Table of Contents
The reasons for manufacturing steel by the duplex process are, briefly: saving of time; increasing output for capital invested; and avoiding the difficulty sometimes experienced in obtaining scrap. On account of the latter reason, some plants duplex only at such times as the price and quantity of scrap in the open market warrant. At some plants the use of the duplex process enables the blast-furnace practice to be simplified, because the furnaces run more smoothly and produce more iron when not held to a strict specification as to the silicon and phosphorus therein.
The duplex process was practiced in Witkowitz as far back as 1878, but it was left to the steel makers of this country to develop it along practical, commercial lines. The American companies manufacturing steel by the duplex process at the present time are: Tennessee Coal, Iron & Railroad Co., Maryland Steel Co., Bethlehem Steel Co., Pennsylvania Steel Co., Jones & Laughlin Steel Co., Colorado Fuel & Iron Co., Lackawanna Steel Co., Dominion Iron & Steel Co. of Canada.
All of these companies, except the Dominion Iron & Steel Co., combine the acid Bessemer with the basic open-hearth process, while the latter combines the basic Bessemer with the basic open hearth.
The Tennessee Coal, Iron & Railroad Co.’s Plant
The installation of a converter of 15 tons capacity at the Ensley plant of the Tennessee Coal, Iron & Railroad Co. in 1904 marked the introduction into this country of the duplex system. The experience gained in the employment of the Bessemer converter had demonstrated that there was a shortening of the time required in the open-hearth furnace and a reduction of the outlay for fuel and lime, thus affording substantial evidence of the economies resulting from this method.
The scarcity of steel scrap in the Birmingham district; its dependence on its own resources for pig iron; its lower cost of fuel; and the lower lime cost with the use of the direct metal in the converter, were the factors
which brought about the construction of the second duplexing plant, which went into operation in the fall of 1907 and has been operated continuously ever since. At the time the original 15-ton converter was installed at the Tennessee Coal, Iron & Railroad Co.’s works, the steel making plant consisted of six blast furnaces, one 250-ton primary regenerative furnace, and eleven 50-ton open-hearth furnaces, of which one was stationary and ten were tilting. The original converter was erected between the 250-ton regenerative furnace and the open-hearth plant, and was served by an electric traveling crane. It was operated by one 75-h.p. electric motor through worm, pinion, and gear, and was the first converter in this country to be operated electrically.
The second plant built by this company marked the beginning of duplexing in this country on a large scale. All the details of this plant were worked out so carefully that practically no changes or improvements have been found necessary, or even desirable, since then. As shown in Fig. 1, this plant consists of six modern blast furnaces and two batteries of basic open-hearth furnaces, each consisting of four 100-ton hydraulically tilting furnaces, having hearths 15 ft. wide by 44 ft. 2 in. long. Between the two batteries of open-hearth furnaces, and in line with them, is located the Bessemer building. The converters and the converter-building floor are served by a 100-ton traveling crane. This building houses the two 20-ton converters; one 250-ton and one 600-ton hot-metal mixer; and two 10-ton cupolas for melting scrap, located directly back of the pouring-end of the mixers, with the necessary equipment of troughs so that they can be tapped into the converter-charging ladle which plies between the mixers and converters.
The iron comes from the blast furnaces in 25-ton hot-metal cars, and is poured into the mixers by means of hydraulic lifts. The iron is poured from the mixers into the converter-charging ladle, which travels over a charging floor at an elevation of 14 ft. 7 in. above the open-hearth charging floor. The molten iron is charged into the converter by means of a hydraulic post crane. After it has been blown, it is discharged into a 20- ton ladle car and carried directly to the open-hearth furnace. The bottom house, situated directly opposite the converters, contains seven bottom-drying ovens, crusher, wet and dry pans, and the necessary bins, etc., for making up the bottoms. After the bottoms have been made up here and dried, they are placed on the hydraulic jack cars, of which there are two, and transported to the converters as required.
The distinctive feature of this plant is that the converters are located directly between, and in line with, the two batteries of open-hearth furnaces, thus minimizing the haul of the blown metal. The track over which the blown metal is conveyed to the open-hearth furnaces is located in the open-hearth building, adjacent to the furnaces and between the charging-box track and the furnaces. The ladles are drawn up in front of the furnace doors and the contents poured directly from the ladle, without removing it from the car, into the charging spout. The ladle is tilted by an overhead traveling crane.
The vessels, as shown in Fig. 2, are swung on well-designed, heavy, cast-iron column stands and are 40 ft. center to center. Instead of following the usual practice of riveting the trunnions directly to the shell, they are secured to an annular supporting ring, the vessel being secured in place by means of lugs and keys. This supporting ring not only serves to prevent the wearing of the sides of the vessel in the rivet holes which have become distorted by the constant reversal of stresses on account of turning the vessel from time to time, and which has been a source of great inconvenience in the past at some of the works manufacturing Bessemer
steel, but also facilitates the removal of the vessel for relining and repairs. A spare vessel, lined and ready for service, is kept standing convenient to the vessels in operation. The tuyere plate has 26 tuyere openings. The vessels are operated hydraulically by two vertical racks working on one pinion for each vessel. Blast is supplied to the converter from an Allis horizontal, cross compound, Corliss blowing engine (46 by 88 by 84 in. and 60 by 84 in.) through a 30-in. diameter air line to the 24-in. air valves beneath the pulpit, thence through an 18-in. air line to the blast trunnion of each vessel. The blast line, just before connecting with the trunnion sleeve, is provided with a gas-escape valve, which allows any back flow of gas to escape to the atmosphere rather than into the main air line. The blast elbow and wind box are of the usual design. The unusual size of the converters was a matter that received careful consideration at the outset by the Tennessee Coal, Iron & Railroad Co.’s engineers, and the 20-ton vessel was adopted, since it afforded economies in operation, by decreasing the refractory cost and reducing the expense of blowing.
While it is not the intention of this article to go into either the chemistry or the metallurgy of the duplex process, a brief outline of the method of operation of some of the followers of the process may prove of interest: The methods employed at this plant of bringing the iron from the furnace, charging the mixer, charging the converter, and pouring from the converter, have been previously described. The hot metal coming from the blast furnaces to the mixer is of the following analysis: Silicon, 0.80 to 1.25; phosphorus, 0.9 to 1.0; manganese, 0.3 to 0.4 per cent. In the converter, all of the metal is desiliconized and partly decarbonized. Four ladles of blown metal are required for each open-hearth heat. Ordinarily the first two are blown soft, analyzing: carbon, 0.1; phosphorus, 0.7 to 1.0; manganese, 0.08 per cent.; and the second two ladles are partly decarbonized, the percentage of carbon blown out depending on the amount of scrap charged in the open-hearth furnace. Before the blown metal is poured into the open-hearth furnaces, burnt lime, iron oxide (the latter in the form of scale or ore), and about 15 per cent, of scrap are charged; then the two ladles blown soft are poured in, and lastly the two ladles partly decarbonized, containing 2 per cent, carbon, or slightly more, are added. When the second two ladles are poured into the open-hearth furnace a violent reaction takes place, which transfers practically all of the phosphorus into the slag. It is here that the advantage of the tilting type of open-hearth furnace, over the stationary type, comes in, as at this juncture the furnace is tilted back, allowing the excess slag to run out of the doors into the slag cars beneath the furnace. Recarbonizing of the steel at the end of a heat is not often found necessary, the practice making it possible to catch the carbon on the way down. Ferro-manganese is added for the manganese. It took from 1 to 1½ hr. to charge the blown metal into the furnace, and about 1 hr. to finish the heat. Records kept show a variation of from 4 to 8 hr. per heat. The time required for blowing the heats in the converters varies, depending on the silicon content, the blast pressure, and other factors. Desiliconizing takes from 2 to 10 min., and decarbonizing from 12 to 20 min.
The Dominion Iron & Steel Co.’s Plant
At about the same time the Tennessee Coal, Iron & Railroad Co., situated at the southern American boundary of the steel industry, was considering the question of duplexing on a large scale, the Dominion Iron & Steel Co., situated at the extreme northern boundary of the steel industry, concluded to install a duplexing plant. The Nova Scotian ores were similar in many respects, but had a higher phosphorus content, and the chief reasons why duplexing was considered advantageous were the long period of time otherwise required in the open hearth, and the difficulty of operating the blast furnaces under a strict specification as to silicon and phosphorus. Consequently, in July, 1906, they let the contract for two 15-ton Bessemer converters, with the necessary building and equipment. Construction started in December of the same year and the first heat was blown in May, 1907. The vessels were operated for some time with an acid Bessemer lining with very satisfactory results, which, however, seemed short of the maximum possibilities. It was thought that, by operating with a basic lining, better results might be achieved. This was at the time considered somewhat experimental in view of the fact that in Europe, where the basic Bessemer practice was commonly pursued, it was considered that at least 1.75 to 2.25 per cent, phosphorus was necessary. However, the necessary alterations in the bottom house were made, the mica schist lining of the vessels was removed and one of stamped dolomite and tar substituted, and the basic Bessemer process was begun. This method has been in use ever since.
In the year 1910 a third vessel, of the same size and design, was added to the original plant. At this time, the steel-manufacturing department consisted of four blast furnaces, one 300-ton hot-metal mixer, three 15-ton Bessemer converters, two in actual service and one spare, and ten 50-ton basic open-hearth furnaces of the Campbell tilting type. Of the ten open-hearth furnaces, nine are operated according to strict open-hearth practice, furnace No. 1 alone being used in conjunction with the duplex process. Also, there were under construction at this time two blast furnaces and two 500-ton mixers. The mixer building and the converter building are situated between the blast furnaces and the open-hearth plant. The vessels are served by a traveling crane, which operates throughout the full length of the building. The three vessels are arranged in line in the Bessemer building, 36 ft. centers. The vessels are of the eccentric type, having a shell diameter of 10 ft. 9 in., with trunnions riveted directly to the shell. The wind box, blast elbow, and trunnions are of the usual design; but the tuyere plate, instead of being of the usual type with 6-in. openings in which refractory tuyeres are placed, is a solid plate provided with 73 ¾-in. tuyere openings. The vessel is electrically operated, the power being transmitted through worm, pinion, and gear directly to the trunnion, which gives ample power at all times, although when the vessel is in a horizontal position with bottom off, it requires about all of the power to bring it to the vertical position. The blast for blowing the vessel is furnished by the blast-furnace blowing engines through a 36-in. diameter main, 1,365 ft. long. We mention this length on account of the unusual distance over which the blast is carried. The 18-in. branch blast mains on each vessel are provided with air-relief valves. The blast is delivered to the vessels at a pressure of 18 to 20 lb.
At this plant the iron coming from the blast furnaces has the following average analysis: Total carbon, 4.25; silicon, 1.00; sulphur, 0.05; phosphorus, 1.50; manganese, 0.20 per cent. The iron is delivered from the blast furnace to the mixer, and from the mixer to the converters, by means of hot-metal ladle cars, and charged into the mixer with overhead traveling crane, and into the converters by means of an electric ladle hoist.
From 2,600 to 2,800 lb. of burned lime is charged into the empty converter, after which is charged about 11 tons of fluid pig iron from the hot-metal mixer. After the metal has been blown, the slag is skimmed into a cast-iron box car made for the purpose, and the metal is then poured into the ladle car, which transports it to the open-hearth furnace, the entire blow consuming from 12 to 15 min. Under good average conditions the blown metal has the following analysis: Carbon, 0.03; phosphorus, 0.07; sulphur, 0.05 per cent.; manganese, none; and the slag is constituted as follows: Silica, 13.0 to 14; alumina, 1.0; lime, 48.0 to 51; magnesia, 2.0 to 4; phosphoric acid, 17.0 to 19; manganous oxide, 1.5; iron protoxide, 13.0 to 15. Five ladles of the blown metal are charged into the open-hearth furnace as they are delivered from the converters, but, prior to this, the open-hearth furnace has been charged with about 4,000 lb. of burned lime and 6 to 8 tons of molten iron, direct from the hot-metal mixer, the latter iron being depended upon to give sufficient carbon for the chemical reaction. Ten to twelve heats are made in No. 1 open-hearth furnace in 24 hr. One of the economies resulting from the practice of the basic duplex process is the revenue derived from the Bessemer slag after it has been ground and prepared for agricultural purposes.
The Bethlehem, Steel Co.’s Plant
In 1910 the Bethlehem Steel Co., desiring to increase and add flexibility to the output of its new Saucon plant and to render itself more independent with respect to the fluctuations of the scrap market, decided to adopt the duplex process, and, consequently, in 1911, a plant was installed. Rather than further burden its own organization, it let the contract to the Pennsylvania Engineering Works for the complete plant, which was designed, built, and turned over to it in operating condition. The
original Saucon Steel Works, which were put into operation in 1907, consisted of ten 60-ton stationary open-hearth furnaces and one 250-ton hot-metal mixer, a Gray universal structural mill for rolling wide-flange I-beams- and H-column sections, a standard structural shape mill, and a rail mill. In 1913, the Bethlehem Steel Co. added to the open-hearth department of the Saucon Works, six 75-ton open-hearth furnaces of the stationary type, locating them on the east end of the original open-hearth plant, and added to the mixer capacity one 1,000-ton hot-metal mixer of what is known as the German type. The Bessemer converting plant occupies a position east of, adjacent to, and in line with, the open-hearth building, thus making it possible to
connect the track for the transport of the blown metal from the converters to the open-hearth department directly with the track in the open-hearth building running parallel with the furnaces, but back of the charging-machine track. We might point out here that the location of the converters with respect to the open-hearth furnaces in this process is of the utmost importance, because the quick and easy transfer of the blown metal is one of the essential factors of success. The output of this department at present, operating on a straight open-hearth basis, is 70,000 to 75,000 tons of ingots monthly. As duplexing is practiced only part of the time, it cannot be said just what the output would be if the works were operated continuously under the duplexing method; but actual results have shown that for a given tonnage of steel there is a saving of about 65 per cent, in time.
The Bessemer converting plant, the general arrangement of which is shown in Figs. 3 and 4, is contained in two buildings, one known as the mixer-converter building, where the hot-metal mixers and converters are housed, and the other as the bottom house, where the bottoms are made up, dried, ladles repaired, etc. The floors of these buildings are on the same level as the charging floor of the open-hearth building. The mixer-converter building is of steel, and of the usual heavy mill type construction. It is provided with two 75-ton capacity, 70-ft. span, traveling cranes for serving the hot-metal mixers and converters. The converters occupy the west end of the building nearest the open-hearth plant, while the hot-metal mixers occupy the east end.
There are two hot-metal mixers, one of 400 tons capacity, of the type indicated in Fig. 5, and one of 1,000 tons capacity, of what is known as the German type. While these mixers have a combined nominal capacity of 1,400 gross tons, their actual capacity is considerably in excess thereof, since the larger mixer will hold at least 1,200 gross tons of molten iron. The 400-ton mixer was originally built to operate hydraulically, but has since been converted to operate electrically. It is mounted on heavy, cast-iron rocker stands, which furnish tracks for the cast-iron rollers. The two cast-steel rockers serve the dual purpose of a cradle for supporting the plate work and a tire for revolving the mixer on the rollers. The shell, which is semi-cylindrical in form with bulging convex ends and domed roof, with receiving and pouring spouts on the straight portion of the cylinder, is made of 1-in. steel plates. The mixer is lined throughout, to well above the slag line, with 9-in. thick magnesite brick, backed up by 9 in. of good grade fire brick, while the roof has a 13½-in. lining of furnace-roof brick.
The 1,000-ton hot-metal mixer, constituting the other unit of this plant, is interesting on account of its large capacity as compared to former mixers in this country, 600 tons being the limit of capacity up to that time. At the time of making the contract for the building of the mixer, the Bethlehem Steel Co. stipulated that the builder should, before designing the mixer, send his engineers to Germany to investigate both the design and method of operation of the large mixers of that country, the result of which investigation was that the engineers came home and designed the present mixer after the German type, making such alterations and improvements as were found necessary to meet American conditions. (See Fig. 6.) The mixer consists of a cylindrical shell with spherical ends, It is provided with receiving spout on one side and pouring spout on the opposite side. The receiving spout, except when metal is being poured into the mixer, is sealed by a door, which is opened and closed by means by a 7½-h.p. electric motor. The pouring spout is closed by means of a number of flat brick arches held in steel stirrups, except a very small opening for the egress of the metal, thus making it possible to conserve from 90 to 96 per cent, of the original heat of the iron charged into the mixer.
A comparison might be made here between the two types of mixers: In the case of the 400-ton mixer it will be noted that the area of the surface of the metal is large compared with the depth and total volume of the metal, whereas, in the 1,000-ton mixer, the area of the surface of the metal is small as compared to the depth and total volume. This feature also
has its bearing on the conservation of heat. The 1,000-ton mixer is provided with a heating apparatus in which oil, producer, coke-oven, or blast-furnace gas is used. During the investigation of mixers in Germany it was found that, while most of the mixers were provided with a means of artificial heating, nevertheless the artificial heat was unnecessary except in one instance, and, in most cases, the ports for this heat entry were blanked off. At South Bethlehem it has been found to be of advantage, however, to use a small amount of artificial heat. The cylindrical shell of the 1,000-ton mixer is provided with four cast-steel bands, spaced uniformly between the two ends. The two outer bands encircle the cylinder about half way, while the two inner bands form a complete circle. These bands serve the dual purpose of reinforcing the shell and supplying tires on which the mixer rotates on the rollers. There are four groups of 11 cast-steel rollers, 16 in. in diameter with 16-in. tread. Each group of rollers is formed into a cradle by means of heavy side bars, with shafts extending through the side bars and rollers, thus insuring equal spacing of the rollers in the groups at all times. Two lines of heavy struts are provided between the cradles, to insure the action of all the groups as one unit. The weight of the mixer is transmitted directly from the rollers to four heavy cast-iron roller stands, thus producing true roller bearings, and minimizing the friction. It may be worthy of mention here that, with this type of mixer, the center of rotation coincides with the center of gravity, whereas, in the former type, it is necessary to lift the center of gravity about the center of rotation, from which it will easily be seen that the larger type of mixer requires, relatively, considerably less power to operate. In order to insure alignment of the rocker stands, and to tie the mixer more firmly to the foundations, two heavy I-beam girders are provided, extending longitudinally under the rocker stands the full length of the mixer. These girders are provided with shear plates, while the bases of the stands are provided with shear lugs. This feature is also of considerable advantage when lining up the mixer at the time of erection. The 1,000-ton mixer is operated by two 75-h.p. electric motors, either of which is capable of furnishing the required power. The motors are controlled by a magnetic switch-type controller, and are arranged so that they will operate in series during the pouring period and in parallel during the return of the mixer to its normal position, thus reducing the time for pouring and the return of the mixer to a minimum. The motors are placed one at either end of the mixer and are both connected to the line shaft, which is provided with a clutch adjacent to either motor, which may be disengaged in case of accident or for repairs. The 1,000-ton mixer has a surface lining 9 in. thick of magnesite fire brick extending well above the slag line, which is backed with 13½ in. of fire brick, which, with the packing between the lining and the shell, makes a total thickness of lining of about 2 ft. The extraordinary thickness of the lining also tends to conserve the heat of the mixer contents.
The converters, which are of 20 tons capacity, are spaced 40 ft. center to center, and are similar to those described at the plant of the Tennessee Coal, Iron & Railroad Co., with the exception that in this case it was thought desirable to contract the body of the vessel where it joins the bottom, in order to make the diameter of the vessel less, thus bringing the tuyeres nearer to the side walls. This has a tendency to deeper the bath slightly for a given charge of metal; but, on the other hand, brings the bath more directly over the tuyere openings. The converters are operated by means of hydraulic cylinders through racks and pinions, similar to those of the Tennessee Coal, Iron & Railroad Co. The hydraulic cylinders are on a pressure line of 550 lb., which is provided with tank accumulator to balance the pressure. The converters are operated by means of Aiken valves, and the pressure lines throughout are made of double extra pipe. The blast for blowing the converters is furnished by Southwark horizontal cross-compound engine with barometric condenser, with steam cylinders 46 and 84 by 60 in. and air cylinders 84 by 60 in. The engine is designed to furnish 45,000 ft. of free air per minute, at 30 lb. pressure, and is located in the power house adjacent to the open-hearth
plant. The blast is conducted to the converters through a 30-in. main about 500 ft. in length, which is provided with air-relief valve to prevent back pressure to engine. It is also provided with a tank air receiver near the converters to balance the pressure. The air is delivered at a pressure of 18 to 20 lb. from the receiver tank to each converter through an 18-in. air line provided with an 18-in. air valve operated from the pulpit. Heavy steel construction operating floors and platforms are provided about both the mixers and the converters. One 75-ton track scale is provided directly under the pouring spout of each mixer, and another between the converters and the open-hearth furnaces, on which the metal is weighed prior to charging into the converters and again after it has been blown, on its way from the converters to the open-hearth department.
The bottom house is located just south of the mixer-converter building. It has a 16-ft. leanto extending throughout the full length of the building, which is divided into ten equal bays. Five of these bays in the leanto are occupied by the five ovens for drying the bottoms. The ovens, shown in Figs. 7 and 8, have flue connection with a common draft stack, and are heated by firing from the rear with small anthacite coal, for which special grates are provided. Forced draft is furnished by an Eynon & Evans blower on each fire box. The ovens are equipped with Kinnear roller curtain doors and each one has a floor space of 14 by 16 ft. This house
contains a bottom pit, over which the bottoms are made up, a Blake crusher for crushing stone for linings, an 8-ft. wet pan, a 9-ft. dry pan, and the necessary bins and conveyor for handling the raw material. The machinery is driven by a 100-h.p. electric motor. There are also ten ladle rests for the repair of the linings of the steel ladles. For lifting the bottoms on and off the cars and bottom pit, handling the ladles, etc., there is provided a 25-ton electric traveling crane. The burned-out bottoms are brought from the converters, and the newly made up bottoms returned to the converters, on hydraulic jack cars.
The method of operation at the Saucon Works is practically as follows: The molten pig iron is brought from the blast furnaces situated at the Lehigh Works, If miles distant, in trains of 40-ton capacity hot-metal cars drawn by the usual standard-gauge locomotive. Just before entering the mixer building, the metal is weighed on a 100-ton capacity track scale. It is then drawn into the building directly opposite the mixers and is poured into the mixers by means of the 75-ton overhead electric traveling crane. The metal is poured from the mixer into a 25-ton capacity ladle car, weighed on the 75-ton track scale placed in the floor directly under the pouring spout of each mixer, and then transported to the converter, where it is charged by means of the overhead traveling crane. The ladle is of special design with respect to the pouring-spout, the object being to retain as much of the slag as possible in the ladle. For this purpose the spout is made so that the metal will pour through a narrow and rather deep opening. The slag is retained in the ladle for several charges and then dumped out. At some plants skimming is resorted to. This is especially true in Germany, where the ladles of metal are skimmed both before pouring into the mixer and before charging into the converter. After the metal has been blown in the converter, it is poured into 25-ton ladle cars (two of which are in constant use for the transfer of metal when duplexing), and transported by an electric locomotive over a standard-gauge track to the open-hearth furnaces. The hot metal is poured by the overhead traveling crane into the furnace, through a portable spout, which is placed in position by the charging machine at time of charging. Five of the ten 60-ton stationary open-hearth furnaces are used in the duplexing process; the remaining five 60-ton furnaces and the six new 75-ton furnaces are kept on the straight open-hearth practice making steel from the hot-metal mixer iron and scrap. Ordinarily three ladles of converter iron are charged into the open-hearth furnace, one after another, as rapidly as they can be blown. All of the metal is desiliconized in the converter and, of the three ladles of metal constituting the open-hearth furnace charge, the former two have practically all of the carbon eliminated, while, in the last one, about 2 per cent, of carbon is left, to bring about the reaction in the open-hearth furnace. The average open-hearth furnace charge is 40,000 lb. scrap, 15,000 lb. burnt lime, and 95,000 lb. of converter iron. The time required in the open-hearth furnace varies in general practice from 4 to 6 hr., although a single heat has been put through in 3½ hr. At times, recarbonizing is found necessary, and, for this purpose, there is in the open-hearth building a 250-ton hot-metal mixer employed as a receiver for the recarbonizing iron, which is of a special Bessemer quality made from low-phosphorus ores. This metal is poured from the mixer into ladles, and added to the bath in the open-hearth furnaces, as needed.
The Pennsylvania Steel Co.’s Plant
The steel-making department of this company, in which duplexing is carried on, consists of six 75-ton and two 200-ton open-hearth furnaces, two 20-ton Bessemer converters, one 300-ton and one 800-ton hot-metal mixer, and a bottom house equipped with the necessary crushing and grinding machinery, drying ovens, etc., for preparing the material, making up, and drying the bottoms. The plant was built in 1913, with the exception of the six 75-ton open-hearth furnaces and the 300-ton hot-metal mixer, which, previous to this time, were run on straight open-hearth practice. The contract for the 800-ton mixer and the two converters was let on April 19 and the converters blown in on the following December 1, making a record time of 7 1/3 months for the construction of such a plant. As indicated in Fig. 9, the mixer-converter department is situated in the main open-hearth building on the charging-floor side. Extending round about both the mixers and the converters there is a spacious working platform of steel construction, 20 ft. above the ground floor and at the same elevation as the open-hearth charging floor. The molten pig iron, coming from the blast furnaces in trains of 45-ton hot-metal cars, is poured direct into the receiving spouts of the mixers without removing the ladles from the cars. The mixers pour into ladles resting on the ground floor, which are hoisted and charged into the converters by the overhead traveling crane. The converters in turn pour into ladles resting on the ground floor, which are hoisted to the open-hearth charging floor and transported by the overhead traveling crane to the open-hearth furnace to be charged.
The hot-metal mixers are of the semi-cylindrical, bulging-end type, and are tilted by electric motors operating through suitable trains of gears and screws. The control equipment is of the magnetic switch type. The converters, shown in Fig. 10, are placed 42 ft. center to center. They are duplicates of those of the Bethlehem Steel Co., with the exception of the overturning arrangement, which is electrical. Each converter is provided with two 100-h.p. motors controlled by magnetic switch-type controller. Either motor is capable of operating the vessel and there are shaft couplings provided so that either motor may be disengaged at any time. The power is transmitted from the motors through one gear reduction on the motors, a worm and worm wheel and pinion on the worm-wheel shaft to the driving gear on the converter trunnion. Mention is made here of the worm wheel, which has the wearing faces of the teeth lined with 5/16 in. of babbitt metal, which reduces the friction, thus prolonging the life of the teeth. The arrangement of this plant deserves special attention, as
it represents one of the best conditions for economy and convenience of operation which has been attained up to the present time.
General Remarks
The two 20-ton vessels as installed in the plants of the Tennessee Coal, Iron & Railroad Co., the Bethlehem Steel Co., the Jones & Laughlin Steel Co., and the Pennsylvania Steel Co., are capable of producing 100,000 tons of blown metal per month. The benefits derived from the duplex process for making steel have been enumerated in the reasons given for duplexing; but we may say in conclusion that the process has brought about the development of the Bessemer converting plant to a higher state of perfection and efficiency, has created a desire for larger and better hot-metal cars and mixers, and has aided those practicing it to solve some of their problems. Since the process has been practiced in this country for seven years only and is still in an imperfect state, it is hoped that some of the master minds working on it will succeed in bringing about a more perfect stage of development within the near succeeding years, and thus another step will have been taken toward the uplift of mankind.
Discussion
W. McA. Johnson, New York, N. Y.—On discussing this paper I am open to the criticism of “bringing coals to Newcastle,” as I, a zinc man, am bringing new ideas on steel to Pittsburgh. But still the view of an outsider can be valuable to the insider. Any multistage process, where each apparatus operates on its particular part of the work at a high efficiency, constitutes an advance in the state of art. But in multiplicity there can be complication and ensuing loss and inefficiency.
The duplex steel process is not the pronounced success which was predicted for it by its adherents, for several of such plants have reverted to plain open-hearth methods.
If we regard broadly refining processes, such as the Bessemer, open-hearth, puddling, copper refining, lead cupelling, nickel refining, we find that in general refining processes are intermittent and concentration processes are continuous. (This generalization I believe to be original with me; it was communicated to Dr. E. F. Roeber, editor, and appeared as an editorial in Metallurgical and Chemical Engineering, March, 1905.)
Where we desire primarily quality in a metallurgical operation we must put a batch of metal in the furnace, work on it until we get it to the required purity, test it, and take it out; whereas, if we desire primarily quantity we shove ore into a furnace and smelt it as fast as possible, allowing conditions to make a non-uniform product provided only we get tonnage.
From general commercial principles, I believe that the weak point of the duplex process is that the operation is not a money maker unless the plant is kept at 90 to 95 per cent, of its rated capacity, or unless the Bessemerizing is done so often that it is practically continuous. For in some manner the operation should be made continuous and the control on the tonnage should be commercially flexible. The commercial rigidity of having to control purity exactly increases operating costs without a corresponding gain. Conversely, the chief reason for failure of “steel from ore direct” is that it makes a final operation continuous, which should be naturally intermittent.
Arthur G. Mckee, Cleveland, Ohio.—I would like to ask a couple of questions in regard to this paper, and in asking them I appreciate the difficulty that Mr. Furst has encountered in preparing a paper of this sort and in getting the information, which really, to my mind, is the important information to the owner of a plant for the producing of steel, and also to the man who is responsible for the building of such a plant.
In the first sentence is stated:
“ The reasons for manufacturing steel by the duplex process are, briefly: saving of time; increasing output for capital invested; and avoiding the difficulty sometimes experienced in obtaining scrap.”
That is briefly stated, surely, but how effective is such a plant in giving the results referred to in that statement?
At the close of the paper, Mr. Furst remarks:
“The benefits derived from the duplex process for making steel have been enumerated in the reasons given for duplexing; but we may say in conclusion that the process has brought about the development of the Bessemer converting plant to a higher state of perfection and efficiency, has created a desire for larger and better hot-metal cars and mixers, and has aided those practicing it to solve some of their problems. Since the process has been practiced in this country for seven years only and is still in an imperfect state, it is hoped that some of the master minds working on it will succeed in bringing about a more perfect stage of development within the near succeeding years, and thus another step will have been taken toward the uplift of mankind.”
Does the process make, as claimed, a larger tonnage per day, and approximately how much? Does it reduce the cost per ton? Does it increase the production per dollar of plant investment, and if so, how much? And, also, another very pertinent question: How does this process affect the quality of the product, if at all?
Mr. Furst doubtless does not have an opportunity to get these facts, but can somebody else enlighten the Institute, so that we can know from actual experience in operation what conditions justify the installation of the equipment required for the use of this process; what profit and other advantages will be obtained; in short, whether it has justified the claims made for it.
Henry D. Hibbard, Plainfield, N. J.—Regarding Mr. Johnson’s remarks, when you come to make a finished product, such as steel, you want to take a batch of material and keep it in hand until it is in proper shape and then cast it. Where you are running for a crude product, as in the case of the blast furnace, it is all right to run continuously, but when you want a finished product, to try to avoid taking a batch and keeping it under control until it is done, will be a mistake. In the open-hearth furnace we take a charge and keep it until it is done; in the Bessemer, we have, to some extent, to catch it on the fly; but in each of these cases the charge is treated until it is as near as we can get it to what we want when it is cast. Ever since the Bessemer process was established, there have been proposals to make steel by treating iron with blast as it moved forward, and some of the pyrotechnic displays occasioned thereby have been very wonderful. Such plans are all failures. Within a few years patents have been taken out for processes of that description, but I think no progress has been made with any of them.
As to the output of the duplex process, I think it varies from about three open-hearth heats of finished steel to about 20 heats in 24 hr. There are furnaces in this country that have produced over 1,000 tons of steel a day and have kept it up for a month. On the other hand, three open-hearth heats of 50 tons each would give an output of 150 tons a day.
Bradley Stoughton, New York, N. Y.—As to the question whether the duplex process increases the output, it is possible to answer this in either of two ways:
The output of the duplex process, when properly operated, is much more than the output of the open-hearth process alone, but is not so great as the combined output of the open-hearth process and the Bessemer process each working independently of the other. This, however, is not the point really involved, because the output of the two processes working independently has now no longer the same industrial possibilities, because we have not in this country sufficient Bessemer ore to operate the Bessemer process economically and up to its capacity. But when the two processes work together they can use ores now available in this country in very great quantities, which are above the Bessemer limit, and can produce a good quality of steel.
As to the question whether the interest on the investment required to install the duplex process is more than compensated for by the increased profits, we can answer this by inference through our knowledge that several companies which are wisely managed, and which years ago abandoned the Bessemer process, have recently re-installed converters in order to employ them in the duplex process.
I believe that the duplex process has very decided commercial and industrial advantages, and hope that those who are operating it will co-operate with this Institute by coming forward and exchanging their information with others in order that benefit may be accorded to all.