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were marketed for reducing flow resistance and waste of gas. Waste- heat boilers were more generally installed, but not universally adopted because of their interference with concentration and general electri- fication of plants. Marked superiority or inferiority was not shown for the tilting construction of furnace when tested by use beside the stationary type. Natural gas disappearing in America, producer gas was the more generally adopted fuel. Powdered coal was tried with some success but without proved superiority ; one difficulty was that checker chambers got clogged by ashdust. By-product tar and crude oil proved fuels well suited for the purpose if available at low price and in large quantities.

Electric Steel Furnaces. The electric steel furnace for refining and melting iron and steel developed to a surprising extent in the decade 1910-20 in size and in number of installations. It proved ideally suited for quality products and high-grade materials, because no complication through fuel medium exists and because atmosphere and temperature are attainable practically at will. From soo-lb. capacity, single furnaces were built to 40 tons, with most of them of 5- to 8-ton capacities. (For electric furnace statistics, see Iron Age, Jan. I 1921 .) Of the 960 known electric steel furnaces in existence in Jan. 1921, 356 were in the United States, 150 in England, 100 in Germany, 69 in France and 43 in Canada. Of the total, 308 were Heroult arc furnaces, 102 Rennerfelt induction furnaces and 90 Greaves-Etchells furnaces. The electric furnace was adopted for making metal mixtures, ferro-alloys, special steels of high quality in large amounts-j-strict repetition being possible in an absolute positive way. A disadvantage was that the metal is not at rest but always in motion, through electric or magnetic influences. Though agitation was often desirable, the action hampered the separation of the slag and the rising of impurities out of the molten mass. A remedy for this was repeated skimming of slag and careful super- vision. One unusual utilization of the electric furnace was the making of pig-iron out of scrap, especially in the United States, to supply deficiencies in the amount of low phosphorus pig-iron, particularly in the manufacture of ordnance. It amounted to a synthetic recon- version of steel into pig-iron. Fine coke was added to the slagged refined scrap for carburization, and the method promised to be com- mercially feasible in regions having electric power but little local fuel available and situated so that delivered pig-iron was high in price. For deoxidation in the refining process and for recarburization, ferromanganese and spiegeleisen retained their popularity in spite of high prices under erratic market conditions. In Europe pre-heating, often pre-melting, of the addition was the current practice, to save in the amount needed and to accelerate effects. In America the wasteful method of cold additions prevailed. Ferrotitanium, with carbon or carbon-free, was used, as well as ferrosilicon and aluminium in small quantities. Some steel plants made additions in the ladle, others finished the operation in the furnace.

Steel-making Operations. The outstanding feature of steel- making operations was the recognition of splitting the refining process into two phases, or the two-slag method, to increase production and to lower production costs. The efforts of Bertrand-Thiel and Talbot recognized in effect this principle; and duplexing and triplexing were only operating variations of the same principle, to remove the im- purities of the pig-iron stepwise in the furnaces best suited for each purpose. Thus sulphur and manganese pass out in the mixer; silicon and part of the carbon in the converter; the rest of the carbon and phosphorus in the open-hearth furnace; additions were made and alloys were added in the electric furnace. The plant necessitated considerable equipment, but it secured ease of operation, exact control of results and made possible quantity production. Below 1 ,600 tons per 24 hours, savings in operation were regarded as hardly possible, as in slack market periods overhead expense was too large. During the World War about 10 duplexing plants, refining in an acid converter and finishing in basic open-hearth furnaces, were built in the United States under the pressure created by an ammunition famine. Electric duplexing plants (meaning melting and preparing in open-hearth furnaces and finishing in electric furnaces) were built in large numbers, offering a special-quality product on a large scale.

A number of new independent efforts were made to produce steel direct from the ore without the interpolation of the iron blast fur- nace, but none could be said to have been proved feasible on a scale beyond that of the laboratory.

The problem of casting crude steel, particularly the ingot problem, received close study. The mould may be stationary, located in pits, or put on railway bogies moved on tracks by locomotives. Both systems have their field, the former being more suited for small plants. The sizes of the ingots varied from 1,000 Ib. to 6 tons. In America 6,ooo-lb and 8,ooo-lb. ingots were in wide use, while in Europe 4,000- kgm. to 5,ooo-kgm. sizes were adopted in large up-to-date plants. To facilitate the stripping operation, that is the separation of mould from ingot, about 80% of all moulds were made slightly conical with top smaller than bottom. Most of the pouring was done direct into the mould from the ladje, some by attaching to the ladle a little dished pan to break the jet and to produce a quiet overflow pouring, while in another class the metal flowed upward from the bottom by means of a special riser connecting through refractory channels with the several moulds. About 20 % of the steel-makers used the conical mould that is larger at the top than at the bottom, and in some cases a refractory or heated top was placed on top of the mould to secure

better results; these moulds require a tilting-over to allow for the stripping. All these mould forms were evolved by the study of the cooling of steel in ingot form and the defects occurring in the metal the volume shrinkage due to change of physical state from liquid to solid ; cooling by strata ; crystallization and segregation phenomena; inclusion of solid and gaseous impurities, called blowholes, piping, sonims, etc. One type of ingot mould which was well received in America provided a bulk of metal in the lower part, thus to absorb more heat from the lower strata of the molten steel and leave the up- per ones as the last to freeze or solidify and afford an opportunity for the segregation of gaseous and solid impurities.

The Shaping of Steel. Rolling-mills (used if the demand for a product is large and if its shape lends itself to a continuous process, like rails, angles, plates, bars, etc.) and the forge-shop (if the shapes to be produced are complicated, short in length, unsuited for the rolling-mill), both change the shape of the metal heated at high temperature, about 2,000 to 2,300 F. Both require finishing de- partments to straighten, shear or bundle the rolled product or to clean off the fins, rough off the unevenness of the forging operations, and they may need annealing and pickling facilities to improve the quality of the product. A special process of milling the top and bot- tom of rail blooms, to remove cracks and roughness from the semi- finished steel and also surfaces decarbonized in the heating furnaces, was put into use at the Lackawanna mills in America and resulted in a reduction in the number of finished rails classed as seconds.

In the period 1908-20 the development of the rolling-mill was influenced, first, by the great manufacturing principles of concen- tration and specialization, and, second, by the electrification of the motive power. Concentration demanded large production in one unit and suitable equipment to attain that aim; in other words, mechanical devices in preference to hand operation. Specialization was applied to the shape to be rolled as well as to the mill used for production. Standardization of rails, beams, and angles, the reduc- tion of the number of profiles, and the simplification of shapes were consequences, as well as the installation of mills for specific purposes. The application of these rational principles was accelerated by the use of the electric motor. The advantages were recognized about 1905, but the next 15 years brought their practical realization. The numerous little steam-engines disappeared and the electric motor revolutionized the handling of the material by cranes and overhead trolleys as well as the mill accessories, like tables, skids, transfers, etc. The first step was the creation of central power plants where electricity was generated either in turbine or gas-engine generators, preferably with the help of the surplus gas from the blast furnace. Many steel plants in 1920 were equipped with 20,000- to 4O,ooo-K.W. power stations. The second step was the development of speed-re- ducing devices made necessary by the high speed of electric motors. The advance of the gear-cutting industry and the advent of spiral- type teeth, single or herringbone, and the development of new types of teeth giving less wear, more rolling surface, and, later, the use of special hardened, heat-treated steels were eagerly taken up by the designers of mill machinery to increase the quality of their product. Reduction gears transmitting up to 5,000 H. P. came into daily use, and the ratioof 10 or 12 to I in one reduction gave satisfactory ser- vice. The third step was the development of speed-regulating de- vices, especially in connexion with alternating-current motors, to secure efficient operation for variable conditions. The fourth step was the solving of the load problem of large, intermittently operating motors, reversing their direction of rotation by means of the motor- flywheel set advocated by the Austrian engineer Ilgner in connexion with suitable controllers of which the Ward-Leonard system was the prototype. Much work and inventive genius were concentrated on these difficulties to bring about in less than 15 years the high effi- ciency and great safety of operation by electricity of steel-mills. The development of the rolling-mills by 1921 is shown in the diagram.

A rolling-mill proper consists of its motor (steam-engine or elec- tric motor), a universal coupling (speed-reducing drive or not), pinion stand transmitting power to all rolls by means of toothed pinions, together with spindles and couplings, and one or more roll stands solidly bolted to foundation shoes. A roll stand has two hous- ings with adjusting mechanism and is fitted with two or three rolls and called either two-high or three-high, according to the number of rolls. But rolling-mills bear various other designations that are confusing. Sometimes they are characterized by their roll diameter (a 2O-in. mill or a 35-in. mill) ; sometimes they are called after their inventor (Mannesmann mill, Lamberton mill); sometimes they get their name from the product (blooming-mill, plate-mill, wire-mill) ; sometimes their direction of operation is judged most important and then they are called reversing or non-reversing mills. Slabbing- mills are large mills with two horizontal rolls of 30- to AO-in. diam- eter and two vertical rolls of 24- to 32-in. diameter, built to roll slabs, which have a rectangular section. They roll the four sides of the slab without the need of handling or tilting. They are expensive in installation, requiring two reversing motors developing 15,000 and 10,000 H.P. respectively. They are seldom provided for in new

C" its (perhaps the latest installation being that in the Gary plant, iana, 1910) and were superseded either by universal-mills or blooming-mills. Blooming-mills have two horizontal rolls of 24- to 4p-in. diameter, mostly of the reversing type equipment, with manipulators for the mechanical turning-over of the ingot, and side-