Vibration Applications of Vibrating Screens

8/17/2019 Vibration Applications of Vibrating Screens

1/15

Use of this document is governed by the termsand conditions contained in @ptitudeXchange.

PaSummary

This article discusses the many facets of monitoring vibrating

screens by providing an overview of the type of data associated

with vibrating screens, and the standards that control theindustry. It also provides data examples and advanced analysis

techniques, such as orbital and vibration analysis. Finally, a

listing of some common bad actors and their solutions is presented.

Vibration Monitoringof Vibrating Screens

JM02017Andy Page15 pagesOctober 2002

SKF Reliability Systems

@ptitudeXchange5271 Viewridge CourtSan Diego, CA 92123United Statestel. +1 858 496 3554fax +1 858 496 3555email: [email protected]: www.aptitudexchange.com


2/15

Vibration Monitoring of Vibrating Screens

© 2004 SKF Reliability Systems All Rights Reserved 2

Introduction

In most traditional applications of vibrationanalysis, data is collected on rotating

elements, and analyzed to determine the

mechanical condition of the equipment. For

example: bearing faults, gear faults,misalignment and coupling problems can be

diagnosed using vibration analysis. More

advanced uses could include buildings andother structures, where data collected could

detect certain design flaws and/or structural

degradation. These types of structuralapplications are certainly appropriate in the

material handling industry. They are being

implemented throughout the industry, and

established programs are starting to realize themany benefits of a vibration analysis program.

However, a key component in the industry

that escapes the more traditional analysts is

the vibrating screen. The vibrating screen is

normally overlooked as being a keycomponent for analysis on the initial sight

assessment. This is, in part, due to their size

and seemingly violent motion. However, thevibration analyzer is capable of providing awealth of data that can help both maintenance

and production get full utilization out of their

screen.

A vibrating screen is a piece of equipment thatseparates different size material. Separation of

material is accomplished by means of

screening media, commonly referred to as

decks, which act like filters. The screen deck

has certain size opening in the mesh. Thesmaller material falls through the opening

while the larger material remains on top of thescreen deck. The entire screen can vibrate at

up to 1000 cycles per minute and can have as

Figure 1. Typical 8’ x 24’ Inclined Vibrating Screen. This illustration shows two spring systems that support thevibrating screen as well as the shaft and mounting plate that holds the shaft in place.


3/15



many as three decks. The decks are arranged

above each other, usually with the largeropening screen deck being on top and the

lower screens having smaller opening

respectively. As material is feed onto the topdeck, the screen can vibrate at over 5 g. Thematerial falls through the openings and is

separated. Each deck’s overflow is usually

directed into a chute and the material that fallscompletely through is sent to another chute.

The screen is supported on all four corners by

either steel springs or rubber donuts, and

either rests on the floor or is suspended by

rods or chain. An eccentric shaft on the

vibrating screen provides the motion of thescreen. This shaft is contained within a

housing that serves as the mount for the bearing. Screens can have up to three shafts,

each in their respective housing.

This article discusses the process of collecting

vibration data on a vibrating screen, including

signal processing techniques and the methodin which data should be obtained. This method

includes a checklist that can be used to makecertain the screen is thoroughly evaluated. The

article then describes examples of data

obtained from screens operating in good and poor conditions. Analysis techniques such as

screen gages or screen cards and vibration

analysis are discussed in depth.

Signal Modulation Concerns

Signal modulation is a concern when trying to

obtain a vibration signature on the drivemechanism. The screen is moving at a speed

of up to 1000 CPM and can be producingforces in excess of 5.0 g. Modulated data provides little useable information about the

condition of the bearings or gears in the drive

mechanism.

Typical modulated data would only appear as

a single peak at turning speed. To get usableinformation, the modulation would have to be

corrected for as it was collected. That means

that the carrier frequency would be filtered

out, leaving only the higher frequency data(impacting) of the bearings and/or gears, e.g.

by the enveloping technique.

Enveloping is a signal processing technique in

which a filtering method is used to filter

vibration that is associated with the generalfunctions of the machine. Vibration caused by

items such as running speed of the machine

and in the case of vibrating screens, the product that is moving across the screen mesh

can cause vibration that is not associated with

the components in the machine.

In figure 2, a “good” spectrum contains a once per revolution impact as indicated by the peakat running speed. This is normal in vibrating

screens due to the eccentric shaft in the drive

mechanism. The “bad” spectrum contains peaks that are non-synchronous to rotation

speed. These peaks matched the inner race

fault frequency of the bearing. A normal

waveform usually shows peaks of over 1 g,due to the eccentric shaft a peak alarm of 2 g

is chosen (Figure 3). The increase in vibration peaks is illustrated Figures 4 and 5, due to

bearing damage.

Sec - Shaker Screens

S-4 -RFB Right Feed Bearing

Route Spectrum

09-SEP-97 10:56

(PkVue- HP 500 Hz)

OVRALL= .3617 A-DG

RMS = .3597

LOAD = 100.0

RPM = 812.

RPS = 13.53

0 100 200 300 400 500

0

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

Frequency in Hz

R M S

A c c e l e r a t i o n i n G - s

Figure 2. Spectrum of a bearing in good condition.

Single elevated peak on the right side is running speed

of the machine.


4/15



Sec - Shaker Screens

S-4 -RFB Right Feed Bearing

Waveform Display

09-SEP-97 10:56

RMS = .4037LOAD = 100.0

RPM = 812.

RPS = 13.53

PK(+) = 2.01

PK(-) = .8839

CRESTF= 4.97

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

-1.5

-1.0

-0.5

0

0.5

1.0

1.5

2.0

2.5

Time in Seconds


PK ALARM

Figure 3. Time waveform of a bearing in good

condition. The g-values read on the y-axis are elevated from the normal levels of 0.5 to –0.5 g’s that are

typically seen in this machine.

Ter - Shaker Screens

S-3 -LFB Left Feed Bearing

Route Spectrum

09-SEP-97 13:57

(PkVue- HP 500 Hz)

OVRALL= 2.28 A-DGRMS = 2.27

LOAD = 100.0

RPM = 812.

RPS = 13.54

0 100 200 300 400 500

0

0.1

0.2

0.3

0.4

0.5

0.6

Frequency in Hz

R M S A c c e l e r a t i o n i n G - s

Figure 4. Spectrum of bearing with inner race fault

frequencies. The multiple peaks are the inner race

defect frequencies and sidebands of running speed surround the inner race peaks.

Ter - Shaker Screens

S-3 -LFB Left Feed Bearing

Waveform Display

09-SEP-97 13:57

RMS = 2.49LOAD = 100.0

RPM = 812.

RPS = 13.54

PK(+) = 21.01

PK(-) = 3.63

CRESTF= 8.45

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

-6

-3

0

3

6

9

12

15

18

21

24

Time in Seconds


PK ALARM

PK ALARM

Figure 5. Time waveform of bearing with the inner race

fault frequencies. The peaks in this time waveform are

due to impacts in the bearing.

Traditional InspectionTechniques

Traditional techniques for identifying

problems with vibration screens include:

• Measuring spring height

• Checking for level spring mounts

• Checking the level of screen (side to side)

• Checking for evenly distributed flow fromfeed chute

• Checking for restrictions to motion

• Checking the stroke (trace of the motion)

• Measuring the stroke length

• Measuring screen speed

The traditional analysis of a screen’s motion,acceleration, and angle is accomplished with a

screen card or screen gauge. A screen card is

a rectangular, magnetic card that has several black circles of varying diameters on it. It also

has several straight lines all at different angles


5/15



from the edge of the card. This card is placed

squarely on the screen. While the screen isrunning the circles will appear as an oval. The

oval with the most solid center is the correct

throw of the screen. The straight line that isclearest is the proper angle of the screen.

To get an idea of the orbital motion of thescreen a white sticker is applied to each corner

of the screen. A pen or pencil, held firmly,

lightly applied to the sticker, allows themotion of the screen to be traced onto the

sticker. The resulting “plot” is the motion of

the screen, and the length of the long axis of

the oval is the screen’s “throw” or "stroke

length." The speed of the screen can beassessed with a contact tachometer or strobe

light. The acceleration of a screen isapproximated by the following equation:

Acceleration (g) =

(screen speed in RPM)2 x (screen throw in

inches) / 100,000

In the table below, example screen

accelerations are summarized.

Application

NominalAperture

Size (mm)

ScreeningElements

Stroke

(mm)

HD ND

Speed

(Rpm)

HD ND

g-Index

(target)

Loaded

Scalping >75 12.0 - 10.5 750 - 800 3.8

Ballast 75 to 32 10.0 - 8.5 850 - 900 4.0

Aggregates 25.4 to 6.7 9.0 - 8.0 900 - 950 4.1

Fines

Separation


6/15



Prim - Road Rock Screen

Road Scrn -FLV Screen Stroke - Front Left Vert

Waveform Display

06-FEB-97 10:20

RMS = 4.91

LOAD = 100.0

RPM = 998.

RPS = 16.63

PK(+) = 7.08

PK(-) = 7.02

CRESTF= 1.45

0 100 200 300 400 500

-8

-6

-4

-2

0

2

4

6

8

Time in mSecs


Figure 7. Waveform of vibrating screen in good

condition; the time waveform data of a vibrating screenindicates a sinusoidal movement of the screen. This

means that the screen is moving up and down similarly

to a wave in a body of water.



Route Spectrum

06-FEB-97 10:20

OVRALL= 4. 89 A-DG

RMS = 4.86

LOAD = 100.0

RPM = 998.

RPS = 16.63

0 20 40 60 80 100

0

1

2

3

4

5

6

Frequency in Hz

R M S A c c e l e r a t i o n i n G - s

Freq:

Ordr:

Spec:

16.63

1.000

4.859

Figure 8. The conversion of the time waveform, Figure

7, to a acceleration spectrum. The spectrum contains a

peak indicating imbalance at 16.63Hz or 997.8 rpm, the

running speed of the shaft on the vibrating screen. Thisis a normal spectrum and time waveform example

collected from a screen in good operating conditions.

The imbalance seen is part of the design of the screen. It allows the screen to move material across the mesh.

The vibration data in Figure 7-8 show thespeed of the screen. Notice in the top right

hand corner of this spectrum we see the RPM

= 998. This is accomplished through the factthat for each complete rotation of the shaft the

screen makes one complete cycle up anddown. Therefore, by measuring the number of

cycles per minute, we know the number of

shaft rotations per minute.

Knowing the differences between a “good”

vibration signature and a "poor" vibrationsignature on a vibrating screen, allows

problems to be detected in time. Consider the

examples shown in Figures 9-11.

WAVEFORM DISPLAY

17-OCT-96 18:44

RMS = 4.40

PK(+) = 7.41

PK(-) = 11.39

CRESTF= 2.59

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

-12

-8

-4

0

4

8

Time in Seconds

A c c i n G - s

D&F - Eljay Screen

Eljay Scrn-BL Screen Stroke - Back Left

ROUTE SPECTRUM

17-OCT-96 18:44

OVRALL= 4.15 A-DG

RMS = 4.14

LOAD = 100.0

RPM = 799.

RPS = 13.32

0 20 40 60 80 100

0

1.0

2.0

3.0

4.0

Frequency in Hz

R M S A c c i n G - s

Freq:

Ordr:

Spec:

13.32

1.000

3.979

Figure 9. This screen data reflects that something is

allowing the screen to travel outside of its designed

parameters. The data in the top graphic show several

peaks after the first peak. These peaks indicate something that is loose in the system. A weak cross

member was suspected. And upon inspection some

broken bolts on the cross member connection platewere found and replaced. New data was taken after the

repair and the spectrum returned to normal.


7/15



WAVEFORM DISPLAY

25-OCT-96 12:30

RMS = 3.43

PK(+) = 6.66

PK(-) = 5.59

CRESTF= 1.95

1600 1800 2000 2200 2400 2600 2800

-8

-4

0

4

8

Time in mSecs

A c c i n G - s

ST - Shaker Screens

Tertiary -FL Screen Stroke - Front Left

ROUTE SPECTRUM

25-OCT-96 12:30

OVRALL= 22.80 V-DG

PK = 22.66

LOAD = 100.0RPM = 730.

RPS = 12.16

0 20 40 60 80 100

0

6

12

18

24

Frequency in Hz

P K

V e l i n I n / S e c

Freq:

Ordr:

Spec:

6.078

.500

.770

Figure 10. This particular screen had rubber donutsused as baffles for the movement of the screen rather

than steel springs. Further inspection revealed that the

rubber donuts were supposed to be 10” high but hadcollapsed to 7” high. The rubber donuts were replaced

and data was taken and recorded in the graphic

following this one

WAVEFORM DISPLAY

28-OCT-96 16:12

RMS = 3.59

PK(+) = 5.50

PK(-) = 5.20

CRESTF= 1.53

1400 1600 1800 2000 2200 2400 2600

-6

-4

-2

0

2

4

Time in mSecs

A c c i n G - s

ST - Shaker Screens

Tertiary -FL Screen Stroke - Front Left

ROUTE SPECTRUM

28-OCT-96 16:12

OVRALL= 3.59 A-DG

RMS = 3.57

LOAD = 100.0

RPM = 818.

RPS = 13.64

0 20 40 60 80 100

0

1.0

2.0

3.0

4.0

Frequency in Hz


Figure 11. The data following the replaced baffles is

shown to the left. Notice there is no wasted energy in

the spectrum, exhibited as extra peaks other than the first peak, like in the prior graphic above this set of

graphics.

Orbit Analysis

It was mentioned earlier that the data neededto be collected in the vertical and horizontal

planes at the same time. And to accomplish

this, a dual channel analyzer is needed. The

data needs to be in phase to provide us withthe capability to make a so-called orbit plot.

An orbit plot is a plot of the relative motion

between two transducers. In the case of avibrating screen it is referred to as the trace of

the screen’s stroke.

Why is that necessary when we have the

screen waveforms and spectra already?

Because the pure waveforms and spectra do

not always alert us to everything we want toknow about the motion of the screen.

For example, the 4 plots in Figures 12-13

reflect what would be considered a normalscreen, with nothing in the spectra or

waveforms to alert a problem.

WAVEFORM DISPLAY

06-FEB-97 14:40

RMS = 2.59

PK(+) = 4.06

PK(-) = 3.80

CRESTF= 1.57

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

-6

-4

-2

0

2

4

Time in Seconds

A c c i n G - s

Ter - Hewitt Robbins - Incline

8X20 W -FLV Screen Stroke - Front Left Vert

ROUTE SPECTRUM

06-FEB-97 14:40

OVRALL= 2.59 A-DG

RMS = 2.57

LOAD = 100.0

RPM = 782.

RPS = 13.04

0 20 40 60 80 100

0

0.5

1.0

1.5

2.0

2.5

3.0

Frequency in Hz

R M S A

c c i n G - s

Figure 12. Front left verticals.


8/15



WAVEFORM DISPLAY

06-FEB-97 14:40

RMS = 2.41

PK(+) = 3.65

PK(-) = 3.80

CRESTF= 1.58

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

-6

-4

-2

0

2

4

Time in Seconds

A c c i n G - s


8X20 W -FLH Screen Stroke - Front Left Horiz

ROUTE SPECTRUM

06-FEB-97 14:40

OVRALL= 2.40 A-DG

RMS = 2.39

LOAD = 100.0RPM = 782.

RPS = 13.04

0 20 40 60 80 100

0

0.6

1.2

1.8

2.4

3.0

Frequency in Hz

R

M S A c c i n G - s

Figure 13. Front left horizontals.

However, if we plot the two waveforms

simultaneously, a different graph is obtained,(Figure 14). Tracking the orbit plot can

provide a wealth of data not seen in the

spectra and waveforms. It becomes easier tospot a screen with problems when we compare

its orbit plot to that of a good one, for example

in Figures 15-16.


8X20 W - PTS=FLV FLH

ORBIT DISPLAY

06-FEB-97 14:40

RMSX= 2.59

RMSY= 2.41

LOAD = 100.0

RPM = 782.

RPS = 13.04

-6 -4 -2 0 2 4 6

-6

-4

-2

0

2

4

6

FLV in G-s

F L H

i n G - s

Figure 14. From the plot to the left, the motion,

indicated by the circle-like object, has two flat spots,

located at approximately the 4 and 10 o’clock

positions. The flat spots indicate that the screen is nottraveling in a smooth circular motion as designed but

instead in a chopping motion. Investigating the

components of the screen reveled broken internal cross

members


Road Scrn - PTS=FLV FLH

ORBIT DISPLAY

06-FEB-97 10:20

RMSX= 4.89

RMSY= 4.73LOAD = 100.0

RPM = 1800.

RPS = 30.00

-8 -6 -4 -2 0 2 4 6 8

-8

-6

-4

-2

0

2

4

6

8

FLV in G-s

F L H

i n G - s

Figure 15. This would be the perfect orbit plot for an

inclined screen. The smooth circle indicates that the screen is traveling smoothly without bottoming out on

the frame or that components on the machine are notexcessively loose or broken.

IPS - Shaker Screens

1 - PTS=FLV FLH

ORBIT DISPLAY

21-JAN-97 10:18

RMSX= 2.63

RMSY= 2.46

LOAD = 100.0

RPM = 811.

RPS = 13.52

-6 -4 -2 0 2 4 6

-6

-4

-2

0

2

4

6

FLV in G-s

F L

H

i n G - s

Figure 16. Horizontal screens, screens that have a flat

mesh angle, should have an orbit plot like this. Notice

the motion is all in a line. This indicates smooth motion

and throw of the material from one end of the screenmesh to the other.

Knowing those facts makes it very easy to identify a bad

actor when it looks like the examples in Figures 17-

18.


9/15



CPS - Shaker Screens

3 - PTS=FRV FRH

ORBIT DISPLAY

22-JAN-97 17:26

RMSX= 3.04

RMSY= 2.20LOAD = 100.0

RPM = 766.

RPS = 12.77

-8 -6 -4 -2 0 2 4 6 8

-8

-6

-4

-2

0

2

4

6

8

FRV in G-s

F R H

i n G - s

Figure 17. This screen had several broken springs. The

lack of spring resilience is causing the screen tobottom-out onto the frame or possibly the ground. In

the bottom left area of the trace, the flat spot indicates

the bottoming out.

CPS - Shaker Screens

3 - PTS=FRV FRH

ORBIT DISPLAY

13-FEB-97 15:55

RMSX= 2.32

RMSY= 2.15

LOAD = 100.0RPM = 780.

RPS = 13.00

-6 -4 -2 0 2 4 6

-6

-4

-2

0

2

4

6

FRV in G-s

F R H

i n G - s

Figure 18. The springs were replaced and the follow-updata looked like this. Further inspection found that the

top screen deck had excessive wear on the right hand

side. This condition allowed a large percentage of the

material to pass through on the right hand side of the

screen and thus overload it on that side. It wasoverloaded so much that is caused the screen to throw

material from right-to- left rather than the designed

direction of left-to-right.

Relating Traditional Inspectionswith Vibration Analysis

Relating the traditional inspections with the

vibration data provides a tool fortroubleshooting and “tuning” screen

performance. The collection of the vibrationdata in the vertical and horizontal planes at the

same time provides us with key data.

Screen Speed: The frequency of the up and

down motion of the screen is the speed of thescreen.

Orbit Plot: By graphing the screens vertical

and horizontal vibration at the same time we

get and actual trace of the motion of thescreen.

Screen Angle: By treating the vertical andhorizontal vibration at the speed of the screen

as vectors in the x and y planes, we can use

the following equation to calculate the angleof throw of the screen.

Arctangent (y/x) = Angle of Throw

Screen Force At Angle Of Incidence: Again by using the vectors we can solve for the

resultant vector. Which would be the actual g

of acceleration by which the material on thescreen is handled, Figure 19.

Figure 19: "a" is equal to the hypotenuse of the

triangle formed by x and y. Therefore, by solving for a

by a = √ (x 2 + y

2) , we arrive with the resultant vector of

x and y.

Actual Length Of Stroke: By taking theacceleration of the resultant vector a in g’s

(RMS) and converting it to displacement in


10/15



mils (Peak - Peak)) at the speed of the screen,

we can calculate the actual stroke length by:

Stroke Length = (2 × (G’s RMS × 386.4 ×

1.414)) ÷ (2π (RPM/60))2

with Stroke Length in mils Peak - Peak.

Example Screen Information Derivedfrom Vibration Data

Consider the data viewed in Figures 20-22.With this data we can derive:

• Speed: 998 rpm

•Horizontal Force: X = 4.694 g's

• Vertical Force: Y = 4.859 g's

• Angle Of Stroke: 45.98°

• Force At Angle Of Stroke: 6.756 g’s

• Stroke Length: 0.676 mils (peak –peak)

WAVEFORM DISPLAY

06-FEB-97 10:20

RMS = 4.90

PK(+) = 7.08

PK(-) = 7.02

CRESTF= 1.45

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

-8

-4

0

4

8

Time in Seconds

A c c i n G - s



ROUTE SPECTRUM

06-FEB-97 10:20

OVRALL= 4.89 A-DG

RMS = 4.86

LOAD = 100.0

RPM = 998.

RPS = 16.63

0 20 40 60 80 100

0

1

2

3

4

5

Frequency in Hz


Freq:

Ordr:

Spec:

16.63

1.000

4.859

Figure 20. Front left corner - vertical.

WAVEFORM DISPLAY

06-FEB-97 10:20

RMS = 4.74

PK(+) = 6.77

PK(-) = 6.67

CRESTF= 1.43

0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4

-8

-4

0

4

8

Time in Seconds

A c c i n G - s


Road Scrn -FLH Screen Stroke - Front Left Horiz

ROUTE SPECTRUM

06-FEB-97 10:20

OVRALL= 4.72 A-DG

RMS = 4.70

LOAD = 100.0

RPM = 998.

RPS = 16.63

0 20 40 60 80 100

0

1

2

3

4

5

Frequency in Hz

R M

S A c c i n G - s

Freq:

Ordr:

Spec:

16.63

1.000

4.694

Figure 21. Front left corner - horizontal.


Road Scrn - PTS=FLV FLH

ORBIT DISPLAY

06-FEB-97 10:20

RMSX= 4.89

RMSY= 4.73

LOAD = 100.0

RPM = 998.

RPS = 16.63

-8 -6 -4 -2 0 2 4 6 8

-8

-6

-4

-2

0

2

4

6

8

FLV in G-s

F L H

i n G - s

Figure 22. The orbit plot of the screen from Figures 20

and 21 shows that the orbit is the normal ellipse

without any sudden flat spots in the orbit that are

caused by bottoming out or broken/loose components.


11/15



Bad Orbit Causes

Various reasons for detected problems are:

• Pedestals not equidistant from screen body

• Trunion not level

• Springs not plumb

• Screen not level

• Weak Column

• Broken Welds

• Weak Beams (Torsional Weakness)

• Structural Resonance

• Belts Too Tight

• Motor Broke Over Center

• Broken Cross Member

• Weak or Broken Springs

• Uneven Feed

Example weak cross member

MSP - Shaker Screens

43 - PTS=FLV FLH

ORBIT DISPLAY

21-JAN-97 16:27

RMSX= 2.61

RMSY= 2.65

LOAD = 100.0

RPM = 880.

RPS = 14.66

-6 -4 -2 0 2 4 6

-6

-4

-2

0

2

4

6

FLV in G-s

F L H

i n G - s


43 - PTS=FRV FRH

ORBIT DISPLAY

21-JAN-97 16:28

RMSX= 1.91

RMSY= 2.68

LOAD = 100.0

RPM = 882.

RPS = 14.69

-6 -4 -2 0 2 4 6

-6

-4

-2

0

2

4

6

FRV in G-s

F R H

i n G - s

Figure 23. Orbit plots of the vibrating screen at the left

and right discharge chutes. These orbits are not smooth

circles with a singular path but instead multiple paths. In this example, the bolts that attach the cross member

to the screen frame had rusted and sheared. Without the

cross member attached to the frame, the screen lost its’rigidity. This loss in rigidity caused the screen to

vibrate in an uncontrolled manner.


12/15




43 - PTS=FLV FLH

ORBIT DISPLAY

18-FEB-97 14:49

RMSX= 2.57

RMSY= 2.57LOAD = 100.0

RPM = 877.

RPS = 14.61

-6 -4 -2 0 2 4 6

-6

-4

-2

0

2

4

6

FLV in G-s

F L H

i n G - s


43 - PTS=FRV FRH

ORBIT DISPLAY

18-FEB-97 14:50

RMSX= 2.54

RMSY= 2.65

LOAD = 100.0

RPM = 879.

RPS = 14.65

-6 -4 -2 0 2 4 6

-6

-4

-2

0

2

4

6

FRV in G-s

F R H

i n G - s


and right discharge chutes. These were taken after the

cross-member was replaced and re-bolted.

Example mesh degradation


8X20 E - PTS=BLV BLH

Orbit Display

04-APR-97 14:23

RMSX= 1.88

RMSY= 2.16

LOAD = 100.0

RPM = 656.

RPS = 10.93

-6 -4 -2 0 2 4 6

-6

-4

-2

0

2

4

6

BLV in G-s

B L H

i n G - s


8X20 E - PTS=FLV FLH

Orbit Display

04-APR-97 14:24

RMSX= 2.09

RMSY= 2.42

LOAD = 100.0

RPM = 656.

RPS = 10.93

-6 -4 -2 0 2 4 6

-6

-4

-2

0

2

4

6

FLV in G-s

F L H

i n G - s


and right discharge chutes. These orbits are not smooth

circles with a singular path but instead multiple paths.

The problem in this scenario was that the screen mesh

had degraded in several areas and material was fallingthrough in several places, which caused the material to

build up and bottom-out the screen mesh.


13/15




8X20 E - PTS=BLV BLH

Orbit Display

06-FEB-97 14:33

RMSX= 1.90

RMSY= 1.93

LOAD = 100.0

RPM = 1796.

RPS = 29.93

-4 -3 -2 -1 0 1 2 3 4

-4

-3

-2

-1

0

1

2

3

4

BLV in G-s

B L H

i n G - s


8X20 E - PTS=FLV FLH

Orbit Display

06-FEB-97 14:34

RMSX= 2.22

RMSY= 1.89

LOAD = 100.0

RPM = 653.

RPS = 10.88

-4 -3 -2 -1 0 1 2 3 4

-4

-3

-2

-1

0

1

2

3

4

FLV in G-s

F L H

i n G - s


and right discharge chutes. These were taken after themesh was replaced and the material was cleared from

underneath the screen.


14/15



Example structural problem

Vibration readings were taken on this corner in the same

manner and the amplitudes are noted.

The amplitudes on this corner are lower than the dischargeend, but still are above the recommended levels.

Vibration readings were taken on this corner in the samemanner and the amplitudes are noted.

The vertical amplitude on this corner is considerably lower

than the other corners and within the tolerable limit. This

indicates that the structural movement at this corner in the

vertical plane is not a problem. However, the horizontalamplitude remains high. The maximum axial movement

was noted on this corner.

Discharge Left No structural readings were collected on this corner. It was

surmised that the reading on this corner would be similar to

the other corners. And that the other readings weresufficient to display the structural issues.

Discharge Right

Feed Right

Feed Left

Horizontal

.859 in./sec

Axial

.991

Vertical

.518

Vibration readings were taken on the pedestals supporting

the springs on several corners. The arrows above representthe vibration amplitudes in all three planes. The vertical

reading was collected with the transducer mounted in

position A. The horizontal reading was collected with thetransducer in position B. And the axial reading was alsocollected in position B, but with the transducer facing the

body of the screen. The vertical and horizontal readings are

too high and indicate that the structure on which the screenis resting is unstable or loose. Corrective action should be

taken to stiffen the structure.

Vertical

.389 in/sec Horizontal

.591 in/sec

Horizontal

.661 in/sec

Axial

1.243 in/sec

Vertical

.095 in/sec

A

B


15/15



Conclusion

Vibrating screens are used in many types ofapplications and should be maintained

regularly to keep them running trouble-free

during production schedules. It is important to

address many of the potential problems withvibrating screens though continued monitoring

and analysis of the components that comprise

the system. Through an insight of the overallsystem and common problems and possible

solutions, the reader is helped to better

understand the process and solutions to manyof those problems.

References

For more information on vibration analysis

techniques and vibrating screens, please

explore the additional resources on

@ptitudeXchange such as:

SKF Handbook Vibrating Screens, publication

number SKF_4202_E

Bearing Failure Case Study, MB02009

Early Warning Fault Detection in Rolling

Element Bearings Using Microlog Enveloping , CM3021

Vibration Principles, JM02007

An Introductory Guide to Vibration, JM02001

SKF Copperheadhttp://www.skf.com/copperhead

Documents

Vibration Applications of Vibrating Screens