Monitoring and Analysis Flashcards
True or false: Excessive vibration is a symptom of a machine that can lead to machine damage or failure.
True
All machines have some vibration during operation.
What is vibration analysis?
Measuring and determining if vibrations are within normal parameters.
True or false: Vibration monitoring can be both periodic sampling or constant monitoring.
True
This depends on the type of machinery in use.
What is the main limitation of a preventative maintenance program (changing oil at scheduled internals) vs. an oil condition monitoring program?
The levels of oil contamination.
Preventative maintenance oil programs are based off of the expected lifespan of the oil and additives off of running conditions, and are unable to detect excessive contamination.
True or false: Over time, lubricating oils lose their ability to separate metal surfaces.
True
As it pertains to maintenance, what is infrared thermography (IRT)?
A temeprature analysis programs.
True or false: An infrared thermometer is a contact radiant energy detector.
False
It is a noncontact radiant energy detector.
____ is the movement of a body about its reference position.
Vibration
For rotating equipment, what is the reference point used for vibration analyisis?
The shaft centreline.
This test is the only way to find the direct cause of vibration on a machine.
A vibration signature analysis.
A signature is a graphical depiction of vibration frequency.
As it pertains to vibration analysis, what is a signature?
A graphical representation of vibration frequency.
True or false: With a proper vibration analysis, all vibration in a machine can be eliminated.
False
There will always be some vibration in a machine.
All objects vibrate in response to a:
Forcing function
The forcing functions and their signatures indicate the cause of vibration.
As it pertains to vibration, what is a forcing function?
An input or influence that causes a system to vibrate.
These can be internal (unbalanced rotor) or external (wind).
In machinery, vibration is the accumulation of what three things?
- the application
- wear of the machinery
- machine design
What two physical properties of a machine have a direct effect on the vibratory signature of the machine?
- stiffness
- mass
Changing either of these will result in a change in the vibratory signature.
In vibration analysis, what are sine waves?
Graphical depictions of a vibration cycle.
True or false: With vibration, one cycle per minute (cpm) = 1 hertz (Hz).
False
1 cycle per second (cps) = 1 hertz (Hz)
How many hertz (Hz) does a vibration signature of 60 cpm equal?
60 cpm = 1 Hz
Hertz is how many cycles per second → 1 cps = 1 Hz = 60 cpm.
True or false: With vibration, 1 cps = 1 Hz.
True
1 cps = 1 Hz = 60 cpm
With vibration, ____ is how often an event happens in a unit of time or in one cycle.
frequency
What are three ways that the frequency of a vibration can be expressed?
- cycles per second (cps)
- cycles per minute (cpm)
- orders*
*Orders are multiples of the operating speed of the machine ⟶ 1x is the same as the rpm, 2x is twice the rpm, etc.
When completing vibration analysis on rotating machinery, vibration cycles (frequency) are referenced to what?
The rpm of the machine.
This is the fundamental frequency → Do not confuse cpm with rpm.
When it comes to vibration analysis, what are orders?
Multiples of the operating speed of the machine.
2x order → 2x machine rpm = twice per revolution.
With vibration analysis, what is the frequency with the highest (loudest) spike called?
The predominant frequency
This is the lowest or first frequency normally associated with a problem
On vibration analysis, what is the fundamental frequency?
The frequency that corresponds to the machine rpm.
This can also be the most prominent frequency with the highest spike.
With vibration analysis, what is amplitude?
How much the machine is vibrating.
How “loud” the vibration is.
This is the distance from the at rest position and indicates the magnitude of the vibration.
What are three ways that the amplitude of a vibration are measured?
- displacement
- velocity
- acceleration
These are the three parameters used to describe the amplitude of a vibration, and are selected based off of the frequency of the vibration.
This type of vibration amplitude measurement is the total distance a vibrating part moves either side of its neutral axis.
Displacement
On a displacement sine wave, this measurement is peak to peak.
With vibration analysis, how is the total displacement (peak to peak) measurement measured in:
1. Imperial
2. Metric
- Imperial → mils pk to pk
- Metric → microns pk to pk
pk = peak
This vibration amplitude measurement is the peak to peak measurement of the sine waveform.
Displacement
This is measured in mils pk to pk and microns pk to pk.
When completing a vibration analysis, what type of amplitude measurement parameter would be used for below 600 cpm or 1000 rpm?
Displacement
This is often used where stress conditions such as flexing and bending are suspected and in balancing procedures.
This type of vibration amplitude measurement is often used where stress conditions such as flexing and bending are suspected and in balancing procedures.
Displacement
This is best used on equipment and vibrations below 600 cpm or 1000 rpm.
This type of vibration amplitude measurement is the rate of change of displacement for a given time.
Velocity
Velocity combines displacement (how far it moves) and frequency (how often).
With vibration analysis, when placed on a sine wave, when does maximum velocity take place?
At the neutral axis
The velocity of a part changes from zero at one extreme of the motion to a maximum velocity in the middle (as it crosses the zero axis) and then back to zero velocity at the other extreme of the movement.
When using velocity to measure the amplitude of a vibration, what velocity measurement is used?
Maximum velocity
This is the measurement of velocity as it passes the zero axis.
With vibration analysis, velocity is measured in what units in:
1. Imperial
2. Metric
- Imperial → in/sec or ips*
- Metric → mm/sec
*ips = inches per second
When completing a vibration analyisis, what type of amplitude measurement parameter would be used between 600 cpm and 60,000 cpm?
Velocity measurements
- Which vibration amplitude measurement parameter is the best indicator of overall machine condition?
- Why is this?
- Velocity measurements
- It provides a balance between sensitivity to small vibrations and the ability to detect larger issues
Velocity is proportional to the energy transmitted by vibration, which correlates well with the potential for mechanical damage or wear. This makes velocity readings a good indicator of how “destructive” the vibration is to the machine.
Which vibration amplitude measurement parameter works over the widest range of frequencies?
Velocity
From 600 cpm to 60,000 cpm
This type of vibration amplitude parameter is the rate of change in velocity.
Acceleration
Acceleration is measured in g’s force.
What type of vibration amplitude is measured in g’s force?
Acceleration
When measuring amplitude with acceleration, where does maximum acceleration occur on a sine wave?
At the top and bottom of the waveform.
Maximum acceleration occurs twice during one time period.
The greatest acceleration occurs when the object begins to move from zero velocity at the extremes of travel ⟶ this is the area of the greatest rate of change in velocity.
With acceleration amplitude measurements, where does the least amount of acceleration happen?
At the zero axis.
This coincides with the greatest velocity ⟶ velocity ↑ = acceleration ↓
When completing a vibration analyisis, what type of amplitude measurement would be used on frequencies over 60,000 cpm?
Acceleration
This is because at high frequencies displacement and velocity measurements don’t accurately indicate how severe the vibration is.
- On vibration analysis, what is phase?
- What is phase used for on a vibration analysis?
- A time relationship between two points measured in degrees.
- To indicate the relative position of a vibration and a reference point (either a fixed location or another vibration).
Phase is measured or expressed in degrees.
On a vibration analysis, what is an in-phase vibration?
A vibration where both pick-up spots are moving in the same direction and at the same time.
On a vibration analysis, what is an out of phase vibration?
A vibration where both pick-up spots are not moving in the same direction or at the same time.
The phase difference is measured in degrees.
When taking a vibration phase reading, keep the accelerometers facing the same direction. What needs to be done if this is not possible?
Change the reading of one accelerometer by the corresponding degree angle.
This ensures that the accelerometers read the proper phase angle on the vibrations.
When measuring vibration, what determines which parameter is selected for amplitude measurement?
The frequency
Depending on the frequency, either displacement, velocity, or acceleration would be selected.
This vibration frequency is the frequency at which an object or system naturally vibrates when a forcing function has been introduced.
Natural frequency
Factors that affect the natural frequency of an object are size, material, length, and shape.
In the case of shafts, the natural frequency is ____ (lower/higher) depending on the stiffness of the shaft.
higher
Stiffer = higher frequency
This type of frequency is where the system or machine amplifies the energy from the forcing function, causing a large amplitude (greater vibration).
A resonant frequency
Resonant frequencies destroy machines.
Resonance occurs in any system if the forcing function frequencies are not kept at least ____% outside the natural frequency’s range.
20%
If not, the forcing function aligns with the natural frequency of the system, resulting in the energy of the forcing function amplifying the natural frequency.
In vibration analysis, a ____ is the time required to complete on cycle of a periodic signal.
period
What is the critical speed of a machine?
The speed of a shaft or rotor when it is near its natural frequency and begins to resonate.
What happens to a rotor or shaft at critical speed?
It begins to resonate.
This increases vibration drastically, resulting in failure.
Machines should not be operated at or near the critical speed of the shaft or rotor, and should be kept ____% outside of a rotor’s critical speed.
20% to 30%
In vibration analysis, what is a harmonic?
A multiple or sub-multiple of the fundamental frequency.
The fundamental frequency is the rpm of the machine.
True or false: You must know the running speed of a machine or shaft rpm in order to properly diagnose a vibration issue.
True
This becomes your baseline or fundamental frequency.
As it pertains to vibration analysis, what is a synchronous vibration?
A vibration frequency that is a whole multiple of the fundamental frequency (rotating speed) of the machine.
These are phase locked to the rpm of the machine, such as 1x rpm, 2x rpm
As it pertains to vibration analysis, what is a non-synchronous vibration?
Vibration frequencies that are not whole multiples of the rotating speed of the machine.
As it pertains to vibration analysis, what is a sub-synchronous vibration?
Vibration frequencies that occur at less than the rotating speed (fundamental frequency) of the machine.
True or false: When using ISO vibration severity charts, when using velocity to determine the level of vibration, you ignore frequency.
True
In this example, the velocity is 0.200 in/sec.
Velocity is the only parameter that is selected without having to meet two points together on the severity chart.
True or false: When using ISO vibration severity charts with displacement to determine the level of vibration, you use both the frequency and the peak to peak measurement, and where these two lines instersect indicates the severity of the vibration.
True
In this example the displacement was 0.20 mils pk to pk at 1200 cpm.
True or false: When using ISO vibration severity charts with acceleration to determine the level of vibration, you use both the frequency and the peak g’s measurement, and where these two lines instersect indicates the severity of the vibration.
True
In this example, the acceleration was 0.26 g’s at 30,000 cpm.
With vibration analysis, this type of processor capability allows it to change the signal received from the transducer from amplitude vs. time to amplitude vs. frequency, allowing it to create a signature by adding up the sine waves at each frequency and stacking them up in order of the frequency.
A fast fourier transformer (FFT) processor
This converts a sine wave (time vs. amplitude) into a vibration signature (frequency vs. amplitude).
This type of vibration measurment tool is used for precautionary measurements and to establish quick measurements of a specific vibration characteristic.
Vibration pencils/pens
This diagnostic tool measures the one amplitude of the frequency ⟶ usually the dominant or fundametal frequency.
True or false: Portable vibration meters are capable of taking overall vibration readings, and if equipped with a FFT, break down the vibration into a series of discrete frequencies and amplitudes.
True
Vibration ____ are meters that are permanently installed in a plant to continually check the vibrations of a certain piece of equipment.
monitors
These are used on equipment that must maintain a high degree of quality control, with some monitors being capable of shutting down the machine if excessive vibration is detected.
Which type of vibration measuring device is capable of separating individual frequencies, making problems easier to identify.
Vibration analyzers
Vibration ____ are more complex and expensive than meters and monitors, and are capable of measuring vibrations by all of their characteristics.
analyzers
These are capable of separating individual frequencies, making problems easier to identify.
What is the most important component of a vibration measurement system?
The transducers
This are responsible for providing accurate information to the analyzer.
What are the three basic types of vibration transducers?
- Displacement transducers
- Velocity transducers
- Acceleration transducers (accelerometers)
A transducer is a device that converts mechaincal motion of a vibration into an electrical signal which is then translated into a numerical value.
This type of vibration measurement uses proximity probe transducers to measure the relative distance between a bearing housing and a bearing journal.
Displacement transducers
These are non-contact eddy current proximity probes.
This type of vibration transducer works by generating a magnetic field that induces eddy currents in the conductive surface. Changes in distance alter the eddy currents, which are converted into an electrical signal proportional to the vibration.
Displacement proximity probes
The change or loss in voltage is proportional to the distance between the probe and its target.
What type of material does the shaft need to be made out of in order for an eddy current vibration probe to work?
Metal
It must be made of a conductive material.
Which type of vibration transducer requires an external power supply?
Displacement (eddy current) transducers
A power supply is required to create a small magnetic field near the shaft.
What are two conditions that adversely affect the proximity probes used to measure displacement vibrations?
- shaft run-out
- scrates or variations on the shaft surface
This type of vibration transducer is used for general vibration measurements and balancing.
Velocity transducers
These are physically the largest types of vibration transducers.
This type of vibration transducer is made of a coil of wire that is fixed in the case, with a permanent magnet moving within the coil. When held against a vibrating object, the magnet moves back and forth relative to the coil, inducing a voltage.
A velocity transducer
The faster the motion of the vibration, the larger the voltage ⟶ the voltage is proportional to the velocity of the motion.
True or false: Velocity vibration transducers require an external power supply.
False
Velocity transducers generate their own internal power through the relative motion between a coil and a permanent magent.
True or false: While primarily used to measure velocity, velocity transducers are capable of measuring displacement and acceleration.
True
They are not very reliable when measuring low frequencies for displacement or very accurate when measuring the high frequencies for acceleration.
What are the most common types of vibration transducers used in industry?
Acceleration transducers (accelerometers)
This type of vibration transducer uses piezoelectric materials as the sensing component, which produces a small voltage proportional to the amount the material is strained or compressed.
Acceleration transducers
The two common types of piezoelectric materials are quartz and ceramics.
Of the two types of piezoelectric materials listed in the module, which one is better for high temepratures?
Ceramics
Quartz is more stable, but the ceramics can handle higher temperatures.
True or false: Accelerometers are affected by magnetic fields.
False
Piezoelectric materials are not affected by magnetic fields.
What are the two types of excitation methods for the piezoelectric materials found in accelerometers?
- Compressive mode
- Shear mode
Both methods produce a voltage that is porportional to the amount of compression.
Which type of vibration transducer is especially sensitive to vibration occuring at very high frequencies?
Accelerometers
These are best suited for vibrations over 60,000 cpm.
With which type of vibration transducer is proper mountin critical?
Acceleration transducers
Mounting for all types of vibration transducers is important.
What type of vibration transducer would be used to measure the vibrations of larger turbo machinery?
Displacement transducers
Which type of vibration transducer can be used to measure all of the vibration frequency parameters?
Accelerometers
What issues arise if vibration transducers are not properly mounted?
Inaccurate readings
Poor mounting can amplify or distort the readings
The transducer and the mounting arrangement is the most important component of the vibration system → poor data fucks everything up.
What are the five methods of mounting vibration transducers and identify which one is the best, good, and fair.
- Stud mount → best
- Magentic pick-up mount → good
- Hand-held probe → fair
- Adhesive bond to surface
- Shaft rider assembly
Ensure that the transducer is mounted the same way each time measurements are taken, as this could introduce another variable into the data.
When mounting vibration transducers, why is silicone grease applied to any two flat mating surfaces?
Improved surface contact
This reduces signal loss between flat surfaces.
Surfaces, even very smooth ones, have irregularities on them. The silicone grease fills these, improving the transfer of vibrations between surfaces.
This vibration transducer accessory is used to continuously and accurately monitor the absolute shaft vibration of a machine through a long-wearing, non-metallic tip installed near the bearing area.
Shaft rider accessory
The contact tip needs to be lubricated.
These accessories are used to continuously monitor vibration.
True or false: Vibration transducers are only able to pick up vibrations that are in line with the transducer.
True
This makes the direction or position important when measuring vibration.
As it pertains to vibration analyisis, what are HVA positions?
Horizontal, Vertical, and Axial positions
These are the ideal transducer locations on each bearing, resulting in the most complete vibration picture.
On rotating equipment, where should vibration tranducers be mounted?
As close as possible to the bearing locations and on solid surfaces only.
Ideally in HVA positions (if possible).
Vibrations in flexible surfaces may be amplified by the resonant frequency of the surface, resulting in inaccuracte readings.
What are the two main fuctions of a strobe light when being used for vibration analysis?
- Freeze motion to observe rotating components
- Measure the phase angle when balancing parts
These are also known as stroboscopes.
When using a strobe light during a vibration analysis, what four issues could be identified by using the strobe light to freeze motion to observe the rotating components of the machine?
- Misalignment ⟶ components that appear offset or wobble
- Imbalance ⟶ asymmetrical rotation of rotors or fans
- Bent shafts ⟶ A “wobbling” or elliptical motion of the shaft rather than smooth circular rotation
- Loose parts or couplings ⟶ loose bolts, couplings, or other parts visibly shifting during rotation
True or false: Strobe lights can be adjusted manually so that it can be used as a tachometer or so you can study the slow motion response of machine parts.
True
With vibration analysis, stobe lights can be set to be triggered by vibration transducers at the same speed as the dominant frequency. What are two things that this helps to identify?
- Identify which components are producing the vibration signal.
- Determine the relationship (phase) of the components that are excited by the vibration.
This helps to identify the phase angle between the transducer and the predominant vibration.
What are the two overall steps used in vibration analysis procedures?
- Data aquisition
- Data interpretation
With vibration analysis, what four steps make up the data aquisition phase?
- Identify the nature of the problem
- Gather information about the vibrating system
- Make a sketch of the machine, with support data
- Take vibration readings
With vibration analysis, what two steps make up the data interpretation phase?
- Analyze vibration data
- Make corrective recommendations
True or false: the more complete the initial vibration analysis investigation, the more accurate the conclusion reached.
True
Why is it imporant to check for vibration after the machine has stopped?
Significant backround vibrations can make the origional readings inaccurate
If certain vibrations persist after the machine has been shut down, the vibration model will have to be adjusted in order to get an accurate picture.
True or false: noise and vibration are the same thing.
False
Noise can be associated with vibration, but they are not the same thing.
When dealing with vibration and noise issues, 1.________ solves noise issues, while vibration is solved by 2.________.
- isolation and insulation
- correcting the root problem
With vibration analysis, ____ is a disturbance caused by a sudden applied force.
shock
Shock vibratons die out before the next impulse vs. vibration which is a continuous condition.
True or false: Noise and shock issues can be identified with vibration analysis.
False
Vibration analysis is not effective at determining the cause of shock or noise frequencies.
What can cause the amplitude of a harmonic to exceed the amplitude at the force’s frequency?
Resonance within the system
True or False: Resonance always decreases the amplitude of harmonics.
False
How does a sketch of the machinery aid with vibration analysis (3 things)?
- Allows you to determine the best data collection points
- Aids in determining potential sources of vibration
- Consistency*
The sketch allows you to re-take measurements from the same locations in the future, which ensures consistency in the measurements.
In most machines, a vibration has a 1.________ level and its frequency spectrum has a 2.________ shape when the machine is in good condition.
- typical
- characteristic
This is the vibration signature of the machine.
- What is the vibration signature of a machine?
- When should it be first taken?
- A unique pattern of vibration characteristics generated by a machine during operation
- When it is first installed ⟶ this provides the baseline
In a vibration signature, the loweset frequency is usually the:
fundamental frequency
This is the rpm of the machine.
On a vibration signature, what is the largest frequency known as?
The (pre)dominant frequency
This can sometimes be the same as the fundamental frequency.
What kind of frequency would an imbalance characteristic have?
1x the machine rpm (fundamental frequency)
Imbalance is always 1x the fundamental frequency.
What is the grass on a vibration graph?
The small vibration amplitudes to each side of the dominant frequencies.
These should not be ignored, as they can indicate future issues.
What kind of frequency would a misalignement or mechanical looseness show up as?
2x the fundamental frequency
What are the two most common causes of vibration in rotating machinery?
- Imbalance
- Shaft misalignment
On vibration analysis, a rotor or shaft imbalance can be indentified by a vibration frequency ____x rpm.
1x rpm
This would be a 1x order.
- On a vibration analysis, a rotor or shaft imbalance usually has the largest amplitude in what HVA direction?
- When is the above not the case?
- The radial (horizontal and vertical) direction
- With an overhung rotor ⟶ then the largest amplitude is in the axial direction
On a vibration analysis, in what HVA direction would the largest amplitude be on an overhung rotor indciating imbalance issues?
In the axial direction
With a vibration analysis indicating imbalance, what happens to the amplitude of the vibration as the shaft speed increases?
shaft speed ↑ = amplitude ↑
With imbalance, amplitude increases with the speed of the machine.
True or false: On vibration analysis, if imbalance is causing the vibration, the phase of the exciting force changes on each revolution.
False
With imbalance, the phase of the exciting force does not change.
With vibration analysis, what kind of phase readings would be expected with imbalance issues?
Stable, following the location on which the transducer is mounted.
This means that the phase angle between the horizontal and vertical measurements is constant when readings are taken on opposite ends of the rotor.
True or false: With vibration analysis, the amplitude of an imbalance vibration is proportional to the degree of imbalance.
True
With vibration analysis, what kind of frequency order would a slightly misaligned shaft have?
1x order (usually)
A severely misaligned shaft could see orders of 2x or 3x.
With vibration analysis, what kind of frequency order would a severely misaligned shaft have?
2x or 3x order
An order is a multiple of the machine rpm ⟶ 2x = twice machine rpm, etc.
With a HVA vibration analysis, what type of misalignment causes a high axial vibration component (1/2 or more of the radial amplitude)?
Angular misalignment
With a HVA vibration analysis, what type of misalignment causes the radial component (H&V) of the vibration to be high?
Parallel (offset) misalignment
True or false: With vibration analysis, the amplitude of a misalignment vibration is proportional to the to the misalignment.
True
The more misaligned the coupling, the greater the vibration.
With vibration analysis, an axial vibration of ____% or more of the radial is a good indicator of misalignment.
50% or more
With vibration analysis, a misaligned shaft will have what kind of phase angles between the horizontal and vertical measurements?
Erratic, and often different at opposite ends of the rotor
This type of vibration signature acts like an imbalance and has radial vibration frequencies at 1x rpm and 2x rpm.
Eccentricity of the electrical field
This example is due to stator (motor) eccentricity.
What are the main differences between a vibration signature due to rotor electrical eccentricity vs. one indicating imbalance?
Rotor eccentricity generates a more dominant two times frequency with smaller frequency side bands at both the 1x rpm and 2x rpm
What are the two main causes of vibration due to eccentricity of the electrical field?
- soft foot
- incorrect/uneven air gap (between the rotor and stator)
When troubleshooting a vibration analysis, and eccentricity of the electrical field is suspected, what should happen to the vibration (amplitude and frequency) when power is shut off to the motor?
The vibration amplitude should drop immediately.
If the amplitude “coasts” down in proportion to the rpm of the machine, the vibration is being caused by some other issue → misalignement or imbalance.
When performing a vibration analysis, what does component eccentricity act like?
Imbalance
Component eccentricity will have a predominant vibration in the radial direction at 1x fundamental frequency.
On vibration analysis, what kind of frequencies would be expected when examining gearboxes?
A multiple of the number of teeth x the rpm
This is called the gear mesh frequency (GMF).
An input shaft rotating at 1000 rpm driving a gear with 8 teeth → 1000 rpm x 8t = 8000 cpm frequency
What formula is used to calculate the gear mesh frequency of a gearbox when performing a vibration analysis?
GMF = # teeth on the gear x rotational speed of the gear (in Hz or RPM)
This is an approximate method of finding the vibration frequency.
When examining a vibration analysis of a gerabox, the frequency of the vibration should usually be several times higher than 1x rpm (due to rpm x teeth). When is that not the case?
When only one tooth on a gear is bad.
This will show up as a 1x rpm vibration frequency.
On a vibration analysis, this type of issue produces a series of sharp, high-frequency impulses that have many sharp edges.
Anti-friction bearing issues
Frequencies for bearing problems in the early stages are very high.
BPFO = ball pass frequency outer race
What four things affect the vibration frequencies of defective roller bearings?
- ball diameter
- number of balls in the bearing
- pitch diameter of the path of the balls
- speed of the shaft
What formula is used to calculate the ball pass frequency (in cpm) for a bearings inner race?
BPFI (frequency) = 0.60 x n x rpm
- BPFI → ball pass frequency inner race (in cpm)
- n → # of rolling elements
- rpm → rotational speed of the bearing
This formulas assume a single defect on the bearing.
What formula is used to calculate the ball pass frequency (in cpm) for a bearings outer race?
BPFO (frequency) = 0.40 x n x rpm
- BPFO → ball pass frequency outer race (in cpm)
- n → # of rolling elements
- rpm → rotational speed of the bearing
This formula assumes a single defect on the bearing.
True or false: When examining a vibration analysis, the vibration frequency of an anti-friction bearing is usually an exact multiple of the shaft rpm.
False
Anti-friction bearing vibration frequencies depend on the ball pass frequency of one or both of the races, and is usually not an exact mulitple of the shaft rpm.
True or false: With plain bearings, if the bearing clearances are too loose, the shaft can move around and pount on the bearing, causing a vibration signature.
True
This is also known as eccentric journals
____ ____ (2 words) occurs when the shaft in a plain bearing climbs the oil wedge created by the shaft rotation, moving to a different position within the bearing, resembling an orbit.
Oil whirl
This instability of the shaft causes vibration.
What type of vibration frequencies are created by oil whirl?
45% to 50% of the fundamental frequency
True or false: Plain bearing oil whirl is usually caused by the wrong viscosity oil (or cold oil), excess clearances, or improper lubricaion.
True
Pivoted shoe radial bearings are often used where oil whirl is a chronic problem.
When taking a vibration analysis, and bearing damage is suspected, what HVA plane(s) would the vibration amplitude be the greatest?
In the direction of the load
With radial bearings, that would be in the H and V planes, and in the axial plane for thrust bearing issues.
This cause of vibration is identified by a dominant vibration at 2x rpm and vibrations at other frequencies such a 1/2x and 4x rpm.
Mechanical looseness
Mechanical looseness refers to loose hold-down bolts on motors, pumps, bearing caps or pillow blocks, etc.
When measuring vibration caused by mechanical looseness with an HVA assembly, where would the greatest forces be observed?
In the radial direction
There may be close to no axial movement, depending on the machine.
True or false: If adjacent parts on a machine show different amplitude and phase readings, the relative motion between the parts could be the cause of the vibration.
True
If you get different phase readings at any spot, it means that location is moving differently.
True or false: Single drive belt arrangements are more susceptible to belt vibrations.
False
Multiple belt drives are more susceptible to belt vibration.
True or false: When completing a vibration analysis, belt vibrations usually show up as mutliples of the machine speed (1x, 2x, 3x, or 4x the rpm of the belts).
True
With vibration caused by belts, the vibration from the belts is greatest in the direction of:
belt tension
With vibration analysis, what issue could cause a vibration signature with 1x and 2x orders, along with different phase readings at opposite ends of the bearing housing?
A bent shaft.
Remember bearing housing.
These may look like a misalignment or imbalance issue, but with very high vibration readings in both the axial and radial directions.
Why are blade and vane problems associated with higher orders of the fundamental frequency of the fan?
These frequencies correspond with a multiple of the blades or vanes passing.
The more blades a fan has, the higher these frequencies will be.
How is the frequency of vibration typically calculated for fan blades or vanes?
of fan blades x rpm (fundamental frequency) of the shaft
This means that each blade contributes to the overall vibration frequenc
fan frequency = # of blades x rpm ⟶ 6 blades x 1500 rpm = 9000 cpm frenquency
What formula can be used to calculate the vibrational frequency that a fan could introduce into a vibration signature?
fan frequency = # of fan blades x fan rpm
This is known as the blade pass frequency of the fan.
What happens to the vibration signature if a fan blade is missing or damaged in a system?
An imbalance situation, resulting with a 1x rpm predominant frequency
This can lead to increased vibrations and potential damage.
What is rubbing in the context of machinery?
Unwanted friction between two machine parts
This is a common issue in machines like steam turbines and compressors.
What types of machines commonly experience rubbing problems?
- Steam turbines
- Centrifugal compressors
- Axial flow compressors
- Other high-speed turbo machinery
These machines are particularly susceptible due to high surface speeds.
What causes rubbing in machines?
Deflection of rotors or impellers, wearing of components resulting in smaller gaps, etc.
Anything that results in the spaces between components getting smaller.
At what frequencies does rubbing typically vibrate?
- 1x rpm
- 2x rpm
- Higher frequencies
- Less than 1x rpm
Rubbing can generate vibrations at various harmonic frequencies.
True or false: Belts are capable of both dampening shock and vibration, while at the same, can also be the cause of vibration.
True
Belt vibration is due to some underlying condition affecting the belts, such as misaligned sleeves, loose belts, etc.
What type of motion can belts develop due to disturbing forces?
Bouncing or whipping motion
What can cause belts to exhibit a bouncing or whipping motion?
Loose, misaligned belts or eccentric sheaves
What can result from radical torque variations in belts?
Stretch and bounce of the belts
True or false: Adding or removing weight, standing on a part, or clamping or bracing it can cause changes to occur in a vibrating object.
True
This will change the vibration signature of the object.
What is indicated when the vibration of a machine changes due to weight adjustment?
This could be from adding or removing weight, standing on a part, or clamping or bracing it.
The machine is resonating.
This weight changes the natural frequency of the machine, which results in a different critical speed.
When a machine is resonating, where does most of the resonance originate from?
From a non-rotating part, usually within the first 3 to 4 metres from the rotating part.
What types of machines commonly have resonance issues?
Fans and blowers
True or false: The piping is often the source of resonance in systems.
True
To correct for this type of resonance, it is best to “stiffen” the piping assembly by adding additional supports.
What occurs when the running speed coincides with the natural frequency of the pipe?
Resonance
This is the critical speed of the machine, and the resulting vibrations can tear the machine apart.
What methods can change the natural frequency of a pipe?
Extra braces, supports, or expansion joints.
The idea is to “stiffen” the piping, changing its natural frequency.
Fill in the blank: Almost all of resonance originates from a:
non-rotating part
What is the frequency of vibration caused by imbalance?
1x rpm
What is the phase characteristic of imbalance vibration?
Stable and repeatable
The vibration will happen in the same spot, and at the same phase angle.
How does the amplitude of vibration behave for imbalance?
It is proportional to the imbalance
The greater the imbalance, the “louder” the vibration.
What frequencies are associated with misalignment?
1x, 2x, or 3x rpm
What percentage of axial amplitude is typically seen in misalignment?
50% or larger of radial amplitude
How does the phase behave in misalignment vibration?
It can show in 1, 2, or 3 positions
The phase angle between H and V measurements are often different at opposite ends of the rotor.
What is the frequency characteristic of vibration caused by anti-friction bearings?
Very high frequency, several times rpm
Look for very high frequency vibrations with sharp pulses.
What is the amplitude of vibration for anti-friction bearings?
Not large
How is the phase described for anti-friction bearing vibration?
Erratic
What should you look for with anti-friction bearing vibration?
Look for very high-frequency vibrations with sharp pulses
What is the frequency of vibration caused by eccentric journals?
1x rpm
This often acts like an imbalance, and could be mistaken for one.
How is the amplitude of vibration for eccentric journals?
Not large
What is the phase characteristic of eccentric journal vibration?
A single phase location
How does eccentric journal vibration behave?
Acts like an imbalance
What is the frequency of vibration caused by gear problems?
A very high frequency ⟶ gear teeth × rpm
What is the amplitude characteristic of gear problems?
Low
Use velocity or acceleration transducers to detect the vibrations.
How is the phase described for gear problems?
Erratic
What should you use to identify gear problem vibrations?
Use velocity or acceleration at higher frequencies
What frequencies are associated with mechanical looseness?
2x rpm or 4x rpm
The dominant vibration is usually the 2x order of the fundamental frequency.
How is the amplitude for mechanical looseness described?
Erratic
What is the phase characteristic of mechanical looseness?
Two reference marks
What is a common observation about mechanical looseness?
It may be accompanied by imbalance or misalignment.
What frequencies are associated with drive belt problems?
1x, 2x, 3x, or 4x rpm of the belts
How is the amplitude of drive belt problems described?
Erratic pulsing
What is the phase characteristic of drive belt problems?
1 or 2, usually unsteady
What tool can be used to observe drive belt problems?
A strobe light ⟶ this can freeze the belts.
What is the frequency of vibration caused by electrical forces?
1x rpm or 1x or 2x synchronous frequency
How does the amplitude behave for electrical forces?
It disappears when power is removed from the machine
What is the phase characteristic of electrical forces vibration?
1 or 2 marks
What happens to the amplitude of electrical forces vibration when power is turned off?
The amplitude drops off
Which reading is used to see how one part is shaking/vibrating in relation to another part?
Phase
Phase angles are expressed in degrees.
This cause of vibration creates similar amplitude in both the horizontal and vertical planes.
Imbalance
This type of amplitude reading is usually only found when imbalance is the cause of the vibration.
Why can you not ignore the small vibrations showing up at each side of the dominant frequency on the graph?
They could be indications of impending bearing troubles.
What two maintanence analysis programs can be used together to form an overall picture of a machine’s condition?
- Vibration analysis
- Oil analysis
Infrared thermography allows for the measurement of:
heat being emitted
For many industries, 1.________ analysis has been the primary technique for monitoring machine health, while 2.________ analysis is the preferred method used in the mobile and heavy equipment industry.
- vibration
- oil
Combining the two techniques is an effective way to monitor machine condition.
Which type of machine conditioning analysis program would be best to identify component wear from sliding parts?
Oil analysis
Vibration monitoring won’t indicate an issue until the parts have worn to a point where there is excessive clearance.
How does water affect oil properties?
Water can change oil’s viscosity, lubricity, and load carrying characteristics.
What chemical reaction does water cause in lubrication systems?
Water causes additive depletion, leading to oxidation due to the formation of acids.
What is the main cause of oxidation in lubrication systems?
The main cause of oxidation is heat.
List the three products of oxidation.
- Gum and varnish
- Sludge
- Acids
What harm does gum and varnish caused by oxidation cause to an oil system?
Sticky valves
What harm does slude caused by oxidization cause to an oil system?
Blocked pilot passages
What harm do acids caused by oxidization cause to an oil system?
Corrosion of parts
What four things does routine oil analysis identify?
- metallic particles
- contaminants
- oxidation
- water content.
How does routine oil analysis assist with predictive maintenance?
It helps to determine how often the oil should be changed.
Water in oil can change what three oil characteristics?
- viscosity
- lubricity
- load carrying characteristics
True or False: Overheating the lubrication system can damage fluid or system components.
True
When taking an oil sample from a machine, it should be taken from a ____ zone.
live zone
This is for circulating (pumped) oil systems.
This is an area where in the ciculating oil has aquate turbulent flow to ensure that the oil is propelry mixed.
True or false: When taking an oil sample for analysis, the sample should only be collected when the machine is running at its normal operating temeprature, pressure, speed, and load.
True
You want the sample to be the most accurate representation of the oil flowing through the machine.
When collecting oil samples, the sample should be taken 1.________ (upstream/downstream) from system components and 2.________ (upstream/downstream) from fitlers or separators.
- downstream (after)
- upstream (ahead)
True or false: Do not collect oil samples at points located at dead pipe legs where the fluid is not moving or after filters or separators.
True
This would be an inaccurate representation of the oil in service.
How is contamination measured in oil analysis’?
By particle size and the number of particles of a particular size
What are the three micron size of particles measured using ISO cleanliness standards?
4µ, 6µ, and 14µ
µ = micron ⟶ one millionth of a metre (micrometre)
True or false: All objects, even cold ones, emit infrared radiadion.
True
The warmer the object, the more radiation is emitted.
What is a thermogram?
an image that represents the distribution of surface temperatures of an object or area
These are captured with thermal imaging camera.
As it related to thermal imaging, what is emissivity of a material?
A materials ability to emit radiation.
What is thermal emissivity tape used for with IR scans?
To calibrate the camera.
The tape has a known and consistent thermal emissivity that is used as a baseline.
What effect does reflection have on IR scans?
Inaccurate readings
Adjusting the angle of the camera so that reflection is not an issue eleminates this issue.
A thermal imaging camera produces an image called a:
thermogram
What contaminant can cause additive depletion and create oxidation of lubricating oils?
water
