vibration and its impact on reliability and costs - case ... · (from company’s several mills)...

Vibration HistoryPulp & Bleach Area

0.19

0.170.16

0.25

0.21

0.16

0.17

0.18

0.19

0.2

0.21

0.22

0.23

0.24

0.25

0.26

1980 1981 1982 1983 1984

Year

Ave

rage

Am

plitu

de V

eloc

ityips

1 2 3 4 5

1 2 3 4

•

•

•

•

44

42

40

38

36

34

32

30

28

26

24

44

32

2824

Dol

lars

/ To

n

Year

R&E Maintenance ExpensePulp & Bleach Area

1 2 3 4 5

Vibration History

0.19

0.170.16

0.25

0.21

0.16

0.17

0.18

0.19

0.2

0.21

0.22

0.23

0.24

0.25

0.26

1980 1981 1982 1983 1984

Ave

rage

Am

plitu

de V

eloc

ityips

1 2 3 4

•

•

•

•

44

42

40

38

36

34

32

30

28

26

24

44

32

28

24

Dol

lars

/ To

n

Year

R&E Maintenance Expense

1 2 3 4 5

Intellectuals solve problems; geniuses prevent them.

Albert Einstein

What percentage of your machines are the highest HP?

…medium HP?…low HP?

Average Maintenance Costs By Machine Size

500 hp 500 hp ……………………………………..............

150 hp 150 hp …………..……………………......$2x / hp / yr

$1x hp / yr

$4x / hp / yr

1 hp 1 hp ……..……......

Vibration vs. Maintenance Costs1800 rpm pumps

Machine0

10

20

30

40

50

0

0.05

0.1

0.15

0.2

0.25

0.3Velocity, ipsDollars, Thousands

< $4,000 0.03 in/sec

Velocity, ipsDollars, Thousands

Vibration vs. Maintenance Costs1800 rpm pumps

Machine0

10

20

30

40

50

0

0.05

0.1

0.15

0.2

0.25

0.3

< $7,750 0.05 in/sec

Velocity, ipsDollars, Thousands

Vibration vs. Maintenance Costs1800 rpm pumps

Machine0

10

20

30

40

50

0

0.05

0.1

0.15

0.2

0.25

0.3

0.08 in/sec

Velocity, ipsDollars, Thousands

Vibration vs. Maintenance Costs1800 rpm pumps

Machine0

10

20

30

40

50

0

0.05

0.1

0.15

0.2

0.25

0.3

< $15,000

Fastest means to determine your own actual costs

Maintenance Expense vs Vibration History

Machine type Highest Velocity, ips

Maintenance Cost, $

Lowest Velocity, ips

Maintenance Cost, $

Total Highest Lowest

Difference in maintenance costs for 3 machines with highest vibration vs 3 machines with lowest vibration:

Difference in 12 month maintenance costs = $

Maintenance Expense vs Vibration History

Difference in maintenance costs for 3 machines with highest vibration vs 3 machines with lowest vibration:

Difference in same period maintenance costs =

Machine type Highest Velocity, ips

Maintenance Cost, $

Lowest Velocity, ips

Maintenance Cost, $

Pump - 1800 rpm 0.15 10298 0.012 2668

Pump - 3600 rpm 0.26 46383 0.021 2503

Fan 0.338 16793 0.052 226

Total Highest 73474 Lowest 5397

$$ 68,077

Simplest, Easiest Procedures to Lower Amplitudes on Existing Plant Machinery

Eliminating Foot – Frame related Resonance

1.0

0.8

0.6

0.4

0.2

00 200 400 600 800 1000

Frequency in Hz

Pk

Vel

ocity

in In

./Sec

1-A-REACTOR BLD. SPRAY MIH MOTOR INBOARD HORIZ.

SPECTRUM DISPLAY12-NOV-90 18:22PK=.7089LOAD=90.0RPM=3594RPS=59.91

2x RPM

1x RPM

0.03

0.06

0.09

0.12

0.15

0.18

0.21

0.24

00 200 400 600 800 1000

Frequency in Hz

Pk

Vel

ocity

in In

./Sec

1-A-REACTOR BLD. SPRAY MIH MOTOR INBOARD HORIZ.

SPECTRUM DISPLAY15-NOV-90 18:32PK=.1970LOAD=90.0RPM=3585RPS=59.75

2x RPM

1x RPM

1.0

0.8

0.6

0.4

0.2

00 200 400 600 800 1000

0.03

0.06

0.09

0.12

0.15

0.18

0.21

0.24

00 200 400 600 800 1000

Before After

Auto scaled

1.0

0.8

0.6

0.4

0.2

00 200 400 600 800 1000

1.0

0.8

0.6

0.4

0.2

00 200 400 600 800 1000

Before After

Added 2‐3 mils of shimunder one flange bolt!

Adjusted to same scale

Electric motor

Two bolts loose

All bolts tight

10

0

2

4

68

DIS

PLA

CE

ME

NT

IN M

ILS

10

0

2

4

68

DIS

PLA

CE

ME

NT

IN M

ILS

Primary production Machines(from company’s several mills)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 2095

96

97

98

99

100

Ultimate Target

% Large pulp and paper company’s goals for additional production running time

Initial Target

Present production

Primary production Machines(from company’s several mills)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 2095

96

97

98

99

100% Goals for additional production running time

250,000 Tons / year ÷ 365 = 685 tons / dayAdditional

Initial Target250,000 Tons / yr

Primary production Machines(from company’s several mills)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 2095

96

97

98

99

100

Additional500,000 Tons / yr

% Goals for additional production running time

500,000 Tons / year ÷ 365 = 1370 tons / dayAdditional

VP Production - major paper company:

“I can get an additional large papermill - not through the expenses and problems of building one - but by getting only 20 of our present machines to run just a little bit longer each day.

How?? Through our new very practical machinery improvement / precision maintenance efforts.”

Large Aluminum manufacturing facility

Machinery

5000 pieces of rotating equipment

Maintenance PhilosophyBefore starting the program: run to failureAfter: machinery improvement / precision

Average Vibration Levels for all Equipment

Year 10

0.05

0.1

0.15

0.2

0.25

0.3

0.35

Year 6

Inches/Second

Unscheduled vs Scheduled Maintenance

Year 10

20

40

60

80

100Scheduled 15 %

Year 6

Unscheduled 85 %

Unscheduled 9 %

Scheduled 91 %

%

1,500 Pumps (100 - 350 Hp)

• MTBF - 4 Years

• Average rebuild / replacement cost -$25,000 / pump

• Total pump maintenance cost -$9,375,000 / year

Annual Pump Maintenance (Run to Failure)

• Same 1,500 Pumps (100 - 350 Hp)

• First four years• $4,687,500 / year

• Fifth year - present: • < $1,000,000

Annual Pump Maintenance Costs:

Production Increase(through machinery improvement efforts)

Mill

ion

P oun

ds p

e r M

o nth

Year 1 Year 6

30 million pounds per month

0

10

20

30

40

50

60

70

60 million pounds per month

With no increase in expansion of capital machinery!

ISO Balance Standards• G 100 Crankshaft -drives of fast diesel engines with six or

more cylinders, complete engines of cars, trucks and locomotives

• G 16 Propeller shafts, carden shafts, parts of crushing machinery, parts of agricultural machinery

• G 6.3 Parts of process plant machines, paper machinery rolls, fans, fly wheels, pump impellers, electric motor armatures

• G 2.5 Gas and steam turbines, Turbine driven machines, machine tool drives, motor armatures with special requirements

• G 1 Tape recorder and phonograph drives, grinding machines, small motor armatures with special requirements

Page 225

G 6.3

G 2.5

G 1

G 6.3

G 2.5

G 1 API

AmericanPetroleumInstitute

Shaft centerline orbit around center of massISO Rotor Balancing Standards: circa 1956

Con

vert

ed to

inch

es

RPM1800

0.0011

1.1 mils radius = 2.2 mils orbit

2.2 mils @ 1800 RPM = approximately 0.22 in /sec

Not so good for long production life !

Con

vert

ed to

inch

es

RPM2000500200

0.001

0.004

0.012centerline orbit radius of 12 mils

Total displacement 24 mils! How will this affect the gearmesh?

Pitch circles

AddendumDedendum

Addendum : Portion of tooth above the pitch circle

Dedendum : Portion of tooth below the pitch circle

AddendumDedendum

AddendumDedendum

AddendumAddendum

DedendumDedendum

Gearmesh frequency12,498 cpm

Excessive barring on paper napkin machine

Gearmesh frequency

Apply sideband cursor

Gearmesh frequencySideband difference frequency 118 cpm

Gear rpm = 117.9 cpm(closest data point at 120 cpm)

The peak in velocity is only 0.1 ips

Gear rpm = 117.9 cpm

But the displacement is 16.6 mils!

The peak in velocity is only 0.1 ips

Indicates a large rotor imbalance

The gear was balanced and the barring eliminated

1200500200

0.001

0.004

0.012

If the width of the rotor is less than ¼of the diameter, then it only requires a single plane balance.

False !

Balancing Narrow and Overhung Rotors

Usually calls for single plane balance

Usually calls for single plane balance

Calls for two plane balance

If the rotor is overhung (cantilevered), regardless of width, then it most often requires a single plane balance.

False !

Vibratory motion of shaft centerline

Greatest amplitude at the top

Cooling fan

what a convenient place for balancing at the top plane

False !

Static imbalance (overhung) creates large couple

Couple (rocking motion) pivot point

If Resonant in the rocking mode, bracing usually does not work

Instead, use a tuned dynamic absorber (works only on a resonant system)

Page 234

G 1 Parts of process plant machines, paper machinery rolls, fans, fly wheels, pump impellers, electric motor armatures

Develop your own company standards for precision balancing

Balancing time, from G 2.5 to G 1 (or API) another ½ hour

Balancing time, from G 6.3 to G 2.5, ½ hour

Balancing time, including cleaning the rotor, removing burrs, adding proper key, mounting on balancing machine, adjusting drive unit and positioning end stops.

Balance to G 6.3 Time: 1 to 1½ hours

Total extra time for balancing from G 6.3 to G 1, One hour

Total for true precision balance 1 hour

Motor solo test and touchup ½ hour

Extra for true precision alignment 1 hour

Foot related resonance test ½ hour

Additional resonance improvement 1 hour

Total 4 hours

At $100/hour = $400

Eccentricity at 200 RPM = 12 mils

Vibration amplitude in displacement :12 x 2 = 24 mils

Most common places where alignment goes wrong

Actual thermal growth situations

From Update International SurveysFrom Update International Surveys

Typical responses from Supervisors and Managers

“My plant already has modern alignment instruments (laser and/or reverse indicator).”

“My people have received a good training from:

instrument manufacturer

alignment seminar specialists

internal training staff

Update International……..etc”

Responses from those who perform alignmentResponses from those who perform alignment• “Nobody has ever complained about my work”

• “I can get the job done with one indicator, faster than setting up the fixtures.”

• “I love using the laser system. I use it all the time.”

• Question: “How do you know when to quit?”Typical answer: “I have a lot of experience. I just know it.”

“Almost never”

“When it is a brand new machine, with manufacturer’s representative present.”

“Nobody tells me when. I don’t believe they’re hot enough!”

“It’s not my job to figure it out.”

“When in doubt, I ask my supervisor / maintenance planner.”

Responses on:Responses on:““WWhen do you offset for thermal growth?hen do you offset for thermal growth?””

Fan (very hot)

History:• 10 years of vibration amplitudes from 1.0 to 1.5 in / sec• Replaced worn bearings, every 4 to 6 months• Each shutdown resulted in an outage of half the plant• Repeatedly balanced in-place• Repeatedly realigned, (including offsets for thermal

growth)• Thermal growth offsets supplied by fan manufacturer• Manufacturer’s calculations based on one motor / fan

assembly

Fan (very hot) Fan (very hot)

Actually there were two fans back-to-back

Fan (very hot) Fan (very hot)

notice the exceptionallyhot area for each

outboard pedestal.

Generator

3000 rpm

HotSteam

Turbine

A B

Noise enclosure

History:• 4 years of high vibration amplitudes• 4 different consultants (with no solutions)• thermal offsets estimated for generators internal

temperatures (same for each end) - - - - - - no actual temperatures measured

• consider temperature pedestal A relative to pedestal B

Now, what else can magnify these vibrations?

Resonance at new operating speed

How can we tell ahead of time?

½ HP variable speed vibration shakerRange 0 to 6,000 RPM

Shaker large enough to shake a whole section of a paper machine

(36) i

Not resonant

1st Resonance Frequency

2nd Resonance Frequency

Not resonant

1st Resonance Frequency

2nd Resonance Frequency

3rd Resonance Frequency

3rd Resonance Frequency

A F G H IC D EB

ON

0.08

Testing for resonance with a shaker using a 10 division modal shape plot

(38)mdsh ai

First resonance excited by shaker

0.050.23 0.27 0.240.04 0.18 0.24 0.16 0.05 0.07 0.15

5

7

8

9

Dynamic imbalance:Composed of static and couple

To counterbalance first resonance “whip” remove static imbalance

To counterbalance second resonance “whip” remove couple imbalance

Notice: no balance weights or holes, no tough point indicated between shaft and bore

This did not start with bad gearteeth.It started with no dynamic balance and poor assembly fitsFinally magnified by resonance with cracks forming at the node

Distance (feet)Number of bars

Surface speed: feet/minute

Bars FtFt Minute

X = Bars/Minute

First determine what is not causing the problem

Frequency causing the barring

=

Often involves a resonance

Barring on a roll: number of bars X roll RPM

Equal angles

Aligned

Unequal angles

Misaligned

Before

After alignment

Lum

ens

Frequency CPM

Coupling bindingand resonant pipe

Lum

ens

Fans

Frequency CPM

Out of balance fans 30’ away from resonant headbox

Resonated section of headbox above the slice

Lum

ens

Frequency CPM

Centri-screen drive motor

Lum

ens

Frequency CPM

Centri-screen drive motor

Coupling bindingand resonant pipe

Headbox

Pipe resonant to 2x RPM of pump below

Normal

Resonant

Resonant