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By B. Barry, M. S. Klima

"Testing was conducted to evaluate the effects of hydroacoustic cavitation (HAC) treatment on two bituminous coal slurries and the subsequent separation of each slurry in a classifying hydrocyclone. HAC treatment was performed using a pilot-scale circuit fabricated by Furness-Newburge Inc. The circuit was designed to induce cavitation by means of flow through an ultrasonic resonator chamber or enhanced cavitation by initial flow through a cavitation chamber followed by flow through the ultrasonic chamber. The test materials were nominal -1,500-micron and -150-micron Illinois-basin bituminous coal slurries, which were obtained from an operating coal preparation facility. After 5 sec of HAC treatment, the median size of the -1,500-micron material was reduced, with ash values for certain size fractions decreasing more than 5 percent compared with untreated samples. Extending treatment time led to greater degradation of the +1,180-micron material and an increase in the -25-micron material, with ash reductions occurring for material in the -850+150-micron size range. Size degradation was less for the -150-micron material. Subsequent separation of the treated slurries was carried out in a hydrocyclone with diameter of 102 mm. HAC treatment led to a decrease in the ash value and an increase in the heating value of the underflow stream compared with the feed material. For example, the ash value was reduced by about 16 percent for the -1,500-micron material and 25 percent for the -150-micron material with heating value increases of 7 and 33 percent, respectively, after HAC treatment. Overall, HAC treatment appeared to have a slight effect on the size selectivity curves.IntroductionUltrasound in the range of 20 to 1,000 kHz, referred to as power ultrasound, consists of high energy waves that can create zones of compression and expansion when used to irradiate liquids (Frederick, 1965; Leighton, 1994; Mason and Lorimer, 1988). This action generates varying pressure regions leading to cavitation or the formation, growth and near-immediate collapse of microscopic voids or bubbles (Frederick 1965; Leighton 1994; Mason and Lorimer 1988). Collapse occurs when the bubble reaches critical size and cannot absorb additional sound field energy, and the critical size is governed by the ultrasound frequency (Shchukin et al., 2011)."

Jan 1, 2015

By B. Orberger

The fine fraction (< 2 mm) of the high grade Mn-ore from the world class Moanda deposit, Francevillan basin, in Gabon, contains up to 30 wt. % of manganese and about 0.4 wt. % phosphorous. A pilot study at laboratory scale integrating mineralogy and geochemistry before and after ultrasonic treatment was conducted on the fine fraction (< 2 mm) of oxidized Mn ore in order to reduce the phosphorous content and enrich this fraction in manganese. The fine fraction was dried, crushed at 2 cm and sieved at 2 mm. The two fractions (< 2 mm and 2 mm ? 2 cm) were investigated by X-ray diffraction and scanning electron microprobe ? electron dispersive spectroscopy analyses. Both fractions contain lithiophorite, cryptomelane and pyrolusite as Mn carrier, and goethite, muscovite, illite and quartz as contaminants. The Mn hydroxide nsutite was only found in the fraction 2mm ? 2 cm.The < 2 mm fraction is significantly richer in goethite, muscovite/illite, and quartz. Phosphorous carriers are mainly goethite (up to 2.8 wt. % P2O5), while the Mn minerals contain up to 0.8 wt. % P2O5. The Mn minerals are partly included in an agglomerate of goethite, muscovite/illite, and quartz. The < 2 mm fraction was treated by ultrasound for 30 s in normal water. Mineralogical and chemical analyses after ultrasound treatment showed that the Mn-minerals were largely liberated from the goethite-muscovite-illite agglomerate. Mass balance calculations show that after ultrasonic treatment the < 2 mm fraction was ? 50 % enriched in Mn and ?50 % impoverished in P.

Sep 1, 2012

By F. Göktepe

Flotation gases and conditioning of the pulp with them are one of the important parameters of flotation and should be taken into account especially in the flotation of sulphide ores. In this study, flotation of pure chalcopyrite and pyrite samples were investigated with air, oxygen and nitrogen as flotation gas and the effect of conditioning with these three gases also were performed. Flotation gas was introduced for 5min, 10min, 15min and 20 min. For chalcopyrite flotation there was no drastic change in recovery when air, oxygen and nitrogen were used as flotation gas but conditioning the pulp with oxygen for 10 minutes increased the recovery about 8% where pulp potential has been approximately 25 mV with chalcopyrite and 150 mV with platinum electrodes. Conditioning with all three gases decreased the pyrite recovery by about 20% with 20 minutes conditioning. Pulp potential decreased in the presence of nitrogen while conditioning with air and oxygen increased the pulp potential for both electrodes. Generally potential increased for both minerals with oxygenation and aeration time but it was stable or slightly decreased with nitrogenation. Comparison of the gases showed that the different flotation gases do not effect flotation recovery but conditioning the pulp with these gases at pre-flotation effects chalcopyrite and pyrite flotation recovery, most dramatically pyrite.

Jan 1, 2014

By K. C. Corin, Z. G. Song, J. G. Wiese

In the present investigation flotation was used as a diagnostic to understand the effects of changes to the media during the grinding stage. The observations from flotation for different media are discussed in terms of particle size distribution, water recovery, solid recovery and valuable mineral recovery. The chemical parameters; pH, redox potential (Eh) and dissolved oxygen (DO) levels were measured. A Base Metal Sulphide (BMS) ore was ground under media of different shapes and compositions to determine the effect of different rod/ball material on the flotation performance of the ore. For a given grind (D80 = 75 µm), media shape had no effect on flotation performance of a BMS ore. Different grinding media had significant effect on slurry chemical properties and flotation performance. Mild steel rods (RMMS) produced the highest solids recovery, nickel and pyrrhotite (Po) recovery, with the highest ethylenediaminetetraacetic acid (EDTA) extractable iron and the lowest DO level. Chrome steel balls and stainless steel rods produced the lowest metal recovery, EDTA extractable iron and the highest DO level. A complementary study was conducted to investigate the effect of using different grinding media compositions, viz, ceramic, forged steel, 15% chrome steel, stainless steel and a mixture of stainless steel and 15% chrome steel (50:50) balls were investigated using a Platinum Group Mineral (PGM), UG2 ore. Grinding products of five different media produced the same solids and water recovery, but the grades and recoveries of Platinum Group Elements (PGE) and chromite were different. Grinding products of ceramic media showed the best flotation performance, with the highest PGE recovery and the lowest Cr2O3 recovery. While grinding products of stainless steel balls (SS) produced the lowest PGE recovery and highest Cr2O3 grade and recovery in the concentrates.

Jan 1, 2016

By K. C. Corin, Z. G. Song, J. G. Wiese

In the present study the effect of using different grinding media, viz, ceramic balls, forged steel balls, 15% Cr steel balls, stainless steel and mixture of stainless steel and 15% Cr steel balls (50:50) on the flotation performance of a Platinum Group Mineral (PGM) UG2 ore was investigated. Test work was conducted using a laboratory scale horizontal tumbling mill and a batch flotation cell. Power draw to achieve a specific P80 was determined for each media type. Changes in flotation behaviour were evaluated in terms of particle size distribution, water recovery, solid recovery and valuable mineral recovery. pH, Eh and DO levels were also measured. Grinding products of five different media produced similar solids and water recovery, which is indicative of the froth characteristics, but the grades and recoveries of PGE and chromite were different. The product obtained when using ceramic media showed the best flotation performance, producing the highest PGE recovery and the lowest Cr2O3 recovery. The products obtained when using stainless steel balls (SS) produced the lowest PGE recovery and highest Cr2O3 grade and recovery. The paper proposes possible reasons to explain these observations which may have significant importance for the operation of a PGM concentrator.

Jan 1, 2015

By Yang Xiao, Zhang Yimin, Bao Shenxu, Liu Chun

Stone coal is a unique vanadium-bearing resource in China. Many techniques, such as salt roasting-water leaching, blank roasting-acid leaching, direct acid leaching etc. have been developed for vanadium extraction from stone coal. The vanadium leaching rate can reach 74.9% for stone coal from Jiangxi, but only about 27% of vanadium is leached for Hubei ore by applying salt roasting-water leaching technique. This paper investigats the vanadium occurrence in stone coal by microscope observation and electron probe, and compares the minerals components of stone coal from Jiangxi and Hubei. Although most vanadium exist as an isomorphism by replacing Al(III) from dioctahedral structure in mica group minerals in stone coal from two regions, the free vanadium is remarkably abundant in Jiangxi stone coal than in Hubei stone coal, which results the fact that vandium is relatively readily extracted from former. Moreover, the content of calcite in Hubei stone coal is much higher than that in Jiangxi stone coal. Calcium can react with V2O5 to form water insoluble calcium vanadates during roasting and this may be the reasone why the water leaching rate of vanadium is low for Hubei ore. Acid leaching is more beneficial to the vanadium leaching but other extra methods, such as adding aid-leaching agent and/or increasing acid concentration is need for the ore where vanadium is embeded firmly. This study can effectively guide the selection of vanadium extraction techniques for stone coal from different regions.

Jan 1, 2014

By A. Mitrašinovic, A. Wolf

"The aim of this investigation was to determine the most suitable additive for recovering metals from converter slags generated during Ni extraction. Fluxes analyzed were silica and lime and reductants included pig iron, ferrosilicon and copper-silicon compound. Slag was settled at 1300°C for one hour to simulate the smelting environment. The newly formed matte and slag were characterized by chemical composition and morphology. Microstructural studies showed that slag formed after adding reductants consisted of primarily fayalite, with traces of magnetite. Entrained matte was present in the slag mostly as prills of Ni3S2-FeS matrix and a Cu2S-FeS secondary phase below 10µm in diameter. Kinetic parameters of matte formation, valuable metal recovery rates and partition coefficients were deduced. Silica additions generated higher partition coefficients for copper and nickel than the addition of lime. Additives used as reducing agents had higher valuable metal recovery rates and partition coefficients. Silica additions favoured the formation a higher grade matte while lime additions will hinder metal recovery. Pig iron, ferrosilicon and Cu30Si were the most effective reductants for valuable metals recovery. Cu10Si and coke additions had little to no effect on valuable metals recovery."

Jan 1, 2015

By M. A. Reyes, J. Bickson, J. R. Srednicki

Federal laws mandate the presence of refuge alternatives (RAs) in underground coal mines and provide guidelines for harmful gas removal. After an explosion, harmful gases can follow survivors into an RA and can reach a deadly concentration. Investigators from the National Institute for Occupational Safety and Health (NIOSH) tested 12 ventilation system configurations (VSCs) to purge sulfur hexafluoride (SF6) tracer gas from a built-in-place (BIP) RA in the Experimental Mine in Bruceton, PA. Using a borehole air supply, tests were conducted with airflows of 750 and 1,000 standard cubic feet per minute (SCFM). Excluding a VSC where the air inlet was 1.98 m (78 in) from the air outlet, the results show that the time to purge the SF6 concentration from 1,000 parts per million (ppm) to 25 ppm ranged from 26 to 29 minutes for an airflow of 750 SCFM and ranged from 18 to 23 minutes for an airflow 1,000 SCFM. Mines can use this information to reduce purge time in case of a mine disaster and determine which VSC to avoid. INTRODUCTION After a fire or an explosion in an underground mine, the concentration of carbon monoxide can reach a fatal level. In a mine disaster, the main goal is to escape. However, if miners cannot escape, they have to migrate to a location to find refuge and, if possible, communication, and a borehole source for a fresh air supply. To ensure survival of the miners, Federal laws mandate the presence of a refuge alternative (RA) within 304.5 m (1,000 ft) of the nearest mining face. In addition, Code of Federal Regulations Title 30 CFR Section 7 sets the guidelines for personnel tracking, RAs, and the removal of noxious gases in underground coal mines (Mineral Resources, 30 CFR, 2014). Federal regulations define an RA as a protected, secure space with an isolated atmosphere and integrated components (Mineral Resources, 30 CFR, 2014). There are three types of RAs: portable metal RAs, portable tent-type RAs, and built-in-place (BIP) RAs. A BIP RA is constructed using masonry or other stoppings to create an isolated space in a mined-out area. Blast doors are installed in one or both of the stoppings for the miners to enter the RA. Furthermore, RAs must provide the following components: breathable air, food, water, air monitoring, and harmful gas removal. Federal regulations have emphasized the mandate for breathable air and harmful gas removal in the following words: “Purging or other effective procedures shall be provided for the airlock to dilute the carbon monoxide concentration to 25 ppm” (Mineral Resources, 30 CFR, 2014). The purpose of the mine ventilation system is to provide a sufficient quantity of air to the underground mine workings, to dilute methane and other contaminants, to maintain a suitable working environment, and to prevent accidents from happening (Cheng and Wei, 2014). In addition, the organic nature of coal amplifies risks from poisonous gases, explosions, and fires (Engström et al., 2018). If an underground coal mine ventilation system fails after an explosion, the concentration of toxic gases, most notably carbon monoxide, will increase. Carbon monoxide is dangerous because it creates tissue hypoxia by binding to hemoglobin (Özmen and Aksoy, 2015).

Jan 1, 2019

By Amaneh E. Kenarsari

Among the different sources of uncertainty in pile bearing capacity prediction including inherent heterogeneity, measurement and model uncertainties, the inherent heterogeneity of soil properties is of particular interest and is considered in this study. Cone tip resistance data are utilized to calculate pile bearing capacity by considering vertical soil variability. In this regard, cone tip resistance component of CPT data is assumed as a random parameter. Realizations of this parameter are achieved with the aid of local average subdivisions and random field theories. Monte Carlo simulation is used to generate different realizations of CPT or CPT-u data. Pile bearing capacity was then calculated by the use of direct method. Pile bearing capacity are predicted for a project in south of Iran using this method and probability density function for the total bearing capacity of pile is plotted. Coefficient of variation of 33% for ultimate bearing capacity shows the variability of bearing capacity due to variation of soil strength in depth. Cumulative probability chart for the ultimate bearing capacity are plotted as an efficient tool for estimating ultimate bearing capacity of piles with different desired confidence levels for vertically variable soil strength properties. Significant difference between mean value of pile bearing capacity (18 MN) and limit with 95% confidence level (8 MN) emphasizes the importance of considering soil variability.

Jan 1, 2011

By R Castedo, P Segarra, I del Castillo, L M. López, J A. Sanchidrián

This work investigates some suggested methods for blast vibration monitoring on a hard surface based on 53 tests on a vibration exciter. Errors in the measurement attributable to coupling have been described as function of frequency by the rock-to-mount (or coupling) transmissibility, ie ratio of the velocity of the vibration sensor mount to the velocity of the rock motion. Transmissibility has been measured from 2 to 200 Hz, at two vibration levels (5 and 20 mm/s), in four seismographs. Attachment methods with an anchor, thermal adhesive and gypsum plaster allow stiff rock-to-mount coupling. They ensure accurate measurements (errors below 0.3 dB) for frequencies commonly found in blasting (below 100 Hz) irrespective of the mount characteristics and the vibration level. Free laid mounts and sandbagged vibration sensors lead generally to a poor, weak coupling. Errors are non-linear errors with the input velocity, ie the operating frequency window narrows as the velocity of the ground increases. Free mounts follow ground motion acceptably well (error up to 0.4 dB) at both vibration levels and frequencies below 15 Hz. At higher frequencies, free mounts lead to the largest distortions with expected errors ranging from 0.8 to 6.6 dB. Sandbagging limits the expected errors below 1.3 dB, but it does not prevent large errors that can be up to 4.5 dB. Both frequency and velocity should be considered together to assess the measurement errors instead of the expected accelerations, as it is currently made.CITATION:Segarra, P, Sanchidri&#225;n, J A, Castedo, R, L&#243;pez, L M and del Castillo, I, 2015. Effect of vibration sensor mounting method on the quality of vibration measurements, in Proceedings 11th International Symposium on Rock Fragmentation by Blasting, pp 545–552 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 24, 2015

By A. A. el-Geassy, A. A. el-Tawil, Hesham M. Ahmed, Bo Bjorkman

The Iron and steel industry is one of the most intensive energy consuming processes. The majority of iron making processes is now directed towards the uses of fossil-based energy sources like coke, coal and oil. Recently, emphasis has been paid to replace part of fossil- based energy sources with renewable biomass-derived reducing agents. In the present work, the possibility of the effective use of woody biomass in carbon-iron oxide composites was investigated. Wood powder was carbonized in N2 atmosphere at 300 up to 450oC. The carbon content in the produced bio-char increased with temperature. The porosity of the char arises from maintaining the cellular structure inherent in wood biomass increases with temperature. The reduction behavior of four iron oxide-bio char composites having different fixed carbon content were carried out non-isothermally up to 1200oC in Ar atmosphere using thermogravimetric anlyser (TGA). Quadruple mass spectroscopy (QMS) was also adopted to measure the CO, CO2 concentrations in the off gases resulted during reduction process. The effect of volatile matter on the reduction of iron oxide was intensively studied. The different phases developed in the reduced product were identified by X-ray diffraction (XRD). The reduction of composites was found to proceed in a stepwise manner (Fe2O3?Fe3O4?FexO?Fe).

Jan 1, 2015

By James Ransford Dankwah

This work investigates the effect of waste plastics addition on the reduction of iron oxide by sawdust. Composite pellets of iron oxide containing sawdust (SD), high density polyethylene (HDPE) and blends of SD/HDPE were fired under argon in a horizontal tube furnace at temperatures between 1300 and 1500 °C. Reduced samples were weighed after 10 minutes of reduction and the extent of reduction was calculated from the measured oxygen contents of the compact. The results showed improved extent of reduction when SD was blended with HDPE. The highest extent of reduction was achieved at SD:HDPE ratio of 2:3.

Jan 1, 2014

By Stuart Brashear, Lee Schettler

The effect of water on several ANFO/emulsion blend ratios are documented by both physical observations and analytical testing to demonstrate the effect even small quantities of water can have on water resistant blends.

Jan 1, 1996

By Xiaochun Xiao, Xin Ding, Yishan Pan, DI WU, Xiangfeng Lv

Rockburst is a sudden disastrous instability of coal mass that poses a serious threat to underground exploitation of coal resources; therefore, approaches of prediction and control methods are valuable for improving mining environments. The mechanical properties and bursting liability of coal with drying, under-saturated, and saturated moisture content under uniaxial compression are investigated, and the charge induction signal during coal deformation both in the laboratory and on-site is recorded in this study. The presence of water reduces the cohesion and increases the internal stress caused by non-uniform deformation of minerals, resulting in the strength, elastic modulus, and bursting liability being weakened. The charge induction precursor main frequency band is 1–100 Hz and belongs to the very-low-frequency signal regime, and it indeed varies with the loading stage, leading to specimen failure owing to changes in amplitude and continuity of the charge pulse in both the time and frequency domains. Water inhibits the richness of charge induction and reduces the bursting liability, and the earlier the precursor appears, the more total charge emerges. Moreover, measurement results indicate that the amplitude and continuity of the charge pulse decrease over a longer time, as recorded in a coal seam with water injection, further verifying the weakening of the coal dynamic characteristics. Charge induction can be a valuable tool with which to obtain the precursors for rockburst and to aid the evaluation of water injection.

Dec 26, 2022

By H. Y. Sohn, M. Y. Mohassab-Ahmed

"As part of research to develop a novel flash ironmaking process using reduction of iron ore concentrate by natural gas or hydrogen, sulfur and phosphorus distribution ratios between MgOsaturated slag and iron were determined in the temperature range 1550-1650°C under three different gas atmospheres: H2/H2O, H2/H2O/CO/CO2, and CO/CO2. The distribution coefficients of sulfur (Ls) were 4.0, 2.0, and 0.8, respectively, under these atmospheres. The distribution coefficients of phosphorus (Lp) were, respectively, 8, 17, and 20 under these atmospheres. In the flash process over -25 wt% P and S volatilize during ore concentrate downward flight in the reactor shaft in addition to avoiding coke. Therefore, iron produced by the flash ironmaking process would have much lower sulfur contents than the typical hot metal produced by the BF.IntroductionGiven the issues related to large carbon dioxide emissions and energy consumption in the existing ironmaking technologies, a novel flash ironmaking technology was conceived by Sohn [1-3] at the University of Utah. This technology is the first ironmaking process that will convert iron ore concentrate directly to metallic iron in-flight. This process will produce iron directly from concentrate without requiring pelletization or sintering and avoid the need for coke. In addition, this process concept takes full advantage of the fine particle size of concentrate with a large surface area, which permits rapid reduction by a gas. In this novel ironmaking process, potential reductants and fuels are H2, natural gas, and coal gas. Therefore, an iron-slag bath is expected to be at equilibrium with gas atmospheres of mainly H2/H2O or CO/CO2/H2/H2O, respectively, corresponding to the use of H2 or natural gas/coal gas. Since the effects of an H2O- containing atmosphere on slag properties have not been studied before, it is critical for the development of the novel flash process to determine these effects. In H2-H2O-CO-CO2 gas mixtures under ironmaking conditions, H20 was found to have the most pronounced effect on the slag chemistry [ 4, 5]. In addition, it was found in this laboratory that water in the gas atmosphere affected the distribution of Mn between slag and molten iron [6]. Most previous work used CO/CO2 gas mixture to control oxygen partial pressure (p02) [7, 8]. Others used only inert atmospheres [9], although Kor and Richardson [10] used a mixture of C02/H2 to control p02. For phosphorus, previous research focused on Ar [11], Ar-CO mixture [12], CO [13], CO/CO2 [14] or N2/CO [15]. Therefore, it was necessary to investigate the effect of water vapor content in H2-H2O-CO-CO2 mixtures on the equilibrium distribution of sulfur and phosphorus between CaO-MgOsatSiO2-Al2O3-FeO- MnO (0.2-0.8 wt%)-P2O5 (0.1-0.9 wt%) slag and molten iron as part of the development of the novel flash ironmaking technology."

Jan 1, 2014

The basic objectives of mine roadways are to provide sufficient cross sections in order to meet the needs of accommodation of equipment, transport, personnel travel and ventilation. However, many roadways become damaged to the extent of needing maintenance, generally dinting, and in some cases requiring re-ripping. The damaging of a roadway is a result of several factors including geological properties of surrounding strata, method of roadway formation, type and spacing of support and so on. Among these factors, strata conditions play an important effect on the stability of roadway. Weak rocks cause excessive roadway closures and water softens some rocks and promotes the closure problem. In this paper, a scientific discussion on the effect of water on the stability of roadways is given on the basis of results obtained by means of in-situ investigation and laboratory rock tests.

Jan 1, 1996

"The Merensky Reef is a platinum group minerals (PGM) bearing reef in the Bushveld Igneous Complex in South Africa. The reef has been treated by bulk PGM and sulphide flotation with the aim of maximisingthe valuable minerals recovery and gangue minerals rejection.Synthetic water with a calcium concentration of 80 ppm and 500 ppm was prepared and the flotation results obtained were compared to a simple electrolyte in order to determine the effect water quality has on pentlandite and pyroxene surface alteration and, ultimately, floatability. During the study, the possible effect of interactions between the minerals investigated and Ca2+ ions in the presence of sodium isobutyl xanthate was studied at pH 6 and pH 9 by means of zeta potential determinations, microflotation tests and ToF-SIMS analysis.The results obtained on 1:1 pentlandite-pyroxene mixtures showed that the quality of process water plays an important role in flotation. The flotation recoveries of pentlandite and pyroxene were lower in synthetic process water compared to those obtained in a simple electrolyte solution."

Jan 1, 2003

By E. Chilton

The National Institute for Occupational Safety and Health (NIOSH) has been conducting re-search to determine the influence of mining machine mounted water sprays on airflows and methane concentrations at the face when blowing ventilation systems are used. Tests were conducted in a full-scale ventilation gallery. Airflow speeds and directions were measured at several locations near the face with ultrasonic anemometers. Methane was released from the face and concentrations were measured in the entry at locations above the mining machine using fixed point methanometers. Changes in airflow speed, direction, and methane concentrations were correlated with water spray operations. The test results using different spray arrangements and water pressures showed that operation of the machine-mounted sprayers can improve face ventilation effectiveness by increasing the velocity of airflow moving toward and away from the face. The improved ventilation resulted in reduced methane levels near the face.

By H. Al-Kazzaz

The 2-mm butt joints of ZE41A-T5 sand castings were laser welded using 1.6 mm EZ33A-T5 filler wire and a continuous wave Nd:YAG system at a power of 4 kW, surface defocusing and various welding speeds, Compared with the base metal, the fusion zone showed significant grain refinement due to high cooling rate, No grain coarsening was observed in the heat affected zone (HAZ). The porosity area percentage and total solidification crack length in the fusion zone (FZ) were reduced as the welding speed increased from 4 to 7 m/min, Fusion zone area, total penetration depth, and weld width decreased with increased welding speed, The hardness in the FZ was similar to or higher than the base metal after a natural aging of about one year, but there was a drop in the hardness of the HAZ, The HAZ width decreased with increasing the welding speed, Tensile test showed that a joint efficiency of approximately 75 ? 90 % was obtained.

Jan 1, 2005

By J. W. van der Merwe, A. S. Bolokang, M. J. Phasha, V. J. Matjeke, C. Moopanar

"Excessive wear rates on railway wheels can result in rolling-stock derailments. If wear is detected early the possible derailments can be prevented by prematurely replacing wheelsets, although the inventory cost and maintenance downtime remain a challenge. In the current study, wheels were introduced and monitored in-service for two years to investigate the cause of excessive wear rates. The wear rates and stresses were calculated for the wheels suitable for a maximum load of 26 t per axle. Microstructural and mechanical properties were analysed. As expected, the general microstructure of all the wheels tested was pearlitic. Although all the wheels complied with the tensile strength requirements, stress calculations confirmed material distortion on excessively worn wheels whereas trial wheels revealed yield strength exceeding the yield criterion. High wear rates observed on the wheels were a result of low yield strength relative to the load per axle. The typical wear mechanism found was due to a combination of rolling contact fatigue and abrasive brake wear. Despite compliance of the wheels with existing requirements regarding material and mechanical properties (hardness, ultimate tensile strength), it is recommended that the yield strength must also be taken into consideration as a critical parameter.IntroductionRailway wheels are used to support the wagon mass and guide the wagon along the tracks (Park, 1974). The wheels and rails must be able to tolerate the applied tangential forces in order to effect wagon dynamic performance and reduce material deformation (Ghidini et al., 1994; RSE_TE_SPC_0045, 2011; AAR M107/M 208 Specification, 2011. Over the past ten years, the South African coal wagon maintenance depot has experienced excessive hollow wheel wear rates on the heavy haul line wheels. The maximum load of Jumbo wagons on the coal line is 104 t, or 26 t per axle. Although the maintenance intervention cycle for wheelsets was two years, between February 2011 and August 2012 some wheels experienced excessive hollow wear. Hollow wear is regarded as wear exceeding 2 mm on the central portion of the wheel tread (RSE_TE_SPC_0045, 2011). This happened despite the fact that these wheels were manufactured and certified according to the requirements of AAR M107/208 standard for carbon steel wheels (AAR M107/M 208 Specification,. 2011) and the local wheel RS/ME/SP 021 standard specification (RS / ME / SP / 021 REV 5 (2013). The AAR standard only specifies a minimum hardness as a required mechanical property and the local standard specifies hardness and minimum tensile strength only. In general, an increase in hardness will improve the rolling/sliding wear resistance of steel. This relationship of hardness and wear resistance was found to be true only in a situation where solid and similar alloys are in contact (Singh, Khatirkar and Sapate, 2015). The sliding wear resistance of a material is usually estimated using Archard’s equation (Liu and Li, 2001)."

Jan 1, 2016