This document discusses vibration monitoring of industrial gearboxes using accelerometers. It provides examples of analyzing both low-frequency and high-frequency vibration data to diagnose various gearbox faults. Proper sensor selection and mounting are emphasized, as they can significantly impact the ability to detect high-frequency impacts and friction. Case studies demonstrate how the techniques can be used to identify issues like lack of lubrication, bearing faults, and torsional resonance in different industrial gearbox applications.
Vibration analysis uses FFT to transform time domain vibration data into the frequency domain spectrum. Key parameters like acceleration, velocity, crest factor, kurtosis, and noise levels are used to monitor rotational forces, impacts/shocks, and friction within machines. Fault frequencies corresponding to machine components like bearings and gears are identified and compared to spectral peaks to diagnose issues. Phase analysis can also identify unbalance or misalignment. Proper data collection and machine parameters like RPM are critical for effective vibration analysis.
Rotordynamics is the branch of engineering that studies the vibrations of rotating shafts. There are three main modes of vibration during rotation - torsional, longitudinal, and lateral vibrations, with lateral vibrations being the greatest concern. Factors like unbalance, misalignment, and bearing failures can cause rotor failure. Critical speeds occur when the rotational speed matches the natural frequency of the system, potentially leading to resonance. Stability and unbalance response are also major areas of concern in rotordynamics analysis.
This document discusses machine vibration diagnosis through FFT analysis. It provides examples of using FFT analysis to diagnose issues like rotor unbalance, shaft misalignment, field asymmetry, and a loose belt drive wheel. FFT analysis allows identifying fault frequencies in the machine's vibration spectrum to pinpoint the root cause of issues. The document also discusses ISO standards for vibration severity, components vulnerable to damage, and practical diagnosis techniques.
The document discusses muffler systems and their functions. It describes how mufflers decrease noise from internal combustion engines by using passages and chambers lined with fiberglass or resonating chambers to cause destructive interference of sound waves. It then discusses three main types of mufflers: chamber mufflers, which have multiple chambers to slow and absorb sound; straight-through mufflers, which allow straight exhaust flow to quickly remove noise; and turbo mufflers, which use a turbine to quickly decrease noise pressure from high engine exhaust pressures. Diagrams of exhaust flow versus sound and muffler material are also included.
The document describes a vibration measuring instrument used to measure displacement of vibrating systems. It consists of a frame with a seismic mass supported by a spring and damper. The mass vibrates along with the vibrating body and its displacement is measured relative to a scale on the frame. For large frequency ratios of the vibrating body to the instrument, the instrument can accurately measure the amplitude. With sufficient damping, it provides a good approximation over a wide frequency range, allowing high frequencies to be measured using a low frequency instrument.
5 automatic braking system in hill stationSathis Kumar
The document discusses automatic braking systems for vehicles in hill stations. It describes the common problem of vehicles rolling backwards when starting to move uphill. It proposes using a ratchet and pawl mechanism to prevent rollback. This mechanism would allow forward motion but prevent backward motion. It discusses how previous solutions had limitations and were not fully effective mechanical solutions to prevent rollback.
This document discusses free vibration in mechanical systems. It defines free vibration as the vibrations of a system that is initially disturbed and then left to vibrate on its own without external forces. Key topics covered include degrees of freedom, natural frequency, types of damping, critical speeds of shafts, and causes of vibration such as unbalance and misalignment. Both undesirable effects and potential useful applications of vibrations are mentioned.
Vibration analysis uses FFT to transform time domain vibration data into the frequency domain spectrum. Key parameters like acceleration, velocity, crest factor, kurtosis, and noise levels are used to monitor rotational forces, impacts/shocks, and friction within machines. Fault frequencies corresponding to machine components like bearings and gears are identified and compared to spectral peaks to diagnose issues. Phase analysis can also identify unbalance or misalignment. Proper data collection and machine parameters like RPM are critical for effective vibration analysis.
Rotordynamics is the branch of engineering that studies the vibrations of rotating shafts. There are three main modes of vibration during rotation - torsional, longitudinal, and lateral vibrations, with lateral vibrations being the greatest concern. Factors like unbalance, misalignment, and bearing failures can cause rotor failure. Critical speeds occur when the rotational speed matches the natural frequency of the system, potentially leading to resonance. Stability and unbalance response are also major areas of concern in rotordynamics analysis.
This document discusses machine vibration diagnosis through FFT analysis. It provides examples of using FFT analysis to diagnose issues like rotor unbalance, shaft misalignment, field asymmetry, and a loose belt drive wheel. FFT analysis allows identifying fault frequencies in the machine's vibration spectrum to pinpoint the root cause of issues. The document also discusses ISO standards for vibration severity, components vulnerable to damage, and practical diagnosis techniques.
The document discusses muffler systems and their functions. It describes how mufflers decrease noise from internal combustion engines by using passages and chambers lined with fiberglass or resonating chambers to cause destructive interference of sound waves. It then discusses three main types of mufflers: chamber mufflers, which have multiple chambers to slow and absorb sound; straight-through mufflers, which allow straight exhaust flow to quickly remove noise; and turbo mufflers, which use a turbine to quickly decrease noise pressure from high engine exhaust pressures. Diagrams of exhaust flow versus sound and muffler material are also included.
The document describes a vibration measuring instrument used to measure displacement of vibrating systems. It consists of a frame with a seismic mass supported by a spring and damper. The mass vibrates along with the vibrating body and its displacement is measured relative to a scale on the frame. For large frequency ratios of the vibrating body to the instrument, the instrument can accurately measure the amplitude. With sufficient damping, it provides a good approximation over a wide frequency range, allowing high frequencies to be measured using a low frequency instrument.
5 automatic braking system in hill stationSathis Kumar
The document discusses automatic braking systems for vehicles in hill stations. It describes the common problem of vehicles rolling backwards when starting to move uphill. It proposes using a ratchet and pawl mechanism to prevent rollback. This mechanism would allow forward motion but prevent backward motion. It discusses how previous solutions had limitations and were not fully effective mechanical solutions to prevent rollback.
This document discusses free vibration in mechanical systems. It defines free vibration as the vibrations of a system that is initially disturbed and then left to vibrate on its own without external forces. Key topics covered include degrees of freedom, natural frequency, types of damping, critical speeds of shafts, and causes of vibration such as unbalance and misalignment. Both undesirable effects and potential useful applications of vibrations are mentioned.
The document discusses different types of gearboxes used in vehicles including sliding mesh, constant mesh, and synchromesh gearboxes. It explains their basic workings, advantages, and disadvantages. The document also covers topics like vehicle resistance, torque converter, and epicyclic gear sets used in automatic transmissions.
Brakes use friction between brake pads or shoes and the drum or disc to convert kinetic energy of a moving vehicle into heat energy, slowing the vehicle down. There are different types of brakes such as air brakes and hydraulic brakes. Dynamometers are used to measure the power output of engines. There are absorption dynamometers which absorb all the engine's energy as heat and transmission dynamometers which transmit the energy for work. Common absorption dynamometers are prony brake and rope brake dynamometers, while common transmission dynamometers are epicyclic train, belt transmission, and torsion dynamometers.
This document discusses forced vibration, which occurs when a body vibrates under the influence of an external force. There are three types of external excitation forces: periodic, impulsive, and random. For a spring mass system undergoing harmonic disturbances, the amplitude and maximum amplitude of forced vibration are given by formulas involving the excited force, phase lag, and angular velocity. Phase lag and magnification factor are also discussed. Forced vibration due to unbalance and support motion are described. Transmissibility and vibration isolation are then defined and different types are explained.
The document discusses balancing of rotating masses. It explains static and dynamic balancing, and balancing of single and multiple rotating masses using balancing masses in the same plane and different planes. Methods for analytical and graphical determination of balancing masses are provided for single and multiple rotating masses. Conditions for static and dynamic balancing are outlined for cases where disturbing masses are balanced by masses in different planes as well as when multiple masses rotate in different planes.
Governing of the Turbine | Fluid MechanicsSatish Taji
Watch Video of this presentation on Link: https://youtu.be/LmJtNo-zgjo
For notes/articles, Visit my blog (link is given below).
For Video, Visit our YouTube Channel (link is given below).
Any Suggestions/doubts/reactions, please leave in the comment box.
Follow Us on
YouTube: https://www.youtube.com/channel/UCVPftVoKZoIxVH_gh09bMkw/
Blog: https://e-gyaankosh.blogspot.com/
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Vibration analysis is used to identify issues in rotating machinery by analyzing vibration signatures. Common issues that can be identified include unbalance, misalignment, looseness, bearing faults, and resonance. Vibration signals are analyzed in the time, frequency, and phase domains to identify characteristic frequencies, amplitudes, and phase relationships that correspond to different problem sources. Overall vibration levels and narrowband spectrum peaks are monitored over time for trends that may indicate developing issues.
This document provides information on various vibration signatures and their potential causes. It discusses signatures related to unbalance, misalignment, looseness, resonance, gears, bearings, electrical issues, and other faults. Key points covered include the relationships between frequency peaks, phase measurements, speed-dependent amplitudes, and how different fault types affect the vibration spectrum.
This document provides an overview of fundamentals of vibration. It discusses what vibration is, common causes of vibration, effects of vibration, reasons for studying vibration, degrees of freedom in vibratory systems, classifications of vibration, and the typical procedure for vibration analysis. Vibration is defined as oscillatory motion about an equilibrium point that is usually caused by external or internal forces disturbing a mechanical component from its resting position. Causes can include things like irregular road profiles or unbalanced engine forces. Effects include passenger discomfort, mechanical failures, and material fatigue over time. Vibration analysis involves mathematically modeling a system, deriving governing equations, solving those equations, and interpreting the results.
This document contains lecture notes on mechanical vibrations. It covers topics such as two degree of freedom systems, principal modes, double pendulums, torsional systems with damping, coupled systems, vibration absorbers, centrifugal pendulum absorbers, vibration isolators, and dampers. Examples of two degree of freedom systems include two masses connected by springs. Equations of motion are derived using mass and stiffness matrices. Torsional vibrations in shafts can be caused by inertia forces or shock loads. Centrifugal pendulum absorbers have a natural frequency that varies with rotational speed, making them well-suited for applications like engines.
The document summarizes the governing mechanism of a Francis water turbine. It describes the major components which include an oil pump, relay valve, servomotor cylinder, centrifugal governor, regulating ring, and regulating rod. It explains how these components work together in a closed loop control system to regulate the supply of water through partial opening and closing of the guide vanes based on the load. When the load is low, the governor senses the higher speed and causes the relay valve to direct oil to push the servomotor piston forward, partially closing the guide vanes.
1. Unbalance vibration occurs when the center of mass of a rotating object is not aligned with its center of rotation, causing a wobbling motion.
2. There are three main types of unbalance: static, couple, and dynamic. Static unbalance can be corrected by adding or removing weight in one plane, while couple and dynamic require weights added in two or more planes.
3. Unbalance vibration produces a single frequency vibration at the object's rotational speed and can cause damage, noise, and reduced machine life if not addressed.
This document discusses the design of flywheels. It begins by introducing flywheels as inertial energy storage devices that absorb mechanical energy and serve as reservoirs, storing energy when supply exceeds demand and releasing it when demand exceeds supply. It then discusses two stages of flywheel design: determining the required energy and inertia, and defining the geometry. The document provides equations for determining inertia based on required energy change and speed fluctuation coefficient. It also discusses stresses in flywheels due to centrifugal force and modern high-speed composite flywheel designs. Applications mentioned include smoothing speed fluctuations in engines and powering electric vehicles.
Friction clutches, brakes and dynamometerajitkarpe1986
This document discusses clutches, brakes, and dynamometers. It provides theories and types of clutches like plate clutches, cone clutches, and centrifugal clutches. It also discusses different types of brakes such as shoe brakes, band brakes, block brakes, and disc brakes. Finally, it covers absorption dynamometers including Prony, rope, and band brake dynamometers as well as transmission dynamometers like epicyclic train and belt transmission dynamometers.
This document discusses the cam jump phenomenon in cam and follower mechanisms. It defines cam jump as occurring under high speeds when the unbalanced forces during negative acceleration exceed the spring force, causing the cam and follower to separate. It presents the equations of motion for a follower under the forces of inertia, spring, and cam. It identifies the critical speed as when the force on the follower is zero, indicating no contact. Above this speed, hammering noises occur due to cam jump. The document recommends increasing preload and spring stiffness to avoid cam jump to some extent.
The turning moment diagram graphically represents the torque required by an engine at different crank angles. It is used to determine the fluctuation of energy in the engine and the role of the flywheel in reducing speed variations. The flywheel stores excess energy produced during power strokes and releases it during non-power strokes, allowing the crankshaft to rotate at a more uniform speed. The maximum difference between the energy stored in the flywheel at its highest and lowest points is known as the maximum fluctuation of energy. Larger flywheels can reduce speed fluctuations more, but require more space.
Unit 7-gear trains, Kinematics of machines of VTU Syllabus prepared by Hareesha N Gowda, Asst. Prof, Dayananda Sagar College of Engg, Blore. Please write to hareeshang@gmail.com for suggestions and criticisms.
The document discusses vibration theory, including definitions of acceleration, velocity, displacement and simple harmonic motion. It describes quantifying vibration amplitude using peak-to-peak, peak, average and RMS levels. It also covers the differences between time and frequency domain analysis and concepts of phase angle measurement in condition monitoring. Condition monitoring strategies aim to focus on critical machinery by defining detectable faults and relevant measurement parameters.
This document discusses the calculation of bearing life and dynamic load ratings. It provides formulas and factors for calculating the radial and axial forces on bearings based on machine design and operating conditions. It also summarizes the Lundberg-Palmgren and SKF equations for calculating an equivalent dynamic bearing load and adjusted rating life of a bearing based on operating load and speed.
A gearbox manages a series of gear ratios to deliver power from an engine to a transmission. It provides multiple torque ratios for varying acceleration and climbing gradients, and allows for reversing the vehicle's motion. A sliding mesh gearbox typically has 3 forward gears and 1 reverse gear. It uses spur gears on the main shaft that engage with gears on the lay shaft by sliding into position. When the engine is running and clutch engaged, power flows from the clutch shaft gear to the lay shaft gears, but the main shaft remains idle until a gear is engaged to transfer power through the transmission.
This document summarizes information about journal bearings. It defines a journal bearing as a block of cast iron with a hole for supporting a rotating shaft. It describes how lubricating oil is fed into the bearing and dragged by the shaft, creating hydrodynamic lift and resisting shaft motion. There are three types of journal bearings: dry, hydrodynamic, and hydrostatic. The document discusses the pressure distribution in a journal bearing due to the flow of viscous fluid in a converging channel, and defines the eccentricity ratio as the ratio of eccentricity to radial clearance. It concludes with discussing the study of bearing functions and types, and viewing the pressure distribution curve of a journal bearing.
Fundamentals of vibration_measurement_and_analysis_explainedvibratiob
The document discusses fundamentals of vibration measurement and analysis. It begins by explaining how measurement and analysis has been improved by microprocessors but the basic processes remain unchanged. It then covers basics of vibration including relationships between displacement, velocity, acceleration. It discusses measuring vibration using accelerometers and calculating overall values and frequency spectra. Finally it discusses concepts like resonance, damping, and natural frequencies and how understanding these fundamentals is important for vibration analysis and fault diagnosis.
Fundamentals of vibration_measurement_and_analysis_explainedmanojkumarg1990
This document discusses fundamentals of vibration measurement and analysis. It explains that vibration data can now be collected and analyzed more quickly due to advances in microprocessors, but the basic processes remain unchanged. It then describes the fundamentals of vibration in machines using a mass-spring-damper model, and how vibration is measured using sensors like accelerometers. It discusses overall vibration values and frequency spectra analysis to understand the frequency components that make up complex vibration waveforms.
The document discusses different types of gearboxes used in vehicles including sliding mesh, constant mesh, and synchromesh gearboxes. It explains their basic workings, advantages, and disadvantages. The document also covers topics like vehicle resistance, torque converter, and epicyclic gear sets used in automatic transmissions.
Brakes use friction between brake pads or shoes and the drum or disc to convert kinetic energy of a moving vehicle into heat energy, slowing the vehicle down. There are different types of brakes such as air brakes and hydraulic brakes. Dynamometers are used to measure the power output of engines. There are absorption dynamometers which absorb all the engine's energy as heat and transmission dynamometers which transmit the energy for work. Common absorption dynamometers are prony brake and rope brake dynamometers, while common transmission dynamometers are epicyclic train, belt transmission, and torsion dynamometers.
This document discusses forced vibration, which occurs when a body vibrates under the influence of an external force. There are three types of external excitation forces: periodic, impulsive, and random. For a spring mass system undergoing harmonic disturbances, the amplitude and maximum amplitude of forced vibration are given by formulas involving the excited force, phase lag, and angular velocity. Phase lag and magnification factor are also discussed. Forced vibration due to unbalance and support motion are described. Transmissibility and vibration isolation are then defined and different types are explained.
The document discusses balancing of rotating masses. It explains static and dynamic balancing, and balancing of single and multiple rotating masses using balancing masses in the same plane and different planes. Methods for analytical and graphical determination of balancing masses are provided for single and multiple rotating masses. Conditions for static and dynamic balancing are outlined for cases where disturbing masses are balanced by masses in different planes as well as when multiple masses rotate in different planes.
Governing of the Turbine | Fluid MechanicsSatish Taji
Watch Video of this presentation on Link: https://youtu.be/LmJtNo-zgjo
For notes/articles, Visit my blog (link is given below).
For Video, Visit our YouTube Channel (link is given below).
Any Suggestions/doubts/reactions, please leave in the comment box.
Follow Us on
YouTube: https://www.youtube.com/channel/UCVPftVoKZoIxVH_gh09bMkw/
Blog: https://e-gyaankosh.blogspot.com/
Facebook: https://www.facebook.com/egyaankosh/
Vibration analysis is used to identify issues in rotating machinery by analyzing vibration signatures. Common issues that can be identified include unbalance, misalignment, looseness, bearing faults, and resonance. Vibration signals are analyzed in the time, frequency, and phase domains to identify characteristic frequencies, amplitudes, and phase relationships that correspond to different problem sources. Overall vibration levels and narrowband spectrum peaks are monitored over time for trends that may indicate developing issues.
This document provides information on various vibration signatures and their potential causes. It discusses signatures related to unbalance, misalignment, looseness, resonance, gears, bearings, electrical issues, and other faults. Key points covered include the relationships between frequency peaks, phase measurements, speed-dependent amplitudes, and how different fault types affect the vibration spectrum.
This document provides an overview of fundamentals of vibration. It discusses what vibration is, common causes of vibration, effects of vibration, reasons for studying vibration, degrees of freedom in vibratory systems, classifications of vibration, and the typical procedure for vibration analysis. Vibration is defined as oscillatory motion about an equilibrium point that is usually caused by external or internal forces disturbing a mechanical component from its resting position. Causes can include things like irregular road profiles or unbalanced engine forces. Effects include passenger discomfort, mechanical failures, and material fatigue over time. Vibration analysis involves mathematically modeling a system, deriving governing equations, solving those equations, and interpreting the results.
This document contains lecture notes on mechanical vibrations. It covers topics such as two degree of freedom systems, principal modes, double pendulums, torsional systems with damping, coupled systems, vibration absorbers, centrifugal pendulum absorbers, vibration isolators, and dampers. Examples of two degree of freedom systems include two masses connected by springs. Equations of motion are derived using mass and stiffness matrices. Torsional vibrations in shafts can be caused by inertia forces or shock loads. Centrifugal pendulum absorbers have a natural frequency that varies with rotational speed, making them well-suited for applications like engines.
The document summarizes the governing mechanism of a Francis water turbine. It describes the major components which include an oil pump, relay valve, servomotor cylinder, centrifugal governor, regulating ring, and regulating rod. It explains how these components work together in a closed loop control system to regulate the supply of water through partial opening and closing of the guide vanes based on the load. When the load is low, the governor senses the higher speed and causes the relay valve to direct oil to push the servomotor piston forward, partially closing the guide vanes.
1. Unbalance vibration occurs when the center of mass of a rotating object is not aligned with its center of rotation, causing a wobbling motion.
2. There are three main types of unbalance: static, couple, and dynamic. Static unbalance can be corrected by adding or removing weight in one plane, while couple and dynamic require weights added in two or more planes.
3. Unbalance vibration produces a single frequency vibration at the object's rotational speed and can cause damage, noise, and reduced machine life if not addressed.
This document discusses the design of flywheels. It begins by introducing flywheels as inertial energy storage devices that absorb mechanical energy and serve as reservoirs, storing energy when supply exceeds demand and releasing it when demand exceeds supply. It then discusses two stages of flywheel design: determining the required energy and inertia, and defining the geometry. The document provides equations for determining inertia based on required energy change and speed fluctuation coefficient. It also discusses stresses in flywheels due to centrifugal force and modern high-speed composite flywheel designs. Applications mentioned include smoothing speed fluctuations in engines and powering electric vehicles.
Friction clutches, brakes and dynamometerajitkarpe1986
This document discusses clutches, brakes, and dynamometers. It provides theories and types of clutches like plate clutches, cone clutches, and centrifugal clutches. It also discusses different types of brakes such as shoe brakes, band brakes, block brakes, and disc brakes. Finally, it covers absorption dynamometers including Prony, rope, and band brake dynamometers as well as transmission dynamometers like epicyclic train and belt transmission dynamometers.
This document discusses the cam jump phenomenon in cam and follower mechanisms. It defines cam jump as occurring under high speeds when the unbalanced forces during negative acceleration exceed the spring force, causing the cam and follower to separate. It presents the equations of motion for a follower under the forces of inertia, spring, and cam. It identifies the critical speed as when the force on the follower is zero, indicating no contact. Above this speed, hammering noises occur due to cam jump. The document recommends increasing preload and spring stiffness to avoid cam jump to some extent.
The turning moment diagram graphically represents the torque required by an engine at different crank angles. It is used to determine the fluctuation of energy in the engine and the role of the flywheel in reducing speed variations. The flywheel stores excess energy produced during power strokes and releases it during non-power strokes, allowing the crankshaft to rotate at a more uniform speed. The maximum difference between the energy stored in the flywheel at its highest and lowest points is known as the maximum fluctuation of energy. Larger flywheels can reduce speed fluctuations more, but require more space.
Unit 7-gear trains, Kinematics of machines of VTU Syllabus prepared by Hareesha N Gowda, Asst. Prof, Dayananda Sagar College of Engg, Blore. Please write to hareeshang@gmail.com for suggestions and criticisms.
The document discusses vibration theory, including definitions of acceleration, velocity, displacement and simple harmonic motion. It describes quantifying vibration amplitude using peak-to-peak, peak, average and RMS levels. It also covers the differences between time and frequency domain analysis and concepts of phase angle measurement in condition monitoring. Condition monitoring strategies aim to focus on critical machinery by defining detectable faults and relevant measurement parameters.
This document discusses the calculation of bearing life and dynamic load ratings. It provides formulas and factors for calculating the radial and axial forces on bearings based on machine design and operating conditions. It also summarizes the Lundberg-Palmgren and SKF equations for calculating an equivalent dynamic bearing load and adjusted rating life of a bearing based on operating load and speed.
A gearbox manages a series of gear ratios to deliver power from an engine to a transmission. It provides multiple torque ratios for varying acceleration and climbing gradients, and allows for reversing the vehicle's motion. A sliding mesh gearbox typically has 3 forward gears and 1 reverse gear. It uses spur gears on the main shaft that engage with gears on the lay shaft by sliding into position. When the engine is running and clutch engaged, power flows from the clutch shaft gear to the lay shaft gears, but the main shaft remains idle until a gear is engaged to transfer power through the transmission.
This document summarizes information about journal bearings. It defines a journal bearing as a block of cast iron with a hole for supporting a rotating shaft. It describes how lubricating oil is fed into the bearing and dragged by the shaft, creating hydrodynamic lift and resisting shaft motion. There are three types of journal bearings: dry, hydrodynamic, and hydrostatic. The document discusses the pressure distribution in a journal bearing due to the flow of viscous fluid in a converging channel, and defines the eccentricity ratio as the ratio of eccentricity to radial clearance. It concludes with discussing the study of bearing functions and types, and viewing the pressure distribution curve of a journal bearing.
Fundamentals of vibration_measurement_and_analysis_explainedvibratiob
The document discusses fundamentals of vibration measurement and analysis. It begins by explaining how measurement and analysis has been improved by microprocessors but the basic processes remain unchanged. It then covers basics of vibration including relationships between displacement, velocity, acceleration. It discusses measuring vibration using accelerometers and calculating overall values and frequency spectra. Finally it discusses concepts like resonance, damping, and natural frequencies and how understanding these fundamentals is important for vibration analysis and fault diagnosis.
Fundamentals of vibration_measurement_and_analysis_explainedmanojkumarg1990
This document discusses fundamentals of vibration measurement and analysis. It explains that vibration data can now be collected and analyzed more quickly due to advances in microprocessors, but the basic processes remain unchanged. It then describes the fundamentals of vibration in machines using a mass-spring-damper model, and how vibration is measured using sensors like accelerometers. It discusses overall vibration values and frequency spectra analysis to understand the frequency components that make up complex vibration waveforms.
1) The document discusses using discrete wavelet transforms to analyze vibration signals from roller bearings to detect faults. It proposes a new feature - summing the squared wavelet decomposition coefficients at each level - and compares it to the traditional energy-based feature.
2) An experiment is described where vibration signals are collected from a test rig under normal conditions and with introduced inner race, outer race, and combined faults. The signals are decomposed using discrete wavelet transforms.
3) Features are then extracted from the wavelet decompositions using both the proposed summed squared coefficient feature and the traditional energy-based feature. A decision tree is used to classify the features and determine which feature performs better at detecting the faults.
This document summarizes research on using vibration signal analysis to detect wear and identify multiple faults in rolling element bearings operating under harsh conditions. A test rig was used to accelerate wear in bearings filled with contaminated grease. Vibration signals were analyzed in the time and frequency domains. Frequency analysis clearly identified faults developing on bearing raceways over time as peaks emerged at the expected fault frequencies, regardless of noise from random particle contamination. Post-test inspections verified the vibration analysis results had correctly identified the fault sources.
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
Assessment of Gearbox Fault DetectionUsing Vibration Signal Analysis and Acou...IOSR Journals
Maintenance is a set of organised activities that are carried out in order to keep an item in its best
operational condition with minimum cost acquired. Predictive maintenance (PdM) is one of the maintenance
program that recommends maintenance decisions based on the information collected through condition
monitoring techniques, statistical process control or equipment performance for the purpose of early detection
and elimination of equipment defects that could lead to unplanned downtime of machinery or unnecessary
expenditures. Particularly Gears and rolling element bearings are critical elements in rotating machinery, so
predictive maintenance is often applied to them. Fault signals of gearboxes or rolling-element bearings are nonstationary.
This paper concludes with a brief discussion on current practices of PDM methodologies such as
vibration analysis and Acoustic Emission analysis, which are widely used as they offers a complimentary tool
for health monitoring or assessment of gears in rotating machineries
IRJET- Design and Fabrication of Digital Fuel Meter with the Help of Ultrason...IRJET Journal
The document describes the design and fabrication of a digital fuel meter that uses ultrasonic sensors to measure the amount of fuel entering a vehicle's fuel tank. It has two phases: 1) A measuring tank with an ultrasonic sensor at the top to measure the distance to the fuel surface and calculate the fuel volume. 2) A storage tank that receives the fuel after measurement and supplies it to the engine. The device aims to accurately measure the fuel amount provided, which is often incorrectly reported. It works by sending and receiving ultrasonic waves and calculating the time for their propagation to determine the fuel level based on known speed of sound in air.
This document contains frequently asked questions and answers about acceleration envelope measurements. Enveloping enhances repetitive impact signals and can detect early-stage bearing and gear defects. It is most useful for low-force impact defects on rotating equipment. Both fixed-mount and portable sensors can be used, but readings may differ depending on sensor coupling. Minimal training is required for taking measurements, but interpretation requires understanding machine components and defect frequencies. Both enveloping and normal vibration analysis should be used for effective condition monitoring.
Mems Based Motor Fault Detection in Windmill Using Neural NetworksIJRES Journal
Today wind turbine technology is one of the fastest growing power generation technologies operating in large numbers at harsh and difficult environment sites and it is difficult to monitor each and every windmill separately. There are times when faults occur in motors of windmills are not detected in earlier stage and we come to know about damage when motor gets fully damaged. Here we using wireless monitoring based on MEMS accelerometer sensor which senses the vibrations occurring in the motor and based on the severity of vibrations, sensor sends the data to the controlling unit to take further action. Neural network based work is included to get the accurate and precise vibratory signals to detect fault at a very early stage to avoid full damage to the motor.
This document summarizes a research paper on using MEMS sensors and neural networks to detect faults in the motors of wind turbines. It begins with an abstract that overviews using an accelerometer sensor to detect vibrations in the motor and send the data to a control unit. It then provides background on existing vibration-based fault detection methods and proposes a new method using MEMS sensors, wavelet packet transform analysis of the sensor data, and a neural network classifier to detect faults at an early stage. The document concludes that this method allows accurate and reliable condition monitoring of wind turbines to prevent motor damage.
Fault location and correction are important in case of any power systems. This process has to be prompt and accurate so that system reliability can be improved , outage time can be reduced and restoration of system from fault can be accelerated.
Fault location calculation using Magnetoresistance sensor is described here.
WHY IS TORSIONAL VIBRATION A BETTER TECHNOLOGY?AkhilMurthy1
The information one can obtain from lateral-vibration readings concerning the condition of a machine
is well known. But by gathering torsional vibration a lot can be learned about a machine from this
data too.
This document discusses vibration sensors. It defines vibration sensors as sensors that measure linear velocity, displacement, proximity, or acceleration. Vibration sensors are used to detect problems in industrial machines early by measuring abnormal vibration. The document discusses different types of vibration sensors including velocity sensors, acceleration sensors, and proximity sensors. It provides examples of different technologies used in each type. The document also discusses characteristics to consider when selecting a vibration sensor like sensitivity range and frequency range. Finally, it provides a table matching industries to ideal sensor traits for different applications.
Microwave Radiometer Analysis for Imaging and Vehicular SystemsIRJET Journal
This document summarizes a research paper about using microwave radiometry for fire detection around moving vehicles. The paper proposes using a ground-based microwave radiometer mounted near a road or rail track to image potential fire areas on a passing vehicle. Simulations were conducted using 30 GHz microwave radiation to analyze transmission through typical vehicle walls of different materials, thicknesses, and properties. The research suggests microwave radiometry may provide early fire detection by measuring changes in emitted radiation transmitted through dielectric vehicle walls, as an alternative or supplement to existing infrared sensor systems.
This document outlines standards for instruments used to measure vibrations from sources other than earthquakes. It discusses recommended instrumentation including accelerometers, signal conditioners, and signal processors. Accelerometers are preferred for vibration studies due to their versatility, ruggedness, and accuracy. Signal conditioners amplify and filter accelerometer signals, while signal processors analyze vibration data in real-time using computers. The document provides guidelines on installing accelerometers, collecting experimental vibration data, and ensuring instrumentation is calibrated and functioning properly prior to taking measurements.
Ulas Ayaz has designed several optical sensors using microspheres as the sensing element. His shear stress sensor was the first to directly measure wall shear stress of reattaching flows. It has a flexible design that allows adjustment of resolution and bandwidth by changing the sphere material and size. Testing showed it performed well in measuring both steady and unsteady flows. Ayaz also developed a seismometer that directly measures acceleration up to 1 micro-g with high sensitivity and bandwidth up to 20 Hz using whispering gallery mode optics. Further, he designed miniature pressure, electric field, and prosthetic sensors using similar microsphere techniques.
Railway track crack detection based on GSM techniqueIRJET Journal
This document describes a proposed system for detecting cracks in railway tracks using operational amplifier (op-amp) circuits and a microcontroller with GSM capability. The system is intended to provide a cheap and automated solution for crack detection. It works by using op-amps connected to the railway tracks to detect changes in voltage from cracks. The microcontroller receives the op-amp outputs and can send crack detection information via GSM to be viewed on software. When a crack is detected, a message will be displayed on an LCD and an LED will turn red to indicate the issue and its location. The goal is to allow for low-cost and large-scale monitoring of railway tracks to improve safety.
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The braking process used on railroad cars is known to create tensile stresses in the circumferential direction due to the thermal expansion and subsequent cooling of the wheel rim. This tensile stress can significantly accelerate the growth of small cracks on the rolling surface which can cause a spall or catastrophic failure
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Vibration monitoring of Gearboxes.pdf
1. W H I T E P A P E R | # X 1
VIBRATION MONITORING
OF GEARBOXES
Written By
James C. Robinson,
Technical Consultant, IMI division of PCB Piezotronics
Curated By
Meredith Christman,
Product Marketing Manager, IMI division of PCB Piezotronics
www.PCB.com/imi-sensors | imi@pcb.com | 800.828.8840
SENSORS FOR MACHINERY HEALTH MONITORING
2. 1
VIBRATION MONITORING OF GEARBOXES
Article by:
James C Robinson, Technical Consultant, IMI division of PCB Piezotronics
Curated by:
Meredith Christman, Product Marketing Manager, IMI division of PCB Piezotronics
INTRODUCTION
Gearboxes are a common component in many industries, including chemicals, sugar, steel, mining, plastics, oil &
gas, power and petrochemical. Because their operation is essential to many manufacturing processes, planned
downtime is inconvenient and unplanned downtime can be catastrophic.
The objective of this paper is to demonstrate a wide variety of fault types and the importance of employing
proper sensors and analysis tools. Particular emphasis is placed on vibration monitoring employing
accelerometers as sensors on industrial gearboxes.
SECTION 1: SENSOR SELECTION AND MOUNTING
Potential Faults of Gearboxes: Prior to selecting sensors and addressing their mounting on a gearbox, it will first
be beneficial to remind ourselves of the characteristics of the vibration signature that can be expected from
common gearbox faults. For example, if there is a crack in a gear, it will likely introduce a slight speed change
when the defective tooth enters the load zone. This leads to impacting every time that tooth enters into its load
carrying responsibility (typically once per revolution of that gear). Now consider a situation where there is a lack
of sufficient lubrication for the gear teeth going into and out of the load zone. This leads to friction between the
teeth with the maximum activity typically occurring twice per tooth mesh (once on the addendum and once on
the dedendum). Of course, both friction and impacting can also occur within the gearboxes. In gearboxes,
impacting will generally be periodic and friction generally non-periodic (random).
If a fault is present that is generating stress wave activity on a set of meshing gears, that energy will be
transmitted to the outer housing via the shafts where the gear set is attached through the bearings (providing
they are rolling element bearings). An accelerometer fastened to the outer surface in the proximity of that
bearing would capture the stress wave activity providing the accelerometer has sufficient bandwidth and
sensitivity. If the bearing is a sleeve bearing, significant attenuation will occur to the stress waves in coupling
across the gap from inner race to outer race and thus may not be sufficient for capture by the sensor. A
proximity probe lacks sufficient sensitivity for the relatively high frequency stress wave activity.
In addition to the relatively high frequencies present in the stress wave packets generated by friction and
impacting, the lower frequencies generated by faults such as misalignment, looseness and balancing issues must
also be captured and analyzed. These stress wave packets contain frequencies in one of the following two
ranges:
• About 0.3 times running speed to about 3.25 times the gear meshing frequency.
• About 0.3 times running speed to about 50 times running speed.
The analysis of the low-frequency band is carried out by capturing a time waveform and proceeding to
transform that time waveform into spectra data on which most of the diagnostics are carried out. For the high-
frequency band, the most common procedure is to run the signal from the sensor through a high-pass filter
followed by full-wave rectification. The rectified signal is then demodulated to extract any periodic or random
3. 2
activity that is occurring. If periodic or random activity is occurring, the analyst needs to know the periodic rate
as well as the amplitude of the activity.
Classic demodulation techniques do not
maintain the true g-level. The cases
presented in this paper use the PeakVue™
methodology developed by Emerson Process
Management, which does maintain the true
peak g-level.
When the analyst does find a fault in a piece
of equipment and reports it to operations,
the typical response from operations is to
ask about the severity of the fault and how
long can the equipment continue to operate.
These questions sometimes are difficult to
answer. For the low-frequency band data,
there are several charts available in the
industry that can be used to make intelligent
judgment calls on both fault severity and
continued equipment operation. For the
high-frequency band, assuming the true peak acceleration level and
speed (RPM) are available, the chart in Figure 1 has been created to
provide similar intelligent answers on both fault severity and
continued equipment operation. The level given in the chart is the
recommended alert level; the recommended fault level is twice the
alert level.
ICP® Accelerometer Use: The most common sensor type employed in
vibration analysis on gearboxes are ICP® accelerometers with a
sensitivity of 100 mV/g, a resonant frequency in the 25 kHz range and
a noise floor of approximately 100 μg/√Hz at 1 Hz (or less). IMI
Model 603C01 (top exit with ¼-28 female mounting thread) would be
an example of an ideal model. The specification sheet for the
accelerometer typically specifies the sensitivity is nominally flat to
within 3dB from a fraction of 1 Hz to 10 kHz. See
Figure 2 for an example of the characteristic
compliance of Model 603C01.
The implicit assumption is that the sensor is
attached to a clean flat surface with a stud at a
specified torque. Because stud mounting is both
expensive and time consuming, its requirement
encourages sparse data acquisition. The analyst
will often turn to a much simpler means of
attaching the sensor to the surface, such as using
a two-rail magnet placed on a curved surface with
the sensor attached to the magnet. This approach
will often lead to not capturing the higher
frequencies associated with impacting or friction.
4. 3
To explore the impact that sensor mounting has on the sensor frequency response, frequency response data
was captured (presented in Figure 3) for a sensor that was:
• Mounted with a stud with grease on a flat dry surface.
• Mounted with a stud without grease on a flat dry surface.
• Mounted with a flat magnet on a flat clean surface.
• Mounted with a dual-rail magnet mounted on smooth curved surface.
• Mounted with a dual-rail magnet mounted on rough curved surface.
• Mounted with a dual-rail magnet mounted on painted curved surface.
For faults that manifest themselves in the frequency range of less than 2 kHz such as alignment, unbalance and
looseness, the results would be independent of how the sensor is mounted. For faults identified with higher
frequencies (impacting and friction), the results would be highly dependent to how the sensor is mounted
ranging from no response to distorted response.
Of course, the best way to mount would be stud-mount with a specified torque. This could get expensive as it
requires a dedicated accelerometer at every measurement point. An acceptable alternative mounting would be
to use a flat magnet placed on a flat smooth surface such as a mounting pad. The flat magnet approach to all
measurements points combined with stud mounting the sensor in radial direction on the inboard and outboard
ends would be a recommended
method for sensor mounting.
To illustrate the type of effect that
sensor mounting can have on friction
activity, data is presented in Figure 4
from a case where it was known that
bearing lubrication was needed. In the
lefthand time trace, the sensor was
mounted using a flat magnet attached
to a flat smooth surface. A second set
of data on the righthand time trace
was acquired from a sensor attached
to a curved surface via a dual-rail
magnet. Both time traces were taken at the
same time using a two-channel data
collector. The bearing was lubricated
(greased) at the time the sudden level of
noise decreased.
SECTION 2: COOLING TOWER GEARBOX
A metals plant lost the use of one of its
cooling towers due to a two-speed gearbox
becoming unusable. The gearbox
replacement had a long lead-time but
sufficient parts were available to put
together a temporary gearbox replacement.
When the cooling tower was placed back in
service with the temporary gearbox at low
speed, vibration velocity spectral data was
5. 4
acquired and is presented in Figure 5. The peak-to-peak g-level is less than 10 g’s, and the spectral data is a “ski
slope”. This is typical for an ICP® accelerometer that is being overloaded. The sensor was a 100 mV/g
accelerometer with a 9-11 VDC bias voltage.
The accelerometer was replaced with a 10
mV/g accelerometer with a similar bias
voltage. Using the 10 mV/g sensor, a 40 kHz
acceleration spectra data set with
waveform was captured and is presented as
Figure 6. The peak-to-peak g-level was close
to 200 g’s, explaining why the 100 mV/g
sensor’s output was unstable. The primary
cause of the high g-levels was friction
occurring within the bearings as well as
between the gear teeth as a result of an
inoperable lubrication system driven by a
gear oil pump.
The operators chose to continue operating
the cooling tower rather than take the time
to correct the lubrication problem. They did
ask the analyst if it would be best to run the gearbox at high speed or at low speed. It was decided to run high-
frequency analysis at both speeds to see if the best speed could be determined from the data. The high-
frequency band chosen for the analysis was 2-40 kHz. The results for the gearbox running at high speed are
presented in Figure 7. There was significant periodic activity at one and two times gear mesh frequency. The
peak g-level in the waveform is 150 g’s, which is very high. The results for the gearbox running at low speed are
presented in Figure 8. The significant difference between the high-speed and low-speed activity is the lack of
any gear mesh frequency or twice gear mesh frequency activity in the high-speed data relative to the low-speed
data. The peak g-level in the high-speed data is 140 g’s, which is slightly lower than the peak g-level of 150’s in
low-speed data. The presence of the gear mesh frequency and twice gear mesh frequency in the low-speed data
suggests that debris from the friction between gear teeth was being thrown out into bearings. The conclusion
was that there was sufficient oil in the bottom of the gearbox to permit the gear to sling oil out to lubricate the
gear teeth when running at high speed. Therefore, it was decided that less damage would occur with the
gearbox running at high speed. The gearbox was run at high speed until replaced with the new gearbox.
6. 5
SECTION 3: MULTI DRILL HEAD GEARBOX
Vibration measurements were taken on
several multi drill head gearboxes at an
automobile transmission plant. The primary
objective was to demonstrate that vibration
analysis of the high-frequency band could
reliably detect early-stage bearing faults in
drill heads. In addition to bearing faults,
several other faults were found. One of
those other faults was a torsional vibration
problem on a particular gearbox with ten
drill heads. The gear arrangements were
accomplished with the two levels depicted in
Figure 9. Assuming the two-pole motor was
running with no slip (3,600 RPM or 60 Hz),
the gear mesh frequency for the level 1 gear
set is 2,280 Hz. Three times gear mesh
frequency is 6,840 Hz, thus the use of a low-
frequency bandwidth of 20-8,000 Hz was
most appropriate. There are possibly three
additional gear mesh frequencies associated
with the gear configurations in the level 1
configuration presented in Figure 9. The gear
mesh frequency for the cluster of gears
driven by I-1 is 2,146 Hz. The other two gear set
clusters driven by I-3 and I-4 are 2,280 Hz.
The low-frequency band spectra and waveform
data are presented in Figure 10. The peak-to-peak
g-level in the waveform data is about 14 g’s. There
is definite periodic activity around 1,000 Hz. There
are probably two individual gear mesh frequencies
in the expected frequency range of 2,100 to 2,300
Hz. Additionally, there is a broad band of spectra
activity in the 2,500 to 2,800 Hz frequency range.
The high-frequency (5 to 40 kHz) rectified
waveform and spectra data taken at the same time
as the low-frequency band data are presented in
Figure 11. The spectra bandwidth of the high-
frequency data in Figure 11 was specified at 1,000
Hz, which was an oversight. It should be slightly
greater than twice gear mesh frequency (5 kHz). The
peak g-level in the rectified waveform is about 8 g’s. The
bothersome feature of concern in the high-frequency
spectra data in Figure 11 is the activity at slightly greater
than 0.5 times running speed. It is an indication of a
possible torsional resonance. Based on this observation,
it was decided to inspect the motor shaft/key. A picture
of the motor shaft/key is presented in Figure 12. There
7. 6
has been considerable wear in the motor shaft keyway. The recommended solution was to decrease the
tolerances in the keyway fit to the shaft. This corrected the shaft/key wear problem.
Spectra data taken after the motor shaft replacement is presented in Figures 13 and 14. The resolution is
sufficient to clearly show the gear mesh frequency at 2,275 Hz as well as a probable torsional resonance at a
frequency slightly greater than gear mesh frequency. The periodic activity that was seen in the high-frequency
rectified waveform data before motor shaft change is gone. Additionally, the periodic activity that was seen at
about 1,000 Hz in low-frequency spectra data before motor shaft change is also now absent. The most obvious
change between the two sets of data is the significant increase in the vibration waveform amplitude. The peak-
to-peak waveform in the low-frequency data went from 14 g’s peak-to-peak to 40 g’s peak-to-peak. A similar
change occurred in the high-frequency rectified waveform. This is probably because the torsional stiffness
increased with the tightening of the system at the motor shaft/key thereby increasing the torsional resonance
frequency. The increase in vibration is more desirable than the shaft/key interaction.
SECTION 4: CRUSHER GEARBOX
This is a large gearbox measuring roughly 8 x 10 x 20 ft
used for crushing rocks at a mining facility. A plan view
of the gearbox is presented in Figure 15. There are
twelve vibration-monitoring points identified in Figure
15 as 1 through 12 which are used for scheduled
acquisition of vibration data.
Routine monthly vibration data was acquired from all
the measurements points on the gearbox. The high-
frequency spectra data and rectified waveform from
measurement point #2 are presented in Figure 16. The
high-frequency band is from 1 kHz to 40 kHz. The 1 kHz
is well above 2.25 times gear mesh frequency. (Gear
mesh frequency is 330 Hz, which equals running speed
of motor [15 Hz] times the number of teeth [22]). The
bearing has an inner race fault in the early stages of
failure based on relatively low peak g-level of 3.6 g’s.
The measurement was repeated approximately one
month later and results are presented in Figure 17. The big difference in Figures 16 and 17 is the peak g-level has
increased from 3.6 g’s to 51 g’s, which is significant. This bearing, based on high g-level of 51 g’s, requires
frequent monitoring with a replacement plan set in motion.
8. 7
To assure the faulty bearing was bearing #3 and not bearing #1 or bearing #2, data was acquired from
measurement point #1 at same time as the data in Figure 17 was acquired. The peak g-level in the high-
frequency data from measurement point # 1 was 25 g’s versus the 54 g’s from measurement point #2. The
defective bearing was concluded to be bearing #3. Frequent monitoring with the sensor set on measurement
point #2 was then carried out. The peak g-level trend is presented in Figure 18. From the time the 50 g peak
level was detected, it took about 25 days to get the bearing replaced. A picture of the defective bearing is
presented in Figure 19. The peak g-level recorded was about 80 g’s.
SECTION 5: PRECISION TENSION BRIDLE GEARBOX
A plan view of a precision tension bridle gearbox is presented in Figure 20.
The gearbox has a single shaft input with a dual shaft output that ultimately
drives the work rolls. The low-frequency and high-frequency band spectra and
waveform data were taken with sensor placed over bearing at input to
gearbox. The low-frequency band data is presented in Figure 21. The input
gear mesh frequency (approximately 351 Hz with second harmonic) is being
modulated. The lower gear mesh frequency (approximately 202 Hz) for the
90-tooth gear set is sharp (no indication of modulation) and the second
harmonic is not discernible. The rectified waveform and spectra data for the
high-frequency band of data from 0.5 to 40 kHz are presented in Figure 22.
9. 8
The spectra data indicates a significant event is occurring once per output shaft revolution. The waveform
clearly demonstrates there are two distinct impulses per turn that could mean there are two cracks on one gear.
When inspected, two cracked teeth on one gear were found.
SECTION 6: POST REBUILT GEARBOX WITH CRACKED TOOTH
A gearbox was removed from a mining machine and sent
back to the shop for rebuild. A plan view of the gearbox is
presented in Figure 23. This gearbox has four gear mesh
frequencies. After the rebuild, the machine was subjected to
vibration analysis for high and low-frequency bands prior to
sending it back to the field. The vibration analyses are carried
out on the twelve measurement points (as needed) identified
on the gearbox as points G1 through G12. There is a
measurement point placed over each bearing. In this case,
focus is directed to the low-frequency band up
to 1.5 kHz and the high-frequency band from 1
kHz to 40 kHz data from measurement point
G5.
10. 9
The waveform and spectra data for the low-frequency band are presented in Figure 24. The peak-to-peak g-level
in the waveform data is about 1.1g’s, which is not considered to be indicative of a problem. The high-frequency
band rectified waveform and spectra data are presented in Figure 25. There is a spike (about 14 g’s) occurring
once per revolution of the shaft immediately below measurement points G5 and G6. This is the expected
signature from a cracked tooth in the gear immediately below measurement point G5. Upon inspection of this
gear, it was found to have a crack in the root.
SECTION 7: POST REBUILT GEARBOX WITH ECCENTRIC GEAR
A gearbox was removed from service and sent
to the shop for rebuild. Upon completion of
the rebuild, the gearbox was subjected to low
and high-frequency vibration analysis. The low-
frequency measurement showed no sign of a
problem. The high-frequency band (from 0.5 to
40 kHz) rectified waveform and spectra data
are shown in Figure 26. The high-frequency (0.5
to 40 kHz) rectified waveform is showing a
definite repeating pattern of increased activity
over approximately 65% of a single revolution
and low amplitude activity over the
remaining 35% of the revolution. This is the
pattern expected for an eccentric gear. In
the spectra data, there is significant activity
at gear mesh frequency, which is indicative
of a stable rotational speed of the gear.
Following replacement of the eccentric gear,
the high-frequency rectified waveform and
spectra were acquired and are presented in
Figure 27. Someone was not convinced
the gear was eccentric and placed the
defective gear in another gearbox. When
it was subjected to testing, the results
presented in Figure 28 were obtained
which was basically the same as that
presented in Figure 26.
SECTION 8: FATIGUING IN BEARINGS
AND GEARS
Many failures in bearings and gears are
initiated by residual stress building up in
the metal (e.g., bearings or gears) under
usage. When the sum of residual stress and current usage stress exceeds certain levels, the residual stress will
be relieved by cracks (fatiguing) starting beneath the surface and proceeding to the outer surface as the cracking
progresses under use. When stress relief cracks are initiated, they are accompanied with the emission of stress
wave packets that travel at the speed of sound in the material to the outer edge of the component and away
from the initiation site. The frequency within the packets is similar to packets emitted when friction occurs (ie.
11. 10
higher frequencies than when impacting
occurs). To illustrate this type of failure, a case
from a 1.5 MW wind turbine generator gearbox
has been chosen for illustration. The gearbox is
made up of a three-wheel planetary gear
section driving a two-stage spur gear section.
Both sections were housed in a compact
housing. An online continuous vibration
monitoring system was monitoring the
gearbox.
The rectified high-frequency band (2-40 kHz)
waveform and spectra data are presented in
Figure 29 from a sensor mounted over the
outboard spur section of the gearbox. The
spectra data is dominated by activity at 5.253
orders with many harmonics. This is the outer
race fault frequency for the bearing used on the
outboard end of the intermediate shaft in the
spur gear section. The observed peak g-level of
1.15 g’s for this speed shaft (538 RPM) is very
low. The recommended alert level is 4-5 g’s. This
fault could very well be from the early stage
fatiguing with cracking occurring under the
outer race surface. The fault may not be visible
if examined at this time by sight or by feel.
Typically, wait until peak g-level reaches 6-8 g’s
(for this speed machine) before a plan is put in
place for changing out the bearing unless there
are special circumstances such as it is most economical to implement the change at this time.
The data in Figure 30 was chosen to illustrate how the fault signature can vary over reasonably short times. Each
rectified time waveform is for a period encompassing 18 revolutions (2 seconds) of the intermediate shaft
turning at 538 rpm. The last trace of data in Figure 30 is the same set of rectified waveform data presented in
Figure 29. The three remaining data traces were acquired one day previous.
There is very little fault signature showing up in the first rectified waveform data. In the middle two traces of
rectified waveform data, a fault signature is present but with considerable variability. If the signature was a
result of impacting from a defect in the inner surface of the outer race, the rectified time waveform would not
be expected to have the variability seen in Figure 29.
SECTION 9: CONCLUSIONS
Several faults common to gearboxes were presented in this paper. The objectives were to:
• Demonstrate a wide variation in fault types.
• Demonstrate the importance of employing proper sensors and analysis tools.
Many faults generate a short burst of stress wave activity (from impacting and friction) that requires sensors
responsive up to 15-25 kHz, such as IMI Model 603C01. The sensor frequency response is strongly dependent on
how the sensor is attached to the surface of the machine. Accelerometer mounting by stud, by flat magnet on a
12. 11
flat smooth surface and by dual-rail magnet on a curved surface (smooth, rough or painted) were all considered.
The conclusion was that the stud-mounting technique was the preferred choice. Mounting the accelerometer
with a flat magnet attached to a smooth, flat surface provided sufficient bandwidth for impacting and friction
detection. The use of a two-rail magnet on a curved surface would miss several situations where impacting and
friction was occurring.
The analysis tools used in this study consisted of the normal spectra data in velocity units and waveform in
acceleration units. To cover the high frequency burst of stress waves from impacting, friction and fatiguing, the
waveform used was the band-limited rectified signal. The band-limited rectified signal was 0.5-40 kHz, 1.0-40
kHz or 2.0-40 kHz. The rectified waveform was also transformed to spectra data in acceleration units. In addition
to waveform and spectra data, the autocorrelation coefficient data was computed from the waveform data
graphically displaced. It was a very useful diagnostic tool in both fault identification and severity assessment.