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By E. C. Wright

THIS paper describes some properties of steels in the composition range 0.10 to 0.30 per cent carbon and 1 to 7 per cent chromium. It is well known that some steels of this type develop high tensile strengths upon receiving comparatively simple heat treatments, such as ordinary air cooling from appropriate temperatures, with "or without subsequent tempering treatments. These high strengths are frequently associated with unusual toughness as measured by the Izod or Charpy impact test. The chromium content, in addition to imparting the above properties, enhances the resistance to corrosion and improves the strength and oxida-tion resistance at elevated temperatures. Moreover, these steels have good forging and fabricating properties, as evidenced by the fact that several thousand tons of seamless tubing have been made during the past five years from steels containing 0.10 to 0.25 per cent carbon and 5 per cent chromium.

Jan 1, 1933

By J. R. Linney

THE Eastern Magnetite Industry produced approximately 7,850,000 long tons of crude ore in 1945 from which was obtained approximately 3,650,000 long tons of shipping product or a ratio of 2.10 to 1. Lack of skilled or experienced miners was the greatest handicap. Veterans returning to work improved the underground labor shortage in some localities but as a whole the labor shortage was keenly felt throughout the industry. One cannot now predict what may be accomplished in 1946 but barring major steel strikes a worthwhile improvement can be expected. At the Richard mine of the Richard Ore Co., the shipping product for the year amounted to approximately 124,650 long tons of concentrate and lump ore. Crude-ore production was 160,600 long tons. The average analysis for lump ore was 63 per cent iron and for concentrates 66.05 per cent. The Warren Foundry and Pipe Corp. at their Mt. Hope mine produced 73,000 long tons of lump ore averaging 59.5 per cent and 57,000 long tons of concentrate averaging 67 per cent. The total mine hoist was approximately 209,000 long tons. Operations were commenced through the new Leonard shaft on Jan. 18; the Brown shaft through which operations had been conducted since 1912 caved beyond repair on Sept. 26. No one was injured but pumping facilities were somewhat disrupted. In order to reach designed capacity a total of 400 men will be required with 300 underground. Due to shortage of labor all operations in 1945 were concentrated on the 1700 level. As fast as men can be hired and trained development of the 2100 and 2500 levels will commence. Mt. Hope has a consider-

Jan 1, 1946

Falconbridge Nickel, the one-time subsidiary that grew up to swallow its own parent, Ventures Limited, in 1962, is not about to be left behind by rising nickel consumption. At a cost of several hundred million dollars, this Canadian firm has undertaken a series of new projects that will not only ensure its present share of the market, but also lead it into new areas of the nickel business. Although Falconbridge Nickel Mines Ltd. was not formed until 1928, it actually had its start in 1917- 18 with the discovery of a large, good grade nickel- copper deposit in Falconbridge, near Sudbury, Ontario. However, due to several factors, financing could not be obtained and the orebody lay fallow. It was not until 1928, when the Thayer Lindsley interests bought the property from the original owner, that it was developed.

Jan 10, 1968

By John C. Smock

The question of the proper valuation of mines of iron ore was suggested to me by the difficulties experienced in getting answers for the United States Census Office, while I was engaged in the work of collecting the statistics of mines in New Jersey and New York. The answers to the questions relating to values of real estate of mine properties varied so greatly that it was necessary to revise them according to some general principles of valuation. Generally the returns of mine proprietors seemed to be too low. There were, however, examples of what would be termed excessive valuation. The subject appeared to be of practical importance, and led to the paper here presented. The following table of selected mine statistics is given, prefacing the discussion of the principles of valuation. It is in part made up of census returns and partly of data obtained directly from mine owners and managers. The mines which were selected for the several groups and mining districts include nearly all of those from which the more full and carefully filled returns were received, and are also representative of their respective districts. Hence the averages obtained from them become good types of these groups or districts. The mines of New Jersey appear in six groups, each containing from three to eleven mines, or, in all, thirty-four mines. The magnetic iron ores of New York are in four well-marked groups, and there are twenty-six mines in them. Then follow the red hematite mines of St. Lawrence and Jefferson counties; and, lastly, the brown hematite groups of Dutchess and Columbia counties, and those of the adjacent parts of Connecticut and Massachusetts. The whole number of mines represented by the table is eighty-eight, of which twenty-eight are hematite mines. The first column gives the value of the real estate; the second that of the plant; the third is the sum of these two, or the capital invested. Then follow the number of men employed, the amount of wages paid during the census year, and the value of materials used in mining and preparing the ores for market." The seventh column gives the total expendi-

Jan 1, 1882

By R. Salter, C. K. Chase

Although Asarco's Silver Bell Unit, 40 miles west of Tucson, Ariz., is known primarily for copper production, molybdenite is also produced as a byproduct in the 8000 tpd flotation mill. The Silver Bell ore comes from two pits approximately two miles apart. Copper mineralization is essentially chalcocite resulting from two to three-fold secondary enrichment in a highly altered zone. A typical porphyry copper deposit, Silver Bell ore is of medium hardness. The ore consists of about one part molybdenum to 65 parts of copper. In the copper concentrate which is the starting point for separate molybdenum recovery, the ratio is also one part molybdenum to 65 of copper. Molybdenum mineralization is primary. Enrichment is not evident but it is notable that the molybdenite is more common in the more siliceous, harder rocks. The actual molybdenite occurs as diversely oriented flakes of fairly constant grain size, mostly in fractures associated with quartz veins. Most of the mineral appears unoxidized; secondary coatings on the molybdenite flakes are fortunately rare. In May 1962 a modified, improved version of the molybdenite circuit was put into operation.

Jan 7, 1964

Jan 1, 1967

Jan 1, 1968

POSITIONS VACANT (Under this heading will be published notes sent to the Secretary of the Institute by members or other persons.) Opening for man as head of laboratory of large brass manufacturing plant in Ohio; must also be competent to manage foundry making brass castings, following practice of malleable iron castings and insulating materials. Good opportunity for right man. No. 36. Professorship in Mining at a Western university; requires man competent to give instruction in ore dressing, in metal and coal mining, and in zinc smelting, and capable of gaining confidence of mining interests. Salary $2,200 to $3,000. No. 37. ENGINEERS AVAILABLE (Under this heading will be published notes sent to the Secretary of - the Institute by members or other persons introduced by members.) Member, graduate engineer, aged 44, with over 20 years' experience in connection with large coal and coke operations in different parts of the country, desires position as general superintendent of large coal company, or will take an interest with the management in a smaller company. No. 206.

Jan 6, 1915

By J. E. Burke, C. W. Mason

In attempting to study precipitation from a tetragonal lattice, using solid solutione of bismuth in tin, it was found that although a Widmanstätten pattern is observed1,4 only a qualitative analysis of the orientation relationships is possible, because of the unusual structural changes that accompany the precipitation process. Microscopical Studies Alloys were made from Chempur tin (Standard samples 42b and 426, National Bureau of Standards), and bismuth (Kahl-baum C.P.) by melting weighed quantities together under palm oil, stirring well, and castilig in a heated graphite mold. The polishing and etching techniques employed largely govern the visibility of the structural changes. The preliminary surfacing operations were similar to those recommended by Villela and Bergekoff,5 through Behr-Manning 3/0 abrasive papers, lubricated by a solution of paraffin in kerosene. A rough metallographic polish was next given, using a thin cotton cloth charged with relevigated alumina (maximum particle size of about 4µ) and soap solution; repeated etching and polishing served to remove disturbed metal. For high-power examination better preparation was necessary. It was found that on such soft metals the threads of the fabric, rather than the abrasive, cause most of the scratching. Cotton outing flannel, which had been brushed so that the nap lay down, was fairly satisfactory, but a heavy grade of silk velvet (not the noncrushable kind) was found to be better, especially after some use. A better procedure was as follows: The metal lap was warmed slightly, and a 4-in. circle of woolen broadcloth was cemented to its center by a thin film of melted paraffin. The broadcloth was then moistened with water, and a 30 to 40 per cent solution of sodium hydroxide heated to about 50°C. was poured over it, allowed to stand for I to 2 min. and then washed off. It was neither necessary nor desirable to remove all the sodium hydroxide from the cloth, since its etching action aided in the removal of the flowed layer from the sample. The cloth was then charged with a paste of the relevigated alumina in water. Since this lap did not remove deep scratches, it was necessary previously to polish the specimen on some material such as the silk velvet. The sodium hydroxide softens and partly gelatinizes the woolen lap covering, permitting a scratch-free polish, but its action continues, and the cloth deterioratcs after about 24 hr. This is not serious, because a new lap can be prepared in about 5 min., and only small pieces of cloth are used. Etching with a strongly acid solution of ferric chloride was found satisfactory for removing the flowed layer. For the final etching, the most satisfactory reagent was that of Tafls,7 the formula for which is: FeC13.6H2O, 2 grams; HC1, 5 c.c.; H2O, 30 c.c.; C2H5OH (95 per cent), 60 C.C. This etchant reveals differences in com-

Jan 1, 1942

By J. E. Burke, C. W. Mason

In attempting to study precipitation from a tetragonal lattice, using solid solutione of bismuth in tin, it was found that although a Widmanstätten pattern is observed1,4 only a qualitative analysis of the orientation relationships is possible, because of the unusual structural changes that accompany the precipitation process. Microscopical Studies Alloys were made from Chempur tin (Standard samples 42b and 426, National Bureau of Standards), and bismuth (Kahl-baum C.P.) by melting weighed quantities together under palm oil, stirring well, and castilig in a heated graphite mold. The polishing and etching techniques employed largely govern the visibility of the structural changes. The preliminary surfacing operations were similar to those recommended by Villela and Bergekoff,5 through Behr-Manning 3/0 abrasive papers, lubricated by a solution of paraffin in kerosene. A rough metallographic polish was next given, using a thin cotton cloth charged with relevigated alumina (maximum particle size of about 4µ) and soap solution; repeated etching and polishing served to remove disturbed metal. For high-power examination better preparation was necessary. It was found that on such soft metals the threads of the fabric, rather than the abrasive, cause most of the scratching. Cotton outing flannel, which had been brushed so that the nap lay down, was fairly satisfactory, but a heavy grade of silk velvet (not the noncrushable kind) was found to be better, especially after some use. A better procedure was as follows: The metal lap was warmed slightly, and a 4-in. circle of woolen broadcloth was cemented to its center by a thin film of melted paraffin. The broadcloth was then moistened with water, and a 30 to 40 per cent solution of sodium hydroxide heated to about 50°C. was poured over it, allowed to stand for I to 2 min. and then washed off. It was neither necessary nor desirable to remove all the sodium hydroxide from the cloth, since its etching action aided in the removal of the flowed layer from the sample. The cloth was then charged with a paste of the relevigated alumina in water. Since this lap did not remove deep scratches, it was necessary previously to polish the specimen on some material such as the silk velvet. The sodium hydroxide softens and partly gelatinizes the woolen lap covering, permitting a scratch-free polish, but its action continues, and the cloth deterioratcs after about 24 hr. This is not serious, because a new lap can be prepared in about 5 min., and only small pieces of cloth are used. Etching with a strongly acid solution of ferric chloride was found satisfactory for removing the flowed layer. For the final etching, the most satisfactory reagent was that of Tafls,7 the formula for which is: FeC13.6H2O, 2 grams; HC1, 5 c.c.; H2O, 30 c.c.; C2H5OH (95 per cent), 60 C.C. This etchant reveals differences in com-

Jan 1, 1942

By G. W. P. Rengstorff, L. E. Olds

High purity molybdenum ingots containing controlled amounts of a single impurity element (oxygen, nitrogen, or carbon) were prepared. These ingots were tested for ductility by bending test specimens at various temperatures. The relationship between the plastic behavior of the ingots and their chemical composition has been determined. MANY proposed applications for molybdenum require ductility at or near room temperature. At the present time, it is possible to obtain wrought molybdenum with considerable ductility only if special fabrication techniques are used to control the grain structure. Starting with are-cast or powder metallurgy ingots, the usual methods for obtaining ductility rely on fabrication procedures that result in fibered microstructures in the finished product. Recently, it has been found that the ductility of either powder metallurgy or are-cast molybdenum can be improved by uniform recrystallization of the metal to a very fine equiaxed grain structure.' The need for a fibered or a fine grained structure may limit the practical usefulness of molybdenum. For example, welding. which may be used in fabricating the metal, generally produces coarse grained structures that lead to brittleness. This applies, certainly, to currently available commercial molybdenum. Although commercial molybdenum is brittle when the grains are coarse, it has been shown experimentally that fine grained structures are not always essential for ductility. For instance, as-cast molybdenum with a coarse columnar grain structure is ductile if it is sufficiently pure.' Because high purity cast molybdenum has good ductility even when coarse grained, it is probable that the brittleness in coarse grained commercial molybdenum is caused by the impurity content of the metal. Although the general effects of impurities on the cold ductility of molybdenum have been known in a qualitative manner for some time, no quantitative evaluation of these effects has been available. The present investigation was made in order to determine more accurately the effects of oxygen, nitrogen, and carbon on the cold ductility of cast molybdenum. Oxygen has long been known to be detrimental to ductility, although the minimum amount which will embrittle molybdenum has been open to speculation. Parke and Ham" showed that ingots with oxygen contents above 0.003 pct could not be forged. Maringer and Schwope have described the embrittle-ment of molybdenum wire by oxygen. A discussion on the effects of heat treatment on the distribution of oxygen in molybdenum has been given by Perry, Spacil, and Wulff." Although nitrogen would also be expected to have harmful effects on ductility, no extensive work has been done previously to determine whether this is so. However, Tury and Krausz" found that wires presumably with less than 0.007 pct N were brittle. Carbon is added to commercial cast molybdenum for deoxidation. Parke and Ham" have shown that molybdenum containing as much as 0.06 pct C could be forged if the oxygen was kept below 0.003 pct. Also, Bruckart and others' found that the room temperature ductility of sintered molybdenum improved with carbon contents up to 0.84 pct. However, Rengstorff and Fischer' found that residual carbide particles in cast molybdenum apparently had an unfavorable effect on room temperature ductility.

Jan 1, 1957

By A. L. Blomfield

THE Golden Cycle Mining and Reduction Co. operates its custom mill at Colorado Springs on Cripple Creek ores exclusively. These ores are straight sulpho-tellurides, with practically no base metals such as Pb, Cu, Zn, As, or Sb. Upon entering the mill, the ore all passes through the sampler to storage bins, where beds of 5000 tons each are made to insure uniformity in roasting. CLASSIFICATION OF ORES For efficiency, it has been found advisable to separate the ores into two classes according to their line content. Other constituents have their effect, such as alumina and magnesia, but, speaking generally, these are roughly proportional to the line, which, as CaO, is used as the indicator. Class A contains not more than 2 per cent. CaO and comprises about 66 per cent. of the ore treated. Class B contains over 2 per cent. CaO, and comprises 34 per cent. of the ore treated. Typical analyses of both classes are as follows: Class A Class B Insol 56.70 75.90 Al203 2.30 3.40 Fe 3.26 3.48 CaO 1.57 5.12 S 1.79 1.80 Mg0 0.21 1.08 Ignition loss 3.20 6.50 99.03 97.28 The beds of each class of ore are made as large as possible with the available ore as it comes in, to avoid changing from one bed to the other any oftener than necessary. Each roaster will handle 50 percent. more of class A ore than of class B, with practically the same results. This necessitates changing the rate of feed for each new bed and tends toward a poor roast and loss of tonnage at each change.

Jan 8, 1918

Division of Geology, State of Tennessee, 401 Seventh Ave, North, Nashville, Tenn. Walter F. Pond, State Geologist A selected list of Bulletins available: Bulletin 1(B), Bibliography of Tennessee geology (1911); 2(A) Outline introduction to mineral resources (1910), 2(D) Marbles (1911); 2(G) Zinc deposits (1910), 16, Red iron ores of east Tennessee (1913), 22, Geology and natural resources of Rutherford County (1920), 24(A) Geology and oil possibilities of parts of Overton, Clay, Pickett and Fentress counties (1920); 24(B) Oil and gas resources of northeastern Sumner County (1920), 26, Mineral resources of Waynesboro Quadrangle (1921); 28, Marble deposits of East Tennessee (1923), 29, Magnetic iron ores of east Tennessee (1923), 31, Zinc deposits of east Tennessee (1923), 33, Tennessee coal fields, 37, Geology and mineral resources of Hardin County, 38, Stratigraphy of the Central Basin (in press), 39, Brown iron ores of the Eastern Highland Rim (in press) From 1911 to 1919, inclusive, volumes were issued annually on The Resources of Tennessee Only a few of the separate papers contained in those volumes are now available Vol. 2 (1911): No 1, Explosions of coal dust in mines, and other papers, No. 4, Lignite and lignitic clays in west Tennessee, and other papers; 5, The growth of knowledge of Tennessee geol¬ogy; 9, The valley and mountain iron ores of east Tennessee, 10, The iron industry of Lawrence and Wayne counties, and other papers; 11, Barite deposits in the Sweetwater district, and other papers, 12, The iron ore deposits in the Tuckalioe district, and another paper Various oil maps (15 to 40 cents each) and traverse maps of counties (25 cents and 31 each) can be had, as well as pertinent U. S topographic maps.

Jan 1, 1933

Jan 1, 1961

By N. A. Gokcen, John Chipman

D. C. Hilty (Union Carbide and Carbon Research Laboratories, Niagara Falls, N. Y.)—This paper is a very nicely detailed analysis of a difficult problem. I would like to point out that the results that Mr. Crafts and I published a few years ago had no reference to activity, or anything else of a similar nature; our results were strictly empirical. It is quite gratifying that we now have a case where results involving activity coefficients and results derived from direct observations on actual steel melts are practically identical. When two different laboratories, working from two entirely different approaches, come out with results in such good agreement in their major significance, that is an achievement. It is something that was not possible 15 or 20 years ago. There is one question I would like to ask Dr. Chip-man. It has to do with a very minor point of disagreement in these results. When we reported the kink in the Si-O solubility curve I think you may recall that it came at the different temperature levels at about the order of 0.015 to 0.03 pct 0 and 0.03 to 0.07 pct Si—we also pointed out that we had difficulty in obtaining data at that level, although we finally did get some. I note in going through the data for the present paper, that there are no samples in those particular silicon and oxygen ranges. I wonder if that was purely accidental or was there a reason for it. D. E. Babcock (Republic Steel Corp., Youngstown, Ohio)—Mr. Hilty, do you have any explanation for that discrepancy between Dr. Chipman's curve and your own Mr. Hilty—Our explanation for it at that time was that for some reason our system probably was not in true equilibrium with SiO, that is, in equilibrium with the silica crucible at that level. We did observe, however, that that was the level at which both the metal and the slag became saturated with SiO,. On the average, in studying inclusion formation in small ingots permitted to solidify normally from the molten state, we observed pure silica inclusions at silicon contents over about 0.05 pct and FeO type inclusions at silicon

Jan 1, 1953

By F. F. Aplan

Pollution control will be of utmost importance in the 1970's. In this area, the mineral process engineer has a special competence to understand and remedy many pollution situations. There is an old adage that goes, "Build a better mouse- trap and the world will beat a path to your door." Would that it were so, but the reality of the situation is such that, just as a supplier must sell his machine, a professional man must sell his competence. It is a sad but true fact that mineral processing engineers have not done a very good job in selling their extensive competence in the control of a broad range of pollution problems. Recently one of our students visited a paper pulp mill where he was shown a foam fractionator used to remove paper pulp fibers from plant discharge waters. "Foam fractionator hell, that's a flotation cell!'' was his comment. Ah so, it would appear that large numbers of technical people consider themselves experts on "foam fractionation" Or is it that we have been very remiss in demonstrating the usefulness of our equipment and processes and our professional competence to solve, these pollution problems?

Jan 1, 1970

By G. A. Vissac

The only fine coal washer with proved automatic controls, the feldspar jig is capable of good efficiencies even at low separating gravities, handles a variety of products, and treats 150 tph and over. IN continental Europe the feldspar jig is used almost exclusively for cleaning the fine sizes of coal; it operates with an artificial bed, made up generally of pieces of feldspar or of any other hard and heavy rock with good cleavages. A primitive form of this machine requiring close supervision was used in this country years ago, but output was small. The modern machines are generally air-pulsated Baum-type jigs, with capacities up to 150 tph, and treat sizes from % in. to 0, usually previously dedusted or deslimed. These jigs are equipped with very accurate and sensitive automatic controls insuring satisfactory operation even at low separating gravity and with feeds irregular in quality and quantity. This paper will deal more particularly with coal cleaning separation, but the technical studies apply equally to all minerals. Theory of the Feldspar Jig To understand fully the operation of the feldspar jig and to appreciate its potential value, it is necessary to measure and analyze the motion of small particles of various specific gravities, falling in various media, under various conditions. As no practical formulas were available for that purpose, the writer has developed new theories and established new sets of formulas, which cannot be demonstrated here. They are applicable to all minerals and to many problems of coal or mineral concentration. These formulas do not pretend to absolute accuracy, but results, tested by comparison with experimentally recorded data, are sufficient for practical purposes, as they give definite indications of trends, relative values, and order of magnitude of the many factors involved. For pulsating motions no earlier formulas are available. In the case of continuous currents or motions, such formulas as Rittinger's, Allen's, or Stokes', over a hundred years old, apply only to special shapes and sizes of particles, involve factors and coefficients difficult to measure or appreciate, and deal only with free motions. They are of little use in solving practical problems. Units used with the formulas presented here are in the CGS system. Lateral friction and suction have been taken into account according- to methods currently used in aerodynamics, and only hindered motion is dealt with. As the feldspar jig is primarily intended to create a fluid bed condition, the mixture of fluids and solids obtained is homogeneous, and the apparent specific gravity of the separating medium is calculated accordingly. For instance, if 20 pct of the volume is coal and shale, with an average of 1.60 sp gr, in a liquid of 1.10 sp gr, the actual specific gravity of the separating fluid is 0.80 x 1.1 + 0.20 X 1.6 = 1.20. The fundamental equations are as follows: The general motion of a particle falling in a medium of specific gravity equal to u, hindered motion. is dv/dt = g/Ls [ L (s-u) - u/g v2 [1] g = 981 cm per sec, acceleration of gravity, and L = thickness of the particle of specific gravity (s) and velocity (v). The initial acceleration dv/dt = g (1-u/s ) [2] is a function of the specific gravity of the particle, only for a given medium, and independent of its dimensions—an ideal separating condition. The terminal velocity Vt = gxL- (s-u)/u, [3] for a given value of u, is a function of s and L. Two particles, L, s, and L2 s2, are said to be equivalent if they have the same terminal velocity, and accordingly L1/L2=s2-u/s1-u. [4] Two such particles cannot be separated by continuous currents, in any concentrating device. Because the initial accelerated motion, which provides for efficient separation, is followed by a constant velocity, which has a limiting effect, it is essen-

Jan 1, 1956

By A. L. Blomfield, M. J. Trott

ThE Golden Cycle Mining and Reduction Co. operates its custom mill at Colorado Springs on Cripple Creek ores exclusively. These ores are straight sulfo-tellurides, with practically no base metals such as Pb, CU, Zn, As, or Sb. Upon entering the mill, the ore all passes through the sampler to storage bins, where beds of 5000 tons each are made to insure uniformity in roasting. Classification of ORes For efficiency, it has been found advisable to separate the ores into two classes according to their lime content. Other constituents have their effect, such as alumina and magnesia, but, speaking generally, these are roughly proportional to the lime, which, as CaO, is used as the indicator. Class A contains not more than 2 per cent. CaO and comprises about 66 per cent. of the ore treated. Class B contains over 2 per cent. CaO, and comprises 34 per cent. of the ore treated. Typical analyses of both classes are as follows: Class A a B Insol.......................... 86.70 75.90 Al2O3........................:.. 2.30 3.40 Fe.............................. 3.26 3.48 CaO............................. 1.57 5.12 S............................... 1.79 1.80 MgO........................... 0.21 1.08 Ignition loss..................... 3.20 6.50 99.03 97.28 The beds of each class of ore are made as large as possible with the available ore as it comes in, to avoid changing from one bed to the other any oftener than necessary. Each roaster will handle 50 per cent. more of class A ore than of class B, with practically the same results. This necessitates changing the rate of feed for each new bed and tends toward a poor roast and loss of tonnage at each change.

Jan 1, 1919

By B. M. Larsen, W. E. Shenk

This paper describes a method of reversal control of the open-hearth furnace that obtains in practice those effects considered below as essential to a completely automatic control, without appreciable interference with the natural rise and fall in temperature of the regenerative portions of the furnace system. Growing out of some studies of radiation pyrometry in open-hearth regenerators, it was developed during 1934-1938, and has been successfully applied to a number of commercial furnaces. The goal of open-hearth furnace operation is the highest rate of production of steel of proper quality consistent with good refractory life and fuel economy. This requires rapid heat transfer from furnace to charge, which in turn is dependent upon heating the furnace refractories to the highest safe operating temperature. The greater the heat input to the melting chamber, the sooner this limiting temperature will be reached, so that control methods in general that are designed to protect against overheating of refractories should help to maintain maximum fuel input and production rate. For the typical open-hearth system, with fixed regenerator capacity and with rate of fuel input usually restricted in its range of variation, our basic assumption is the idea that the only other important variable —that is, the time interval between successive reversals—should also be held constant or within a small range. The present reversal control was designed therefore so that, under normal operating conditions, no arbitrary limitation is imposed other than to keep the reversal interval within the optimum time range. However, since a near approach to completely automatic operation involves protection of refractories through the balancing of furnace end temperatures as well as emergency protection against temperature peaks above some upper limit, it was also felt essential to employ, as an integral part of the control unit, a temperature-measuring instrument to register the true temperature of the refractory surfaces at some critical region in the hot ends of the regenerative zones. As the basic elements of the control, we thus have one "maximum" and one lLminimum" time relay and a potentiometer recorder-controller, combined with switches and relays to operate as follows: I. Reversal normally occurs within an optimum range limited by the maximum and minimum settings to about 4 to 6 min. variation, but the actual interval usually is less variable and closer to the minimum setting. 2. The margin between minimum and maximum time is utilized, together with a "floating temperature limit" in the potenti-ometric control instrument, to correct any tendency toward temperature unbalance between ends of the furnace. 3. A second "maximum temperature

Jan 1, 1945

By Robert E. Hochscheid

The subject article appears in the February, 1978, edition of Mining Engineering, and on page 190 carries the statement, "As most operators know, in a Water-Only cyclone, ability to adjust the vortex finder is quite important due to the sensitivity of this type of operations to variance in feed conditions and having to take them apart to make this adjustment is always a nuisance." Our experience as a manufacturer and supplier of Water Only cyclones does not agree with the above statement, and we offer the following brief discussion. Our company finds that the sensitivity of the Water-Only cyclone is a function of the fineness of the coal being washed, with the sensitivity to vortex finder length being greatest for coals coarser than 3/4-in. and virtually insensitive to raw coal finer than 1 mm. For coals finer than 1 mm, we find that we can use the shortest standard vortex finder in either our 10- or 15- in. Water Only cyclone without exception. For coals 5/8-in. x 1 mm ceramic vortex finders of fixed length have been satisfactory in all cases following an initial testing period in which the length was determined. Coals coarser that 5/8-in. are more sensitive to the vortex finder length, and two installations handling coals coarser than 1-in. continued to experiment with vortex finders of various lengths long after the initial startup period. For coals of all sizes, final adjustment of product quality has been achieved by determining the optimum size of apex orifice, which is accessible and readily changed, if necessary. Comments above assume no unusual change in the coal being washed or the required quality of clean coal.

Jan 1, 1979