Digitising sheave wheel profiles for condition monitoring

Abstract

In both open-cast and underground mining operations, sheave wheels are an integral part of the conveyance system. Sheave wheels are usually made of ductile cast iron which assists with lubrication of the rope as it passes over the sheave. This in turn subjects the sheave to considerable (although usually not rapid) wear during its normal operation. When a sheave is misaligned or incorrectly machined, it can experience rapid deterioration. Although a worn sheave wheel could lead to failure of the sidewall, a more concerning aspect is its effect on the rope: a worn sheave will damage a rope significantly in a short time. Ropes are critical for the safety of miners in an underground mine and for production on both open-cast and underground mines. As far as the deterioration of sheave wheels go, catastrophic failure is unlikely. Failure is indicated well in advance and thus the situation lends itself to a condition based maintenance strategy. Bi-annual inspection of sheaves is therefore mandated by legislation and several different methods exist for the recording of sheave profiles. A survey was done to determine the current state of the art. It was noticed that the methods that are used in the industry at the moment have several drawbacks and none of the manufacturers provided information as to the accuracy or repeatability of these measuring instruments and techniques. This was concerning since the measurements serve as the input for critical engineering decisions that may have costly (or fatal) consequences. The study was aimed at the development of a new method for the profiling of sheave wheels. It was further aimed at determining the repeatability and accuracy of the methods currently employed in the industry and to then provide an objective comparison between the current state-of-the-art and the newly developed profiler. An α-prototype profiler was developed using structured light photogrammetry together with a low cost webcam and the MATLAB® Image Processing Toolbox®. An analytical verification of the profiler was conducted to ensure that it will meet the requirements as determined in the document. To validate the results, the profiler was subjected to the same experiments that the profilers/methods from t he current state of the art were subjected to. It was then compared to the analytical solution. There were technical challenges with the hardware that was developed and accurate conclusions could not be drawn for the developed prototype profiler. The study does however conclude with a critical evaluation of the areas that could be investigated and with recommended areas of further research as well as other areas of application of the same technology to determine profiles of other wear components.