout tolerance
• Coplanarity of mounting feet tolerance
• End float

Neville Sachs, P.E.
Applied Technical Services, Inc.,
Syracuse, NY

This technical paper, presented at the 2014 EASA Convention, will help you understand how and why shafts and fasteners fail. This paper covers:

• Discussion of material properties typically found in motor shafts, machine shafts and common fasteners
• Differentiating between overload and fatigue failures
• Understanding and identifying the difference between ductile and brittle materials, and how their fracture appearances differ
• A detailed explanation of how to identify fatigue failures, including the rate and direction of force application and the effect of stress concentrations
• Examples of several failure analyses

This book ws developed in conjuction with EASA's two-day Fundamentals of DC Operation & Repair Tips seminar.

This book is not meant to replace the many good texts that cover the theory and design of DC machines, but to supplement them. Its purpose is twofold: to help the technician understand DC machine theory without complex formulae; and in a larger sense, to record in one place the repair procedures and tips usually learned the hard way during a long career of DC machine repair. It may take a decade or longer for a technician to become proficient and knowledgeable. We hope this book will cut many years from that timeline.

The text begins with DC theory (no math, we promise!), and then follows the logical progression of a DC machine through the service center. Disassembly, inspection and testing are covered in the initial chapters. 

Subsequent chapters are organized around the main parts of a DC machine. The final chapters cover assembly, final testing and application issues. Sections focusing on components explain how those parts work, how they are made and how they can best be repaired.

Repair tips gleaned from EASA members’ decades of experience are liberally sprinkled throughout the book. While many texts about DC machines explain how they should work, this is the first (to our knowledge) to discuss all the exceptions that a repairer is liable to run across during a lifetime of working with DC machines. These might otherwise be labeled “lessons learned the hard way,” except that the reader can benefit from having all these special cases collected in one source. When possible, it is better to learn by reading than by trial and error; otherwise, the first encounter with a unique design can result in a painful “learning experience.”

A DC machine can be used interchangeably as a motor or generator, simply by changing the connection. Any DC motor can be driven and used to produce power, and any DC generator can be motorized to provide mechanical power. Although this text predominately refers to “motor;” the material applies to both motors and generators.

As with the other EASA publications—Principles of Large AC Motors, Mechanical Repair Fundamentals of Electric Motors, and Root Cause Failure Analysis—each section is designed to stand alone. The small amount of duplication is intentional, to save the reader from flipping back and forth between sections.

Table of Contents - (Download the complete Table of Contents)

• Nomenclature and Nameplate Information
• DC Motor Theory
• Disassembly and Inspection
• Testing
• Armatures
• Commutators
• Frames
• Ventilation and Accessories
• Motor Assembly and Final Testing
• On-Site Troubleshooting
• Failure Analysis

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Automatic alignment instruments are no substitute for the underlying process of aligning direct-coupled machines. This presentation explains the simple calculations that govern the alignment process. That understanding will allow technicians to use any alignment tool more effectively and deal with issues that confound the process.

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.

The purpose of this guide is to provide repair/rewind practices and tips that will help service center technicians and motor winders maintain or increase the efficiency, reliability and quality of the motors they repair.

Some of the included procedures derive directly from the 2019 and 2003 rewind studies by EASA and AEMT of the impact of repair/rewinding on motor efficiency. Others are based on the findings of an earlier AEMT study [1998] of small/ medium size three-phase induction motors and well-established industry good practices . 

The procedures in this guide cover all three-phase, random-wound induction motors. Much of the guide also applies to form-wound stators of similar sizes. 

(Note: This guide provides many specific procedures and recommendations. Alternative practices may accomplish the same results but must be verified.)

Table of Contents Overview

• Terminology
• Energy losses in induction motors
• Motor repair processes
  • Preliminary inspection
  • Dismantling the motor
  • Removing the old winding and cleaning the core
  • Rewinding the motor
  • Reassembling the motor
  • Confirming the integrity of the repair

El propósito de esta guía es suministrar prácticas y consejos de reparación/rebo­binado que ayudarán a los técnicos y a los bobinadores del centro de servicios a conservar o aumentar la eficiencia, confiabilidad y calidad de los motores que reparan.

Algunos de los procedimientos incluidos derivan directamente de los estudios sobre el impacto de la reparación/ rebobinado en la eficiencia del motor realizados por EASA y AEMT en los años 2003 y 2019. Otros se basan en los hallazgos del estudio previo efectuado por AEMT [1998] en motores trifásicos pequeños/medianos y en las buenas prácticas industriales bien establecidas.

Los procedimientos de esta guía cubren todos los motores trifásicos de inducción de alambre redondo. Mucha información también aplica a motores con bobinas preformadas (pletina o solera) de tamaños similares.

(Nota: Nota: Esta guía proporciona muchas recomendacio­nes y procedimientos específicos. Se pueden lograr los mismos resultados con otras prácticas, pero deberán ser verificadas.)

Tabla de Contenido

• Terminología
• Pérdidas de energía en los motores de inducción
• Procesos de reparación del motor
  • Inspección inicial
  • Desmontaje del motor
  • Remoción del antiguo bobinado y limpieza del núcleo
  • Rebobinado del motor
  • Montaje del motor
  • Confirmando la integridad de la reparación

Pat Douglas Kirby Risk
Mechanical Solutions & Service

Shaft currents have always been a concern for large motors due to magnetic asymmetries within the motor. Manufacturers strive to keep these to a minimum.

With the widespread use of Variable Frequency Drives (VFDs), shaft current issues have become a concern in all sizes of motors. If these currents are discharged through the bearings, electrical discharge machining (EDM) occurs. Proper installation of VFDs can play a large part in mitigating issues with shaft currents. 

Many end users are not aware of shaft currents or their destructive paths. All too often they think that the motor bearings keep failing because the motor repair was not completed properly. 
Service centers need to be on the lookout for these issues when repairing a customer’s equipment. Many repairs arrive at the service center with no history and no hint of what the problem with the motor might be. The technicians have to do an “autopsy” of the motor to be sure the causal problem is repaired and not just the symptom.

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

When a shaft is in need of repair, often the first step is to determine the corrective method required. Econom­ics and best practices are typically sig­nificant factors in the decision-making process in selecting the method of repair. The types of shaft repairs that will be dealt with here are:  opposite drive end bearing journal, drive end bearing journal and a bent shaft. The objective is not to detail the repair processes, but to identify the most common methods appropriate to the types of repair and considerations associated with each method. Table 1 summarizes the methods for various load conditions.

Chuck Yung
EASA Senior Technical Support Specialist

One of the more mundane things we as repairers must be concerned with is motor storage. For many of us, storing large motors for major customers is its own profit center. For all of us, being aware of how our customers store the motors we repair and send to them is critical to customer satisfaction. A poorly stored motor is likely to suffer winding or bearing failure, and we don’t want unrealistic warranty claims over something outside our control.

Our primary concerns when storing motors, especially long-term, are windings, bearings and shaft sag.

Eugene Vogel
EASA Pump & Vibration Specialist

It is common for vertical turbine pumps (VTP) to be designed with mul­tiple mixed flow impellers (sometimes 12 or more) and for the pump rotor to be supported by the vertical pump mo­tor.

Vertical pump motors can be solid shaft or hollow shaft. Solid shaft motors have an annular keyway in the shaft that is engaged by a solid coupling that supports the pump rotor. 

Hollow shaft motors support and drive the pump rotor from the top by means of a head shaft fitted through the hollow motor shaft to the pump line shaft. In either case, there is an adjustment that lifts the pump rotor so it is supported by the motor shaft. This adjustment is obviously critical to the proper operation of the pump and motor and can have a significant effect on the motor load (current). Presented here are some of the main concerns for setting this pump lift ad­justment.

This video explains how to measure the diameter of a bearing journal accurately to within five hundred-thousandths of an inch or one-thousandth of a millimeter. This critical step will determine if the shaft needs any repairs for proper bearing fitment.

Topics covered include:

• Tools and supplies needed
• How to validate micrometer accuracy
• Minimum number of measurement locations
• How to measure a bearing journal

DESCRIPTION
This 94-page handbook (3.5" x 6", 9cm x 15cm) contains carefully selected materials designed to assist repair firms in their everyday work. Just as important, your customers and potential customers can use this pocket handbook as a handy reference for mechanical data for motors and driven equipment. Buy this great resource as is OR custom brand your company logo and information on the cover to turn it into a great marketing piece for your salespeople!

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TABLE OF CONTENTS

Alignment
Alignment Information
Suggested Alignment Tolerances
ANSI/ASA Alignment Quality

Balancing And Vibration
Single-Plane Versus Two-Plane Balancing
Vibration Tests
Unfiltered Housing Vibration Limits
FFT Vibration Analysis
Vibration Constants
Vibration Conversion Factors
Electric Motor Vibration Diagnostic Chart

Motor Application Forumlas
Output
Shear Stress
Speed–AC Machinery 
Affinity Laws–Centrifugal Applications

Conversion Factors, Equivalencies & Formulas
Conversion Factors
Temperature Conversion Chart
Common Fractions Of An Inch–Decimal & Metric Equivalents
Prefixes–Metric System
Formulas For Circles

Bearings
Nominal Dimensions For Radial Ball Bearings
Nominal Dimensions For Cylindrical Roller Bearings
Radial Ball Bearing Fit Tolerances
Cylindrical Roller Bearing Fit Tolerances
Lock Nuts And Lock Washers For Ball Bearings

Motor Bearing Lubrication
Lubricating Oil Viscosity Conversions
NLGI Grease Compatibility Chart
Grease Classifications
Grease Relubrication Intervals

Metals And Alloys
Properties Of Metals And Alloys
Weight Formulas For Steel
Thermal Linear Expansion

Bolts
ASTM And SAE Grade Markings For Steel Bolts And Screws
Precautions For Tightening Bolted Joints
Bolt Tightening Torque Values
Tap Drills And Clearance Drills For Machine Screws

Keys And Keyseats
NEMA Keyseat Dimensions–Foot-Mounted AC & DC Machines
IEC Shaft Extension, Key And Keyseat (Keyway) Dimensions
Square And Flat Stock Keys
Standard Keyseat Sizes
Metric Keys–Standard Sizes

Belts And Sheaves
Pulley Formulas For Calculating Diameters and Speeds
Belt Installation
Belt Tensioning
Belt Deflection Force And Elongation Ratio
Standard V-Belt Profiles And Dimensions
V-Belt Sheave Dimensions
V-Belt Sheave Dimensions For AC Motors With Rolling Bearings
Application Of V-Belt Sheave Dimensions To AC Motors With Rolling Bearings
Mounting Of Pulleys, Sheaves, Sprockets, And Gears On Motor Shafts
Minimum Pitch Diameter For Drives Other Than V-Belts

Welding, Brazing And Soldering
Recommended Copper Welding Cable Sizes
Types Of Weld Joints 
Brazing
Basic Joints For Brazing
Soldering
Melting Temperatures Of Tin-Lead-Antimony Alloys
Flux Requirements For Metals, Alloys And Coatings

Slings, Wire Rope, Shackles and eyebolts
Types Of Slings
Typical Sling Hitches
Wire Rope
Spreader Bars
Lifting Capacity
Forged Shackles
Eyebolt Strength

Common Signals For Crane

Fundamental to every good mechanical repair is the ability to disassemble, repair and reassemble the motor correctly without unnecessary damage to any of the motor parts. This sounds simple, and yet too many costly mistakes are made in this process of taking things apart. If every motor repaired was in “as new” condition, the task would be much simpler. But this would be no guarantee that the reassembly would be correct.

​There is usually an easy way and a hard way to remove and install parts. Brute force is seldom the easiest or the correct way. The old saying of “don’t force it, get a bigger hammer” is seldom the best way.

When a service center is paid to repair equipment, the service center wants it to stay in operation. If the equipment fails again—within the warranty period—the service center pays to repair it again. It makes sense to repair it correctly the first time.

In order to improve equipment, it is important to know how and where it operates. Without understanding why a motor fails, it is impossible to deliberately improve its mean time between failures.

To do this, there must be communication between the service center and the motor user. Not only does this help the repairer decide the best course of action, but it helps the user appreciate the professionalism of the service center.

Repair procedures, like motors themselves, are affected by changes in technology. This book attempts to include the latest proven technologies. Time-honored methods of repair, in many cases, may still be the most practical option. Options presented throughout this book are intended to help the technician select the appropriate repair method, recognizing that the ultimate decision rests with the equipment owner.

Repair methods sometimes fall into disfavor, not because better methods are introduced, but because of poor techniques. Other repair methods are well-suited to some applications but not to others. It is the job of the repairer to decide what is the best method for each case.

This book is divided into sections for basic motor components with repair methods and tips dispersed throughout. Where practical, reasons for failures are also discussed. These will aid the technician in selecting the most appropriate method of repair for each unique application.

The information presented draws from EASA publications, IEEE publications, technical journals and literature supplied by vendors, motor manufacturers and established service centers.

This book contains many suggestions on how to correctly handle the various parts of a motor during the repair process so as to minimize damage. However, it is impossible to develop an all-inclusive list. Instead, the basic principle of taking the time to use the correct tool and correct procedure will usually lead the technician down the right path. Always remember, if it has to be forced beyond reason, it might be that neither the proper tool or procedure is being used or something is wrong with the parts. Step back and ask “What am I overlooking?”

Table of Contents

1. Motor Nomenclature
2. Motor Applications and Enclosures
3. Test and Inspection Procedures
4. Motor Disassembly Tips
5. Bearings
6. Bearing Housing Repair, Shaft Openings, Seals and Fits
7. Shafts
8. Rotors
9. Motor Assembly
10. Motor Accessories and Terminal Boxes
11. Motor Dynamics
12. Vibration and Motor Geometry
13. Shaft/Bearing Currents
14. Special Considerations for Explosion-Proof Motors
15. Failures in Mechanical Components
16. Miscellaneous Repairs

This book is available as part of EASA's Fundamentals of Mechanical Repair seminar.

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PRINTED BOOK DOWNLOAD

Chuck Yung
Especialista de Sénior de Soporte Técnico de EASA

Una de las cosas más mundanas de las que debemos preocuparnos como reparadores es el almacenamiento de los motores y para muchos, almacenar motores grandes para clientes importantes representa ganancias. Para todos nosotros, ser conscientes de cómo nuestros clientes almacenan los motores que les reparamos es crítico desde el punto de vista de la satisfacción del cliente. Es probable que un motor mal almacenado sufra fallos en el devanado o en los rodamientos, y no queremos reclamos por garantía poco realistas sobre algo que está fuera de nuestro control.

Nuestras principales preocupaciones al almacenar motores, especialmente a largo plazo, son los devanados, los rodamientos y el pandeo del eje.

Gene Vogel
EASA Pump & Vibration Specialist

Shaft alignment is a critical step in the installation of rotating machinery, in a new installation or a repaired machine. Skipping or botching this step can decrease operating efficiency and shorten machine life. The procedure for aligning two rotating machines requires measuring their relative shaft positions and adjusting one or both machine cases, usually by shimming at the feet. Until recently, though, how closely the shafts need to be aligned was an open question. That changed with the publication of American National Standards Institute/Acoustical Society of America (ANSI/ASA) standard 2.75-17. Here is a summary of what it covers and how it will benefit users involved with shaft machinery alignment.

• The need for a standard
• Purpose and scope
• Tolerances
• Alignment principles
• Alignment quality grades
• Making machine moves

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Gene Vogel
Pump & Vibration Specialist
EASA
St. Louis, MO

The paper "Overview of the New Shaft Alignment Standard" by Gene Vogel, presented at the EASA Convention 2018, introduces the ANSI ASA S275 Part 1: General Principles, Methods, Practices, and Tolerances standard for shaft alignment. This standard was developed by the Vibration Institute in collaboration with the Acoustic Society of America (ASA) to provide a comprehensive and consistent approach to shaft alignment across various industries. Prior to this, there was no national or international standard for shaft alignment, leading to inconsistencies in methodologies and tolerances.

The standard focuses on machine configurations commonly found across industries, specifically "4 bearing sets," which consist of two independent shafts each supported by a pair of bearings and coupled by a flexible coupling. Examples include horizontal motor-pump or motor-fan combinations. The intention is to expand this initial document with additional standards addressing other machine configurations, such as vertical machines and 3 bearing sets.

The standard provides guidelines on shaft alignment tolerances, base flatness and level, shaft runout, coupling runout, pipe and conduit strain, soft foot, and offline-to-running (OLTR) machinery movement. It emphasizes the importance of turning both shafts when making alignment measurements to ensure accuracy. Tolerances for pipe and conduit strain are set to prevent changes in shaft alignment greater than 50 micrometers (2 mils) vertically or horizontally at the coupling.

A holistic approach to the shaft alignment process is presented, including a flow chart documenting key steps and decision points. The standard includes informative annexes covering alignment principles, machine move calculation formulas, identifying and correcting pipe strain, OLTR methods, laser detector systems, graphic alignment modeling, repeatability, and an alignment and machinery installation checklist.

Alignment principles are explained through two common methods: offset and angularity between shaft centerlines, and flex plane angles at the coupling mechanical link (CML). The flex plane angles more accurately represent the work done by the coupling and are used to establish alignment tolerances. Alignment Quality Grades are provided based on flex plane angles and machine operating speed, with three grades: AL4.5 (Minimal), AL2.2 (Acceptable), and AL1.2 (Excellent).

The standard also addresses practical concerns related to moving machine cases, such as soft foot, base-bound, and bolt-bound conditions. It provides guidelines for controlled machine positioning and emphasizes the importance of proper axial spacing (coupling gap).

Several annexes offer detailed instructions on related topics. Annex B covers correction move formulas for various dial indicator setups. Annex D explains OLTR movement and how to establish target values for alignment. Annex F discusses alignment modeling, which helps visualize and calculate machine case moves. Annex H provides a machinery installation checklist to ensure important steps are not missed.

Key Points Covered:

• Development and scope of the ANSI ASA S275 Part 1 standard
• Focus on "4 bearing sets" machine configurations
• Guidelines on shaft alignment tolerances and related factors
• Holistic approach to the shaft alignment process
• Alignment principles and methods
• Alignment Quality Grades based on flex plane angles and machine speed
• Practical concerns related to moving machine cases
• Detailed instructions in annexes on correction moves, OLTR movement, alignment modeling, and installation checklist

Key Takeaways:

• The new standard provides a consistent approach to shaft alignment across industries.
• Focus on common machine configurations with plans to expand to other setups.
• Emphasis on accurate alignment measurements and tolerances.
• Holistic approach includes flow charts and detailed annexes.
• Flex plane angles are used to establish alignment tolerances.
• Alignment Quality Grades help determine acceptable alignment based on machine speed.
• Practical guidelines for moving machine cases and addressing alignment issues.
• Comprehensive annexes offer valuable instructions for various aspects of shaft alignment.

Las versiones impresas y en forma de descarga del valioso manual didáctico / recurso de EASA, “Principios de Motores C.A. Medianos y Grandes”, se encuentran ahora disponibles en inglés y en español. El manual incluye gráficos e ilustraciones, fotografías y mucha información técnica sobre máquinas C.A., incluyendo como funcionan, información específica sobre los tipos de encerramientos, fabricación de componentes y aplicaciones.  Muchos de los principios incluidos en el libro aplican a todos los motores C.A., especialmente a aquellos accesorios que fueron asociados en el pasado con las máquinas más grandes (como encoders, RTDs, termostatos, calentadores de espacio, sensores de vibración, etc.).

Las versiones  forma de descarga ofrecen funciones prácticas ya que contienen toda la información que contiene el manual impreso, pero en formato PDF, fácil de usa, ya que contiene marcadores que permiten a los lectores navegar rápidamente por el documento y “saltar” a la página deseada.

Las secciones del manual incluyen:

• Terminología y Definiciones del Motor
• Tipos de Encerramientos de Motores
• Aplicaciones Típicas para Motores
• Consideraciones de Manejo y Seguridad
• Teoría Básica del Motor
• Normas para Motores
• Estatores
• Rotores de Jaula de Ardilla
• Ejes
• Lubricación y Rodamientos
• Accesorios del motor & Cajas de Conexiones
• Procedimientos de Inspección y Prueba
• Alineamiento del Motor, Vibración y Ruido
• Procedimientos de Almacenamiento
• Máquinas Sincrónicas

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

NEMA - English NEMA - Español

This valuable instructional/resource manual is available in printed, downloadable and CD-ROM versions.

For this second edition, this 320-page manual has been reorganized, updated with new information, including revised standards and published articles, and edited extensively. The manual includes drawings, photos and extensive text and documentation on AC motors, including how they work, specific information on enclosures, construction of components and applications. Many of the principles included apply to all AC motors, especially those with accessories that were associated with larger machines in the past (such as encoders, RTDs, thermostats, space heaters, vibration sensors, etc.).

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

This manual focuses primarily on NEMA motors.

Sections in the manual include:

• 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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This book is also available focusing on IEC Standards ... IEC VERSION

Eugene Vogel
Especialista en Bombas y Vibraciones de EASA

Es común que las bombas de turbina vertical (VTP) se encuentren diseñadas con varios impulsores de flujo mixto (algunas veces 12 o más) y que los rotores de las bombas estén soportados por los motores verticales. Los motores de las bombas verticales pueden ser de eje macizo o hueco. Los motores de eje macizo tienen una cuña o chaveta anular (en forma de anillo) en el eje, para asegurar un acoplamiento sólido que soporta el rotor de la bomba.

Los motores de eje hueco soportan y accionan el rotor de la bomba desde la parte superior, mediante un cabezal de eje que está asegurado al eje lineal intermedio (line shaft) a través del eje hueco del motor. En cualquiera de los casos, existe un ajuste que eleva el rotor de la bomba para que quede soportado por el eje del motor.

Obviamente este ajuste es crítico para el funcionamiento adecuado de la bomba y el motor y puede llegar a tener un efecto significativo en la carga del motor (consumo de corriente en amperios). En este artículo se presentan algunos puntos importantes para ajustar la elevación del eje de la bomba.

Cyndi Nyberg 
Former EASA Technical Support Specialist 

Have you ever wondered why the shaft of an electric motor is often larger than that of the driven equip­ment? One reason for this is that the standard shaft sizes specified for the standard NEMA frame machines are larger than the minimum required, as we will see in the examples below. Manufacturers tend to design using an ample safety factor. Given the dire consequences if a shaft breaks, that is understandable. 

Even so, the difference between a T and TS shaft can raise questions for those unfamiliar with mechanical design. It is important that the shaft is large enough to (a) transmit the required torque without exceeding the maxi­mum allowable torsional shearing stress for the shaft material, and (b) prevent torsional deflection, or twisting, during service. All this, with a substantial safety factor. 

This book was developed to help electric motor technicians and engineers prevent repeated failures because the root cause of failure was never determined. There are numerous reasons for not pursuing the actual cause of failure including:

• A lack of time.
• Failure to understand the total cost.
• A lack of experience.
• A lack of useful facts needed to determine the root cause.

The purpose of this book is to address the lack of experience in identifying the root cause of motor failures. By using a proven methodology combined with extensive lists of known causes of failures, one can identify the actual cause of failure without being an “industry expert.” In fact, when properly used,  this material will polish one’s diagnostic skills that would qualify one as an industry expert.

The book is divided into the various components of an electric motor. In addition to a brief explanation of the function of each component and the stresses that act upon them, numerous examples of the most common causes of failure are also presented.

For this second edition, the manual has been reorganized and updated with new information including a new approach to methodology, new case studies and a new section covering synchronous machine failures. This could not have been done without many contributions from EASA members and the Technical Education Committee. 

The all new “Root Cause Methodology” section goes into great detail explaining that effective root cause failure analysis must take place within the context of a practical problem-solving methodology or framework. It covers a modified Plan-Do-Check-Act process that emphasizes the importance of planning and the related problem-solving methodology components. This section also explains A3, a high-level reporting tool that is very effective for problem solving.

In addition, besides a systematic approach to problem solving, root cause failure analysis of motors and motor systems requires familiarity with contributing factors attributable to various kinds of applications, environments and industries. This includes how various stresses can affect motor components and the reciprocal impact the motor system may have on the motor. This section includes a table with a detailed summary of motor stresses. 

There also is a new section on “Synchronous Machine Failures” and an expanded “Case Studies” section. Readers are guided through eight case studies.

With 328 pages, the book provides extensive information, including a wide range of failures, the likely causes listed, and the methodology for confirming the probable cause of each failure. 

Members may purchase a printed manual and/or a PDF download. The printed manual is in black and white, while the download shows most of the failure photos in color.  

Sections in the manual include:

• Root Cause Methodology (all new)
• Bearing Failures
• Stator Failures
• Shaft Failures
• Rotor Failures
• Mechanical Failures
• DC Motor Failures
• Synchronous Machine Failures (all new)
• Accessory Failures
• Case Studies (expanded)
• References

This book is available as part of EASA's Root Cause Failure Analysis seminar.

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DISCOUNTED BLACK & WHITE BOOKS!
Prices are now DISCOUNTED on remaining black & white books while supplies last! If you have already purchased a black & white manual and are interested in the color version, please contact EASA Customer Service (+1 314 993 2220).

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Gene Vogel
Pump & Vibration Specialist
Electrical Apparatus Service Association
St. Louis, MO

The paper "Shaft Alignment: Rock ’N’ Roll Machinery Style" by Gene Vogel, presented at the EASA Convention 2015, delves into the intricacies of shaft alignment in industrial machinery. Vogel emphasizes that while technicians often learn shaft alignment as a procedural task, a deeper understanding of the relationship between shaft centerlines and their response to alignment moves is crucial for handling unexpected situations in industrial environments.

The paper begins by discussing the fundamental concept of misalignment, explaining that shaft centerlines can be coincident, parallel, or skew. The most general case is skew centerlines that do not intersect, which becomes the defining case for alignment. Vogel explains that the severity of misalignment is determined by the angle between the spool centerline and the shaft centerlines at the flex planes. This angle is crucial for understanding alignment tolerances.

Vogel then transitions to visualizing misalignment in vertical and horizontal planes, using an XYZ coordinate system. He explains that offset and angularity in these planes are described by the intersection lines of the vertical planes containing the shaft centerlines with a horizontal plane. The paper provides a detailed example of calculating offset and angularity, illustrating how to determine the necessary correction moves.

The paper also addresses the challenges of aligning machines with base-bound or bolt-bound conditions, where both machines need to be moved to achieve proper alignment. Vogel explains how to calculate the required moves by drawing a zero line that minimizes the moves and avoids limiting bounds.

Tolerances are discussed in the context of limiting the angle between the shaft centerline and the spool centerline. Vogel explains that the objective of shaft alignment is to reduce vibratory forces to an acceptable level. He provides examples of alignment tolerances published by alignment tool vendors and industry experts.

The concept of target values is introduced, emphasizing the importance of aligning the centerlines to an offset position to account for thermal growth, torque strains, and piping strains. Vogel explains the OL2R (off-line to running) measurement process, which involves measuring the change in position from cold, off-line conditions to normal operating conditions.

The paper concludes with practical advice on moving the machine cases and addressing soft foot conditions. Vogel highlights the importance of ensuring that the machine is stable and free from soft foot conditions, which can affect alignment and machine reliability. He also emphasizes the need for proper training on alignment tools and understanding the alignment process beyond just using the tools.

Key Points Covered:

• Fundamental concept of misalignment and shaft centerlines
• Visualizing misalignment in vertical and horizontal planes
• Calculating offset and angularity for alignment corrections
• Addressing base-bound and bolt-bound conditions
• Understanding alignment tolerances and their importance
• Using target values to account for thermal growth and other strains
• Practical advice on moving machine cases and addressing soft foot conditions

Key Takeaways:

• A deeper understanding of shaft alignment is crucial for handling unexpected situations in industrial environments.
• Misalignment severity is determined by the angle between the spool centerline and the shaft centerlines at the flex planes.
• Visualizing misalignment in vertical and horizontal planes helps in understanding and correcting alignment.
• Properly addressing base-bound and bolt-bound conditions is essential for achieving alignment.
• Alignment tolerances are important for reducing vibratory forces to acceptable levels.
• Using target values helps in aligning machines to account for thermal growth and other operational strains.
• Ensuring machine stability and addressing soft foot conditions are critical for successful alignment and machine reliability.

Presented by Chuck Yung
EASA Senior Technical Support Specialist

This webinar explains what shaft currents are, what causes them, and differentiates between the two common causes:

1. Circulating currents which affect DC motors and AC motors not operating from a drive
2. Shaft currents caused by operation from a VFD, and how to tell the difference between the two.

This webinar also discusses and compares methods to mitigate shaft currents and explains why the different causes of shaft currents require different solutions. It covers:

• Shorted rotor iron
• Uneven air gap
• Unbalanced voltage
• What type of grounding brush works best?
• Role of carrier frequency in causing shaft currents
• How to recognize the problem on site
• Insulation thickness, capacitance, and types of insulated bearings

This information is useful to engineers, service center managers, mechanics and anyone interacting with customers.

Presented by Gene Vogel
EASA Pump & Vibration Specialist

There are heat methods and press methods for straightening shafts. This webinar reviews those methods, their pros and cons, and when one method or another may be applicable.

• Various shaft bend modes and how to identify them 
• An illustration of an effective method using heat to straighten a shaft 
• A description and precautions for use of a press to straighten a shaft 
• An explanation of how metallurgy impacts shaft straightening

This webinar is intended for service center engineers, machinists and mechanics.

Gene Vogel
Pump & Vibration Specialist
Electrical Apparatus Service Association
St. Louis, MO

The paper "Steel—Metallurgy and Practical Application of Various Grades of Steel" by Gene Vogel, presented at the EASA Convention 2016, provides an in-depth exploration of steel alloys, their composition, processing, and applications, particularly in the context of machinery repairs and replacement shafts. Vogel emphasizes the importance of selecting the appropriate type or grade of steel for specific applications, drawing on both practical application information and technical metallurgy theory.

Steel is an iron-carbon alloy, with carbon content varying from 0.01% to 5%. Increased carbon content generally enhances strength but reduces malleability. The paper explains that the characteristics of steel are also influenced by heat treating, processing, and the presence of other alloy elements. Vogel likens the process of making steel to cooking, where the right ingredients and proper processing yield the desired results.

The paper references EASA’s "Mechanical Repair Fundamentals of Electric Motors" manual, which provides basic recommendations for steel types and grades for manufacturing replacement shafts. Vogel notes that manufacturers use different alloys and transition points for higher-strength steels, depending on the application and horsepower. Common types of engineering steel include carbon steel, stainless steel, and duplex steel, each with various grades designated by standards such as SAE, EN, BS, and ISO.

To determine the alloy of a part to be replaced, Vogel suggests providing a sample to a test laboratory for analysis. Spectroscopy can identify the approximate concentrations of alloy elements, while portable X-ray fluorescence instruments offer quantitative information. For practical purposes, the choice of material often balances strength, corrosion resistance, machinability, and cost.

The paper discusses the properties of common shaft materials, including their tensile and yield strengths, and highlights the importance of pump shaft quality (PSQ) shafting for certain applications. PSQ shafting is normalized to remove residual stress and precision ground to increase fatigue cycle life.

Vogel explains that the properties of alloy steel depend not only on alloy content but also on microstructure, which is influenced by processing methods and heat treating. Heat treating involves holding the steel at specific temperatures for set periods, affecting the microstructure and resulting properties such as tensile strength, yield strength, ductility, hardness, machinability, and magnetic properties.

The paper includes a phase diagram to illustrate the effect of heat treating on the iron-carbon solution, showing how different microstructures form at various stages of solidification. Stress-strain diagrams are used to explain the relationship between stress, strain, yield strength, ultimate strength, and fracture strength. Vogel also addresses machinability, magnetic properties, and corrosion resistance, noting that these factors are critical for specific applications.

In conclusion, the paper provides a comprehensive overview of the science of metallurgy and practical considerations for selecting and processing steel alloys for machinery components. Vogel emphasizes the importance of understanding alloy content, heat treating, and processing methods to achieve the desired properties in the finished product.

Key Points Covered:

• Importance of selecting the appropriate steel type or grade for specific applications
• Composition and characteristics of steel alloys
• Recommendations for steel types and grades for replacement shafts
• Methods for determining alloy content of parts
• Properties of common shaft materials and PSQ shafting
• Influence of microstructure and heat treating on steel properties
• Explanation of phase diagrams and stress-strain diagrams
• Considerations for machinability, magnetic properties, and corrosion resistance

Key Takeaways:

• Selecting the right steel type or grade is crucial for machinery repairs and replacement shafts.
• Steel properties are influenced by carbon content, alloy elements, heat treating, and processing methods.
• Practical considerations include balancing strength, corrosion resistance, machinability, and cost.
• Understanding microstructure and heat treating is essential for achieving desired properties.
• Phase diagrams and stress-strain diagrams help explain the effects of heat treating and mechanical properties.
• Machinability, magnetic properties, and corrosion resistance are important for specific applications.

The slender dimensions of many pump shafts make them susceptible to distortion, which affects pump performance and reliability. This recording presents a methodical approach and effective techniques for measuring and correcting shafts which are bent or twisted.

Target audience: This presentation is intended for service center supervisors, managers and machine shop technicians.

Austin Bonnett
EASA Education and Technology Consultant
Gallatin, MO

In the paper "The Most Unlucky Things That Can Happen To A Customer’s Motor," presented at the EASA Convention 2004, Austin Bonnett explores the common causes of motor failures and provides insights into how these failures can be predicted, prevented, and repaired. The paper emphasizes the importance of understanding the root causes of motor failures, which are often predictable, repeatable, and preventable.

Bonnett outlines a methodology for identifying the root causes of motor failures, which includes examining the failure mode, failure pattern, appearance, application, and maintenance history. He stresses the importance of recording critical data and measuring results to benchmark performance and make necessary upgrades or revisions.

The paper identifies the most common sources of motor problems, including issues with bearings, stators, rotor cores, shafts, misalignment, and other factors. Bearing problems are often caused by improper lubrication, contamination, and excessive vibration and shock. Improper lubrication can result from using too much or too little lubricant, incompatibility of lubricants, or using the wrong type of lubricant. Contamination can occur due to moisture, foreign materials, and corrosion, leading to bearing damage. Excessive vibration and shock can be caused by rotor unbalance, coupling unbalance, system unbalance, sudden stops or loading, and environmental influences.

Stator problems are typically related to thermal overload, severe electrical abnormalities, and contamination of the insulation system. Thermal overload can result from horsepower overload, excessive ambient temperatures, load cycling, too many starts, or failure to accelerate. Electrical abnormalities include overvoltage, undervoltage, unbalanced voltage, single phasing, transients, and partial discharge. Contamination of the insulation system can be caused by moisture, condensation, abrasion, and foreign materials.

Rotor core failures are often due to poor geometry, out of balance, defective or damaged squirrel cages, and improper joining of bars to end rings. Common shaft failures include metal fatigue, rotational bending, torsional bending, extreme temperatures, residual stress, and environmental factors. Misalignment issues can arise from problems with the motor, coupling, driven equipment, mounting base, and other factors.

Bonnett also discusses other frequent causes of motor failures, such as misapplication, misuse, inappropriate repairs, alteration of the cooling system, hazardous terminal boxes, and coupling failures. He emphasizes the importance of proper maintenance and monitoring to prevent these failures and ensure reliable motor operation.

Key Points Covered:

• Root cause methodology for identifying motor failures
• Common sources of motor problems, including bearings, stators, rotor cores, shafts, and misalignment
• Causes of bearing problems, such as improper lubrication, contamination, and excessive vibration and shock
• Stator problems related to thermal overload, electrical abnormalities, and contamination
• Rotor core failures due to poor geometry, defective squirrel cages, and improper joining of bars to end rings
• Common shaft failures, including metal fatigue, rotational bending, torsional bending, and residual stress
• Misalignment issues and other frequent causes of motor failures

Key Takeaways:

• Motor failures are often predictable, repeatable, and preventable.
• Understanding the root causes of motor failures is essential for effective troubleshooting and repair.
• Proper lubrication, contamination prevention, and vibration control are crucial for bearing health.
• Thermal overload, electrical abnormalities, and contamination are common causes of stator problems.
• Rotor core failures can result from poor geometry, defective squirrel cages, and improper joining of bars to end rings.
• Shaft failures are often due to metal fatigue, rotational bending, torsional bending, and residual stress.
• Misalignment and other factors can lead to motor failures, emphasizing the importance of proper maintenance and monitoring.

Jasper Fisher 
Rexel Motor Repair 
Alton, Illinois 
Technical Education Committee Member 

Like most maintenance and repair tasks, a successful outcome is gen­erally predicated on good planning and preparation. The first steps in the process are often the most critical. 
When preparing to remove a shaft from an armature (Figure 1) or rotor core (Figure 2), first measure and record the location dimensions of all shaft-mounted components. This in­
cludes materials such as bearing spacer collars, flingers, and removable cool­ing fans and the shaft-to-core location dimensions. 

A common reference measurement is from the outer edge of the lamina­tion stack to a bearing journal shoulder and/or the shaft extension end. These location measurements should be made to 1/32” +/-1/64” (0.8 mm +/-0.4 mm) (or better) and be permanently recorded in the job record. 

Steve Skenzick
HPS Electrical Apparatus Sales & Service

At my service center, we have seen problems with previously repaired shafts that were metal sprayed. In these cases we received motors for overhaul. Upon inspection and measuring the bearing shaft fits, we found something that just didn’t “feel” right. We could tell from the appearance that the shafts had been repaired prior to the current overhaul.

Cyndi Nyberg
Former EASA Technical Support Specialist 

Shaft failures are not an everyday occurrence, but when they come in, it can be an interesting challenge to determine the cause of failure. Regardless of what caused the shaft to fail, what actually happens when it bends or breaks? 

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

Two common scenarios that service centers deal with regarding belt drive applications are failure of a motor drive end ball bearing or breakage of the shaft at the drive end bearing shoulder. The cause of these failures often is over-tensioning of the v-belts. However, there are many other faults or undesirable practices that can lead to premature bearing failure, belt wear and sheave wear. 

Due to practical space limitations, this article won’t be exhaustive in its coverage but will deal with common scenarios other than motor bearing failure and shaft breakage.

This presentation covers:

• Shaft material and specs
• Shaft coupling types
• Machining for shafts
• Bronze, plastic, graphite and cutlass bearing options
• Bearing clearance concerns and reference data 
• Bearing housing fits

Target audience: This webinar will benefit service center technicians and supervisors.

The rules of thumb often applied to journal bearings in horizontal machines don’t apply to vertical machines. Vertical turbine pumps are a common example.

This presentation explains the characteristics of bearings in these pumps and provide examples of manufacturers specifications.

In addition, specialty bearing materials will be discussed in regard to applications, specifications and installation.

Target audience: This webinar is most useful for service center technicians and engineers. The content is beneficial for supervisors and managers who are responsible for pump failure analysis and testing.

A special discounted collection of 9 webinar recordings focusing on a wide variety of vibration, balancing and alignment topics.

Once purchased, all 9 recordings will be available on your "Downloadable products purchased" page in your online account.

Downloadable recordings in this bundle include:

An Overview of Vibration Tolerances
Presented August 2019

When it comes to machine vibration, “how much is too much” depends on a number of factors. Knowing which standard and/or tolerance applies requires a working knowledge of the standards and some basics of vibration terminology. This  presentation provides an overview of where and how NEMA, IEC, ISO and Hydraulic Institute standards may apply to machines commonly encountered in EASA service centers.

• NEMA, IEC, ISO and Hydraulic Institute standards
• Basic vibration terminology
• What standard applies?

Target audience: Service center managers, engineers, in-shop and field service technicians can benefit from a clearer understanding of vibration standards and terminology.

Basics of Machinery Foundations and Bases
Presented November 2012

A faulty machine foundation or base can lead to excessive vibration and premature failure. This presentation explains the fundamentals of machinery foundation construction and how to identify and troubleshoot machine base problems, including basic vibration techniques and ODS analysis.

Fundamentals of Shaft Alignment
Presented November 2012

Automatic alignment instruments are no substitute for the underlying process of aligning direct-coupled machines. This presentation explains the simple calculations that govern the alignment process. That understanding will allow technicians to use any alignment tool more effectively and deal with issues that confound the process.

Shaft Alignment
Presented March 2016

This webinar recording provies a straightforward look at the simple relationship between shaft centerlines that is known as shaft alignment. Bypassing the common discussion of laser and manual instruments, this presentation gets to the heart of the shaft alignment process. Topics covered will include:

• Fundamental concepts
• How to visualize machine case position
• Practical solutions for moving machine cases
• Applying tolerances
• The foot-base-foundation connection

ANSI's New Shaft Alignment Standard
Presented July 2018

This presentation introduces you to ANSI's new shaft alignment standard. Topics covered include:

• A discussion of alignment Quality grades, AL 1.2, AL 2.2, AL 4.5
• Shaft alignment tolerances
• Issues affecting measurements
• Conditions affecting alignment stability

Target audience: This presentation benefits service center technicians and supervisors looking to improve shaft alignment knowledge and skills. 

How to Balance Overhung Fans
Presented October 2011

Often an overhung fan is balanced in a single plane, only to find that the vibration has shifted to the outboard bearing. Attempts to use standard two-plane techniques may result in calculated correction weights that are very large and produce poor results. There are more effective ways to approach this common problem. This presentation shows a methodical approach and techniques for tackling this difficult balancing problem.

Target audience: This presentation is intended for field service balancing technicians, supervisors and managers.

Vibration on Belt Driven Machines
Presented June 2013

This presentation focuses on:

• Identifying belt vibration
• Identifying pulley pitch line run-out vibration
• Other vibration sources
• ODS analysis

The FFT (aka Spectrum): What It Is and Ways to Use It
Presented July 2012

This presentation examines:

• How the spectrum is generated from the vibration signal
• The effect of f-max ad resolution settings
• Averaging techniques
• Scaling and demodulation

Vibration Problems on Vertical Motors and Pumps
Presented December 2010

When motors are installed on top of vertical pumps, high vibration is a common problem. The problem may be mechanical, hydraulic or structural.

This presentation provides an understanding of the nature of this style pump and the various forces essential to diagnosing and correcting vibration problems on vertical pump motors.