No description available.

No description available.

The object of this thesis is to establish the necessary design criteria for a number of special feedback networks which were required to allow the final development of the Strip Mining Industry's first Automatic Crowd-Hoist Regulator. The introduction considers the purpose and needs for such a regulator by briefly outlining the present manual dipper loading operation. Section IV and Appendix 1 presents the analytical system requirements which are basically determined from an analysis of the system's inherent mechanical oscillatory frequency. Section VA is concerned with the development of the hoist and crowd motion transfer functions which are necessary to accomplish the stability analysis of the system. A general determinantal solution is obtained based on linear analysis to allow expression of the motion transfer functions as a factored polynomial. In section VB, the development of the necessary Crowd-Hoist feedback circuits is accomplished in terms of the system parameters defined from the analysis of the oscillatory mechanical system. Section VIA outlines the procedures to be followed in going from the basic mechanical system parameters to the specific control system hardware. The general requirements for a Bode analysis of the system GR is defined in section VIB, including the general procedures to follow in the utilization of the two lead compensation circuits provided. / M.S.

M. Tech. Industrial Engineering / The Reconfigurable Vibrating Screen is a newly designed beneficiation machine to be used for mineral particle separation in mines and quarries with adjustable screen capacity and structure in order to respond to changes in production and quantity demand required by the customers. In order to increase the durability, availability, reliability and maintainability of a reconfigurable vibrating screen, an effective method is required to functionally appraise and improve its working condition. The aim of this study is to develop a tool for functionally assessing reconfigurable vibrating screens and existing vibrating screens.

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M.Phil. / In an ever - increasing competitive business world it is essential to optimise the replacement of expensive mining equipment. The decisions regarding the replacement of assets used in a coal mine are usually based on life cycle costing models. Financial methods such as Net Present Value, Internal Rate of Return or Payback are applied to determine the feasibility of replacement of the asset. Whereas these methods and other models such as life cycle costing, challenger / defender and the Non-Homogeneous Poisson Process models can be applied in most cases, it is deemed to be insufficient as the sole decision making tool for the replacement of mining equipment. The development of another tool to assist in the decision making process is required for specific use by the engineer to be used in conjunction with the traditional financial models. Key performance indicators are used extensively in the mining industry to manage the performance of equipment and are deemed to be essential components in achieving the organisation's objectives. There are certain limitations when using only the traditional financial life cycle costing methods when viewed from the engineer's perspective, since they do not directly incorporate the level of the maintenance function and the performance effectiveness of the asset. The engineer usually requires more insight into the performance of the asset to assess the feasibility of replacement, hence the need for an additional tool that incorporates these key performance indicators. In most cases there are relationships between the various key performance indicators themselves as well as between them and the operating and maintenance cost of the asset. The key performance indicators used are availability, reliability (mean time to failure), maintainability (mean time to repair) and the operability (tons per direct operating hour). There are certain factors that may lead to the excessive operating and maintenance cost of an asset, especially if there is no investigation into the reasons for the excessive cost. Examples are sub-standard maintenance practices and an insufficient level of service from suppliers. Both are issues that can be resolved with a consequent decrease in the cost of ownership of the asset. Cost as the only indicator of the feasibility of replacement may therefore not be a true reflection of the real status of the performance of the asset. Weighting factors are used to allocate values to the key performance indicators in terms of their contribution towards achieving the organisational objectives. The equipment effectiveness is derived from these values to give an indication of how well the equipment is performing against predetermined benchmarks. This dissertation attempts tb find a solution to the problem through the use of the key performance indicators in addition to the existing models that focus on the financial aspect in order to provide a more accurate assessment of the replacement requirement of an asset in an opencast coal mine.

M.Phil. / In the modern world maintenance organisations are exposed to rapid changes in equipment complexity and the maintenance thereof. Maintenance people have to adopt completely new ways of thinking and managing. If organisations and their management do not adapt to these changes and challenges they are destined to oblivion. Moubray (1991:1) states that: "Managers everywhere are looking for a new approach in maintenance. They want to avoid the false starts and dead ends which always accompany major upheavals. Instead they seek a strategic framework which synthesizes the new developments into a coherent pattern, so that they can evaluate them sensibly and apply those likely to be of most value to them and their companies" One of the viable alternative business strategies and maintenance approaches in dealing with equipment complexity and hence the management thereof, is by means of maintenance outsourcing and contract setting. If done correctly it reduces the risk of organisations and increases flexibility. During outsourcing initiatives organisations will look for benefits such as improvement of its profit margins by means of inventory reductions, improved reliability, maintenance efficiency and expert skills maintaining their assets. Coetzee (1997:24) explain that the task of the maintenance function is "to support the production process with adequate levels of availability, reliability and operability at an acceptable cost". The same principles apply in adherence to the maintenance contracts where the Original Equipment Manufacturer (OEM) or contractor also needs to support the customer with the adequate levels of availability, reliability and operability at defined costs. This can only be achieved by quality maintenance; "the right level of maintenance performed at the right time to the right equipment by workmen able and willing to deliver quality workmanship and using correct task specifications" (Coetzee, 2000a). The method used in maintenance outsourcing negotiation and binding agreements between the organisation and the contractor is a Repair and Olivier-2008 Department of Mechanical and Manufacturing Engineering - UJ Maintenance Contract; commonly known as R+M or MARC contracts. Essentially a Repair and Maintenance contract is the outsourcing of a long term Service Level Agreement (SLA) or maintenance project, normally to the OEM, or its authorised service organisation. "A maintenance and repair contract is a contractual agreement between the OEM (original equipment manufacturer), or contractor, and the equipment owner or user, where the OEM or contractor carries out all maintenance and repair activities at a guaranteed rate per hour" (Lugtigheid, et al. 2007). When organisations adapt outsourcing as a business strategy, it creates a framework of uncertainty and risk to Original Equipment Manufactures and/or maintenance contractors who has to perform the maintenance services. The focus of manufacturing and selling is thus disrupted by the challenge of the unknown playgrounds of competitiveness