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By A. Broussaud

The paper describes the advanced grinding control system implemented at Newmont Ahafo gold mine, Ghana in 2009 and 2010. It shows how the different components of the Advanced Process Control (APC) system cooperate for increasing plant performance. The SABC circuit processes hard rock from different pits mixed with a variable proportion of oxides. The control strategy is designed to address specific disturbances, including start/stops of pebble crushers, unavailability of oxides, changes in rock size distribution resulting from segregation in the stockpile, and changes in ore type and hardness. The system consists of an expert system per se with extensive use of fuzzy logic, supplemented by an online dynamic model of the process used as a soft sensor, a VisioRock? rock size measurement system over SAG mill feed before addition of recycled pebbles, and an AudioMill? system to analyze the SAG mill sound and detect impacts on liners. All these components are embedded in the same OCS© software platform, which, among other benefits, makes it easy to support the entire system remotely. The paper details the physical constraints and the variables that are manipulated. It describes the control strategy and the contribution of each component of the system. It also describes the project implementation and the performance of the system. In addition to a strong involvement and support of management, the very good acceptance of the operators has been facilitated by the remote access system that made it possible to immediately modify the system each time it was needed during the baby sitting phase. The system made it possible to increase gold production significantly through increases in tonnage and recovery thanks to a better control of the grind size through a stabilization of the secondary ball milling circuit and an improvement of the operating conditions of the classifying cyclones.

Jan 1, 2012

By Luciano E. Ramírez, Jesús L. Valenzuela, José R. Parga

"An innovative process for removing copper cyanide complexes including silver and zinc from cyanidation circuits has been developed. The technology was based on the inducing the nucleated precipitation of copper and silver in a tube serpentine reactor, using sodium sulfide as the precipitate and sulfuric acid as pH control. The results showed that pH had a great effect on copper cyanide removal efficiency and the optimum pH was about 3 to 3.5. At this pH value copper cyanide removal efficiency could be achieved above 97 and 99 % ,when influent copper concentration ions were 650 and 900 ppm respectively. In this process (sulphidizaton-acidification-recycle-thickening), the cyanide associated with the copper cyanide complexes is released as HCN gas under weakly acidic conditions, allowing it to be recycled back to the cyanidation process as free cyanide. This system was successfully commercial applied at Minera William in Mexico.IntroductionThe recovery of gold and silver from minerals and concentrates with cyanide is an important hydrometallurgical process, which has been studied for more than 124 years. Patented by MacArthur in 1888 [1], the process relies on the fact that gold dissolves in aerated cyanide solutions to produce the gold cyanide complex. The stoichiometry by wich this reaction occurs is known as the Elsner equation as shown here. Silver is accomplished in the same fashion."

Jan 1, 2012

By Rajiv Kalra, Ji Jiangang

"This paper reviews the following aspects of the world’s largest manufactured Grinding Mill’s in terms of diameter and power, along with the world’s biggest shop assembly and trial run of the mills delivered to Sino Iron Magnetite Project in Australia.1. An overview of the basic flow sheet of the Sino Iron (Magnetite) Project located in Australia2. An overview of in-house designed CITIC Heavy Industries 12.2 m (40ft) F x 11 m(36ft) LG – 28MW AG mills including FEA and major components3. In-house manufacturing at CITIC-HIC work in Luoyang China of all major components for 6 off Ø12.2 m(40ft) AG mills and 6 off Ø7.9 m(26ft) x 13.6 m(44.6ft) LG – 2 x 7.8 MW Ball Mills4. Major aspects of design and preparation of the biggest shop trial run of Ø7.9 m(26ft) x 13.6 m(44.6ft) LG Ball Mill witnessed by international EPCM’s and clients in July 2009.5. Major aspects of one piece assembly of 1300 tonne rotating element of the Ø12.2 m(40ft) x 11 m(36ft) LG AG Mill and Ø7.9 m F (26) x 13.6 m(44.6ft) LG Ball Mill at the port of the export China and transport to Australian Port and then to site.6. An insight to unique installation methods used for Ø12.2 m(40ft) and Ø7.9 m(26ft) rotating element lifting on the mill foundation in one piece assemblies.7. CITIC Heavy Industries present capability for in house design and manufacture of Grinding Mills up to Ø13.7 m (45 ft) with 35 MW Gearless drives and Ø12.2 m(40ft) with 2 x 10 MW Geared Mill drives"

Jan 1, 2012

The accompanying supply/demand flow diagrams and 10-year tables for mineral and fuel commodities present essential data required by government, industry, and others to formulate policies and programs that can help assure an adequate and continuing supply of mineral raw materials. The 10-year data base terminates with 1975 figures because adequate world information was not available beyond that date. The selected mineral supply/demand tables and flow diagrams comprise but one "output" from the massive body of information and data collected and compiled by the Bureau of Mines on a continuing basis covering mineral production, consumption, prices, shipments, imports, exports, and stocks, as well as industry activities in all States and abroad.

Jan 1, 2012

By Thys B. Johnson

The mine system analysis and evaluation study presented in this report was part of the U. S. Bureau of Nines' Tertiary channel project conducted under the Heavy Metals program. The Badger Hill pit, located on the west end of the San Juan Ridge area, near Nevada City, California, was the site of the Bureau's field work. The objectives of this study were: (1) Determine potential alternative mining systems for some of the large tertiary channel gold-bearing gravel deposits, and (2) Identify areas of technology where further investigation would be merited because of their potential inclusion in a mining system for such deposits, The study involved the development of a mineralized block inventory, an economic block inventory, determination of optimum ultimate mining limits and a preliminary economic mining system evaluation. Computer programs were developed and utilized for each of the study phases stated above. The sampling program conducted at Badger Hill by the Bureau Delineation Group together with confidential drill hole data provided by the San Juan Gold Co. formed the basic gold values and distribution information from which a deposit model was developed. The deposit was divided into minable block units and net economic values were assigned to each block for various configurations of both open-pit and underground mining methods based on cost and performance data provided by the various Bureau of Mines Research Centers. A number of controllable variables such as: (1) Mining method (open-pit and underground), (2) depth of mining cut, (3) production rate and (4) equipment type and capacity were evaluated. The prime measures of effectiveness on which the mining systems where judged were discounted cash flow rate of return and maximum utilization of natural resources. The analysis showed that underground mining of the Six-Mile Tertiary channel gold-bearing gravel deposit under consideration was uneconomical and did not permit maximum recovery of the resources within the channel. It was also apparent that mining the Six-Mile Deposit for gold alone is uneconomical or at best marginal at a gold price less than $80 per ounce. The analysis showed that the potential for an economic mining operation within the Six-Mile Deposit exists when the gravel resources of the channel are considered together with the gold. It was determined that the highest rate of return would be realized with a 20-year open-pit mining operation yielding 745,000 ounces of -gold and 55 million cubic yards of usable gravel.

Jan 1, 2012

The control of AG mills fed by ores with harder and softer components can be challenging due to the sensitivity of the mill to the ratio of hard to soft components. The mills at LKAB?s iron ore operations are generally well controlled, but there are periods when the throughput falls off dramatically, due to a loss of mill filling. As the ore is upgraded in the sorting plant through magnetic separation prior to milling, this presents an opportunity to manipulate the feed blend in advance. In order to assess this opportunity, a fullscale mill charge was dumped and assayed by size to quantify the build-up of competent waste in the mills. This was supplemented by pilot and locked-cycle laboratory tests at a wide range of feed blends in order to facilitate the development of an appropriate multi-component AG mill model. This paper reports the experimental campaign requirements and methodologies, as well as the major outcomes from analysis and modelling exercises using the industrial, pilot and laboratory multi-component data.

Jan 1, 2012

By Truan-Sheng Lui, Li-Hui Chen, Hao-Wen Hsueh, Fei-Yi Hung

"Since Ag wires have similar hardness and bonding properties to Au wires, they can be applied in some pads. In the present study, the annealing effect (at 225°C~275°C for 30min) on the tensile mechanical properties of silver wires with f=23µm was investigated. In addition, the micro-structural characteristics and the mechanical properties before and after an electric flame-off (EFO) process were also studied. Experimental results indicate that with annealing temperatures of more than 250°C, the silver wires possessed a fully annealed structure, the tensile strength and the hardness decreased, and the elongation was raised significantly. Under the thermal effect of EFO, the necks of the Ag balls underwent recrystallization and grain growth was induced, and the annealed Ag wires had a shorter zone of HAZ (220µm). The bonding strength and the neck-strength of the Ag wires were more than 7gf and possessed excellent bonding properties.IntroductionThermosonic ball bonding is one of the preferred processes for electronic packaging to connect a semiconductor chip and a lead frame by a thin metal wire. At present, gold wire and copper wire are the preferred interconnect materials to bond with the aluminum metallized wafer pads [1, 2]. Since gold is expensive and the reliability of copper is poorer [3], the study of silver wire has attracted a lot of attention already. In addition, the inherent properties of high ductility and low hardness of silver as well as its workability effectiveness compared to gold, have made it a preferred alternative .[4, 5]"

Jan 1, 2012

By P. Kordi, L. Egorova, R. J. Bowell, D. Gurevich, V. Sedov, A. Mikhailov, D. A. Holwell

ABSTRACT Reconnaissance exploration in the Kuene region Namibia has included geological mapping, soil and stream sediment geochemistry, and ground geophysical methods. Copper mineralization occurs within a well-defined belt with north-northwest to south-southeast trend, parallel to the regional strike of the sedimentary rocks. The occurrences vary in size but are generally stratabound. The mineralization is centred on the transition from calcareous shale and interbedded limestone, through carbonate rocks, to quartzite. Geochemical anomalies have been identified correlating to induced polarization (IP) and magnetic anomalies. The anomalies identify one potential metallogenic zone more than 17 km in strike length.

Jan 1, 2012

By T. Hudaverdi

Control of the particle size distribution of a muckpile after blasting is always an important subject for mining industry. Blasting has a significant impact on downstream processes such as loading, crushing and grinding. Improvement of blasting results provides increase in loader and excavator productivity due to increased diggability capacity, and increased bucket and truck fill factors. Suitable and uniform particle size distribution results increase in crusher and mill throughput and decrease in energy consumption in size reduction process. Digital image analysis technique has been used for many years in mining industry in order to determine blast fragmentation. The images of muckpile surface can be used to determine the mean fragment size (x50). The source of digital images can also be haul truck, leach pile, waste dump, stockpile, and conveyor belt. The screening that is conventional method to measure blast fragmentation is time consuming and expensive. Digital image analysis is a cost effective and faster method (1).

Jan 1, 2012

By Xuling Chen, Yi Wang, Xiaohui Fan

"The current control method of grate-kiln iron ore oxide pellet production is lack of accuracy and normalization due to the limited detection conditions. Therefore, mathematical models of grate-kiln temperature field are presented. With calculation of gas-particle heat transfer as well as enthalpy changes of moisture evaporation and magnetite oxidation, the thermal history of pellets throughout grate-kiln process can be acquired and used for production status estimation. Taking the calculated results as well as detected data in production as inputs, process parameters such as running speed, fan opening and coal injection rate as adjusting objects, expert system for grate-kiln pellet production is outlined. And the preheating section dominated control strategy is explained. Results of production application show that the stability rate of gas temperature in gas hood of preheating section is increased from 91.0% to 94.2%, compressive strength and first grade rate of pellet are increased by 3.62% and 2.36%, respectively, while FeO content is 18.18% lower. Control guidance of this expert system can solve production anomalies effectively, stabilize grate-kiln iron ore oxide pellet production and improve pellet quality.IntroductionSteel industry in China has developed rapidly in recent years. China’s crude steel production in 2010 is nearly 627 million, which is 44.2% of the world total production. Burden with higher quality is demanded by enlargement and modernization of blast furnaces. And oxide pellet production has become a growing concern. In 2010, the total production of pellet in China is 110 million, and about 60% is produced by grate-kiln process."

Jan 1, 2012

By B. S. Kim, Y. D. Kim, T. S. Kim, T. B. Kim, H. J. Chae

"The Nd-Fe-B scrap was placed in Fe crucible with pure Mg in an Ar atmosphere, and the scraps were melted using an induction heating method. The effects of experimental parameters such as melting temperature (range of 993K to 1073K) and holding time (15min-600min) on the ability of extraction were investigated. The microstructure and diffusion layers were analyzed by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS), and the constituent phases were characterized using XRay Diffraction (XRD). Diffusion of Nd through the Nd-Fe-B scrap into liquid Mg was described, and the diffusion coefficient of Nd in liquid Mg was estimated.INTRODUCTIONNd-Fe-B magnets are usually produced either from comminuted melt-spun ribbons as bonded magnets or hot pressed bulk magnets, or by sintering in conjunction with prior green compaction in an applied magnetic field (Sagawa et al., 1984). These magnets have been widely used for various electromechanical and electronic devices such as voice coil motors (VCMs) and magnetic resonance imaging (MRI) (Samardzija et al., 2012; Matsuura et al., 2006). The production of the Nd-Fe-B magnets is increasing by about 20% per year because of their excellent magnetic properties. However, the expansion of Nd-Fe-B magnet market induced a concern for the scarcity of Nd at the aspect of natural resource. Therefore, the development of an effective recycling process for Nd-Fe-B magnet scraps is an extremely important issue from the viewpoint of resource and energy conservation. Several recycling processes for the Nd-Fe-B magnets have been proposed (Uda et al., 2002; Lyman et al., 1993]. It has been reported that the best separation of rare-earths from the Nd-Fe-B magnets is obtained by sulfuric acid dissolution followed by precipitation of recyclable rare-earth salts. However, this process can make a large amount of waste water including dangerous solutions. Recently, (Xu et al., 2000) have reported a technique to extract Nd from 18Nd-72.4Fe-0.9B-1.82Pr-5.3Dy (wt.%) magnet scrap by using liquid metal extraction (LME) processing. However, these techniques seemed to be difficult for application, because the scraps consist of an infinitesimal amount of other minor elements (Pr, Dy, Cu, Al and Tb), and these minor elements can make a new intermetallic compounds with Mg. Also, some oxides or the plated Ni metal can be preventable to reaction between solid-liquid (S/L) interfaces. For these reasons, the substantive reaction mechanism between Mg and Nd-Fe-B scrap is not clear. In this study, the simple composition of 33Nd-66Fe-1B (wt.%) magnet scraps were prepared using an induction melting process. The effects of the experimental parameter on the diffusion properties between Mg and scraps were investigated to determine whether these methods could be used in industrial application in a liquid metal extraction (LME) process."

Jan 1, 2012

By J. E. Nesset, F. Rosenblum, J. A. Finch, R. Payant

ABSTRACT Under certain conditions of moisture and oxygen, sulphides can spontaneously self-heat. We tested a hypothesis that galvanic interaction between some sulphides can promote self-heating. Galvanic interaction is controlled by the rest potential difference between sulphides and particle size. A series of binary sulphide mixtures was tested. Individual sulphides and mixtures with low rest potential difference did not self-heat, but mixtures of high rest potential difference did. When testing pyrite-sphalerite mixtures, self-heating increased inversely with particle size, with the fineness of the pyrite governing self-heating, indicating the rate-limiting step is the reduction reaction. The results support the hypothesis that galvanic interaction contributes to sulphide self-heating. A possible mechanism based on hydrogen sulphide as an intermediate product is proposed. The understanding gained will be of interest to those involved in storage, shipping, and disposal of sulphides.

Jan 1, 2012

By P. Chris Pistorius

"Ilmenite smelting involves partial reduction of iron oxide from a slag consisting mainly of T1O2, T12O3 and FeO, yielding as products iron (with approximately 2% carbon) and titanium slag. Slag purity requirements preclude any fluxing additions, and the aggressive nature of the slag necessitates a furnace freeze lining. Large departures from thermal and chemical equilibrium hold in the smelter, with possible implications for process stability. The slag is approximately 150K. hotter than the metal, which means that the metal temperature is below the slag melting point; this difference in temperature has been shown to lead to formation of a solid TisOs-rich layer between the slag and metal. Recent equilibrium measurements have confirmed that the slag and metal are not in chemical equilibrium either, with significantly more reducing conditions in the metal than in the slag. After solidification, the pseudobrookite slag structure is metastable below approximately 1400K, and may transform upon slight oxidation.IntroductionThe natural mineral ilmenite is the main source of titanium, which is mainly used to produce Ti02-based pigments. Ilmenite has the ideal formula FeTiC>3, but natural minerals can be partially oxidized (to contain some Fe3+), and typically contain MnO and MgO as well, together with associated silicate minerals. Smelting is one of the methods to upgrade ilmenite for subsequent T1O2 pigment production; smelting involves partial reduction of FeO to form metallic iron as a byproduct and titanium slag as the main product. Reduction is typically controlled to yield a slag which contains around 10% FeO, 85% (Ti02+Tij03) and 5% impurity oxides (mainly MnO, AI2O3 and S1O2). An example of a typical average slag composition from reduction of South African ilmenite is shown in Table I. As this indicates, a significant side reaction is reduction of some T1O2 to T12O3. The relative extents of reduction of FeO to Fe and of Ti02 to T12O3 are such that the slag stoichiometry is close to that of the pseudobrookite phase [1]. Pseudobrookite has the structure AB2O5 (where ""A"" and ""B"" are different cation sites); the phase which makes up the bulk of solidified titanium slag has the AB2O5 structure and stoichiometry [2], and can be viewed as a solid solution of FeTi20s, T13O5, ÌçÔÀ2è5, MgTi20s, AI2T1O5 and C^TiOs [1]. This solid-solution phase is referred to as ""pseudobrookite"" or ""M3O5"" in this paper."

Jan 1, 2012

By J. R. Porter, C. Panaou

"A significant effort is expended on preparation of the capital estimate for feasibility studies. The development of the operating cost estimate is usually allocated a significantly smaller budget and less emphasis is placed on ensuring the accuracy of the operating cost. This paper presents a comparison of capital and operating costs of hydrometallurgy processing plants in order to demonstrate the importance that variations in operating costs have on the overall life-of-mine costs. The analysis is supported by a case study on the operating costs of a water treatment plant at an existing Australian hydrometallurgy facility at the feasibility design level. INTRODUCTIONDetermination of the economic validity of a minerals processing project is a critical outcome of a feasibility study. In many cases, the financial results of the feasibility study will determine if the project should proceed to execution. Ensuring that these results are reliable and built upon sound engineering practices allows companies to make informed decisions on resource opportunities and the selected technology.The methodology for developing a capital cost estimate at the feasibility level is well established. Specialist engineering estimators use budget quotations, first principle estimation and rules-of-thumb to develop an estimate with an accuracy of typically -10% to +15%. Cost reporting software packages are used to methodically build up the estimate from design information supplied by the engineering disciplines. Risk analysis and capital expense workshops are carried out to identify potential deficiencies in the estimate. It is widely recognized that in order to successfully produce a feasibility level capital estimate with an appropriate level of accuracy, a rigorous development process is necessary.The development of the operating cost estimate is typically less rigorous than the capital cost estimate. The operating cost is normally derived by the process engineering discipline and rarely are specialist estimators used to support the development. The allocated budget for producing an operating cost is usually smaller and less emphasis is placed on ensuring the accuracy and contingency reflect the most likely operating cost scenario."

Jan 1, 2012

By Brian Sandhuas, Robert McClure

All flyrock incidents have the potential to result in injuries or fatalities that can result in loss of company reputation, license to operate with clients, and bear the exposure to high cost liability. From 2007 to 2009, one North American Quarry and Construction Business experienced a series of flyrock incidents. In the spring of 2009, this business declared that the frequency and severity of Flyrock Incidents had reached an unacceptable level. A Flyrock Elimination Program was launched.

Jan 1, 2012

The Discrete Element Method (DEM) is a powerful tool for analysing the flow of charge, the energy consumption and the pattern of energy utilisation of a SAG mill. With the development of laser scanning measurement, the detailed internal working surfaces of a SAG mill can now be included in DEM models. Using scanned results for new and worn shell liners for a 32? (9.75 m) SAG mill, it is shown that the feed and discharge lifters have significant effect on the flow of the charge introducing significant threedimensionality. The effects of the resolution accuracy of liner geometry and the lower cut-off of the rock size distribution are explored. Finally, using a matched new and end of life worn liner and operating conditions taken from site surveys, the effect of wear on charge motion, distribution and energy utilisation are evaluated.

Jan 1, 2012

By M. Clotilde Apua, A. F. Mulaba-Bafubiandi

"The efficiency of hydrochloric acid (HCl) leaching of gold from low grade gold-bearing material has been investigated in the presence of sodium hypochlorite (NaOCl) to produce in situ chlorine gas which is an oxidizing agent able to oxidize gold metal to its soluble forms. The effect of concentrations of HCl, NaOCl, and mixtures of HCl + NaOCl was sought. Iron and potassium present in the feed were leached and consumed all the HCl. Gold found as inclusion in pyrite was not exposed to the lixiviant. Therefore, leaching of gold from low grade gold-bearing material in aqueous chlorine solution is not an effective process for now.INTRODUCTIONHydrometallurgy of gold is commonly based on cyanide leaching solution. Due to the environmental concerns related to cyanidation and mercury processes, and inefficiency of cyanide gold leaching to dissolve refractory ores, sustainable alternative lixiviant systems, capable of generating gold (I) and gold (III) complexes must be studied. Amongst non-cyanide gold lixiviants there is the chloride/chlorine system (Hilson and Monhemius, 2006; Senanayake, 2004; Pilsniak and Trochimczuck, 2007; Wang et al., 2007; Reeves et al., 1999; Khodadad et al., 2008).In practice, the most oxidizing agents utilized for the leaching of gold as chloride, are chlorine (Cl2) or hypochlorite (HOCl) which are either generated in situ by suitable reaction or added in solution (Adamson, 1972). The dissolution of gold concentrate using hydrochloric acid, sodium chloride and sodium hypochlorite (Cl-/HOCl system) were studied (Puvada and Murthy, 2006). The effect of NaOCl and NaCl concentrations were also investigated. The leaching was performed under the following conditions; time: 4h, solid–liquid ratio = 1:4, at room temperature. It was found that the increase of the NaOCl concentration from 25 to 75 g/L did not have any meaningful effect on the recovery of gold which was about 30% (experimental conditions; S/L ratio = 1:4, NaCl concentration: 25 g/L, HCl concentration: 0.35 M). It was also found that from 25 g/L to 200 g/L NaCl, the recovery of gold rose from 30% to 40% (experimental conditions; S/L ratio: 1:4, NaOCl concentration: 25 g/L, HCl concentration: 0.35 M)."

Jan 1, 2012

By Jorge Beim

Helical Piles are increasingly being used to support and rehabilitate structures subjected to compressive axial loads. Traditionally, empirical correlations between installation torque and load capacity of helical screw piles are used as the field quality control. Load tests, however, are always recommended to validate the installation process and design methodology. This paper describes a test program performed on helical piles installed at the National Geotechnical Experimentation Site of the University of Massachusetts - Amherst campus (UMass-Amherst), well known for its deep varved clay deposit. Seven of these piles were submitted to Dynamic Load Tests using the Pile Driving Analyzer® (PDA), and also to Static Load Tests. Good agreements were obtained between the results of the dynamic and static load tests, encouraging the use of the former testing method as a viable alternative to the latter for determining the compressive load capacity of helical piles installed in cohesive soils. The results of the load tests were also compared to the predictions based on torque correlations, resulting in correlation coefficients which were higher than the ones traditionally used.

Jan 1, 2012

Lonmin RoM ball mills are treating two types of feed ore produced by conventional mining and mechanised mining methods. It was reported that reduction in mill throughput was observed when treating the mechanised mining ore. Detailed grinding surveys were conducted for troubleshooting. Ore samples were collected for breakage characterisation using a JKRBT based on different particle density components. XRD analysis was conducted to investigate the association of minerals with density components. The plant surveys and the breakage characterisation tests all suggested that the two mining methods did not significantly affect either the ore breakage properties or the RoM mill performance. Instead, the mill discharge open area exerted a remarkable influence on mill throughput. The RoM ball mill operated at Lonmin K4 Concentrator has been proven to be a versatile mill that performed stably with variations in feed size distribution and feed ore changes by different mining techniques. The reasons are elucidated by the multi-component breakage characterisation and the plant surveys data.

Jan 1, 2012

By A. S. Azman

In collaboration with Kennametal Inc. and corry rubber corporation, the U.S. National Institute for Occupational Safety and Health (NIOSH) developed a drill bit isolator to address noise overexposures associated with roof bolting machines in underground coal mines. NIOSH laboratory studies confirmed that the drill bit isolator reduces noise during drilling. Field studies were needed to confirm that a noise reduction could be obtained under working conditions and that the device was sufficiently durable. This paper reports results of field tests of the device conducted at five underground coal mines. Noise reduction was assessed by comparing the operator?s noise exposure during drilling with and without the drill bit isolator. Durability was assessed by recording the number of holes and total feet drilled with each bit isolator until either the test period ended or the device failed. The results from these tests showed that the device is an effective noise control in a mine environment. The field-tested drill bit isolators provided a noise reduction of 3-5 db(A). Of nine devices tested for durability, five exceeded 610 m (2,000 ft) drilled and two exceeded 762 m (2,500 ft) drilled before failure. Durability issues found in the field tests led to final production optimizations that have resulted in a commercially available product for drilling with 35-mm- (1.3-in.-) diameter roof bits and hexagonal drill steels.

Jan 1, 2012