Engineering Failure Analysis 39 (2014) 135–148

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Engineering Failure Analysis

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Failure analysis of irreversible changes in the constructionof rubber–textile conveyor belt damaged by sharp-edgematerial impact

http://dx.doi.org/10.1016/j.engfailanal.2014.01.0221350-6307/� 2014 Elsevier Ltd. All rights reserved.

⇑ Corresponding author. Tel.: +421 6023147.E-mail address: gabriel.fedorko@tuke.sk (G. Fedorko).

Gabriel Fedorko a,⇑, Vieroslav Molnar a, Anna Grincova b, Miroslav Dovica c, Teodor Toth c,Nikoleta Husakova a, Vladimir Taraba d, Michal Kelemen c

a Faculty of Mining, Ecology, Process Control and Geotechnology, Technical University of Kosice, Park Komenskeho 14, 042 00 Kosice, Slovak Republicb Faculty of Electrical Engineering and Informatics, Technical University of Kosice, Letna 9, 042 00 Kosice, Slovak Republicc Faculty of Mechanical Engineering, Technical University of Kosice, Letna 9, 042 00 Kosice, Slovak Republicd Continental Matador Rubber, s.r.o., Terezie Vansovej 1054, 020 01 Puchov, Slovak Republic

a r t i c l e i n f o a b s t r a c t

Article history:Received 23 November 2013Received in revised form 5 January 2014Accepted 28 January 2014Available online 6 February 2014

Keywords:Conveyor beltDamageMetrotomographySharp-edged materialAnalysis

One of the most frequently damage of rubber–textile conveyor belt is caused by sharp-edgematerial impact. The paper deals with study of process of irreversible changes formation inthe internal structure of rubber–textile conveyor belt caused by sharp-edge materialimpact. The aim of the paper is knowledge of damage process which is required for thecorrect regulation of operation conditions for conveyor belt. The aim is to determineconditions caused this type of damage (height of impact and weight of material impact).Non-destructive methods (computer metrotomography) is used for study of changes inthe construction of conveyor belt. The paper presents theoretical and experimentalevaluation of the process of conveyor belt damage.

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction

Belt-conveyor, which has advantages of long transmission distance and big power, is one of the most important bulkmaterials handling equipment [1]. In the working condition of conveyor belt, the conveyor belt is exposed to operation con-ditions which cause its wear and damage. The wear on conveyor belts is characterized by the almost evenly distributed abra-sion of the covers, and by local damage, such as tears, nicks in the cover, penetration of the belt and longitudinal slitting [2].The loading station is the point at which the conveyor belting is most exposed to damage. Dynamic loads produced by fallingsharp-edged lumps of the material handled result in punctures, slits of the belt cover and damage to the cables [3]. It appearsfrom this that detecting the state of conveyor belt is important in production process [4,5]. Several protection systems existfor conveyor belt control and monitoring.

Xu et al. [6] realized design of protection system for belt conveying. The protection system can automatically detect, diag-nose corresponding fault, and give alarm signal with sound and light to stop the defect belt machine in due course. Li et al.[4] designed automatic defect detection method for the steel cord conveyor belt based on its X-ray images. Li et al. [7] dealtwith the problem of protection systems for belt conveying in the work Design of Online Monitoring and Fault Diagnosis Sys-tem for Belt Conveyors Based on Wavelet Packet Decomposition and Support Vector Machine. Intelligent detection system

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for mine belt tearing based on machine vision was designed by Li et al. [8]. For design of protection system for belt conveyingis indispensable more detailed study of the problem of conveyor belt wear. Gurjar et al. [9] dealt with research of failures ofbelt conveying system in thermal power plant. They analyzed technical characteristics of coal handling system and operatingcharacteristics of relevant machinery and equipment and described the maintenance method of prevention and eliminationfailure to ensure the operation of belt conveyor.

Xie et al. [10] realized the study on conveyor belt materials to heat-resistant performance characteristics. Fedorko et al.[11] presented experimental measurements of selected properties of pipe conveyor belts, which are dynamically damaged.Recent years presented several papers dealing with the problem of conveyor belt wear and they used different researchmethods and procedures. Andrejiová et al. [12], dealt with analysis of non-operating states causes in the belt conveyingby basic methods of quality control and they used Saaty method [13]. Andrejiová and Marasová [14] applied multiple regres-sion method in their works.

Lowndes et al. [15] made experimental and computational study conducted to characterize the initiation and spread offire along the upper and lower surfaces of a conveyor belt mounted within a ventilated full-scale experimental fire test gal-lery. Reicks et al. [16] made a comparison of calculated and measured indentation in rubber belt covers. Zimroz and Król [17]studied failure analysis for condition monitoring. Falkenberg and Wennekamp [18] dealt with doping of conveyor belt mate-rials with nanostructured fillers to adapt innovative performance characteristics.

It is possible to apply different methods for research and monitoring of conveyor belts damage process [19,20]. One ofthese is the use of specially designed test stand as it described Ballhaus [21]. The next alternative of study is utilizationof different progressive research technologies. Fedorko et al. [11] dealt with experimental analysis of inner structure of con-veyor belt by computer tomography. Ákos [22] dealt with problems of measurement by this computer measuring method indetail. Blazej et al. [23] used for research of steel-cord conveyor belts damage multi-channels NDT signals. Pascual et al. [24]made analysis of transient loads on cable-reinforced conveyor belts with damping consideration. Liu et al. [25] gave detailintroduction to several types of broken belt protectors used in home, analyzed its working principle and advantages and dis-advantages, provide certain reference for the user choice. Moni et al. [26] presented results of the measurements on anexperimental model conveyor with a closed material transport way. Czuba and Furmanik [27] presented an analysis of grainmotion in a parallel chute and a methodology of calculating the impact angle and tangential speed of the grain at the point ofcontact with the receiving conveyor belt. Based on calculations made on developed model it was determined which of thebasic input parameters have the most significant impact on the changes of observed output parameters.

Research of irreversible changes in the structure of conveyor belts is needed in terms of describing and understanding ofthe process of their procedure during conveyor belt operation [28]. In recent times it is not known presented work whichshould be comprehensively addressed this problem. All previously published studies deal with this problem only marginally.

2. Material and methods

2.1. Problem formulation

The aim of this paper is knowledge of the gradual process of damage which is needed for correct regulation of operationconditions for rubber–textile conveyor belt.

During the operation of belt conveyors with rubber–textile conveyor belt in difficult conditions is the most common dam-age, the damage which is induced by sharp-edge falling material. The primary signalization of damage shows by small localsurface defects of the covering layer, different intensity, depending on the variability of the place of impact and falling mate-rial fragmentation.

Damage of covering layer presents only a secondary problem for belt conveyors operators. By the effect of circulate im-pact of material on the sample, or more precisely approximately the same place, irreversible destructive processes are gen-erated in the conveyor belt, which give rise to degradation of conveyor belt construction and by that it conduces to itsdamage. Within the frame of research, aimed at detailed knowledge and description of these processes, it was necessaryto monitor the interaction among falling material and subsequently induced changes in the structure of conveyor belt.

2.2. Description of the experiment and methods

Monitoring of irreversible changes in the internal structure of rubber–textile conveyor belt by sharp-edge material im-pact was realized by the series of experiments with the same initial conditions by the scheme DOE presented by Fig. 1. Con-ditions of experiment simulating real operation conditions. Therefore, the place of impact was periodically repeated duringthe experiment. Subsequently it was realized mutual comparison of tested samples. The experiment was finished at the mo-ment of conveyor belt breakdown. Metrotomography was used for visualization and assessment of internal structure dam-age as expert method.

X-ray computer tomography (CT) is a non-destructive measuring method for the control of internal and external geom-etry of component parts. We can get complete three-dimensional volume model of the scanned measured sample of con-veyor belt by CT using in a short time. In comparison with other measuring techniques, for example with touch-sense,the component parts are scanned by CT technique with high information about the material density. This advantage,

Fig. 1. Block scheme of DOE.

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together with the factor of time allows wide use of CT method in different industrial areas. CT method performance is ef-fected by factors regard to hardware (source of X-ray, accuracy of rotating table, X-ray detector), software and data process-ing, environment factors (temperature, moisture), geometry and material of measured object and the operator [29].

Following of these facts for monitoring of the course of irreversible changes in the internal structure of rubber–textileconveyor belt it was used the measuring machine METROTOM of the company Zeiss with the emitter power 225 kV/225 W and detector resolution 1024 � 1024 [30].

2.2.1. Aim of the experimentIt was defined the expected aim of the experiment: analysis of conveyor belt damage. On this base edge conditions were

subsequently defined. Edge conditions determined height of drop hammer impact, weight of the drop hammer, size ofstretching force and determination of frequency for data record during the experiment. The aim of the experiment was toinvestigate influence of energy of fall on the degradation of mechanical properties of the conveyor belt.

2.2.2. Preparation of test specimenPreparation of test specimen included its extraction from the conveyor belt. Selection of the test specimen was planned

with reference to the operation conditions of stressed conveyor belt. At this stage the specimen was visually controlled, itwas investigated visible cracks on its surface. At the same time the specimen surface was cleansed.

2.2.3. Fixation of the test specimen and preparation of the drop hammerThe test specimen was fixed to the jaws of the test stand, marked and stretched by the stretching force equals to 1/10 of

the conveyor belt strength. The drop hammer was weighted by necessary weight (determined on the basis of the aims of theexperiment) and it was uplifted to the required height.

2.2.4. Test procedureThe drop hammer was released and it hit on the test specimen by free-fall. The aim was to monitor the processes related

to the simulated impact of the sharp-edge material on the conveyor belt.

2.2.5. Data record IMonitored data were recorded to the data file. During the drop hammer fall with the frequency 1 kHz these data were

recorded to the data file: time, height of the drop hammer, impact force, stretching force. Record of the drop hammer heightby its rebound from the test specimen presents the greatest benefit of the paper. At the same time it was realized a visualrecording of the test specimen damage.

2.2.6. Belt breakdownIt was visually assessed the test specimen damage after the drop hammer impact. In the case of the test specimen non-

breakdown by the effect of the drop hammer impact, the test was repeated under the same edge conditions until the testspecimen breakdown and the number of impacts was increased by one.

2.2.7. Test specimen releaseAfter the drop hammer impact, or the test specimen breakdown the testing procedure was finished and the test specimen

was released from stretching jaws of the test stand.

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2.2.8. X-ray analysisAfter the test specimen releasing it was decided about the metrotomographic measurement continuation or visual control

on basis of the damage level.

2.2.9. Visual controlVisual control was used for the assessment of top covering layer damage for the series of measurements realized by drop

hammer fall from the height 1.6 m and 1.8 m.

2.2.10. Preparation of metrotomographic sampleFor the preparation of metrotomographic sample it was selected a piece with sizes 150 mm � 150 mm by deliberate

selection from each test specimen, which included the place of drop hammer impact on the test specimen or the place ofbreakdown on the test specimen.

2.2.11. Metrotomographic measurementMetrotomographic measurement was realized on the basis of generally applicable methodology. Fig. 2 presents the meth-

odologies of measurement (light) and testing (dark). The aim of metrotomographic measurement was to describe the state ofirreversible changes in the internal structure of conveyor belt due to repeated fall of sharp-edge material.

2.2.12. Data record IIInformation and parameters about the changes in the structure of rubber–textile conveyor belt were recorded by com-

puter metrotomography. Information was presented above all in graphical form.

2.2.13. General assessment of experimentGeneral assessment of experiment includes sum of all information which are the object of the step Data record I and Data

record II.

3. Theory/calculation

3.1. Analysis of the causes of rubber–textile conveyor belts damage

Process of conveyor belt damage is possible to characterize on the basis of decomposition into partial causes of damage bythe cause and effect diagram presented by Fig. 3.

Fig. 2. Modified methodology of measurement (light) and testing (dark) [31]. (See above-mentioned reference for further information.)

Fig. 3. Cause and effect diagram of rubber–textile conveyor belt damage.

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Damage of conveyor belt is identified by eight key factors, without determination of the sequence in term of their dom-inance. By cross-combination it comes to damage formation which is mainly irreversible.

Installation, as a factor influencing on the conveyor belt damage is mainly reflected in the time of conveying device to theplanned location. Improper installation can cause breakdown of the internal structure of conveyor belt, which can graduallyincrease up to catastrophic proportions. At the same time poor-quality or unsystematic realized installation can cause dam-age of basic constructive elements of belt conveyor (for example rollers displacement, construction deformation) and it re-sults in incorrect conveyance of infinite conveyor belt and by that increased damage of conveyor belt‘s edges etc. (Fig. 4).

Human factor is the first identified cause. Its influence on the conveyor belt damage relate mainly with qualification ofservice, responsibility and length of service. From the perspective of conveyor belt operator it is a factor that can be effec-tively eliminated by selection of suitable operating personnel and by organizing of regular education and training. The wholeprocess can be also more effectively by participation of conveyor belts producers.

Transported material exercises an influence to the conveyor belt damage by its composition, type, granularity, transportedamount, powder density and temperature. It is the second factor which operator of conveyor belt can eliminate by selectionof suitable type of conveyor belt and construction of the place of shifting. Producer of conveyor belt can help to eliminate thisfactor by suitable consultation activity and formulation of recommendations for users based on the realization of experimen-tal tests.

Production has direct influence on the process of conveyor belt damage by used technology, meeting norms and standardsof quality, material parameters (modulus of elasticity, length, thickness, weight, specified load). Influence of the productionfactor on conveyor belt damage can influence producer at most. User of conveyor belt can influence this factor at least. It ispossible only on the basis of own knowledge and also by obtained information data, but these data can be distorted in a greatmeasure.

Technological process presents the latest identified exercising an influence on the process of conveyor belt damage. In thecase of improper selection of conveyor belt type for concrete technology, this is influenced by systematic damage, which canend by its total damage. Similarly, conveyor belt is also influenced by continuous changes which are realized in thetechnological process regardless of used conveyor belt.

Fig. 4. Example of conveyor belt damage by improper installation.

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Maintenance and monitoring relate with regular prophylactic inspections of conveyor belt, regular change of damagedparts and lifetime monitoring. This factor markedly influences the degeneration process for rubber–textile conveyor beltand operator can influence its effect in a great measure. The used methodology is one of the key factors. Its suitable selectionsignificantly influences operational–economic aspects of belt conveying. Operator must take into account the fact that thecosts for the process cannot exceed benefits from this process. Precision and regularity of the maintenance and monitoringprocess should be adequate for operation conditions. Formulation of these facts is based on the consultations with conveyorbelts producers.

Service equipments also significantly influence conveyor belt damage process. It includes influence of hopper, shifting,cleaners of conveyor belt, support rollers, stretching devices etc. Operator can correct the influence of service equipmentson the process of gradual degradation of rubber–textile conveyor belt in the first place, but in the first phase of conveyingsystem design, this process can be corrected by realization or constructive team.

Operation conditions relates with specified belt load keeping, way of stretching, automatization of operation, way of con-trol, environment influence and ecological demands. This group of factors is influenced by designer of the conveying systemin the primary phase, namely by selection of suitable type of conveyor belt. This responsibility is shifted to the operator ofconveying system later during the user phase of the belt conveyor.

3.2. Description of the belt structure

Upper covering layer, lower covering layer, textile insert, adhesive layer, protection side edge and additional structuralcomponents (aramid bumper etc.) form the structure of rubber–textile conveyor belt (Fig. 5).

It is possible to identify four basic zones A, B, C and D in terms of the defects occurrence and damages by influence ofoperation.

The fist zone A is the area which keeps in touch with material – upper covering layer. The most frequently damage of thiszone is a damage caused by transported material breakdowns, cracks by high temperature, wear, etc.

The second zone B is presented by lower covering layer, this is the area which is in contact with rollers. This area is char-acteristic by the type of wear – abrasion (gradual decrease of the thickness of the lower covering layer). Abrasion size isincreasing by the number of conveyor belt rotations and it is directly proportional to the size of the rollers pollution.

The third zone C, with frequency of conveyor belt damage, is a protection side edge. This zone is typical by damages whichare caused by abrasion of conveyor belt edges to constructive elements forming the route of conveyor belt. Minimalization ofthis damage is possible by installation of safety elements, or by supplementary modification and setting of conveyor belt.

The last fourth zone D is presented by the internal structure of conveyor belt (textile insert, adhesive layer, aramid bum-per, etc.). It is the zone in which it is technologically very difficult to identify damage of operational conditions. However, thiszone has a decisive influence on the total strength and flexibility of the conveyor belt and the ability to transfer load by ten-sile forces.

Operated conveyor belt is characteristic by frequent damage of several zones simultaneously. Breakdown of conveyor beltis the most frequent type of this combined damage and it is caused by sharp-edge material impact in the place of shifting.The breakdown causes combined damage of the zone A, D and subsequently the zone B.

This type of rubber–textile conveyor belt damage can be effectively minimized by right construction of the conveyor beltand selection of optimal operational conditions. Design of the right construction and operational conditions is possible torealize on the basis of conditions investigation caused this process and search dependences among key parameters, suchas relationship among the weight of sharp-edge material, height impact and size of conveyor belt damage.

Fig. 5. Conveyor belt cross-section with marked zones of damage frequency.

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4. Results

The range of the conveyor belt damage is largely determined by the size of the kinetic energy of the material (body) fallingby free fall to the conveyor belt. From the physical point of view on the basis of mechanical energy conservation by negligibleinfluence of the environment (environment resistance) it is possible the size of kinetic energy Ek of the body with the weightm right before body impact with the speed m on the conveyor belt to compare with the size of potential energy Ep of the bodyright before the body falling from the height h. Expression (1) is valid at ignore of energy dissipation by slide friction.

So:

Ek ¼12

mm2 ¼ mgh ¼ Ep ð1Þ

The same is true for bounce of the body from the conveyor belt. In this case it is not a free fall but it is shot up. By thisaction the falling body hands the part of mechanical energy in the conveyor belt, and it comes to specific damage of a con-veyor belt and the remainder of energy is used for material bounce from the conveyor belt. During this experiment it wasregistered the height of impact and bounce for the determination of the size of potential energy in extreme positions.

The object of the experiment was the test specimen of the conveyor belt P2500 4 + 1;8 + 4A with dimensions1400 � 150 mm. It is a common type of a conveyor belt with the strength 2500 N mm�1. The internal construction of thebelt is created by four textile inserts which create its frame and one aramid bumper for increase of breakdown resistance.This type of conveyor belt is often applied in various mining operations or quarries.

The aim of the experiment was to determine impact force and describe the course of damage for the test specimen of theconveyor belt with repeated drop hammer impact on the identical place until the breakdown. The breakdown was repre-sented by the damage of all constructive parts of the test specimen of the conveyor belt, i.e. the top covering layer, frameand bottom covering layer. The weight of the drop hammer is 82 kg. This process was preceded by several measurementswith determined initial conditions for demanded breakdown formation.

The drop hammer fell from the height 1.6 m in the first series of measurements, it corresponds with impact energy 1287 J.The experiment was repeated nine times, the type and size of damage were evaluated only visually. The next damage of thetop covering layer was documented by photos. There was not a breakdown by this process (Fig. 6).

Fig. 6. Sequential damage of the top covering layer of the conveyor belt P2500 4 + 1; 8 + 4A with the height of impact 1.6 m.

Fig. 7. Graphic presentation of energy changes by the drop hammer impact from the height 1.6 m.

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Fig. 6 presents gradual increase of top covering layer damage by repeated simulated impact of the sharp-edge material.The intensity of the range of damage increases with repeated impacts of the test specimen at the direction into the conveyorbelt. The increasing level of the damage was declared with sequential formation of cracks of which surface range increasedby increasing number of impacts.

After the last, the ninth repeated experiment, it was stated, that the conveyor belt was not punctured and it had only vi-sual damage of the top covering layer. The damage of the bottom covering layer was not visually identified and on the basisof this fact, we determined a hypothesis, that it was not markedly damaged the internal structure of the conveyor belt. Thisdamage would enable the next use of the conveyor belt by renovation in real operational conditions.

Energy change, which the conveyor belt was able to pass on the drop hammer by bounce, is presented by Fig. 7.It was confirmed a hypothesis on the basis of monitoring of the course of particular curves of impact energy during exper-

iments, the first impact caused damage only of the top covering layer and the existence of the breakdown was not registered.The energy of bounce is nearly constant from the fifth impact by the graph of Fig. 7. It formed the supposition that repeatedexperiment did not cause conveyor belt breakdown by impact energy 1287 J.

In the second series of measurements the drop hammer fell from the height 1.8 m, which in this case equals to the impactenergy 1448 J. The experiment was repeated only four times, the type and size of damage were evaluated only visually, whatdocuments four photos. The fourth experiment was determined by the breakdown formation.

Fig. 8 presents sequential damage of the top covering layer of the conveyor belt. The damage showed by formation of localdeformation which copied the form of the used impactor. The second symptom signalizing damage, is a sequential extensionof symmetric cracks, their intensity was increased by repeated impacts. By contrast to the previous series of experiments, inthis series after the second retry the damage of the top covering layer was of such range that it was possible to monitor theinternal structure of the conveyor belt. This fact was more intensive after realization of the third retry. On this basis, it waspossible to state that the test head of the impactor with the most probability damaged the conveyor belt frame, respectivelyits part. Further evaluation was not possible to realize by visual control. Realization of the fourth retry caused the conveyorbelt breakdown, and it confirmed the failure of the conveyor belt construction.

Energy change by drop hammer impact from the height 1.8 m which the conveyor belt was able to pass to the drop ham-mer during the bounce is presented by Fig. 9. We can monitor some decrease of this energy by the curves which character-ized the second and third impact. As the cause of this fact it was defined hypothesis that it was caused by the result ofcreated irreversible destructive processes in the internal structure of the conveyor belt. During the fourth impact, the beltwas punctured and this fact is presented by zero size of impact energy. Formulated hypothesis was confirmed by the secondand third impact.

It appears from this the fact that the results of the visual control and graphic records evaluation signalized gradual pro-gress of the conveyor belt internal structure damage which caused its breakdown.

In another series of measurements the drop hammer fell from the height presented by the Table 1 with the same weightof the drop hammer as it was in previous experiments, i.e. 82 kg, but the damage was evaluated not only visually, but also byX-ray computer tomography.

For assessment of the level of damage for the test specimen by X-ray computer tomography it was used the function ofextraction except for views and cross-sections. The extraction is a function of a special software for processing of measure-ments by metrotomograph and it allows to create a view of the test specimen (rubber and textile) also from particular partsof material separately, and it is not necessary to separate by physical process individual parts of the material. By this functionit was possible to analyse the level of rubber–textile conveyor belt structure damage in more detail and to monitor damagesof layers across the conveyor belt (Fig. 10).

Fig. 8. Sequential damages of the top covering layer of the conveyor belt P2500 4 + 1; 8 + 4A by the impact height 1.8 m.

Fig. 9. Graphic presentation of energy change by drop hammer impact from the height 1.8 m.

Table 1List of the other realized experiments and their results.

Height of drop hammer impacts (m) Number of drop hammer impacts (–) Visual assessment of damage Mark of test specimen

1.9 1 Damage of TCLa and a part of frame 190/11.9 2 Damage of TCL and a part of frame 190/22.0 1 Damage of TCL 200/12.0 2 Breakdown 200/22.1 1 Breakdown 2102.2 1 Breakdown 220

a TCL- top covering layer.

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The final images of the test specimens arranged by the time sequence respect the test course and the same images of sam-ples were used for presentation of a destructive effect of the sharp-edged material impact.

By the experiment, where the drop hammer fell from the height 1900 mm to the conveyor belt, it was created a markeddamage in form of used impactor as a result of drop hammer impact on the conveyor belt in the bottom covering layer. It was

Fig. 10. Example of extraction function use for analysis of conveyor belt test specimen damage.

Fig. 11. Analysis of the sample 190/1 by X-ray computer thomography.

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possible to monitor by applied method of extraction that the damage did not include only the area of the top covering layer,but also the construction of the conveyor belt (Fig. 11).

After the realization of the experiment with two impacts of the drop hammer from the height 1900 mm with the impac-tor on the test specimen, the damage of the internal structure of the conveyor belt was more expanded. The impactor brokethrough to depth equals to half the conveyor belt thickness. The top covering layer was markedly damaged by the influenceof the impact (see Fig. 12).

In case that the similar type of damage is in the real operational conditions, it is possible on the basis of the determinedrange of the conveyor belt frame damage by the method of extraction, to suppose the next continuation of the process of theconveyor belt gradual degradation. This fact is more highlighted by other factors, such as influence of transported material,

Fig. 12. Analysis of the sample 190/2 by X-ray computer thomography.

Fig. 13. Analysis of the sample 200/1 by X-ray computer thomography.

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eventually weather conditions. If this process is not stopped by right technological action, it will gradually extend up toconveyor belt disruption, or to gradual separation of particular layers of the conveyor belt.

For increase of operating safety for conveyor belt it was required to submit this process to the next testing with the aim toidentify the height which causes breakdown of this type of rubber–textile conveyor belt. Therefore the experiment was real-ized at the same conditions but the height of impact was increased to 2000 mm, which at the same time increased the size ofthe impact energy.

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Fig. 13 presents the test specimen, it is evident very extensive penetration of the conveyor belt by the test impactor fromthis. It results from the presented results that the impactor penetrated completely through the top covering layer and frameat the cross direction of the conveyor belt test specimen and it stopped at the top part of the bottom covering layer. In thisregard it was created a defect in the internal structure and its basic characteristics was a break of the parts of fibres whichcreate the frame of the conveyor belt. At the same time, we can suppose by detailed analyse of images obtained by computermetrotomography that the next accompanying effect of the impact energy influence on the conveyor belt was gradual startof separation of the conveyor belt layers which create its internal structure.

From the next analysis of available views it is possible monitor that the total strength was greatly disrupted and the belthas undisturbed only the bottom covering layer in the defect place but this part of the conveyor belt can not reliably cover itsstrength and at the same time we can monitor disruption of consistency and compactness of the layers.

On the basis of these results it was continued with the research with the aim to focus on the fact that in the case of tworepeated impacts on the identical place of the conveyor belt it occurs to its breakdown or energy caused by the drop hammerimpact causes only extension of existing damage of the conveyor belt. This idea was realized with the aim to answer to thequestion how it is necessary to proceed by formation of identical type of damage in real conditions. It is possible to solve thisproblem by two ways, the first way is the extraction of the damaged part of the belt and re-connect the belt and the secondway is the next operation. The final damage of the analyzed test specimen of rubber–textile conveyor belt after two repeatedidentical drop hammer impacts is presented by Fig. 14.

The drop hammer broke down the test specimen of the conveyor belt by the second impact to the identical place as it wasby the first impact. Re-application of the extraction method by analytic software metrotomograph we can monitor irrevers-ible and devastating changes in the textile frame of the conveyor belt. The range of damage is very good visible from all viewspresented by Fig. 14. It appears from this, that repeated impact of the drop hammer caused extraction of a significant numberof fibres in all directions. It was completely disturbed the internal structure of conveyor belt, and the part of top coveringlayer was extracted. From the views it is possible to suppose that the disturbance of conveyor belt structure in not onlyin the place of simulated impact of the sharp-edge material, but it continues at longitudinal and cross direction out of theconveyor belt. It means that the homogeneity in the surrounding of the place of impact is markedly changed.

If this kind of damage was ignored and the conveyor belt was also operated, the damage would be expanded at the lon-gitudinal direction by the influence of tensile force and it would be separation of frame layers, top and bottom covering layer.By this process the conveyor belt would destroy gradually and it would need change. The speed of this process is size andnumber of damages dependent.

Because of the previous measurements results confirmation it was realized impact test from the height 2000 mm and2100 mm at the end of testing. The main goal of the measurement was to confirm the hypothesis that impact of the drophammer with the same weight as it was in the previous experiments from the height of 2000 mm causes immediately break-down of the test specimen.

Realization of these experiments confirmed this hypothesis. As in the case of the drop hammer impact from the height2100 mm, and also from the height 2200 mm, it came to immediate damage of the conveyor belt test specimen by break-down. The final damage of the test specimen by drop hammer impact from the height 2200 mm is presented by Fig. 15.

Fig. 14. Analysis of the sample 200/2 by X-ray computer thomography.

Fig. 15. Analysis of the samples 220/1 by X-ray computer tomography.

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It is clearly visible damage of the test specimen from the presented results. Edges of the place of damage are relativelyclean in the result of impact energy and also edges of impactor which simulated the sharp-edge material. For better high-lighting of damage level of the complex test specimen it was not used the method of extraction for the analysis.

5. Conclusion

Process of irreversible changes formation in the internal structure of rubber–textile conveyor belt caused by sharp-edgematerial impact is a complex problem. Its formation is caused by combination of factors (height of impact – weight ofimpacting material – number of impacts to the identical zone). In this way the conveyor belt is marked by changes whichcan damage conveyor belt immediately or during its next operation.

For increase of operational reliability of conveyor belts, for better understanding of destructive processes in the conveyorbelt, it is required detailed study, suitable use of new and progressive technologies, such as computer metrotomography.Interest for realization of these researches is on the part of conveyor belt producers, designers and operators. Study of theseproblems can present generally true postulates but they must be further examined in relation to the concrete type and con-crete operational conditions.

Suitable selection of conveyor belt type by transported material and set initial conditions (weight of flatling material,height of impact) in connection with the research of conveyor belts damages by breakdown can eliminate these damages.By experiments it was determined by which limiting initial conditions (weight, height) it comes to breakdowns by repeatedtests. Users can determine on the basis of this fact acceptable height of shifting and by the help of crushers modify the weightof flatling material and in this way there is no damage of conveyor belt by breakdown.

The article presented realized experiments for rubber–textile conveyor belts P2500 4 + 1; 8 + 4A. For a different type ofconveyor belt it will be referred other initial boundary conditions.

Acknowledgments

This work is a part of these Projects VEGA 1/0922/12 Research of effect of material characteristics and technologicalparameters of conveyor belts on size of contact forces and resistance to motion in pipe conveyors with experimental andsimulation methods, VEGA 1/0085/12 New strategy for effective measurements with coordinate measuring machines withmulti sensor systems, VEGA 1/0258/14 Study of input parameter relations for interoperable transport effectivity based onmathematical model application, KEGA 005STU-4/2012 Virtual laboratory for 3D coordinate measurement, University Sci-ence Park TECHNICOM for Innovation Applications Supported by Knowledge Technology, ITMS: 26220220182, supportedby the Research & Development Operational Programme funded by the ERDF.

148 G. Fedorko et al. / Engineering Failure Analysis 39 (2014) 135–148

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