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The dual ema-fem approach to dynamic analysis.Grobler, Steven Robert January 1990 (has links)
A dissertation submitted to the Faculty of Engineering, University
of the Witwatersrand, Johannesburg, in fulfillment of
the requirements for the degree of Master of Science in Engineering / It has been said that experimental modal analysis (EMA) "grew to prominence
because the engineering community was incapable of properly analyzing
the dynamics of commercially significant structures" [24]. The advent
of powerful theoretical methods, such as the Finite Element Method (FEM)
has not, however, resulted in the demise of EMA. In fact both FEM and
EMA have undergone rapid growth and the merging of the two into an effective
design and diagnostic tool has had a major impact on the engineering
community's approach to dynamics related problems. In this study, the
term dual has no mathematical connotations and is used to describe the
complementary use of the techniques of EMA and FEM. The mining industry,
worldwide, has experienced dynamics related problems in the operation
of conveyances in vertical shafts. A study undertaken in South Africa investigated
the behaviour of shaft steelwork and skips, resulting in a set of design
guidelines for future shaft steelwork designs. This work only investigated
the dynamic behaviour of skips. In this project, the ABAQUS and MODEL
SOLUTION FEM codes were used to construct models of a. mine cage. An
impact modal test was carried ant on the cage, using a GenRad 2515 CAT
system, An impact hammer, suitable for exciting large structures, and a
strain gauge force transducer were designed and built for the purpose of the
test. The natural frequencies and mode shapes obtained from both FEM
and EMA are compared by means of the modal assurance criterion (MAC).
The test data is used to tune the model to produce accurate results. The
model Could then be used (with minimal further test work) for predicting
the response of the structure to dynamic loading or the effects of structural
modifications. / Andrew Chakane 2020
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Konstruktion av alternativ gripperlösning till tunnelborrningsmaskin / Design of an alternative gripper solution for a tunnel boring machineStenberg Forsberg, Niklas January 2013 (has links)
Modern tunnel boring machines require large drilling forces, and need to be fastened in the tunnel to generate such forces. The fastening of tunnel boring machines is traditionally accomplished by means of hydraulic cylinders that fasten and position the machine prior to drilling, known as grippers. A problem encountered in this solution is that the hydraulics suffers from an undesirably low stiffness, which makes the mechanism sensitive to vibrations generated by the drilling. Replacing the hydraulics with some kind of mechanical force transfer mechanismis believed to reduce said sensitivity. The purpose of the thesis is to develop a new gripper concept, evaluate if it is possible to substitute any of the hydraulic actuators with a mechanical counterpart, and assess if a mechanical solution increases the vertical stiffness of the grippers. The CAD-models were created in PRO/Engineer Wildfire 4.0 and the FEM-analysis was conducted using ANSYS Workbench 14.0. The calculations were done using MATLAB R2012a. With an extensive pre-study conducted, a number of gripper concepts were generated and evaluated (using a Pugh´s matrix), and a suggestion of a mechanical force transfer mechanism was created using the information from the concept evaluation. The most suitable force transfer method turned out to be a jack screw mechanism, thanks to its high load carrying capacity and self-locking characteristics. The jack screw will be powered using a hydraulic motor, ashydraulic power is easily accessible on the tunnel boring machine. The analysis conducted points to a significant increase in vertical stiffness, but also to an added degree of complexity which might not be fully desirable. An analysis of the dynamic behavior of the system would also be necessary to fully understand the component interactions. / Moderna tunnelborrningsmaskiner fordrar höga borrkrafter, och behöver fixeras i tunnelgången för att generera dessa. Inspänningen av tunnelborrningsmaskiner görs traditionellt med hydrauliska cylindrar som fixerar och positionerar maskinen inför borrningen, så kallade gripprar. Ett problem med denna metod är att hydrauliken har en viss vekhet som gör konstruktionen känslig för de vibrationer som borrningen skapar, och som eventuellt tros kunna reduceras med en mekanisk lösning. Syftet med detta examensarbete är att ta fram ett nytt gripperkoncept och utreda om det är möjligt att ersätta någon del av hydrauliken med en mekanisk kraftöverföring, för att öka denvertikala styvheten hos mekanismen. CAD-modellerna av koncepten skapades i PRO/EngineerWildfire 4.0 och FEM-analysen gjordes i ANSYS Workbench 14.0. För beräkningarna användes MATLAB R2012a. Med en omfattande förstudie genomförd togs ett antal gripperkoncept fram och utvärderades (med hjälp av Pughs matris), och ett förslag på en mekanisk kraftöverföringsmekanism genererades. Den mest lämpliga kraftöverföringen visade sig vara en skruvdomkraftsanordning,tack vare dess höga lastkapacitet och självhämmande beteende. Mekanismen avses drivas av en hydraulisk motor, då det är en kraftkälla som är lättillgänglig på maskinen. Analysen pekar på att styvheten i konstruktionen kan ökas avsevärt med en mekanisk kraftöverföring, men en sådan tillför också en viss komplexitet till konstruktionen som kanske inte är önskvärd. En analys av det dynamiska beteendet hos konstruktionen är också nödvändig för att till fullo kunna förutse mekanismens beteende.
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Noise measurements of pneumatic equipments in Canadian underground minesJauron, Richard L. January 1975 (has links)
No description available.
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Encumbered space and its effect on mine transportationLineberry, G. T. January 1979 (has links)
The concept of encumbered space is recognized and defined. The components and their subcomponents are identified and isolated. The relative interactions between them are noted. Initial families of velocity-clearance curves for several haulage media are derived, noting the vital need for future research. The basic assumption that production is proportional to the product of capacity and velocity is utilized and the concept of derating the maximum theoretical production rate of an underground mining situation to obtain a more realistic estimate of the actual production rate is introduced. An example of the use of derating factors (derived from the results of questionnaires) in obtaining an estimate of production is presented. An order of magnitude check is made on the weighting of the initially selected derating factors. Results proved to be consistent, confirming the approach. Recommendations for future research are made. / Master of Science
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A mixed integer model for optimizing equipment scheduling and overburden transport in a surface coal mining operationGoodman, Gerrit V. R. January 1987 (has links)
Recently, competition has increased in the surface coal mining industry, which has necessitated the development of more efficient methods for coal removal. Despite this trend, very little emphasis has been placed on the development of optimization techniques applicable to the surface coal industry. The available methods are inadequate in that they recognize neither the complex equipment interactions present in a surface mining operation nor the interdependence of overburden removal and spoil placement.
The lack of available techniques prompted the development of a mixed integer model to optimize the scheduling of equipment and the distribution of overburden in a typical mountaintop removal operation. Using this format, a (0-1) integer model and transportation model were constructed to determine the optimal equipment schedule and optimal overburden distribution, respectively. To solve this mixed integer program, the model was partitioned into its binary and real-valued components. Each problem was successively solved and their values added to form estimates of the value of the mixed integer program. Optimal convergence was indicated when the difference between two successive estimates satisfied some pre-specified accuracy value.
The performance of the mixed integer model was tested against actual field data to determine its practical applications. To provide the necessary input information, production data was obtained from a single seam, mountaintop removal operation located in the Appalachian coalfield. As a means of analyzing the resultant equipment schedule, the total idle time was calculated for each machine type and each lift location. Also, the final overburden assignments were analyzed by determining the distribution of spoil material for various overburden removal productivities.
Subsequent validation of the mixed integer model was conducted in two distinct areas. The first dealt with changes in algorithmic data and their effects on the optimality of the model. The second area concerned variations in problem structure, specifically those dealing with changes in problem size and other user-inputted values, such as equipment productivities or required reclamation. For each of these optimal schedules and assignments obtained from the model, analyses were conducted in manner similar to that discussed above. / Ph. D.
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A study of the effects of the maintenance system at an open cast iron ore mineSetzkorn, Kevin Anthony January 2017 (has links)
A research report submitted to the Faculty of Engineering and the Built Environment,
University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for
the degree of Master of Science in Engineering
Johannesburg 2017 / The study assesses the drilling, loading and trucking stages of the mining cycle of an
iron ore mine situated in the Northern Cape province of South Africa for the period of
1 January to 30 June 2011. The purpose of this study is to investigate the effect of
increasing reliability and maintainability of mining equipment in an effort to increase
throughput of iron ore. The data processing indicated that both availability and
utilisation are contributing to the sub-optimal performance of the mine. Data
regarding reliability (MTBF), maintainability (MTTR), planned and unplanned
maintenance was analysed, and this provided input for the simulation model. The
intention of the simulation model is to simulate scenarios of proposed improvement
in MTBF and MTTR through increasing planned maintenance activities. A simulation
model provides insight regarding where to invest in interventions. It is determined
that the drilling equipment is the problem area. / MT2018
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Pennies from heaven: The Queensland Government Mining Journal, 1900-1929Murray, Alan Unknown Date (has links)
No description available.
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Pennies from heaven: The Queensland Government Mining Journal, 1900-1929Murray, Alan Unknown Date (has links)
No description available.
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