夹矸岩对采煤的影响.pdf

Effects of Bit Geometry in Multiple Bit-Rock Interaction Rizwan A. Qayyum Thesis ted to the College of Engineering and Mineral Resources at West Virginia University in partial fulfillment of the requirements for the degree of Master of Science in Mining Engineering Abdul Wahab Khair, Ph.D., Chair Syd S. Peng, Ph.D. Y. Luo, Ph.D. Department of Mining Engineering Morgantown, West Virginia 2003 Keywords Bits, Bit geometry, Respirable dust, Bit spacing, Continuous miners. Copyright 2003 Rizwan A. Qayyum UMI Number 1415004 ________________________________________________________ UMI Micro 1415004 Copyright 2003 by ProQuest Ination and Learning Company. All rights reserved. This micro edition is protected against unauthorized copying under Title 17, United States Code. ____________________________________________________________ ProQuest Ination and Learning Company 300 North Zeeb Road PO Box 1346 Ann Arbor, MI 48106-1346 Abstract Effects of Bit Geometry in Multiple Bit-Rock Interaction Rizwan A. Qayyum The impact of bit-coal/rock interaction during the cutting process in underground mines is great concern to the mining community of the world. Rock/coal cutting bears directly on rock/coal dust generation that causes “black lung/silicosis” in miners. On the other hand, rock cutting generates radiance of sparks that has potential to cause face ignition. Bit wear affects productivity, safety and economy. Hundreds of face ignitions and millions of dollars in productivity and compensation for respirable rock/coal dust related diseases are attributed to the cutting action of continuous miners/shearers. These undesirable impacts could be minimized by proper selection of bit types, bit design, cutting parameters of the cutting head, and amount of water and position of water jets. This thesis uates the effects of bit geometry in multiple bits – rock interaction, utilizing an automated rotary coal cutting simulator ARCCS and synthetic rock. Five types of bit/cutting tool with different cone and tip geometry were tested against the synthetic rock of 16” x 14” x 4” dimension. The rotation of the cutting drum was kept at 100 rpm and the cutting drum was advanced at 0.14 in/sec of advance. Cutting force, penetration force, rate of advance and respirable dust were measured during the cutting process. Specific energy and specific dust were also calculated for each experiment. iii Acknowledgments As many before me have noted, completing a thesis requires the cooperation and support of many individuals. To mention everyone who contributed to this undertaking would be difficult. I have thus decided to limit my acknowledgements to those who inspired much of what I have done, those who helped me in my endeavor, and to those who encouraged me during those times when the completion of the task seemed far away. I would like to express my sincere gratitude to my academic advisor Dr. A. Wahab Khair. Without his knowledge, guidance and previous experience this research would not have been possible. I would like to convey my thanks and appreciation to the other committee members, Dr. Syd S. Peng and Dr. Yi Luo for their ideas and inspiration. This research has been supported by Coal and Energy Research Bureau CERB, I am thankful for their financial support during the course of this research work. Special Thanks to Mr. Bo Yu for his help in the experimental work, Ms. Karen Centofanti for her assistance in the official work. I would like to express to all my friends who helped me in many ways during my stay in Morgantown. Finally I am greatly indebted to my parents whose support and help can never be expressed in words. iv To My Parents v Table of Contents Content Page ABSTRACT ......ii ACKNOWLEDGMENTS.iii TABLE OF CONTENTS...v LISTOF FIGURES.....................................................................................................vi LIST OF TABLES......................................................................................................ix Chapter 1 1.1 INTRODUCTION.... 1 Chapter 2 2.1 LITERATURE REVIEW.. 3 Chapter 3 3.1 OLOGY.13 3.2 DESCRIPTION OF THE ARCCS.15 3.3 SYNTHETIC MATERIAL ...19 3.4 PHYSICAL AND MECHANICAL PROPERTIES OF SYNTHETIC MATERIAL.19 3.5 DATA ACQUISITION S..20 3.6 DUST SAMPLING....22 3.7 CHARACTERISTICS OF CUTTING BITS..24 3.8 ROCK CUTTING EXPERIMENTS .31 Chapter 4 4.1 RESULTS AND ANALYSIS36 4.2 BIT GEOMETRY AND PENETRATION FORCE..37 4.3 BIT GEOMETRY AND CUTTING FORCE 37 4.4 RESULTANT FORCES 37 4.5 BIT GEOMETRY AND SPECIFIC DUST.. 38 4.6 BIT GEOMETRY AND SPECIFIC ENERGY 38 4.7 ANALYSIS59 4.8 CONCLUSIONS....61 4.9 RECOMMENDATION..61 vi LIST OF FIGURES Figure 2.1. Test and Monitoring equipment facilities 8 Figure 2.2. Typical specimen located in the confining chamber and ready for experiment. 8 Figure 2.3a – c. Coal blocks cut with different cut spacing. a. 3 in. spacing face cleat, b. 1.5 in. spacing face cleat, c. 1.5 in. spacing butt cleat 9 Figure 2.4. Typical experimental setup 10 Figure 2.5. Photograph of the cut surface, tested Godula sandstone block. 10 Figure 2.6. cut surface of the rock at 12 11 Figure 2.7. Cut surface of the rock at 18 mm and 9mm depth of cut utilizing US2 bit depth of cut, utilizing US2 bit. 11 Figure 2.8. Variation of mean normal force/mean cutting force with increasing depth of cut 11 Figure 2.9. Variation of mean peak normal force/mean peak cutting force with increasing depth of cut 12 Figure 2.10. Variation of specific energy with depth of cut 12 Figure 3.1. Automated Rotary Cutting Simulator ARCCS 15 Figure 3.2 . Control Panel of Automated Rotary Cutting Simulator ARCCS 18 Figure 3.3 . Data Acquisition System of Automated Rotary Cutting Simulator ARCCS 21 Figure 3.4. Cascade Impactor assembly 23 Figure 3.5. Bit A Bit with the largest tip 25 vii Figure 3.6. Bit B Bit with medium size tip 26 Figure 3.7 . Bit C bit with small size tip 27 Figure 3.8 . Bit D Bit with ridges/groves on the tip 28 Figure 3.9. Bit U76K 29 Figure 3.10. All bits used in this study compared 30 Figure 3.11 . Experimental Setup 32 Figure 3.12 . Multiple Cutting in the specimen block Bit C 33 Figure 3.13 . Multiple Cutting in the specimen block bit B 34 Figure 3.14 . Multiple Cutting in the specimen block Big A 35 Fig 4.1 Graph showing penetration force for bit A 40 Fig 4.2 Graph showing cutting force for bit A 41 Fig 4.3 Graph showing resultant force for bit A 42 Fig 4.4 Graph showing penetration force for bit B 43 Fig 4.5 Graph showing cutting force for bit B 44 Fig 4.6 Graph showing resultant force for bit B 45 Fig 4.7 Graph showing penetration force for bit C 46 Fig 4.8 Graph showing cutting force for bit C 47 Fig 4.9 Graph showing resultant force for bit C 48 Fig 4.10 Graph showing penetration force for bit D 49 Fig 4.11 Graph showing cutting force for bit D 50 Fig 4.12 Graph showing resultant force for bit D 51 Fig 4.13 Graph showing penetration force for bit U76K 52 Fig 4.14 Graph showing cutting force for bit U76K 53 viii Fig 4.15 Graph showing resultant force for bit U76K 54 Fig. 4.16 Graph showing penetration force for all bits 55 Fig. 4.17 Graph showing cutting force for all bits 56 Fig. 4.18 Graph showing resultant force for all bits 57 Fig. 4.19 Graph showing specific dust for all bits 58 Fig. 4.20 Graph showing the specific energy for all bits 59 ix LIST OF TABLES Table2.1. Criteria for Repairable Dust 4 Table 3.1. Components of the synthetic material 19 Table 3.2. Physical and Mechanical Properties of the material 20 Table 3.3. Different stages and their GMD in a cascade impactor 23 1 CHAPTER 1 1.1 Introduction The high demand for coal production has increased the need for mechanical coal cutting and roof support in underground coal mines. On the other hand our coal reserves are shrinking, forcing operators to mine thin coal seams and subsequently to cut roof/floor rocks in order to maintain sufficient clearance for equipment. At the present time approximately 57 longwall faces and more than 2000 continuous miners are in operation. Enormous miles of entries are developed by these continuous miners for longwall operations as well as room and pillar mining. The amount of silica and respirable dust generated by excavating coal and cutting roofs with continuous miners is the major concern for the industry. A U.S. Government printing office stressed that every year more than 250 workers in the U.S. will die silicosis and more than 1 million U.S. workers are exposed to crystalline silica. Unfortunately, coal mine operations contribute significantly to these statistics. The continuous mining machines, which were introduced in 1950s, now account for approximately half of the coal production from the underground mines. Unfortunately, these continuous miners, which were designed for increasing productivity, have also increased the concentration of respirable dust in the mines. Dust control techniques such as conventional water sprays and dust collectors are only partially effective and require additional equipment expenditures. A better approach would be to reduce respirable dust at the sources, the continuous mining machine cutting head/drum, where the fragmentation process occurs. Improving the fragmentation process by understanding the 2 mechanisms of coal/rock breakage will not only reduce respirable dust at the face, it will also reduce dust liberated during the secondary handling such as loading and transportation etc. 3 Chapter 2 2.1 Literature Review Research conducted by USBM 1 showed that the most significant underground quartz dust source was found in the continuous miner section where the miners are excavating rock. Another interesting result derived from this study 1 was that quartz dust generation and its size characteristics are affected by the morphology of the quartz bearing rock. Furthermore, the free silica bonding matrix in the rock is most likely responsible for quartz dust produced mechanical comminution. According to Kissel’s 2 observation, 73 of dust generated from continuous miner, 25 from bolter, and 2 from beltway. If the continuous miner is cutting roof, floor or rock partings the amount of silica dust generated is beyond of an acceptable limit. Repairable dust is defined by the criteria given in Table 2.1 3. From table 1 it is obvious that less than 10 m particles reach the alveolar region, whereas 50 of the 3.5 m particles reach the alveolar regions, and so on. 4 Table2.1. Criteria for Repairable Dust 3 Aerodynamic diameter Percent respirable USAEC Percent passing section, ACGIH 2.0 2.5 3.5 5.0 10.0 100 75 50 25 0 90 75 50 25 0 A message from the Secretary of Labor says, “if it’s silica it’s not just dust” 4. The mining community has centered its attention on achieving two goals; first to minimize energy required for cutting operation and second to decrease the amount of respirable dust generated during the cutting process. Unfortunately these tasks have not been met successfully. There is a need to understand the mechanism of coal/rock breakage. One of the primary factors influencing mechanical comminution of rock/coal cutting is selection of proper cutting tool.5,6,7,10,11,13,14. Since the introduction of continuous miners in 1950’s, much work has been done to improve the phenomenon of the cutting tool. In a rotary cutting action the shape of the groove along the path of an individual bit resembles a crescent moon. Each bit on the drum starts the cutting face from zero depth of cut and as the bit penetrates further in the face, the depth of cut increases to a maximum at the center line of the path of each cutting bit, then the depth of cut decreases to zero when the bit exits the cutting face. Researchers in USBM addressed the problem of non-linier cutting action of the rotary cutting drum 15. In this study a linear cutting concept was developed from the analysis of rotary technology. The liner cutting drum cuts material to an open face most of the time with minimal secondary fragmentation 15. The liner cutting drum did not get out of the 5 laboratory because of two major reasons a the concept was totally unfamiliar to the mining industry; b the drum required high torque gear box to be practically utilized. In the past, enormous research has been carried out to select the design parameters for cutting tools on a trial and error basis 11. The mining industry is yet to receive a solution, which could provide optimum parameters for coal/rock cutting in underground coal mines. A few metals were tested at USBM 11 for their incendivity in methane air explosive mixtures. The results have suggested that materials like polycarbonate resin, an ultra high molecular weight polyethylene, and zinc alloys were potential metals that could be used. But these were not acceptable of holding the carbide tips during coal/rock cutting. Nickel-based alloys proved to be safer than iron based alloys as far as ignition was concerned. Research continued to find proper bit tip to prolong the life of the bit and reduce friction ignition. There are two shapes of cutting bits commonly utilized, namely, wedge type and point attack type. Although point attack type bits are used more frequently in the US, research indicates point attack bits suffer a lot of bit tip wear and damage 6. This is largely due to their inefficient rubbing contact with the wall of the cut grove ridges/lands as they profile. Bit wear can be defined as the removal of material from the surface as a result of mechanical action. The mechanism of bit wear can be adhesion, abrasion, oxidation, or diffusion depending on cutting conditions. A study carried out to study the principles of bit wear and dust generation 6. In this study, four types of point attack/ conical used bits were obtained from different underground coalmines. The analysis showed that many bits did not rotate properly during cutting. The intention of using conical bits in the United