R. Błażej

Novel Approaches for Processing of Multi-Channels NDT Signals for Damage Detection in Conveyor Belts with Steel Cords

Belt conveyors are one of the most popular methods of material transport in many branches of industry, especially in mining. The average length of mining belt conveyor is about 1000 m. Taking into account that total length of transportation ways in averaged mine can approach several dozen of kilometers and network of several conveyors may cover large area, maintenance of such specific transportation system is very difficult. In this work we propose an automatic multi-channel system for data acquisition and processing for damage detection in belts. Belts with steel cords are considered here, they consist of top and bottom rubber covers and steel cords in between them. Due to many reasons (mainly sharpness of transported materials) covers may be damaged and it may initiate degradation process or straight damages in steel cords. Properties of steel cords are therefore crucial for overall strength of belts, if they are damaged, it may cause catastrophic failure of the whole conveyor. So, monitoring of belts conditions is a crucial issue. We proposed a monitoring system that measure and process data from array of magnetic sensors. The system allows to acquire up to 24 channels of NDT signals and uses automatic algorithms to process them in order to get information about begin of the belt loop, location of joints of particular belt segments and the final location and size of damages related to corrosion or cuts of steel cords inside belts. These techniques will be presented in the paper. Our approach has been validated in a lignite mine for several conveyor belts.

Operational Safety of Steel-Cord Conveyor Belts Under Non-stationary Loadings

To ensure the safe work of a conveyor high values of a conveyor belt safety factor (BSF) are applied for obtaining peak tensions and belt strength. The BSF of steel-cord conveyor belts is derived from the splice dynamics fatigue strength (as identified by the laboratory tests that were made almost half a century ago), as well as degradation from age, factory and field installation error factors and non-steady momentary factors. The users’ experience suggests that the steel-cord belt tensile strength is overestimated, especially for the long, high capacity conveyors. The authors propose the use of the recently implemented complex methods of steel-cord belts in situ condition monitoring methods for identification of the actual belt tensile strength and the accurate methods of calculation of a conveyor’s resistances to motion and belt tension in order to identify and monitor the operational belt safety factor (OBSF) for steel-cord belts.

Impact of Selected Parameters on the Fatigue Strength of Splices on Multiply Textile Conveyor Belts

Splices are the weakest points in the conveyor belt loop. The strength of these joints, and thus their design as well as the method and quality of splicing, determine the strength of the whole conveyor belt loop. A special zone in a splice exists, where the stresses in the adjacent plies or cables differ considerably from each other. This results in differences in the elongation of these elements and in additional shearing stresses in the rubber layer. The strength of the joints depends on several factors, among others on the parameters of the joined belt, on the connecting layer and the technology of joining, as well as on the materials used to make the joint. The strength of the joint constitutes a criterion for the selection of a belt suitable for the operating conditions, and therefore methods of testing such joints are of great importance. This paper presents the method of testing fatigue strength of splices made on multi-ply textile conveyor belts and the results of these studies.

Maintenance of Belt Conveyor Systems in Poland – An Overview

The tendency to increase efficiency and safety in mining industry leads to quick development of monitoring, diagnostic and management systems. It can cover different aspect of mining activities. In this paper recent achievement in Polish mining industry related to machinery systems will be discussed. Selected solutions deployed by research teams from Wroclaw University of Technology in both opencast and underground mining companies in Poland will be briefly presented and discussed. The purpose of this paper is to provide current state of the research and practices focused on maintenance of belt conveyors. In particular, among others, following projects will be overviewed :i) Online monitoring system for drive units developed for lignite mine, ii) Portable monitoring system for conveyor belt with steel cords developed for lignite mine, iii), Diag Manager – maintenance system for belt conveyor transport network, iv) Laboratory and in situ research on belt conveyor technology (belts, joints, idlers resistance to motion, energy efficiency, etc). The Authors will try to summarize challenges in this field and point out future work at the end of the paper

Condition-Based Conveyor Belt Replacement Strategy in Lignite Mines with Random Belt Deterioration

In Polish lignite surface mines, condition-based belt replacement strategies are applied in order to assure profitable refurbishment of worn out belts performed by external firms specializing in belt maintenance. In two of three lignite mines, staff asses belt condition subjectively during visual inspections. Only one mine applies specialized diagnostic device (HRDS) allowing objective magnetic evaluation of belt core condition in order to choose the most profitable moment for the dismantling of worn out belt segments from conveyors and sending them to the maintenance firm which provides their refurbishment. This article describes the advantages of a new diagnostic device called DiagBelt. It was developed at the Faculty of Geoengineering, Mining and Geology, Wroclaw University of Science and Technology. Economic gains from its application are calculated for the lignite mine and for the belt maintenance firm, taking into account random life (durability) of new and reconditioned belts (after the 1st and the 2nd refurbishment). Recursive calculations for following years allow the estimation of the length and costs of replaced, reconditioned and purchased belts on an annual basis, while the use of the Monte Carlo method allows the estimation of their variability caused by random deterioration of belts. Savings are obtained due to better selection of moments (times) for the replacement of belt segments and die to the possibility to qualify worn out belts for refurbishment without the need to remove their covers. In effect, increased belt durability and lowered share of waste belts (which were not qualified for reconditioning) create savings which can quickly cover expenditures on new diagnostic tools and regular belt inspections in the mine.

Condition Monitoring of Conveyor Belts as a Tool for Proper Selection of Their Replacement Time

Condition monitoring of steel cord belts using magnetic scanners is known since late 70s however it has not been widely used in Polish mines due to difficult interpretation of signals and cost of services and diagnostic devices. Recent integrated diagnostic tool developed in Machinery Systems Division at Wroclaw University of Technology showing 2D/3D state of belts core and calculating aggregated measures (e.g. wear density of belt segments) allows on better interpretations and prediction of remaining belt life and optimal selection of their time for replacement. Proposed approach utilise experience and models of belt wear developed and verified statistically on belts durability data. Now addition of new dimension (current belt condition) allows on observation of increasing belt degradation process (belt wear density trajectory) which extrapolation allows on prediction of remaining life and replacement time.

Conveyor Belt Condition Evaluation via Non-Destructive Testing Techniques

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.

Conveyor Belt 4.0

Industrial revolution known as Industry 4.0 is present in all branches of industry and in all areas of production. It also stimulates changes in the mining industry, known as Mining 4.0. Transportation processes have a significant impact on the technological chain, from the working of minerals to the selling of the final products. Continuous transportation with the use of belt conveyors allows cost reductions and increased range. It also allows fully automatic operation as well as remote monitoring and control from the centralized control room. Presently, the conveyor belt is the least sensor-monitored system in Polish mines. This paper demonstrates that appropriate methods and devices for the monitoring of conveyor belts and splices already exist. Polish mines have been collecting and recording data on the installed belts, splices and repairs. The authors propose to introduce diagnostic systems and integrate data from a number of sources in order to include the idea of conveyor belt 4.0 into the digitally controlled conveyors 4.0, and – in wider perspective – into the Mining 4.0 intelligent solutions.

Random Deterioration Process of Conveyor Belt Evaluated by Statistical Analysis of Core Failures Detected Along Belt Axis and Elapsed Time

Magnetic diagnostic methods are used for steel cord belt condition evaluation since the beginning of 1970s. Initially they generated an analogue signal for several tens of centimetres of conveyor belts scanned sequentially with one measuring head in several cycles or the whole width of the belt at one time thanks to the installation of many measuring heads across the entire cross section. This did not allow identification of single centimetre failures, but rather an aggregate assessment of the state of quite wide waist. Modern diagnostic devices, thanks to miniaturization, allow up to 200 heads per belt width to identify damage of individual cords. Instead of analogue signals, they generate a zero-one digital signal corresponding to a change in the magnetic field sign, which can illustrate damage on 2D images. This makes it easier to identify the location and size of the damage in the belt image. Statistical analysis of digital signals summed up for consecutive sections along the belt axis allows to present both the source signal and its aggregation for band of a given width to form aggregate measures of belt damage such as the damage density per 1 meter of belt. Observation of changes in these measurements at different times allows on evaluation of its rate of change over time, which can be used to forecast future belt condition and to select the proper moment of preventive belt replacement to another one to avoid emergency downtimes (egg in underground mines) or to recondition of belts (egg. in lignite surface mines). The paper presents the results of investigations of the damage condition of a core of a single belt segment working in one of the copper ore underground mines. Scanning of the belt condition was performed few times at intervals of several months. The paper presents the results of the analysis of the changes in core condition, showing the random character of the damage process along the axis and its change over time.

Evaluation of the Effectiveness of an Eco-Friendly Technology for Splicing Steel Cord Conveyor Belts

A new eco-friendly method of splicing steel cord conveyor belts without the use of noxious materials has been developed by the Mining Institute at Wrocław University of Technology in collaboration with the Bełchatów Lignite Mine – the two leaders in implementing state-of-the-art and environment friendly technologies in mining in Poland [1,2,3]. Polish lignite mines use belts with steel cords. Such belts are spliced through high temperature vulcanization, which is not safe for the environment and has an adverse impact on human health. Strength and durability are the two main properties of belt splices, having a bearing on the failure-free operation of the belt conveyors used for the haulage of stripped rock or muck in open pit mines [4,5,6]. This means that properly made steel cord belt splices should have the strength and durability parameters similar to the ones of the belt without splices. Many factors contribute to the quality of the splice, including the ones connected with the splicing technology, workmanship and with the fact that splices are made directly on conveyors in heavy mine conditions.