Search Documents

By Charles C. Hawes

DETERMINATION OF SILICA OXIDE iron ores usually are found in intimate association with silica and phosphorus compounds. Their quantitative separation and purification sometimes present difficult problems to the chemist. Silicic acids may represent various degrees of dehydration. They are exceedingly weak, but combine with metallic acids and form some of the most stable oxides in nature, the silicates. When iron ores are treated with hydrochloric acid, they yield practically all their iron. However, apart from rare exceptions, varying amounts of insoluble residues of silica, alumina, lime, magnesia and compounds of phosphorus, sulphur, titanium, chromium and others will be left. If the oxides of silicon, aluminum and titanium are present in small quantities, the insoluble residue is generally very small, but the presence of these oxides more usual in larger quantities. Therefore, only a special treatment can break the bond between these elements. Ore Residues Acids remove the soluble constituent of the ore, leaving the insoluble residue, which chemically is rock or gangue and must be treated accordingly. Alkali carbonates are used frequently to break up the residue, but other fluxes have also been recommended, such as a number of lead and boron salts. The introduction of these salts, which offers certain advantages, requires, however, their removal before the other constituents can be analyzed, and this elimination is sometimes difficult. Usually in quantitative analysis silicates are dissociated by fusing them in a platinum crucible with sodium carbonate, thereby forming sodium silicate, Na2SiO3, sodium aluminate, Na2A1204, sodium titanate, Na2TiOs, and carbonates of other elements. All the carbonates are soluble in hydrochloric acid, but also some silicic acid is formed that must be rendered insoluble. To this end the solution is evaporated several times, as the first evaporation still leaves as much as 5 per cent of the silica soluble. Even after a number of evaporations, minute quantities of silica may be found with the iron and alumina present. Perchloric Acid as an Agent for Dehydrating Silicic Acid Perchloric acid, HCI04, (60 per cent), has been used for years as a solvent, but few chemists have used it to dehydrate silica. It is derived from anhydrous perchloric C1207, which is most unstable and dangerous. Perchloric acid is a strong oxidizing agent, which boils at 203°C. It is more effective in rendering silica insoluble than any other known agent, and most rapid in action. After perchloric acid is added to a mixture containing silicic acid, the resultant solution is

Jan 1, 1945

By E. P. Klier

THE work of Klier and Lyman1 on the bainite reaction has led to the full description of this reaction for medium-carbon low-alloy steels. Certain experimental data reported by Klier and Lyman appear, however, to be improbable of obtaining in very high-carbon steels. The study herein reported consists of an analysis of the transformation characteristics of a 3 per cent chromium, 1 per cent carbon steel by means of X-ray and metallographic methods. From the results obtained it is concluded that the bainite reaction in this steel is more complicated than that reported by Klier and Lyman for the low-carbon low-alloy steels. However, the mechanism of bainite formation in this steel appears to be essentially the same as proposed for the low-carbon low-alloy steels with the modification that the first volumes to transform are carbon-rich rather than carbon-poor. EXPERIMENTAL PROCEDURE The analysis of the steel studied was: Cr, 2.89; C, 1.02; Mn, 0.33; Si, 0.35; S, 0.012; P, 0.020. The stock was received from the Carpenter Steel Co. in rolled bars. Specimen Preparation Specimens were austenitized at 1200°C. (2192°F.) for 25 min. in purified nitrogen. The resultant A.S.T.M. austenite grain size was 0-1. Isothermal transformation was allowed by quenching the specimens into liquid metal baths controlled to ±5°C. at 540°C. (1004°°F.) and above, and to ±2°C. at 490°C. (914°°F.) and below. Following the desired degree of transformation all specimens were water quenched. Metallographic Examination Specimens 1/4 in. round by 1/4 in. were used for metallographic examination. Etchants used were Vilella's reagent (1 gram picric acid, 10 ml. hydrochloric acid to make l00 ml. ethyl alcohol solution) and alkaline sodium picrate (electrolytic). Vilella's reagent was effective in revealing all microconstituents, while the alkaline sodium picrate developed the carbon-rich structures or carbides only. X-ray Examination Two X-ray techniques were used-the Debye-Scherrer method and a back-reflection method. The small specimens necessary for the Debye-Scherrer method were austenitized and then allowed to transform, or were cut from the larger metallographic specimens. The metallographic specimens were used for the back-reflection X-ray analysis. When it was desirable to determine the structure of the carbide present, sliver specimens were electrolytically etched to develop a carbide coating, then were exposed in the cameras. This technique was frequently necessary to allow positive identification of the carbide.

Jan 1, 1945

The effect of change in slag composition upon metal losses to the slag and the relationship between slag composition and slag matte separation was investigated at 1400°C. The synthetic slags containing CaO, MgO, SiO2,, A1,0, and FeO were similar to those employed in the electric furnace smelting of sulphide Cu-Ni concentrates containing PGM (Precious Group Metals) from the Merensky Reef of South Africa. The matte with a grade of 9.3% Cu and 16.0% Ni was a typical electric furnace product. The results indicated that the Cu and Ni solubility in the slag increases with the increase of the basicity ratio and CaO and MgO contents of the slag. At constant CaO/MgO ratios the rise in basicity decreases the metal losses. When FeO and SiO2 contents of the slag are kept constant, the substitution of MgO with CaO decreases the metal losses. The relationship between slag composition and matte-slag separation was found to depend primarily on the basicity ratio and the FeO content of the slag. The net effect comes from a strong interaction of the two in such a way that increasing basicity and decreasing FeO contents deteriorate the clean separation of the two phases.

Jan 1, 1994

By CHENCHEN SUN, GUOPING LUO, GUOCHENG ZHANG

In this study, the conditions of raw materials and fuels were simulated for Bayan Obo iron ore concentrate by adding pure calcium fluoride (CaF2) in various concentrations to Australian iron ore. The mechanism by which the fluorine (F) content of the lattice influenced the reduction swelling properties of the iron ore briquettes during various stages of the reduction process was investigated. The results provide insight into the mechanism governing the reduction swelling process in Bayan Obo ore briquettes, which could be used to direct real?world production practices, particularly those related to the rational utilization of Bayan Obo ore resources.

By E. J. Murphy

The Bureau of Mines developed a fast, reliable modification of the Griess-Ilosvay procedure suitable for field analysis for NO2 in the fumes from explosives. Known concentrations of NO2-air mixtures were analyzed for the nitrous acid or nitrite formed in the reaction with three Griess-Ilosvay-type reagents by diazotizing and coupling. Comparison was made of the Rider-Mellon, Saltzman, and Patty-Petty procedures; the three procedures are in agreement if sufficient time of contact between NO2 and the reagents is allowed. In experiments to obtain an accurate factor for converting NO2 to nitrite, overnight contact was allowed in order to be sure conversion was complete. The factor was found to be 75 percent with a standard deviation of ±3.2. Low and erratic results were found using either the Saltzman or Patty-Petty reagents as absorbing liquids unless several hours' contact was allowed. If dilute NaOH solution was used as the absorbing liquid instead of a Griess-Ilosvay-type reagent, 92 percent of the overnight conversion factor was found after a 3-minute shaking time and a la-minute standby time. The Saltzman reagent was preferable for fieldwork with the dilute NaOH solution as the absorbent because of its easy application, rapid reaction, and intense color even at low NOB concentrations.

Jan 1, 1967

By H. Conrad, K. Janowski, E. Stofel

In a previous paper,1 the occurrence of (0001) and (0111) twins was reported for compression tests of 60-deg-oriented sapphire rods in the temperature range from 1100° to 1300° C. Subsequent to this initial work, additional tests have been conducted, and twinning has been found to occur at temperatures as high as 1500° C. Also, the temperature and strain-rate conditions for the two types of twins and for slip have been established in more detail. The present note covers this more recent work. The compression-test data are summarized in Table I. The techniques for identifying the twins are optical examination up to X1000 and X-ray analysis.' It is evident that (0711) twins are pre-

Jan 1, 1965

By Steven M. Shope

The Bureau of Mines electromagnetic trapped miner location and communications system requires a thorough understanding of through-the-earth electromagnetic wave propagation. An earth model incorporating a magnetic dipole buried in a three-layered earth has been developed. The dipole source is located in the second subsurface layer. By application of proper limiting values, the three-layered model is reduced to two different two-layered models and eventually to the homogeneous half-space model. The solutions are in the form of infinite integrals. A numerical analysis was carried out and a computer program written to evaluate the surface magnetic fields. Numerical values for the magnet- ic field at the point above the source are presented in a variety of models.

Jan 1, 1982

By J. L. Rodda

A large amount of time has been devoted to the microscopical study of the copper-zinc alloys, emphasis naturally being placed upon the commercially important alloys of the system. Suitable methods are available for microscopically recognizing the two phases richest in copper, but none appear to have been developed for the positive identification of the other phases. This is, however, accomplished, for the phases normally encountered, by an electrolytic method described in the following pages. Five phases of the copper-zinc diagram (Fig. I) are considered for the purpose of this paper: the solid solution of zinc in copper, alpha (a); the intermediate phases, beta (ß), gamma (?), and epsilon (e); and the solid solution of copper in zinc, eta (11). Beta prime is not considered a separate

Jan 1, 1937

In order to do the discharge estimation better, it is valuable to find out appropriate formulas for estimating discharge in various pits, based on accumulating data, summarizing discharge patterns applying optimum seeking method and principle, by seeking redical exponent with help of the method of exhaustion, as well as testing and making statistics, in accordance with the quality standards established by our practical experience.

Jan 1, 1988

By J. D. Bosman, L. J. Gardner

"The Bushveld Complex is a large layered igneous intrusion, located in the northern parts of the Republic of South Africa. The complex hosts the largest known reserves of Platinum Group Metals in the world. On the western limb of the complex, mining of the Merensky economic horizon and UG2 chromitite layer has been conducted for many years by several mining companies, including Impala Platinum Limited. Over the past decade, Impala has planned a new generation of greenfield vertical shafts, commencing with comprehensive geological and geotechnical studies. As part of the geotechnical studies, numerous tests have been conducted to quantify the mechanical properties of the various near-reef rock types. These tests include point load tests conducted in the field, as well as uni-axial compressive strength, triaxial compressive strength, and Brazilian disc tensile strength tests conducted in specialist laboratories. The authors have compiled an extensive database containing a large number of tests for different rock types, ranging from felsic Anorthosite to mafic Pegmatoid. The database was analysed to quantify the mechanical properties and values for Mohr Coulomb and Hoek Brown failure criteria for each rock type typically exposed by mining. The paper will provide a data set of rock mechanical properties typically used in numerical modelling and other design processes. Using the significant number of tests available, data describing the variability of the various parameters will be included."

Jan 1, 2015

By M. Mirnezami, D. Lascelles, J. A. Finch, E. El-Ammouri

"Aggregation, i.e., the tendency of particles to cluster, can be expected to influence flotation selectivity. In this paper, a method of measuring aggregation is introduced and used to conduct plant surveys.Aggregation is measured using settling rate and turbidity converted to an aggregation index (AI) where 0 corresponds to most dispersed and 1 to most aggregated over the range of conditions tested, normally pH. Surveys of Cu and Zn flotation stages at four concentrators showed the AI increased significantly above pH 9. The metal ions identified in the process waters, principally Ca and Mg, were tested to determine which might be responsible. The presence of Mg was found to be the most important. In doping tests, Mg was shown to cause significant variation in AI over the pH range of 9 to 12.The impact of Mg was restricted to pH > 9. Over this pH range, Mg forms a range of hydroxy species, including Mg(OH)2 precipitates. An aggregation mechanism associated with these precipitates, electrostatic bridging, is suggested. Possible problems and opportunities in flotation practice arising from the findings are discussed."

Jan 1, 2002

By C. Jay Hodgson, P. J. MacGeehan

"The gold ore zones of the Campbell and Dickenson mines occur within a km-wide, 2 km-long zone of highly altered and anomalously fissile and deformed volcanic and subvolcanic intrusive rocks, cut by a series of mainly post-deformation mafic and quartz-feldspar porphyry felsic dykes.Three main periods of gold ore-forming hydrothermal activity are recognized. In the first, the mine rocks were extensively altered and gold and arsenic enriched; syn-volcanic auriferous veinlet and low-grade chemical sedimentary ores were deposited in what was a major discharge zone of a submarine hydrothermal system. The chemical sedimentary ores are closely associated spatially and temporally with domal rhyolitic extrusions. Because of its mechanical and chemical properties, this synvolcanic alteration zone became the locus of later deformation, and the site of the generation of auriferous hydrothermal solutions, perhaps by pressure solution processes at depth. These solutions deposited, synchronously with deformation and metamorphism, the second and most economically important type of ore zones in the mine: large foliation-parallel and foliation-oblique banded carbonate- 'chert' Rssure-filling veins.In the third and final mineralizing event, high-grade, pipeshaped zones of siliceous replacement-type mineralization, and quartz-arsenopyrite-gold veins, were superimposed on the previous mineralization types after most of the deformation, but before the emplacement of the late dykes. The source of heat and also possibly the fluids for the third mineralizing period may have been the dyke-forming igneous activity. The textures and mineralogy of the banded carbonate- 'chert' veins suggest a near-surface (<3 km) environment of deposition, but their relationship to the fabric of their host rocks indicates they were emplaced in an environment, presumably at considerable depth (5-10 km?), in which the rocks were undergoing intense penetrative deformation. This anomaly is unresolved."

Jan 1, 1982

By L. P. Lamprecht

Traditionally, South African shaft sinking operations have used electric detonators for the initiation of blastholes. Globally, the trend in shaft sinking is to use the shock tube and detonating cord (STDC) initiation system, with value adding benefits. In pursuing this global trend, Cementation Mining of South Africa in partnership with SMX have ventured the STDC route. This paper explores the work carried out to date, and identifies a number of benefits to be gained by using the system.

Jan 1, 1999

By V. Rajaram

A mine fire or roof collapse may necessitate the reversal of main fans to isolate the fire or provide an escapeway. Hence, to assist the mine operator in estimating the flow and pressure during reversal, Engineers International, Inc. conducted a laboratory and field study of the reverse performance characteristics of main mine fans. Laboratory tests were performed using a 96-inch (2.4 m) diameter vane axial fan to establish the forward and reverse performance characteristics under controlled conditions. Subsequently, a field test was conducted in a Colorado oil shale mine during which two 79-inch (2 m) diameter fans were reversed. The data obtained indicate that reverse performance characteristics are dependent upon the blade angle and the hub to tip ratio. The quantity in the reverse mode ranged from 30 to 65% less than in the forward mode, and the static pressure was directly proportional to the square of the quantity.

Jan 1, 1985

By J. E. Sepulveda, R. Morrow

"In full scale mineral grinding operations, the steel balls normally utilized as auxiliary grinding media get to be consumed at different specific rates, as determined by 3 basic mechanisms: abrasion/corrosion (wear), impact ball breakage and impact surface spalling, the latter relating to the removal of rather small pieces of steel coming off the exposed surface of the balls due to repetitive impact with other balls in the charge or the surrounding mill liners. In conventional ball milling applications, the clearly predominant mechanism is gradual wear by abrasion/corrosion. In the case of SAG mills, where the make-up balls may be as large as 6”f diameter, breakage and spalling mechanisms are significant contributors to total ball consumption, although not to the extent of overriding wear mechanisms.Ball wear has been well characterized by the Linear Wear Theory, as presented at the last CMP 2014. Impact breakage has been customarily monitored, at the ball manufacturing site, via Drop Ball Tests (DBT) consisting of repeatedly dropping balls from a standard height and accounting for the number of broken balls and the weight loss (spalling) of the remaining unbroken balls. When properly conducted, DBT’s should provide meaningful indications of the breakage and spalling resistance of large diameter balls. The current publication is focused on the interpretation and projection of DBT results to full industrial scale, taking into account all 3 mechanisms of grinding media consumption in SAG mills.INTRODUCTIONA thorough, quantitative understanding of the independent contribution of all active grinding media consumption mechanisms is of the highest practical relevance, particularly in semiautogenous (SAG) milling operations where ball breakage and spalling can not be ignored or neglected, as it has been normally acceptable for conventional ball milling processes. The high severity impact conditions currently imposed in typical SAG mill environments create serious challenges to the manufacturers and suppliers of large diameter (5”–6”) SAG balls, whose products must be capable of surviving such harsh operational conditions with minimum breakage or spalling."

Jan 1, 2015

By Leonard B. Lipson

Boyer, Morgan and Muskat,&apos; with improvements by Morgan, McDowell, and Doty,l and Laird and Putnam,&apos; have described a scheme for the determination of fluid saturatic in porous media by measuring the x-ray linear absorbing power of particular fluids in the media. This method is one of several which depend on the linear absorbing power of the fluids in the porous medium. Other examples of linear absorption methods involve measurement of dielectric constant, gamma ray absorption, and ultrasonic attenuation. It is the purpose of this note to demonstrate by theortical considerations that the absorption versus saturation curve for a linear absorption method is not necessarily a single valued function of the saturation. Such non-unique behavior must be considered and evaluated before suitable saturation determinations can be made by a linear absorption method. To illustrate the discussion, examples will be given only for the simplest cases of combinations of two different dielectrics. The dielectric constant method was chosen for illustration because it was thought to demonstrate most graphically the point in question. According to Argue and Maass,4 the resultant dielectric constant of a combination of two different dielectrics depends on the orientation of the dielectrics in the electric field of the test condenser used to measure the dielectric constant. One ease involves alternate slabs of dielectrics E1 and E2 perpendicular to the electric field of the test condenser, as shown in Fig. 1A. For this case: l/&apos;E, = A/E, + B/E,.......(1) where E,,, is the dielectric constant of the combination, A is the ratio of the path length through dielectric E, to the distance between the plates of the condenser (assuming the dielectrics have the same cross sectional area as the condenser), and B is the ratio of the path length through dielectric E2 to the distance between the plates of the condenser. It will be noted that the constants A and B are numerically equal to the fractional "saturation" of the region between the test plates of the condenser by the two dielectrics E1 and E2, respectively. Another case involves alternate columns of the two dielectrics parallel to the electric field and forming a continuous path between the condenser plates, as shown in Fig. 1B. For this case: E., = AE1 + BE2.........(2) where E., is the dielectric constant of the combination, A is the ratio of the cross sectional area of dielectric E, to the cross sectional area of the condenser plates (assuming the lengths of the dielectrics equal the distance between the condenser plates) and B is the ratio of the cross sectional area of dielectric E2 to the cross sectional area of the condenser plates. As before the constants A and B are the effective "saturation" of the condenser by the two dielectrics. Still another case is described by Lichtenecker5 where dielectric E2 is shown in the form of small particles distributed at random in dielectric E1. This is shown in Fig. 1C. For this case: log Em = A log E1 + B log E2.....(3) where Em is the dielectric constant of the combination. A is the ratio of the volume of dielectric E1 to the volume of the condenser, i.e., the effective "saturation" of the condenser by dielectric E,. B is the ratio of the volume of dielectric E2 to the volume of the condenser, i.e., "saturation" of dielectric El. Equations (l), (2) and (3) are plotted in Fig. 2 for E1 = 2.5 (oil) and E2 = 80 (water). Equations (1) and (2) may he thought of as representing the limiting cases of the configuration of two fluids which might be expected to exist in a porous medium. Equation (3),

Jan 1, 1951

By Leonard B. Lipson

Boyer, Morgan and Muskat,&apos; with improvements by Morgan, McDowell, and Doty,l and Laird and Putnam,&apos; have described a scheme for the determination of fluid saturatic in porous media by measuring the x-ray linear absorbing power of particular fluids in the media. This method is one of several which depend on the linear absorbing power of the fluids in the porous medium. Other examples of linear absorption methods involve measurement of dielectric constant, gamma ray absorption, and ultrasonic attenuation. It is the purpose of this note to demonstrate by theortical considerations that the absorption versus saturation curve for a linear absorption method is not necessarily a single valued function of the saturation. Such non-unique behavior must be considered and evaluated before suitable saturation determinations can be made by a linear absorption method. To illustrate the discussion, examples will be given only for the simplest cases of combinations of two different dielectrics. The dielectric constant method was chosen for illustration because it was thought to demonstrate most graphically the point in question. According to Argue and Maass,4 the resultant dielectric constant of a combination of two different dielectrics depends on the orientation of the dielectrics in the electric field of the test condenser used to measure the dielectric constant. One ease involves alternate slabs of dielectrics E1 and E2 perpendicular to the electric field of the test condenser, as shown in Fig. 1A. For this case: l/&apos;E, = A/E, + B/E,.......(1) where E,,, is the dielectric constant of the combination, A is the ratio of the path length through dielectric E, to the distance between the plates of the condenser (assuming the dielectrics have the same cross sectional area as the condenser), and B is the ratio of the path length through dielectric E2 to the distance between the plates of the condenser. It will be noted that the constants A and B are numerically equal to the fractional "saturation" of the region between the test plates of the condenser by the two dielectrics E1 and E2, respectively. Another case involves alternate columns of the two dielectrics parallel to the electric field and forming a continuous path between the condenser plates, as shown in Fig. 1B. For this case: E., = AE1 + BE2.........(2) where E., is the dielectric constant of the combination, A is the ratio of the cross sectional area of dielectric E, to the cross sectional area of the condenser plates (assuming the lengths of the dielectrics equal the distance between the condenser plates) and B is the ratio of the cross sectional area of dielectric E2 to the cross sectional area of the condenser plates. As before the constants A and B are the effective "saturation" of the condenser by the two dielectrics. Still another case is described by Lichtenecker5 where dielectric E2 is shown in the form of small particles distributed at random in dielectric E1. This is shown in Fig. 1C. For this case: log Em = A log E1 + B log E2.....(3) where Em is the dielectric constant of the combination. A is the ratio of the volume of dielectric E1 to the volume of the condenser, i.e., the effective "saturation" of the condenser by dielectric E,. B is the ratio of the volume of dielectric E2 to the volume of the condenser, i.e., "saturation" of dielectric El. Equations (l), (2) and (3) are plotted in Fig. 2 for E1 = 2.5 (oil) and E2 = 80 (water). Equations (1) and (2) may he thought of as representing the limiting cases of the configuration of two fluids which might be expected to exist in a porous medium. Equation (3),

Jan 1, 1951

By R. S. Kinasevich, D. D. Crabtree, D. W. Fuerstenau, T. P. Meloy, A. L. Mular

This paper presents details of the concept that size reduction in comminution machines takes place by three mechanisms; namely impact, abrasion, and chipping grinding. Experimental evidence is presented to show that each of these comminution mechanisms produces particles of a characteristic size distribution. The actual product from a comminution device has been postulated to be the result of a composite of these three types of mechanisms. Composite curves are demonstrated for a material following the Gaudin-Schuhmann, Gaudin-Meloy, and Rosin-Rammler size distributions. About forty years ago, Gaudin1 showed that grinding may be considered a combination of impact and attrition. Since that time, major efforts have been devoted to studies, both experimental and theoretical, of impact and compression fracture, while attrition has been almost wholly neglected, at least quantitatively. A significant attempt to distinguish between attrition and impact grinding is the work of Tanaka2 in Japan. By means of an instrumented abrasion grinder and a drop weight device, he determined coefficients relating the increase in surface area of various materials to the energy expended by the two methods of comminution. He showed that physical properties of a material determine its response to attrition and impact grinding. By extending his ideas to ball milling, he concluded that to a large extent the basic comminution process in a ball mill is due to the impact of falling media. Because Tanaka used a mass of particles in his drop weight device, however, he did not obtain pure impact size reduction. The purpose of this paper is to define basic mechanisms of size reduction, to verify that each has a characteristic and meaningful distribution curve, and to show how a combination of these mechanisms results in a size distribution very like that produced by grinding mills. DEFINITION OF COMMINUTION MECHANISMS The product from a grinding device will be considered to be the sum of the contributions resulting from the action of three basic mechanisms of size reduction which operate in a ball and rod mill. These are impact grinding and two forms of attrition, namely abrasion grinding and chipping grinding. Each is defined below. Impact Grinding: If a straight line is obtained when the cumulative weight fraction finer than a given size is plotted on log-log paper as a function of that size, the slope of the line is defined as the distribution modulus. A number of investigators 3,4,5 have shown that impact fracture of single specimens of different composition and shape results in a distribution of daughter particles that exhibit a distribution modulus of unity. This has also been true for materials broken in slow compression. Moreover, under slow compression or impact fracture conditions, theoretical distribution equations6*&apos; which approximate the Gaudin-Schuhmann distribution when the distribution modulus is close to unity agree reasonably well with the experimentally obtained products. If one now considers a comminution process where many impact or compression fracture events are taking place, then any rational summation of the individual events yields, in the finer size range, a Gaudin-Schuhmann distribution whose distribution modulus is also unity. If the size distribution of the product from a mill has a distribution modulus of unity, it is implied that particles are fractured in a manner which results in a comminution event having a distribution like that obtained for the breakage of single specimens. These impact events would occur when a particle is smashed between balls or between a ball and the mill liner. Attrition, on the other hand, is that form of grinding which cannot be called impact grinding, and comprises both abrasion and chipping grinding. Abrasion Grinding: Abrasion is a form of surface wear resulting when particles rub against each other or against balls or the mill liner of a tumbling mill, somewhat like a piece of wood being rubbed over a piece of sandpaper. The surface wears at a more or

Jan 1, 1964

By K. G. Davis, P. Fryzuk

A study has been made of the effect of undercooling on the grain structure and solute distribution in small ingots of pure bismuth and of a 100 ppm Ag in bismuth alloy. Autoradiographic evidence shows that in undercooled melts a network of dendrites is formed throughout the melt immediately after nu-cleation. At large undercoolings the dendrites are very thin and closely spaced. The origin of the observed grain morphology can be explained on the basis of information about the mode of solidification revealed by the impurity substructure. WHILE a great number of studies of nucleation in undercooled molten metals have been made, comparatively little attention has been given to the mode of solidification from melts with large undercool- ings. Colligan and Bayles1 and Walker2 have measured the rate of advance of the solid-liquid interface in undercooled nickel melts, but the morphology of the solidifying material remained a matter of speculation. Fehling and Scheil3 have described the grain structure in ingots formed from undercooled melts of nickel, palladium, and copper, and a series of Ni-Cu and Ni-Pd alloys. At small undercoolings, equiaxed structures are observed, the grain diameter tending to increase as the temperature of nucleation is lowered. At greater undercoolings, a columnar structure is developed, while with still further undercooling there is a smaller grain size incorporating rather coarse subgrains. All-bright and Colligan4 examined the grain structure shown by ingots solidified from melts of nickel and of Ni-Ag alloy at an undercooling of 105°C, and concluded that considerable grain growth had taken place after solidification. The object of the present work is to correlate the mode of solidification from undercooled melts with both the grain structure and impurity segregation, using tracers to examine the latter.

Jan 1, 1965

By Guy A. Johnson

The Bureau of Mines, through research and development contracts with the FMC Corp., has developed and tested two automatic fire sensing and suppression systems for large haulage vehicles. This work was undertaken to enhance driver safety, to lessen substantial property damage from fires on large trucks, and to increase the vehicle operator&apos;s productivity. One automatic truck fire protection system protects both the engine compartment and brake rid areas, while the second system is used in the engine compartment and fuel tank area. Both systems have redundant fire-sensing capabilities and manual override controls. Upon sensing flames and/or heat, the systems suppress the fire with pressurized, E-C class dry chemical. Both fire protection systems are flexible in design and can be modified for use on other mobile minim&apos; equipment. Prototypes of both systems have been subjected to long-term, in-mine validation testing and actual Eire tests on 100-ton-capacity trucks at the Puma mine near Tucson, Ariz., and the Erie mine at Hoyt Lakes, Minn. During the 4-month endurance test of the first system at Pima, an accidental flash fire occurred in the test truck while it was working in the pit. The system successfully sensed and automatically extinguished the fire with no injury to the driver and little damage to the truck.

Jan 1, 1975