Fig. 2.—General Arrangement of 12-in. Merchant and Guide-Mill Plant. (Thomas Perry & Son Ltd., Bilston.)
A, First roughing rolls. B, Second ditto (C, Guide rolls for ovals or diamonds. D, Ditto for rounds or squares. E, Driving pinions. Engine, 30 in. × 22 in. cylinder, direct-coupled to rolls. Runs from 100 to 180 revolutions per minute to suit work. The shears are used for cutting the smaller sections the hot saw for cutting the merchant iron.
Fig. 3.—12-in. Merchant Guide-Mill and Engine. Four-set mill.
A, B, Three-high sets. C, Works either three-high or two-high; a, being a dummy roll. D, Two-high set (guide rolls). E, Coupling pieces. F, Housings. G, Pinions. The mill is capable of rolling rounds, squares, flats, angles, tees or similar sections by changing the rolls. The guide rolls D are used for small sections, and the second set B for merchant iron (larger sections).
pass, An alternative is the three- the rolls seldom exceed 30 in. in diameter, and thely are chilled. high min, in which three 1.0115 are The size of sheetjmills has within the last few years een consr er-7*" I
wig d H h 1 . h h ably increased (since the introduction of steel sheets), and all new Q use - ere the P ate 15 run t mug mills are made from 28 to 30 in. diameter. The mills are of the two- Q gg the l0Wer rolls and back through the high type and are almost the only instance of the retention in 4 upper ones, so that there is no reversal present practice of the non-reversing mill. It is found more con§ l|, ='.=, 'i of direction of the Hlill as 3 Whole venient in this case than the reversing or the three-high mills, because two men roll two ieces at once one handing over a sheet S N “ b t the lower and u er rolls draw - - - p cf wgg u PP » just rolled to his fellow Just as the latter has entered a sheet between G' the P13te5 U1 0PP0S1tC d11'eCf1011S (563 the rolls on his side. Strip-mills are a smaller but similar type, also IRON AND STEEL, § 129). used for rolling the thin narrow strips required for the hoops of / barrels, ties for cotton bales, &c. The details of these mills cannot Plate-Mills.-In Great Britain plate- be discussed here, nor the numerous arguments in favour of the mills are generally two-high reversing
mills, in America three-high mills. Another difference is that in British practice two stands of rolls are used, in America one only. In the two-stand design there are two sets of rolls coupled endwisa, one set being grain-rolls for roughing, and the other chilled rolls for finishing. Sets of live rollers conduct the plates to and from the separate rolls. The plate-mills proper are those which roll from § in. to about 2 in. thick. Armour plate-mills are a special design for massive plates and sheet-mills are for thin plates or sheets having a less thickness than § in. Armour plate-mills are of twohigh reversing type usually, with forged steel rolls. They are of immense proportions, the rollers ranging from IO to 14 ft. in length, by from 3 to 4 ft. in diameter. In sheet-mills, on the other hand, two systems. English practice retains the two-high reversing mill for all heavy work, the exceptions being those just noted. American practice retains the three-high mill.
Groor/ed Rolls.-In the mills designed for rolling various sectional forms the same distinction between two-high and threeihigh remains, but new problems arise. By “sectional forms IS meant all those which are not plates and sheets, such as bars of round and square section, angles, channels, rails and allied sections (fig. I), for the production of which grooved rolls are required. The shapes and proportions of these grooves are such that reduction is effected very gradually. When metal is squeezed or hammered, one effect is to spread it laterally, since the metal cannot be appreciably squeezed in on itself. But the lateral extension is very muc less than
