Search Documents

By E. J. Roberts

Prior to 1916, thickening was an art, and any accurate decision as to what size of machine to install to handle a given tonnage of a specific ore must have been one of those intuitive conclusions, based on both intimate and extensive acquaintance with thickners and ore pulps. Then in 1916 "knowledge of acquaintance," became "knowledge about" with the publication of the Coe and Clevenger paper.' The unit operation of thickening had graduated to the status of an engineering science. The fundamental similitude relationships for the two major phases of the operation were defined so clearly that batch tests on models as small as liter cylinders could serve to specify protypes as large as 325 ft in diameter.

Jan 1, 1949

By NEWTON B. KNOX

THE war has forced the principal industrial nations of the' world into the strait jacket of a closely controlled economy; taxes have been heaped upon all enterprises in order to maintain the armed forces and to deprive the people of the ability to bid for goods now unavailable. These restrictions, controls, and taxes are unlikely to disappear entirely after the war has been won, for debts will remain to be paid with a long period of difficult readjustment. Although the new economy will doubtless offer plentiful opportunities for the advantageous use of capital, no investor can ignore the favorable conditions offered by industry in Latin America, where taxes are relatively low and the restrictions on free enterprise comparatively mild. In mining in South America, the great international corporations have

Jan 1, 1944

By Howard S. Bryant

FROM the viewpoint of the oil producer, the oil refiner, the oil marketer, and the investor, in oil securities, a brief picture of the crude oil supply and demand in the present critical season of the year will be timely and interesting. Although crude oil production has been in a comparatively poor statistical position this year, increased sales and sustained refinery and crude oil prices have allowed increased profits for many oil companies. The large amount of crude oil going into storage during the present period of peak consumption, just previous to the major yearly fall decline in consumption, has caused oil producers to make plans to leave the oil in the ground for the present in several of the areas of large flush production. The present moment is looked on as the turning point in the current year.

Jan 1, 1929

By F. D. Hoyt, H. L. Hartman

The development of new processes and methods by The Pennsylvania State University to improve slate quarrying technology has centered in recent years on cutting and sawing stone in the quarry to eliminate a second cutting process in the mill. Two machines exhibit promise for this work: 1) a circular saw mounting diamonds or hard inserts to produce smaller sizes of stone and 2) a chain saw with insert cutting teeth to produce stone in the larger dimensions. Prototype machines have been constructed and tested in several Pennsylvania slate quarries, and one commercial installation has been operated for several months with a circular diamond saw. Other kinds of dimension stones may be cut by these saws. Research at Penn State has begun to study the fundamental cutting action of rotary tools or saws in slate and other dimension stones. A laboratory drill press is being instrumented to permit thrust-torque-rotational speed us penetration rate studies of single tooth cutting surfaces on stone. Machinability studies of slate conducted with tungsten-carbide inserts have been performed. The dimension stone industry generally accepts the rather basic premise that the larger the block removed from the quarry, the more practical and economical the operation. Thus, the concept of cutting to size any dimension stone while it remains in place in the parent bed would receive little consideration from the majority of members of the industry. However, the slate industry, which is usually considered a separate member of the dimension stone family, is pioneering in the development of an in-place sawing method. Before any final decision can be reached concerning a proposed new system, it is essential to take a long, hard look at the present method of operation in order to determine if the new system is indeed an improvement or even desirable. In the following section is a brief description of present quarry practice in the slate quarries of eastern Pennsylvania. PRESENT METHOD OF QUARRYING SLATE In the numerous slate quarries of Lehigh and Northampton Counties of Pennsylvania, the grain and cleavage of the slate are most often at right angles to each other; if a third surface is broken at right angles to these two natural planes of weakness, blocks of more or less rectangular shape can be separated.' In conventional quarrying a large calyx core drill prepares holes of 36-in. diam in which wire-saw standards are positioned. By wire sawing between strategically located core-drill holes, large sinks or benches of virgin slate are opened up. The sides freed by wire sawing will vary from quarry to quarry but generally are rectangular in shape with dimensions averaging 20 ft in length and about 15 ft in depth. Some quarries are fortunate in having a joint or natural parting to work to, which of course diminishes the amount of core drilling and wire sawing required. Once the various benches have been developed either through wire sawing alone or through a combination of wire sawing and natural jointing planes, the block removal proceeds in the following manner. A plug hole is drilled in the block with a compressed-air hammer and a feathering chisel is inserted in the hole to cause a fracture of the rock either with or against the grain as indicated by the positioning of the so-called feathers. This operation is referred to as sculping. After a block has been freed with and against the grain by means of wedging from the cross fracture with long bars or levers, the block is further freed along the cleavage plane by shimming it up with small wooden pieces in an operation known as styling. A large steel loading chain is wrapped around a block thus freed and the chain is attached to the wheel of an overhead cable. The block is then hoisted vertically to the cableway and moved along this cableway laterally to the lip or edge of the quarry. From here it is unloaded onto a rail car or truck for transportation to the processing mill. Except for occasional blasting to free stubborn blocks,

Jan 1, 1961

By Reynold Q. Shotts

INTRODUCTION THE small domestic underfeed stoker as now designed is unusually sensitive to the coking and plastic properties of coals, and when the attempt is made to burn the high rank coking and caking coals of the Appalachian fields, serious trouble may occur. Part of the trouble may be caused by the ash content and clinkering characteristics of the particular coal in use, but more often it is the result of an excessive accumulation of coke in the form of "trees" or masses in the fuel bed. Often the zone of burning becomes so restricted that the fire goes out, and in extreme cases the fire may be lifted completely out of the fuel bed and away from the air ports. Even if the fire is preserved, excessive coking may cause response to subsequent heat demand to be slow and irregular. Coke trees seem to grow. most readily during periods of hold-fire operation, so that in order to preserve the fire in mild weather it is often necessary to set the timer for such a long operating period each hour that much unneeded and unwanted heat is developed, causing discomfort. During demand periods the fire may pick up so slowly that the intense burning which develops just before stoker cut-off causes a serious overshooting of the thermostat. Stoker coal performance tests which have been made in a number of laboratories 1, 2, 3, 4, 5 are one method of approach to the problem of selecting stoker coals. As yet these tests have not been standardized and they are expensive and time-consuming. The value of the results probably increases with the length of the test. Sherman and co-workers at Battelle Memorial Institute believe that even a one-week test is not too reliable a trial2 and it is quite likely that others will agree. A great advantage of such tests is that characteristics of coals, other than the tendency to form coke masses, may be evaluated from them. The selection of stoker coals would be greatly facilitated if there existed some simple measure of the tendency of a coal to form coke in a fuel bed. Although possessing all of the disadvantages of any small-scale laboratory test, the test for the free-swelling index of coal has been found useful for evaluating the probable effects of swelling properties upon combustion. 7 Ostborg, Limbacher and Sherman, have shown that the test can predict, roughly, the tendency of coke to accumulate in the fuel bed of a domestic stoker. They also gave instances of its value in predicting combustion behavior in some large installations. The use of the test for free-swelling index has become well established and has been adopted as a standard by the American Society for Testing Materials.8 When domestic stoker coal investigations began at the State Mine Experiment Station in the summer of 1944, it was decided

Jan 1, 1948

By W. H. Andrews

THE constantly increasing consumption of Portland cement in the State makes the above subject of partlcular interest at this time. The increasing demand is due to the rapid settling of the country and the fact that new uses are being found frequently for the above named commercial article. The industry is one that is bound to grow as the population increases, and this being the case, it may be well ,it this time to consider briefly- the matter of the chemical and physical com-position of proper raw materials. A cement mixture is one that contains approximately 75 per cent. carbonate of lime, 15 per cent. Silica, and 5 to 7 per cent. alumina, and iron oxides; the other elements being magnesium carbonate and small quantities of the rarer elements general associated with limestone deposits. It call be readily seen from the above composition that it is possible to build up this mixture from a number of different materials. First.-A rock high in carbonate of lime can be mixed with clay or shale in such proportions as to bring about the desired composition ; the chief difficulty in the building up of such a mixture is that it is hard to find a clay or shale in which the silica-alumina, ratio lies .between 4 to 1 and 3 to 1 and at the same time shows physical characteristics which will make certain its adaptability to the practical manufacture of Portland cement. Very often clays or shales are found which are right chemically but contain large quantities of grit or free silica. Such clays or shale must be ground to extreme fineness in the mixture in order to make the silica and alumina combine with the lime when the mixture is burned. On the other hand, clays or shales are often found that have the proper physical characteristics but in which the amount of alumina, is too great.

Jan 9, 1913

By W. G. Sinclair

THE North Texas district presented in this paper includes the counties of Archer, Baylor, Clay, Cooke, Foard, Hardeman, Jack, Knox, Montague, Wichita, Wilbarger and Young. It corresponds with the Texas Railroad Commission's district No. 9. Table I conforms with the nomenclature of pools as designated by the Commission. Most of the oil and gas produced in this region, generally referred to as the Red River uplift, comes from the Pennsylvanian strata. In recent years, however, increasing amounts are being developed in both the Mississippian and Ordovician.

Jan 1, 1946

By Arthur F. TQggQrt

THE approximate status of education in ore dressing in 1871 is reflected by Rossiter W. Raymond in an article written at that time presenting the curricula and descriptions of the laboratories at the various mining schools in the United States. For the most part, the curricula in which ore dressing was taught were for mining engineering. They comprised courses in geology, mining, and pyrometallurgy about equal in point or credit weights; a short course in ore dressing, and a somewhat longer course in assaying; and courses in surveying, hydraulics, power, and strength of materials-all superimposed on a broad foundation of physics, chemistry, and mathematics. Some curricula contained a fair content of the humanities. Then, as now, the emphasis on fundamentals was greater in the older colleges and universities. The report on the Columbia School of Mines, then relatively young, emphasized that a large percentage of its students were college graduates. As technical and scientific knowledge grew, first metallurgy and then geology were set up as separate curricula. So far as curriculum designation is con-

Jan 1, 1947

By THOMAS G. FEAR

THE COAL DIVISION started its share of the annual meeting Monday morning with a study of coal classi fication. A. C. Fieldner was in the chair. The report of the tellers of the ballot for division chairman, stating that Thomas G. Fear had been elected to that office, was read by M. D. Cooper. Mr. Fear acknowledged the honor in a few words. In reviewing the history of the Coal Classification Committee the chairman pointed out that this was its third symposium, the last previous one having been held at the 1930 Annual Meeting. Throughout its work the com¬mittee has had the active cooperation of the Canadian workers who are interested in the subject which should result in a uniform scheme of classification in Canada and the United States. F. E. Lathe, of the National Research Council, Ottawa, abstracted the first two papers of the session entitled "Determination of the Alkali-Soluble Ulmins in Coal," by Edgar Stansfield and K. C. Gilbart, and "Moisture Determination for Coal Classification," by the same authors. The third paper "Condition of Water in Coals of Various Ranks"' was presented by its author, A. W. Gauger. Written discussions of these papers were presented by H. C. Porter and Gilbert H. Cady. In the oral discussion which followed, W. T. Thom, Jr., brought out the advisability of considering age as a factor in classification. Mr. Fieldner favored retaining bed moisture as a partial classification basis, stating that a review of many coal analyses revealed a remarkable consistency in this item in samples from a given mine particularly where the moisture content was not high. Mr. Porter pointed out that the structure and porosity of coal often have much to do with its moisture content and that these vary in different parts of a seam, particularly in anthracite. Mr. Gauger expressed doubt as to whether the Stansfield method gives the true moisture content of coal, which is needed for classification purposes.

Jan 1, 1932

By F. D. Delve

RECENT studies by the author on the reduction of titanium from TiO2-bearing slags have been accompanied by difficulties that are attributed to

Jan 1, 1959

C. Edward Stafford, Chester, Pa.:—Doring all my business life, I have been engaged in the manufacture of Bessemer and open-hearth steels, but, during my long connection with the Shoenberger Steel Co. of Pittsburg, I had some experience in the manufacture of high-grade puddled iron for horseshoes, and in making, by Dr. Otto Wuth's process, extremely pure, low-phosphorus puddled blooms (analyzing from 0.005 to 0.01 per cent. of phosphorus and sulphur), which were melted with low-phosphorus pig-iron in acid open-hearth furnaces, to make extra locomotive fire-box steel. I have also seen the Danks puddlers in operation at different times and places, notably where they were most successful, at the Otis Steel Works, Cleveland, Ohio; then under the management of our friend, Mr. S. T. Wellman. These Danks blooms were made solely for open-hearth melting-stock, to which they were well adapted. (The unavoidable presence of bits of ore-fix imbedded in the mass of the metal always prevents the profitable manufacture of merchant iron from Danks' blooms.) With the experience just described, I was to some degree in position to value fairly the means, methods and results of Mr. Roe's mechanical puddling from the metallurgical or technical and economic points of view, when given an opportunity by Mr. Roe to see his puddling-furnace or machine in operation in Pottstown, Pa. Briefly, the furnace, with water-cooled bottom, is rectangular in plan, about 20 by 8 ft. in the clear, suspended by trunnions at the middle of the long sides, at a height of 17 or 18 ft. above the general level. The oscillation (65" each way from the vertical) is accomplished by geared segments (attached to the downward-projecting side or trunnion-plates) with which engage pinions driven by a reversing engine. The whole section

Jan 1, 1906

By D. S. Sanders

IN the four mills of the Cerro de Pasco Copper Corp. in Peru, some 3000 tons of complex sulphide ores are treated daily, with four kinds of concentrates produced: copper, lead, zinc, and pyrite, each containing values in silver, gold, bismuth, and some other metals. Copper occurs in the various ores as chalcopyrite, enargite, tetrahedrite, tenantite, bournonite, and chalcocite; lead as galena; and zinc as sphalerite and marmatite. Small amounts of silver and tungsten minerals are also present. The gangue consist mainly of shale, quartzite, calcite, rhodochrosite, pyrite, and pyrrhotite. In general the values are freed with a relatively coarse grind, about 70 prr cent minus 200 mesh being the finest to which the pulps are ground. In Morococha and Casapalca however. sphalerite particles much finer than this contain inclusions of chalcopyrit r. At Cerro de Pasco the silver and gold are present in all sizes of the ground pyrite.

Jan 1, 1945

By E. H. Citron

CLEANING fine coal in jigs is not new in Europe, where the feldspar jig is being used almost exclusively for this purpose. A feldspar jig operates with an artificial bed made up generally of feldspar or other hard rock material. Dimensions and specific gravity of this material must be of suitable values for good bedding qualities. For good efficiency, the size should range between 1x2 in. and 2x2x½ in. thick. The disadvantage of an artificial bed is that it is not mobile and must be replaced every so often with new material to obtain good cleavage characteristics. A semi-mobile bed has been developed to retain only a part of the feldspar on the sieve screen— the other part is drawn off with the refuse material, from which it is reclaimed and returned to the jig feed. Recirculating this feldspar rock offers definite advantages. However, in time it will lose its original shape because of wear, and new bed material must be added to the jig feed. The latest feldspar jigs arc generally air-pulsated, Baum-type jigs, although more than 70 pct of the feldspar jigs operating in Continental Europe are still of the piston type. These jigs are very popular in Europe, but they do require a great deal of time and attention. New Theory to Eliminate Artificial Bedding: At the preparation plants of Pittsburg & Midway Coal Mining Co. it has always been the contention that a small piston-type jig could be developed to clean fine 1/4x0-in. coal down to 28 to 60 mesh efficiently by obtaining and admitting bedding material from the present plant refuse circuit to the jig feed. This eliminates use of artificial bedding materials. The jig should incorporate these essential adjustable features as follows: Adjustable Sieve Screen A screen that can be raised and lowered to increase or decrease washing compartment depth. The sieve screen also can be set on an incline level, or decline. Adjustable Plunger Eccentric Length of stroke can be adjusted to increase or decrease pulsion and suction. Variable Plunger Speed Variable speed reducer for decreasing and increasing the number of strokes per minute. Water Distribution Adjustable baffle plate separating the plunger and sieve compartment so the water can be distributed uniformly over the entire sieve screen area. Refuse Ejector Special unique rubber-type refuse ejector gate operated by air and electrically controlled (as a conventional jig). Automatic Control Conventional float that measures the specific gravity of the coal-water refuse medium in the jig is of the submerged type. The float is mounted on a vertical stem held in position by two parallel arms. A movable weight regulates the effective specific gravity of the float. The float stem can be raised and lowered, having a graduated scale to indicate the depth of bed for the setting of the float. Hutch Drawoff Hutch material is drawn from the cell compartment to the elevator compartment by gravity. The first one-cell experimental jig incorporating all these features was built in January 1955 by Ore

Jan 1, 1959

By R. B. Ladoo, C. A. Stokes, R. N. Secord, A. L. Hall

INDUSTRIAL mineral history shows that the entrance of new, nonmetallic minerals into commercial production can be expected to occur from time to time. Latest entrant into the field is wollastonite. Except for one short-lived period in Kern County, Calif., starting in 1933, wollastonite has never before been produced on a commercial scale. But the signs are up for its entrance as an economic factor in the mineral market. Small scale experimental production from a deposit near Willsboro, N. Y., started about 1943. A pilot plant was built in 1949-50 and irregular, small scale, production has continued. In early 1951 Godfrey L. Cabot, Inc. of Boston, world's largest producer of carbon black, took an operational lease on the property to study the deposits and make market surveys. This became Cabot's first venture in the mineral field, when they took over operations and began design of a new mill, expected in production in 1953. Properties The properties and major uses of wollastonite are comparable to New York fibrous talc. It has about the same specific gravity and index of refraction as talc, but is somewhat whiter and softer. The two most important fields of use, paint and ceramics, are the same as for talc. Ground wollastonite has a fiber length as much as 13 to 15 times the diameter. This particular property makes it applicable in the paint field and others. In addition, the length-diameter ratio may be controlled to rather narrow limits by choice of grinding method. Another important commercial property is brightness or whiteness. Wollastonite reads from 92 to 96 pct of MgO on the G.E. brightness meter for a 99 pct -325 mesh grind. Purity and uniformity of product are important. Chemically, the wollastonite now being mined analyzes SiO2 51.76, CaO 47.56, FeO 0.46, MnO 0.04, and H2O 0.09 pct. Theoretically pure wollastonite analyzes SiO2 51.75 and CaO 48.25 pct. This analysis indicates over 98 pct calcium silicate, with only small amounts of contaminating ingredients. That these ingredients are not detrimental to color or brightness is shown by the high brightness value of the fine ground material. [ ] By-product calcium silicate from electric furnace production of phosphoric acid has little physical re-semblance. to this wollastonite, being an off color white, and lacking in fibrous crystalline character. Minerology Wollastonite is a calcium metasilicate, CaSiO3, a white, medium hard, fibrous mineral. In this deposit wollastonite occurs as well crystallized aggregates of bladed crystals intergrown with garnet, and with a few percent of green diopside. The beneficiated product is about 75 pct wollastonite, 15 pct garnet, and 10 pct waste, largely middling. Wollastonite-garnet ore occurs in at least two beds. The main bed, varying in true thickness from 30 to 70 ft, dips into the hill at an average 30° and is enclosed in gneisses. Diamond drilling has proven the orebody to an average depth of 200 ft along 2000 ft of outcrop with adequate tonnage for many years of quarry operation. The wollastonite-garnet ratio varies locally, but average composition is uniform over long distances. A friable ore, it is easy to drill, shoot, and crush. Beneficiation Unlike talc this ore has to be beneficiated. Successful treatment depends upon the fact that it contains virtually nothing but wollastonite, garnet and a minor percentage of diopside. A very pure wollastonite product can be made by high intensity magnetic and/or gravity separation methods.

Jan 1, 1952

Pumping coal to market may help Appalachian coal operators increase their share of the eastern seaboard fuel business. Transporting it by pipeline is already an accomplished fact, but until recently it had to be dewatered to be used in boiler furnaces. The campaign for these eastern markets was begun in earnest last November by the widely publicized announcement of successful plant-scale firing of a central station boiler with coal slurry pumped to the burners. This latest advance makes coal similar to oil and gas in convenience in handling and controlling at the consumption end of the pipeline. Slurry could be considered a new commodity for the fuel market. HUGE POTENTIAL MARKET The heaviest concentration of power plants in the U.S. is along the line Washington, Baltimore, Philadelphia, New York and Boston which makes this region the best hunting ground for selling pipelined coal brought from western Pennsylvania and northern West Virginia. Furthermore, if this region is assumed to consume 125 million tons of coal annually, on a comparable basis, the consumption of oil and gas would be about 180 million tons. Even if all of this fuel is not consumed in central stations, it is still a very big market for coal at the right price. Consolidation Coal Co. and Texas Eastern Transmission Co. are trying to line up customers in this area so that a pipeline can be built. This is not to say that there are not many other areas in the U.S. that could not be supplied advantageously by a mine-to-market pipeline.

Jan 1, 1962

By C. M. Weld

In the course of my professional work in China during the fall of 1907, I had an opportunity to visit the iron-ore mines at Ta-yeh in Hu-pei province (long. 114O 50t E., lat. 30' 20t N.). It occurs to me that a rescript and discussion of my notes taken at that time should be of interest, particularly as supplementing the exceedingly interesting recent paper of Thomas T. Read on The Mineral Production and Resources of China.' Ta-yeh is situated near the right bank of the Yangtze river. The mines are at an average distance of about 16 miles from the river-port Shi-hui-yao, which in turn is some 70 miles SE. of Hankom. The ores are shipped to the works of the Han-Yeh-P'ing Iron & Coal Co. at Hanyang, as also very largely to the Japanese government iron- and steel-works at Wakamatsu, Japan. Smaller qnantities have been exported to the Pacific coast of the United States. These ore-deposits have been briefly noticed in a number of publications, but, so far as I know, Mr. Read's description, in his chapter or1 the iron-ores of the Chinese Empire,2 contains the first attempt to define their geological character. In his more recent paper Mr. Read follows very closely the text of his earlier description. To quote briefly from the recent paper, he says : " The iron-ores at Ta-yeh .... lie along the contact between a marble and an intrusive body of a dark-gray syenitic rock." He refers to a figure which exhibits in plan, but not in section, the relative positions of the syenite, ore-bodies, and limestone. The contact is seen to trend approximately E-W., with the syenite on the north and the limestone on the south. " The syenite lies to the north of the marble, and a few miles farther north the marble again appears, iron-ore again being present along the contact." No litho-

Jan 1, 1913

By Walter C. Holmes

IN the recently published book entitled "Man in a Chemical World," by A. Cressy Morrison, the several pages discussing explosives were included in the chapter on "Serving Industry." Such a classification is entirely correct, as blasting explosives function only as a tool for accomplishing certain useful work, a tool which is completely destroyed in one use. Explosives are so important to industry and to modern society, in fact, that it seems impossible to imagine the existence of civilized nations without access to commercial explosives as ready servants. Two main types of explosives are now in use, the low-velocity or deflagrating type, such as black powder, which is adapted for use in coal mining and other applications where a slow, heaving effect is desired, and high explosives of the dynamite type,

Jan 1, 1938

Gus C. Henning, New York City: In taking up the discussion of these specifications it is necessary that I give definitions of what I understand under the term " Specifications." There may be three kinds, viz.: (1) Specifications in general; (2) Standard Specifications; (3) Standard International Specifications. 1. A Specification is a document used in commerce which should clearly define the qualities of material to be supplied by the producer, the tests which shall be applied for their determination, and the methods which shall be applied for the purpose of determining that the entire product shall possess such qualities, properties and finish as are desired. The terms used in such document must be applied in accordance with their strict technical definitions as used by those most conversant with them, and the language should be of such accuracy that there can be but a single interpretation of each and every clause. A specification is a part of a contract, and should be legally perfect and accurate. Inaccuracy of definition and dic-

Jan 1, 1903

By Jack White

W. I. Garms-—The authors state that when they added 11 tons of balls to the 45 pct volume ball load, the power needle did not budge. The question arises as to whether any increase in capacity accompanied the 11-ton addition. It is hardly conceivable that all of the balls making up the l l-ton addition were sterile. However, as the work done in the ball mill is not by kilo-watthours per se or balls per se but by kilowatthour-balls, it is possible that the kilowatthourballs in the mill before the ll-ton addition had a different amperage, voltage or robustage than those in the mill after the addition and that the overall outcome was that equal work was done before and after the addition. The authors can keep the efficiency that they got with the 45 pct volume 1-in. ball charge and get additional capacity by putting more kilowatthourballs to work in the form of the addition of 11 tons of 2-in. balls to the present ball charge, and subsequent makeup additions by weight of 20 pct 2-in. balls and 80 pct 1-in. balls. J. F. Myers (authors' reply)-—Mr. Garms points his finger at the 11 tons of "sterile" balls added to the Tri-cone mill. A fact so interesting to us that we felt it should be reported. Clearly, ball slippage at the existing mill speed prevented any further transfer of power from the shell to the ball mass. We agree that the kilowatthourballs would increase, were we charging rough 2-in. balls as suggested by Mr. Garms. The assumption is, of course, that we would get a corresponding increase in work done. Our reported data (CIME meeting, Vancouver, 1946) shows a gain of work accomplished of 7.6 pct as we decreased the ball size from 2 in. to 1% in. and a further gain of work accomplished of 2.1 pct when we went from 1 % in. to 1 in. The small ball results reported by H. R. Banks at Chapman Camp are also very convincing. In the case of 2-in. balls they would take the conventional ball path and start cascading. They would thus destroy the classifying pool over the "foot" of the

Jan 1, 1951

By Jack White

W. I. Garms-—The authors state that when they added 11 tons of balls to the 45 pct volume ball load, the power needle did not budge. The question arises as to whether any increase in capacity accompanied the 11-ton addition. It is hardly conceivable that all of the balls making up the l l-ton addition were sterile. However, as the work done in the ball mill is not by kilo-watthours per se or balls per se but by kilowatthour-balls, it is possible that the kilowatthourballs in the mill before the ll-ton addition had a different amperage, voltage or robustage than those in the mill after the addition and that the overall outcome was that equal work was done before and after the addition. The authors can keep the efficiency that they got with the 45 pct volume 1-in. ball charge and get additional capacity by putting more kilowatthourballs to work in the form of the addition of 11 tons of 2-in. balls to the present ball charge, and subsequent makeup additions by weight of 20 pct 2-in. balls and 80 pct 1-in. balls. J. F. Myers (authors' reply)-—Mr. Garms points his finger at the 11 tons of "sterile" balls added to the Tri-cone mill. A fact so interesting to us that we felt it should be reported. Clearly, ball slippage at the existing mill speed prevented any further transfer of power from the shell to the ball mass. We agree that the kilowatthourballs would increase, were we charging rough 2-in. balls as suggested by Mr. Garms. The assumption is, of course, that we would get a corresponding increase in work done. Our reported data (CIME meeting, Vancouver, 1946) shows a gain of work accomplished of 7.6 pct as we decreased the ball size from 2 in. to 1% in. and a further gain of work accomplished of 2.1 pct when we went from 1 % in. to 1 in. The small ball results reported by H. R. Banks at Chapman Camp are also very convincing. In the case of 2-in. balls they would take the conventional ball path and start cascading. They would thus destroy the classifying pool over the "foot" of the

Jan 1, 1951