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By Thys B. Johnson

Traditional mine planning concepts are discussed and suggestions for improvement through use of the developed model are proposed. The approach developed in this paper allows optimal planning of the complete mining-concentrating-refining system over the entire planning horizon and permits the system to dictate how and when to process a block of material, i. e., a dynamic cutoff.

Jan 1, 1969

By C. H. Green

Recently two papers on the structure of eutectics were read before thc British Institute of Metals, one by F. L. Bradyl and the other by A. Portevin. 2 In the preparation of photomicrographs of laboratory specimens as illustrations for student work, and in connection with various researches, the writer has been working along the same line for some time and, therefore, was much interested in the results given, especially those of Portevin. He has correlated the information on the subject and has outlined a broad scientific basis for future work along this line. It is largely with the idea of adding something by way of illustration to the work already done that this paper is written. The eutectic is generally understood to mean the alloy having the lowest melting point of any alloy of the system, and in which the melt becomes supersaturated with reference to the two or more phases which separate out simultaneously or alternately. From the surface pattern, the eutectic means a structure with no primary crystals. It is not always easy to get the exact eutectic composition in making any alloy; in fact, a slight range in composition may be expected and some of the coarser particles may be richer in either of the composing metals. Even when chemical analysis shows the right composition, differences in density of the pure metals may cause segregation, or supercooling resulting from different crystallizing properties may give a surface pattern the appearance of being on one side of the eutectic point. However, the alloys on either side of the eutectic composition, showing primary crystals of one of the phases and the effect of the proeutectic form on the surface pattern of the eutectic make a very interesting study, which is slightly touched upon in this paper. The phases, or microconstituents, of a eutectic may be pure metals (Pb-Sb, Tl-Au), solid solutions (Cd-Zn), a pure metal and a solid solution (Ag-Sn), or a pure metal or solid solution with an intermetallic compound (Sb-Mg, Sb-Cu, As-Cu, Bi-Te, etc.).

Jan 1, 1925

By C. F. Cornell, Henderson, A. F. Dunyon, D. A. Dahlstrom

IN processing magnetic taconites several steps of crushing, grinding, classification, and magnetic separation are required to produce a 60+ pct Fe concentrate. Usually the final concentrate is in a slurry form of 55 to 70 pct solids by weight and is further characterized by a particle size of 60+ pct -325 mesh. In taconite plants already completed or under construction the conventional method used to obtain pellets suitable for blast furnaces is to filter the concentrate slurry, ball the filter cake, and then harden the green pellets in a traveling grate or in a vertical shaft furnace. Large tonnages must be handled in minimum floor space, with reduced maintenance and lowest possible operating cost. Filtration must therefore achieve two objectives: 1) high filtration rate-in terms of pounds of dry solids per hour per square foot of filtration area-at a low filtrate solids concentration, and 2) a filter cake moisture that will always permit efficient balling within the normal fluctuations of plant operating conditions. If moisture contents are too high, balling may be impossible or result in a mushy ball without enough green strength for the firing operation.

Jan 3, 1957

By A. T. Tye

WHEN the roughing tables operated in 1923 were abandoned, all the coarse iron pyrite for-merly removed by the tables had to be ground to flotation size, which caused an increased power con-sumption of 2 kw.-hr. per ton. Recently, by increasing the tonnage, this has been reduced to a total of 16.6 kw.-hr. per ton. The cost of repairs has been slightly reduced by using an alkaline circuit instead of the acid mine water used in 1923. Other economies from elim-inating roughing tables and the finishing tables have more than compensated for the extra grinding and the total costs have remained practically the same, until the first part of 1927, when, with increased tonnage, the total cost has decreased to 72 cents and the repair cost to 9 cents. In 1923, with a combined gravity and bulk flotation flowsheet, the grade of concentrate was only 4.38 per cent copper. With preferential flotation this has in-creased to over 17 per cent copper. The tailing has decreased from 0.29 per cent -copper to 0.18 per cent. The copper recovery, instead of decreasing; as might be expected, has increased from 87.4 per cent to, 91.5 per cent. The silver recovery has also increased from 88

Jan 8, 1927

By R. L. Templin, D. A. Paul

The modulus of elasticity is defined as the ratio of stress within the proportional limit to corresponding strain. This property, as thus defined, is a constant for each kind of material; and in tension or compression is usually designated by the symbol E. The modulus of elasticity serves as an index of the stiffness of a material or a measure of its ability to resist change of shape under stresses not higher than the proportional limit. In view of the frequency with which the modulus of elasticity is used in engineering calculations, it is surprising to note the uncertainty that exists as to authentic values, and the marked lack of published information relating to the variation of the constant E within individual alloy systems. A value of 10,000,000 Ib. per sq. in. has been quoted as representative of aluminum and its alloys. This value has been found to be approximately corrcct for pure aluminum and aluminum alloys in which the total percentage of the alloying elements is low, but seriously in error in the case of alloys that contain relatively large amounts of the alloying elements. a National Metals Handbook. b Intcrnatiunal Critical Tables. '' Aluminum Co. of America. " Based on density of alurminum (2.70). c Smithsonian Pliysical Tables.

Jan 1, 1931

By P. A. Beck, A. H. Lutts

IN the classical picture of recrystallization the growth of strain-free grains at the expense of a strained and work hardened matrix is responsible for the softening of cold worked metals on annealing. It has been commonly assumed that the release of the stored energy of cold work, softening, and re-orientation take place simultaneously, as the high angle boundaries of the new recrystallized grains sweep over the cold worked matrix. However, recent evidence indicates',' that, at least in some cases, considerable or even complete soften- ing may take place essentially without reorientation (i.e., without the migration of ordinary high angle grain boundaries, or "recrystallization'') and the release of most of the stored energy of cold work may precede softening. These cases suggest that the property changes, taking place during the annealing of cold worked metals, may be associated with various distinct processes. The study of such situations is of considerable interest, since quantitative data are still scarce. In the present work, isothermal softening curves were determined for a heavily rolled aluminum single crystal, under such conditions that no "recrystallization" occurred until after complete softening. The hardness data were correlated with X-ray diffraction pinhole patterns in order to detect any reorientation that may occur and with measure-

Jan 1, 1955

By Noel W. Kirshenbaum, George A. Pouska, James M. Link

Literally millions of words have been written on the subject of mineral slurry pipelining. The sheer bulk of literature on the subject should be enough to convince the interested observer that the method is both viable and widely applied. It is the intent of this paper to examine typical mineral slurry applications. This examination should reveal the reasons that the slurry system was selected over other transport modes and it should provide a framework for determining the applicability of the technique to new projects. Slurry transport involves the conveyance of solid particles by suspension in a moving liquid. Almost any combination of solids in liquids may be imagined, and the conduit may be an open channel or a closed pipe. Historically, the most numerous slurry transport applications consisted of mineral particles in water. However, current research investigations are emphasizing other liquid carriers, specifically those which have greater economic value. Among these are gaseous and liquid fuels and chemical feedstocks. Another area being investigated involves the use of the pipeline as a chemical reactor system. The long residence time and turbulent flow characteristics of the pipeline make it particularly attractive for certain chemical reactions. Because these new systems involve a valuable liquid as well as a valuable solid, there is increased attention to solid-liquid

Jan 1, 1980

By Carl Samans

THE attention of physicists and metallurgists has been directed toward the study and explanation of the deformation textures in metals for the past 15 years. In 1920 N. Uspenski and S. Konobejewski1 were first able to show that the symmetrical X-ray diffraction effects that had been previously reported by E. Hupka2 and others in metal foils were caused by a directed arrangement of the crystallites. Since then, the systematic study of textures resulting from the application of the pure forces of tension or compression to polycrystalline materials hag been supple-mented by many investigations on deformed single crystals, which have greatly added to our knowledge of deformation. However, despite the valuable information secured from these comparative studies only four investigations upon cold-rolled single crystals of any of the face-centered cubic metals have been reported in the literature. This lack of quantita-tive data is especially unfortunate because of the much greater practical significance of rolling textures and their effects in both cold-rolled and annealed materials. This investigation was undertaken for the purpose of specifying the deformation of rolled single crystals in the hope that such information might later facilitate the explanation of polycrystal-line textures.

Jan 1, 1934

By C. G. Fink

A PART of the material incorporated in this paper was derived from the studies of ancient metal objects examined by the authors from time to time for museums and art collectors, in order to verify the age of the metal. The data thus accumulated during several years was systemati-cally surveyed and supplemented by new material obtained in examina-tion of a set of specimens that had been generously donated by museums for this study. Altogether over 50 pieces were investigated, of which 39 are described in this paper. Every specimen is at least 1500 years old; the majority are considerably older. Exact conditions to which these bronze and copper objects were exposed in the ground are unknown, unfortunately. It is safe to say that exposure conditions did not remain constant during the long period of burial. Although the collection of specimens studied represents a wide variation in location and age of the objects, as well as in the nature and composition of the metals, it was found that fundamental changes in the metal structure were limited to a few typical cases which, therefore, may be considered as more or less general. The authors' chief aim was to study the effect of extremely long periods of corrosion on the structure of bronze and copper.

Jan 1, 1936

By H. B. Huntington

Some of the basic problems in understanding elec-tromigration in metals are discussed, along with the attempts that are being made to handle them. One such problem is the effect of the electrostatic forces. It is now acknowledged that the momentum exchange with charge carriers plays generally a dominant role in the driving force but the question remains to what extent the electrostatic force may still be effective. The electromigration of interstitial impurities is also an area which presents some intriguing questions. For the substitutional impurity, moving by the vacancy mechanism under the influence of an electric field, the correlation considerations are somewhat more complex than have been previously recognized. Another problem of basic importance in the calculution from first principles is the strength of the "electron friction" force, say for a simple one-band metal. A related problem growing out of the preceding is the prediction of the direction of the "electron wind" force for metals with band structure involving both holes and electrons. THE term electromigration has come to be used to describe the flow of matter in condensed phases carrying high electronic currents such as metals and alloys, whereas one usually reserves the term electrolysis for situations where the current is largely ionic, particularly in the liquid state such as molten salts. It follows that the mass transport number in electromigration is always very small, of the order of 10-7. Studies of electromigration date back some 30 years but the modern period would appear to date from the work of Seith and Wever1 who in the mid 1950's first incorporated markers to display mass motion relative to the lattice and first suggested that the direction of the mass flow was primarily determined by the sign of the charge carriers. Since that time interest in the field has grown steadily and more rapidly recently as certain technological applications became apparent. Chief of these is certainly the deleterious effects that electromigration can cause, even at relatively low temperature, to current-carrying elements in integrated circuitry.2 These phenomena have been the subject of intense study and considerable ingenuity. On the constructive side electromigration has proved a useful tool in the purification of certain metals.3 The interest of this paper is, however, centered more on the basic aspects of the subject than on its technological applications. That high electric currents should give rise to mass flow in metals and that the driving force should be more directly associated with momentum exchange with the charge carriers than with the electrostatic field are ideas that no longer cause surprise or particular interest. The field has matured to the point where the general concepts are widely accepted and continued progress in basic understanding rests on more detailed and quantitative exploration. It is the purpose of this paper to point out what are some of the current problems. As a result, we expect to raise more questions than we answer. The first of these will be the role of electrostatic forces, if any, in electromigration. A second section will deal with the electromigration of interstitials. A third and final section treats with electromigration of substitutional impurities or of the matrix atoms themselves. ELECTROSTATIC DRIVING FORCE In the conceptual treatments of electromigration it has been customary to write the driving force in terms of an effective charge number Z* and to divide it into two terms F = e£Z* = e£[Zel- z(pd/Nd)(N/p)(m*\m*\)] [1] The first of these represents the electrostatic force under immediate consideration in this section and the second and usually dominating term for metals arises from momentum exchange with charge carriers, commonly called the "electron drag" term. As can be seen it is set proportional to the electrons per atom, z, and the ratio of the specific resistivity of the moving entity to the corresponding resistivity per matrix atom. The (m*/Im*I) factor takes into account the fact that the sign of the charge carrier determines the sign of the driving force. The specific resistivity of the moving entity is averaged over its path. In the case of motion of the matrix atoms by vacancies this gives rise to approximately one-half the resistivity at the saddle point since the scattering power of the atom at its equilibrium position bordering the vacancy differs only slightly from that of a normal matrix atom. Although the formulation of the "electron drag" term in Eq. [I] is based on a highly simplified model for electron defect scattering, the essential features implicit in the expression are common to all the theoretical approaches that have so far appeared in the literature.4-6 As for Zel, most treatments of electromigration have included the quantity as the parameter which measures the direct interaction of the electrostatic field with the ion and equated it to the nominal valence of the latter. However, there has been considerable discussion whether this interaction may not be 0 in many cases.6 If the moving ion is always enveloped by the same distribution of shielding charge, then clearly its motion will not involve any work done by the electric field and one can expect there will be no electrostatic force exerted on such a neutral composite. From this point of view the shielding charge around the ion would be said to be complete and hence the entity within the Debye shielding sphere would be unaffected by the electrostatic field per se. There is, however, the prospect that, as the moving ion progresses, new charge comes in to participate in the shielding action

Jan 1, 1970

JUDGE Samuel E. Schull, in the Court of Quarter Sessions of Monroe County, Pa., handed down a decision on July 2, declaring the Pennsylvania law for the Licensing of Professional Engineers and Land Surveyors to be in violation of the Constitution of the State of Pennsylvania and also of the 14th amendment of the Constitution of the United States. The case was that of George E. Stevenson, who was arrested in June, 1922, charged with the practice of the profession of land surveying without first obtaining a state license. Mr. Stevenson had had forty years of practical experience as an engineer and land surveyor, and as set forth in the findings "had attained unusual skill, distinction and reputation in his said profession, and, on said date and for a considerable period thereto-fore and down to the present time, was and is President of the Engineer's Society of Northern Pennsylvania." That part of the decision referring to the unconsti-tutionality of the act is quoted in full as follows: This matter now comes on to be heard on argument as to the constitutionality of the said Act of May 25, 1921, P. I. 1131. The defendant urges that the same is unconstitutional: First: Because it is in violation of Article 3, Section 3, of the Constitution of Pennsylvania, which provides: "No bill, except general appropriations bills, shall be passed containing more than one subject which shall be clearly expressed in its title." Second: That the same is discriminatory and, therefore, in violation of the 14th Amendment of the Federal Constitution. In this case, we: are confronted by the Act of Assembly bearing the title "an act to regulate the practice of profession of Engi-neering and Land Surveying; creating a State Board for Regis-tration of Professional Engineers and Land Surveyors; defining its powers and duties, imposing certain duties upon the Common-wealth and Political subdivisions thereof, in connection with public work and providing penalties." We meet in the title of this act, a recognition of the fact that it is the legislative intent to deal with two professions: First: Engineering. Second: Land Surveying.

Jan 8, 1923

By William P. Blake

This camp is just now startled by the alarming suggestion that unless there shall speedily be an appreciation in the value of silver, and a decrease in the cost of salt, it will be prudent business policy to close the Alice mines and mills until the conditions of production are more favorable. Such an event would be a great blow to the prosperity of Butte. It would throw some hundreds of men out of employment, and it might lead to the adoption of the same policy by other companies, which, like the Alice, have not been able to pay dividends to their shareholders for a long time. The question arises, and becomes emphatic: If, under the present adverse conditions, the mines and mills cannot be made to pay a proper profit, why should they continue to be worked ? The owners mentally ask: Shall we go on exhausting our mines, pouring out a stream of silver for the maintenance of the community, and the support of the rail ways, or shall we husband our reserves, withdraw the miners from our slopes, and wait for more favorable conditions ? This is the impending question, and all concerned dread to meet and answer it. Let us briefly review the situation and forecast, if possible, what the solution of' the problem will be. It must be understood that the discussion does not include, or refer to, the immense copper-producing interests of the camp, which may or may not be upon a very much more satisfactory basis. It will be confined chiefly to the operations of the Alice company, sta tistics of which are at hand, without involving the other silver com panies in the conclusions beyond those inevitable from well-known facts, patent to all. There are at present in Butte and in its vicinity in the principal mills an aggregate of 290 stamps dropping upon silver-ores: Alice,...........80 stamps. Moulton,. .........40 " Lexington,...50 " Silver Bow,.........30 " Blue Bird,..........90 " The Alice mills at present, with their 80 stamps, devour, in round numbers, from 100 to 120 tons a day. The actual amount

Jan 1, 1888

John Chipman (Massachusetts Institute of Technology, Cambridge, Mass.)—After looking over the authors' shoulders for several years and after many discussions on the interesting diagrams of the types shown, it is a pleasure to see a formal paper published on this subject. There can be no doubt of the practical usefulness of the concepts shown. Inclusion formation in steel is such a highly complex matter that any system for understanding the subject is bound to be welcomed by those who must work with steels and who see in their day-to-day experience the good and evil effects of inclusions. A feature of the work with which the discusser has been concerned, and which he would now like to attempt to explain, is the relation between the schematic diagrams which the authors use and the phase diagrams for related systems. Obviously, the authors' diagrams are in no sense complete phase diagrams. However, there is a relation between this type of diagram and the true phase diagram, and the understand- ing of this relation ought to help in understanding the general picture which the authors are presenting. Consider the authors' Fig. 4, which shows the liqui-dus relations in the Fe-Mn-S-0 system. To show the complete relations between temperature and composition in these four ternary systems would require four triangular prisms, the vertical axes of which would represent temperature. The four triangles of Fig. 4 represent basal projections of certain lines from the four prismatic phase diagrams. Readers of the paper are all more or less acquainted with this type of projection and its usefulness and limitations are generally understood. In order to concentrate on the interesting parts and to minimize the less interesting features, the composition scale may be shifted to de-emphasize regions containing gaseous sulphur and oxygen. Such a diagram is shown in Fig. 16, which is a distorted version of the authors' Fig. 4. Here the oxide of iron is wiistite, denoted by W, and it is to be noted that between W and MnO lies the entire MnO-FeO "binary" system. Similarly, between MnS and FeS lies another binary whose

Jan 1, 1956

In the General Alphabetical and Analytical Index of A I M E Publications for the years 1926 through 1935, a complete list of the volumes covered is printed on page 5, but the dates of publication of the volumes are not given Therefore the following information regarding the volumes that were printed without numbers may be useful to users of the Index

Jan 1, 1937

[For the year ending February, 1936 PRESIDENT AND DIRECTOR HENBY A. BUEHLER3 ROLLA, Mo. PAST PRESIDENTS AND DIRECTORS FREDERICK M. BECKET1 NEW YORK, N. Y. HOWARD N. EAVENSON2 PITTSBURGH, PA.]

Jan 1, 1936

OFFICERS AND DIRECTORS For the year ending February, 1934 PRESIDENT AND DIRECTOR FREDERICK M. BECKET NEW YORK ,N . Y. PAST PRESIDENTS AND DIRECTORS ROBERT E. TALLY JEROME ARIZ SCOTT TURNER WASHINGTON D. C.

Jan 1, 1932

By J. Elmer Thomas

If 1929 witnessed a growing realization on the part of the oil industry that supply must be balanced against demand, 1930 proved conclusively that excessive inventories constitute a price depressant even with balanced conditions. Increased attention was certainly paid to economic considerations last year, and the achievement of holding daily crude production, with a constantly mounting potential, to levels 500,000 bbl. below the output of the summer before, deserves special mention. The ill-advised accumulation, however, of gasoline stocks, at least 10,000,000 bbl. larger than necessary, nullified the restraint exercised by the producers and finally necessitated drastic downward price revisions. An event of special significance was the appointment by the Federal Oil Conservation Board, last March, of a temporary Committee on Petroleum Economics that attempted a forecast of demand, an estimate of supply, and an allocation of the latter between the principal producing states. Thus for the first time was an economic program for an entire basic industry drafted by an independent body under the auspices of the Federal Government. The report was widely discussed and generally approved, but its schedules were not adopted by the refining division nor by oil producers in the State of Texas until too late to contribute to the industry's prosperity during 1930. If the restraint of November had been exercised in May a profitable year might have been the result: The gasoline price war in California during June, however, illustrated the point that even with a fairly sound statistical position insistent pressure to expand normal marketing outlets must result in losses to all concerned. The balanced program so painfully attained by producers must be maintained by refiners and distributors to be completely effective. Again in November the Federal Oil Conservation Board, acting on the request of the directors of the American Petroleum Institute, called its Committee on Petroleum Economics back into existence to prepare a new estimate for the next six months. An economic program adopted in advance of the winter period of accumulating inventories may aid this large and essential industry toward the profits to which it is entitled

Jan 1, 1931

By J. W. Eckerd

Anthracite mining developments have not been as spectacular as the advances made for bituminous coal. The reasons are well known, i.e., steeply pitching seams of the western, eastern, middle and southern fields, and the physical conditions of the strata in which the seams are situated. Beds with moderate pitches (30º to 35º or less) have been mined with coal planers, longwall with movable props, shaker chutes, coal borers and large diameter boring machines. However, the use of this equipment has been limited to a relatively small portion of the production. Long-hole drilling has been developed from a point where holes of 25 or 30 ft have been replaced by those up to 130 ft. This has been possible through the introduction of primacord and similar detonating agents that can fire a long train of explosives with one cap. The usual practice in long-hole mining is to drive a gangway, chutes and monkey heading, or return airway, in the normal development manner. Two breasts can then be driven from the lower to the upper level to act as openings for the beginning of the long-hole work. Following completion of the development, holes can then be drilled from the monkey headings 100 ft or more up the pitch through the coal to within 15 ft or more of the upper level, depending on the nature of the coal on the roof. The thickness of the coal bed determines the spacing of the long holes, although they usually are on 6-ft centers for a 6-ft thick coal seam. The Bureau of Mines has conducted extensive investigations and tests on the development of a hydraulic mining system to be used in conjunction with hydraulic hoisting. Tests were conducted in cooperation with a large anthracite producer in a coal seam from 10 ft 6 in. to 15 ft in thickness and on a pitch from 0º to 20. This particular mining procedure is adaptable only to thick seams on relatively flat pitch as the maneuverability of the hydraulic jumbo is an important restricting factor.

Jan 2, 1968

By Sidney Powers

Discussion of the paper of SIDNEY POWERS and ALFRED C. LANE, presented at the New York meeting, February, 1916, and printed in Bulletin No. 110, February, 1916, pp. 535 to 548. N. L. BOWEN, Washington, D. C. (communication to the Secretary*). -This detailed study and. complete demonstration of differentiation as a result of the sinking of crystals has a great general significance in petrogenesis. If this action can be demonstrated in an effusive body, even though a very thick one, how can one doubt its possibility in large intrusive bodies? The authors speak of the sinking of augite and the rising of plagioclase but I should consider that they should depend entirely on the former action to obtain their results. It is true that in my experiments, to which the authors refer, a floating of crystals was in one case obtained, viz., in the case of tridymite crystals, but it must be remembered that tridymite has an exceptionally low density. Plagioclase crystals, on the other hand, are of nearly the same density as basaltic liquid. Under magmatic conditions they might be a little heavier than the liquid or a little lighter, we do not know which, but the margin would be exceedingly small and any motion resulting, whether upward or downward, would be correspondingly small in the usual case. For this reason I should think that the sinking of pyroxene should be considered probably the sole factor in producing the observed result, for which purpose it appears to be entirely adequate. The measurements of grain have also a certain significance in this connection. In the experiments referred to a difference of grain was obtained in different parts of the charge, which was entirely independent of the rate of cooling but connected with the fact that a sinking crystal does not depend entirely upon diffusion for the collection of its material from the surrounding liquid. The crystals which sank a considerable distance were therefore exceptionally large. Now in the Cape Spencer flow the augite crystals are normally (top and bottom) somewhat smaller than the plagioclase crystals, but in the layer somewhat below the middle,

Jan 5, 1916

By D. M. Bondurant

AT the present time, the coal industry is greatly interested in any method or machine that will cut the cost of producing a ton of coal, while at the same time producing a product of quality and grade suitable to the customer. Comparatively new and, as yet, little known, auger mining is proving a profitable method of coal recovery. It may be used for the production of low-cost, high-quality coal with equal success from both the hard-to-mine seams, those with banded impurities and bad roof conditions, and the more easily mined seams as classified according to conventional mining methods. A number of units are now in operation and production information is available that should be of particular interest to coal operators and of general interest to anyone associated with the coal-mining industry. Auger mining refers to coal extraction with large size augers capable of drilling to great depths and having a high capacity. Consideration of the equipment and methods used in drilling an ordinary shot-hole will give a picture of auger mining on a smaller scale. At present, auger mining is used largely for recovery of coal from the highwall after strip mining becomes uneconomical because of the type and the thickness of the overburden which must be moved. Coal augers have many of the advantages of present continuous mining machines, along with many more. The four distinct operations of conventional mining-—cutting, drilling, shooting, and loading— are eliminated and replaced by the combined operation of boring and conveying of the coal. The coal recovery auger is an adaptation of the horizontal rock drill used for drilling shot-holes to shatter and loosen overburden in strip mining operations. During the war the Becker County Sand and Gravel Co. of Summersville, W. Va., experimented with drilling coal with 6 and 9-in. rock augers. The results led to the successive development of the 20, 24, 30 and the 36-in. machines, the latter having appeared in the coal fields within the past six months. Because of the great success of the smaller size

Jan 1, 1952