ADVANCES IN THE NON-DESTRUCTIVE TESTING OF CONVEYOR BELTING

Transcription

1 ADVANCES IN THE NON-DESTRUCTIVE TESTING OF CONVEYOR BELTING 1. SUMMARY G.J. BARFOOT TUNRA BULK SOLIDS HANDLING RESEARCH ASSOCIATES THE UNIVERSITY OF NEWCASTLE, AUSTRALIA Nn-destructive testing (NDT) f cnveyr belting has becme cmmn practice thrughut the wrld. This paper reviews sme f the techniques used t date and discusses sme advances in technlgy that has led t increasing applicatins f NDT systems fr cnveyr belting. Recent studies have demnstrated the value f simultaneus measurement f a number f cnveyrs peratinal characteristics alng with NDT f the belt itself. In additin, increased sensr perfrmance and cmputer prcessing has resulted in better infrmatin frm a simpler measurement prcess. This type f data has seen an increase in the capabilities f nn-destructive testing fr prblem slving and maintenance prgramming in belt cnveying systems. 2. INTRODUCTION Cmparisn f the relative perating csts between a number f truck, rail and cnveyr systems in Australia, shwn in figure 1, demnstrates that cnveyrs are a cst effective methd fr transprting bulk material fr distances up t 50km [1]. This cst advantage may be a factr in the lw pririty ften given t prgrammed maintenance f cnveyr belt systems. An peratr running a fleet f re trucks wuld nt cnsider ding s withut cnsiderable expenditure n prgrammed maintenance and perfrmance mnitring, yet belt cnveyrs are ften perated using crisis management principals. The applicatin f NDT and prgrammed maintenance, even t relatively small cnveyrs, can result in cnsiderable cst savings. As cnveyr systems have becme mre cmplex, with speed, thrughput and tensin all steadily increasing, the capital cst f cnveyr installatins has gne up accrdingly. This increased cst has seen a higher emphasis placed n btaining the maximum perating efficiency frm cnveyr belt systems, part f this prcess has been the use f NDT. As the develpment f this equipment cntinues, the applicatins fr its use have widened. High gain sensrs and cmputer prcessing have seen an increase in the infrmatin derived frm cnveyr belt NDT while the measurement prcess itself has becme simpler. A cnveyr system cnsists f a number f cmpnents, drives, take-ups, idlers and supprt structure, brakes, pulleys, lading and transfer pints, hrizntal and vertical curves and bster drives all cntribute t the verall perfrmance f the system. It is simply nt pssible t cnsider any cmpnent in islatin and while this paper deals primarily with the nn-destructive testing f the belts reinfrcing layer it is imprtant t nte that cnditin mnitring shuld cver all aspects f the cnveyrs peratin. 1

2 Figure 1 - Cmparative cst f bulk material transprt A recent study by a NSW cal-mining peratin estimated the delays t prductin attributed t its belt cnveyr systems amunted t 30hrs per mnth [2]. Based n a 24hr peratin, this number represents what might be cnsidered an acceptable availability, apprx. 95%. Hwever, if we apply this t lst prductin, at an average f l000tph n the cnveying system 30,000 tnnes/mnth amunts t 360,000 tnnes f lst prductin each year attributed t cnveyr system dwntime. If we nte that 40% f Australia s exprts cme frm the mining sectr, a further significant amunt frm agriculture, and that a high prprtin f all f thse exprts will at sme stage pass thrugh a belt cnveyr system yu start t get a feel fr the ptential cst savings thrugh imprved availability. 3. OBJECTIVES OF NON-DESTRUCTIVE TESTING The bjective fr applying nn-destructive testing varies between installatins. Up until recently the main applicatin fr this technlgy has been with high pririty belts, where stppages will have a severe effect n peratins. Regular cnditin mnitring has been used t reduce the pssibility f unscheduled dwntime. Current applicatins, hwever, increasingly invlve ne ff prblem slving where nn-destructive testing is used t islate a particular peratinal prblem such as premature belt deteriratin, regular splice r jint failure r belt tracking prblems. As research int the use f mnitring techniques cntinues, cnveyr belt peratrs are becming mre aware f the pssibilities f using this equipment t imprve the availability and reliability f their belt cnveying systems. It is imprtant t realise that damage t the cnveyr belt is usually a symptm f ther prblems. Cnveyr system peratrs have been using NDT as a measure f the perfrmance f the cnveyrs peratin and maintenance prgrams. Utilising NDT t identify and eliminate prblems that are wearing r damaging the belt will ultimately lead t cnditin mnitring being necessary nly as a check n perfrmance. Much in the same way as measurements and cntrls are used t maintain a quality assurance system. T achieve greater prductivity, three main areas can be targeted using cnditin mnitring. Reduce Maintenance Csts Reduce Dwntime Increase System Life 2

3 Reduce Maintenance Csts Mst belt cnveyr peratrs will have sme srt f maintenance prgram fr their cnveyr systems. It will generally include manpwer fr repairs, visual inspectins and clean up peratins as well as spare parts such as idlers, idler frames, pulleys, belting and splice kits. On cnveyrs which generally prvide few prblems the maintenance budget may be relatively lw and applicatin f cnditin mnitring n a significant scale may nt be justified. In many cases, hwever, the annual maintenance budget fr the cnveyr far exceeds the cst f a cnditin-mnitring prgram. The main cst savings t be made are in the reductin in labur fr majr repairs and inspectins, reduced spillage and a smaller spare parts inventry. Precise data regarding the cnditin f the belt will enable mre accurate estimates f the amunt f belting required in stck t deal with belt replacement requirements. Reduce Dwntime The cst f dwntime can be extremely high, in an ecnmic climate where many peratins are nly just viable, unscheduled stppages can mean the difference between prfit and lss. In many cases, if cnditin mnitring can reduce dwntime by as little as 1 hur ver the perid f the measurement (this may be 6 r 12 mnths), the cst f the measurement is recuped. Any reductin in dwntime after that is a cst saving t the peratr. Increase System Life A steel crd cnveyr belt system culd be expected t last apprximately 10 t 15 years, life spans fr fabric belts vary with the applicatin but a figure f 5 years is quite cmmn. This can be significantly shrtened by a number f unsatisfactry perating practices particularly incrrect material lading and failure t quickly repair damaged belt cvers. Cnditin mnitring will highlight the existence f such prblems befre they reduce the life f the cnveyr. A cnveyr n the NSW suth cast has been running fr ver 20 years with the use f cnditin mnitring playing a significant part in its cntinued reliable peratin. With a replacement cst in the millins f dllars the cst saving t the peratr f extending the life f this cnveyr is significant. Cmmn Belt Cnveyr Prblems Sme f the types f prblems that cnditin mnitring can help reduce r eliminate are: Failure f jints r splices Achieving high quality jints and splices in the field is a difficult task and ften these are the weakest pints in the belt. Cmbined with pr starting and stpping practices jint failure is a majr prblem fr many cnveyr installatins. Failure in parent belt Can result frm minr damage ging unrepaired fr a lng perid f time, the belt-reinfrcing layer eventually deterirating t the pint where the strength f the belt is cmprmised. Psitin and cnditin f the reinfrcing layer during manufacture is als imprtant and can be checked with NDT. Belt mis-tracking Alignment f splices and psitin f the reinfrcing layer in the rubber play a significant rle in hw the belt tracks. Tracking can als be affected by damage t the reinfrcing layer. Premature belt, idler r pulley wear An uneven distributin f tensin in the reinfrcing layer has been knwn t 3

4 prduce speed differentials acrss the width f the belt. The resulting accelerated wear f pulleys and idlers is ften extremely high. In many cases, the main purpse f the belt mnitring is t prvide accurate, quantifiable data n the belts cnditin. Based n this, the surce f a particular prblem can ften be identified and a strategy fr belt replacement r repair can be established. 4. NDT TECHNIQUES Figure 2 - Typical Belt Cnstructins Figure 2 shws three f the mst cmmn types f cnveyr belt. Cnveyr belt is nrmally cnstructed frm a high strength material vulcanised inside a rubber cmpund. The main area f cncern when discussing cnditin mnitring is the high strength material, ften referred t as the reinfrcing layer. S the fundamental requirement fr any cnditin mnitring equipment is the ability t detect the cnditin f the belts reinfrcing layer by penetrating the surrunding rubber cmpund. In additin t this basic design criteria, attentin must be paid t the cnditins under which the nn-destructive test equipment will be required t perate. Invariably cnveyr belts exist in harsh envirnments, ften the measuring equipment needs t be transprted lng distances t get t site and then may be carried by hand sme distance undergrund r ver rugh terrain. Pwer supply may nt be available, intrinsic safety may be an issue fr undergrund wrk and minimal interruptin t nrmal belt peratins is very imprtant in gaining access t the cnveyr ver the peratrs prductin cmmitments. On tp f all these issues, the reliability f the equipment is crucial. In many cases, the cst f getting t site t cnduct the measurement exceeds the value f the instrumentatin, there is n rm fr equipment failure. The frmula which has been used successfully is t keep the equipment simple, it must be nn-cntact and there must be a back-up plan fr the failure f any cmpnent in the measurement prcess. There are a multitude f methds, devices and cnfiguratins that can be utilised fr cnveyr cnditin mnitring. Fr a particular applicatin, ne r a number f these techniques may be emplyed t btain the required infrmatin. 4.1 Steel Crd Mnitring The mst suitable methds fr detecting the cnditin f steel crds are electrmagnetic, the fundamental reasn being the rubber is usually invisible t these types f sensrs. The mst cmmn methds fr NDT f steel crd cnveyr belting are listed belw. 4

5 Inductive Reluctance Induced Vltage Eddy Current X-Ray Ultrasnic Discussin here will be limited t the first three techniques. Eddy current and x-ray methds have been applied t steel crd belts in the field by thers with a gd deal f success. Eddy current devices, hwever, require mre cmplex prcessing than the methds currently used by the University f Newcastle and n this basis are nt in general use at this time. X-ray techniques prvide accurate data n the steel crds but it is a time cnsuming prcess mre suitable t detailed analysis f a single area than t mnitring f the whle belt. X-Ray vide equipment used n a number f sites requires the belt t be run at lw speed and prduces hurs f tape that must analysed manually. Figure 3 - Active NDT Sensr fr Steel Crd Cnveyr Belting The sensr illustrated in figure 3 is referred t as an active sensr. It generates a field that encmpasses the steel crd-reinfrcing layer f the belt. This type f sensr is well suited t measuring the psitin f the crds within the belts crss sectin and determining the mass f steel at a given belt crss sectin. This is particularly useful fr detecting areas f crrsin. 5

6 Figure 4 - Passive NDT Sensr fr Steel Crd Cnveyr Belting Passive sensrs, shwn in figure 4, utilise the magnetic characteristics f the steel crds t detect very small changes in the reinfrcing layer. The ability f this type f sensr t detect crd damage f nly a few strands have made this measurement the mst widely used f current cnditin mnitring techniques. 4.2 Fabric and Slid Wven Mnitring Cnditin mnitring f fabric and slid wven belting is mre difficult than measuring steel crds. The techniques available will invariably be sensitive t the cnditin f the rubber cvers as well as the reinfrcing layer. Methds which have been applied t this type f belting include: Capacitive Ultrasnic X-Ray Of these, capacitive sensrs have prven t be the mst reliable. The slight difference in density between the rubber cmpund and the reinfrcing layer is nt always sufficient t prduce gd quality x-rays and ultrasnic transmitters and receivers ften lack the sensitivity t achieve the required penetratin thrugh the rubber. The capacitive sensr is an active device which generates a high frequency field. The magnitude f the field is a functin f the belt characteristics and any changes in the belt r reinfrcing layer prduce variatins in the sensr utput. 6

7 Figure 5 - Active NDT Sensr fr Fabric r Slid Wven Belt 5. NDT Signals 5.1 General Measurement Principals All f the sensrs used by the University f Newcastle are mdular, lightweight units designed t be carried by ne persn. The equipment has been kept simple and t a minimum, the signals are recrded n data recrders, the prcessing and analysis is perfrmed back at the labratry. The mdular sensrs can be cascaded end t end t accmmdate any belt width, the small units used fr crd plane measurement can be used hand held r n a mtr driven carriage. As a general cncept t analysis f the signals, a perfect belt wuld prduce a cnstant utput frm the instrumentatin, any deviatin in the signal represents sme change in the belts prperties r cnditin. Figure 6 shws a typical system cnfiguratin fr cnveyr belt NDT. 5.2 Steel Crd Cnveyr Belting Mst f the NDT up t this pint has been cncentrated n steel crd cnveyr belts. The main reasn fr this is that steel crd belting is significantly mre expensive and is generally used n larger, mre cmplex cnveyr systems where perfrmance and reliability are f utmst imprtance. Measurements cnducted n steel crd belts have had ne r mre f the fllwing bjectives: Lcate and mnitr the deteriratin f all damage and crrsin in the steel crds thrughut the belt. Lk fr signs f deteriratin in splices. Islate and quantify a particular prblem. Measure the prfile and wear rate f the rubber cvers. Determine the psitin f the steel crds in relatin t the verall crd plane. 7

8 Figure 6 - Cnveyr Belt Cnditin Mnitring, System Setup Damage and Crrsin in the Steel Crds When cnsidering the cnditin f the steel crds in the parent belt, three items are usually f imprtance: Hw much damage? (i.e. hw many crds invlved) Where is the damage lcated? Is it deterirating r is it stable? The brader questin f what effect the damage has n the belts peratin usually requires further analysis, ften invlving cmputer mdelling and simulatin. In the majrity f cases, damage in the steel crds is the result f the rubber cver being penetrated and misture gaining access t the crds. Once the crds begin t crrde, the chemical reactin can cause delaminatin f the cvers and the misture can spread t ther crds. If the effected area is nt repaired a large number f crds can crrde t the pint where the strength f the belt is severely cmprmised. Anther majr cause f crd damage is the failure f the rubber cvers at cver jins. Once the cver has pened up at the jin, the ingress f misture quickly starts the crrsin cycle. There have als been a number f examples f crds failing due t fatigue, usually the result f being psitined utside the nminal crd plane. Figure 7 shws the sme f the signals prduced by damaged r crrded steel crds. The tp trace is an active sensr measuring the mass f steel present at any given crss sectin. The large spike is a splice, where as expected the amunt f steel is significantly greater than the rest f the belt. The step in the signal which fllws the splice shws where an edge crd has been ripped ff resulting in a reductin in signal level equivalent t ne crd. The bttm trace is a passive sensr, nce again the large signal is the splice, the smaller signals shw crd damage f varius magnitudes. The amplitude f the signal is prprtinal t the magnitude f damage, the lcatin f the site can be determined by measuring the distance frm the splice signal and scaling up by an amunt calculated frm the belt and chart speed. 8

9 Figure 7 - NDT Signals frm Damaged and Crrded Steel Crds 9

10 10

11 Figure 8 - Characteristic NDT signal fr crd plane deviatins High Gain Passive Sensrs Advances in the design f passive NDT sensrs fr steel crd belts has enabled detectin f crd plane anmalies which until nw have been difficult t measure. The new sensrs can detect the variatin in the field f steel crd which is undamaged but is ut f psitin in the crd plane. Figure 8 shws a labratry test t evaluate the sensrs where the psitin f a steel crd has been varied by 10mm ver a distance f 250mm. As the graph shws the slight change in the crds field is readily detected by the sensr. Figure 9 is field data f crd plane deviatins ccurring at regular intervals in a steel crd cnveyr belt. Figure 9 - Field measurements shwing regular crd plane deviatins 5.3 Fabric and Slid Wven Cnveyr Belts The principle use f NDT techniques with fabric and slid wven belting has been t determine the wrst area s f a particular belt in rder t prgram the required maintenance. With belts where the amunt f replacement is significant these measurements have been f great benefit t simply keeping track f the repairs. The mnitring equipment can be used t generate a belt "map", accurately laying ut the number f jints and where they are lcated. This type f infrmatin has prven invaluable t planning stck levels and maintenance crew requirements. Applicatin f ther measurements, belt acceleratin, mtr currents and belt tensins have been successfully cmbined with the capacitive sensrs t reduce r eliminate prblems with belt and jint failure n start-up, belt tracking r drive slip. Figure 10 shws the signal frm an active sensr munted n a fabric belt, the cnstant signal prduced by belt in gd cnditin can be seen clearly. The large deviatins in signal are caused by a number f different belt damage cnditins. 11

12 Figure 10 - NDT signal frm an active sensr measuring a fabric belt 6. NDT OF STEEL CORD SPLICES Splices are used in steel crd belts t jin manufactured lengths during installatin, t replace sectins f belting and t repair extensively damaged belting. While the theretical strength f the splice can be equal t that f the belt, generally fatigue and ther cnditins will mean the splice ften represents the weakest sectin f a cnveyr. 6.1 Steel Crd Splice Cnstructin A steel crd splice is cnstructed by interlaying the steel crds f each sectin as shwn in Figure 11, adding rubber abve, belw and between the crds and then vulcanising. While in peratin the belt tensin is transmitted frm ne sectin t the next by the shear strength f the rubber between the crds. The higher the expected belt tensin, the greater the length rubber required t transmit the frces and the lnger the splice will need t be. Figure 11 - Steel crd splice cnstructin, stage 1 splice 6.2 The Mechanism f Tensin Transfer 12

13 When a steel crd splice is subjected t an increase in tensin the length f the steel crd verlap decreases by a small amunt. This decrease in length is a result f the rubber defrming in shear. The actual change in length fr a particular splice will depend n a number f factrs including the number f crds, crd diameter, crd spacing, applied lad and the shear characteristics f the rubber. Figure 12 shws the relative mvement f crd ends when the splice is subjected t tensile lad. Crd mvement f between 1mm and 2mm has been bserved in splices subjected t peratinal tensins. Figure 12 (a). Steel crd splice with n lad (b). Steel crd splice under tensin 6.3 Current NDT Techniques Visual Inspectin The mst cmmn methd f checking splice cnditin is by visual inspectin. Irregularities in the surface f the cnveyr belt are nrmally an indicatin f adhesin prblems. Bulges in the belt surface are frequently caused by crds with pr adhesin pulling back frm the splice under tensin then nt being able t return t psitin as the rubber encraches n the vid left at the end f the crd. Dimples appear at the end f a crd where adhesin alng the crd is pr but gd at the crd end. Frequently, hwever, these indicatins are mst prminent in sectins f the cnveyr where access is pr and the speed f the belt make visual inspectins an unreliable methd f detecting a failing splice. Grid Line Methd A technique fr measuring adhesin lss in steel crd splices was described by Harrisn in 1983 [9]. It invlves marking ut an accurate grid n the surface f the belt in a lwtensin area f the cnveyr. The splice is then run up t a high-tensin area and the distrtin f the grid measured. This distrtin gives a direct indicatin f the splices lad sharing characteristics. 13

14 While this methd prduces gd results, it is limited by the need t stp the cnveyr and the fairly time cnsuming prcess f marking ut and measuring the grid. In the event f a particular splice being regarded as suspect by ther methds the grid line technique culd prvide accurate infrmatin n that splice. Bulge Detectin The mechanism which causes the steel crds in a failing splice t bulge is described in sme detail by Harrisn [9]. Fr the purpses f this paper it is sufficient t recgnise that the bulging f crds in a splice is a cmmn indicatin f imminent failure. Detectin f such a bulge by varius means, sme f which are shwn in Figure 13, can be utilised t shut dwn the cnveyr prir t a splice failure. X-Ray Figure 13 - Methds f Detecting a Bulging Splice X-Ray techniques are well suited t evaluating steel crd cnveyrs including the splices. Recent advances in x-ray equipment, in particular the running x-ray recrded n vide, have increased the applicatins fr this technlgy in the area f belt cnditin mnitring. Clse inspectin f the x-ray f a steel crd splice can reveal areas f pr adhesin between the rubber and the steel crds. This measurement, hwever, generally entails stpping the cnveyr r at least mving it at lw speed fr each splice. The analysis f the results is time cnsuming and requires sme expertise. Impact NDE 14

15 A methd f determining the adhesin between crds and rubber thrugh variatins in the stress velcity thrugh the belt was utlined by Harrisn in 1989 [10]. By strategically attaching accelermeters t the belts surface, the speed f a stress wave induced n ne side f the splice can be measured. Harrisn shwed that a nn-unifrm distributin f speed as measurements are cnducted acrss the belt indicate prblems with adhesin r crd placement. This test methd has been primarily used fr analysis f belt splices in the labratry. Magnetic Signature Analysis Nn destructive testing f steel crd cnveyr belts thrugh the analysis f magnetic signatures is a well-established practice. Applicatin f this technique t cnveyr belt splices can prvide accurate infrmatin n splice cnstructin (Harrisn, 1985 [11]), but s far has nt yielded a prven methd f determining the integrity f a splice. Trends regarding the de-magnetising f the steel crds as a result f crd mvement have been bserved during a number f field measurements. These trends ccur ver sme perid f time and the likelihd f a splice failing in between a series f measurements is high. Difficulty has als been experienced in magnetising the steel crds f a splice where significant mvement is taking place. While this is an immediate indicatin f pr adhesin, nly a small percentage f splices exhibiting this characteristic have been knwn t fail. This culd be regarded as a result f sufficient safety factrs being available in mst installatins t tlerate sme adhesin breakdwn in the splices. The main prblem with this analysis is that a splice suffering frm a breakdwn f adhesin will nt always exhibit these characteristics during the magnetising prcess. 6.4 A New Applicatin f Magnetic Signature Analysis A splice with a significant area f pr adhesin will nt share lad unifrmly acrss the width f the belt. This measurement technique evaluates the lad sharing characteristics f a splice withut the interruptins t nrmal peratins f sme f the methds discussed s far and has the ptential t prvide accurate infrmatin n the splice s integrity. The measurement technique present here is a variatin f magnetic signature analysis but the emphasis is n the change in the signature as the splice passes frm high tensin t lw tensin. The Field arund a Magnetised Splice A magnetised steel cable has a field similar t a bar magnet. One end will be a nrth ple, the ther a suth and the field will fringe utside the crd at the ends and at any damage r buckle alng the crds length. Of interest in splice analysis is the fringing at the crd end. The magnetic field intensity at the end f the crd is f a useable magnitude up t 200mm frm the crd and 300 t 400mm dwn the crd frm the end depending n the level f magnetisatin. 15

16 Figure 14 - Simplified view f the magnetic field arund a splice The magnetic field arund a splice is a cmpsite f the fields generated by each crd. Figure 14 gives a simplified view f hw the field f a splice is cnstructed. In reality the verall field will be mre cmplex as the magnetised crds interact with each ther but the diagram gives an indicatin f hw the crd end psitins determine the field shape. Field Distrtin frm Nn Unifrm Lad Sharina Wrk by Harrisn shwed a crd in a steel crd belt which des nt share lad puts a higher stress n the adjacent crds. This uneven lad equalises ver a number f metres f belting by crd elngatin (see figure 15). It is this difference in elngatin f a nnlad sharing crd which results in a slight difference in the psitin f the crd ends in a splice. Having established that the end f a crd which is nt sharing lad will be ut f psitin, the effect f this n the splice s magnetic field needs t be examined. Clearly a single crd ut f psitin by as little as 1mm will have a minimal effect n the magnetic field arund the splice. In rder t reach detectable levels, a number f crds will need t be ut f psitin. The sensitivity f the measurement is a functin f the number and size f sensrs. As a general guide, the sectin f splice nt sharing lad will need t be as wide as a single sensing element fr reliable detectin. 16

17 Figure 15 - Steel crd mvement resulting frm uneven lad sharing 6.5 The Measurement Technique Detecting the Magnetic Field Figure 16 shws the arrangement f the sensrs fr the carry and return strand f the cnveyr and Figure 17 is a typical splice signature fr a single sectin f the splice. The A sensrs are lcated n the carry side befre the drive r at a suitable lcatin in a hightensin area. The B sensrs are psitined near the take up r a lw-tensin area. The change in the directin and magnitude f the magnetic field as splice passes is detected by the sensrs and prduces a signal which is prcessed and recrded fr later analysis. The arrangement shwn in Figure 16 divides the belt int six equal sectins and wuld require 12 recrding channels. Data Analysis Figure 16 - Sensr arrangement fr magnetic field detectin This measurement technique requires cmputer aided analysis f the data. Fitting sensrs t ne side f the belt nly in different areas f the cnveyr make it difficult t match the results frm the A and B sensrs. This cmbined with variatins in belt tracking mean that averaging is required in interpretatin f the data. By dividing the width f the cnveyr int six sectins the minimum reslutin f the measurement is an area f adhesin lss equal t 1/6 the belt width. Given that mst cnveyrs are designed with a safety factr f between 6:1 and 10:1 the minimum reslutin f the measurement is well belw the failure pint f the splice. It shuld be kept in mind that the aim f the measurement is t highlight splices with abnrmally high distrtins in tensin distributin as ptential belt failure pints. The signal prduced by each sensr is a functin f the magnetic field surrunding that sectin f the splice. As this field is directly effected by the psitin f the crd ends, the signal can be used evaluate crd end mvement. A unifrm change in the signal frm 17

18 each sensr as the splice mves frm high tensin t lw tensin wuld indicate unifrm crd end mvement and unifrm lad sharing. The data is analysed by cmparing the distance between the peaks f the signals fr each sectin f the belt as the splice passes frm high tensin t lw tensin. Fr example, the signals fr a particular splice frm sensrs Al and B 1 (see Figure 16) are fed int the cmputer, nrmalised and displayed n the same screen. The distance between the peaks fr each signal is nted. A perfect splice wuld give the same signal variatin fr each pair f sensrs, 1 thrugh 6, cvering each sectin f the splice. The technique f cmparing the signals fr the splice in high and lw tensin allw any irregularities resulting frm splice lay up r the effect n the magnetic field f the cnveyed material t be dealt with during the data analysis. The measurement infrmatin is cntained in the signal variatin and the errrs are eliminated during the cmputatin. Figure 17 - Difference between splices signals taken in high and lw tensin Using the signal variatin the mvement f the crd ends can be determined. This cmbined with the rubber and crd characteristics can be used t calculate belt tensin fr each sectin f the splice. 7. SIGNAL ANALYSIS NDT signals frm cnveyr belting are cmplex and typically require sme expertise fr interpretatin. Develpment f analysis sftware has the ptential t enhance the presentatin f data btained frm NDT as well as reducing the reliance n the ability f the peratr during the analysis phase. The lng-term aim is an expert system which can be permanently installed n a cnveyr system and deliver infrmatin n the belts cnditin withut the need fr lengthy, manual interpretatin f signals. The first step in this prcess is the develpment f prgrams t assist in the analysis and presentatin f NDT signals. Current sftware can read field data frm the recrder and quickly quantify the magnitude and lcatin f all relevant signals. This infrmatin can then be presented in a number f ways depending n the requirements. Figure 18 shws the damage density alng the length f a particular cnveyr. The cmputer calculated the number f NDT signals abve a certain threshld fr every 50m f belting. The result is an indicatin f which sectins have the highest number f damage lcatins, which in this case did nt cincide with the largest magnitude lcatins shwn in Figure 19. The 18

19 peratr can nw prgram t repair the largest magnitude lcatins and replace the sectins f highest damage density. Figure 18 - Cmputer generated data n damage density alng a cnveyr Once the data is in the cmputer many ther frms f analysis can be quickly evaluated. Separating the number f damage lcatins n the left and right side f the belt has been used t identify prblems with lading. A particular sectin f the belt, fr example the belt edges, can be islated t lk at specific prblems. A belt which is mistracking can have a tracking measurement cmbined with data n the belt cnditin t assist in identifying the cause f the mistracking. A particular signal can be expanded n the cmputer fr detailed analysis, this culd include splice signals r large magnitude damage lcatins. Figure 19 - Cmputer generated data n damage magnitude alng cnveyr 19

20 8. CONCLUSION As develpment f bth sensr technlgy and signal analysis techniques cntinues the rle f NDT f cnveyr belting will expand. Already we have seen stringent tlerances placed n manufactured belting in regard t steel crd psitin. Such tlerances can nly be measured and cntrlled with the assistance f NDT. The use f NDT in the field has been and will cntinue t be a valuable tl in the peratin and maintenance f belt cnveyr systems. The applicatin f NDT fr belt cnveyr research will lead t better understanding f cnveyr characteristics and imprved design and cnstructin prcedures. This paper has utlined sme f the areas f advancement and research which are currently underway at the University f Newcastle. 9. REFERENCES 1. Rberts, A.W., Harrisn, A. and Hayes, J.W. Ecnmic Factrs Relating t the Design f Belt Cnveyrs fr Lng Distance Transprtatin f Bulk Slids, Bulk Slids Handling, Vl. 5, N. 6, Dec 1985, pp Pmfret, D. Realising Maximum Prductin Ptential with Safety, Engineering Safety Seminar, Dept. Mineral Resurces NSW, Penrith, May Harrisn, A. Predicting the Tracking Characteristics f Steel Crd Belts, Bulk Slids Handling, Vl. 10, N. 1, 1990, pp Harrisn, A. Stress Distributin in Steel Crd Belts with Crd Plane Defects and Inlaid Repairs, Bulk Slids Handling, Vl. 8, N. 4, 1988, pp Harrisn, A. A New Develpment in Fabric Belt Mnitring, Bulk Slids Handling, Vl. 8, N. 2, 1988, pp Kwun, H. and Burkhardt, G.L., Nn-destructive Measurement f Stress in Ferrmagnetic Steels using Harmnic Analysis f Induced Vltage, NDT Internatinal, Vl. 20, N. 3, June 1987, pp Cnveyr Belt Engineering Wrkshp, Gdyear Tyre & Rubber Cmpany. 8. Harrisn, A., A new technique fr measuring lss f adhesin in cnveyr belt splices, Aust. J. Cal Mm. Tech. Res., N. 4 (1983). pp Harrisn, A., Examinatin f Adhesin Failure in belt splices by impact NDE, Prc. Cmpsites Asia Pacific Cngress 1989, Adelaide, Vl. 2, pp Harrisn, A., Testing steel crd belt splices with a magnetic cnveyr belt mnitr, J. Nn destructive Evaluatin, Vl. 5, N. 1, 1985, pp Lubrich, W., Theretical Analysis f the Tensile Strength f Steel Cable Cnveyr Belt Jints, Brunkhle, Warme und Energie, Vl.12, Nv 1960, pp Harrisn, A., Perfrmance f Crded Cmpsites with Damaged and Misaligned Reinfrcement, Prc. Cmpsites Asia Pacific Cngress 1989, Adelaide, Vl