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By Elizma Ford, Vincent Sithole

"Two shortened test procedures for estimating the Bond ball work index are compared for suitability of use on Zambian/DRC-type copper–cobalt ores. The first procedure is based on a batch milling test while the second procedure is based on a limited locked-cycle test. Both procedures were conducted using a standard Bond test mill. INTRODUCTION The Bond ball work index is widely used in the field of minerals processing as an indicator of ore grindability. The work index is determined by means of a locked-cycle test procedure that typically requires seven to eight cycles to stabilise at a re-circulating load of 250%. A typical test requires between three to four kilogram of ore sample and around eight hours of operator time. For geometallurgical test work applications, where a large number of variability samples are to be tested, it would be highly beneficial to use a test procedure that requires less sample mass and operator time. Certain test work laboratories, for example SGS and JK Tech, are already offering various types of shortened test procedures for estimating the Bond ball work index. This paper discusses a comparison of two shortened test procedures that were evaluated for suitability of use on Zambian/DRC-type copper–cobalt ores. EXPERIMENTAL Test Procedure 1 – Batch Milling The first test procedure is derived from a batch milling approach proposed by the University of Hacettepe (Aksani, 2000). Some modifications were, however, made to the data analysis method from that originally proposed. During this test procedure, a 700 mL volume of sample is milled in a standard Bond test mill for a pre-determined number of revolutions. The feed and product particle size distributions are measured for each test. These results are then used to back-calculate a cumulative breakage rate parameter (k) for each particle size, according to the following formula:"

Jan 1, 2015

By K. K. Kelley

The first bulletin (245)3 in this series, which appeared in 1932, summarized the entropy values then available for the elements and inorganic compounds, results being listed for some 150 substances. In the interim advances in the realms of spectroscopy applicable to the determination of thermodynamic properties and in the development of methods of calculation therefrom have added many highly accurate values. Moreover, through the efforts of Prof. W. M. Latimer (286) and his coworkers, satisfactory entropy values are now available for all but a few of the common inorganic ions in aqueous solution. At the same time rapid progress has continued in the study of low-temperature heat capacities in several laboratories, In addition, compilation and correlation of data pertaining to vapor pressures (247), thermodynamic properties of carbonates (258), thermodynamic properties of sulfur and its inorganic compounds (250), and the thermodynamic properties of metal carbides and nitrides (251), which were published as members of this series, have yielded many values. As a result, over 500 usable entropy values for inorganic substances may now be tabulated. This bulletin originally was planned as a second revision of the first member of this series, the first revision (249) having appeared in 1936; however, because of requests for the explanatory section of the first bulletin from those teaching thermodynamics, it was decided to com¬bine the information in the first bulletin and its revision with the data that have appeared since 1935 and to repeat the explanatory material in somewhat more detail. The purpose of this bulletin is therefore to give the available values of the entropies at 298.1° K. of the elements and inorganic compounds, together with enough explanation of the methods employed in calculating entropies to make the results comprehensible.

Jan 1, 1941

By E. Ghali, N. Sorour, G. Houlachi

"The binary Fe53Mo47 and ternary Fe54Mo30P16 coatings have been electrodeposited from citrate-based electrolyte on mild steel (MS) substrates. The electrodeposition has been conducted for 6 hours at 20 mA cm-2 and 30°C. The electrochemical tests were carried out in chlorate solutions containing 300 g L-1 NaCl and 4 g L-1 K2Cr2O7 at pH 6.4 and 80°C. A number of surface characterization techniques such as SEM-EDS, XRD and EMP were used to study the microstructure of the alloys. The electrocatalytic activity of these coatings was investigated using steady-state polarization and galvanostatic technique. This study revealed that the Fe-Mo-P coating could be considered as a promising cathode material for the hydrogen evolution reaction (HER). The results showed an important decrease of hydrogen overpotential for Fe-Mo-P alloy as compared to that of Fe-Mo and especially MS which is a traditional cathode in chlorate industry. The HER overpotential for Fe54Mo30P16 at current density of 250 mA cm-2 was decreased by 30% in comparison to that of MS (1029 mV), and by 16.5% to that of Fe53Mo47 coating (857 mV).INTRODUCTIONSodium chlorate is used for manufacturing of several daily consumption products. This chemical is mainly employed for the production of chlorine dioxide (ClO2) that is a bleaching agent used in the pulp and paper industry. The ClO2 is also consumed for generation of perchlorates, chlorites and other chlorates, as an herbicide and in uranium processing (Cornell, 2002). Sodium chlorate is produced industrially via following overall formula in un-divided electrochemical cell (Nylén & Cornell, 2009):"

Jan 1, 2016

By Howard Smith

AT the meeting of this Institute in February 1933, I presented a paper on potash development in southeastern New Mexico1, which contained a brief review of the Geological Survey's 20-year search for commercial sources of soluble potash minerals and of the events, that led to the discovery, exploration, and first development of the deposits in that state. As a more comprehensive review of the subject was published in December2, the present paper is intended only to discuss recent developments in the domestic potash industry, particularly in New Mexico. A summary of the findings of potash in the Permian Basin, by. G: R. Mansfield and W. B. Lang, geologists of the United States Geological Survey, is now in process of publication by the University of Texas and will be omitted from this paper. In New Mexico prospecting for potassium salts during the past two years has increased materially the known area .of commercial deposits; development has resulted in an increase from one to three in the number of shafts and the starting of a fourth; an increase of annual productive capacity to 1,000,000 tons of crude salts, or 250,000 tons of K20; and an increase in annual refining capacity to 140,000 tons of muriate of 62.5 per cent grade. Construction has been completed to increase still further the production of high-grade salts. In California the American Potash & Chemical Co., operating on Searles Lake brines, has increased its plant capacity from about 100,000 tons to 180,000 tons of muriate a year and is now producing soda ash and salt cake in addition to potash and borax. Potash production from cement-plant and industrial-alcohol wastes remains unimportant.

Jan 1, 1935

By Helmut Hass, Marco Ziller

"Abstract: 1 Sophia Spoortunnel Marco Ziller, Trevi S.p.A.:For the construction of 14 cross passages connecting the twin tunnels of the Sophiaspoortunnel the Artificial Ground Freezing technique was applied as temporary soil improvement. AGF by Brine and Liquid Nitrogen was implemented. Automatic data acquisition and recording systems were installed to monitor the variation of the temperatures in the soil during the freezing intervention in order to control the behaviour and the efficacy of the treatment.IntroductionThe Sophia rail tunnel is a bored tunnel with a length of 4.24 km, comprising two separate parallel tubes with an outside diameter of 9.45 m. The twin tunnels were excavated by a TBM equipped with hydroshield. Seven service shafts, approximately 30 m deep, were constructed in between the tunnels. From each shaft two cross passages were constructed connecting the shaft with both tubes, for a total of 14 cross passages.The Artificial Ground Freezing technique utilizing both the Brine and Liquid Nitrogen methods was used for temporary waterproofing and soil support to allow the excavation of the cross passages. The natural soil to be frozen was consisting in loose sand and clay under a hydrostatic pressure up to 250 kPa.For the measurement of the ground temperature. Automatic data acquisition and recording systems were installed to monitor the variation of the temperatures in the soil and at the contact with the tunnel lining. Furthermore, a comprehensive computerized system of sensors and cryogenic valves was designed and implemented in order to manage the whole Nitrogen process.Soil Main CharacteristicsThe soil stratigraphy is generally consisting in Clay (Holocene) from ground level to -15 m depth, followed by Pleistocenic Sand, from -15 to -25 m, and Clay below -25 m."

Jan 1, 2014

By Roy Moreby

Dartbrook Coal is currently developing a modern, high production (3.5 Mtpy) single longwall retreat coal mine in the Upper Hunter Valley of NSW, Australia. The location is a green field site, with no surface or underground mining operations ever having taken place in the initial target seams. The coal seams of the working section, floor and immediate roof average a total 20 m in thickness and contain a mixed carbon dioxide 1 methane seam gas ranging from 6.5 to 11.0 m3/t. The target seams have undergone detailed characterisation to assess hazards and quantify the controls required to minimise associated risks during mining. Risks identified during initial phases of exploration and 14 months of development include: • High gas emission during development. • Probable high longwall gas emission rate. • Medium to high propensity to spontaneous combustion • Possible carbon dioxide outbursts on geological structures • The main controls currently in place include, • Mine geometry and ventilation circuits • Exploratory drilling ahead of development • Intensive in seam pre drainage • Goaf drainage plants • Comprehensive monitoring systems • Underground environmental management plan. • Pre mining predictions of gas emission provided an indication of gas emission rates which have proven to be an under estimate. Current mine issues are; • Both surface fans are at full capacity (250 m3/s 1.4 kPa) • Both gas drainage pumps are at full capacity (2.3 m3/s) • Alternatives to extensive in seam pre drainage being investigated (surface to in seam hydro fracture) Review of mine design underway This paper describes the seam characterisation, assessment of mining hazards and summary of the management plan developed to address the risks identified. A review of current mine underground environmental performance is also provided

Jan 1, 1997

By Howard J. Smith

At the meeting of this Institute in February 1933,I presented a paper on potash development in southeastern New Mexico1, which contained a brief review of the Geological Survey's 20-year search for commercial sources of soluble potash minerals and of the events that led to the discovery, exploration, and first development of the deposits in that state. AS a more comprehensive review of the subject was published in December2, the present paper is intended only to discuss recent developments in the domestic potash industry, particularly in New Mexico. A summary of the findings of potash in the Permian Basin, by G. R. Mansfield and W. B. Lang, geologists of the United States Geological Survey, is now in process of publication by the University of Texas and will be omitted from this paper. In New Mexico prospecting for potassium salts during the past two years has increased materially the known area of commercial deposits; development has resulted in an increase from one to three in the number of shafts and the starting of a fourth; an increase of annual productive capacity to 1,000,000 tons of crude salts, or 250,000 tons of K2O; and an increase in annual refining capacity to 140,000 tons of muriate of 62.5 per cent grade. Construction has been completed to increase still further the production of high-grade salts. In California the American Potash & Chemical Co., operating on Searles Lake brines, has increased its plant capacity from about 100,000 tons to 180,000 tons of muriate a year and is now producing soda ash and salt cake in addition to potash and borax. Potash production from cement-plant and industrial-alcohol wastes remains unimportant.

Jan 1, 1938

By Howard J. Smith

At the meeting of this Institute in February 1933,I presented a paper on potash development in southeastern New Mexico1, which contained a brief review of the Geological Survey's 20-year search for commercial sources of soluble potash minerals and of the events that led to the discovery, exploration, and first development of the deposits in that state. AS a more comprehensive review of the subject was published in December2, the present paper is intended only to discuss recent developments in the domestic potash industry, particularly in New Mexico. A summary of the findings of potash in the Permian Basin, by G. R. Mansfield and W. B. Lang, geologists of the United States Geological Survey, is now in process of publication by the University of Texas and will be omitted from this paper. In New Mexico prospecting for potassium salts during the past two years has increased materially the known area of commercial deposits; development has resulted in an increase from one to three in the number of shafts and the starting of a fourth; an increase of annual productive capacity to 1,000,000 tons of crude salts, or 250,000 tons of K2O; and an increase in annual refining capacity to 140,000 tons of muriate of 62.5 per cent grade. Construction has been completed to increase still further the production of high-grade salts. In California the American Potash & Chemical Co., operating on Searles Lake brines, has increased its plant capacity from about 100,000 tons to 180,000 tons of muriate a year and is now producing soda ash and salt cake in addition to potash and borax. Potash production from cement-plant and industrial-alcohol wastes remains unimportant.

Jan 1, 1938

By E. H. Greener, M. E. Fine

The internal friction (1/Q) of cobalt Fig. 1 (measured by an electrostatic dynamic method1) near 250°C begins to increase rapidly on heating and continues to increase until 560°C, the highest tem- perature measured. In the plot of log of 1/Q against 1/T, above 250°C the data nearly fit two straight lines intersecting at 400°C, approximately the temperature of the hexagonal-cubic transformation. The higher temperature branch corresponds to an effective activation energy of 6500 cal per mole, the lower temperature branch 11,000 cal per mole. Young's modulus Fig. 2 increases approximately

Jan 1, 1959

By J. A. Ruppert, P. M. Sullivan

A study was made of filtration techniques for recovering the major part of the tin contained in iron - tin alloys known as hardhead . Special smallscale filtering apparatus and a three - stage cyclic process were developed . Eighty- seven percent of the tin contained in an alloy of 82 percent tin and 17 percent iron was recovered as pure metal by pressing at 975° C followed by a second pressing at 800 ° C and a final filtering at 250 ° C. Small amounts of Sb , Cu , and Fe impurities were removed by adding Al to the molten product and performing another filtration at 250 ° C.

Jan 1, 1964

By J. F. Kemp

PAGE Introductory Description of Deposits of this Type,.....244 Topography of the Ducktown Region,...247 Geology and Petrography,...248 The Mineralogy of the Ores and Gangue,..249 The older minerals : Amphibole, 250 ; Pyroxene, 250; Garnet, 251; Zoisite, 252; Calcite, 258 ; Quartz, 259 ; Apatite, 259 ; Rutile, 259. The Sulphides: Pyrite, 259; Zincblende, 259; Galena, 260; Pyrrho tite, 260; Chalcopyrite, 260. Later minerals, not belonging to the Gossan: Quartz, and certain sul phides, 261 ; Graphite, 261. The Formation of the Ore,...262 The Gossan Minerals,...........263 Bibliography,............265 Introductory Description of Deposits of this Type. Ore-bodies of more or less lenticular shape and lying parallel with the foliation of schists and slates form a group of

Jan 1, 1902

By W Lunwongsa, S Meffre, S Nuanla-ong, K Zaw, R James, A Salam

Gold and silver mineralisation at the Chatree low sulfidation deposit is hosted in andesitic volcanic and volcaniclastic rocks and characterised by multiple hydrothermal alteration assemblages and quartz-carbonate (chlorite-adularia) replacements, veins and breccias. The ore-bearing veins are influenced by intersecting structures and host rock lithologies. Emplacement of the host succession occurred at 250 ¦ 6 Ma (dated with laser ablation ICP-MS U-Pb zircon techniques), which was closely followed by mineralisation at 250.9 ¦ 0.8 Ma based on the analysis of adularia from coarse-grained quartz-sulfide (chalcopyrite-pyrite- sphalerite) veins using laser ablation Ar-Ar methods. An EXTENDED ABSTRACT is available for download. A full-length paper was not prepared for this presentation.

Jan 1, 2008

Estimated Receipts Dues Arrears $ 3,500 00 Current 108,115 00 New Members - 11,937 00 In Advance 1,763 00 $125,315 00 Initiation Fees - 7,250 00 Initiation Fees-Additional if increased to $20 00 7,250 00 Sale of Transactions 3,000 00 Sale of Binding 7,092 00 Sale of Magazine 2,913 00 Sale of Pamphlets 370 00 Sale of Indexes and Emmons Vols 313 00 Sale of Pyrometry 900 00 Sale of Raymond Vol 100 00 Interest received on Bank Balance . 500 00 Interest received on Life Memberships 500 00 Advertising-Gross 27,000 00 Voluntary Subscriptions-Estimated 16,000 00 Income from James Douglas Fund 5,000 00 Total $203,503 00

Jan 1, 1923

[Estimated Receipts Dues: Arrears $ 3,500.00 Current 108,115.00 New Members 11,937.00 In Advance 1,763.00 $125,315.00 Initiation Fees 7,250.00 Initiation Fees-Additional if increased to $20.00 7,250.00 Sale of Transactions....3,000.00 Sale of Binding 7,092.00 Sale of Magazine 2,913.00 Sale of Pamphlets 70.00 Sale of Indexes and Emmons Vols 313.00 Sale of Pyrometry 900.00 Sale of Raymond Vol 100.00 Interest received on Bank Balance 500.00 Interest received on Life Memberships 500.00 Advertising-Gross 27,000.00 Voluntary Subscriptions-Estimated 16,000.00 Income from James Douglas Fund 5,000.00 Total $203,503.00] [ ]

Jan 1, 1925

By M. E. Fine, A. A. Henderson

Investigation of the tensile properties of silver based aluminum alloy crystals was undertaken because it appeared attractive for studying strengthening effects due to Suzuki locking with minimum complication. Yield drops were observed in all alloy crystals (1, 2. 3. 4, and 6 at. pct Al) after strain aging at room temperature. No yield drops were found in similarly grown and tested silver crystals. The yield effects are attributed to Suzuki locking but the major portion of the solid solution strengthening to other mechanisms. INVESTIGATION of the tensile properties of single crystds of silver alloyed with aluminum was undertaken because it appeared to be a system in which segregation at stacking faults associated with partial dislocations1 would be the dominant factor in anchoring dislocations. First, silver and aluminum have closely similar atomic sizes and thus solute atom locking of a dislocation due to elastic interactions should be unimportant. Second, while both X-ray2 and thermodynamic3 investigations show short-range ordering in silver-based aluminum alloys, the degree of local order is quite small (X-ray measurements give v = EAB - 1/2(EAA + EBB) = - 0.025 ev and thermodynamic measurements give v r -0.007 ev) and should not be important in strengthening dilute alloys. Third, the stacking fault energy of silver is probably low (as indicated by the profusity of annealing twins) and is very likely diminished further and quite rapidly by aluminum additions since the A1-Ag phase diagram shows a stable hexagonal phase at only 25 at. pct Al. Also, a careful investigation in this laboratory4 has shown that the ratio of twin to normal grain boundaries in recrystallized alloys increases with aluminum content. Thus, with minimum complication from other factors, Ag-A1 alloys seem attractive for studying strengthening effects due to segregation at stacking faults of extended dislocations. EXPERIMENTAL METHOD Single crystals measuring 250 by 5 by 1.5 mm of pure Ag (99.99 pct) and Ag-A1 alloys (A1 of 99.999 pct purity) of nominal compositions* 1, 2, 3, 4, and 6 at. pct were grown in high-purity graphite molds from the melt under a dynamic vacuum (1 x l0-5 mm Hg). The technique consisted of moving a furnace having a hot zone (which melted about 0.5 cm of alloy) over a horizontal, evacuated quartz tube con- taining the mold and alloy at a rate of 3/8 in. per hr. Chemical analysis showed roughly the first inch of the crystal to be solute poor, the last inch solute rich; and the center section uniform in composition within the sensitivity of the analytical method (± 0.2 at. pct Al). The center section of the crystal was cut into five specimens. Gage lengths of reduced cross section, measuring from 1.5 to 2 cm in length, were mechanically introduced by means of jeweler&apos;s files and fine abrasive cloth with the crystal firmly held in polished steel guides. One-third of the cross section was then removed by etching and electro-polishing, the crystals were all subsequently annealed for several days at 850°C in a dynamic vacuum (<1 x 10-5 mm Hg) and furnace cooled to 200°C. The crystal orientations were determined using the usual back-reflection Laue technique. The Laue spots were sharp and of the same size as the incident beam. However, microscopic examination showed the crystals to contain substructures with subgrains of the order of a micron in diameter. The details of this substructure are presently under investigation. Tensile testing was done with a table model Instron using a cross-head speed of 0.002 in. per min. For testing at various temperatures the following media were used: 1) 415oK, hot ethylene glycol; 2) 296ºK, air, acetone, water; 3) 273ºK, ice water; 4) 258ºK, ethylene glycol "ice" in ethylene glycol; 5) 200°K, dry ice in acetone; 6) 77ºK, liquid nitrogen. EXPERIMENTAL RESULTS A) Yield Behavior—A portion of an interrupted stress-strain curve for a 6 at. pct A1 crystal of the indicated orientation tested at room temperature is shown in Fig. 1. Initially, at (a), there is a small, gradual yield drop of about 10 mg per sq mm2. However, on stopping the test, and aging for a few minutes at (b), a sharp yield drop is found. Aging for longer times at (c) and (dl results in larger yield drops (and larger AT&apos;S). At, defined in Fig. 1, is usually larger than the yield drop by about 20 pct; however, this increase in the lower yield is transient since extrapolations of the flow stress curves join as may be seen from Fig. 1. (Both Laue and low-angle scattering photographs revealed no evidence of precipitation in a strain-aged 6 at. pct A1 crystal.)

Jan 1, 1962

By N. Fardin, O. Stephansson, L. Jing

A pair of silicon rubber replicas of size 250 mm by 250 mm, from a natural rock joint, was used to produce several high strength concrete fracture replicas of different sizes, from 50 mm by 50 mm to 200 mm by 200 mm. The morphology of the concrete fracture replicas were digitized at the laboratory using a 3D-laser-scanning machine with high accuracy and resolution. The scale dependency of the geometrical properties, including surface roughness and aperture, of the samples were investigated using fractal method. The investigation was extended to study the scale effect on the mechanical properties of the concrete fracture replicas. Four concrete replicas having same geometry from each sampling size were sheared under four different normal loads. The results show that normal and shear stiffness and peak shear strength decrease with increasing sample size and decreasing normal stress. It is concluded that for accurate determination of geometrical and mechanical properties of rock joints in the laboratory and field scales, samples with size equal to or larger than stationarity limit are required. Silikongummiabdrücke der Größe 250 mm x 250 mm einer natürlichen Kluft dienten als Vorlage für mehrere Hochfestbeton Rissreplikas verschiedener Größe. Die Morphologie der Beton Rissreplikas wurde mittels eines 3D-Laserscanners hoher Genauigkeit und Auflösung im Labor digitalisiert. Die Skalenabhängigkeit der geometrischen Eigenschaften, dies inklusive Oberflächenrauhigkeit und Öffnungsweite, wurden mittels Fraktalen bestimmt. Die Studie wurde durch die Untersuchung der mechanischen Eigenschaften der Betonrepliken erweitert. Hierbei wurden vier Betonrepliken der selben Geometrie jeder Probengrösse unter vier verschiedenen normalen Belastungen abgeschert. Die Ergebnisse zeigen das sowohl Normal- und Schersteifigkeit als auch die Spitzenscherfestigkeit mit zunehmender Probengrösse und abnehmender Normalspannung abnehmen. Es hat sich gezeigt, daß für eine genaue Bestimmung der geometrischen und mechanischen Eigenschaften von Felsklüften im Labor und im Feld Proben einer Größe gleich oder größer des stationären Limits verlangt werden. Deux répliques en gomme de silicone d’une fracture naturelle, de dimension 250 mm par 250 mm, ont été utilisées pour produire des répliques en béton de haute résistance de dimensions allant de 50 mm par 50 mm à 200 mm par 200 mm. La morphologie de ces répliques a été digitalisée au laboratoire à l’aide d’un laser-scanner 3D haute résolution et haute précision. L’influence de l’échelle des propriétés géométriques, incluant rugosité et ouverture, a été étudiée en utilisant la méthode des fractales. Des essais complémentaires ont été réalisés afin d’étudier l’effet d’échelle sur les propriétés mécaniques des répliques de fracture en béton. Quatre répliques béton de même géométrie pour les différentes tailles d’échantillons ont été cisaillées sous quatre valeurs de contrainte normale. Les résultats montrent que la rigidité normale et tangentielle ainsi que la résistance de pic diminuent en proportion de l’augmentation de la taille de l’échantillon et de la diminution des contraintes normales. On peut en conclure que, pour une détermination précise des propriétés géométriques et mécaniques des fractures au laboratoire et sur le terrain, des échantillons de taille égale ou supérieure à la limite stationnaire sont nécessaires.

Jan 1, 2003

By F. W. Hoertel

Near-optimum parameters were determined by the Bureau of Mines for vapor deposition of rhenium on heated copper substrates by hydrogen reduction of rhenium hexafluoride (ReF6). High-purity deposits of nearly 90-percent theo¬retical density were obtained with the reaction chamber at 250° C, with an H2 to ReF6 volume ratio of 25 to 1, and with an ReF6 flow rate of 5 grams per hour. Some rhenium deposited as a loose, black powder. When the established near-optimum parameters were carefully followed, this could be minimized but never completely avoided. Varying the reaction chamber pressure, both above and below atmospheric, yielded excessive quantities of rhenium powder. Deposition efficiencies, based on only the coherent metal, ranged between 70 and 75 percent. Massive deposits contained only spectrographic traces of impurities. The average microhardness (Knoop, 100-gram load) of vapor-deposited rhenium was 907. Limited research on the deposition of rhenium-tungsten alloys by reduction of the mixed hexafluorides produced deposits in which linear composition gradients were pronounced; this nonhomogeneity was attributed to the wide variation in optimum hydrogen-reduction temperatures of the two hexafluorides (250° C for ReF6 and 550° C for WF6). Using deposition temperatures between 250° and 550° C did not eliminate the composition variations.

Jan 1, 1967

"Chairman: Dr R. E. ROBINSON Rapporteur: Dr R. P. COLBORNPapers:The simulation of crushing plants by W. J. WhitenSimulation of multi-component flotation plants by B. K. Loveday and G. R. MarchantComputer control of flotation at the Ecstall concentrator by M. P. Amsden C. Chapman and M. G. ReadingModel for the design and control of flotation plants by R. P. KingIn presenting his paper Dr W. J. Whiten outlined the basic concepts on which the control model was based and emphasized the fact that empirical models based as much as possible on theory were used to simulate each unit of the crushing plant. The final parameters of each model were computed using data collected from the plant. Unfortunately, the system did not permit accurate extrapolation but was successful when operating in the region from which the parameters were calculated.He concluded from the results of the test work that the crusher amperage was a critical parameter and that the utilization of the model gave a 15 per cent increase in the plant output. This was because the model predicted that a marginally fine grind would provide a significant increase in throughput. Dr Whiten elaborated on what constituted the multiple spline regression, explaining that it was a least-squares curve-fitting technique in one or more dimensions, where the calculation of coefficients in analytic expressions was replaced by the calculation of typical points on a very smooth curve called a spline function. The emphasis was placed on the shape and value of the curve or curves instead of on the coefficients as in analytic regression. A spline function was the line drawn between all points constituting the data set.Dr B. K. Loveday commented that the simulation was unusual in that the optimum throughput was considered to be the maximum throughput, which, surely, was limited by the crusher size. He also emphasized the importance of the interaction between both crushing and grinding circuits and added that in practice the optimum operating conditions were inter-dependent. Dr Whiten replied that in the case of the plant under consideration, the crushing process was not, in fact, the limiting operation.Mr C. E. Clifford indicated that the model was being used to simulate a number of crushing and grinding circuits at Mount Isa Mines. He reported that the model simulated the circuit satisfactorily for primary and secondary gap settings of 0,625 in. to 0,375 in., but that adjustment had to be made to the model parameters for gap settings of 0,250 in. to 0,125 in.In reply to a question from Dr D. M. Hawkins, Dr Whiten said that he preferred to use low-order splines with smaller segments rather than high-order spline functions with large segments."

Jan 1, 2014

By O. Schaaber

THE existence of isothermal martensite without the presence of the athermal form thus far has been established only in a 6 pct Mn, 0.6 pct C steel&apos; and a 23 pct Ni, 3.5 pct Mn-Fe alloy.&apos; " Theoretical calculations, moreover, predict this phenomenon to be observable only within narrow composition limits.&apos; In all other steels, it is generally considered that martensite inevitably forms upon cooling below the M, temperature. Even the possibility of isothermal martensite transformation has been questioned for the common steels, although Averbach and Cohen" showed that martensite formation does not stop when the cooling is arrested and that as much as 5 pct retained austenite may transform isothermally to martensite at room temperature. This note presents some observations made on a number of low alloy steels by dilatometric and inductive measurement of isothermal austenite transformation at various temperatures close to the Ms. In the dilatometer studies reported previously, austenitized specimens were immersed in a salt bath maintained at proper temperature and immediately inserted into the dilatometera8&apos; already at thermal equilibrium with the bath. The dilation was read on a dial gage divided into 0.001 mm intervals. Induction measurements were made with a separate excitation source and a test coil, sealed together in a salt-tight case. The increase in the induced voltage caused by the transformation products was recorded at a paper speed of 4 mm per sec. The steels studied are listed in Table I. Specimens prepared from steels 1 and 2 were in the form of hollow cylinders 60 mm long, 10 mm ID, 14 to 16 mm OD, while specimens of steels 3 and 4 were in the form of notched-bar impact test specimens, DVM type. Specimens of steel 5 were in the form of strip, 7x0.3 mm. In the bainitic range, curves representing the amount of transformation vs log time have a single step appearance, as is shown by the curve of isothermal transformation at 320°C in Fig. 1.Y ransformation proceeds in accordance with the Austin-Rickett equationo P -----------= k t" 100-P where P is the percentage of transformed austenite, t is time, and k and n are constants. Near the M, temperature, however, complex curves having two steps are observed. As shown in a previous papera for steel 3 isothermally transformed at 245"C, such complex curves can be separated into two separate transformations or reactions each following the Austin-Rickett equation. The values of n in the equation for a number of such two-step transformations are listed in Table 11 for steel 1. At transformation temperatures of 250" and 235"C, evidence of a second transformation is very

Jan 1, 1956

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Jan 1, 1939