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By G. W. Tuffnell, S. Floreen

Three Fe-18 pet Ni-base ternary alloys cortaining carbon, molybdenum, or cobalt were aged to pgroduce hardening by carbides, Ni3Mo, or ordering, respectively. Each alloy was tested in rotating-beam fatigue tests after hardening to 195 ksi ultim.ate tensile strength. The fatigue properties of three alloys soere essentially identical. The results suggest that tlze fatigae strength of an igron-base alloy should depend primarily upon the tensile strength, and not iipon the hardening mecaanisrn. THE fatigue strengths of many steels have been found to be directly related to their ultimate tensile strengths. For ultimate strengths below 200 ksi, the fatigue endurance limit at 107 to 10' cycles is approximately half the ultimate strength. Essen- tially all of the steels that have been tested, however, have been hardened by carbon. Thus it is not certain whether the relationship between fatigue and ultimate strengths is a general one that applies for other types of hardening in steels, or whether it applies only for the particular method of hardening by carbon. The recent developments of the martensitic precipitation-hardened stainless steels and the marag-ing steels have shown that it is possible to achieve high strengths in iron-base alloys by other hardening mechanisms than that due to carbon. Therefore, it is now possible to compare the fatigue properties of several iron alloys having the same ultimate strengths but hardened by different mechanisms. For the present study a binary Fe-18 pct Ni martensite was selected as a base material. This particular matrix composition has been found to have deformation characteristics very similar to pure iron.' Three ternary alloys were prepared by adding either 0.23 wt pct C, 5 wt pct Mo, or 20 wt pct Co to this base composition. After suitable heat

Jan 1, 1965

By Charles H. White

Methods in colorimetry are based on the assumption that the intensity of the' color of a definite volume .of solution is directly proportional to the quantity of the color-producing substance present. In the preparation and examination of colored solutions there are three ways in which the depth of color may be varied. These variables are : (1) the quantity of' the coloring matter; (2) the quantity of the solvent, or the dilution ; and (3) the thickness or depth of that portion of the solution examined. With these three variables as a basis, three general methods in colorimetry have been devised, all of which have been used in the determination of carbon in steel. In the first method, the quantity of the solution is kept the same for both the unknown steel and the standard, and the sections compared are of equal thickness, while the quantity of the standard is varied until the color obtained is of the same intensity as that produced by a definite quantity of the unknown steel. In laboratories where this method is used there is prepared and kept for permanent use a series of solutions with varying amounts of the standard, representing the percentages of carbon from the lowest to the highest demanded in that laboratory. These standard solutions are kept in bottles or test-tubes of equal diameter, and are arranged in series from the faintest to the most intense color, so that it is a simple matter to find the place of the unknown steel in the series, when the solution is of a definite volume and is contained in a tube of the same diameter as the standard tubes. In the second method, equal quantities of the standard and of the unknown steel are dissolved, the standard is diluted to a definite volume, and the solution of the unknown steel is di-

Jan 1, 1907

By Eric L. Christiansen

A dynamic simulation model for the iron blast furnace has been developed which predicts flow rates, compositions, and temperatures of the top gas, slag, and hot metal exit streams as a function of time from specification of the time-dependent tuyere inputs and raw material charges. As a matter of convenience, a previously developed steady- state model is employed to fix furnace-dependent parameters. It also provides initial conditions for the internal states of the furnace for subsequent dynamic solution of the simultaneous differential equations which describe the local rates of chemical reaction, heat transfer, and mass transfer in the stack, bosh, combustion zone, and hearth of the furnace. The dynamic model was tested by a demonstration of its ability to relax to steady-state representations of the time-averaged data from two separate industrial blast furnaces and of its ability to follow eight days of time-dependent operating data for one of them. Simulated responses to step changes in tuyere input and burden variables have been shown to be of the correct magnitude and duration. Although complex functions of many variables, a proper description of these responses is needed for the development of optimization and control strategies . The model correctly predicts the non-minimum-phase type dynamic response observed in real furnaces in which the output variables proceed through local minima or maxima, often including inverse responses (i.e., opposite signs from their final steady-state values ) .

Jan 1, 1984

By G. St. J. Perrott

AN explosive of, balanced composition might be expected, on first consideration, to develop maximum propulsive strength.1 This hypothesis is based on the assumption that an excess of oxygen would act simply as an inert material with a consequent lowering of flame temperature, also that a deficiency of oxygen would tend toward incomplete reaction of the combustible materials, thereby preventing development of the full strength of the explosion. Actually, however, it can be shown both theoretically and experimentally that an explosive having a certain oxygen deficiency will develop the greatest propulsive strength. This fact has been known to the technical staffs of explosives manufacturers for many years, but it has not always been recognized by explosives engineers in the field. For example: There: is a fairly widespread opinion that the wrapper of a stick of dynamite is merely a container for the explosive and that it plays little if any part in the development of propulsive strength. Actually, it can be shown that the wrapper enters fairly completely into, the explosive reaction. In the case of most gelatin dynamites, a given weight of explosive from which the wrappers have been removed will develop considerably less strength than the same weight of explosive plus wrapper, in spite of the fact that the latter combination contains less weight of the actual explosive ingredient. It can also be shown that a cartridge 7/8 in. in diameter may be stronger, weight for

Jan 1, 1928

By R. R. Kimpel, L. G. Austin

An equation is derived describing fragment size for single fracture of brittle solids. It contains the equations of earlier workers as special or approximate cases and, in addition, is capable of describing coarse distributions in which a few large particles are produced on fracture. The equation can be fitted well to single fracture experiments where over-breakage is avoided. In 1956 Broadbent and callcottl described a method of analyzing the unit operation of grinding, applicable to homogeneous breakage of brittle materials. In essence, the grinding process was split into two parts: 1) the fractional amount of a given size which is selected for grinding per unit time, 2) the size-weight distribution of the fragments produced by breakage of this certain size (primary breakage distribution function). The theory was formulated using matrix algebra. They attempted an experimental verification of the theory using an assumed primary breakage distribution but the results were not very satisfactory. Austin and Gardner2 showed that this assumed distribution was widely different from experimental values and that it led to the poor agreement of predicted size-weight distributions with experiment found by Broadbent and Callcott. In addition, Austin and Gardner2,3,4 reformulated the original approach in terms of differential equations of grinding and demonstrated that the approach led to a very satisfactory description of the grinding process, providing that the descriptive parameters were measured experimentally. Recent work5 has substantiated these findings and the distribution functions of several materials ground under different conditions in different mills have been determined experimentally. The fraction underweight versus size used by

Jan 1, 1965

By R. A. Jr. Flinn

A CONSIDERABLE number of experiments in recent years have definitely established the fact that the internal friction or mechanical hysteresis of a metal under cyclic stress is a property that is highly "structure sensitive." Because of this fact, it has been suggested that an observa-tion of this property, which often is referred to as "clamping capacity," might he a useful indicator of structural changes taking place when a metal or alloy is subjected to any of a number of metallurgical treatments. Damping capacity is of interest to both engineer and metallurgist, but from a rather different point of view, and the information that each desires from such observations is of a different nature. The metallurgist is in search of various external indications of changes taking place in the interior of a metal; changes which are in themselves not directly observa-ble. Even if the observed phenomenon cannot be explained in funda-mental terms, it may be empirically related to certain characteristics of the material and prove of real value in research. Internal friction or mechanical hysteresis occupies such a position, and, although it is not well understood in terms of basic metallic theory, an observation of its changes can serve in a very useful capacity. Of course, there is nothing new in the measurement of damping, but the use of this property in metallurgical research constitutes a vast field, which has received all too little attention. The present work is essentially of an exploratory nature in this field and is an attempt to evaluate the process as a research tool. The phenomenon of age-hardening was chosen as a typical example of a structural change and one method of measuring damping was examined in considerable detail.

Jan 1, 1938

By Anthony Sharkey

Introduction In Europe, longwall mining accounts for over 95% of coal produced from deep mines, whereas in the U.S.A., longwall accounts for less than 5% of deep mine coal production. There are many reasons for the difference, but in general: a. U.S. mine operators have invested heavily in continuous mining or conventional equipment which continues to produce acceptable results; b. There 1s a reluctance to change from, a familiar (and proven) mining method to an unfamiliar one, despite promises of huge production increases,; c. Multi-seam mining in Europe has made longwall the only really viable mining method, whereas In the U.S.A. multi-seam mining (particularly in "below-drainage" mines), is relatively rare; d. Although some spectacular results have been achieved by longwall in the U.S.A.(I), the general performance of longwall in this country has not been good enough to generate much enthusiasm for its wide application; e. The much higher level of investment in face equipment required for longwall when compared to alternative methods (approximately $7.5 million for a medium seam longwall installation and $1 million to $1.5 million for a continuous miner section). However, declining productivity, national energy requirements and safety legislation are creating a situation in which longwall as a viable mining method is being examined more closely and in more places than hitherto. This paper, therefore, attempts to identify some of the principal criteria needing examination in any assessment of the feasibility of longwall application, the limitations of information for those criteria in the decision making process and the need for further research and development to assist the mine operators make the decisions.

Jan 1, 1981

By John W. Tieman

Coal is a term applied to vegetable matter which, through geological processes of heat and pressure, has had both its physical and chemical properties changed. Because its chemical composition is variable, geologists classify coal as a rock rather than a mineral. Peat represents the initial stages in the development of coal, although not classified as coal itself. PHYSICAL PROPERTIES OF COAL The physical properties are concerned with the characteristics of coal in its natural state, or prior to its end use as a fuel. For example, the hardness of coal determines the maintenance cost on coal handling equipment; the specific gravity of coal determines the coal preparation techniques used in a cleaning plant as well as the capacity of coal bins, boats and size of cargo, and other coal storage facilities. The physical properties are, of course, dependent upon the chemical constituents that make up coal, and thus all properties are interrelated. Specific Gravity The specific gravity of a body is the ratio of the weight of the body in air and the weight of an equal volume of water. The specific gravity of pure coal ranges between 1.25 and 1.70, generally increasing with rank. The most important use of this physical characteristic is the part that it plays in the cleaning of coal by wet wash methods. The basic principle on which these operate is that the specific gravity of coals differs from their associated impurities and that there is a relationship between the velocity of the fall of particles in water and their density. Since the specific gravity of slate is around 2.5 and pyrite is about 5.0, pyrite and slate will fall to the bottom of a container filled with water more rapidly than coal. If the water is given a pulsating motion by

Jan 1, 1973

By R. S. Shoemaker, D. L. Harris

Past investigations into the possibility of concentrating the low-grade iron ores of the Gogebic Range in Wisconsin have been hampered by the complex association of the constituent minerals. In part the problem arises from the fact that the iron occurs essentially as two minerals, hematite and goethite, having nearly the same chemical composition but exhibiting different physical properties. Individual grains of these minerals are usually so small that the ore must be ground to a size finer than 325 mesh if substantial liberation of the minerals is to be secured. Appraisal of beneficiation tests on this iron ore requires, therefore, some method of determining quantitatively the contents of constituent minerals in the various products of the beneficiation. Because of the chemical similarity of the two iron minerals, chemical analyses do not provide a means of differentiation. Although the minerals are different physically, they are both opaque and friable, and as the ore must be ground to a very fine size for liberation to be secured, quantitative microscopic methods of analysis are extremely difficult at best. In an effort to overcome these analytical problems, a quantitative X-ray diffraction analysis method has been developed at the University of Wisconsin for the research program on iron ore beneficiation.

Jan 5, 1955

By John F. Blandy

IT is not my intention in this article to consider this subject in the light of the geographer or geologist, but rather in that of the mining engineer, and to endeavor to show the necessity and value to him of studying the minor details of the field or district in which he may be engaged. I t has been said by a distinguished geologist that "the natural boundaries of the geographer are rarely described by right lines. Whenever they occur, however, the geologist may look for something remarkable." And again : " Physiognomy is no idle or doubtful science in connection with geology. The physiognomy of a country indicates almost invariably its geological character." Our country furnishes examples enough of the truth of these remarks, and in no part of it is it so beautifully illustrated as in our own State, which has been so ably described by Prof. Lesley in his admirable little work on the "Topography of Coal." As the great mountain lines become guides to the geologist in determining and mapping out the geography of the formations, so do the minor details of topography become guides to the mining engineer in conducting his explorations, discovering of dislocations, and determining the character of the deposits which are the object of his search. I t is therefore requisite that he should, whilst making his surveys, pay the strictest attention to every variation of the landscape and surface of the ground. Until he has mapped out every feature he may be unable to read the geological changes which may have

By Walter W. Lilly, Issa S. Oweis

Application of rock engineering in geotechnial consulting practice considered herein is in areas of: (a) bedrock verification for foundation support, (b) bearing capacity and settlements, and (c) excavations. A routine geotechnical investigation usually provides data on depth to rock, rock classification, and rock quality. In cases of rock outcrop, such outcrops are mapped for geologic structures and rock mass description. In addition, the regional geology and the general aspects of the groundwater regime are usually known from either published literature or previous experience. The predominant technique for ground and site investigation are usually drilling and geologic reconnaissance. Other techniques involving seismic and geophysical soundings, borehole camera, and oriented cores are used by by no means routine. Performing laboratory strength and compressibility tests is often made to be considered as routine. The use of the point load test is gaining increasing use in the United States and would, perhaps, become a routine field or laboratory test due to its simplicity and, more importantly, its relatively low cost. The purpose of this paper is to describe cases where mostly routine investigation and testing were used to arrive at engineering decisions. Bearing Capacity and Settlements The allowable bearing values for foundation support on rock is usually dictated by local building codes which presumably should reflect local experience. The interpretation of the code, however, can present a problem, especially if the interpretation is made by a designer under the delusion of knowledge in rock engineering. For

Jan 1, 1982

By M. Albertson

The purposes of this statement are to define a problem that exists in regard to the estimation of developed petroleum reserves, to analyze the problem in an abstract manner, and to discuss it as an introduction to certain papers that follow. The problem is to devise and develop a suitable procedure to permit more accurate estimates of developed petroleum reserves. Part of the problem is to make such estimates available earlier in the life of any particular pool. The problem of securing more accurate estimates of developed petroleum reserves existed prior to curtailment of production. With curtailment, however, the problem became acute, some of the more prominent reasons being as follows: 1. The standard method of estimation depended on production-decline curves. This method is inapplicable while curtailment prevails and available methods arc insufficient. 2. The retarding influence imposed by wide open flow conditions upon overdevelopment is absent. Great losses of capital by overdevelopment can now occur before realization of the true situation occurs, or before effective steps can be taken to stop such wastage. This increases the need for early, accurate estimates. 3. Above-ground stocks have diminished and the equivalent of such supply tends more and more to be retained underground in the natural reservoirs. It becomes increasingly necessary to know accurately the amount of these stocks. To direct attention to an additional point of different nature: improved accuracy of reserve estimation can be obtained only by closer scrutiny of the factors that determine recovery. This examination and the resulting efforts to measure the effect of these factors in terms of ultimate recovery must tend to improve ultimate recovery. The statements regarding the acute nature of the problem also indicate to some extent the importance of the problem and the necessity of finding a solution. Developed reserves of the industry, and of individual opera-tors, are one of the great factors that properly should determine explora-

Jan 1, 1936

THE Bergbüchlein and Probierbüchlein occupy a unique position in the literature of mining and metallurgy, for, they are the first printed books on any aspect of the two related professions. The first printed book on any subject has an allure that may not be entirely warranted by the strict historical significance of its contents. Among the books of the first century of printing there are very few that contain information that was new at the time of publication. Much' of what they recorded had been previously circulated in manuscript form. Printed books are nevertheless of great value because they mark the time when the author's words, free from errors-or at least with the same errors-became available to large numbers, of readers, who thus could easily and cheaply acquire a common background for their future work. Moreover, though there is occasionally some doubt as to the exact year of publication'(as in the case of the present works), it is generally easier to date a printed work than a manuscript, and thus to provide a fixed coördinate in history. The Bergbüchlein, "The Little Book on Ores," is the first printed work in the field of mining. It is an introduction to mining geology, which means that it was not addressed to the practicing expert but was intended to rouse the interest of beginners in the various aspects of a future vocation. It touches on the theories of the generation of ores, introduces and defines some of the most frequently encountered technical terms of the profession, and indicates what knowledge and tools are required for successful prospecting and mining. It also describes the ores of the seven most important metals. For those parts that deal with theory the author accepted uncritically the traditional teachings of the alchemists and the astrologers; his hints on where to find promising ores are based partly on superstition; but, there is enough factual,

Jan 1, 1949

By James A. Barr

Ferrophosphorus, an alloy of phosphorus and iron or perhaps a physical mixture of definite compounds of iron and phosphorus, has become of increasing importance as the use of the basic open hearth has extended. Commercial ferrophosphorus is a porous, brittle metal of crystalline structure and often with a bluish metallic luster. A typical analysis is as follows: Per Cent. Phosphorus......................................... 18.0 to 22.0 Iron............................................... 80.0 76.0 Oxygen............................................ 0.2 Sulfur............................................. 0.3 Silicon............................................. 0.1 Carbon............................................ 0.1 Manganese......................................... 0.2 This alloy was first made in an electric furnace, as it was thought that the high heat of the electric arc together with the reductive effect of carbon was necessary. About 1898, J. J. Gray, Jr., was producing a high-phosphorus pig iron in his furnace at Rockdale, Tenn., by using high-phosphorus, local iron ores. As these high-phosphorus ores were difficult to obtain, he conceived the idea of increasing the phosphorus content of the pig iron by the addition of phosphate rock to the furnace burden. When the phosphorus content of the pig was kept low and only small amounts of phosphate rock were added to the burden, no particular troubles were encountered, but when he increased the amount of phosphate rock to produce an 18 per cent. alloy, his furnace troubles rapidly multiplied. After many failures and freeze-ups, he was partly successful in making short campaigns on 18 to 20 per cent. "ferro." At first, when the furnace got in bad shape on ferro, he would switch to a regular pig-iron burden until the furnace was brought around sufficiently to start on ferro again. About this time, Mr. Gray applied for and obtained his first patent. As he grew more skilled in the furnace operations, he was enabled to extend the furnace campaigns and produce ferrophosphorus continuously for the life of the furnace lining. These improvements were made the subject of another patent issued in 1916.

Jan 1, 1925

By E. De Golyer

The only known direct method of discovering oil deposits is by the drilling of test wells. Such exploration is always hazardous and generally very costly. The problem of the prospector, therefore, is one of selecting test sites that are favorably located and so to reduce the odds against his venture. Early in the history of the oil industry, it was realized that oil and gas deposits, other conditions being favor- able, were usually found in anticlinal types of structure. This very understandable and rational habit of occurrence furnished the first substantial clue to the prospector. Oil occurs in sedimentary rocks, and beds of such rocks are deposited originally in parallel planes. An anticline at the surface, therefore, could be accepted as an indication of an anticline in lower beds. Structural geology became the tool of the prospector, and by its use in the past two decades, the majority of the known important oil deposits of the world have been discovered. This is but an incomplete, and the simplest, statement of the problem. Nine-tenths and more of the important oil pools of the world belong to the great class of accumulations controlled by structural traps- anticlines, faulted structures, salt domes, etc.-but by

Jan 1, 1932

By Samuel Lasky

THE writer has been interested in determining the mineralogic dis-tribution of silver in the base-metal ore of the Ground Hog mine of the Asarco Mining Co. in the Central mining district of New Mexico.1 This ore consists of a varitextured mixture of sphalerite, chalcopyrite, galena and pyrite in a quartz gangue. The average ore contains 14 per, cent of zinc, 9.5 per cent of lead, 5 per cent of copper, and 10 oz. of silver per ton. Generally it is accepted that the silver in ores of this type, in which no definite silver minerals can be recognized, is contained in the base-metal minerals. Published assays of pure mineral specimens from many dis-tricts show that each of the base-metal minerals contributes in some degree to the total silver content of the ores, and to determine the pro-portionate amount contributed by each mineral in any specific ore it has been the practice to assay selected specimens of each mineral, the purity of which has been determined microscopically. There being no such assays available for the Ground Hog ore, and it being impract cable to have enough of them made to give average results, the writer resorted to a mathematical attack upon composite assays of large quantities of ore and concentrates. Surprising results were obtained, and it is the threefold purpose of this paper to present these results, to describe the mathe-matical method used, and to point out the value of using this method even when assays of pure specimens are available.

Jan 1, 1934

By F. Keeler, C. M. Craighead

Aluminum alloys containing magnesium and silicon are susceptible to strengthening and hardening by suitable heat-treatments, and they constitute a class of alloys of considerable commercial importance. Generally, they contain these two elements in the proportions required for the formation of the intermetallic compound Mg2Si, or an excess of silicon; no commercial wrought alloys are made with an appreciable excess of magnesium. The reason for not having excess magnesium is obvious from the results given in this paper, since it is shown that excess magnesium results in a proportional decrease in the solubility of Mg2Si. This is the eighteenthl of a series of papers from the Aluminum Research Laboratories dealing with the equilibrium relations in aluminum-alloy systems; most of the previous publications concerned binary aluminum-alloy systems; this is the fourth of a group pertaining to ternary aluminum-alloy systems. The work on this system was completed in 1930, but the results were not published because of the pressure of other work. Hanson and Gaylor2, in 1921, presented the results of an extensive investigation of the aluminum-magnesium-silicon system. Their results indicated that an excess of magnesium over the amount required to form the compound MgzSi caused a noticeable decrease in the solid solubility of MgzSi in aluminum. A more recent investigation3 in these laboratories showed that the solid solubility of MgzSi in aluminum was 1.85 per cent at 595' C. and decreased to 0.30 per cent at 300' C. The results of the latter investigation were used as the basis for the present work. The Present Investigation In the present investigation, a study was made of the effect of various amounts of excess magnesium upon the solid solubility of MgzSi in

Jan 1, 1936

By F. E. Marcy

IT is not my purpose to write a lengthy article or to attempt the solotion of the problem I am presenting, but to call attention to what I believe an important issue, hoping that it may arouse in some one, or in some company, a sense of responsibility. I am referring particularly to modern up-to-date milling plants discharging tailings which under existing conditions cannot be further treated or from which a recovery cannot be made at a profit, but where a quantitative and qualitative analysis shows that a portion of these tailings might profitably bee treated, at some future time when our metallurgical knowledge has advanced, when we have cheaper power, chemicals, labor or other advantageous conditions. Early Methods In our early milling methods very little attention was given to the care of tailings. It was thought that if the mill could be located by a stream or a river where the final disposal of the tailings could be forever lost sight of, it was highly desirable. We can now see acid estimate what was lost in these rich tailings, not recoverable from the streams and the great rivers. Fortunately for many, the depositing of tailings in these streams and rivers was objected to by the farmers and finally prohibited by the State Legislatures. In looking back over our past milling methods, it seems that, the first endeavor was to make the maximum amount of money for a particular period, or year, regardless of the future, the depletion of the mine, or the conservation of the total mineral content. The dumping and sluicing of 3,000 tons per day, for a period of many years, of a copper tailing carrying

Jan 8, 1917

By Frederic E. Carter

THE history of all the civilizations of the Eastern Hemisphere is underlaid and interwoven with the story of gold. Great nations rose, welded by the hand of the conqueror, flourished gloriously because of the wealth of gold inevitably attracted to them, only to fall, either through the sapping of their original virility by the softer living their material prosperity made possible, or by wars made upon them by enemies who craved possession of what was theirs. Imposing fleets sailed the seas, seeking gold or tangible wealth that might be converted into gold. Men suffered untold tortures in its quest. It sent Columbus out into unknown oceans, caused the migration of hordes of people from our Atlantic to our Pacific seaboard in '49 and accelerated the final subjection of our last frontier, probably by as much as a century. The mystic may see both something sinister and something beneficent in this metal that has played such a tremendous part in the shaping of the destinies of men. It has showered blessings and taken them away. It "hath deposed the mighty from their seats and hath exalted men of low degree" and, sardonically, reversed the order yet again. Its peculiar color, its incorruptibility, and its rarity all have contributed to excite the imagination of all races of men. In the Eastern Hemisphere and now in the entire modern world, the predominant emotion excited by gold is avarice. But in the social and economic organization of the civilizations native to the western half of the world, gold has a far different history. Before the advent of the white man, these sun-worshipping peoples saw in the permanently

Jan 1, 1953

By John P. Ashby

Mine production blasting is a process of destruction of rock masses in order that ore may be extracted. Many open pit operations are faced with the apparently conflicting requirements of providing large quantities of fragmented rock for the processing plant and of minimizing the damage inflicted upon the surrounding pit slopes. A reasonable compromise between these two conflicting demands may often be found by means of simple engineering of production blasts. Many operations tend to rely too heavily upon traditional wall control techniques to alleviate a problem already created by the production blasts. Various production trends including use of larger blastholes and patterns have tended to aggravate the situation. These practices only serve to emphasize the need for engineered improvements. Central to blasting engineering is the process of systematic trial and evaluation. Changes to the blasting system should be made singly, starting with the simplest. This paper discusses simple changes involving drill pattern control, effective use of blastholes and explosives, adequate delaying including use of down-the-hole sequential techniques, effective utilization of free faces, and avoidance of "choked" situations. By directing explosive effort where it is needed, such changes generally result in a significant improvement of slope conditions and of production blasting cost and performance.

Jan 1, 1983