Introduction_E [Compatibility Mode]

8/7/2019 Introduction_E [Compatibility Mode]

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DEVELOPMENT OF


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Develo ment of Maintenance Philoso h

Before WW II machineries were simple, heavy and robust

a n enance was s mp e => rea own ma n enance

Mass production systems require more reliable productionmachineries. Machiner break downs cause loss of revenue.

Machineries have evolved to modern machineries Water wheels => water turbines

team eng nes => steam tur nes Mechanical control => electronice control

and more) => machine dynamic behaviour become more

complex ee new new s ra egy Need speciallist within maintenance group


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Before 1960 it was beliefed thal all components failed

As a matter of fact only 4% of component population (eg:

bathtub failure pattern.

Rate Start up

cycleBreak down

cycle

Failur

Useful life period

Time


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The meaning of bath tube curve

Start up cycle: failures are due to defective

material, manufacturing defects, errors inassembly, operator errors. Matting surface ofcomponents are not smooth at the beginning of

runn ng per o . Useful life: components fit to each other

Break down cycle: failing due to fatigue,

excessive wear, erossion, abrasion etc.Bath tube curve is good for modelling mechanical

components


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7%4%

14%

5%

A e unrelated failure 4 5 6, ,


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FAILURE PATTERN POPULATION

PERCENTAGE

1

2

3

4

5

6


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CATEGORY OF PRODUCTION

EQUIPMENTS

Production equipments can be classified based

on their complexity, cost, role in a productionchain as:

Critical

Essential

This classification determines the appropriate


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DEVELOPMENT OF

FAILURE PATTERN THEORY


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DEVELOPMENT OF

MAINTENANCE STRATEGY

3rd Generation

-Better availability andreliability

-Better safety

- er pro uc qua

-Non environmentally harmfull

-Longer equipment life

2nd Generation-Better availability

-Longer equipment life1st Generation-

-Beter cost effectiveness-Fix when it breaks


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DEVELOPMENT OF

MAINTENANCE STRATEGY

3 rd generation-

-Design for reliability andmaintainability

-

-Small and high speed computer-FMEA

-Ex ert s stems

-Scheduled overhaul-Systemfor work planning and

controlling1st eneration

-Multi tasking and team works-Large and slow computer-Fix it when it breaks


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DEVELOPMENT OF MAINTENANCE

STRATEGY

ra egy eac ve,

Run To Failure

reven ve

Maintenance

re c ve

Maintenance

roac ve

Maintenance

Definition Fix it when it Conduct Maintain based Redesign to

breaks, Run to

Failure

maintenance at

regular intervals

upon known

condition/standard

eliminate root

cause of failure

(whenimplemented

correctl

for or scheduled

failure

maintenancerequired

Disadvantages

(when

High spare

stock level.

Unnecessary

replacement of

Costly if

implemented

Could be

expensive

correctly)

outages

.

utilization of labor.

Component you Head light Oil change Automobile tires 2 year lease

wou manan


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Can be dangerous when break down

equipment break down cause.

ower to Ex ensive investment

Expensive repair cost

Long repair time


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Smaller than critical equipments, usually

rovided with standb unit. Examples: Process pump, boiler feed

, .


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Does not endangered people and environment

Does not affect production process when itbreaks down

Inexpensive repair cost

stand by unit

Single unit equipment but not critical toproduction process


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, , , Break down (run to failure) maintenance : No

ma n enance un mac ne rea s. r mary a uresalways cause secondary failures.

performed based on fixed schedule (or based onoperating hours)

Predictive (on condition based) maintenance (PdM):Health condition of machines is continuously monitored.

be performed.

Proactive (prevention) maintenance: the cause ofpremature failures are investigated using RCFA.Findings are followed up by redesign.


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Preventive Maintenance(Time Based Maintenance)

revent ve ma ntenance: ma ntenance act v ty to

prevent equipments from break down by, .

Based on fixed schedule (weekly, monthly,, , , .

Implementation is easy, just follow the schedule:, , , , .

Budget planning is easier, done yearly.


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A r ri i m n r wi h PM

Equipments that can cause

a o s u ow

product quality degradation

failure to related components dan er eo le.

Lighting, floor, ceiling that can cause poor


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Equipments not to be treated with PM

Equipments with stand by unit Equipments with investment cost less than their

Equiments with long life expectancy without PM


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Distribution of load vs. distribution of strength

There is probability of load > strength (statics,fatigue, wear etc) as shown bellow

y

robab

ilit

e an

Rata2Rata2 MPa


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Predictive maintenance tries to predict machinecondition along bathtub curve, when critical wearoccurs

reRate

Start upcycle

Break downcycle

Failu

Useful life period

(wealth cycle)

me


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Predictive Maintenance (PdM)

Breakdown beforescheduled PM

Machine is repairedbefore it needs it

Time based preventive maintenance (PM)


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Technology needed for condition monitoring ino e ec w en cr ca wear occurs

Oil analysis errograp y Chemical analysis

n rare Magna flux ra on Ultrasonic imaging rason c c ness gaug ng Advanced visual inspection


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Need investment for instruments and specialist

If correctly implemented can reducemiantenance cost

carefully studied.

Reduction ofmaintenance

Investment fortools and specialist


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, ,


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, ,


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Predetermined Maintenance, Fix it

Corrective maintenance,

e ore rea s, anne

Maintenance, Histor ical

Maintenance, Calender Based

Maintenance Predictive Maintenancea

te

un o a ure

Maintenance, Breakdown

Maintenance

Hi h risk of secondar failure

Machines are repaired when there are

no faults

Repair often causes more harm than

If it is not break dont f ix

it, Condition based

maintenance

Failure

High down timeHigh cost of spare parts

goo

There are still unscheduled breakdown

Miantenance is performed in controlled

g nves men cos

Additional skills required

Unexpected breakdowns

Safety hazardous

Machines are not over

manner

Fewer catasthropic failures

Greater control over stored parts and

are re uce

Parts are ordered when

needed

No condition monitoring

related cost

Unexpected machinery failures should

be reduced

anenance s per orme

when convenient

Equipment life is extended

Maintenance Strategy


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Proactive Maintenance(Prevention Maintenance)

remature a ures can appen on equ pments

To prevent premature failure from reoccuring The cause of failure is analyzed using Root

Cause Failure Analysis (RCFA)

Improvement / redesign is performed based onthe results of RCFA


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VIBRATION AND MACHINE

CONDITION

Vib i d hi di i


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Vibration and machine condition

When a machine gets older its vibration

level becomes higher. This is due to:

Foundation settlement causing deformation

missalignment of shaft

ange n ynam c e av our o t e mac nesuch that its natural frequency shifted


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.


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Machine vibration

Not dangerous if the machine is designed to generatevibration

Dangerous if the machine is not designend togenera e v ra on

Forced vibration (frequency = rotational speed) => remedy:re lace defective elements balancin ali nment

Resonance (frequency = fixed) => remedy: changeoperational speed, increase stiffness, increase damping,

,


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Vibration as measured: it is an effect in ractice it canonly be measured on the outside part of the machine

Abnormality, faults: it is cause (ex: unbalance, geardefects dll), occurs on the inside parts of the machine,practically can not be measured

How can we know the cause from the effect?


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FUNCTION:Unbalanced, bent

shaft, misalignment,

MACHINESTRUCTURE: Gear

wheel, rotor disks, RESPONSEear ng e ect,

rubs, gear meshproblems

s a t, ear ngs,coupling, housing

Response

Forcing function


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cause from the effect

modeled and verified by measurements)

Fault Vibration Signature

n a ance x, e c

Misalignment 1 x, 2 x, etc

Bent shaft 1 x, 2 x, etc

Bearing defect BPFO, BPFI, BPS, etc


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How to solve this type of invers problems

Machineanatomy

Calculatetheoreticalfrequencies

Corelate Causes Normal?

Vibration Reduce into

vibrationnt (effect)

components


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Working principle

Main components Kinematicrelationship

components


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MACHINERY VIBRATION

Major Axis of Machine Vibration


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Major Axis of Machine Vibration

Y

Y

Z

XZ

H M hi Vib t ?


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How Machine Vibrates?Shaft on journal bearing: Relative Displacement.

Y

Bearing clearancewith lube oil Rotation, low speed,

Y

Rotor

Bearing

no vibration

X

Shaft

Base plate

Precession, higher,

How Machine Vibrates?


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How Machine Vibrates?

Shaft on rolling bearing: No relative displacement.

Rolling bearingY

Rotor

X

Shaft

Base plateRotation, high speed,no vibration

Absolute (left) vs Relative (right)


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Absolute (left) vs. Relative (right)

Vibration Measurement

=

Abs (100%) Abs (100%)

- =

Abs (100%) Abs (10%) Rel (90%)

Bearing clearance

Rolling bearing Rotor

w u e o

ShaftShaft

ear ng


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Phase of Vibration


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Phase of Vibration

Phase represents timing relationship between 2 signal.

n v ra on, s gna can e cause s mu us an e ec response ,as seen in mass spring system with input at A and response at B.

.relative phase.

Responsed

Input Response

m

k

A Phase different, in


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Phase of Vibration


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Phase of Vibration

dPhase

t

op: s gna rom avibration sensor

Keyphasor event

e

Middle: Signal fromke hasor

Trigger levelV

olta

transducer

td

Bottom: Combinedsignal

tKeyphasor event


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YXY

tTra ector

X

of shaft

center Precessioncenter

tKeyphasortransducer

a ea odeg


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signals are not

sinusoide. Phase

Filtered 1 X

measurement canbe done if thesignals aredominated by their

harmonics ( 1X,2X, 3X, dst .

Filtered 2 X


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Vibration theory in general is explained by the

use of mathematical formulation => it can bedifficult and not interesting

Can it be studied in a more easier and

interesting way? Y m inl fr m r i i n r hr h

Graphs and pictures can be easily understood


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Pendulum movement =Harmonic movement, with

g......

L

Hertzg.......1=


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Pendulum movement can be used to helin understanding vibration theory, for

exam le relationshi betweendisplacement, velocity and acceleration

What can we observeYang dapat diamati t owest pos t on: sp acement zero, ve oc ty

maximum, acceleration zero (in this position

At farthest position: displacement maximum,,


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Displ phase = Accel phase+ 180 (displacement lag

180 relative to accel)Displ phase = Velocityphase + 90

Velocity phase = Accelphase + 90


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e at ons pbetween displ,

at constant freq


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Vibration system consisting of mass and spring

Vibration will sustain


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atura requency n ra et

k g

m

Natural frekuency in Hz

mn yn

k

2n

nf =

m=mass, k=spring constant, g=gravity, y= static

fl i n


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mp y suppor e s a

Critical speed in Hz,g

nc1

=

EI

LWY rotor

48=

32I =

L/2 L/2


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Overhung shaft

Critical speed in Hz

g

nc

1=

where

LcLWY rotor )/1(3

+=

Lc


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ng over ungmass supported

spring is tuned tohave natural

eque cy sa e

with frequency ofi vi r i n

Pipe vibrationenergy will beabsorbed byoverhung mass


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Vibration system consisting of mass and spring

Vibration will die out


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Vibration will die out

The larger the damping the faster vibration dieout.


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Excitation in the form of sinusoidal force withconstant amplitude

=

m

o

k


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An en ine and com ressor with a mass of 1000 ksupported by 4 springs as isolator, each with k = 10 kN/mm. Detemine natural frequency fn.

re spr ng cons an s e ec ve y a enua e v ra on w enoperated at 3000 Rpm?

Engine

Vibration

Compressor

isolator

Vibration of


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Rotating Unbalanced Mass Excitation: sinusoidal force

with amplitude of em2

Vibration of


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Rotating Unbalanced Mass

Vibration of


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Measurement results

Vibration of


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Beside lateral vibration, torsional vibration alsooccur on shaft


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.

Peak to zero: for velocity dan acceleration

A = peak

or s nuso e

RMS = 0.707 A

Average = 0.637 A

2A = peak topeak

t

VCrest factor =Peak/Rms

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Introduction_E [Compatibility Mode]