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By C. C. Griggs

From its inception, a limestone quarry or mine should be under the direction of a capable engineer. Before it becomes a reality, he should outlinc the future results, plan the most economical methods for moving the materials and the most efficient equipment, and pilot the undertaking along the narrow pathway of success, avoiding the pitfalls of uneconomical production and the precipitous walls of scanty profits. Inspection of successful limestone properties shows that all have had difficult engineering problems, the solution of which have required keen engineering ability. In approaching a subject of this nature, it is logical to follow the progress of the limestone operation from its inception to the end, as reflecting the engineering required. There are four major divisions: Investigation, equipment, development, and operation. Investigation On the reliability of the engineer's estimates and the soundness of his judgment depend the success or failure of the enterprise. When one visits a prosperous concern, realizes that the limestone is of a constant chemical composition, sees the mechanical devices installed, and watches the output leave the plant in trains of railroad cars or fleets of vessels, he may overlook the fact that in the remote past this great creation was born in some man's brain and evolved through competent engineering. Many factors must be considered before a promoter could procure the money necessary to launch such an enterprise, for a conservative banker will only recommend a successful producer while the promoter must provide funds on his own and his engineer's judgment. An engineering investigation must be made preliminary to expenditure for actual operation, which, for a limestone deposit, would' naturally embrace such subjects as : ' Readily available. 1. Tonnage available........ Possibly available. Chemical analysis.

Jan 1, 1925

By David White

Jan 1, 1925

By Henry Fay

The erosion of guns is a complex problem which can be solved only by a detailed study of all the factors involved. In the present paper it is proposed to submit the results of observations and experiments which have extended over several years. Certain facts have been established and preliminary reports have been published.' Conclusions have been reached since then which, it is believed, are worth presenting for the purpose of promoting discussion, and with the hope that ultimately the whole truth will be known. The particular phase of the problem which will be presented here is the hardening of the inner surface of the gun tube. It has been known for a long time that after firing a large caliber gun for some time, the surface of the metal becomes hard and brittle, cracks, and wears away.2 The character of this phenomenon may be learned by an examination of some results which are typical, obtained from a detailed study of a 12-in. gun. The gun was trepanned and rings representing various sections of the gun were cut out for examination. The first ring represented the metal at the muzzle end, and the other rings were removed at approximately 120, 240, 325 and 337 in., respectively, toward the breech end. The appearance of the surface of the metal in the different sections is shown in Fig. 1. The greatest amount of wear and maximum amount of hard surface layer was found in section marked E, which is nearest the powder chamber and at the beginning of the rifing; the maximum amount of cracking in D; the maximum amount of copper deposition in C. Section B showed heat cracks on both lands and grooves, and section A showed heat cracks on the driving edge of the lands only. There was much flow of metal in both sections E and D, and there was progressively less effect noticeable toward the muzzle end. The polished cross-section of these same pieces is shown in Fig. 2. The extent of the erosion is greatest nearest the powder chamber, and diminishes toward the muzzle end.

Jan 1, 1917

By Leon McCulloch

WIIen clean iron and metallic zinc dust, protected from the air, arc heated below the melting point of zinc, the iron takes on a coating that has excellent protective value. This coating is a brittle alloy of zinc and iron, and the process is called sherardizing. Although the zinc particlcs are covered with oxide and cannot touch the iron, an extremcly small amount of the zinc vaporizes and the vapor, reaching the iron, alloys with it. Other zinc then vaporizes to replace that which has been removed from the atmosphere. This process continues indefinitely at a decreasing rate, for the coating already formed permits zinc to diffuse through it to combine with the iron beneath. In this way, the coating grows outward from the surface of the iron, as the bark grows from a tree. The method of growth was clcarly seen while sherardizing small cubes of cast iron, at about 450" C., in a srnall glass-stoppcrcd bottle enclosed in a rotating drum. The dust contained about 3 per cent. iron, which prevented caking, and coatings % in. thick were grown in a few hours. After a heavy layer had been formed, the cubes mere again treated for a shorter time. The layer last formed was seen to lie next to the iron, instead of at the outer surface, showing that the growth was from the surface of the iron outward. The coatings split at the edges and corners, leaving the iron exposed there. Flakes of graphite from the iron were lifted upward and embedded in the coatings. The composition of sherardized coatings varies from the outer surface inward, as would be expected from the mode of growth. That is, the iron content increases slowly at first, then more rapidly as the iron is approached. At the surface the least amount of iron possible is 6 per cent., as the experiments described below have shown. A study was made of the effect of iron in zinc dust on the proccss and on the resulting coatings. Glass bulbs, holding the small pieces to be sherardized, together with enough zinc dust to make them two-thirds full, were heated in a small, rotating electrically heated and controlled furnacc. The bulbs had 6-in. (15 cm.) necks, of 96-in. (9.Fj mm.) tubing, plugged

Jan 1, 1923

By Leon McCulloch

WIIen clean iron and metallic zinc dust, protected from the air, arc heated below the melting point of zinc, the iron takes on a coating that has excellent protective value. This coating is a brittle alloy of zinc and iron, and the process is called sherardizing. Although the zinc particlcs are covered with oxide and cannot touch the iron, an extremcly small amount of the zinc vaporizes and the vapor, reaching the iron, alloys with it. Other zinc then vaporizes to replace that which has been removed from the atmosphere. This process continues indefinitely at a decreasing rate, for the coating already formed permits zinc to diffuse through it to combine with the iron beneath. In this way, the coating grows outward from the surface of the iron, as the bark grows from a tree. The method of growth was clcarly seen while sherardizing small cubes of cast iron, at about 450" C., in a srnall glass-stoppcrcd bottle enclosed in a rotating drum. The dust contained about 3 per cent. iron, which prevented caking, and coatings % in. thick were grown in a few hours. After a heavy layer had been formed, the cubes mere again treated for a shorter time. The layer last formed was seen to lie next to the iron, instead of at the outer surface, showing that the growth was from the surface of the iron outward. The coatings split at the edges and corners, leaving the iron exposed there. Flakes of graphite from the iron were lifted upward and embedded in the coatings. The composition of sherardized coatings varies from the outer surface inward, as would be expected from the mode of growth. That is, the iron content increases slowly at first, then more rapidly as the iron is approached. At the surface the least amount of iron possible is 6 per cent., as the experiments described below have shown. A study was made of the effect of iron in zinc dust on the proccss and on the resulting coatings. Glass bulbs, holding the small pieces to be sherardized, together with enough zinc dust to make them two-thirds full, were heated in a small, rotating electrically heated and controlled furnacc. The bulbs had 6-in. (15 cm.) necks, of 96-in. (9.Fj mm.) tubing, plugged

Jan 1, 1923

By Zay Jeffries

This paper will include a brief discussion of Prof. Howe's paper on The Supposed Reversal of Inheritance of Ferrite Grain Size from that of Austenite.l The general subject of grain refining in steel and iron will also be treated. The conclusions reached are stated in the following hypotheses which are discussed more in detail below. 1. The ferrite grain size in pure iron, the ferrite and pearlite grain size in hypoeutectoid steel, the pearlite grain size in eutectoid steel and the cementite and pearlite grain size of hypereutectoid steel are not inherited from the grain size of the mother austenite. 2. The only structural feature that is generally inherited from the austenite of hypo- and hypereutectoid steels on cooling through their transformation ranges is the position of the excess ferrite or cementite at the austenite grain boundaries, sometimes causing complete and sometimes incomplete networks which outline the old austenite grain boundaries. Rapid cooling through the transformation range will cause the non-inheritance of this structural (network) feature. 3. The austenite grain boundaries themselves are nearly always effaced in all steels and also in pure iron during the At transformations. 4. The grain-size refining of steel and iron is brought about by the combined effect of non-inheritance of the transformation products on either heating or cooling, i.e., the austenite transformation products do cst inherit their grain size from the austenite on cooling through the transformation range nor does austenite inherit its grain size from the products which form austenite on heating. 5. In general, in both iron and carbon steel the larger the austenite grain size, the larger will be the grain size of the transformation products on cooling. This, of course, assumes all other conditions constant except the austenite grain size. An exception is found to this general rule in very pure iron such as electrolytic iron. In this instance small austenite grains may form very large ferrite grains on cooling through Arg.

Jan 1, 1918

By S. W. Miller

During the examination of welds made in steel by the oxy-acetylene and electric-arc processes, the writer has met with some unusual structures, which he has not encountered elsewhere. They seem to be quite closely associated with the welding methods used, and characteristic of them, and would seem to be worth noting, especially as the references to them in the literature are few, and their explanation not clear or complete. An introductory word or two about fusion welding may not be out of place. The oxy-acetylene process is based on the great and very local heat generated by the burning of acetylene in the presence of commercially pure oxygen, the two gases being thoroughly mixed before combustion. The theoretical temperature is somewhat under 4000" C, but on account of various losses, the actual maximum temperature is probably about 3000" C.' The electric-arc process, using a metal electrode, which is also the filling rod, generates a still higher and more local temperature. The actual temperature of the positive crater of the carbon arc is given as 3500" C.2 NO figures have been found for the temperature of the arc using a metal electrode, but it would probably not be very different from that of the carbon arc, and probably higher than that of the bxy-acetylene flame. The greater localization of the electric arc is due to the fact that it is not surrounded by a large envelope flame, as well as to its higher temperature; while the oxy-acetylene white cone, or welding flame, in which the carbon of the acetylene is burned to CO, is surrounded and preceded by a long envelope flame, itself of quite high temperature, in which the CO is burned to GO2, and the hydrogen of the acetylene to H2O. This flame spreads around and over the pieces being welded, heating them to a further distance from the weld than does the electric arc.

Jan 1, 1918

By H. M. Howe

Page 1. Introduction............................514 2. Definitions.............................517 3. Brevity of the Heating........................517 I. THE HARDENING OF THE BORE..............517 4. The Hardening of the Bore.....................517 5. The Thickness of the Hardened Layer.................517 6. Martensitization..........................518 7. The Hardening Repetitive ......................519 8. The Temperature Cycle.......................519 9. The Hardened Layer is the Merged Layer............... 521 10. The Progressiveness of Merging....................521 11. The Progressive Thickening of the Hardened Layer from Round to Round. 523 12. Merging and Hardening are Cumulative................523 13. Three Additional Causes of the Progressive Thickening of the Hardened Layer 525 14. Progressive Roughening of the Bore..................525 15. Avoidance of an Endothermic Transformation.............525 16. Asymptotic Retardation of the Thickening of the Hardened Layer.....527 17. The Troostitic Layer........................ 529 18. The Usual Lack of Martensitic Markings................529 19. The Thickness of the Hardened Layer Should Increase with the Quantity of Heat Taken up by the Walls of the Bore.................530 20. The Decrease of the Thickness of the Hardened Layer from Breech to Muzsle 531 21. Phstic Deformation as a Contributory aCause of Hardening........531 22. In What Way May Plastic Deformation Hasten Hardening?....... 535 23. Possible Need of Coarsening.....................535 24. Carburization as a Cause of Hardening..........:.....536 25. Does Hardening Increase Erosion?..................-538 11. THE CRACKING OF THE BORE ...............539 26. Appearance of the Bore and Cracks in Elevation............539 27. The Cracks in Elevation in the Rear Ring...............539 28. The Cracks in Elevation in the Forward Ring.............540 29. The Copper Network in the Grooves.................540 30. The Cracking of the Lands......................541

Jan 1, 1918

By A. E. Bellis

The time effect in reheating certain steels below the critical range is very marked. The increased toughness, shock-resisting power, and machinability of steel subjected to a long, high drawing temperature has been thoroughly demonstrated and is of practical importance, particularly in the manufacture of L'smokeless" rifle-barrel steel. The time effect in tempering is most important when a maximum drawing effect is desired, in which case the highest physical properties as well as ease of machining are important considerations. These are the conditions in drilling a rifle barrel. A hole, 0.30 in. in diameter and 24 in. long for the Springfield rifle, and 30 in. long for the Russian military rifle, has to be drilled in the heat-treated material. This barrel-drilling operation is probably the most difficult one in rifle manufacture, and anyone who has been connected with rifle manufacture knows how seriously production is affected when "hard" or non-uniform steel for barrels is encountered. The importance of high physical properties (tensile strength, toughness and resilience) in a rifle barrel is obvious. The physical properties of two different lots of barrel steel are given below. The first lot, No. 1, gave serious trouble in the drilling operation; the second gave no trouble at all. No. 1 No. 2 Elastic limit, lb. per sq. in.................... 117,450 116,800 Tensile strength, Ib. per sq. in................. 132,500 131,750 Elongation, per cent........................ 16.0 20.0 Reduction of area, per cent................... 42.1 51.0 Impact strength, ft.-lb. per sq. in.............. 450.0 520.0 This difference in machining and physical properties was due entirely to the time of reheating. The first lot was given a reheating time of 30 min., the second lot remained at the reheating temperature 2 hr. Both

Jan 1, 1918

By E. W. Davis

On the eastern end of the Mesabi Range, in Northern Minnesota, is a large formation of siliceous rock which contains bands and fine grains of magnetite. The magnetite comprises about 35 per cent. of the rock, the remainder being chiefly quartzite and iron silicates. The rock has a specific gravity of 3.4, a hardness of 7, and is extremely tough. This large deposit was located early in the history of the Minnesota iron-ore industry but has not been utilized because of its low percentage of iron as compared with the other Mesabi ores, and because of the difficulty and expense of any milling treatment that would concentrate the iron. An investigation, begun about 3 years ago, shows that the magnetit,e is finely disseminated throughout the entire formation and that there are bands or lenses of higher- and of lower-grade material, in which the magnetite and silicate are intimately mixed. As a result, the scheme of milling adopted must include a fine-crushing plant. As it is necessary to crush to 200 mesh in order to produce the desired grade of product, the fine crushing is one of the largest items of expense and for this reason has been given detailed study. It is the purpose of this paper to present some of the results of the work on fine crushing, as to both theory and practice. Previous to fine crushing the part of the rock that contains little or no magnetite can be discarded by magnetic concentrators after each reduction in size in the dry-crushing plant. This-makes it possible to fine-crush a minimum of rock and also establishes the feed to the ball-mill as below % in. The fine-crushing problem, then, consists simply in crushing the rock from 1/4 in. to 200 mesh at the minimum expense. Equipment of the Testing Plant In order to determine, among other things, the operating conditions of the ball-mill when working on this rock, a test mill of about 300 T. daily capacity was erected at Duluth, Minn. The fine-crushing plant contains a Hardinge 8-ft. by 22-in. (2.4-m. by 55.8-cm.) conical mill, a 6- by 27-ft. (1.8 by 8.2-m.) Dorr duplex bowl-type classifier, a 41/2-ft. (1.37-m.) standard Akins classifier, and the auxiliary machinery necessary to handle the products. Each machine is driven by an individual motor, each of which is provided with meters for measuring the power required. Over 150 tests have been made in the ball-mill, varying in

Jan 1, 1920

By T. D. Yensen

In the investigation of the magnetic properties of iron-nickel alloys,' it was found necessary in order to make the alloys forgeable, or malleable, to add small quantities of some other element. Iron-nickel alloys have been known for nearly a century, but have been made in commercial quantities only since 1885. Their remarkable mechanical properties were disclosed by Riley in 1889 and from that time on a large amount, of research work has been done both to discover new properties and to correlate the results obtained.2 Lately the Bureau of Standards has collected the published data in a special circular" giving in compact form an account of the properties of the iron-nickel alloys. It also contains a clear historical sketch of the development as well as a selected bibliography. The chief difficulty with the development of iron-nickel alloys was that the "pure" alloys do not forge readily. The addition of small amounts of manganese, however, made the alloys forgeable, and manganese has therefore come to be regarded as a necessary constituent of nickel steels. The present paper shows to what extent manganese is needed for various nickel contents and also what is the effect of other alloying elements on the forgeability. It also touches upon the cause of forgeability but refers to other sources for more exhaustive treatises on the subject. The alloys were prepared by melting electrolytic iron and electrolytic nickel with or without other alloying elements in the desired proportions in a magnesia crucible in a vacuum furnace under a pressure of 1 mm. mercury. The ingots, weighing about 2 kg., were allowed to cool in vacuo. If pipes or blowholes were present, the ingots were cut in such

Jan 1, 1922

By T. D. Yensen

In the investigation of the magnetic properties of iron-nickel alloys,' it was found necessary in order to make the alloys forgeable, or malleable, to add small quantities of some other element. Iron-nickel alloys have been known for nearly a century, but have been made in commercial quantities only since 1885. Their remarkable mechanical properties were disclosed by Riley in 1889 and from that time on a large amount, of research work has been done both to discover new properties and to correlate the results obtained.2 Lately the Bureau of Standards has collected the published data in a special circular" giving in compact form an account of the properties of the iron-nickel alloys. It also contains a clear historical sketch of the development as well as a selected bibliography. The chief difficulty with the development of iron-nickel alloys was that the "pure" alloys do not forge readily. The addition of small amounts of manganese, however, made the alloys forgeable, and manganese has therefore come to be regarded as a necessary constituent of nickel steels. The present paper shows to what extent manganese is needed for various nickel contents and also what is the effect of other alloying elements on the forgeability. It also touches upon the cause of forgeability but refers to other sources for more exhaustive treatises on the subject. The alloys were prepared by melting electrolytic iron and electrolytic nickel with or without other alloying elements in the desired proportions in a magnesia crucible in a vacuum furnace under a pressure of 1 mm. mercury. The ingots, weighing about 2 kg., were allowed to cool in vacuo. If pipes or blowholes were present, the ingots were cut in such

Jan 1, 1922

By William B. Phillips

This paper was prepared at the request of Capt. A. F. Lucas, Chair man of the Institute's Committee on Petroleum and Gas; as a pre1iminary.discussion of the fuel oils which are used in the Southwest, giving their composition, uses, prices, etc. Should it afterward be found desirable, these observations may be extended over a larger area. In this connection, I suggest that samples of all kinds of fuel oils, including various tars, from all over the country, be collected and sent to some testing laboratory for examination. We would be glad to extend the facilities of the laboratory of the Bureau of Economic Geology and Technology, at the University of Texas, for this purpose, and to do the work free of all expenses. After such examinations are made and the results classified and studied, it would be possible to suggest specifications under which fuel oils should be purchased, and to arrive at some conclusions respecting the uniformity of such specifications, with due allowance for climatic and other more or less local conditions. While such specifications do not now depart from a common standard anything like as much as specifications for illuminating oils do, yet there are discrepancies which should not exist. Some of these discrepancies are of lessening importance, due to the pronounced tendency to distill every crude oil that can be distilled with profit, and to send residues into the market for fuel oil. Residues from the refineries are of a more uniform chemical composition and physical nature than many of the crude oils that go direct into the fuel market. The lower flash-point oils are disappearing from the fuel trade and in place of them we are getting oils that do not flash below 220" F., nor burn under 320" F. In the Southwest, it has not been long since we had fuel oils that flashed as low as 110" F., and the average flash point over a considerable period was 151" F. Now we are using oil that flashes at about 30" lower than the former burning point, which was 258" F. In other words, the flash point has risen, on the average, 100"; and the burning point about 75".

Jan 1, 1915

By Henry Wurtz

Jan 1, 1880

By Walter O. Snelling

In the course of some experiments more than five years ago, made for a totally different purpose than the investigation of the oil used, I placed a small quantity of a transparent yellow lubricating oil in a bomb-like vessel and heated it to a relatively high temperature. At the end of the experiment I removed the oil from the vessel and was amazed to find that instead of bearing any resemblance to the oil which I had put in, it now had the appearance of ordinary crude oil. The green color by reflected light and the rich red-brown by transmitted light were so unmistakable as to at once lead to further investigation. I subjected the material to fractional distillation, and the surprise which I experienced at the appearance of the oil, changed to amazement when I found that it yielded, on distillation, 15 per cent. of gasoline and 30 per cent. of burning oil, and that its constitution resembled crude oil quite as much as did its appearance. Furthermore, the gasoline and kerosene distillates which it yielded were of a clear water-white color, entirely without treatment with acid or alkali, and were entirely free from the odor familiar in "cracked" petroleum distillates. The result of this experiment was quite too remarkable to be credited without further confirmation, and I at once filled the vessel with some of the same oil that I had used before, and again heated to about the same temperature that I had previously used, and for the same period of time. Upon opening the vessel and removing the contents I found, not the material resembling crude oil that I had obtained before, but apparently only the same oil that I had put in, somewhat darkened in color, but nevertheless far different in appearance from the material obtained in the previous experiment. Evidently some condition existed in the first experiment that had not existed in the second test, and here began a series of tests in which I sought by the change of one variable after another to arrive at the identical conditions which must have existed in the first experiment. Only the fact that the bottle of heavy oil used in the first test was still in its place,

Jan 1, 1915

By Zay Jeffries

The object of the present paper is to enlarge somewhat on the general principles advanced in my discussion1 of Mathewson and Phillips' article on The Recrystallization of Cold-Worked Alpha Brass on Anneal-- ing.2 It will also serve as an acknowledgment of Prof. Howe's most important remarks on my contribution. In this paper the writer has adopted Prof. Howe's suggestion to substitute the term "germinative temperature'' for "critical temperature for grain growth." Instead of being an exact or certain temperature it should be considered that the germinative temperature phenomenon exists throughout a small temperature range. v Factors Influencing Fast Growth Phenomena The development of grains of macroscopic size at the germinative temperature should be considered the extreme condition of a general rule. When considered in this light it is not strange that the development of these large grains should be the exception and not the rule. The principal factors influencing the operation of the laws of fast growth temperature are as follows: . 1. Rate of heating. In the original paper,' the germinative temperature was defined as "the minimum temperature at which two adjacent grains can coalesce to form one larger grain, provided that this larger grain will have sufficiently increased its power of attack, to enable it to absorb adjacent grains which cannot coalesce with each other. Time is always to be understood as a factor governing the first stage of grain growth." If the time of heating is short, the germinative temperature is raised. The formation of large grains in metals may occur at relatively high temperatures when the rate of heating is rapid. It is to be understood that in such cases, grain growth

Jan 1, 1917

By Jos. Van Ackeren

Although the Siemens regenerator principle was introduced into byproduct coke-oven design about 40 years ago, many problems of construction, and particularly of heat distribution and pressure conditions, have not been fully solved. Heat should be applied to the walls of a coke oven in such a way that the coking of the charge of coal will be completed everywhere at the same time, and at approximately the same temperature. This means that the application of heat should be uniform from the top to the bottom of the coal mass (except for the thin layer at the top that is purposely kept at a somewhat lower temperature to reduce cracking of the byproducts); also that a little more heat must be applied to the coke end than to the pusher end, because the coal mass is a little thicker at that end. As a modern coke oven is about 40 ft. long and 12 ft. high, a real problem is involved in the proper application of heat to the oven walls so as to secure quick coking time (without endangering the walls through local overheating) and produce coke made at a uniform temperature. Design of Ovens In all regenerative ovens, the points of combustion are arranged in duplicate sets, one set operating in one-half the area of the heating wall and the other set alternately operating in the other half. Because of the reversal of the flow of gases, the points of maximum and minimum temperatures are alternately located at the same places, thus preventing dangerous local overheating. The practicability of the principle of reversal of flow seems to have been recognized at an early date, and has been applied with every conceivable flue arrangement, combustion chamber, and means of air and gas supply. To summarize the various principles that have proved useful for the control of oven-wall temperature, the best practice seems to have resulted from the acceptance of the use of vertical flues; the separate supply of air and gas to the base of these flues, with the resulting flame

Jan 1, 1923

By Jos. Van Ackeren

Although the Siemens regenerator principle was introduced into byproduct coke-oven design about 40 years ago, many problems of construction, and particularly of heat distribution and pressure conditions, have not been fully solved. Heat should be applied to the walls of a coke oven in such a way that the coking of the charge of coal will be completed everywhere at the same time, and at approximately the same temperature. This means that the application of heat should be uniform from the top to the bottom of the coal mass (except for the thin layer at the top that is purposely kept at a somewhat lower temperature to reduce cracking of the byproducts); also that a little more heat must be applied to the coke end than to the pusher end, because the coal mass is a little thicker at that end. As a modern coke oven is about 40 ft. long and 12 ft. high, a real problem is involved in the proper application of heat to the oven walls so as to secure quick coking time (without endangering the walls through local overheating) and produce coke made at a uniform temperature. Design of Ovens In all regenerative ovens, the points of combustion are arranged in duplicate sets, one set operating in one-half the area of the heating wall and the other set alternately operating in the other half. Because of the reversal of the flow of gases, the points of maximum and minimum temperatures are alternately located at the same places, thus preventing dangerous local overheating. The practicability of the principle of reversal of flow seems to have been recognized at an early date, and has been applied with every conceivable flue arrangement, combustion chamber, and means of air and gas supply. To summarize the various principles that have proved useful for the control of oven-wall temperature, the best practice seems to have resulted from the acceptance of the use of vertical flues; the separate supply of air and gas to the base of these flues, with the resulting flame

Jan 1, 1923

By T. F. Witherbee

The following calculation of heat requirement covers the working of the furnace from January 25th to February 14th, inclusive. A short time previous to the first date the furnace had been working rather badly, so that 300 lbs. of ore and 500 lbs. of limestone were taken off. Within the time mentioned the quality of the iron passed

By G. H. Gilman

The campaign now being waged to improve the quality of the rock-drill bit is the natural outcome of the scientific development of the drilling machine during the past twenty years. In this development there has been a great increase of power output per unit of weight of machine. But the development of the rock drilling engine has been seriously hampered by the need of a drill bit that would withstand, without undue wear or breakage, the heavy rapid blows of the improved pneumatic hammer. This problem was difficult to solve because an increase in the weight or section of the drill-steel bar resulted in decreased cutting speed and higher operating costs of both the bit and its actuating engine. The solution, therefore, is to make the bit of steel that, for a given weight or section, will be more shock and wear resisting. In the attempt to meet these requirements, many of the drill-steel manufacturers alloyed the steel with vanadium, chromium, nickel, etc. on the assumption that such elements would improve the rock-drill bit but due to the sensitiveness of such steel to forging and heat treatment, higher cost, and lack of continuity of effort on the part of the steel manufacturer to perfect this product, but little progress has been made in the adoption of these steels and the so-called straight carbon steel is today recognized as the standard material for all rock-drill bits. The first step in improving drill-bit efficiency is the determination of the cause of breakage and wear. For this reason, in 1917, certain rock-drill manufacturers, in conjunction with some of the larger mining interests, conducted exhaustive tests in both the field and the laboratory. It was then found that, in the main, the cause of drill-steel troubles is not attributable to the duty imposed upon it by the normal operation of the drilling engine, but to improper forging and heat treating of the bit and to the subjecting of the bit to improper use. The fact that it is possible to minimize the troubles attributable to improper heat treatment of the drill steel has been demonstrated and it is recommended that such knowledge be made available by teaching those interested in the production, use, and up-keep of drill bits the principles on which success in this direction may be achieved. Unfortunately, but little attention has been given to the education of the drill smith. But a few years ago, the instructions given the man

Jan 1, 1922