Vibration Analysis And Balancing

Question 1

What does vibration analysis refer to?

Answer 1

detecting, measuring, and analyzing the vibration in a machine and determine if its within normal parameters

Question 2

What are some possible sources of vibration?

Answer 2

misalignment, imbalance, bearing damage, gear problems, cracked welds, resonance

Question 3

What conditions can be captured using thermography?

Answer 3

overloaded electrical circuits, loose connections, frictional heating of bearings

Question 4

What do thermography detect?

Answer 4

the thermal radiation (emissivity) of an object

Question 5

What is a forcing function?

Answer 5

The force that an object vibrates in response to (also known as an exciting force); these functions and their signatures indicate the cause of vibration.

Question 6

What would be caused by a change in either the mass or the stiffness of an object?

Answer 6

a change in the vibratory signature of that object

Question 7

What are the 3 terms used to describe vibration?

Answer 7

frequency, amplitude, and phase

Question 8

What is frequency, and how is it expressed?

Answer 8

frequency is how often an event happens in a a unit of time or in one cycle, expressed by cycles per second (cps, Hz), cycles per minute (cpm), or orders

Question 9

What are orders?

Answer 9

multiples of the operating speed

Question 10

What is the total distance a vibrating part moves either side of its neutral axis know as?

Answer 10

displacement

Question 11

How is displacement measured on a sine wave?

Answer 11

from peak to peak

Question 12

What are the 3 measurements of amplitude? Which is the best indicator of overall machine condition?

Answer 12

displacement, velocity, acceleration, velocity is the best indicator of overall machine condition

Question 13

In what range are velocity readings most consistent?

Answer 13

between 600 cpm and 60,000 cpm

Question 14

What is velocity measured in?

Answer 14

in/sec or mm/sec

Question 15

What is displacement measured in?

Answer 15

mils pk to pk, or microns pk to pk

Question 16

What is acceleration measured in?

Answer 16

g’s force (32 feet/sec squared)

Question 17

Which measurement of amplitude is best for lower frequencies (below 600 cpm)

Answer 17

displacement

Question 18

Which measurement of amplitude is best for higher frequencies (over 60,000 cpm)?

Answer 18

acceleration

Question 19

What is the term used to indicate the position of a vibrating part at a given instant with reference to a fixed point or another vibrating part?

Answer 19

phase

Question 20

What is the term used to describe a frequency at which an object naturally vibrates when a forcing function is introduced?

Answer 20

natural frequency

Question 21

What condition can take place when a machine runs at one of its critical speeds, and rpm equal to its critical speed, or an rpm equal to its natural frequency (cpm)?

Answer 21

resonance

Question 22

What is the critical speed of a shaft or rotor?

Answer 22

when the shaft or rotor rotates at or near its natural frequency

Question 23

How far outside a rotor’s critical speed should a machine run?

Answer 23

20-30%

Question 24

On a signature, the most prominent frequency known as the:

Answer 24

dominant or fundamental frequency

Question 25

What type of vibration corresponds to a frequency that is a whole multiple of the rotating speed of the machine? Ones that are not whole multiples?

Answer 25

synchronous vibration, non-synchronous

Question 26

Frequencies that occur at less than the rotating speed of the machine are known as:

Answer 26

sub-synchronous

Question 27

What is a harmonic?

Answer 27

A multiple or sub-multiple of the fundamental frequency.

Question 28

What are 3 types of vibration meters?

Answer 28

vibration pencils, simple data trap, vibration analyzers with FFT capabilities

Question 29

What are the three basic categories of transducers?

Answer 29

displacement transducers, velocity transducers, acceleration transducers (accelerometers)

Question 30

Which type of transducer requires a power source?

Answer 30

displacement transducers

Question 31

Which transducer is capable of measuring all 3 types of amplitude? What material is often used in these?

Answer 31

accelerometer, they often use piezoelectric materials

Question 32

What are the 4 methods of mounting transducers, and which method is the best?

Answer 32

stud mount (best), magnetic pickup mount, hand-held probe, shaft rider accessory

Question 33

What are HVA measurements?

Answer 33

positions the transducers are mounted in, horizontal, vertical, and axial

Question 34

What can be done to avoid errors when determining the rpm of a machine using a strobe light?

Answer 34

locate something like a keyway or bolt or other mark that you know there is only one of

Question 35

What is done to ensure consistency when taking readings from a machine?

Answer 35

always take readings from the same place

Question 36

What is the effect on phase if vibration is caused by imbalance?

Answer 36

phase does not change

Question 37

What would an axial vibration reading of 50% or more of the radial be a good indicator of?

Answer 37

misalignment

Question 38

If you turn off the power to the motor and notice an immediate drop in the amplitude of the vibration, what is this indicative of?

Answer 38

an electrical problem

Question 39

What are the characteristics of a gear problem?

Answer 39

they show up at high frequencies, will be synchronous

Question 40

What are possible characteristics of a bearing problem?

Answer 40

high frequency, non-synchronous

Question 41

When would oil whirl normally occur in vibration analysis?

Answer 41

usually sub-synchronous, at about 40-50% of shaft rotation

Question 42

When would mechanical looseness be identified?

Answer 42

when there's a dominant frequency of 2 x RPM, and vibrations at other frequencies such as 1/2 and 4 x RPM

Question 43

When is vibration from belts the greatest?

Answer 43

in the direction of belt tension

Question 44

Where would an imbalance situation from a missing impeller blade show up?

Answer 44

at 1 x RPM

Question 45

What would be suspected if there is high vibration on the axial plane?

Answer 45

angular misalignment or a bent shaft

Question 46

What temperature condition would cause sludge in the oil of a machine?

Answer 46

too cold

Question 47

What are the 4 products of oxidation in oil?

Answer 47

gum, varnish, sludge, acids

Question 48

When should an oil sample be taken from a machine?

Answer 48

at normal operating, temperature, pressure, speed and load

Question 49

What's an oil sample called that's taken from a point in a circulating system?

Answer 49

a live zone sample

Question 50

What particle sizes are used in an ISO cleanliness standard in reference to machine oil analysis?

Answer 50

4, 6, and 14 microns

Question 51

What machine condition is defined as "the unequal distribution of weight of a rotating body about its centreline"?

Answer 51

imbalance

Question 52

When does eccentricity appear on a vibration signature?

Answer 52

1 x RPM

Question 53

Why is it important not to lose the keys that come with sheaves, pulleys, hubs, gears, or shafts?

Answer 53

They may have been balanced with that/those key(s)

Question 54

What is it called if the required balance correction is at a single point on the rotor?

Answer 54

single plane balancing

Question 55

What type of vibration is caused by extra weight unevenly distributed along the length of the shaft, across the width of the shaft, and/or and different angles about the radius?

Answer 55

dynamic imbalance

Question 56

What is normally required to diagnose the forces and vibrations from dynamic imbalance?

Answer 56

a computer

Question 57

How is static imbalance (shaft's weight unevenly distributed from side to side) detected when the shaft/rotor is suspended between two knife edges or rollers?

Answer 57

the heavy side of the rotor settles at the bottom of the rotation

Question 58

What is balancing?

Answer 58

Trying to find out where the heavy spot is and attaching or welding weights in the location opposite to that heavy spot.

Question 59

If balance weight has to be split, what would the sum of the two weights be in relation to the original correction?

Answer 59

the sum would be a larger value

Question 60

What are 4 ways a machine may become unbalanced?

Answer 60

corrosion and abrasion, distortion, eccentricity, bent shaft

Question 61

How does doubling the rotor speed affect the force caused by imbalance?

Answer 61

it quadruples it

Question 62

How is phase affected with couple imbalance?

Answer 62

there is a 180 deg phase difference between rotor ends