Selection of Open Pit Excavating Equipment - a Systems Approach
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SELECTION OF OPEN PIT EXCAVATING EQUIPMENT - A SYSTEMS APPROACH A thesis submitted to the University of London (Imperial College of Science and Technology) for the degree of Doctor of Philosophy in the Faculty of Engineering by T. Atkinson November, 1973. CONTENTS Page No. 1 INTRODUCTION 1 Systems approach to the selection of open pit mining machinery 2 Purpose of Thesis 10 Acknowledgements 14 References 16 2 GENERAL - EXCAVATION 17 Diggability 18 Other Data 20 CYCLIC AND CONTINUOUS EXCAVATORS 20 DEFINITIONS 22 OPERATING EFFICIENCY 26 EFFECT OF ALTITUDE AND TEMPERATURE 33 REFERENCES APPENDICES 2A REFRACTION SEISMOLOGY TESTING 35 2B OPERATIONS AT WHICH METHOD STUDY TECHNIQUES WERE EMPLOYED 38 CONVENTIONAL ACTIVITY TIME STUDY 39 ACTIVITY SAMPLING 2C LIST OF MINES WHICH PROVIDED INFORMATION ON FACTORS A AND 0 58 2D SOURCES OF PUBLISHED DATA USED TO DETERMINE OPERATING EFFICIENCY bo ii Page No 3 LOADING SHOVELS 61 INTRODUCTION 61 DIPPER SIZE 62 LOADING SHOVEL GEOMETRY 69 LOADING SHOVEL DRIVES 72 Diesel Drives 72 Diesel-Electric Drive 72 Electric Drive 73 The Ward Leonard Drive 75 The Eddy Current Coupling 78 Electrical Load Characteristics 82 ELECTRICAL SYSTEM DESIGN 94 THYRISTOR DRIVE SHOVELS 96 The Hydrostatic Crowd Drive 100 LOADING SHOVEL COSTS 101 Ownership Costs 104 Operating Costs 108 FURTHER STUDIES 110 Electricity Consumption 111 Electrical System Reinforcement 112 Shovel Systems 112 REFERENCES 116 APPENDICES 3A THE PER UNIT SYSTEM 117 EQUIVALENT CIRCUIT METHOD 127 SOLUTION OF THE EQUIVALENT CIRCUIT 131 iii Page No. APPENDICES '3B HEWLET-PACKARD 9100B COMPUTER PROGRAMME FOR SOLUTION OF THE EQUIVALENT CIRCUIT OF THE INDUCTION MOTOR WITH SYSTEM LINE IMPEDANCE FED FROM INFINITE BUSBARS 142 4 DRAGLINES AND CLAMSHELLS 144 DRAGLINE OPERATIONS 144 DRAGLINE DRIVES 151 CRAWLER-MOUNTED DRAGLINE COSTS 151 Ownership Costs 151 Operating Costs 153 CLAMSHELL OPERATIONS 154 REFERENCES 159 5 LARGE STRIPPING MACHINES 160 SINGLE BUCKET MACHINES 165 Walking Draglines 165 Stripping Shovels 166 Shovel Versus Dragline 168 SINGLE BUCKET MACHINE DRIVES 170 Single Bucket Machines on Small Power Systems 174 SELECTION PROCEDURE 176 MACHINE GEOMETRY 179 STRIKE ADVANCE - INCREASING OVERBURDEN THICKNESS 207 Preliminary Dimensions 210 Final Selection 212 OWNERSHIP COSTS - STRIPPING MACHINES 213 OPERATING COSTS - STRIPPING MACHINES 215 iv Page No. TOTAL OWNERSHIP AND OPERATING COSTS - STRIPPING MACHINES 216 SELECTION OF BUCKETS AND DIPPERS 216 CONCLUSIONS 217 REFERENCES 219 APPENDICES 5A THE APPLICATION OF LARGE SINGLE BUCKET STRIPPING MACHINES ON WEAK ELECTRIC POWER SYSTEMS 220 2 Hz Oscilation Phenomena 241 5B DIPPER AND BUCKET CONTROL 243 5C VOLTAGE CALCULATIONS FOR LARGE STRIPPING MACHINES CONNECTED TO WEAK POWER SYSTEMS 257 5D SOME EXAMPLES OF SINGLE BUCKET STRIPPING MACHINES USING REHANDLING METHODS IN THICK OVERBURDEN 272 6 CONTINUOUS EXCAVATORS 281 The Bucket Chain Excavator (BCE) 281 The Bucket Wheel Excavator (BWE) 281 Advantages of Continuous Excavators 283 BCE Versus BWE 286 Transport Systems 292 OUTPUT OF CONTINUOUS EXCAVATORS 293 BCE Output 294 BWE Output 303 The Crowd Action BWE - Upwards Digging 304 The Fixed Boom BWE - Upwards Digging 306 Part Block (or Lateral) Operation 308 Page No. Downwards Digging - Terrace Cut 309 The Drop Cut - Upwards Digging 311 The Drop Cut - Downwards Digging 315 Terrace Versus Drop Cut 316 BWE Output 320 MECHANICAL DESIGN FEATURES 322 Bucket Wheel Drives 334 Crawlers 337 SPECIFIC CUTTING FORCE (BWE) 339 HARD GROUND OPERATION 342 EXCAVATOR QUALITY COEFFICIENT 344 CONTINUOUS EXCAVATORS - ELECTRICAL REQUIREMENTS 31+9 SELECTION PROCEDURE 3+9 Machine Output 31+9 Machine Geometry 352 CONTINUOUS EXCAVATOR COSTS 355 Ownership Costs 355 Operating Costs 358 FURTHER STUDIES 360 REFERENCES 361 APPENDICES 6A A RIGOROUS ANALYSIS OF BUCKET WHEEL EXCAVATOR OPERATION 364 6B BUCKET WHEEL HEAD GEOMETRY 392 7 MOBILE EQUIPMENT 396 DEFINITIONS 396 AIR RESISTANCE 402 CRAWLERS V. RUBBER TYRES 402 vi Page No. TYRE SELECTION 404 THE WHEEL- LOADER OR FRONT END LOADER 405 Production Rate 409 Wheel Loader Costs 417 Wheel Loaders Versus Loading Shovels 421 Operational Experience 424 CRAWLER-TYPE TRACTOR LOADERS 424 Production Rate 425 Crawler-Mounted Tractor Loader Costs 429 THE TRACTOR-SCRAPER 429 Scraper Production 437 Pusher Tractors 440 Push-pull Operations 440 Tractor-Scraper Costs 1+41 Tractor-Scraper Operations in Rock 444 THE BULLDOZER 446 Blade Selection 447 Production Rate 451 Bulldozer Costs 455 RIPPING 456 Rock Classification 462 Ripper Selection 466 Ripping Operations 470 Pit Design 471 Fragmentation 472 Ripping Sequence 473 Ripping V. Blasting 476 vii Page No. THE COMPACTOR 479 Consolidation and Compaction 479 Compactor Application 482 Compactor Production 482 EXCAVATION USING A COMBINATION OF MOBILE MACHINES 483 HYDRAULIC EXCAVATORS 492 Hydraulic Hoe 493 Hydraulic Dragline b 495 Hydraulic Shovel 495 Production Rate 497 Hydraulic Excavator Application Zones 500 Ownership Costs 500 Operating Costs 502. CONCLUSIONS 503 REFERENCES 505 APPENDICES 7A VEHICLE MECHANICS 507 7B TYRE NOMENCLATURE 512 7C WHEEL LOADER CYCLE TIMES 519 8 HYDRAULICKING 521 OPERATIONS 521 . REFERENCES 526 9 ROPE HAULED SCRAPERS 527 REFERENCES 530 10 CONCLUSIONS 531 FURTHER STUDIES 531 1. INTRODUCTION The ever increasing world demand for minerals over the past twenty years has caused mining engineers to . increasingly turn their attention to the economic exploitation of near surface deposits of low grade and high overburden ratio. This has resulted in larger outputs from individual mines because of the increased volumes of waste and the need to achieve economies of scale. Open pit mining machinery has shown a marked tendency to increase in size to enable these deposits to be mined economically at high outputs. Open pit mining has therefore tended to become a problem of materials handling on a massive scale. The economies that can be achieved by the introduction of large machines must however be set against their disadvant- ages. Breakdowns assume much greater importance. The following difficulties arise: Component parts are larger and repairs take longer. Because of their size) spare parts are costly to hold in stock. The custom built nature of the machinery means that spare parts are more difficult to obtain quickly. Loss of production due to breakdowns is greater and more costly. The need for more detailed investigation into the selection of machinery for open pit :pining is readily apparent and a better understanding of machine performance is essential. Additionally greater reliability is essential. Four major lines of action are available to obtain increased reliability: 1. Improved operating characteristics 2. Improved mechanical and electrical design 3. The correct selection of materials 4. The use of high reliability components. Most of these items follow from a better knowledge of machine performance. S stems a I roach to the selection of o•en •it minin: machiner The action of an excavator must be related through its mechanical drive, its electrical system and structure to a cost figure which can provide a quantitative basis for selection. It is obvious that mining, mechanical, electrial and structural engineers cannot work in isolation and a systems approach to the selection of open pit machinery is essential. Similarly although the selection of the excavating machinery is of considerable importance it is also essential to remember that the various operations within an open pit e.g. ground preparation, loading, transport and mineral treatment, are interdependent. As an illustration the increased use of explosives may result in reduced loading, transport and treatment costs which amply repay the additional ground preparation costs. As the various operations are inter- related, the optimum cost per tonne cannot necessarily be obtained by attempting to minimise all costs. The ground preparation method and crusher size must be compatible, while loading and transport equipment must be appropriately matched. The primary crusher size must also be related to the dipper or bucket size of the loading machine. The production requirements have a significant bearing on all operations and the costs of all operations are interlinked to some degree. The logic diagram for a simple shovel/trucking operation (Fig 1.1) shows the sequence of various operations, inter- related items and feedback. It is within this framework that GROUND Inter-related items PREPARATION ----- Feedback Li Drilling Drilling Costs 6,47 El s Blasting lasting Costs Secondary Brer trig Secondary Breaking Maximum , ump Size Costs Ground Preparation I Costs 4 Production Requirements Bucket Size 0-----el Cycle Time Loading Costs I V z Haulage Cycle Time Truck Size Transport { Fleet Size Costs Mill Feed Throughput Crusher Size Crusher Costs Total Costs FIG.1.1 LOGIC DIAGRAM SHOVEL-TRUCKING OPERATION - 4 - the selection of open pit mining equipment must be selected. To further illustrate this, reference is made to an extensive HOCUS Manual Simulation exercise, which although primarily carried out by the author to prove the method for teaching purposes, gives an excellent indication of the interdependent nature of open pit mining operations and the importance of the systems approach. A mine model was prepared (Fig 1.2) using from one to five shovels and with up to 18 trucks in service. Cumulative probability distributions for poorly and well fragmented ground were prepared from data compiled at Sherman Mine, Tergami, Canada, supplemented by discussions with the mine staff to establish any limiting