Letang, Ontisitse

CONDITION MONITORING REPORT

I. TABLE OF CONTENTS

1. INTRODUCTION ....................................................................................................................................... 3

2. PURPOSE .................................................................................................................................................. 3

3. ACCURATELY MONITOR THE HEALTH OF YOUR PLANT MACHINERY ................................. 4

4. COLLECTING DATA ............................................................................................................................... 6

5. DATA TRANSFER AND GIVING RECOMMENDATIONS ........................................................... 8

6. GEAR MESH FREQUENCIES .................................................................................................... 11

7. ROLLING ELEMENT BEARING DEFECTS ...................................................................................... 13

8. LOOSENESS & MISALGNMENT ........................................................................................................ 15

9. ALIGNMENT ............................................................................................................................................ 18

II. TABLE OF FIGURES

Figure 1: Data Collection .............................................................................................................................................. 3

Figure 2: Fixed Frequency Portable Shaker ................................................................................................................. 4

Figure 3: Machine health Analyzer .............................................................................................................................. 5

Figure 4: Calibration Results ........................................................................................................................................ 5

Figure 5: Spectrum ....................................................................................................................................................... 6

Figure 6: Time Wave Form ........................................................................................................................................... 6

Figure 7: Measurement Points on a Gearbox .............................................................................................................. 7

Figure 8: Measurement Points on a Motor ................................................................................................................. 7

Figure 9: Different Accelerometers.............................................................................................................................. 8

Figure 10: Raised noise Floor ....................................................................................................................................... 9

Figure 11: Random Impacting ...................................................................................................................................... 9

Figure 12: Overall Value after Replacement .............................................................................................................. 10

Figure 13: K103022.BGH Details ................................................................................................................................ 11

Figure 14: Gear Mesh Spectrum ................................................................................................................................ 12

Figure 15: Pedestal Bearings Spectrum ..................................................................................................................... 15

Figure 16: 1470 Motor Spectrum ............................................................................................................................... 16

Figure 17: 953 – 1470 Fluid Drive .............................................................................................................................. 16

Figure 18: 1470 Report .............................................................................................................................................. 17

Figure 19: Damaged Coupling .................................................................................................................................... 17

Figure 20: Damaged Coupling Hubs ........................................................................................................................... 18

1. INTRODUCTION

Condition monitoring is the process of monitoring a parameter of condition in machinery, in order to identify a significant change which is indicative of a developing fault. Maintenance departments today are asked to run with fewer staff and smaller budgets than ever before.

In this do-more with-less environment, maintenance personnel cannot afford to continuously chase the next breakdown. They need to quickly and accurately identify developing faults and find the root cause of the machinery problem so that it can be fixed. An effective technology solution must be simple to operate –reducing training requirements – while providing fast, actionable information to help you prioritize maintenance activities. A range of parameters can be used for condition monitoring including Vibration, Oil analysis and Infrared thermography to name a few. The figure below demonstrates data being collected for Vibration Analysis.

Figure 1: Data Collection

2. PURPOSE

The objective of this report is to give considerate record of a sequence of events focusing on Vibration analysis, discussing the outcomes of a decision or course of action, Vibration Analysis is used to detect early signs to machine failure, allowing machinery to be repaired or replaced before any failure occurs. All rotating equipment vibrates to some degree, but as older bearings and components reach the end of their product life they begin to vibrate more dramatically, and in distinct ways. On-going monitoring of equipment allows these signs of wear and damage to be identified well before the damage becomes an expensive problem.

3. ACCURATELY MONITOR THE HEALTH OF YOUR PLANT MACHINERY

The fixed frequency portable shaker from Hardy Instruments is used in this monitoring process. Our vibration analysers’ record machine vibrations using sensors such as accelerometers and they are the 'ears' of our instruments, and are connected to rotating machinery such as electric motors and gearboxes. The vibrations and movements of the equipment is then recorded. It is now very important to make sure that our accelerometers are calibrated to the required standard before any readings are to be taken on machinery. Fig 1 shows a picture of a portable shaker used for calibration.

Figure 2: Fixed Frequency Portable Shaker

This shaker vibrates at a single specific fixed frequency of 80 Hz, the accelerometer must be attached to the shaker and the amplitude readout adjusted to 1G on the shaker, then connect the sensor to the machine health analyser and measure the amplitude output of the sensor. Fig 3 below shows a machine health analyser

Fixed Frequency

Portable Shaker

Amplitude

Readout

Accelerometer

Amplitude Adjuster

Figure 3: Machine health Analyzer

The amplitude readout from the sensor must be approximately or equal to the amplitude readout set on the shaker. On the analyser screen you must observe the 80Hz single frequency and its amplitude readout as set on the shaker.

Figure 4: Calibration Results

After making sure that the machine is calibrated correctly (as seen on Figure 4) then we can now go and take readings on plant machinery.

Approximate or

equal amplitude as

set on the shaker

(0.934)

80Hz single

frequency

4. COLLECTING DATA

The general procedure of data collection is to take measurements and compare them to historical trends baseline or representative data for the same or similar machines. Management of the data collection procedure is often done by arranging the measurements to be taken automatically online or by hand as a route or tour of a plant, Machinery Health Analyser was developed with these requirements in mind. How do we ensure that recordings are always taken of the locations intended, that the recordings that are taken are not confused with one another and that no recordings are left out? A recording list is used. A recording list shows all the recordings that need to be taken on a given round of data collection. These recordings are later transferred to a computer and analysed using our AMS suite machinery health manager software, visually displaying vibration waveforms. Below are examples of a time waveform and a spectrum that we use when doing analysis

Figure 5: Spectrum

Figure 6: Time Wave Form

These recordings can be compared over time, and the gradual development of new vibrations that might indicate wear detected at their earliest stages. To avoid confusion, you must give machines and measurement points unique and meaningful names in the recording list.

The motor and gearbox shafts rotate around the axis of the shaft, which is supported by bearings at each end.The accelerometer should be positioned to maintain a direct path for the vibration from the bearing.

Figure 7: Measurement Points on a Gearbox

Figure 8: Measurement Points on a Motor

We must ensure, therefore, when selecting an accelerometer, that the frequency range of the accelerometer can cover the range of interest. That is why I usually use a bigger magnet on the accelerometer because it has a firmer grip.

Bearings at each end

of the shaft

Accelerometer on the

direct path for

vibration from the

bearing

Figure 9: Different Accelerometers

5. DATA TRANSFER AND GIVING RECOMMENDATIONS

Understanding the basics and fundamentals of vibration analysis are very important in forming a solid background to analyse problems on rotating machinery. Switching between time and frequency is a common tool used for analysis. Because the frequency spectrum is derived from the data in the time domain, the relationship between time and frequency is very important. Units of acceleration, velocity, and displacement are typical. Additional terms such as peak-peak, peak, and rms. are often used. Switching units correctly and keeping terms straight is a must. A fast Fourier transform (FFT) is the one that simplifies this relationship which in simple terms converts, or "transforms" a signal from the time domain into the frequency domain. It is a process or digital calculation routine that efficiently calculates the discrete Fourier transform from the sampled time waveform.

Illustrated below, is the report of an electric motor at the drum plant that showed premature signs of failure. After analysing the frequency spectrum, it was recommended that it be replaced before breaking down completely.

Smaller

accelerometer

magnet

Bigger

accelerometer

magnet

The raised noise floor referred to in the above analysis report is the lifting of harmonics from the base of a spectrum indicating the lack of lubrication on the electric motor. See the illustration on the spectrum below.

Figure 10: Raised noise Floor

The analysis report also refers to points of random impact and a crest factor that is illustrated on the figure below. A Crest Factor is the amount of impacting that happens in a time wave, as well as the ratio of the peak to Root Mean Square (RMS).

Figure 11: Random Impacting

Random Impacting

Raised Noise Floor

Crest Factor

In other words, the crest factor indicates how extreme the peaks are in a waveform, while the impact imparts a force pulse to the structure which excites it over a broad frequency range. The impact signal has high amplitude, short duration events that appear occasionally as the result of looseness. The "RMS" value is calculated by simply multiplying the peak amplitude by 0.707: RMS = Peak x 0.707

Therefore the 4.9 crest factor was also calculated as follows our peak amplitude is 0.776

RMS = Peak x 0.707

= 0.776 * 0.707

= 0.5486

Therefore our Crest Factor will be:

CF = Highest peak / RMS

= 2.716 / 0.5486

= 4.95 as shown in the time waveform

An overview of how different electric motors has been performing over the years can also be viewed on the AMS software. The figure below shows the difference from before the motor was replaced to after it was replaced, as well as the significant change afterwards.

Figure 12: Overall Value after Replacement

Before Replacement

14 / 09 / 2014

After Replacement

06 / 11 / 2014

6. GEAR MESH FREQUENCIES

As components such as ball or roller bearings, drive belts or gears become worn, they are expected to cause vibration. When a roller bearing race becomes pitted, for instance, the bearing rollers will cause a vibration each time they travel over the damaged area. A gear tooth that is heavily chipped or worn, or a drive belt that is breaking down, can also produce vibration. Gear mesh frequencies are frequencies that are seen on a spectrum as a result of meshing gears they are normally on every gearbox when doing analysis, they can also be identified with sidebands around them. The more the sidebands increase the more it shows how critical a certain gear is. Below in figure 16 is actual data identify meshing gears on a spectrum from F881-G1800 at the UCC Plant.

I also requested details for the K103022.BGH unit from the manufacturer that will aid in simplifying the calculation

of gear mesh frequencies. See insert below:

Primary pinion = 34 teeth, Primary Wheel = 62 teeth.

Intermediate bevel pinion = 19 teeth, Intermediate bevel Wheel = 43 teeth.

Final pinion = 12 teeth, Final Wheel = 65 teeth.

Hope you have a wonderful weekend

Regards

Lo-Ami Pieters

Estimator South Africa

Figure 13: K103022.BGH Details

During analysis, the gear mesh frequency peaks may even be visible on the motor drive end spectrum. However, these peaks are not to be confused with bearing fault frequencies of the motor, because they will be also be visible on the gearbox through further analysis on the Time Wave Form (as seen below).

Figure 14: Gear Mesh Time wave

Hence, the following figure illustrates Normal Harmonics of gear mesh frequency and sidebands of running speed with low amplitude values.

Figure 15: Gear Mesh Spectrum

After obtaining the gearbox information from the manufacturer, I could calculate the gear mesh frequency since the motor speed is 1465 rpm. The formula used to calculate gear mesh frequencies are found below:

CPM = RPM =Hz x 60

Therefore the input speed in hertz will be

Hz = 1465 / 60 = 24.4… which makes it a 25 Hz motor

GMF = No. of teeth (input pinion) x Input speed

= 34 x 24.4

= 829.6 Hz... Including for all the other gears until the output shaft

GMF = No. of teeth x Input speed

Gear Mesh Peaks

Frequency at 831.25

As per calculation

7. ROLLING ELEMENT BEARING DEFECTS

Defects in general rolling element bearings can be generated by fatigue, wear, poor installation, improper lubrication in the bearing components. Being the typical bearing found in electric motors and conveyor belt pulleys, the rolling element (anti-friction) bearing is made up of the following components.

1. Outer race 2. Inner race 3. Cage 4. Rolling element

When a bearing spins these are the periodic frequencies that the rolling elements excite in its roundness below.

1. Fundamental Train Frequency (frequency of the cage) 2. Ball Spin Frequency (BSF) 3. Ball Pass Frequency of the Outer Race (BPFO) 4. Ball Pass Frequency of the Inner Race (BPFI)

We can either calculate the defect frequencies ourselves but the vibration analysis software providers often incorporate them in a database. Listed below are formulae for those calculations.

I came across a defective antifriction bearing at the UCC plant where data analysis showed a slight decrease in Raised Noise Floor across the spectrum on both Tail pulley bearings. However, the time wave signal still showed roller elements impacting with crest factors of 10.2 and 9 respectively even after they were lubricated according to our recommendation the previous month. The spectrum and time wave signal as reported below shows impacting of the rolling elements and indicates a Ball Pass Frequency of Inner ring (BPFI) and the Ball Pass Frequency of Outer ring (BPFO) defect.

LEGEND

RPM - Revolutions Per Minute S - Revolutions per second or relative speed

difference between inner and outer race (1)

FTF - Fundamental Train Frequency BPFI - Ball Pass Frequency of Inner ring

BPFO - Ball Pass Frequency of Outer ring BSF - Ball Spin Frequency

Bd - Ball or roller diameter Nb - Number of balls or rollers Pd - Pitch diameter Ø - Contact angle

Report Continue:

Both these 2 bearings reflected in this report were replaced on the scheduled shutdown.

Right-Hand

Bearing

Left-Hand

Bearing

8. LOOSENESS & MISALGNMENT

Looseness can allow any vibration present to cause damage, such as further bearing wear, wear and fatigue in equipment mounts and other components. Misalignment may also be caused during assembly or develop over time, due to thermal expansion, components shifting or improper reassembly after maintenance. The resulting vibration may be radial, axial or both.

The spectrum illustrated below indicates both looseness and misalignment on a drive assembly F953-G1470 at the In-Pit Crusher. Vibration data analysis after follow up data collection still showed multiple running speed harmonics and impacting that came from the fluid drive, both Plummer block bearings running at elevated temperatures and both increasing significantly in overall amplitudes. The fluid drive had wobble noise during operation. This indicates fluid drive internal bearing looseness.

Figure 16: Pedestal Bearings Spectrum

Peaks representing Rotating

Looseness

Figure 17: 1470 Motor Spectrum

Point that showed misalignment Point that showed looseness

Figure 18: 953 – 1470 Fluid Drive

Coupling under guard Fluid Drive Coupling

Peaks Representing

Misalignment

The Motor Drive End (MDE) and Gearbox Input showed signs of misalignment but the closer I got at the pedestal bearings supporting the fluid drive it was then that I picked looseness up.

Figure 19: 1470 Report

After it was recommended that the fluid drive be changed this is how the coupling and the hub looked like, both had to be replaced and laser alignment done

Figure 20: Damaged Coupling

Damage visible on a

coupling

Damaged coupling hub

Figure 21: Damaged Coupling Hubs

9. ALIGNMENT

There are several methods used to align couplings including 'eyeing' it, dial calibration and laser alignment. When

two machines are connected together through a shaft coupling, every effort must be made to eliminate

misalignment of those shafts which can lead to damage or wasteful loss of energy. Using laser shaft alignment

techniques can reduce the amount of time in the alignment process. Lasers are highly accurate and easy to use in

aligning objects

Performing coupling alignment on a scheduled basis will make machinery last longer and perform more efficiently

as this was done. And a picture below shows the results/report of the alignment done on 953-1470. In this case

alignment had to be done twice as this conveyor drive has two points of where alignment must be done. Alignment

has to be done from the gear box towards the fluid drive with the gearbox as a fixed point (reference point) then

move over to the fluid drive and the motor as the second alignment with the fluid drive as a fixed point (reference

point).

Below is the result of the first alignment done (Gearbox to fluid drive)

Fluid drive to motor alignment results are seen below.

The spectra and alignment results of machinery I have recommended that they be changed, also where I helped with alignment during shutdowns are seen below.

SHUTDOWN ALIGNMENTS

The process explained on this report decrease downtime and increase savings. This process is generically known as 'condition monitoring'. When used correctly, it can result in huge cost savings when compared to traditional maintenance methods. Traditional maintenance methods are predictive, components are replaced on a fixed schedule whether worn or not, and reactive maintenance, in which components are repaired only after they have broken down.