Laboratory experimental research on multi-sensor monitoring of belt conveyor idlers

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Specialization: Transport Engineering and Logistics Report number: 2015.TEL.7969

Title: Laboratory experimental research on multi-sensor monitoring of belt conveyor idlers.

Author: E.W.L.A. van Bodegom

Assignment: Research

Confidential: Yes, till September 2018 Initiator (university): Dr. Ir. Y. Pang

Initiator (company): TU Delft

Supervisor: Dr. Ir. Y. Pang, MSc. X. Liu

Date: 28 September 2015

This report consists of 117 pages. It may only be reproduced literally and as a whole. For commercial purposes only with written authorization of Delft University of Technology. Requests for consult are only taken into consideration under the condition that the applicant denies all legal rights on liabilities concerning the contents of the advice.

Delft University of Technology

FACULTY MECHA NICAL, MARITIME AND MATERIALS ENGINEERING

Department Marine and Transport Technology Mekelweg 2 2628 CD Delft the Netherlands Phone +31 (0)15-2782889 Fax +31 (0)15-2781397 www.mtt.tudelft.nl

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Student: E.W.L.A. van Bodegom Assignment type: Research Supervisor (TUD): Dr. Ir. Y. Pang,

MSc. X. Liu

Report number: 2015.TEL.7969 Supervisor (Company): -

Specialization: TEL Confidential: Yes, till September 2018

Creditpoints (EC): 15 Subject:

Belt conveyor systems are widely used for a variety of transportation purposes. Transporting bulk solid materials is one of them. Belt conveyor systems can cover distances of kilometers. A belt conveyor system consists at least of a head and tail

pulley and idler rolls. Maintenance of these long belt conveyor systems can be challenging while many idler rolls are installed and currently each idler roll is checked by humans. Detecting a defect idler roll and replacing this roll before it is stuck is challenging and often the defect rolls are detected when these rolls cannot rotate anymore. The consequences of stuck idler rolls in a running belt conveyor could be a cut belt or the belt catches fire due to the high friction. This must be avoided under all circumstances.

The introduction of a Preventive Maintenance Strategy (PMS) is a promising solution for the current maintenance strategy. The PMS focuses on the detection

and replacement of defect idler rolls at an earlier failure stage. An automated system can be used to detect and replace impeding idler rolls without human involvement. This Automated Maintenance consists of Automated Inspection, Automated Replacement and a Decision-making System.

This research focuses on the automated inspection of the idler rolls. The goal of this research is to test the feasibility of multi sensing technologies for the condition monitoring of idler rolls.

The main research question is formulated as follows:

 Which type of sensor(s) is most feasible for the condition monitoring of idler rolls? In order to answer this main research question best, four sub research questions are formulated:

 Which Key Performance Indicators are important for the evaluation of feasibility of sensing technologies?

 Which sensing technologies are applicable?

 How to design a test rig in order to carry out evaluation of feasibility of sensors, based on KPI’s?  How are the different experiments performed?

Delft University of Technology

FACULTY OF MECHANICAL, MARITIME AND MATERIALS ENGINEERING

Department of Marine and Transport Technology Mekelweg 2 2628 CD Delft the Netherlands Phone +31 (0)15-2782889 Fax +31 (0)15-2781397 www.mtt.tudelft.nl

Figure 1: Rubber belt conveyor which brings gravel to Shasta Dam – 1941 [10]

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Summary

Belt conveyor systems are widely used for a variety of transportation purposes. Transporting bulk solid materials is one of them. Belt conveyor systems can cover distances of kilometers. A belt conveyor system consists at least of a head and tail pulley and idler rolls. Maintenance of these long belt conveyor systems can be challenging while many idler rolls are installed and currently each idler roll is checked by humans. Detecting a defect idler roll and replacing this roll before it is stuck is challenging and often the defect rolls are detected when these rolls cannot rotate anymore. The consequences of stuck idler rolls in a running belt conveyor could be a cut belt or the belt catches fire due to the high friction. This must be avoided under all circumstances.

The introduction of a Preventive Maintenance Strategy (PMS) is a promising solution for the current maintenance strategy. The PMS focuses on the detection and replacement of defect idler rolls at an earlier failure stage. An automated system can be used to detect and replace impeding idler rolls without human involvement. This Automated Maintenance consists of Automated Inspection, Automated Replacement and a Decision-making System.

This research focuses on the automated inspection of the idler rolls. The goal of this research is to test the feasibility of multi sensing technologies for the condition monitoring of idler rolls. The main research question is formulated as follows: Which type of sensor(s) is most feasible for the condition monitoring of idler rolls? In order to answer this main research question best, four sub research questions are formulated: Which Key Performance Indicators are important for the evaluation of feasibility of sensing technologies? Which sensing technologies are applicable? How to design a test rig in order to carry out evaluation of feasibility of sensors, based on KPI’s? How are the different experiments performed?

To determine which sensors are feasible for condition monitoring of idler rolls, lab experiments are performed. In order to evaluate the different sensors after the lab experiments, eight Key Performance Indicators are determined, namely: reliability, signal effectiveness, interpretability, costs, feasibility, accuracy, precision, repeatability. These eight KPI’s are weighted while some KPI’s are more important than other KPI’s.

The KPI’s are determined to evaluate the different sensors. To select suitable sensors for condition monitoring of idler rolls, the parameters that can determine the condition of the idler rolls are determined. It turned out that three parameters are suitable namely: temperature, vibration and acoustic emission. These three parameters form the three types of sensors which will be used for condition monitoring of idler rolls. The specific sensors chosen for measuring temperature are: a thermocouple sensor, an infrared sensor and an infrared camera. The specific sensors chosen for measuring vibration are: an accelerometer and an acoustic distance sensor. The sensor chosen for measuring the acoustic emission is an omni-directional microphone.

The selected sensors are tested at a test rig, by performing the lab experiments on this test rig. The test rig is specially designed for measuring three different idler rolls at the same time and to meet the layout of the installed idler rolls in the field. When bulk solid materials are transported with a belt conveyor system, three idler rolls are placed next to each other and the two wing rolls are installed a t an angle such that the bulk solid material forms a pile in the middle of the belt. The two wing rolls at the test rig can be adjusted such that experiments can be performed with and without a trough angle of these wing rolls. To complete the test rig, the idler rolls used for the lab experiments are threated to simulate defect rolls. In total seven different types of bearing defects are induced to one of the two bearings installed on the idler roll. Four defect rolls are threated per type of defect. Next to these defect rolls, four damaged rolls are created by damaging that part of the idler roll where the bearing is installed.

With the sensors installed at the test rig, it is possible to perform the lab experiments. The collected data is processed using two types of software. Firstly the data is digitalized by sampling the analog signal with a certain sample frequency. Then the data is converted into the right quantity. These steps are all performed with software called Labview. The data is presented in figures using software called Matlab. Time domain plots are generated for the temperature sensors. For the accelerometer and the microphone both time domain and frequency domain plots are generated.

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The performed experiments can be divided into four categories: verification tests, defect roll experiments, damaged roll experiments and endurance tests. The verification tests are performed to check the accelerometers and the microphones on correctness of the measurements and on the correctness of the used software. The performance of the sensors on condition monitoring of idler rolls are tested by the defect roll experiments and the damaged roll experiments. The endurance tests give more insight in the development of the three parameters: temperature, vibration and acoustic emission over time. The focus of the endurance tests is mainly on the temperature development over time. After the experiments are performed for all four categories, the collected data is analyzed and the results are presented. The results of the experiments show that the temperature sensors can detect idler roll failure. The difference in measured temperatures between the healthy roll and the damaged rolls is much higher than the difference in measured temperatures between the defect rolls and the healthy roll. The thermocouple turned out to be not very precise as the temperature deviation was 2°C from the measured mean temperature for the damaged roll experiments. The infrared sensor is much more precise, though the accuracy of the infrared sensor becomes less when the measured temperature increases, due to a low emissivity of the surface of the measured shaft end causing an incorrect readout. The IR camera measured the temperatures correctly, though a slight deviation was experienced a couple of times caused by a misalignment of the measurement box or by the fact that only one sample is taken for the temperature measurements instead of 1000 samples as used for the temperature measurements of the thermocouple sensor and the infrared sensor.

From the results was found that condition monitoring of idler rolls by measuring vibration is not possible. The found vibration frequencies present a very low energy level. After analyzing the found frequencies the ten highest energy peaks are determined. By comparing these peaks with theoretically calculated defect frequencies of three types of bearing defects (namely an outer race, inner race and rolling element defect) no matches are found which indicate bearing failure. From endurance test six was found that the vibration pattern in time domain presented a significant difference in vibration amplitude after one-third of the endurance test. This indicated idler roll failure from the installed damaged rolls. Though these damaged rolls were already detected after the first hour of the endurance test from the temperature measurement. The acoustic distance sensor turned out to be not applicable for measuring vibration under these test conditions, while the results did not presented any difference between rotation and no rotation of the roll. At last the acoustic emissions indicating idler roll failure were not noticed during the different experiments, only at endurance test six. With the scheduled measurements it was not possible to collect the sound potentially caused by idler roll failure while the sample frequency of the measurement was too low. During that last endurance test it was not possible to perform a measurement manually at a higher sample frequency. Though the remarkable sound appeared at the same time when the vibration amplitude significantly increased. From the experiments can be concluded that it is not possible to allocate the acoustic emission to bearing failure.

After the experiments are performed and the results presented, the answer on the main research question can be answered. This is done via a multi criteria analysis in which all sensors are graded on all different weighted KPI’s. The final grade for each sensor presents in the end the most feasible sensing technology for the condition monitoring of idler rolls. From this multi criteria analysis followed that the IR camera is most feasible sensor for the condition monitoring of idler rolls, followed by the thermocouple sensor, the infrared sensor, the accelerometer, the microphone and at last the acoustic distance sensor.

To finalize this summary, three conclusions are formulated about the performed research. At first can be concluded that idler rolls which are at an early failure stage, called incipient failure, are hardly to detect, as found from the defect roll experiments. The damaged rolls which represent the final failure stage, a higher level of bearing failure in which the bearing itself not rotates as it should, can be detected clearly by measuring the temperature. Detection of rolls at this failure level is much safer than the current failure level at which the defect rolls are detected and replaced. From the results can be concluded that for condition monitoring of idler rolls temperature is the best parameter out of the three parameters. The other two parameters, vibration and acoustic emission, do not present clear results that indicate roll failure. This is the second conclusion that can be drawn. The third conclusion from the research is that the IR camera is the most feasible sensor for the condition monitoring of idler rolls, out of the three temperature sensors. The IR camera can measure and present the temperature of an obje ct of interest quickly. Another advantage of the IR camera is the image which displays the temperature distribution

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of the area covered by the camera as well. With this temperature distribution the cause of the measured temperature can be analyzed more easily and precise.

Next to the conclusions, three recommendations are formulated for further research. The first recommendation is to investigate how much operating time of the idler roll is left between the measured temperature at a certain moment and the moment that the idler roll is causing serious damage to the belt conveyor system as it had run stuck. The second recommendation would be to analyze the whole operating lifetime of an idler roll, from healthy roll till stuck/ catastrophic failure. This will give more insight in operating time between the different failure stages of the idler roll, as mentioned: incipient failure, final failure and in the end catastrophic failure. The third recommendation is to perform field tests with the three most feasible sensors, namely: the IR camera, the thermocouple sensor and the infrared sensor. This field test can verify the results from the lab experiments and can determine which sensor performs best at existing belt conveyor systems in the field.

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1

Introduction

Belt conveyor systems are widely used to transport bulk material. Examples in which belt conveyors are used can be found within bulk terminals or between a port and a mining area at the hinterland. Belt conveyors can cover distances over kilometers to reach a port from the hinterland.

A belt conveyor system consists of at least two pulleys, a belt connecting those pulleys, a drive unit and idler rolls. The idler rolls are installed between the two pulleys to support the belt and bulk material when the belt is loaded.

Failure of a component from the belt conveyor system will lead to a shutdown of the whole belt conveyor system. While there are many idler rolls installed at a belt conveyor system, there is a high probability that a failure is caused by an idler roll. Different types of idler roll failures can be distinguished, for example the shell of the idler roll can be damaged or the installed bearings can be damaged. These failures can be caused by wear of the shell due to the belt, overload of the idler rolls or erosion for example.

This report focusses on the condition of the bearings installed in an idler roll, as failure of one of these bearings leads to a higher energy consumption, or in worst case leads to shutdown of the whole belt conveyor system, which needs to be prevented. This chapter will give an introduction on idler rolls. It will explain the relevance of this research and the goal and outline of this report will be presented.

1.1. Idler rolls

Idler rolls are installed at a belt conveyor system to make transport of bulk material possible between the head and tail pulley. The idler rolls support the belt between the head and tail pulley. The idler rolls are installed with a specific distance between them, called idler spacing. Idler rolls are installed in an idler frame. Different configurations of the idler rolls are available for different purposes. This leads to a range of different idler frames as well. Figure 1.1 illustrates idler frames with a trough angle and without a trough angle. A trough angle is the angle in which the wing rolls are placed such that the belt is curved, presented in figure 1.1 at the left side.

Figure 1.1: illustration of an idler frame with a trough angle and without a trough angle

An idler roll consists of a shell in which a shaft is connected to the shell using two bearings. Figure 1.2 shows an idler roll. The shaft is used to install the idler roll in the idler frame. Failure of the idler roll can be caused by the shell, the shaft and the bearings. The shell can break due to wear of the surface which results locally in a very small shell thickness which will break under load. Wear on the surface is caused by particles which are attached to the belt and pushed between the belt and the idler roll. Failure of the shaft can be caused by a small production error of the shaft resulting in for example a shaft that bends under load. Bearing failure can be caused by small particles entering the bearing or wear of the bearing due to overloading, for example.

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Figure 1.2: idler roll used on a belt conveyor system

Figure 1.3 illustrates hypothetical condition changes of an idler roll versus its service time. Initially, the new idler roll performs well. After a certain service time, incipient failures occur in the roll especially in the bearings. The idler roll can still rotate until the final failure appears. The final failure means either the idler roll cannot rotate anymore, impermissible runout or unbalance. In reality, phenomena like dramatically increasing temperature, rotating resistance, vibration or noise can be observed from idler rolls run-to-failure. Idler rolls which have passed the final failure stage need to be replaced in time. Otherwise they will enter the catastrophic failure phase, in which destructive phenomenon occur, for instance causing fire or cutting the belt. Catastrophes caused by failed idler rolls can be very costly, according to Barry, 2014[1], and Persson, 2013[2].

Figure 1.3: Idler condition monitoring (CM ) versus time

1.2. Relevance of research

In the introduction of this chapter the relevance of the research is already introduced, namely that idler rolls are crucial components that can cause failure of the belt conveyor system. At a bulk terminal the shutdown of one belt conveyor in the stacking area for example, results in less total transport capacity when redundancy was implemented in the design of the stacking area. It could result in limited or no accessibility to certain areas within the stacking area otherwise. This should be avoided under all circumstances. Though, when a long distance belt conveyor transporting bulk material is installed between a port and a mining facility located some kilometers from the port, a shutdown of the belt conveyor will result in no transport of bulk material at all. Then it is essential to avoid a shutdown of the belt conveyor due to component failure.

Currently the maintenance strategy focuses on detection and replacement of idler rolls when they have reached the failure stage between final failure and catastrophic failure. Detection and replacement of the failed idler rolls is performed manually when this maintenance strategy is used. Maintenance personnel need to check each idler roll for visible defects. This maintenance strategy is very time consuming and there is still no good insight on the condition of the idler rolls, while only rolls which do not rotate can be detected easily.

The high risk of belt conveyor failure due to replacing the rolls when they reached the final failure stage, results in the introduction of a Preventive Maintenance Strategy (PMS). The PMS focuses on the

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detection and replacement of defect idler rolls at an earlier stage of failure, a stage between incipient failure and final failure.

As a promising solution for the PMS, an automated system can be used to detect and replace impeding idler rolls without human involvement. This Automated Maintenance (AM) consists of Automated Inspection (AI), Automated Replacement (AR) and a Decision-making System (DMS).

With current technology it is possible to implement automated replacement (AR). The automated inspection (AI), necessary for knowing which idler roll needs to be replaced, cannot be implemented due to a lack of knowledge on the failure mechanism of idler rolls.

From literature is found that no experimental research is performed focusing specifically on condition monitoring of bearings installed in idler rolls applied in a belt conveyor system. The found experimental research on bearing failure is not applicable while the conditions in terms of rotating speed and load on the bearing differ much. Thereby only the bearing itself is tested. No tests are performed while the bearing is installed in an idler roll which should result in different dynamics on the bearing compared to the mentioned bearing test.

1.3. Goal and outline of report

The goal of this research is to test the feasibility of multi sensing technologies for the condition monitoring of idler rolls.

This report presents the used approach to reach this goal. First the experiment method is introduced, followed by an overview of all different sensors that are used for the experiments. A detailed overview of the test rig which is used for the experiments is presented. The results from all experiments are presented and analyzed. Lastly the conclusions and recommendations based on this report are formulated.

The main research question is introduced next, followed by a couple of sub research questions. These sub research questions are introduced in order to formulate a well substantiated answer on the main research question. The chapter(s) in which the specific research question is answered is added to the specific research question.

The main research question is formulated as follows:

 Which type of sensor(s) is most feasible for the condition monitoring of idler rolls? Chapter 8.

For answering this main research question best, four sub research questions are formulated. These will be answered in the chapters mentioned for that specific research question.

 Which Key Performance Indicators are important for the evaluation of feasibility of sensing technologies?

Chapter 2.

 Which sensing technologies are applicable? Chapter 3.

 How to design a test rig in order to carry out evaluation of feasibility of sensors, based on KPI’s?

Chapter 2, 4.

 How are the different experiments performed? Chapter 5, 6, 7.

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2

Experiment method

The experimental research contains several series of experiments which will generate data used to answer the main research question. The experiment method used to perform these experiments is presented in this chapter followed by the key performance indicators on which the sensors can be evaluated.

2.1. Lab experiments

The experiment method chosen for this research is: lab experiment. The goal of the lab experiments is to meet the real conditions in which a belt conveyor system operates, best. This is done by mainly two parameters that can be adjusted, namely belt velocity and load on the rolls. Other parameters as ambient temperature, humidity and wind can be controlled during the lab experiments.

To meet the real working conditions best during the lab experiments, a test rig is designed on which the experiments are performed.

By performing simultaneous measurements for a healthy roll and the defect rolls installed at the test rig the feasibility of the different sensors to distinguish healthy and defect rolls from each other can be investigated. Evaluating the different sensors with the Key Performance Indicators which are introduced in paragraph 2.3, will lead to a substantiated answer to the main research question, formulated in chapter one.

2.2. Quasi-experimental design

The experiments done for the research are based on a ‘experimental design’ approach. The quasi-experimental design is in this case a hybrid version of a Between-Group and a repeated measures experimental design [3]. During one series of experiments, one of the three rolls will be ‘treated’ which means in this case a defect roll is installed. At least one of the two other rolls will be a healthy roll, called a roll with ‘no treatment’. During one experiment a given amount of measurements will be performed. Figure 2.provides a schematic overview of the described approach.

Figure 2.1: schematic overview of experimental approach

The main advantage of this type of experimental design is the sensitivity. By repeating the experiments once and performing several measurements during one test, the difference between a defect and a healthy roll can be examined well. While both types, treated rolls and non-treated rolls, are measured under the same experimental conditions, it is possible to attribute the differences to the treatment of the roll.

A disadvantage might be that fatigue can play a role while only the defect roll is replaced during one series of experiments. Therefore during one series of experiments all different defect rolls are tested as

Treatment Measurement Measurement Measurement

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well as one healthy roll, while the other two rolls on the belt are not replaced for all different experiments within one series of experiments.

2.3. Key Performance Indicators

Key performance indicators (KPI’s) are very useful for evaluating which type of sensor is feasible for detecting idler roll failures. By determining KPI’s it is possible to compare different sensors, and select an individual or combination of different sensors that perform best.

The determined KPI’s are:  Reliability  Signal effectiveness  Interpretability  Costs  Feasibility  Accuracy  Precision  Repeatability

All determined KPI’s are explained next by formulating questions which can be answered for the different sensors:

Reliability:

Reliability in this context means if the sensor performs correct when the sensor is installed and used many times. While the sensors are installed on each roll that is checked, the sensor is moved often. Could the sensor be handled many times or is it damaged quite fast?

Signal effectiveness:

Is the signal of interest clear or does the signal need to be processed before it presents valuable information? Examples of process steps are applying filters on the signal or switching between time domain and frequency domain.

Interpretability:

Is it easy to draw clear conclusions out of the collected data from the different sensors, or can the data be interpreted in different ways?

Costs:

What are the costs of the specific sensor over a given period of time? The expected lifetime of the sensor in this application is important as well.

Feasibility:

Is it possible to install and use the sensor in real applications?

Accuracy:

How accurate is the collected data? Is it possible to formulate conclusions based on the collected data in terms of accuracy of the data and the sensor?

Precision:

How precise is the collected data from the different sensors? Thereby is it important to determine what values are acceptable in terms of precision.

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Repeatability:

Does the sensor collect the same data at different measurements when the input signal is equal? This KPI is focusing on the consistency of the readout of the sensor when the input is the same at different measurements.

Not every KPI is as important as others. Therefore an Analytic Hierarchy Process (AHP) from T.L. Saaty [4], is used to make the distinction between all KPI’s. An AHP compares one KPI with all other KPI’s by grading the relative importance between the two of them. This is done for all KPI’s.

The AHP can be viewed in appendix 1. The results are mentioned in table 2.1. Table 2.1: Weighted KPI’s determined using AHP from Saaty

KPI: Priority vector:

Reliability 0.107

Signal effectiveness 0.032 Easy to interpret results 0.138

Costs 0.021

Feasibility 0.127

Accuracy 0.230

Precision 0.099

Repeatability 0.245

In chapter 8 all sensors will be evaluated by performing a multi criteria analysis in which the different sensors are graded for each KPI. While the KPI’s are weighted, it is possible to determine the best feasible sensor for the condition monitoring of idler rolls.

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3

Sensor selection

This chapter focusses on the sensors which will be used for condition monitoring of idler rolls. First a brief introduction on the different types of sensors which are applicable for the experiments is given. Then the given sensor ranges are presented followed by the selected sensors, which are discussed in the third paragraph. At the end of this chapter several sensors are introduced which are not used to primarily detect defect idler rolls, though these sensors are necessary to adjust the test conditions among different experiments.

3.1. Investigation of applicable sensors

The main research question is to find a single feasible sensor or combination of feasible sensors which can detect a defect bearing installed in an idler roll. Generally there are three types of sensors applicable for detecting a defect bearing, namely:

 Temperature sensors  Vibration sensors  Acoustic sensors

The characteristics of each type of sensor will be discussed and some sensors within each type of sensor are presented.

3.1.1. Temperature sensor

There are multiple different sensors that can measure temperature. For example thermometers equipped with mercury are used to measure the temperature of a human body. This type of thermometers can measure very accurate within the small temperature range of a human body. Temperature sensors with a bigger temperature range and therefore more applicable for this experiment, are thermocouple sensors and temperature sensors which use infrared radiation.

Using an infrared camera can be even more sufficient as the temperature differences within the area covered by the camera are measured and presented instead of only one temperature at one location is measured. It is possible to measure the maximum, minimum and average temperature of an area captured by the camera as well.

Thermocouple

A thermocouple temperature sensor consists of two dissimilar conductors which are connected to each other. A voltage is produced when the temperature of the contact area between the two conductors is different from the reference temperature else in the circuit [5]. This voltage can be translated in a measured temperature. Thermocouples are in contact with the object that is measured.

Thermocouples are widely used and are inexpensive. The biggest drawback of a thermocouple sensor is its accuracy. Temperature differences less than one degree Celsius are hard to measure due to system errors. The accuracy of the thermocouple depends on the temperature range which can be measured with that specific thermocouple as well. A smaller temperature range results generally in a higher accuracy.

Infrared temperature sensor

The infrared temperature sensors are non-contact sensors. The working principle behind an infrared sensor is based on the fact that each object with a temperature above zero Kelvin emits infrared radiation

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according to its temperature, called characteristic radiation. The infrared sensor captures the emitted infrared radiation and deflects it on a deflector. The energy from the infrared radiation will be translated in a specific temperature related to the characteristic radiation [6]. Because the infrared sensor is a non-contact sensor, the dimensions of the measured spot is important for a specific application. The object of interest should at least cover the whole spot projected by the sensor on the object, as presented in figure 3.1. The spot diameter at a certain distance from the sensor can vary in diameter between a narrow spot and a wide spot projected on the object of interest. This ratio between the distance towards the object of interest and the spot diameter is expressed in D:S. A ratio of 2:1 means that the spot diameter is half of the length of the distance from the sensor towards the object of interest, as presented in figure 3.2.

Figure 3.1: Correct temperature measurement of target. Adapted from [6]

Figure 3.2: Illustration of the spot diameter measured versus the distance from sensor towards spot, the D:S ratio The emissivity of the metal surface is important for a correct readout of the infrared sensor. Emissivity is a measure for the ability of a surface to emit infrared energy. This energy indicates the temperature of the object. Emissivity can have a value from 0 (shiny mirror) to 1 (blackbody).When the emissivity is almost 1 all energy from the object is emitted and the readout of the infrared sensor is correct. When the emissivity is low, around 0.2 for shiny metals for example, only a fraction of all energy will be emitted and the temperature read out is lower than it is in reality. When a polished metal surface is covered with masking tape of flat black paint for example, the emissivity ratio increases and the temperature of that surface can be measured correctly using an infrared sensor. Tables in which the emissivity is listed for different surface finishes are available [6].

Infrared camera

An Infrared camera measures and presents the temperature distribution of the area which can be captured with the IR camera, while an infrared sensor or a thermocouple can only measure one temperature at a single spot. This temperature distribution can give more insight on how the temperature develops over

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time within the area of interest instead of focusing on one specific spot. Two images made with the IR camera at two different time instants are presented in figure 3.3. The temperature distribution over time is clearly visible, as well as the temperature increase over time measured for three regions presented by bx1, bx2 and bx3.

A drawback of the IR camera might be the installation and use of the IR camera at locations with limited access. The size of the IR camera is large for monitoring the shaft ends of the idler rolls installed in an idler frame.

Figure 3.3: temperature distribution over time and space captured with IR camera.

3.1.2. Vibration sensor

Measuring vibration of the rolls can be performed in different ways. The most commonly sensor used to measure vibration is an accelerometer. Other sensors that are feasible for measuring vibration are acoustic distance sensors or microphones. In this part only the accelerometer and the acoustic distance sensor will be discussed while accelerometers are designed for measuring accelerations and acoustic distance sensors measure the distance from the sensor towards an object.

Accelerometer

The mostly used sensor to detect and measure the vibration of an object is an accelerometer.

An accelerometer consists of a mass and piezoelectric material. The mass will deform the piezoelectric material when a force is applied on the mass, resulting in a voltage that is proportional to the force causing the vibration [7]. As the voltage is proportional to the force and the mass is constant, the voltage is also proportional to the acceleration, according to Newton’s second law: 𝐹 = 𝑚 ∙ 𝑎.

Accelerometers typically measure ‘proper’ acceleration expressed in g force. As gravity is also a force which is pointing vertically towards the earth, this force is measured as well. So a calibrated accelerometer measures a 1g force in the Y-direction towards the earth, which corresponds to the gravitational force. This 1 g force is similar to _{9.81 𝑚 𝑠}⁄ 2

Accelerometers have various ranges in which they measure accelerations correctly. Depending on the type of application, accelerometers with a range of ±2g or with a range of ±200g can be chosen for example.

Acoustic distance sensor

An acoustic distance sensor can measure the distance between the sensor and the object of interest. This is done by sending an ultrasonic sound towards the object of interest. This sound is reflected back to the sensor. By measuring the time it takes to receive the echo of that sound at the sensor, the distance between the sensor and the object can be calculated using the speed of sound. A moving object can be measured by calculating the distance at different time instants for a given period of time and analyzing if this distance between the sensor and the object had changed over time.

The accuracy of the acoustic distance sensor is important when selecting an acoustic distance sensor for a specific application. The time it takes for two successive measurements can be important in some applications, especially when acoustic distance sensors are applied to measure idler roll vibration. The time between two measurements should at least be shorter than the time it takes for one full rotation of

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the idler roll, otherwise the period between two measurements of the acoustic distance sensor is longer than the period of one rotation of the idler roll.

A drawback of the acoustic distance sensor when applied at the test rig is the installation of the sensor. It is hard to focus the sensor at the same spot constantly, while the parts on which the sensors are installed at the test rig vibrate as well.

3.1.3. Acoustic sensor

In most cases a microphone is used to capture sound. There are different types of microphones and depending on the application in which the microphone is used, one type is selected.

First there are different ways of collecting sound with a microphone. An Electret microphone is one of the most used condenser type microphones. It produces electrical signals from variations of air pressure. This electrical signal needs to be amplified, as the signal produced by air pressure differences is very small [8].

Other issues with selecting the right microphone for the application are location at which the microphone is installed and the background noise that is picked up at that location. Omnidirectional microphones pick up sound from all directions, whereas directional microphones can be focused in one direction and the sound from other directions will be minimized. When the surrounding of the object of interest is very noisy, the signal of the directional microphone is clearer than the signal gathered from an omnidirectional microphone. Though, when the application requires to collect sounds from all directions, an omnidirectional microphone is more suitable.

3.2. Sensor conditions for experiments

With the applicable sensors for the experiments investigated, the expected measurement ranges for the lab experiments are important to determine. The measurement ranges are presented in this paragraph. The measurements are, as presented in paragraph 3.1 divided in three categories, namely:

 Temperature  Vibration

 Acoustic emission

Table 3.1 presents the measurement range which is expected for each quantity. The measurement range is based on experience, while it followed that there is no literature which describes this type of lab experiment completely. The presented measurement ranges are set as an initial range and from the experiments will follow if these ranges can or need to be adjusted or not and so if some sensors need to be replaced or not.

Table 3.1: M easurement range for the three different measurement quantities Measurement quantity: Measurement range :

Temperature (°C) 0 to 100

Vibration (g) ± 200

Acoustic (dB) 110

The sensors should at least be able to measure within this temperature range.

Next to the measurement range of the sensors, the operation range of the sensor is important. For example when a accelerometer is installed which can only operate at temperatures between 0°C and 20°C, the accelerometer is not suitable for real belt conveyor applications, as the ambient temperature can be higher than 20°C during summer for example. Table 3.2 presents these operating conditions.

Table 3.2: Operating range conditions required for installed sensors Measurement quantity: Measurement range :

Temperature (°C) 0 to 50

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3.3. Selection of sensors

This paragraph presents the selection of the sensors which will be used for the lab experiments. This selection is based on the suitable sensors presented in paragraph 3.1 and the required ranges determined in paragraph 3.2.

For the selection of different sensors within the same sensor category, the measurement range of the different sensors should be similar when possible. This to prevent limitations on the correctness of the results of all sensors due to one sensor. When one sensor has a much larger measurement range as the other sensor, it will follow that either one sensor is out of its range or one sensor is less sufficient as the sensor used only a part of its total measurement range. The accuracy of the sensor with the bigger range will in general be lower than the one with a smaller range as well.

3.3.1. Temperature sensor

For the lab experiments three different temperature sensors are chosen. Thermocouple sensors, Infrared sensors and an IR camera. As mentioned in section 3.1.1 the working principles behind the thermocouple and the infrared sensor are different. By using both temperature sensors it is also possible to evaluate which principle is most suitable for this application.

Thermocouple sensor:

The chosen thermocouple is: RS components type K Thermocouple BMS-K-C70-MP, presented in figure 3.4. Table 3.3 shows the important specifications of this thermocouple sensor. This specific thermocouple is chosen while it fulfills the conditions of paragraph 3.2 and the thermocouple can be attached easily to metal surfaces using the magnet around the thermocouple sensor. The measurement range of the thermocouple is slightly too big compared to the conditions, though this is the smallest suitable measurement range.

Figure 3.4: Thermocouple sensor RS components - BM S-K-C70-M P Table 3.3: specifications thermocouple sensor RS components - BM S-K-C70-M P

The thermocouple is amplified with the amplifier: The sensor connection - Type K thermocouple amplifier TCA-MS-K-8-A4.

The scale factor of this amplifier is: 4mV/°C. This results in a multiply by 250 on the voltage signal measured to get the temperature in °C.

The data sheet the thermocouple sensor is presented in appendix 2.1

Infrared sensor:

The infrared sensor chosen for the experiments is: Omega OS35-RS-100C-V10-24V. The infrared sensor is shown in figure 3.5. The important specifications of this sensor for the experiments are listed in table 3.4. The entire datasheet is presented in appendix 2.2.

Specification: Value :

Measurement range (°C) -50 to 250

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Figure 3.5: Infrared sensor Omega OS35-RS-100C-V10-24V Table 3.4: specifications of infrared sensor Omega OS35-RS-100C-V10-24V

Measurement range (°C) 0 to 100

Ambient temperature range (°C) 0 to 70 Field of view (distance:spot ratio) 2:1

Minimum spot diameter (mm) 3

Accuracy (°C) ± 1

Maximum Vibration shock (g) 100

The measurement range combined with the minimum spot diameter of the sensor are the main advantages of this infrared temperature sensor. The drawback could be the distance to spot ratio, discussed in paragraph 3.1.1, when the infrared sensor is not installed closely to the shaft end. The specifications of the sensor meet the required conditions mentioned in paragraph 3.2.

Infrared camera

The chosen infrared camera is the Flir AX8, presented in figure 3.6. This infrared camera can make visual images of an object of interest as well as thermal images. Thereby it is possible to make an image which combines the visual and thermal image. This results in a thermal image in which the contours of the object of interest are shown as well.

Figure 3.6: Infrared camera Flir AX8

The important specifications of this infrared camera are listed in table 3.5. The complete data sheet of this infrared camera is presented in appendix 2.3. Important specifications of this sensor are: the temperature measurement range, the accuracy and ambient temperature range.

The Flir AX8 IR camera is chosen while the measurement range meets the prescribed conditions of paragraph 3.2, as well as the other conditions on ambient temperature and vibration shocks. The drawback of this sensor is the fixed focus of the camera which can be problematic when focusing on the shaft end of the center roll.

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Table 3.5: Specifications of infrared camera Flir AX8

Infrared resolution (pixels) 80 x 60 Thermal sensitivity (°C) < 0.10 @ +30°C

Camera focus Fixed

Measurement range (°C) -10 to 150

Accuracy (°C) ± 2

Ambient temperature range (°C) 0 to 50

Vibration (g) 2

3.2.2. Vibration sensor

Initially two different sensors are chosen for measuring vibration of the installed rolls on the belt conveyor system, namely accelerometers and acoustic distance sensors. Both sensors are presented next.

Accelerometer

During the laboratory experiments the vibration of the rolls will be measured with accelerometers. The initially installed accelerometer is: Analog devices ADXL377. This accelerometer is shown in figure 3.7.

Figure 3.7: Accelerometer ADXL377

Typical specifications for this accelerometer are presented in table 3.6. The measurement range, the noise density and the sensitivity are important. The complete data sheet can be found in appendix 3.1. The specifications presented below are applicable for a given temperature TA = 25°C and supply voltage Vs= 3V.

Table 3.6: Specifications of accelerometer ADXL377

Measurement range (g) ± 200

Nonlinearity (%) ± 0.5

Sensitivity at Xout, Yout (mV/g) Between 5.8 and 7.2

Zero g Voltage (V) Between 1.4 and 1.6

Noise density Xout, Yout (mg/√Hz) 2.7

Ambient temperature range (°C) - 40 to 85

The chosen accelerometer can measure accelerations of maximum ±200g. This measurement range meets the conditions mentioned in paragraph 3.2 in terms of accelerations. The accuracy of the sensor, mentioned as nonlinearity in table 3.6 is ±1g. Small amplitude accelerations, below ±1g are not measured accurately.

The signal gathered from the first couple of experiments showed that the signal was within the ±1g, so the chosen accelerometer turned out not applicable for the experiments.

Another accelerometer is chosen with a much smaller measurement range, namely the Analog devices ADXL337 accelerometer, presented in figure 3.8. The important specifications are listed in table 3.7, and the whole datasheet can be found in appendix 3.2.

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Figure 3.8: Accelerometer ADXL337 Table 3.7: Specifications of accelerometer ADXL337

Measurement range (g) ± 2

Nonlinearity (%) ± 0.3

Sensitivity at Xout, Yout (mV/g) Between 270 and 330

Zero g Voltage (V) Between 1.35 and 1.65

Noise density Xout, Yout (μg/√Hz) 175

As can be seen from table 3.6 and table 3.7, the measurement range and the nonlinearity differs between the two accelerometers. The accuracy of the smaller measurement range accelerometer is ±0.006g instead of ±1g for the big measurement range accelerometer. This results in a correct measurement of much smaller accelerations, when using the small measurement range accelerometer.

Acoustic distance sensor

The acoustic distance sensor used during the experiments is: Microsonic, type: ZWS 70/CU/QS. The acoustic distance sensor is presented in figure 3.9. The important specifications of this acoustic distance sensor are listed in table 3.8. The datasheet is presented in appendix 4.

Figure 3.9: Acoustic distance sensor M icrosonic ZWS 70/CU/QS Table 3.8: Specifications of acoustic distance sensor M icrosonic ZWS 70/CU/QS

Measurement range (mm) 120 to 700

Resolution (mm) 0.037

Accuracy (%) ±1

Response time (ms) 70

Table 3.8 shows that the measurement range of the acoustic distance sensor is between 120 mm and 700 mm. the resolution of the sensor is 0.037 mm, which is important while the movements of the roll are very small.

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3.2.3. Acoustic sensor

Microphone

To capture the sound from the idler rolls, a microphone is chosen, namely an Omni-directional foil electret condenser microphone from Challenge Electronics with part number: CEM-C9745JAD462P2.54R. This microphone is pre-amplified with a Texas Instruments opa344 amplifier. The combination of microphone and amplifier is called an electret microphone breakout, and is available as a: Sparkfun BOB – 09964, presented in figure 3.10. The important specifications of this microphone breakout are listed in table 3.9.

Figure 3.10: Electret microphone breakout BOB – 09964 Table 3.9: Specifications of electret microphone breakout

Frequency range (Hz) 100 to 10000

Sensitivity(dB) - 46 at 1000 Hz

Maximum input S.P.L. (dB) 110 at 1000 Hz

Amplification input signal 100

The data sheet of the microphone as well as the data sheet of the amplifier are presented in appendix 5. The maximum sound pressure which can be captured with the microphone is 110 dB and is similar to the conditions mentioned in paragraph 3.2.

3.2.4. Test condition sensors

In order to adjust the test conditions for the experiments, a speed sensor and load cells are chosen. The speed sensor measures the belt speed. The rotational speed of the idler rolls can be calculated from this belt speed. Note that the slip between the speed sensor and the belt, as well as, the slip between the belt and the rolls is neglected.

Load cells are necessary for measuring the belt tension and the load on the idler frame. The installation of these load cells will be presented in chapter five.

Next the specifications of the speed sensor and the load cells are presented.

Speed sensor

The chosen speed sensor is a: Servo-Tek Tachometer Type SB-757A-2, presented in figure 3.11. The important specifications for the experiments are listed in table 3.10. The maximum belt speed is 1.8 m/s and is lower than the maximum rotational speed of 12000RPM, taking the small diameter of the speed sensor into account. The ambient temperature range in which the speed sensor can operate is larger than required in paragraph 3.2.

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Table 3.10: Specifications of speed sensorServo-Tek Tachometer Type SB-757A-2

Maximum rotational speed (RPM) 12.000

Output voltage (V/1000RPM) 7

Load cell

The chosen load cells are: Tedea-Huntleigh model 615 S-type load cells, presented in figure 3.12. Two different measurement ranges are chosen, one with a measurement range up to 200 kg and one with a measurement range up to 300 kg. This is displayed in table 3.11 as well as other important specifications of the load cells.

Figure 3.12: Tedea-Huntleigh model 615 S-type load cell Table 3.11: Specifications of Tedea-Huntleigh model 615 S-type load cell

Load cell ‘200 kg’ Load cell ‘300 kg’

Measurement range (kg) 0 to 200 0 to 300

Rated output (mV/V) 2 2

Rated output tolerance (mV/V) ± 0.002 ± 0.002

Ambient temperature range (°C) - 30 to 70 - 30 to 70

This chapter focused on suitable sensors for measuring failure phenomenon on the idler rolls during the lab the experiments.

Now all sensors are selected, the test rig can be designed. The design of the test rig is presented in chapter four, followed by the installation of the sensors and other components to complete the test rig in chapter five.

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4

Design of test rig

To simulate the working conditions from belt conveyors used in real applications best, a test rig is designed on which the lab experiments will be performed. This chapter will present the design of this test rig, followed by a more detailed explanation of the important components. At last the inducement of the roll defects as well as the inducement on the damaged rolls is presented.

4.1. Design of test rig

The lab experiments are performed on a specially designed test rig. This test rig consists of a belt conveyor system, an idler frame with a height adjustment subsystem and three brackets installed on the idler frame. In each bracket one idler roll is installed, which makes a total of three idler rolls installed on the test rig. Figure 4.1 displays the design of the test rig, and figure 4.2 shows the actual test rig present at the laboratory of TEL.

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Figure 4.2: Test rig installed at TEL Laboratory

As figure 4.2 already displays a fence around the test rig to meet safety regulations. Sensors are installed which make it possible to stop the belt conveyor.

The design of the test rig will be discussed in more detail in the next paragraphs by presenting its components.

4.2. Existing belt conveyor system

The existing belt conveyor system at the TEL laboratory is not directly applicable for the idler roll experiments. Figure 4.3 shows the belt conveyor system. The existing belt conveyor system consists of an engine which drives the drive pulley via a gearbox.

Figure 4.3: Existing belt conveyor system Table 4.1 displays the known parameters of this belt conveyor system:

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Table 4.1: Parameters of the existing belt conveyor system

Parameter: Value:

Maximum belt speed (m/s) 1.8

Type of belt Fabric (3 layers)

Belt width (mm) 1080

Distance between drive and tail pulley (mm) 3000

Maximum belt tension (kN) 135

With this configuration it is not possible to install idler rolls directly on the belt conveyor. Therefore an idler frame is designed, which is presented in paragraph 4.3.

The belt speed and the belt tension, the two important parameters can be adjusted at the existing belt conveyor system such that the test conditions meet the real working conditions best. The maximum values of these parameters are presented as well in table 4.1.

4.3. Idler frame

As mentioned in paragraph 4.2, an idler frame must be designed for installing the three idler rolls. The design for a three roll frame instead of a one roll frame is chosen while with three rolls installed, the correlation between the three rolls can be investigated which is not possible when installing only one roll. Correlation between the rolls and the frame can be investigated as well.

The most important requirement for the design of the three roll idler frame is the possibility to install the wing roll brackets with or without a trough angle. Next to this the idler frame must support the roll brackets and it should be possible to install the sensors at the shaft ends later on. The designed idler frame is presented in figure 4.4. The brackets installed on the idler frame are connected with the idler frame via a plate in between the two parallel beams. As can be seen in figure 4.4 it is possible to rotate the wing roll brackets such that a trough angle up to 15° can be reached. Using a smart configuration of the holes in the plate of the two wing roll brackets, it is possible to install the wing roll brackets at a specific trough angle and then lock them in that position.

Figure 4.4: Design of the idler frame

The idler frame is located in the middle between the drive and retain pulley. The design of the idler frame is such that it can be mounted on the existing connections on the belt conveyor frame. The existing single roll on the belt conveyor which was installed to push the lower belt downward is

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replaced by a 2-rolls return idler set at a different location, while the location where the single roll was placed is used by the idler frame. The 2-roll return idler set is presented in figure 4.5.

Figure 4.5: 2-roll return idler set installed at the belt conveyor system.

A more detailed view on the two parallel beams and the installed wing roll brackets and the center roll bracket is displayed in figure 4.6. As can be seen from the figure, the sensors are installed at the shaft ends. Note that all requirements determined in the beginning of this paragraph are fulfilled.

Figure 4.6: Detailed view on the two parallel beams and the roll brackets.

4.4. Height adjustment subsystem

As mentioned in paragraph 4.2 of this chapter, two important parameters are the belt velocity and the load on the rolls. From that paragraph was found that it is possible to adjust these to parameters with the belt conveyor system. Though the load on the rolls will be adjusted by increasing or decreasing the belt tension. Increasing the load can be done by adjusting the height of the idler frame compared to the height of the drive and retain pulley as well. By increasing this idler frame height, the belt tension increases less than when only increasing the belt tension, as the ratio between the height of the idler frame and the length between the drive and retain pulley which results in relative more tension on the rolls (vertical load) instead of belt tension (horizontal load).

Therefore a height adjusting subsystem is added to the idler frame. With this subsystem it is possible to adjust the height at both ends of the idler frame. With the installation of a load cell in this subsystem, the load on the rolls can be determined easily. A detailed figure of the height adjustment subsystem can be found in figure 4.7 and the height adjustment subsystem installed at the test rig is shown in figure 4.8. When the desired load on the rolls is reached, the idler frame can be tightened to the belt conveyor frame, to make sure that the idler frame cannot move when the belt conveyor starts running.

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Figure 4.7: Detailed projection of height adjustment subsystem. Figure 4.8: Height adjustment system installed on test rig

4.5. Inducement of roll defects

The experiments will give more insight in the feasibility of the condition monitoring of idler rolls. Therefore it is of vital importance to have idler rolls in which a defect is induced. This defect is induced by damaging one of the two bearings that are installed in an idler roll. In order to simulate the defects found in the industry, different types of defects are induced. The level of defect of the bearing is expected between the incipient failure and final failure of the bearing. These stages are represented in chapter one. However, no specific level of defect inducement can be linked to a certain specific bearing failure level, and from literature was found that previous experimental studies on bearing failure commonly rely on empirical or arbitrary sizes of 'seeded' defects. The chosen sizes of ‘seeded’ defects for this research are given in table 4.2.

Generally, three different types of defects can be distinguished. Defect bearings which generate a specific defect frequency, defect bearings of which it is not obvious that they should generate a specific defect frequency and at last damaged bearings of which the damage is more severe compared to the other two defect types. All three different types of defects are discussed next:

For the first type of defects, a specific part of the bearing is damaged, for example the inner raceway, outer raceway or the rolling element. Due to this specific type of defect, the introduction of a vibration with a specific defect frequency is expected. A bearing with this type of defect should at least be recognized by its vibration pattern.

For the second type of defects, it is not possible to address the induced defect to a single part of the bearing and to specify a vibration frequency corresponding to this induced defect. An example of this type of defect is a bearing which is not lubricated.

The third type of defects are the damaged bearings. The damaged bearings are more severe damaged than the other two defect types. From now the third type of defect bearing is called damaged bearings. The defect induced to the damaged bearings was done with the purpose of destroying the bearing such that catastrophic failure of the installed damaged roll should happen within a short period of operating time of the damaged roll.

All different defects induced to the bearings are presented in table 4.2. More details about the amount of prepared rolls and the exact type of defect are given in both table 4.2 and the text afterwards.

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Table 4.2: Different types of defects and damages induced to one of the bearings of the idler rolls type of bearing

defect Code

Number

of rolls defect details

No defect A 4 No defect bearings installed

Outer race defect B 4 Scratch perpendicular on the direction of movement of the rolling elements. Scratch width 1 mm, depth 0.5 mm Inner race defect C 4 Scratch perpendicular on the direction of movement of the

rolling elements. Scratch width 1 mm, depth 0.5 mm Rolling element

defect D 4

Damage on one of the rolling elements. Diameter 0.5 mm, depth 0.5 mm

Debris in

lubricant E 4

MICRON+MDA M4080 particles from ELEMENT SIX (size range 0.04-0.08 mm) in the lubrication oil (Shell Gadus S2 V220 2). The contamination level is around 5 vol. %

Radial

overloading F 4

Roll #1: application of 18kN load for 2 hours

Roll #2: application of 18kN load, roller failed within 2 hours Roll #3: application of 18kN load for 1/2 hours

Roll #4: application of 18kN load for 1/2 hours The tangential speed measured during the test is: 4.42 m/s (13Hz, 781 RPM)

‘Damaged’ G 3

Three different types of damaged bearings are installed. Roll G1: Bearing cover damaged using a hammer, visible damage on the bearing cover

Roll G2: Small hole through up to the bearing.

Roll G3: five holes drilled in the bearing. Broken cage and drilled holes filled with metal particles: mass (~30g) and size (~250µm)

No lubrication H 2 Not lubricate the new bearing

‘Damaged’ H 2

Two rolls H are damaged as follows:

Roll H2: five holes through bearing covers up to the bearing and cage destroyed

Roll H3: give holes through bearing covers up to bearing. The holes are filled with metal particles: mass (~15g) and size (~50µm)

Corroded

bearing I 4

Bearings placed in salty water or acid liquid for one week. Afterwards the bearings are exposed to air till corrosion can be observed on the bearing

The first roll mentioned in table 4.2, roll A, does not have defect bearings. Roll A is used as the reference. Next the different defects induced are explained in more detail.

Defect rolls:

The defect induced to roll B is a scratch induced on the outer raceway, presented in figure 4.9. This scratch is perpendicular to the moving direction of the rolling elements. Each time a rolling element passes the scratch, a vibration will be generated. This makes it possible to calculate the frequency induced by the generated vibration for a given rotational speed of the roll, and measure this calculated vibration frequency with a suitable sensor.

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Figure 4.9: Outer race defect induced to the bearing

Roll C presents an inner raceway damage, shown in figure 4.10. Here a scratch is made on the inner raceway perpendicular to the moving direction of the rolling elements. For this roll it is possible to calculate the frequency of the vibration induced by the damage on the inner raceway and measure this calculated frequency with a suitable sensor.

Figure 4.10: Inner race defect induced to the bearing

For roll D one of the rolling elements used in the bearing is damaged, presented in figure 4.11. The damage is induced by drilling a small hole in one of the rolling elements. As mentioned at roll B and roll C, this damage can generate a vibration of which the frequency can be calculated, and measured with a suitable sensor.

Figure 4.11: Defect induced to the rolling element of the bearing

Roll E is damaged by adding particles to the lubricant of one bearing. This type of defect is also commonly seen in real applications on belt conveyor systems. Although a bearing is equipped with (several) dust covers, particles can still enter the bearing after a long period of time. The particles entering the bearing come from outside contamination as well as from the bearing itself when metal particles are created due to wear of components in the bearing, for example from the cage of the bearing. The defect induced to roll F is radial overloading of the bearing. Overloading can happen due to the dynamic load on the belt at belt conveyors. When for example some specific types of bulk material are

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transported with a belt conveyor, big lumps of bulk material can cause overloading of the idler rolls for a short period of time.

Roll H has one bearing installed which is not lubricated. When bearings are running for a long period of time, grease inside the bearing can be run out of the bearing, causing more friction at that specific bearing.

The last type of defect roll, roll I has one bearing with corroded components. The bearing is firstly putted into salt water for one week. Next the bearing is exposed to air, which causes a chemical reaction and results in a rusty bearing. This resulted in the bearing displayed in figure 4.12.

Figure 4.12: Corroded bearing installed at roll I Damaged rolls:

Next to all the discussed defect rolls in this paragraph, the damaged rolls are not mentioned up to now. The three different G rolls, Roll G1, roll G2 and roll G3 are initially all three healthy rolls which are proper lubricated. The bearings are already installed in the three rolls, and the shaft is placed as well. Roll G1 is damaged by smashing with a hammer on the metal bearing cover, presented in figure 4.13. Due to the damage, the metal cover is pushing the plastic cover inside on the bearing, causing friction. The exact damage done to the bearing is not known, while the bearing itself is not visible.

Laboratory experimental research on multi-sensor monitoring of belt conveyor idlers

Summary

Contents

1

Introduction

1.1.

Idler rolls

1.2.

Relevance of research

1.3.

Goal and outline of report

2

Experiment method

2.1.

Lab experiments

2.2.

Quasi-experimental design

2.3.

Key Performance Indicators

3

Sensor selection

3.1.

Investigation of applicable sensors

3.1.1.

Temperature sensor

3.1.2.

Vibration sensor

3.1.3.

Acoustic sensor

3.2.

Sensor conditions for experiments

3.3.

Selection of sensors

3.3.1.

Temperature sensor

3.2.2.

Vibration sensor

3.2.3.

Acoustic sensor

3.2.4.

Test condition sensors

4

Design of test rig

4.1.

Design of test rig

4.2.

Existing belt conveyor system

4.3.

Idler frame

4.4.

Height adjustment subsystem

4.5.

Inducement of roll defects