Overview: This document is a comprehensive handbook by SKF for industrial designers and end-users, focusing on rolling bearings and seals in electric motors and generators. It provides detailed information on optimizing
bearing arrangements, maximizing service life, and includes recommendations based on SKF's extensive experience.
1. Rolling Bearings in Electric Machines:- Design Requirements: Discusses parameters like power output, dimensions, and materials, emphasizing operating conditions, maintenance, and manufacturing methods.
- Bearing Selection: Covers different types of bearings such as deep groove ball bearings, cylindrical roller bearings, and hybrid bearings, highlighting their applications based on load and speed requirements.
2. Bearing Systems: Focuses on selecting appropriate bearing systems and the importance of preloading with springs to ensure optimal performance.
3. Seals in Electric Machines: Details design requirements for seals, including integral bearing seals and shaft seals, to enhance machine reliability and reduce friction.
4. Tolerances and Fits: Provides guidelines on shaft and housing tolerances and recommended fits to ensure proper bearing function.
5. Lubrication: Discusses lubrication methods, grease selection, and relubrication intervals to extend bearing life and improve efficiency.
6. Bearing Mounting, Dismounting, and Motor Testing: Outlines procedures for mounting and dismounting bearings and preparing motors for transport and testing.
7. Bearing Damage and Corrective Actions: Identifies common causes of bearing damage such as fatigue, wear, and corrosion, and suggests corrective actions.
8. SKF Solutions: Highlights SKF's engineering consultancy services, calculation tools, and condition monitoring technologies to support customers in optimizing their operations.
Conclusion: The handbook serves as a valuable resource for optimizing the design and maintenance of electric machines, leveraging SKF's global expertise and innovative solutions to enhance performance and sustainability.
Specifications and Speed Considerations: Electric motors' speed is determined by their supply frequency. Variable speed operations require careful consideration of all speed intervals for bearing dimensioning and life calculation. Induction motors with frequency converters need special bearing selection due to potential electrical erosion issues.
High-Speed Applications: Ball bearings are generally more suitable for high-speed applications than roller bearings. High-precision or hybrid bearings may be necessary for very high speeds, requiring a thorough analysis of the machine's dynamic performance.
Design Considerations: Key design considerations include boundary dimensions, load magnitude and direction, speed type, shaft and housing materials, and environmental factors. Proper alignment is crucial for coupling drives to avoid additional forces that reduce bearing life.
Environmental and Temperature Factors: Seals and shields are essential in damp or dusty environments to protect bearings. The ambient and operating temperature ranges are critical for selecting the cooling method and grease type.
Vibration and Noise: Ball bearings are recommended in environments with external vibrations. Quiet operation is achieved by selecting bearings with optimal cage material, lubricant, and internal clearance.
Bearing Life and Maintenance: Bearing life is defined by the number of revolutions or operating hours before metal fatigue occurs. SKF bearings can exceed traditional life calculations under specific conditions. Maintenance involves regular lubrication and condition monitoring.
Lubrication: Grease vs. Oil: Grease is preferred for easy maintenance and protection against contaminants, while oil is used for additional cooling in high-speed applications.
Handling and Precision: Proper handling and the use of correct tools are essential for bearing performance. The required precision of bearings depends on the machine's accuracy needs.
Bearing Selection and Internal Clearance: Electric motors use various bearing types, with selection influenced by design requirements and operating conditions. Internal clearance is crucial for accommodating thermal expansion and ensuring adequate operating clearance.
Preload and Clearance: The document emphasizes the importance of selecting the correct preload force for bearing systems. Excessive preload can reduce bearing life due to increased friction and heat.
Cages: Various cage types and materials are available for different applications and operating conditions.
Bearing Selection for Electric Servomotors: The document provides a calculation example for selecting bearings for a servomotor with a gear drive.
Lubrication and Grease Life: The grease life is a critical factor in bearing performance. SKF Explorer bearings with GJN or WT grease are recommended for extended grease life.
Deep Groove Ball Bearings: These bearings are commonly used in electric motors due to their low friction, high-speed capability, and ability to carry radial, axial, and combined loads.
Specifications and Features: SKF E2 deep groove ball bearings are designed to reduce friction and run cooler compared to SKF Explorer bearings.
SKF Quiet Running Bearings: These bearings are tailored for wind turbine generators, offering consistent performance under variable conditions.
Cylindrical Roller Bearings: Used in medium to large electric motors, these bearings handle heavy radial loads and are available in various configurations.
INSOCOAT Bearings: These electrically insulated bearings prevent current passage, enhancing reliability and machine uptime.
Hybrid Bearings: Hybrid bearings, with silicon nitride rolling elements, provide excellent electrical insulation and higher speed capabilities.
Angular Contact Ball Bearings: Primarily used in vertical electric motors for heavy axial loads, these bearings are available in single or double row designs.
Spherical Roller Bearings: These bearings are used in large electric motors and generators, offering high load capacity and self-aligning features.
CARB Toroidal Roller Bearings: Designed for non-locating positions, these bearings support heavy radial loads and accommodate axial displacement and misalignment.
Spherical Roller Thrust Bearings: These bearings handle heavy thrust and radial loads, suitable for applications like vertical power turbines.
Bearing Systems: In electric motors and generators, a typical bearing system includes a locating and a non-locating bearing.
1. Bearing Systems:- Small Motors: Typically use a cross locating system with two deep groove ball bearings.
- Medium to Large Motors: Use two deep groove ball bearings with the drive end bearing as the locating bearing.
- Systems for Belt Drives: May use cylindrical roller bearings or CARB bearings to accommodate radial loads from belt tension.
2. Aluminium Housings: Due to higher thermal expansion, O-rings are recommended to prevent outer ring creep.
3. Bearing Arrangements: Various configurations are discussed, including deep groove ball bearings, cylindrical roller bearings, and spherical roller bearings.
4. Preloading with Springs: Axial preloading using springs is recommended to maintain consistent preload force, reduce noise, and prevent false brinelling.
5. Seals in Electric Machines: Sealing systems are crucial for protecting electric machines from contaminants while minimizing friction and wear.
Seals in Electric Machines:
Design Requirements: The sealing system in electric machines must meet various design parameters, including mechanical conditions, contaminants, speed, and temperature.
Integral Bearing Seals: These seals are crucial for maintaining lubricant and excluding contaminants.
Shaft Seals: Shaft seals are designed to seal the gap between the rotor shaft and stator housing, retaining lubricant and excluding contaminants.
Seal Materials: The material of the sealing lip significantly impacts performance and reliability.
Specifications and Materials: PTFE seal elements require a high-quality seal counterface and careful installation for optimal performance.
Safety Precautions: When handling seals exposed to high temperatures, protective gear such as goggles, gloves, and breathing apparatus should be worn.
Seal Designs and Performance: Table 2 compares various seal designs like gap, labyrinth, and radial shaft seals.
Special Seals: Special applications, such as those in the pharmaceutical industry, require customized sealing solutions.
Tolerances and Fits: Proper shaft and housing fits are crucial for bearing performance.
Recommended Fits: Tables provide recommendations for fits in electric motors, considering factors like load conditions and shaft diameter.
Temperature Considerations: Temperature differences between the housing and bearing can affect fit selection.
Specifications and Tolerances: The document discusses the importance of selecting appropriate fits and tolerances for bearing seats on shafts and in housings.
Recommended Fits and Solutions: For applications with indeterminate load directions, the document suggests methods to prevent outer ring creep.
Lubrication: Lubrication is crucial for bearing reliability and longevity.
Grease Lubrication: Grease is preferred for its simplicity and cost-effectiveness.
Grease Selection: Choosing the right grease involves considering bearing type, size, operating temperature, load, speed, and environmental conditions.
Key Tables and Diagrams: Tables and diagrams provide detailed information on geometrical tolerances, ISO tolerance grades, and suitable SKF greases for different applications.
Specifications and Bearing Types: Cylindrical, tapered, and CARB toroidal roller bearings are discussed with speed classifications.
Lubrication and Grease Selection: Proper lubrication is crucial for bearing performance.
Grease Life and Replenishment: Grease life depends on bearing type, grease type, motor orientation, speed, and operating temperature.
Relubrication Intervals: Relubrication intervals are statistically determined, with recommendations based on speed factor A and load ratio C/P.
Grease Escape Valve: For high-speed applications requiring frequent relubrication, a grease escape valve is recommended.
Automatic Lubricators: SKF SYSTEM 24 and MultiPoint Automatic Lubricators offer reliable alternatives to manual greasing.
Electromechanical Devices and Applications: Electromechanical devices can support up to 20 lines and are suitable for applications requiring longer feed lines or higher feed pressures.
Automatic Lubrication Systems: Automatic lubrication systems extend service intervals and enhance reliability by eliminating the need for manual lubrication.
Grease Life for Capped Bearings: The grease life for capped bearings is defined as L10, indicating the period after which 90% of bearings remain reliably lubricated.
Oil Lubrication: Oil is preferred over grease for high-speed or high-temperature applications.
Bearing Mounting and Dismounting: Proper handling and mounting of rolling bearings are essential for their performance.
Introduction: This document provides detailed procedures and recommendations for mounting and dismounting bearings, specifically focusing on SKF bearings.
Specifications and Preparations: Before mounting, it is crucial to remove any preservative from the bearing's bore and outside diameter.
Mounting Methods: Cold Mounting: Suitable for bearings up to 100 mm bore diameter. Hot Mounting: Necessary for larger bearings where the force required is significant.
Tools for Mounting: SKF offers a range of tools for both cold and hot mounting.
Mounting Non-separable and Separable Bearings: Non-separable bearings should be mounted on the shaft first, followed by the housing.
Alignment and Lubrication: Proper alignment between the shaft and housing is essential to maximize bearing life.
Dismounting Procedures: Before dismounting, study assembly drawings and inspect the motor for damage.
Conclusion: Proper mounting and dismounting of bearings are critical to their performance and longevity.
Dismounting Bearings: When dismounting bearings, especially those with interference fits, various tools and methods can be employed to facilitate the process.
Presses and Heaters: Presses can be used to remove bearings from rotor shafts.
Motor Testing and Transport Preparation: After assembly, motors should be tested for electrical and mechanical compliance.
Bearing Damage and Corrective Actions: Bearings can fail due to various reasons including fatigue, wear, corrosion, and electrical erosion.
Fatigue and Wear: Fatigue can be surface or subsurface initiated, often due to inadequate lubrication.
Corrosion: Corrosion, particularly from moisture, can cause significant damage.
Fretting Corrosion: This type of corrosion occurs due to micro-movements between the bearing and its housing or shaft.
False Brinelling: Occurs in stationary bearings under load due to micro-movements and vibrations.
Corrective Actions: To prevent moisture corrosion, store bearings in dry areas and use protective packaging.
Electrical Erosion: Caused by current passing through bearings, leading to damage similar to electric arc welding.
Corrective Actions for Electrical Erosion: Insulate the shaft from the housing using solutions like ceramic coatings or hybrid bearings.
Plastic Deformation: Occurs when the material's yield strength is exceeded, often due to overload or shock loads.
Introduction: This document provides an in-depth analysis of bearing damage, corrective actions, and SKF solutions.
Bearing Damage and Corrective Actions:- Indentation: Dents on bearing surfaces can result from debris or improper handling.
- Fracture and Cracking: These occur when the material's tensile strength is exceeded.
SKF Solutions:- Engineering Consultancy Services: SKF offers consultancy services to predict bearing performance accurately.
- Calculation Tools: SKF provides a comprehensive set of modeling and simulation tools for bearing design and analysis.
- Application Specific Solutions: SKF offers solutions for electric motors, including shaft grounding rings and magnetic bearings.
Conclusion: SKF's extensive knowledge and advanced tools provide effective solutions for bearing-related issues.
SKF Sensor-Bearing Unit: The SKF sensor-bearing unit is designed to occupy no extra radial space and is well-protected inside the motor.
Large Electric Machines: Commonly, large electric motors use sleeve bearing units, which can be costly and require additional equipment to maintain lubrication.
Traction Motors: SKF provides a traction motor bearing unit (TMBU) that is pre-lubricated and designed for flange mounting.
Wind Turbine Generators: Wind turbines use generators that can suffer from electrical erosion due to high-frequency currents.
Gear Motors: SKF's ICOS units integrate a spring-loaded radial shaft seal into a bearing.
Condition Monitoring Technologies: SKF offers various condition monitoring technologies, including vibration analysis and multi-parameter monitoring.
Continuous Monitoring: SKF's online monitoring systems, combined with SKF @ptitude software, provide real-time analysis and data consistency.
Overview of SKF Solutions for Motor Testing and Monitoring:
1. Introduction to SKF Monitoring Systems: SKF provides a comprehensive range of solutions for condition monitoring and motor testing.
2. Electric Motor Test Equipment: SKF offers a variety of static, dynamic, and online motor test and monitoring equipment.
3. Static Electric Motor Testing: SKF Static Motor Analyzers are portable instruments that perform extensive insulation and circuit tests.
4. Dynamic Electric Motor Testing: The SKF Dynamic Motor Analyzer – EXP4000 is used to evaluate motor and system performance under operational conditions.
5. Online Motor Monitoring: The SKF Dynamic Motor Analyzer – NetEP offers a permanent solution for continuous monitoring of motor systems.
6. Motor Quality Control and Assurance: SKF’s Baker WinAST and Baker WinTATS systems are used by motor manufacturers for quality assurance.
7. Maintenance Products: SKF provides a wide range of maintenance products, including tools like hydraulic jaw pullers.
8. Electrical Discharge Detection: The SKF Electrical Discharge Detector Pen (TKED 1) helps detect harmful electrical discharges in motor bearings.
9. Certification Program for Electric Motor Service Companies: The SKF Certified Rebuilder Electric Motor program enhances the expertise of repair shops through training and technology upgrades.
SKF bearings with Solid Oil
Rolling bearings
