PM, NDT, Vibration

Question 1

Types of maintenance (4)

Answer 1

breakdown
preventive
predictive
proactive

Question 2

This maintenance requires planning

Answer 2

Preventive

Question 3

This maintenance predicts problems before they happen and work continuously

Answer 3

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

Question 4

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

Answer 4

Proactive (identifies and corrects root causes)

Question 5

Other variations of maintenance (4)

Answer 5

total productive
preventive engineering
reliability engineering
productive maintenance

Question 6

This helps determine the urgency and extent of activity needed

Answer 6

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.

Question 7

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

Answer 7

Frequency (cpm or cps)

1 Hz = 1 cps = 60 cpm

Question 8

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

Answer 8

Displacement (important for less than 600 rpm)

Question 9

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

Answer 9

Amplitude (thousandths of an inch or mils)

Detects slow moving equipment less than 600 rpm

Question 10

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

Answer 10

Velocity (inches per second)

Detects problems with frequencies of 600-600 000 cpm

Question 11

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

Answer 11

Acceleration (max occurs at top of sign wave)

Detects high frequency

Question 12

Acceleration value

Answer 12

9.8 meters per second or 32 feet per second

Question 13

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

Answer 13

in phase (phase angle zero)

Question 14

When vibrations have different rhythms or directions

Answer 14

out of phase

Question 15

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

Answer 15

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

Question 16

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

Answer 16

transducer (pickups)

Question 17

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

Answer 17

Characteristic (analyzed from transducer)

Question 18

Two types of velocity transducers

Answer 18

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

Question 19

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

Answer 19

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

Question 20

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

Answer 20

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

Question 21

types of transducer mounting (5) from best to worst

Answer 21

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

Question 22

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

Answer 22

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

Question 23

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

Answer 23

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

Question 24

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

Answer 24

problem component

Question 25

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

Answer 25

Looseness (2 x rpm)

Question 26

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

Answer 26

unbalance (1 x rpm)

Question 27

four types of unbalance

Answer 27

static couple quasi-static dynamic (hardest to correct)

Question 28

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

Answer 28

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

Question 29

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)

Answer 29

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

Question 30

combination of static and couple unbalance

Answer 30

quasi-static

Question 31

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

Answer 31

dynamic unbalance (couple or twist)

Question 32

The oldest and most common form of maintenance inspection.

Answer 32

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

Question 33

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.

Answer 33

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

Question 34

3 types of dye penetrant

Answer 34

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

Question 35

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

Answer 35

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)

Question 36

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

Answer 36

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

Question 37

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

Answer 37

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

Question 38

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

Answer 38

Radiographic inspection (x-ray)

Question 39

measures the weight of contaminants per litre or fluid

Answer 39

gravimetric level analysis

Question 40

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

Answer 40

spectrographic oil analysis

Question 41

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

Answer 41

ferromagnetic analysis

Question 42

indicates how much of the oil additives have been depleted

Answer 42

total base number tests

Question 43

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

Answer 43

total acid number tests

Question 44

reveals the amount of oil degradation occurring

Answer 44

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

Question 45

water content of this amount is allowable in most cases

Answer 45

0.5%

Question 46

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

Answer 46

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

Question 47

2 types of yokes for magnetizing purposes

Answer 47

permanent magnet | electromagnetic

Question 48

Three main tools for remote visual inspection

Answer 48

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")

Question 49

4 types of developers

Answer 49

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

Question 50

3 types of waves in ultrasonic testing

Answer 50

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

Question 51

4 ultrasonic testing methods

Answer 51

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)

Question 52

2 penetrating waves of radiography

Answer 52

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

Question 53

This detects the thermal radiation (emissivity) of an object

Answer 53

thermography (measures heat being emitted)

Question 54

a graphic depiction of a vibration cycle

Answer 54

sine wave

Question 55

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

Answer 55

phase

Question 56

When taking phase readings keep accelerometers facing the ____ direction

Answer 56

same

Question 57

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

Answer 57

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

Question 58

the time required to complete one cycle of a periodic signal

Answer 58

period

Question 59

occurs when the rotor rotates at or near its natural frequency

Answer 59

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

Question 60

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

Answer 60

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

Question 61

HVA measurements meaning

Answer 61

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

Question 62

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

Answer 62

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

Question 63

Where should you not collect oil samples from

Answer 63

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

Question 64

Oil sample 18/16/13 means

Answer 64

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

Question 65

A strobe lights primary purpose in balancing is to check

Answer 65

phase angle

Question 66

misalignments frequency

Answer 66

2 x rpm

Question 67

Belt drive frequency

Answer 67

3 x rpm

Question 68

doubling the rpm _____ the force caused by unbalance

Answer 68

quadruples (weight and rotational speed determine amount of vibration)

Question 69

How much should a trial weight be

Answer 69

sufficient to change the amplitude of the vibration by 30%

Question 70

how thick is a penetrameter shim

Answer 70

2% of the thickness of the specimen being radiographed

Question 71

One of the best uses for x-rays

Answer 71

checking an engine cylinder head for cracks

Question 72

ultrasonic thickness measurements are accurate up to this

Answer 72

1%

Question 73

The most predominant frequency with the highest spike is called

Answer 73

predominant or fundamental frequency

Question 74

three measurements of amplitude

Answer 74

displacement, velocity, acceleration

Question 75

The total distance travelled is called this kind of displacement

Answer 75

peak to peak (measured in mils)

Question 76

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

Answer 76

natural frequency

Question 77

the normal standard for the vibration of a particular machine

Answer 77

baseline

Question 78

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

Answer 78

stand still (measures phase angle too)

Question 79

oil whirl occurs at what frequencies

Answer 79

45-50% of shaft rotation

Question 80

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

Answer 80

imbalance

Question 81

Where is oil analysis more effective than vibration analysis

Answer 81

hydraulic systems, reciprocating equipment

Question 82

a thermal imagining device produces an image called a

Answer 82

thermogram

Question 83

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

Answer 83

single plane balancing

Question 84

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

Answer 84

dual plane (two plane) balancing

Question 85

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

Answer 85

phase lag

Question 86

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

Answer 86

flash angle | phase angle

Question 87

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

Answer 87

imbalance

Question 88

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

Answer 88

misalignment

Question 89

trial weight formula.

Answer 89

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

Question 90

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

Answer 90

greater

Question 91

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

Answer 91

two-plane balancing

Question 92

4 reason for imbalance

Answer 92

wear buildup cracks fatigue

Question 93

how is displacement measured

Answer 93

mils

Question 94

how is velocity measured

Answer 94

inches per second (ips)

Question 95

how is acceleration measured

Answer 95

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

Question 96

whats the most expensive method of measuring vibration

Answer 96

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

Question 97

how is amplitude measured

Answer 97

thousandths of an inch