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By L. Garner McDonald

The U.S. Bureau of Mines tangentially impacted potential coal-cutter bit shank materials against sandstone to investigate the potential of the materials to ignite natural gas by a friction-generated hot streak. The shank material samples were mounted in a 24-in, 550-lb flywheel, which was rotated at surface speeds of 400 to 900 sfpm. The sandstone was advanced toward the rotating flywheel at feed rates of 1 mil per impact. The atmosphere mixture was 7 vol pct natural gas in air. Three grades of polycarbonate resin, an ultra-high-molecular weight polyethylene, and a zinc alloy (ZA27) were among the potential materials. None of these materials caused ignition of the methane at any of the three test speeds (400, 600, and 900 sfpm), but the above materials do not have sufficient strength to hold a carbide tip during coal cutting. Of the materials having sufficient strength to hold a carbide tip, three nickel-based alloys proved less likely to cause a natural gas ignition than did iron-based alloys such as 4340 (a commonly used shank material for coal cutters).

Jan 1, 2010

By G. L. Anderson

The critical importance of wire rope integrity to the mining industry has led to the creation of standards for the retirement of wire rope as well as to the development of electromagnetic devices and procedures that would allow wire ropes to be tested against these standards without destroying them, The U.S. Bureau of Mines (USBM) conducted research to evaluate these devices by measuring loss of metallic cross-sectional area and the number of wire breaks, or local faults. The intent was to define the extent to which the technique can identify degradation within the rope, e.g., broken wires, corrosion, and wear. Experimental results showed that instrument sensitivity depended on a number of factors, including rope diameter, placement of sensors, location and characteristics of flaws, rope speed, and tension on the rope. The experiments also demonstrated the importance of having an elongated recorder trace and a properly trained and experienced operator to interpret overall results. A design of a rope and test procedures for use in laboratory evaluation of instruments have been recommended by the American Society for Testing and Materials Committee E07.07.10, Wire Rope Applications. The USBM is working through this committee to develop standards for an electro-magnetic method of wire rope inspection.

Jan 1, 2010

By I. Nikolic

Twin-roll casting is an integrated casting and rolling process that involves the continuous solidification of a melt and the plastic deformation of the solidified metal between two rotating rolls. Computer modeling is a valuable tool to help engineers understand the metallurgical process during twin-roll casting. However, commercially available software can only model either the fluid flow/heat transfer of the melt or the plastic deformation of the solid, but not both. In this study, an object-oriented finite element program was developed to simulate the steady-state fluid flow, solidification and plastic deformation of an A7,31 magnesium alloy in a horizontal twin-roll caster. The melt, the mush zone and the solid were treated as a generalized Newtonian flow in an Eulerian reference frame and different constitutive equations were employed to describe the material behaviours. The effect of operational parameters on the solidification process was discussed based on the simulation results.

Jan 1, 2010

By Nicholas Matthews, Vilem Petr

This project will report findings on the establishment of a new surface test site at the Colorado School of Mines Edgar Mine. Concerns over the blast effects on site neighbors prompted the study to be conducted. The current maximum charge weight of 20-lb was studied to ensure that all environmental effects were within the range prescribed by state and federal regulations. Geophone locations were surveyed using GPS and monitored using Instantel Minimate Plus instruments. Distances and orientation of measurement sites to the test site were varied according to the local geography and geology. Weather conditions were also observed and recorded during all tests. Neighbor complaints were recorded and taken into account during analysis. Current results show that the current charge limit results in a safety factor of over 200 for all blasting activities at the site. Data collection is ongoing and a review is to be conducted annually. These results will be presented in the future. Results are presented and discussed in the following paper. Copyright

Jan 1, 2010

By Paul J. Sylvester, Yeonuk Choi, Mike Nelson, Louis J. Cabri, Mike Tubrett

"The development and characterization of sulphide standards containing as many as seven precious metals has increased the efficiency and comprehensiveness of micro-analyses for deportment studies using laser ablation microprobe inductively coupled plasma mass spectrometry (LAM-ICPMS). Because trace precious metals occurring in solid solution or as sub-micron inclusions in sulphides, arsenides, and sulpharsenides are often heterogeneously distributed, a significantly large number of analyses are required. Using well-prepared samples it is possible for up to 120 analyses per day, far more than by other comparable methods. Examples will be discussed from projects focused on the deportment of Au and the platinum group elements (PGE).INTRODUCTIONBecause gold and the platinum-group elements (PGE) occur as both discrete minerals and in trace quantities in a variety of minerals (mostly sulphide, arsenide, and sulpharsenide minerals), specialized trace analytical methods were developed and applied to determine the deportment of precious metals in ore deposits, requiring sensitivities ranging originally from about hundreds to presently tens of ppb for individual precious metal or less.In mineralogical studies, micro-analytical techniques such as the electron microprobe were first applied to obtain analyses for major elements in about 1959-60, but as the instrumentation improved early attempts for PGE in potential carrier minerals indicated that reasonable levels of detection (LOD) were of the order of 300-400 ppm, depending on analytical conditions, X-ray spectral lines, and mineral matrix (e.g., Cabri and Laflamme, 1976). Eventually, the lowest detection levels by electron probe micro-analyses (EPMA) obtained for some PGE were of the order of 10s of ppm using high accelerating voltage and current for extended measuring time on peak and background (Gervilla, Cabri, Kojonen, Oberthür, Weiser, Johanson, Sie, Campbell, Teesdale and Laflamme, 2004)."

Jan 1, 2010

By Geir Martin Haarberg

Modern electrolysis technologies can provide possibilities for developing sustainable processes in terms of energy and environment. Laboratory experiments were carried out to study electrodeposition of iron from molten salts and aqueous solutions using an inert oxygen evolving anode to eliminate the emissions of CO2. The possibilities of molten salt electrorefining of metallurgical grade silicon to produce solar grade silicon were also investigated. Electrochemical techniques were used to study the electrochemical behaviour of dissolved iron, silicon, and titanium species. Bulk electrolysis was carried out to deposit pure iron, silicon, and titanium. The quality of the deposits was studied by SEM/EDS and XRD analyses. Calculations based on laboratory studies indicate that great improvements in terms of reduced energy consum

Jan 1, 2010

By Frank J. Perzak

This report describes a U.S. Bureau of Mines study on the hazards of large-scale conveyor belt fires in underground coal mines, as a function of both air velocity and distance from belt surface to gallery roof. The fire hazards considered were smoke obscuration, toxic effects of carbon monoxide (CO), and elevated air temperatures downstream of the fire. All of these hazards scale with the ratio of fire intensity to ventilation airflow. These hazards were all found to be greater at the lower belt-to-roof distance, owing to the greater fire intensities that resulted. The hazards of smoke obscuration and elevated CO levels were greater at lower air velocities. Smoke obscuration was found to be the earliest hazard, reaching critical levels before the stage of belt flame spread. Critical levels of CO and downstream air temperatures were not reached until the later stages of flame spread. Fire growth rates during rapid flame spread were much greater than rates measured during the early stages of belt burning. Data were analyzed to determine the early-warning capability of fire sensors. Smoke sensors provided the earliest warning, followed closely by CO sensors. Thermal sensors did not exhibit any early warning capability.

Jan 1, 2010

By W. W. Roepke

The linear cutting system, developed by the U.S. Bureau of Mines, uses geometric principles developed by Cardan to produce a nearly constant cut depth. The new system has been extensively tested in a synthetic material under laboratory conditions to verify mechanical capability and to identify operational characteristics. Comparisons between 15-rpm linear cutting and 50-rpm rotary cutting systems show significant improvement in respirable dust entrainment, product size distribution, and energy usage. Respirable dust is reduced by as much as 90 pct. Recovered product showed a 67-pct reduction in -0.32-cm (-1/8-in) material and a 200-pct increase in +5.08 cm (+2 in) material. Average power was reduced by 66 pct for the linear cutting. Because the bit cutting paths differ between linear and rotary cutting, it was necessary to compare the two at the same cut depths and bit types. These comparisons show that low revolution per minute rotary cutting entrains about the same amount of respirable dust as the linear cutting system, but the average shaft torque may be 55 to 130 pct greater for the rotary system.

Jan 1, 2010

By D. A. Rice

As part of its mission, the U.S. Bureau of Mines continues to develop technologies that will enable cost-effective compliance with environmental requirements. To this end, investigations to improve the kinetics of chalcopyrite dissolution by simultaneous grinding-leaching in ferric sulfate solution were conducted using the Bureau-designed turbo mill. The development of such a hydrometallurgical process would provide a nonpolluting alternative to conventional smelter technology. The effects of mill rotational speed and volume percent solids on the leaching time and energy required for copper extraction from chalcopyrite were evaluated. The results of this laboratory study have shown that the simultaneous grinding-leaching of chalcopyrite concentrate using the turbomill is technically feasible with essentially 100 pet extraction of copper being possible at 90° C. An optimal energy consumption of 1,153 kW?h/st of copper leached was found in batch testing with the mill operating at 400 rpm with a slurry containing 35 vol pet chalcopyrite. This energy consumption, while higher than other proposed leaching processes (about 600 kW?h/st), is of the same order of magnitude. Further refinement of the energy requirements would require additional testing using a continuous circuit. Leaching times of less than 1 h, for 80 pct copper extraction, are achievable using the turbomill grind-leach process.

Jan 1, 2010

By R. Pakalnis

This paper compiles the research work conducted by the Spokane Research Laboratories in the investigation of shotcrete within underground mines to the applied design of ground support for the operator. It looks at the design methodology in terms of employing shotcrete as a fabric to confine the rock mass between the individual bolts as dictated by empirical charts. The failure mechanism in terms of its implication on design is presented with respect to the design of 6m wide tunnels for temporary and permanent openings within weak rock masses. This is reflected by field observations that relate laboratory tests to the onset of failure for the operator in order to provide guidelines for design and monitoring. This is coupled with guidelines for safe entry in terms of cure times as well as the understanding of the behaviour of the shotcrete in terms of fibres and the overall strengths that result with respect to the design of the mine openings. This enables the operator to better understand his workplace thereby provide a safer work environment.

Jan 1, 2010

By J. Larsson

In the pursuit of increased safety the mining industry has worked to develop systems for remote control and autonomous operation of both stationary and mobile equipment. This paper reports on a newly developed system for teleoperation and autonomous tramming of LHD (Load-Haul-Dump) mining vehicles that not only increases the safety of the operators, but also has the potential to increase productivity.

Jan 1, 2010

By R. T. Swinderman

This paper discusses a series of tests designed to help answer the age old question: ?How much does the belt cleaner wear my belt?? The experimental set up and test method are described. The main variables are: belt cleaner blade materials, cleaning pressures, cleaning angles, belt speeds, and belt top cover grade. The bulk material used is a standard test-grade silica sand. The measured results include: blade mass loss, belt mass loss, and cleaning efficiency.

Jan 1, 2010

By C. L. Karr

Researchers at the U.S. Bureau of Mines (USBM) have developed adaptive process control systems in which genetic algorithms (GA's) are used to augment fuzzy logic controllers (FLC's). GA's are search algorithms that rapidly locate near-optimum solutions to a wide spectrum of problems by loosely modeling the search procedures of natural genetics. FLC's are rule-based systems that efficiently manipulate a problem environment by modeling the "rule-of-thumb" strategy used in human decision-making. Together, GA's and FLC's include all of the capabilities necessary to produce powerful, efficient, and robust adaptive control systems. To perform efficiently, such control systems require a control element to manipulate the problem environment, an analysis element to recognize changes in the problem environment, and an adaptive element to adjust to the changes in the problem environment. The control system also employs a computer simulation of the problem environment. Details of an overall adaptive control system are discussed. A specific laboratory acid-base pH system is used to demonstrate the ideas presented; all results are from the physical laboratory system and not from a computer simulation.

Jan 1, 2010

By Lucas Lopes da Costa

Bamboo fibers were characterized in terms of diameter distribution and tensile properties. Polyester matrix composites reinforced with these fibers were investigated for their flexural mechanical behavior. Specimens with up to 30% in volume of continuous and aligned bamboo fiber composites were bend-tested until fracture. The results showed an improvement in the composite strength and stiffness with the amount of bamboo fiber. A microstructure analysis by scanning electron microscopy revealed a reasonable adhesion between the fiber and the polyester matrix which justifies the improved mechanical properties of the composites.

Jan 1, 2010

By P. L. Swanson

Stability analyses of fractured and faulted rock masses require delineation of the position, extent, and orientation of geologic discontinuities. The size of the smallest active discontinuity that may potentially be resolved using the spatial distribution of microseismic event locations is Limited by the accuracy and precision of the location methods. At a hard-rock mine in the Coeur D'Alene mining district of northern Idaho, two data sets consisting of calibration blast signals from a known source site and origin time and microseismic event signals were recorded using a stope-wide accelerometer array. These seismic signals are used to quantify various sources of error in event location. Five factors influencing source location errors are examined in this U.S. Bureau of Mines study: (1) biases of the numerical source location techniques, (2) receiver array geometries, (3) uncertainties in receiver positions, (4) errors in picking arrival times, and (5) uncertainties in seismic velocity structure, including the effect of mine openings. In addition, synthetic data (accelerometer positions, travel-time picks and wave velocity) are used to determine the effect of known systematic and random errors on source location calculations. It is shown that the commonly accepted association of minimum travel-time residuals with the best location solution does not necessarily hold true when there is a systematic error in seismic velocity. Recommendations are made for increasing the accuracy and precision of locations of microseismic events detected under similar field conditions.

Jan 1, 2010

By J. C. Duchon

The use of extended workdays or compressed workweeks (regular shift lengths exceeding 8 h) is attracting growing interest in many industries using continuous operations. While extended workdays promise increased worker satisfaction due to more days off, including weekends and holidays, there are legitimate concerns about the potential effects on the health and safety of such a schedule. The U.S. Bureau of Mines (USBM) conducted a study at a Canadian underground copper, lead, and zinc mining operation that was designed to study the safety and performance implications of extended workdays. Measures were taken before and after a change from the old 8-h continuous schedule to the new 12-h continuous schedule, including behavioral performance measures to analyze perceptual-motor changes, continuous heart-rate monitoring and aerobic capacity to measure physical fatigue, a variety of self-report questionnaires to measure perceived adaption and satisfaction with the new schedule, and pulmonary-respiratory measures to examine air contaminant exposure. Based upon the overall acceptance of the new schedule by the workers and lack of change in fatigue-sensitive behavioral and physiological performance measures, this study recommends that the mine retain the 12-h schedule. However, certain precautionary measures are suggested to insure the safety of the workers.

Jan 1, 2010

Jigging is a process of particle stratification in which the particle rearrangement results from an alternate expansion and compaction of a bed of particles by a pulsating fluid flow. The rearrangement results in layers of particles that are arranged by increasing density from top to bottom of the bed. The particles, in addition to the vertically expanded and compacted bed motion, move continuously, horizontally across the supporting screen and helped and influenced by the feed material that is introduced at one end. Following the particle stratification, the particle bed is physically ?cut? at a desired horizontal particle density plane to separate the desired product from the less dense gangue material. The issue of correct pulse characteristics (shape, amplitude and frequency) for the optimal metallurgical stratification of air pulsating jigs has been the subject of much discussion over the years. The accuracy of the dissymmetric stratification depends on the control parameters and the mechanical condition of specific equipment used. This paper will touch on some of the control and mechanical parameters affecting the separation efficiency.

Jan 1, 2010

By Richard A. Allwes

This U.S. Bureau of Mines report presents the results of structural analyses and full-scale physical tests conducted on a steel-set arch and tri-set. The purpose of the analyses and tests was to evaluate the suitability of these structures for use in roof-fall prone areas. The arch canopy test and design procedures previously developed by the Bureau were utilized in this evaluation. Theoretical resistance functions were established for the steel-set arch and tri-set and were representative of the experimental behavior of the structures. The resistance functions were used to determine the energy absorption capacity of the structures and to predict their dynamic response to impact loading. The dynamic tests demonstrated that the arch canopy design procedure is appropriate for tri-sets and yields conservative designs for both steel-set arches and tri-sets. As a result of this work, it is recommended that these two structures may be considered for use in roof-fall prone areas and for rehabilitation work, provided the arch canopy design procedure is utilized for each application and the principles underlying the design procedure are understood.

Jan 1, 2010

By S. Cotten

The concept for a Mine Escape Vehicle (MEV) is motivated by the desire to enable personnel to evacuate a mine rapidly as the first and most desirable response to any underground emergency. Under a NIOSH contract, Raytheon UTD developed a conceptual design for a vehicle that coal miners could use to facilitate their rapid exit from an underground coal mine in the case of emergency, including fire or explosion. The vehicle requirements include the capacity to provide life support functions for a number of miners, operate in an oxygen deficient, low or no visibility atmosphere, and travel at speeds faster than miners can walk out of the mine. To develop the MEV concept, three primary tasks were identified and executed. The first task focused on developing a realistic concept of operations (CONOPS) and associated high level vehicle requirements. The second task identified and evaluated currently available equipment and technologies that could be applied to address the CONOPS. The final task developed a design concept that integrated the identified components for the five (5) MEV sub-systems to provide the foundation for future detailed engineering design and prototype construction. The resulting MEV design concept is centered upon retrofitting existing mine personnel carrier chasses with available, mine-worthy equipment capable of addressing the MEV requirements. This approach offers a practical and economic avenue to prototype development and delivery with minimum lead-time and risk. Furthermore, by integrating familiar and available equipment into the design and CONOPS, the resulting Mine Escape Vehicles should also be more readily accepted by the mining industry.

Jan 1, 2010

By Robert L. Kranz

Mining-induced microseismicity data collected by the U.S. Bureau of Mines in a hard-rock mine were analyzed for spatial and temporal patterns that might prove useful for prediction of rock bursts or assessment of rock mass damage changes. Pattern attributes described and illustrated in the previous report (part 1) were applied to the study of aftershock sequences associated with two different stopes. The aftershock sequences were spatially and temporally fractal, and the fractality was maintained for up to 16 h following a sequence progenitor. This suggests mechanical interdependency among the after-shocks. No statistical difference was found in the distributions of fractal dimensions when comparing two different stopes or when comparing aftershock sequences initiated by blasts or bumps. This suggests a lack of sensitivity to both stress perturbation mechanism and local damage states. However, differences between the two stopes were found in other sequence attributes that support inferred differences in the magnitude of stress concentrations and damage near each stope, and over time as a stope is developed.

Jan 1, 2010