The Universal Mill is a type of roiling mill with two horizontal rolls and two vertical rolls designed to turn out a finished product with one rolling. The Grey form of this mill is shown in Fig. 3. The passes are made of such shape as produce almost any dissensions of a given form. Two stands of rolls are used, one di rectly behind the other. The first gives the preliminary shaping and the second stand finishes.
The rolling mill establishments consist of a series or (train* of several mills. They are ar ranged according to the class of product turned out. In the mill the sets of rolls are set one beyond another, and the metal being worked passes-continuously in one direction, coming out tit the further end of the works in a finished condition. The mills which make small rods and wire usually have their stacks of rolls set side by sick in a rank. The bar coming 'fro'm one pair of rolls is caught by the tongs of a workman and curved into a loop, passing back through the adjacent pair rolls. Apother workman catches it and directs it through the next mill in the rank, and thus the one rod may be passing through three or four pairs of soli at the same time. This is called a °looping! mill. It is Adapted only for work of small di. mensions. The general purpose mill or emer. chant° mill, as it is Called, intended to do roll ink or order, is generally a combination of the continuous mill and the loop mill.
Rolling mills are popularly classified by their ultimate product: as the blooming mill (making only the blooms for other mills), billet mill, hoop mill, wire mill, sheet mill, tube mill, etc. The products of rolling mills are of two descriptions, semi-finished and finished. To the first .group belong blooms, slabs, billets and bars. To the second class belong rods, bands and hoops, structural shapes and rails, plates, sheet.,' skein, nail plates, wheels, axles, tires, etc.
The rolls are driven by powerful steam engines, or by electric motors—the latter form of drive coming more and more into favor ex cept for the heaviest work. In mills which run. continuously in one direction the fly-wheel is universally in use to store energy when metal is not actually passing through the rolls. In the reversing type of mill the fly-wheel cannot be used, as the engine must be brought to a full stop and reversed with each pass. For this reason the engines to run reversing mills must be extremely powerful. The of electric drive-are: (1) economy due to the of action and high efficiency of all electric machinery at all loads from the lowest to the maximum; (2) reduced floor space; (3) ease of control; (4) uniform drive with a uni form. current; (5) smaller Initial cost. The motors are coupled direct to the mill, and the speed can be varied from 190 to 270 revolutions per minute. However, in sheet mills, where the speed is cut down to 30-35 revolutions per minute, direct coupling has been proved entirely satisfactory— ; /n" the manufacture of rails, the ingot of cast metal is placed in the soaking pit and heated tQ a white heat. It is then taken to the bloom ing mill and passed through Ole blooming rolls seven limes and reduced to a bar of a section nine inches -square- and 15 feet long which is subsequently sheared into_ two _or three pieces, according to the length of the desired rail.
These pieces called "blooms! are then heated in the bloom furnaces from which they are taken to the rail mill, which consists of a series of grooved rollers arranged in three sets — the roughing rolls, the intermediate rolls and the finishing rolls. These rolls are placed one beyond the other and extend over an interval of about 900 feet. The hot blooms are passed through them successively. Through the rough ing mill the bloom is passed five times and reduced approximately to the section of the de sired rail. It is then passed through the inter mediate rolls five times and brought still closer to the desired section. It is now placed upon a cooling table for a period of time ranging from 45 to 90 seconds, depending upon the weight per pound of the rail and then passed through the finishing rolls and brought to the exact sec tion required. After leaving the finishing rolls the rails are cut into lengths of 30 to 60 feet, as required, then passed through the cambering rolls where they receive sufficient camber to en sure of their remaining true and straight when cooled. Rail rolling mills have a capacity of turning out from 7,000 to 8,000 rails per day, requiring about 3,000 tons of metal. See RAILS, MANUFACTURE OF.
The largest rolling mill in the world is that recently completed for the Lukens Iron and Steel Company of Coatesville, Pa. It is 204 inches in width, capable of rolling plates up to 192 inches (16 feet) in width. In pattern it is a four-high mill, the two middle rolls being the working rolls and the top and bottom rolls be ing merely backing-rolls, running in contact with the working rolls to stiffen them against bending. The working rolls are of a chilled iron 34 inches in diameter and the bacldng rolls are of cast steel 50 inches in diameter. The mill is of the reversing type and the rolls of the 'balance& order, the screw-down rig being operated by two 150-horse-Power motors. The rolls are driven by a 46-inch by 70-inch by 60 inch twin tandem compound condensing steam engine.
The normal production of rolled steel in the United States is best assessed from the output of the year 1914, many of the mills since then having been given over to the making of muni tions. In that year the product was 3,500,000 tons of rails; 3,000,000 tons of plates; 3,000,000 tons of sheets; 2,500,000 tons of wire rods; 2,500,000 tons of structural shapes; 1,000,030 tons of skein; 1,000,000 tons of miscellaneous; 8,000,000 tons of merchant mill products—a grand total of 24,500,000 tons. (See PITT, MANUFACTURE OF, and WIRE, MANUFACFUREOZ). Consult Charuock, G. F. 'Mechanical Tech nology) (London 1915); harbord, F. W., and Hall, J. W., 'The Metallurgy of Steel' (2 vols., New 'York 1916); Kind], F. H., Rolling Mill Industry' (Cleveland, Ohio, 1913) ; Asso ciation of Iron and Steel Electrical Engineers, 'Proceedings llth Annual (Phila delphia 1917).