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By Philip Drinker

IN THE mining and metallurgical industries, numerous problems arise requiring determinations of solid and of liquid particles suspended in air. Frequently, these problems are of local interest and involve purely economic or operating difficulties; on the other hand, toxic effects from the inhalation or the ingestion of substances suspended in air may be a matter of concern. For checking up process improvements or for determining ventilation efficiencies in problems of this general nature, various methods have been proposed. Although simpler methods are often satisfactory, precipitation combines several desirable features that other methods lack. This paper is, therefore, devoted to a discussion of portable alternating-current precipitators applicable to the quantitative determination and microscopy of dusts, fumes, and smokes in air. Small particles suspended in gases, such as air, are referred to in the literature as aerosols or suspensoids. Of these terms, suspensoids appears to be preferable as being more nearly in keeping with words in everyday use. In problems involving air pollution by small, particles-by suspensoids-it is convenient to distinguish three broad classes based on the size, the degree of dispersion, and the method by which the particles become suspended in the air. Dusts.-Particles or aggregates of particles, 150 to 1 micron in diameter, that are thrown into the air by mechanical agencies are termed dusts. Examples are silica, talc, cement, organic dusts such as hard rubber, starch, and cocoa; flocculated fume and smoke products. Fumes.-Particles, 0.2 to 1 micron in diameter, formed from chemical or physicochemical reactions are known as fumes. Examples are ammonium chloride, lead and mercury, zinc and magnesium oxides, fogs, and acid mists.

Jan 3, 1925

"It is evident that the incidence of coal worker's pneumoconiosis (CWP) or black lung disease varies in different coal producing regions of the United States. Many people have hypothesized about the reasons for the differing occurrences. Because underground coal mining involves many mining methods under changing geological conditions, several factors may be involved in contracting CWP such as: the amount of quartz in the respirable dust, the trace elements in the respirable dust, the rank of the coal that produced the respirable dust (bituminous, anthracite), the amount and size of respirable dust, etc.Recognizing the uniqueness of underground coal mining and CWP, research investigations involving seam characteristics, mining system and worker position are being conducted in the center to establish standard procedures for characterizing some coal properties that may be involved in workers contracting CWP. This has been accomplished by the in-mine sampling of airborne dust at various worker locations and mining system configuration and by performing laboratory analyses of mined material (coal and rock) taken from the mines. (FIGURE 49 and 50)The investigations includes a method of classifying coal seams according to their potential to generate respirable dust. It includes statistical analyses of the size and locational variations of the elemental compositions of respirable coal mine dust in operating underground mines from seams located in the eastern, midwestern, and western United States, and is currently completing research which is investigating the relationship between the elemental compositions of respirable dust sampled near a continuous-mining machine and a laboratory-produced respirable dust."

Nov 1, 1988

By Robert D. Rogers

The demand for phosphate will continue into the future, because phosphate is currently irreplaceable as a plant nutrient and in many chemical applications. Phosphate is not recycled, so the supply must be replenished through a process of mining and purification. Numerous microbial isolates. obtained from the environment were screened find those which demonstrated the greatest promise of solubilizing PO4 from the ore of interest. Screening was accomplished in a step wise manner an agar plate bioassay, shake flask studies, and semi continuous growth conditions. It was found that with the proper conditions of nutrient supply and solution pH; the bacteria and. fungus used in the semicontinuous process were able to solubilize in excess of 80% of an Idaho rock phosphate ore (RP) within nine days. A significant amount of solubilization occurred within the first six days. There was a 'reasonable correlation between the occurrence of soluble Ca and PO.4 during the processing of the RP thus providing evidence that the RP was being disintegrated by the organisms. In all cases, HPLC analysis of the solutions in which PO4 had been. extracted from RP showed that organic acids, which have been implicated as the mechanism of solubilization, were present.

Jan 1, 1991

By Edward Medina

El presente trabajo señala el método de minado "sublevel stoping" aplicado a través de la perforación de taladros largos ubicados cada 50 cm. en el yacimiento minero de San Rafael, Puno. Esta perforación acorta el tiempo de ejecución y el costo se reduce considerablemente en la preparación de la labor. Asimismo, la perforación radial minimiza la perturbación al macizo rocoso debido a que se realizan menos voladura en los alrededores, como también se tiene menos área expuesta a deformaciones. Finalmente, el uso de los equipos de última generación, permiten controlar mejor la desviación del taladro a mayor longitud, que en años anteriores fue uno de los principales limitantes.

Sep 13, 2001

By Enrique Mansilla

El presente texto señala la historia y desarrollo económico de la plata como metal peruano en el mundo. El Perú antiguo y tradicional fue productor de este metal desde el siglo XIV. Sin embargo, la mayor parte de esa riqueza fue llevada a la metrópoli española y en consecuencia, se optó por la producción de oro. El Perú produce solo el 0.26 °/o de la producción anual de oro con un valor de U$ cinco millones. Si se lograse reponer el antiguo sistema mundial de monetización de la plata, este sistema recuperaría el valor que tuvo hace 100 años a.C o hasta fines de la Colonia española, o sea la relación de 15 a 1 con respecto al valor del oro.

Jul 1, 1973

By N. A. Caspero, W. E. Eckard, W. T. Wertman

A thermal oil-recovery experiment was conducted in the Venango First sand, Goodwill Hill oilfield, Warren County, Pa., about 10 miles northeast of Titusville. The Quaker State Oil Refining Corp., Bradford, Pa., performed the experiment with assistance from Sinclair Research, Inc., Tulsa, Okla., and the Federal Bureau of Mines. The Goodwill Hill field was discovered in 1885. Primary-production oper- ations continued until 1930 when an air-gas injection project, which is still in operation, was started. At the location of the combustion experiment, the reservoir is 400 feet deep and 30 feet thick, with wide permeability and porosity variations. The crude oil is typical Pennsylvania Grade paraffin- base oil with a gravity of 43.9° API and a viscosity of 4.55 cp at 60° F. The well pattern for the experiment consisted of 5 producing wells, enclosing an area of 1.28 acres, and a central ignition-injection well. An air-natural gas mixture was ignited in the ignition well on July 29, 1961. Ignition was followed by injection of air and natural gas at various rates. The experiment was suspended January 5, 1962, when it became evident that economic oil production could not be achieved. There was no conclusive evidence that self-sustained combustion was achieved or that combustion increased oil and water production. A slight increase in liquid production was attributed to stripping action caused by the air-injection rates, which were higher than those normally used during air-gas injection.

Dec 1, 1963

By Lloyd Pollish, Robert N. Breckenridge

SUCCESS in any underground mining operation is determined by accessibility of the orebody, which in turn is dependent upon maintenance of passageways to the mining zones and temporary support of the voids caused by extraction of ore. This is accomplished by one or a combination of the following methods: timbering, back-filling, pillaring, or, more recently, rock bolting. Timbering has usually been the principal means of maintaining these underground openings necessary for mining operations. Timber, however, does not prevent ground movement beyond the scope of localized sloughing, which is indicated by the gradual failing of the timber itself. Besides this, timbering has always been a costly process, and with the decline of available supplies of timber close to the mining areas, mining men have constantly sought other methods of controlling ground. Rock bolting is now replacing timbering at an ever increasing rate. Experience has proved that this form of ground support is just as applicable to blocky igneous rock as to stratified rock. Besides preventing sloughing of the walls and back of underground openings, Fig. 1, rock bolting has a stabilizing effect on the surrounding ground in much the same manner that steel reinforcing rods add to the strength of concrete structures. Further, rock bolting is flexible and may be applied to any shaped excavation, whereas timber sets are in a fixed pattern and the ground must often be changed to conform with this pattern. Rock-bolting installations were made in metal mines of the Northwest as early as 1939. An exhaust air crosscut was driven that year in one of the Butte mines of the Anaconda Copper Mining Co. The crosscut was rock-bolted and gunited at the time it was driven and is still being used to exhaust hot humid air from the 3400 level of the Belmont mine. It is interesting to note that no sloughing or caving has taken place in the 14 years it has been open. Even though these early installations of rock bolts were successful, few men recognized their potentiality until recent years, when the coal mines started their programs of mechanization and the great trend toward roof bolting began. In some areas of the Northwest stopes that previously required heavy timbering and close backfilling are now being mined by the more economical cut-and-fill and shrinkage methods. When used in conjunction with timbering, rock bolting increases the efficiency of the operation by decreasing hanging wall dilution and by making it possible to blast larger rounds. Most of the rock bolts installed to date in mines of the Northwest have been the 1-in. diam slot and wedge type, but there has been a recent trend to- ward using the 3/4-in. diam expansion shell bolt shown in Fig. 2. In addition to these commercially manufactured steel bolts, wooden bolts have been used with considerable success by the Day Mines of Wall'ace, Idaho. Installation of the slot and wedge type requires three distinct operations, with tools for each operation: 1—drilling the hole to proper diameter and depth, 2—setting the bolt, and 3—tightening the nut. Holes are drilled and bolts set with pneumatic rock drills. A number of setting or driving tools have been used successfully, but most follow the same general pattern. Usually the driving tool is designed to accommodate a short length of drill steel on one end and the rock bolt on the other end. In this manner the hammering effect of the rock drill is transmitted through the steel and driving tool to the bolt. When machines not having stop rotation are used, slippage is allowed between the driving tool and bolt or between the drill steel and driving tool. The rock bolt nuts are tightened either with pneumatic impact wrenches or with hand wrenches. Impact wrenches are desirable because they are faster and assure adequate tightness. Expansion shell bolts have the following advantages over slot and wedge rock bolts: 1—No special equipment other than a wrench is needed for their installation. 2—Installation is faster. 3—They are removable. 4—Holes need not be drilled to a specific depth as the expansion shell will anchor anywhere along the length of the hole. These advantages are offset somewhat by the lesser strength of the bolt, since expansion shell bolts are generally made from 3/4-in. diam steel as compared to 1-in. diam steel for the slot and wedge type. One manufacturer, however, is now fabricating expansion shell rock bolts from steel of high tensile strength, which gives this ¾-in. bolt a much greater strength than that of the mild steel bolt. Table I illustrates tests made by the Anaconda Copper Mining Co. to determine the proper hole size to use with various types of bolts and to determine

Jan 1, 1955

By Kai Wang, Chao Xu, Qiang Fu, Tong Yang, Chunyu Zhao, Wei Zhao

The stress of a coal seam is an important factor that affects the permeability of the coal seam and then affects the coalbed methane (CBM) drainage. In China, adjacent coal seam mining is an important method to reduce stress, which increases the permeability of the coal seam. However, in the process of mining adjacent coal seams, many coal pillars remain, which causes stress concentrations and results in a decrease in permeability. Therefore, it is important to study the influence of coal pillars on the stress of adjacent layers and its distribution and evolution in the floor rock. This paper took the Shendong Baode Coal Mine as a case study and investigated the influence of the coal pillar on the stress and permeability of coal seam #11. The results show that under a coal pillar, the relationship between the vertical stress of different floor depths and the width of the coal pillar can be divided into a negative correlation zone, transition zone, and positive correlation zone. The change in the coal pillar width does not affect the pressure relief range or the degree of pressure relief in the adjacent coal seams below the goaf. The field measurements show that after the mining of panel #81,505, the permeability coefficient of coal seam #11 under the goaf increased from 0.1434 to 26.3545 m2/( MPa2*d), increasing 182.7 times, and the drainage mixing volume of boreholes #1 and #2 increased from 1.24 to 1.52 m3/ min. While the permeability coefficient of coal seam #11 from 12.5 m in the coal pillar has only increased by 2.6 times, the drainage volume of boreholes #3 and #4 did not change significantly.

Nov 19, 2022

Research, whether applied or fundamental, is a human endeavour which increases our understanding of nature. It is insufficient to simply observe, explore, record and classify. It i necessary, as well, to fit the observations into a satisfying theoretical scheme; that is, to synthesize. Two examples of successful research programs in physical metallurgy are di cussed from this point of view. A pessimistic view is taken of the prospects for rapid growth of research activities in the Canadian metallurgical industry. THE term "research" is used indiscriminately to describe any intellectual or experimental activity which leads to a change in society. Proponents of various activities, ex-tending all the way from alloy development to subliminal advertising, use the status of the term for special advantage. With the Canadian Government entering upon a project of support to industrial research, it might be well to determine what definition is most in the public interest. As an academic, I have a rather jealous attachment to the definition that research, whether applied or fundamental, is a human endeavour which increases our understanding of nature.

Jan 1, 1963

This report presents the results of reconnaissance-level investigations of the mill refuse disposal systems for 15 plants throw-heat the conterminous United States. The sites visited represent a cress section f the copper, iron, lead and zinc, and phosphate industries' practices in the field of fine-grained refuse disposal. The reconnaissance-level investigations were carried out to gather supplemental data to tae in-depth studies of Kennecott's Magma and Phelps Dodge's Morenci tailings deposits and Kennecott's Chino leaching dump. The various sites visited were classified according to the different systems and techniques used by the mining industry. The probable effects and relationships between site conditions and disposal methods were determined and evaluated to the extent feasible by a reconnaissance level investigation.

Jan 1, 1974

By E. F. Loiseau

(Read at the Philadelphia Meeting, February, 1878.) UNTIL June, 1868, it had not been attempted, either in this country or abroad, to manufacture by mechanical means, from anthracite coal-dust, artificial fuel for domestic use. Several attempts had been made to utilize coal-waste by converting it into a fuel for manufacturing purposes, but none of the processes were original, and they were merely applications of the well-known European processes and machinery, slightly modified by American ingenuity and mechanical skill. With one exception all those attempts have been failures. The great difficulty in the application of European processes and machinery has always been the limited production, and the excessive cost of the manufactured product, as compared with the cost of mining and preparing the ordinary anthracite coal for the market. The only serious and intelligent attempt to manufacture, on a large scale, artificial fuel for manufacturing purposes, has been made by the Anthracite Fuel Company, whose works are erected at Fort Ewen, near Rondout, New York. This company, organized under the auspices of the Delaware and Hudson Canal Company, had to go through the usual course of difficulties, breakages, and disappointments, which seems to be the lot of every new industry. Thanks, however, to the energy and perseverance of Mr. L. L. Crounsse, a gentleman of means, from Washington, D. C., the enterprise succeeded, and it is to-day established on a permanent basis. In order to increase the production, and to reduce its cost, the Anthracite Fuel Company was compelled to change most of its plant, and to erect more powerful machinery, producing lumps of a larger size, almost twice the size of the lumps made previously by the same company. This increase in the size of the lumps has been resorted to in Europe as well as in this country, in order to increase

Jan 1, 1878

By E. F. Loiseau

Until June, 1868, it had not been attempted, either in this country or abroad, to manufacture by mechanical means, from anthracite coal-dust, artificial fuel for domestic use. Several attempts had been made to utilize coal-waste by converting it into a fuel for manufacturing purposes, but none of the processes were original, and they were merely applications of the well-known European processes and machinery, slightly modified by American ingenuity and mechanical skill. With one exception all those attempts have been failures. The great difficulty in the application of European processes and machinery has always been the limited production, and the excessive cost of the manufactured product, as compared with the cost of mining and preparing the ordinary anthracite coal for the market. The only serious and intelligent attempt to manufacture, on a large scale, artificial fuel for manufacturing purposes, has been made by the Anthracite Fuel Company, whose works are erected at Fort Ewen, near Rondout, New York. This company, organized under the auspices of the Delaware and Hudson Canal Company, had to go through the usual course of difficulties, breakages, and disappointments, which seems to be the lot of every new industry. Thanks, however, to the energy and perseverance of Mr. L. L. Crounsse, a gentleman of means, from Washington, D. C, the enterprise succeeded, and it is to-day established on a permanent basis. In order to increase the production, and to reduce its cost, the Anthracite Fuel Company was compelled to change most of its •plant, and to erect more powerful machinery, producing lumps of a larger size, almost twice the size of the lumps made previously by the same company. This increase in the size of the lumps has been resorted to in Europe as well as in this country, in order to increase

Jan 1, 1879

By McHenry Mosier

The Bell mine operated by the Warner Co. at Bellefonte, Pa., has an annual production of about 600,000 short tons of high-grade limestone. Since 1924, shrinkage stoping has been the mining method. Horizontal, long-hole diamond-drilling for production in stopes was started with one machine in July 1946. It is now standard practice. The burden on the holes is 10 feet. Diamond bits are noncoring EX-size in both concave and pilot types. The two types have little difference in drilling speed at the Bell mine. The diamond drills are mounted on 3-inch single-screw columns. Diamond drilling shows a marked increase in efficiency at the Bell mine, compared to percussion drilling, with respect to tons broken per drill shift, tons broken per foot of hole, and tons broken per pound of explosive. The advantages of diamond-drilling blast-holes also include (a) improved safety, greater footage per drill shift, (c) better frag- mentation of the broken, stone, and (d) reduction in amount of barring down required in stopes because the working places are limited to slots which have a relatively small area.

Feb 1, 1948

By A. K. Snelgrove

Introduction ?Concerning the inland commodities, as wel to be drawen from this land (Newfoundland) there is nothing which our East and Northe.rly countries of Europe doe yeelde, but the like also may be made in (ît) as plentifully by time and industry : Namely, rosen, pitch . . . metalls, and many moe. All which the countries will aford, and the soyle is apt to yeelde ... For besides these alreadie recounted and infinite moe, the mountains generally make shew of minerall substance : Iron very common, lead, and somewhere copper. I will not auerre of richer metalls: albeit ... more then hope may be concieued thereof. " - Narrative of Captain Hayes, second-in-command to Sir Humphrey Gilbert's Expedition, IJ83 (From Hakluyt). The investigations set forth in the following pages were made in the field in Newfoundland during the summer of 1927, and later in the laboratories and library of McGill University, and in the library of the Canadian Geological Survey at Ottawa, with the purpose of collating and adding to our knowledge of the geology of an area roughly wedge-shaped in outline, and nearly nine thousand square miles in extent, stretching across the centre of the island of Newfoundland, from the southwest to the northeast coasts. To the description of this district, which contains most of the known mineral occurrences of Newfoundland, the term mineral belt is here introduced.

Jan 1, 1928

By L. Evrard, S. Brouwer, E. Bosly, E. Boydens

"A partial desulfurization roasting process has been tested on a typical copper-zinc sulfide concentrate in a Nichols Herreshoff monohearth pilot furnace whereby the su!fµr is partially removed and iron is to a certain degree preferentially oxidized. The phase changes that occur in the particles during selective roasting at 650°C and 800°C over a range of residence times were investigated by the use of chemical analysis, optical microscopy, X-ray diffraction and electron microprobe analyses. The purpose of this work was to get an insight into the mineral assemblages formed by controlled oxidation roasting and to evaluate if this non traditional approach could be afterwards used to recover zinc, copper and iron by a physical separation method. IntroductionThere has been considerable interest over the years in improving extraction and processing procedures for recovering non ferrous metals especially from polymetallic ores containing copper, lead, zinc and iron sulfides with very fine intergrown phases. Complex sulfide ores, which represent considerable reserves and resources in copper, lead and zinc, as well as precious metals and sulfur, are difficult to treat by conventional physical processes, leading to impure concentrates at low metal recovery. Some methods that can be used to treat such ores were described by G. Barbery (1). Various metallurgical routes generally combining pyro- and hydrometallurgical methods have been explored to develop new processes to recover the metals from zinc-bearing sulfidic ores and concentrates (2, 3, 4). The feasibility of partitioning complex sulfide minerals to simpler phases in order to improve selective extraction of mineral constituents has also been investigated (5)."

Jan 1, 1999

By B. F. Koch

COPPER reverberatories develop large amounts of exit gases of a temperature in the neighborhood of 2000°F. The gases are not only of a noxious nature but must usually be disposed of at considerable heights above the yard level by a stack. Handling these gases at the temperature mentioned would require rather expensive construction of conveying flues and stack. Moreover, wasting such amounts of heat is certainly most uneconomical. Numerous investigations have indicated that waste heat boilers of the water-tube type are the most practical and economical means for utilizing that heat although the gases are heavily laden with rock dust and copper-bearing slag, which upon cooling form hard deposits on the surfaces of dampers or heat absorbing elements placed in the gas stream. Avoiding Slag and Dust Deposits Based largely on the experience of the paper industry in burning black liquor, a waste heat boiler design was developed a few years ago, providing not only extensive water-wall surfaces for cooling the gases below the fusing point of the slag but also settling out, as far as possible, the solidified particles of slag by creating low gas velocity. Matter carried in a stream of gases or air has a tendency to maintain its original direction upon a change in the direction of the flow of the conveying medium. Reverberatory waste heat boilers installed at Hurley and Morenci endeavored to utilize that tendency for the elimination of slagging particles at predetermined places and before they would strike the tube banks of the boilers. Both installations were successful in minimizing the slagging of boiler tubes and thereby minimizing the need for hand lancing. However, the low draft carried at the up-take of the reverberatory furnaces resulted in a positive pressure in the upper part of the furnace of the waste heat boilers, causing the emission of gases from lancing doors and making more difficult the already unwelcome work of cleaning the boilers by handlancing. Attempting to correct this nuisance as much as possible, the overall height of the Chuquicamata waste heat boilers has been reduced to the minimum considered necessary to obtain proper water circulation in furnace walls. Moreover, it is attempted to solidify slag and dust particles by providing large amounts of water-cooled surfaces before the gas stream reaches super-heater and convection banks of the boilers. The furnaces have been made as deep as an economical and practical arrangement of headers for water

Jan 1, 1952

By Zheng-qi Guo, De-qing Zhu, Feng Zhang, Jian Pan

Iron mainly exists as the magnetite and fayalite, while copper is primarily dispersed in the form of fine matte particles in the copper slag, which is difficult to recover by conventional separation techniques. In this paper, the feasibility of an integrated technological route to improve beneficiation of copper and iron components from copper slag through the modification of molten slag was investigated, and the results shows that: the copper grade of rougher copper concentrate was increased from 6.43 to 11.04%, iron recovery from magnetic separation was increased significantly from 32.40 to 63.36%, and other evaluation indexes were changed slightly, in comparison with unmodified copper slag. Meanwhile, the grains of the target minerals in the modified slag grew considerably to a mean size >50 lm after slow cooling. Ultimately, the beneficiation efficiency of copper and iron was improved because of the ease with which the target minerals were liberated.

Mar 1, 2017

By Markus A. Reuter, Jacob Wood, Robert Matusewicz

Over the last 20 years, significant improvements in copper smelter productivity have been realized through the advent of continuous smelting processes. This progress has until recently however, not been carried through to copper converting. Peirce-Smith converting has been widely used by the copper industry for 100 years but is limited by its batch nature in achieving large scale of production. A logical next step is therefore copper converting on a continuous basis with its inherent environmental benefits. A number of continuous converting technologies are currently in use or being developed within the copper industry, the majority of these operating with calcium-ferrite slags. A notable exception however is the Ausmelt Continuous Copper Converting (C3) technology which has focused on operation with ferrous-calciumsilicate or loosely called olivine type slags. This paper discusses the merits of the Ausmelt C3 process and the advantages offered in terms of operational flexibility and process control arising from the use of lime modified iron silicate slags. It also examines the effects of key process variables pertinent to continuous copper converting from both a theoretical and experimental/operational perspective.

Jan 1, 2009

By R. M. N. Pelloux

This study of aluminum-copper alloys had two aims: 1) To determine the effect of the amount and distribution of a second phase, CuAl2, on the creep-rupture strength, ductility, and fracture characteristics of the alloys. The work of Gemmell and grant' on single-phase aluminum-copper alloys provided a basis for the present study. 2) To attempt to provide a relation between the microstructure and strength of two-phase alloys deformed at comparatively high temperatures (greater than 0.45 T,). The creep behavior of the two-phase magnesium alloys Mg;Ce and Mg-A1, has been treated by Roberts. 9 In work reported by Sully and Hardy4 and by Underwood, Marsh, and Manning~ on A1-Cu two-phase alloys, and also in a portion of the work of Gemmell and grant,' aging took place during the creep tests. 'In the present work, overaged aluminum-copper alloys were subjected to creep deformation at two temperatures, 500 and 700OF. The overaging treatments to produce the precipitate dispersions were performed prior to the test, at temperatures which were the same as the ultimate respective test temperatures. Hence, the present study is concerned with the creep behavior of stable (in contrast to "underaged") two-phase A1-Cu alloys, i.e., alloys in which no depletion of the solid-solution matrix occurred during: creep. MATERIALS AND PROCEDURE A 2 and a 3 pct Cu alloy, supplied by Alcoa, were studied; Table I shows the compositions. The grain size of the specimens, 0.9 to 1.0 mm, was achieved by annealing the machined test bars for 2 hr at 1000°F, followed by furnace-cooling to 900°F, and homogenizing for 4 hr. Both compositions are in the single-phase condition at 900°F. Two types of overaged dispersions, termed "over-aged I" and "overaged 11" were prepared after the grain size and the homogenization anneals. The overaged I alloys were prepared by quenching to room temperature after homogenization, aging at either 500' or 700°F for 72 hr, and air-cooling to room temperature. The overaged I1 alloys were prepared by furnace-cooling after homogenization, to either 500' or 700°F, and holding at the necessary temperature for 72 hr. The times for furnace-cooling from 900°F to 700° and 500°F were, respectively, about 2 and 3.5 hr. The structures of the A1-2 pct Cu alloys are shown in Fig. 1 (overaged I) and in Fig. 2 (overaged 11). A comparison of Figs. 1 and 2 shows that in the overaged I alloys the precipitate particles along the grain boundaries are much more closely spaced and the grain boundaries are straighter than they are in the overaged I1 alloys. Further, the particle size and spacing in the grains are smaller than in the overaged I1 alloys. Microstructures of the A1-3 pct Cu alloys have not been shown; the structures of these alloys differed from those of the A1-2 pct Cu alloys only in that the distribution density of the particles was greater. The creep specimens had a gage section 1 in. long with a diameter of 0.155 to 0.195 in. Before testing, specimens were electropolished in a solution of 100 cc glacial acetic acid, and 30 cc of 60 pct perchloric acid, at 40' to 50°F, at 24 v. The specimens were kept refrigerated prior to testing to avoid precipitation at room temperature. Constant stress creep tests were conducted; the load was applied 75 min after heating of the specimens to test temperature had begun. EXPERIMENTAL RESULTS Creep-Rupture—Fig. 3 shows the log stress-log rupture life plotfor the overaged alloys studied, and also for the underaged A1-2 pct Cu alloy.' At 700°F, the stress-rupture life relationship is nearly independent of both the amount of precipitate (i.e., composition) and of the type of overaging treatment (i.e., precipitate dispersion). At 500°F it is apparent that the increase in rupture life that was ex-

Jan 1, 1960

By B Mohanty, M P. Roy, P K. Singh

"The measured response of residential structures is a critical indicator of troublesomeor potentially damaging ground vibrations. A study was conducted to evaluate theresponse of structures situated in the periphery of four open-pit coal mines in India. Although, most of the structures were at far-off distances from the present blasting sites, an attempt was made to document the response of structures to blast vibration for future applications to optimize the blast designs for the safety of the structures. The study involved a total 215 blasts, employing one-, two- and three-hole calibration study, and production blasts. The bench height varied from 7.5 m to 42 m, and boreholes loaded with emulsion and slurry explosives were 250, 260, 270 and 310 mm in diameter. The explosive detonated in a blast were between 300-198400 kg whereas in a delay it was 33-24800 kg. Up to 12 tri-axial vibration sensors were located in overburden along a linear array from 25 m to 6.5 km distance from the blasts. Altogether, 1512 blast vibration signatures were recorded. Production and specially fi red single-charge blasts allowed the determination of natural ground frequency. The fundamental frequency of the structures ranged between 3.13 to 10.6 Hz, the same as those of the ground vibrations. The amplifi cation of vibration in the structures was in the range of 1.6 to 5.6. The study details the interaction between ground vibrations and selected structures, and the means to reduce amplifi cation of vibrations in the structures and persistence of vibrations through improved blast design."

Jan 1, 2008