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C Drebenstedt and R Singhal eds Mine Planning and Equipment Selection 1119 DOI 10 1007 978 3 319 02678 7 109 Springer International Publishing Switzerland 2014 Conveyor Belt Condition Evaluation via Non Destructive Testing Techniques Ryszard Blazej1 Radoslaw Zimroz1 2 Leszek Jurdziak1 Monika Hardygora1 2 and Witold Kawalec1 1 Machinery Systems Division Wroclaw University of Technology Na Grobli 15 50 421 Wroclaw 2 KGHM CUPRUM Ltd CBR Sikorskiego 2 8 53 659 Wroc aw Abstract Belt conveyors seem to be the primary transportation technique for mining materials in many countries especially it is the case in the mining industry in Poland One of the key and challenging issue is maintenance policy for conveyor belt probably the most critical part of a conveyor The total length of conveyor belts in Polish mining industry exceeds 2 200 km Taking into account safety economic reliability and other aspects maintenance of these belts becomes a serious task How to detect damages in a belt How to relate detected damages and condition assessment When a belt segment splice whole belt loop on a conveyor should be replaced When the actual belt tensile strength matches the operational requirements To answer these questions the up to date results on Non Destructive Testing techniques developed for opencast lignite mining are presented in the paper These techniques are related to vision systems magnetic systems and infrared thermography Some of them are still being tested in laboratory conditions while other are already in deployment phase though it seems to be useful to share recent experience and present the state of the art In the paper a brief idea of each applied method is explained and some both laboratory as well as industrial examples of investigation are discussed Keywords belt conveyors non destructive testing condition monitoring and diagnostics maintenance 1 Introduction A continues belt conveyor based transportation system is very popular method of material transportation in many industrial branches Mining companies are among the biggest users of belt conveyors Today some 500 km of conveyor belts are installed in 4 operating lignite surface mines in Poland namely Belchatow Turow Konin and Adamow Even more conveyor belts are installed in underground mines e g only in KGHM Polish Copper there are over 260 km of belts 1 A common problem for all belts users is how to maintain belts i e how Corresponding author 1120 R Blazej et al to detect damages of a belt how to estimate real condition of the investigated belt how to estimate when a belt segment should be replaced rather than repaired on the spot what criteria should be used to classify the belt for repair procedures etc Recent achievements in the field of metrology IT data analysis non destructive testing structural health monitoring etc give the opportunity to use monitoring and diagnostic systems for belt maintenance management However it should be mentioned that condition monitoring of belt properties is a complex problem 1 10 There is no universal solution Depending on belt type operational condition and material type surface lignite mine underground hard coal or copper ore form of the most frequent degradation processes etc an available solution might be either simple and inexpensive or complex and costly In this paper the belt with steel cords commonly used in the surface lignite mines are considered In this case two significant problems have been identified the condition of a belt core steel cords and of a belt top surface a carrying cover For the steel cords monitoring the magnetic based diagnostic system has been developed Also some new ideas related to infrared thermography are introduced For the analysis of a belt top cover condition the specialized vision system has been created Both systems have been developed on the basis of the LABVIEW environment which allows to integrate them as subsystems into a comprehensive belt condition monitoring system and fuse combine information from different sources 1 Problem of integration of data acquired from different system is known in literature as data information fusion In the proposed approach several technologies are used to compose one platform Depending on defined task technical and financial issues customizing the specific belt condition monitoring system can be assembled by selection required components In the paper mentioned subsystems i e components that constitute the platform are briefly presented with some examples of already completed industrial implementations 2 Test Rig and Real Machine Measurements As it was mentioned results presented in the paper come from measurements obtained both at the laboratory test rig and in situ at belt conveyors working in the lignite surface mine A test rig used in this experiments has been developed especially for investigating the measuring techniques used for belt condition monitoring It consists of drive units several pulleys and idlers and c a 17m of belt Fig 1 The belt consists of three segments connected by vulcanized splices see Fig 7 It gives a good model of a real conveyor belt used in mining conveyors Several damages of cover and steel cords were on purpose introduced to the belt The cover damages of different size and shape were made for testing the vision system After these experiments some additional damages of steel cords in the belt core were created for magnetic NDT system and infrared thermography applications Location of these damages and structure of belt loop is presented in Fig 7 The example of a damage is shown in Fig 8 left Conveyor Belt Condition Evaluation via Non Destructive Testing Techniques 1121 Fig 1 Test rig used in experiments 3 Magnetic Inspection Systems Belt magnetic inspections systems are known for over 30 years 6 Unfortunately they are not used on a daily basis as it could be expected due to high belting costs Here we present advanced solution developed recently for one of Polish mining company It is 24 channels see Fig 3 NDT system designed using National Instrument components for data acquisition and the unique software written in Labview Enviroment The system consists of two parts portable module for data acquisition basic analysis in situ etc and the more advanced software installed on desktop for deep analysis visualization management of data etc Fig 2 presents an example of tests of the system that were carried out on overburden conveyors Fig 2 Steel cords condition measurements with the use of the system installed on conveyors Fig 3 First 10 channels out 24 available in the modified system based on EyeQ hardware D ugo m D ugo m D ugo m D ugo m D ugo m D ugo m D ugo m D ugo m D ugo m D ugo m D ugo m D ugo m D ugo m D ugo m D ugo m D ugo m D ugo m D ugo m 1122 R Blazej et al Acquisition of 24 channels gives a lot of data It is reasonable to provide automatic data analysis tools that might be able to detect and localize damage and finally present results in a clear form 15 Fig 4 presents results of detection for 20 channels belt width was less than size of sensors array as two dimensional map i e spatial distribution of detected damages Further aggregation of data leads to histogram presented in Fig 4 right where number of damages with respect to channel number along belt width for full belt loop alternatively for a given length of belt segment is presented From such a simple histogram describing distribution of damages along belt width one might clearly see that most of damages is located in the middle of the belt because main material stream is located there Other important information is symmetrical distribution of damages around central line of the belt what is a consequence of symmetry of belt tracking Lack of asymmetry shows however that conveyor construction was also symmetrical and there were no big misalignment of the belt during operation Misalignment of conveyor structure supporting belt idlers positioning and belt tracking would lead to asymmetrical distribution of damages Fig 4 Spatial distribution of detected damages and histogram of number of damages with respect to channel number along belt width for full belt loop 4 Machine Vision Diagnostic System Other important problem is assessment of the conditions of belt covers especially top cover that is often exposed endangered to sharp edges of lumps of transported material Typical damages of belt cover are lengthwise cuts abrasion through cuts grooves It is proposed to apply the vision system to manage mentioned issues The concept of experiment using mentioned test rig is shown in Fig 5 The idea of the system is simple with the use of specialized linear camera images are acquired line by line Fig 6 left The specialised software was developed to form and preliminary enhance images 14 The proposed procedure for damage detection is able to find areas on the image that can be interpreted as Conveyor Belt Condition Evaluation via Non Destructive Testing Techniques 1123 Fig 5 The idea of the machine vision system 1 Fig 6 Machine vision hardware and images of inspected belt with detected damages damaged surface Fig 6 right The system is able to detect a single damage estimate its area and type longitudinal or transversal Each detected damage is stored in the database When detection procedure is finished the software supports the decision making process by a suitable statistical analysis damage density along the belt length types of damage etc 5 Infrared Thermography for Belt Condition Monitoring In this section preliminary results of belt condition assessment with the use of infrared thermography is introduced A novel procedure consists of infrared images acquisition and their processing In order to detect damage in top cover and steel cords it is assumed that change of condition will modify distribution of dispersed energy related to internal friction bending resistance etc Energy is transformed into heat and thus it can be detected via infrared thermography Acquired images are often difficult to interpret Fig8 right automation of image understanding and decision making require advanced processing of these images 11 13 It is well known that image can be represented by array of numeric values In this paper we decided to decompose image array into vectors and process images line by line with the use of time series approach 230V Encoder Linear camera LED lighting Cleaning device 230V Encoder Linear camera LED lighting Cleaning device 230V Encoder Linear camera LED lighting Cleaning device 1124 R Blazej et al Fig 7 The model of a belt used for testing Fig 8 Photos of damaged belt the intersection of 5 steel cords and its raw infrared thermography image Fig 9 presents several subplots that display part of the original image with characteristic features Fig 9 left presents uniform temperature distribution no damage top subplot two singularities around x 200 and x 450 related to beginning and end of belt segment with removed top cover middle subplot and sudden change of temperature distribution related to introduced damage x 300 bottom subplot Fig 9 right shows plotted time series corresponding to segmented images showed on Fig 9 left It can be easily seen that for uniform distribution of temperature extracted time series are flat and its variability is relatively low In presence of damage one may see serious change singularity of the signal amplitude Fig 9 Results of thermogram images analysis 5 steel cords broken Conveyor Belt Condition Evaluation via Non Destructive Testing Techniques 1125 Fig 10 Singularity detection for single time series A C borders of belt segment with removed top cover B change related to damage Fig 10 shows the clear picture of singularity in time series extracted line by line from the thermogram By singularity it is meant sudden jump of signal amplitude related to break in steel cords Two of them marked by ellipses A and C are related to begin and end of segment with removed top cover normally would not exist Ellipse B points out clear signature of damage 6 Conclusions In the paper short review of used non destructive testing in condition monitoring of conveyor belt is presented Depending on the damage type to be detected one should use the appropriate method For detection damages of steel cords the best method is magnetic testing In the paper the system for such analysis developed and implemented in the lignite mine the industrial partner of the investigations is shown However it was also proposed to use infrared thermography In fact this technique is still under development preliminary results from laboratory test rig investigation have been presented Solutions for the second important issue related to top cover damage are also discussed It should be underlined that in fact this is the primary problem Damages of cover results in degradation of steel cords by immediate cutting or slow degradation corrosion The holistic final decision on belt condition should combine partial decisions regarding steel cords condition and top cover conditions The idea of integration of these information is discussed in 1 Acknowledgment The research work has been financially supported by Applied Research Programme Program Badan Stosowanych in the path A Intelligent system for automated testing and continuous diagnosis of the conveyor belt 2012 2015 R Blazej L Jurdziak and W Kawalec and KGHM Cuprum R D R Zimroz M Hardygora References 1 Blazej R Jurdziak L Integrated diagnostic device for automatic assessment of conveyor belts condition In Proceedings of 22nd World Mining Congress Expo Istanbul September 11 16 vol 3 pp 675 680 inasiEskikaya Ankara 2011 1126 R Blazej et al 2 Hardyg ra M Bartelmus W Zimroz R Krol R Blazej R Maintenance diagnostics and safety of belt conveyors in the operations Transport Logistics Belgrade 6 s 351 s 354 2009 3 Zimroz R Makowski R Blazej R Method of damage detection in conveyor belts with steel cords by NDT signal processing In Proceedings of the Eighth International Conference on Condition Monitoring and Machinery Failure Prevention Technologies Cardiff UK 2011 4 Zeng Q L Wang J G Wang L Wang C L The research of coal mine conveyor belt tearing based on digital image processing In Yang G ed Proceedings of the ICCEAE2012 AISC vol 181 pp 187 191 Springer Heidelberg 2013 5 Fedorko G Molnar V Zivcak J Dovica M Husakova N Failure analysis of textile rubber conveyor belt d