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