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By Charles de Abreu Martins

An experimental investigation was conducted using laboratory-processed, 0.12C–1.70Mn–0.2V steels with different Cr or Mo additions aiming to evaluate this influence on the microstructure and mechanical properties hot rolled steels. Steels were processed in a pilot rolling equipment, simulating a typical thermomechanical processing, with finishing rolling steps above Ar3, followed by accelerated cooling and 723 K (450 Celsius) coiling temperature. Microstructures and precipitates were analyzed using OM, SEM and TEM, while mechanical properties were evaluated by tensile and hole expansion tests. Since Cr and Mo increase hardenability of austenite, and as a consequence, the volume fraction of the acicular constituents increases with gradual additions of Cr or Mo. Moreover, Cr or Mo impacted V precipitation process, reducing average size of particles. At 0.50%Mo, V precipitation was inhibited. Effects of this microstructure evolution on the final mechanical properties were also analyzed, as well as a comparison between Cr and Mo effects, with Mo presenting more effective influence.

Jul 30, 2018

By C. Dale Elifrits

Observations made from laboratory analysis of samples of fine-grained argillaceous materials (shales) subjected to various changes in moisture content have been correlated to loss of strength in the rock material. This reaction to a change in in-situ conditions (subsequent to mining) at a mine site combined with the observed relationships of surface-disturbing subsidence features at locations where the predominant overburden material is fine-grained, provides a predictive tool for the subsidence engineer.

Jan 1, 1983

By P. Srinivasan

Corrosion is a major operational problem in amine-treating plants causing significant expenditures each year, Corrosion may become more severe when the amine plants contain process contaminants ? namely heat-stable salts. The heat-stable salts enter the plants with feed-gas streams and makeup-solution, and/or are produced within the plants by reactions of alkanolamine and available carboxylic-acid anions, This work investigated interaction corrosion effects that may exist in amine-treating plants containing a mixture of heat-stable salts, The investigation was experimentally carried out in a 5 kmol/m3 monoethanolamine (MEA) solution containing 0,20 mol/mol carbon dioxide (CO2) loading at 80°C under atmospheric pressure using carbon steel 1018, Six heat-stable salts, including formate, oxalate, bicine, acetate, thiosulfate and chloride, were tested with a series of salt combinations, Potentiodynamic Polarization, Tafel Extrapolation, and Cyclic Polarization were used for revealing corrosion behavior, determining corrosion rate, and examining the pitting tendency, respectively, Results show that thiosulfate induces the most corrosive environment when present either individually or in the form of salt mixtures.

Jan 1, 2005

By F. Siciliano, D. Bai, S. Yue, A. M. Elwazri

The influence of niobium addition and very low temperature (`cool') deformation on the microstructure and properties of low carbon microalloyed steels was investigated. In this work, the specimens were heated at 1200°C and held at this temperature for 20 minutes. Some specimens were aged at 400°C for times ranging from 10 minutes to 10 hours followed by air-cooling. Others were subjected to deformation at 400°C (`cool deformation') prior to aging. It was observed that the proportion of acicular ferrite was increased as the amount of Nb was increased. It was found that cool deformation increased both yield and tensile strengths significantly compared to that of the aged only specimens.

Jan 1, 2005

By A. L. Martikainen

In fluctuating airflow, continuous air velocity recording is the most reliable method of air velocity measurement. It allows for fast recognition of changes and the calculation of long-term averages. Also, it enables the mine operator to identify when the airflow has decreased to a point requiring action. Using ultrasonic anemometers provides an accurate option for continuous air velocity monitoring. This paper provides information about the effect of common obstructions in underground mining on air velocity readings. Stationary and moving obstructions are used to represent workers and equipment that would cause discrepancies in measured airflow. Also, it is important to know how large of a sample size is required to ensure reasonable accuracy of results. Statistical analysis is used to evaluate the required sample size. The sampling procedure is further studied by comparing two different sample rates. The results show that obstructions provide noticeable differences in air velocity measurements. Also, movement of obstructions can be recognized from changes in results. Surprisingly small sample sizes provide reliable air velocity information. Standard sample rates are found to be suitable for the underground environment.

Jan 1, 2011

"INTRODUCTIONThe Kidd Creek Concentrator is located 28 kilometers east of the city of Timmins, Ontario. Two types of ore are treated; 'A' type, a copper-zinc-low silver ore producing copper and zinc concentrates, and 'C' type, a copper-lead-zinc-high silver ore producing copper, lead and zinc concentrates.The ore is processed at a combined rate of 12,400 metric tonnes per day through four parallel grinding and flotation divisions. Three divisions treat the 'A' type ore and the fourth treats the 'C' ore. Each division is fed from its own fine ore bin.This paper reviews the grinding section with specific emphasis on grinding media consumption and the factors affecting it as related to 'A' type ore. At Kidd Creek there was an awareness that grinding media consumption varied on a weekly and monthly basis. The reasons for this variation was usually attributed to ore hardness as evidenced by short term variations in the circuit feedrate and head assays. However, there has been a diversity of opinion published in recent years regarding the factors contributing to steel consumption. This initiated a study of historical Kidd Creek operating data, from the period 1970 to 1986 inclusive, to determine the effect of various operating parameters on media consumption. The results of the study could then be used as a baseline for future media consumption testwork."

Jan 1, 1988

By T C. Ooi, L Lu

Owing to ongoing development of new orebodies and changes to existing mining operations, new ore types with distinct mineralogy, porosity and textures are generated as feed for iron and steelmaking. Moreover, further product differentiation occurs as fine ores are increasingly beneficiated to achieve grade. A study was necessary to characterise a suite of iron ore fines in terms of their propensity for formation of quasi-particles and green bed permeability prior to sintering. In this study, two Marra Mamba bedded iron deposit (BID) samples, one Pisolitic channel iron deposit (CID) samples, two dense hematite samples (coarse and fine grained microplaty hematite), one hematite-goethite BID samples and one hematite-goethite bedded/detrital iron deposit (BID-DID) composite sample were investigated. Both Marra Mamba fines and Pisolitic fines exhibit the highest green bed permeability followed closely by hematite-goethite fines, fine microplaty hematite fines, hematite-goethite BID-DID composite fines and coarse microplaty hematite fines at a moderate sintering bed depth of 500 mm. While porous fines generally form better quasi-particles upon granulation than dense fines, the amount of moisture addition increased due to the moisture saturation of the porous fines. As sinter strands become ever larger and deeper, it was necessary to examine the granulation performance of these ore types at a range of bed depths ranging from 300 to 900 mm. On average, the green bed permeability achieved by different ore types, decreased by approximately 7.5 - 9 Japanese Permeability Unit (JPU) as the bed height was increased from 500 mm to 900 mm. In order mitigate the effect of lower bed permeability of the deeper beds, small additions of hydrated lime were investigated as a binding agent to facilitate the formation of strong micro-pellets. With the addition of three per cent hydrated lime, equivalent to approximately 2.3 per cent burnt lime, the majority of fines achieved adequate permeability for deeper bed sintering, with the exception of coarse microplaty hematite fines. In simulated coastal steelmaking sinter blends, it was found that the overall granulation performance of the blend is contributed to by individual fines constituting the blend. Therefore fines possessing favourable granulating properties impart better granulation to the blend as a whole.CITATION:Ooi, T C and Lu, L, 2013. Effects of ore type and binder addition on the formation of quasi-particles and green bed permeability at different sintering bed depths, in Proceedings Iron Ore 2013 , pp 459-466 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 12, 2013

By Youze Xu

The effect of oxalic acid, acetic acid, citric acid and EDTA on extraction of Cr (?) in soils contaminated by chromium- containing slag was investigated using a batch of incubation experiment. The results show that the pH value decreases more obvious with the increase of the amount of organic acid. The amount of Cr (?) extracted increases with increasing the amount of organic acid. When the ratio of organic acids to total Cr was 5:1, citric acid revealed the highest extraction effectiveness, followed by EDTA, oxalic acid and acetic acid, respectively. The amounts of Cr(?) extracted by citric acid, EDTA, oxalic acid and acetic acid increased by 439%, 244%, 215% and 162%.

Jan 1, 2009

By Douglas Tesarik, Mark K. Larson, Habte Abraham, Heather E. Lawson

Dynamic failures, or "bumps", remain an imperative safety concern in underground coal mining, despite significant advancements in engineering controls. While many factors have been empirically linked to the occurrence of dynamic failure events, identifying a consistent, repeatable set of criteria within a field setting has proven elusive; conditions generally associated with dynamic failure might produce an event at one site, but not another. Conversely and more troubling, dynamic failure could occur where relatively few of these factors exist. The presence of spatially discrete, stiff roof units, such as paleo channels, are one such feature that has been linked to the occurrence of dynamic failure events. However, an empirical stratigraphic review investigating the relative frequency of discrete units in bumping versus non-bumping deposits indicates that no significant difference exists based on this criterion alone, and that instead an apparent relationship exists between reportable bump history and the overall character of the host rock with respect to stiffness. Due to the complexity of the bump problem, however, these results are not conclusive, as they do not take into account any variable other than the presence or absence of stiff members in the roof lithology; To weight the relative impact of changes in a single variable, such as the thickness or location of sandstone members, it must be examined in isolation-i.e. in a setting where all other variables are held constant. Numerical modelling provides this setting, and the effects of variability in a stiff discrete member in a hypothetical longwall mining scenario are investigated within the context of three stratigraphic "types'', as determined by the ratio of stiff to compliant stratigraphic members; Compliant, Intermediate and Stiff A modelling experiment examines changes in rupture potential in stiff roof units for each stratigraphic type as discrete unit thickness and location are manipulated through a range of values. Results suggest that the stiff-to-compliant ratio of the host rock has an impact on the relative stress-inducing effects of discrete stiff members. In other words, it is necessary to consider both the thickness and the distance to the seam, within the context of the host rock, to accurately anticipate areas of elevated rupture induced hazard; acknowledging the presence of a discrete unit within the overburden in general terms is an insufficient indicator of risk. Through modelling of anticipated changes in the placement and dimensions of discrete units within their stratigraphic setting, elevated rupture-induced bump hazard can be anticipated on a case by case basis. Were similar modelling studies conducted at mine sites in tandem with tracking of problematic discrete stiff units, areas of elevated rupture risk could be anticipated in advance of mining. Developing this predictive capability beyond identifying rupture potential in discrete roof members is essential to the eventual elimination of dynamic failure related worker injuries and fatalities. As stress is a necessary component in the occurrence of dynamic failure events, this finding helps to refine our understanding of the role of individual stiff, strong roof members in bumping phenomena, and suggests that a more holistic view of overburden lithology, combined with site-specific numerical modelling, may be necessary to achieve greater miner safety.

Jan 1, 2016

By Othon do Rêgo Monteiro Neto

[The present study has investigated the extraction of copper from a chalcopyrite flotation concentrate using an adapted strain of Thiobacillus ferrooxidans and shake flasks, tank leaching and Warburg respirometer techniques. From the shake flask experiments, the activation energy and the frequency factor have been determined to be ?ka = 59.4 kJ and A = 3.3 x 105 S-1, respectively. The temperature coefficient was found to be Q10 = 2.2 in the range of 20 to 35°C. It was suggested that the reaction mechanism of chalcopyrite leaching by T. ferrooxidans involves the formation of an activated complex. whose thermodynamic values have been calculated to be ?G? = 92.1 kJ, ?S? -148.8 J K-1 and ?H$ = 47.8 kJ. The maximum volumetric oxygen mass transfer coefficient for the reactor leaching was found to be achieved by using an optimum air flow rate of 1970 cm min l at a rotational frequency of 1000 min-1. The highest copper extraction in tank (reactor) leaching experiment was 86.8% after 17 days of leaching, while in the sterile runs the corresponding copper extraction was only 40.1%. The copper extraction was suggested to be diffusion controlled. The power requirement of the aerated reactor was calculated to be Pg = 2.02 watts. During leaching, the oxygen saturation concentration was found to be C* = 6.70 mg dm-3. Using the gassing out method the critical oxygen concentration was assessed to be CCrit 0.05 mg dm 3. From the Warburg experiments, the kinetic parameters of the Monad equation were derived with a new evaluation technique to be Vmsp = 9.0 µm3 02 min-1 mg protein-1 and K = 7.4% pulp density for the effect of substrate concentration. The order of reaction and the overall reaction rate constant were determined from the modified van't Hoff plot to be n = 0.0 and k = 1.49 p dm3 02 min-1 mg Protein -1 for the chalcopyrite concentrate oxidation by T. ferrooxidans. On the basis of this experimental work, a preliminary flow sheet has been proposed for the bioextraction of copper from flotation concentrates.]

Jan 1, 1985

By Gungor Tuncer, Ali Kahriman, Abdulkadir Karadogan, Umit Ozer, Ertugrul Kaya, Kagan Ozdemir

The results of bench blasting on quarries, have important influences on the performance of subsequent mining activities such as loading, hauling, crushing, grinding etc., and the total costs of that mine. Drilling and blasting is an important step in mine producing chain and its results such as fragmentation, muckpile shape and looseness, dilution, damage and rock softening effect the efficiency of downstream processes. Within the scope of this study, the three different hydraulic excavators’ working performances have been studied considering the particle size distribution after bench lasting at a quarry in Istanbul Turkey. Five shots have been realized on the quarry and average particle size of muckpile after each shot were assessed by digital image analysis method. Bucket loading times have been measured by stopwatch study after five shots. Excavator bucket loading times were also estimated by bucket loading time estimation formula which was published in ISEE 2007 Conference, Ozdemir et al. 2007. Estimated and measured times have been statistically analyzed and the accuracy rate of formula has been determined for five events.

Jan 1, 2008

By D. J. Judy, D. J. Rabovsky, W. H. Pailes, V. Castranova, K. Van Dyke, J. Rabovsky, N. A. Sapola, M. McPeek

"Platelet activating factor (PAF) can be released from pneumocytes following exposure to occupational dust (Am. Rev. Respir. Dis. 135:83, 1987). In addition, PAF has been shown to induce pulmonary inflammation, edema, and bronchoconstriction (Hosp. Prac. 19, 67, 1983). This investigation reports the effects of PAF on the properties of three types of cells found in the lung. PAF (1-100, K1/2 = 2.5 pH) caused depolarization of neutrophils as well as generation of chemiluminescence and secretion of hydrogen peroxide. These responses were dependent on the presence of extracellular sodium. However, PAF did not alter oxygen consumption of neutrophils. Although PAF (10 uM) caused depolarization of alveolar macrophages, no stimulation of chemiluminestence, superoxide secretion, or oxygen consumption was observed. However, PAF (10 uM). did potentiate chemiluminescence and superoxide secretion in response to zymosan (2 mg/ml) by 55% and 36%, respectively. In addition, PAF (10-90 uM) caused aggregation of alveolar macrophages. PAF (2-10 uM) also caused depolarization of type II cells, but did not affect membrane integrity or oxygen consumption. However, PAF (10-18 PM) enhanced the activities of two distinct forms of cytochrome P-450 in type II cells and caused aggregation of type II cells at PAF doses above 18 uM. These data indicate that PAF can affect the secretory activity of pulmonary phagocytes and the ability• of type II cells to detoxify foreign compounds (Bureau of Mines Grant - G1175142).INTRODUCTIONPlatelet activating factor (PAF) is a glycerophospholipid (1-0-alkyl-2-acetylsn-glycerol-3-phosphoryl choline) which has been shown to Mediate a broad range of biological activities (1-3). Its pulmonary actions include contraction of pulmonary tissue (4), secretion of leukotrienes from leukocytes (5), airway constriction (6), pulmonary edema (7), and enhanced migration of neutrophils into the airspaces of the lungs (8,9).PAF can be released from several different cell types, such as, basophils, neutrophils and alveolar macrophages, in response to a variety of particulates or membrane stimulants which include zymosan, calcium ionophore, phorbol esters, chemotactic agents, and endotoxin (10-13). Therefore, PAP may play an important role in the development of pneumoconioses by mediating pulmonary responses of lung cells to a variety of occupational dusts. To investigate this possibility, we determined the effects of PAF on several physiological parameters of neutrophils, alveolar macrophages, and alveolar type II epithelial cells."

Jan 1, 1988

By Natalie A. Sapola, Knox Van Dyke, Jean Rabovsky, Vincent Castranova, William H. Pailes, Melanie McPeek, Deloris J. Judy

"INTRODCJCTJONPlatelet activating factor (PAF) is a glycerophospholipid (1-0-alkyl-2-acctyl-sn-glycerol-3-phosphoryl choline) which has been shown to mediate a broad range of biological activities. 1·3 Its pulmonary actions include contraction of pulmonary tissue,4 secretion of leukotrienes from leukocytcs,5 airway constriction,6 pulmonary edema,7 and enhanced migration of neutrophils into the airspaces of thelungs.8-9PAF can be released from several different cell types, such as, basophils, neutrophils and alveolar macrophages, in response to a variety of particulates or membrane stimulants which include zymosan, calcium ionophore, phorbol esters, chemotactic agents, and endotoxin. 1~1 3 Therefore, PAF may play an important role in the development of pneumoconioses by mediating pulmonary responses of lung cells to a variety of occupational dusts. To investigate this possibility, we determined the effects of P AF on several physiological parameters of neutrophils, alveolar macrophages, and alveolar type Il epithelial cells.METHODSIsolation of CellsNeutrophils were isolated from human blood by dextran settling and centrifugal elutriation.14 Isolated neutrophils (93% pure) were resuspended in HEPES-buffered medium (145 mM NaCl, 5 mM KCI, 10 mM HEPES, 5 mM glucose, and 1 mM CaC12; pH = 7.4). Cell number and volume were determined with an electronic cell counter equipped with a sizing attachment.Rat alveolar macrophages were obtained by pulmonary lavage with ea2+, Mg2+-free Hanks balanced salts solution. 15 Alveolar macrophages (94% pure) were resuspended in HEPES-buffered medium, counted, and sized electronically.Rat alveolar type Il cells were isolated by enzymatic digestion for 35 minutes at 37°C with 40 µ/ml type I elastasc and 0.1 % collagenase and purified by centrifugal elutriation. 16.17 Type Il cells (92 % pure) were resuspended in HEPES-buffered medium for measurement of membrane potential, oxygen consumption, and trypan blue exclusion. Type Il pneumocytcs were resuspended in 0.1 M NaCl plus 0.05 M HEPES (pH = 7.8) to measure cytochrome P450-dependent activities and aggregation. Cell size and number were determined electronically."

Jan 1, 1990

By Kermit G. Davis, Sean Gallagher, William S. Marras, Kimberly Kovacs

This study evaluated spinal loads associated with lifting and hanging heavy mining cable in a variety of postures. This electrical cable can weigh up to 10 kg per metre and is often lifted in restricted spaces in underground coal mines. Seven male subjects performed eight cable lifting and hanging tasks, while trunk kinematic data and trunk muscle electromyograms (EMGs) were obtained. The eight tasks were combinations of four postures (standing, stooping kneeling on one knee, or kneeling on both knees) and two levels of cable load (0 N or 100 N load added to the existing cable weight). An EMG-assisted model was used to calculate forces and moments acting on the lumbar spine. A two-way split-plot ANOVA showed that increased load (p<0.05) and changes in lifting posture (p<0.05) independently affected trunk muscle recruitment and spinal loading. The increase in cable load resulted in higher EMG activity of all trunk muscles and increased axial and lateral bending moments on the spine (p < 0.05). Changes in posture caused more selective adjustments in muscle recruitment and affected the sagittal plane moment (p < 0.05). Despite the more selective nature of trunk EMG changes due to posture, the magnitude of changes in spinal loading was often quite dramatic. However, average compression values exceeded 3400 N for all cable lifting tasks.

By A L. Randriamanjatosoa, G Small, C Greet

In flotation simulation models, the effects of pulp chemistry other than pH are often ignored and reduced to particles hydrophobicity or contact angle, neither of which can be measured readily in real time in an operating plant. The flotation response of a given sulphide mineral is known to be influenced and can be improved by changing the chemical characteristics of the pulp during grinding and flotation. The on-line measurement of pulp pH, potential, dissolved oxygen, temperature and oxygen demand of a process stream was completed with the PCM&#174; (Pulp Chemistry Monitor) developed by Magotteaux in this study. The data generated together with relevant plant operating parameters were used to construct an empirical model and simulate the metallurgical performance of the ore. The same approach was also applied to laboratory flotation tests data using various grinding media types. The flotation models better fit the actual data when the chemistry of the pulp is taken into account.CITATION:Randriamanjatosoa, A L, Greet, C and Small, G, 2018. Effects of pulp chemistry on plant and laboratory flotation modelling, in Proceedings 14th AusIMM Mill Operators&#39; Conference 2018, pp 423–432 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 29, 2018

By Claud Johnson, G. Roger Miller, Kristine M. Krajnak, Stacey Waugh, Oliver Wirth

Workers exposed to vibrating hand tools are at risk of developing symptoms such as cold-induced vasospasms, loss of tactile sensitivity, and loss of grip strength in the fingers and hands. These symptoms are known collectively as vibration white finger (VWF) or hand-arm vibration syndrome (HAVS). Symptoms of VWF or HAVS are in part due to repeated and prolonged peripheral vasoconstriction[1, 2]. The reduction in blood flow that occurs with vasoconstriction can result in oxygen deprivation (hypoxia) in soft tissues, such as nerves and muscle, and lead to functional and structural changes in these tissues. The present study examined muscle tissue to determine if vibration-induced changes in transcript levels and protein concentrations result in enhanced vasoconstriction and hypoxia. Manual dexterity was also assessed intermittently to determine if vibration-induced changes in cellular factors are accompanied by performance deficits. Methods An animal model was developed to study the biological and functional changes that occur in response to repeated segmental vibration exposures. In this model, the right paw of intact rats was exposed to a platform vibrated at a frequency 250 Hz and amplitude of 49 m/s2 to simulate the vibration characteristics of hand-held grinders. Three groups of 8 rats each were studied: a vibration-exposed group, an exposure-control group, and a cage-control group. Exposure sessions, with or without vibration, were conducted 4 hr/day, 5 days/week for 5 weeks. Manual dexterity was assessed intermittently during the 5-week exposure period with the Montoya stair-case test[3], which quantifies the rat’s ability to reach for, grasp, and retrieve small food pellets placed below the rat on different levels or steps. Following the 5-week exposure period, the flexor muscles of the right forelimb were collected for analysis of gene expression, protein concentrations, and immunohistochemistry. Results Vibration-exposure resulted in an approximate 2-fold increase in the expression of a2C and a1D receptor transcripts in flexor muscles (Figure 1). These receptors mediate norepinephrine-induced vasoconstriction in smaller arteries. Vibration-exposure also resulted in an approximate 2-fold increase in hypoxia-induced factor-1a (HIF-1a), a transcription factor that is expressed in response to tissue hypoxia. Western analyses demonstrated that restraint caused a decrease in a1-receptor protein concentrations in the flexor, but vibration-exposure prevented the restraint-induced reduction (Figure 2). Immunohistochemistry performed on flexor muscles (not shown) demonstrated that a1 receptors are primarily located in arteries; maintained levels of these receptors could contribute to prolonged vasoconstriction following repeated vibration exposure. The staircase test showed some performance improvement, or a training effect, in manual dexterity for the control groups but not the vibration-exposed group (Figure 3).

Jan 6, 2006

By S. K. Kawatra, S. J. Ripke, T. C. Eisele

It was determined by the authors that the water that remains in the filter cake after filtration in iron ore concentrators can contain several hundred times greater concentrations of calcium ions and other cations, due to surface chemical effects carrying the ions along with the water. Filter cake from two plants was analyzed. The water retained in samples of magnetite concentrate filter cake in Plant 1 contained 5088 ppm calcium and 5995 ppm magnesium, while the Plant 2 filter cake contained 231 ppm calcium and 119 ppm magnesium. These levels were dramatically elevated compared to the water that was removed from the concentrate by filtration for recycle to the plants (9 ppm calcium/15 ppm magnesium for Plant 1, and 11.9 ppm calcium/9.3 ppm magnesium in Plant 2). In addition to possible effects on agglomeration performance, the presence of these cations also affected the efficiency of filtration. In order to reduce the effects of these cations on filtration in Plant 2, carbon dioxide was injected into the slurry before it entered the filter press. This was found to increase filtration rates by up to 23.7%. Comparison of the results from the two plants shows that the concentrations of cations present in the filter cake will vary greatly from plant to plant, with correspondingly large variations in their effects on plant operations.

Jan 1, 2004

By Jun Lu

There are many factors affecting the strength of pillar, including width-to-height (W/H) ratio, mechanical properties of coal and surrounding rocks, property of partings in the coal, and the interface property between coal seam and the roof/floor. In this paper, the effect of varying pillar?s width-to-height ratio (W/H=3, 5, 7, and 10) and coal/rock interface cohesion (Cj =50 psi, 150 psi, and 300 psi) on pillar strength has been studied. The confinement effect of W/H ratio and interface shear strength is investigated by studying their effects on the average minimum principal stress developed in the pillar. The deformation behavior of the coal pillar is investigated. It is found that the pillar?s transition from strain softening to strain hardening behavior depends on its W/H ratio and the interface shear strength.

Jan 1, 2008

By John J. Strohl, Henry J. Schwellenbach

This paper relates the results obtained by decreasing the size of feed to a rod mill screen circuit. As would be expected, added production was gained and a finer grind with no tonnage loss was made possible.

Jan 12, 1950

By Myers, J. F.

The purpose of the mill tests reported herein, was to determine the relative power efficiency of fast and slow rod mill speeds on the ores of the Tennessee Copper Co. The tests were carried out at the lsabella Mill of the Tennessee Copper Co. under normal operating conditions. Every effort was made to keep the ore supply and other conditions constant, but it will be noted that some slight variation did occur. The open circuit 6 by 9 rod mill, and ore, used in these tests have been previously described.&apos; Four motor drive pinions were available and the tests were performed in the following manner: each pinion was used to drive the mill for a period of one week. Constant sampling prevailed during the test run, and a composite sample for each speed test was made. Realizing that some slight liner wear took place during the four-week test-run, and that some slight variation of the ore may have taken place, a second and then a third series of four-week test- runs were made with the four different pinions. The screen analysis of each of the thee-week run samples at the various speeds were composited and the results are shown in Table 1. The authors feel that the 12 weeks of operation consumed during these test-runs would represent fairly the effect of each mill speed. The data of line 37 show that within the error of sampling and plant operation, the tons of minus 65-mesh material generated per horsepower hour was the same at all four speeds.

Jan 1, 1949