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4th Year Millwright > Vibration Analysis And Balancing > Flashcards

Vibration Analysis And Balancing Flashcards

1
Q

What does vibration analysis refer to?

A

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

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2
Q

What are some possible sources of vibration?

A

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

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3
Q

What conditions can be captured using thermography?

A

overloaded electrical circuits, loose connections, frictional heating of bearings

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4
Q

What do thermography detect?

A

the thermal radiation (emissivity) of an object

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5
Q

What is a forcing function?

A

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.

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6
Q

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

A

a change in the vibratory signature of that object

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7
Q

What are the 3 terms used to describe vibration?

A

frequency, amplitude, and phase

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8
Q

What is frequency, and how is it expressed?

A

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

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9
Q

What are orders?

A

multiples of the operating speed

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10
Q

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

A

displacement

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11
Q

How is displacement measured on a sine wave?

A

from peak to peak

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12
Q

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

A

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

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13
Q

In what range are velocity readings most consistent?

A

between 600 cpm and 60,000 cpm

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14
Q

What is velocity measured in?

A

in/sec or mm/sec

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15
Q

What is displacement measured in?

A

mils pk to pk, or microns pk to pk

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16
Q

What is acceleration measured in?

A

g’s force (32 feet/sec squared)

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17
Q

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

A

displacement

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18
Q

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

A

acceleration

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19
Q

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?

A

phase

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20
Q

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

A

natural frequency

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21
Q

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)?

A

resonance

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22
Q

What is the critical speed of a shaft or rotor?

A

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

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23
Q

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

A

20-30%

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24
Q

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

A

dominant or fundamental frequency

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25
Q

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?

A

synchronous vibration, non-synchronous

26
Q

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

A

sub-synchronous

27
Q

What is a harmonic?

A

A multiple or sub-multiple of the fundamental frequency.

28
Q

What are 3 types of vibration meters?

A

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

29
Q

What are the three basic categories of transducers?

A

displacement transducers, velocity transducers, acceleration transducers (accelerometers)

30
Q

Which type of transducer requires a power source?

A

displacement transducers

31
Q

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

A

accelerometer, they often use piezoelectric materials

32
Q

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

A

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

33
Q

What are HVA measurements?

A

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

34
Q

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

A

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

35
Q

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

A

always take readings from the same place

36
Q

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

A

phase does not change

37
Q

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

A

misalignment

38
Q

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?

A

an electrical problem

39
Q

What are the characteristics of a gear problem?

A

they show up at high frequencies, will be synchronous

40
Q

What are possible characteristics of a bearing problem?

A

high frequency, non-synchronous

41
Q

When would oil whirl normally occur in vibration analysis?

A

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

42
Q

When would mechanical looseness be identified?

A

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

43
Q

When is vibration from belts the greatest?

A

in the direction of belt tension

44
Q

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

A

at 1 x RPM

45
Q

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

A

angular misalignment or a bent shaft

46
Q

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

A

too cold

47
Q

What are the 4 products of oxidation in oil?

A

gum, varnish, sludge, acids

48
Q

When should an oil sample be taken from a machine?

A

at normal operating, temperature, pressure, speed and load

49
Q

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

A

a live zone sample

50
Q

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

A

4, 6, and 14 microns

51
Q

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

A

imbalance

52
Q

When does eccentricity appear on a vibration signature?

A

1 x RPM

53
Q

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

A

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

54
Q

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

A

single plane balancing

55
Q

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?

A

dynamic imbalance

56
Q

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

A

a computer

57
Q

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?

A

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

58
Q

What is balancing?

A

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

59
Q

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

A

the sum would be a larger value

60
Q

What are 4 ways a machine may become unbalanced?

A

corrosion and abrasion, distortion, eccentricity, bent shaft

61
Q

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

A

it quadruples it

62
Q

How is phase affected with couple imbalance?

A

there is a 180 deg phase difference between rotor ends

4th Year Millwright (11 decks)

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