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Millwright Level 4 > PM, NDT, Vibration > Flashcards

PM, NDT, Vibration Flashcards

1
Q

Types of maintenance (4)

A

breakdown
preventive
predictive
proactive

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2
Q

This maintenance requires planning

A

Preventive

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3
Q

This maintenance predicts problems before they happen and work continuously

A

Predictive (uses vibration, heat, pressure, flow monitoring, oil sampling)

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4
Q

This takes predictive maintenance one step further, also called condition based monitoring

A

Proactive (identifies and corrects root causes)

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5
Q

Other variations of maintenance (4)

A

total productive
preventive engineering
reliability engineering
productive maintenance

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6
Q

This helps determine the urgency and extent of activity needed

A

Priority system - high priority for things that will shut down the plant, next level is for machines that keep whole departments running, and last is for auxiliary equipment etc.

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7
Q

The number of vibrations that happen in a particular unit of time

A

Frequency (cpm or cps)

1 Hz = 1 cps = 60 cpm

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8
Q

The distance of a vibrating object from it’s original rest position. The total movement above and below the axis

A

Displacement (important for less than 600 rpm)

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9
Q

The distance from one extreme to another (when displacement is at it’s maximum). Indicates how much a machine is vibrating

A

Amplitude (thousandths of an inch or mils)

Detects slow moving equipment less than 600 rpm

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10
Q

Speed and direction combined. The rate of change of displacement for a given time. Max occurs on neutral axis

A

Velocity (inches per second)

Detects problems with frequencies of 600-600 000 cpm

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11
Q

When an object increases velocity, measures in g’s force

A

Acceleration (max occurs at top of sign wave)

Detects high frequency

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12
Q

Acceleration value

A

9.8 meters per second or 32 feet per second

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13
Q

When vibrations act together moving in the same direction at the same time

A

in phase (phase angle zero)

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14
Q

When vibrations have different rhythms or directions

A

out of phase

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15
Q

Spike-like shock vibrations with extremely high frequency (400 000 to millions of cpm)

A

Pulse vibrations (indicate very early deterioration of bearings or gears)

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16
Q

This device converts the mechanical energy of the vibration into an electrical signal

A

transducer (pickups)

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17
Q

The shape of the waveform made by the vibration. This indicates the nature and origin of the vibration problem

A

Characteristic (analyzed from transducer)

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18
Q

Two types of velocity transducers

A

moving coil (seismic) - depends on a moving coil of fine wire and a permanent magnet

piezoelectric - no moving parts, electricity generated by transducer by vibration pressure upon ceramic material or crystal

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19
Q

Acceleration transducer that produces a voltage proportional to the acceleration of the vibration. Widely used for vibration measurement (most common)

A

Accelerometers - generate their own power, use an amplifier to increase signal strength

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20
Q

Displacement transducer that detect vibrations from clearances in a journal and bearing housing. Uses eddy current probe, does not generate it’s own power

A

Non-contact transducer (proximity transducer gap from shaft 0.020-0.060)
Sometimes mounted 90 degrees to each other

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21
Q

types of transducer mounting (5) from best to worst

A
  1. threaded stud mount (most accurate)
  2. magnetic pickup mount
  3. epoxy
  4. handheld
  5. shaft rider
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22
Q

Where are vibration measurements taken. Referred to as x, y, z axes

A

at the bearing or as near as possible to it (horizontal/radial/axial positions)

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23
Q

The most common cause of machinery vibration, the unequal distribution of weight of a rotating body about its centreline

A

unbalance (same frequency as machine 1 x rpm, phase stable)

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24
Q

The bearing with the highest frequency is most likely the _____ ______

A

problem component

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25
Q

This vibration is most commonly found in machine foundations at base bolts or anchors, cracks in machine bases. It should be eliminated first

A

Looseness (2 x rpm)

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26
Q

an unequal balance of weight of a rotating part around it’s axis

A

unbalance (1 x rpm)

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27
Q

four types of unbalance

A

static
couple
quasi-static
dynamic (hardest to correct)

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28
Q

unbalance caused when the shafts weight is evenly distributed along it’s length, but unevenly from side to side. The weighted centreline and shaft axis are parallel but misaligned along their length

A

static unbalance (detected by suspending arbor between two knife edges or rollers)

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29
Q

unbalance where there is extra weight at the end of each shaft. The weights are equal but one opposite sides of the shaft (6 and 12 o’clock)

A

Couple unbalance (detected when the shaft is rotated and a 180 degree phase angle is indicated between the ends of the rotor)

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30
Q

combination of static and couple unbalance

A

quasi-static

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31
Q

the most common type of unbalance, usually requires a computer to sort them out.

A

dynamic unbalance (couple or twist)

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32
Q

The oldest and most common form of maintenance inspection.

A

visual (shine light 5-45 degrees to flawed surface toward you)

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33
Q

This method of inspection is used to detect small cracks or discontinuities which cannot be seen by visual inspection. Can be used metals, ceramics, plastics, glass etc.

A

Dye penetrant - Liquid penetrates flaw due to capillary action. A developer is applied which highlights the flaw. Does NOT detect sub-surface flaws

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34
Q

3 types of dye penetrant

A

Water washable - least sensitive, not good for corrosion present. Can be wiped or rinsed off with water
Post-emulsifiable - highly fluorescent, difficult to wash away
Solvent removable - where water is not permissible. High accuracy even on contaminated defects, requires solvent to remove excess. Highly flammable

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35
Q

Machine parts that are to be inspected by this method must be easily magnetized. Detects subsurface flaws not greater than 1/4” (6mm)

A

Magnetic particle inspection. Must be transverse to the magnetic field to produce flux leakage. Ferromagnetic material only. Used fine iron oxide powder (dry=dyed or wet=fluorescent)

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36
Q

This inspection uses electromagnetic techniques, most effective for locating irregularities near the surface of the specimen, even through a thick layer of paint. Not used for preventive maintenance

A

eddy-current - ideal for conductive materials that are non-magnetic
AC power

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37
Q

This inspection uses a high-frequency sound waves over 20MHz to detect discontinuities viewed on a oscilloscope or CRT

A 
Ultrasonic inspection (immersion and contact type, contact more portable)
Tests thickness over 1/8". Needs couplant on the surface. Surface must be uniform
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38
Q

This inspection can reveal internal or surface defects even when they are covered or hidden by other machine parts

A

Radiographic inspection (x-ray)

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39
Q

measures the weight of contaminants per litre or fluid

A

gravimetric level analysis

40
Q

Assesses the amount and type of contamination. Determines the concentrations over a period and accurately predicts the lubricant failure before it occurs

A

spectrographic oil analysis

41
Q

determines quantity, distribution, and appearance by observing (thought a microscope) an oil sample as it is suspended over a magnetic field

A

ferromagnetic analysis

42
Q

indicates how much of the oil additives have been depleted

A

total base number tests

43
Q

determines how much the oil is breaking down into a harmful acidic compound

A

total acid number tests

44
Q

reveals the amount of oil degradation occurring

A

infrared tests (10% increase in viscosity can have serious consequences)

45
Q

water content of this amount is allowable in most cases

A

0.5%

46
Q

these are liquids used to make excess oily penetrant on the surface of a workpiece water-washable

A

emulsifiers
oil-based -function by diffusion
water-based - liquid concentrates

47
Q

2 types of yokes for magnetizing purposes

A

permanent magnet

electromagnetic

48
Q

Three main tools for remote visual inspection

A

videoimagescope (flexible probe, mini colour tv camera, 1/4” probe - up to 65 feet long)
fiberscope (live image in the eyepiece, length up to 20 feet, field of view 10-100 degrees)
borescope (lengths up to 90”)

49
Q

4 types of developers

A

Dry developer - power like substance brushed or sprayed on
Wet aqueous - water based, sprayed, dipped or poured
Wet non-aqueous - drying not necessary, evaporates rapidly
Film type - plastic powder and solvent

50
Q

3 types of waves in ultrasonic testing

A

longitudinal - particles vibrate in same direction as the wave
transverse/ shear - particles vibrate at right angles to direction of wave
surface waves - detects surface cracks

51
Q

4 ultrasonic testing methods

A

resonant frequency - ring test
transit time - determines thickness by time
intensity method - measures amplitude, tests sheet metal
intensity and transit time - most common, measures amplitude and time (used when you can’t reach both sides of workpiece)

52
Q

2 penetrating waves of radiography

A

X-ray - no residual radiation, can be used on all materials (through 20 inches of steel)
Gamma ray - no electrical power, radiation hazard, cannot be used on all materials
Safe distance of 50 feet in all directions
cobalt 60, iridium 192

53
Q

This detects the thermal radiation (emissivity) of an object

A

thermography (measures heat being emitted)

54
Q

a graphic depiction of a vibration cycle

A

sine wave

55
Q

the time relationship between two related events and is measured of expressed in degrees

A

phase

56
Q

When taking phase readings keep accelerometers facing the ____ direction

A

same

57
Q

In this frequency the system amplifies the energy from the forcing function frequency causing large amplitude. It destroys machines

A

resonant (occurs in any system not kept out of natural frequency by at least 20%)

58
Q

the time required to complete one cycle of a periodic signal

A

period

59
Q

occurs when the rotor rotates at or near its natural frequency

A

critical speed (should operate 20-30% outside of rotors critical speed)

60
Q

These transducers are used for general vibration measurements and balancing. They generate their own power. Larger than other transducers

A

Velocity transducers (made with a coil of wire fixed inside transducer case)

61
Q

HVA measurements meaning

A

transducer mounted horizontal, vertical, axial at the bearing of machine

62
Q

When an oil sample is removed from a point in a circulating system it’s called a

A

live zone sample (only collect when machine is running at normal operating temp, pressure, speed, load)

63
Q

Where should you not collect oil samples from

A

dead pipe legs where fluid is not moving, or after filters or separators

64
Q

Oil sample 18/16/13 means

A

18 - particles greater than 4 microns
16 - particles greater than 6 microns
13 - particles greater than 14 microns

65
Q

A strobe lights primary purpose in balancing is to check

A

phase angle

66
Q

misalignments frequency

A

2 x rpm

67
Q

Belt drive frequency

A

3 x rpm

68
Q

doubling the rpm _____ the force caused by unbalance

A

quadruples (weight and rotational speed determine amount of vibration)

69
Q

How much should a trial weight be

A

sufficient to change the amplitude of the vibration by 30%

70
Q

how thick is a penetrameter shim

A

2% of the thickness of the specimen being radiographed

71
Q

One of the best uses for x-rays

A

checking an engine cylinder head for cracks

72
Q

ultrasonic thickness measurements are accurate up to this

A

1%

73
Q

The most predominant frequency with the highest spike is called

A

predominant or fundamental frequency

74
Q

three measurements of amplitude

A

displacement, velocity, acceleration

75
Q

The total distance travelled is called this kind of displacement

A

peak to peak (measured in mils)

76
Q

the frequency at which an object or system naturally vibrates when a forcing function has been introduced

A

natural frequency

77
Q

the normal standard for the vibration of a particular machine

A

baseline

78
Q

When using a strobe light the part causing the vibration appears to do what

A

stand still (measures phase angle too)

79
Q

oil whirl occurs at what frequencies

A

45-50% of shaft rotation

80
Q

amplitude that is similar in vertical and horizontal directions are peculiar to

A

imbalance

81
Q

Where is oil analysis more effective than vibration analysis

A

hydraulic systems, reciprocating equipment

82
Q

a thermal imagining device produces an image called a

A

thermogram

83
Q

If the required balance correction is at a single point on the rotor is it called

A

single plane balancing

84
Q

When assemblies of significant length require two weights at opposing ends of the rotor this is known as

A

dual plane (two plane) balancing

85
Q

the distance that the heavy spot moves past the pickup before the flash occurs is called

A

phase lag

86
Q

the angle of the phase lag is called _____ and the spot where the line remains is called the

A

flash angle

phase angle

87
Q

If the vibration pickup is moved from horizontal to vertical and you get a 90 degree phase shift it is usually caused by

A

imbalance

88
Q

if you get a 180 degree phase shift the problem is probably caused by

A

misalignment

89
Q

trial weight formula.

A

Force= 1.77xRxWx(rpm/1000)^2
Force in lbs
Radius in inches
Weight in oz

Force is 10% of the weight. If supported between bearings force is 10% of half the weight. If overhung force is 10% of full weight

90
Q

The sum of additional weights is always _____ than the original correction weight

A

greater

91
Q

separate single plane balancing when the rotor length to diameter ratio is large is called

A

two-plane balancing

92
Q

4 reason for imbalance

A

wear
buildup
cracks
fatigue

93
Q

how is displacement measured

A

mils

94
Q

how is velocity measured

A

inches per second (ips)

95
Q

how is acceleration measured

A

g’se force (9.8m/s or 32 feet per second)

96
Q

whats the most expensive method of measuring vibration

A

vibration analyzers (measure vibration from all their characteristics, and separate frequencies)

97
Q

how is amplitude measured

A

thousandths of an inch

Millwright Level 4 (5 decks)

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