ROLLING-MILLS. 



397 



direction, and returns in an opposite direction between 

 the middle and the top roll. 



While a majority of existing rolling-mill trains are 

 driven by steam-engines through gearing, new plants 

 are generally directly connected; that is, the engine 

 giving the motive-power has its shaft coupled to the 

 driving-shaft of a roll train, which revolves at the same 

 speed as the engine, and in some cases the engine 

 drives a muck train direct, and is geared to run a mer- 

 chant train at higher speed, or vice versa. In large 

 plants a reversing engine is employed which changes 

 its motion with each pass through the rolls. Some 

 of the older rolling-mills receive all or a part of their 

 power from water-wheels. 



Prominent specialties of manufactured iron form the 

 bulk of business at a number of rolling-mills. Among 

 these are plate, sheet, skelp, bar, nail-plate, wire 

 beams and angles, etc., and the practice of making 

 one or two specialties is becoming more common con- 

 tinually. Smooth or grooved rolls of various design or 

 sizes are required for each purpose, and many mills 

 require a large stock of extra rolls to fill the orders of 

 different sizes and shapes. For certain purposes chilled 

 rolls (made of iron cast in chills so as to give a hard 

 surface) are employed. These are principally used for 

 cold rolling or finishing, and are often highly polished. 



Nail-plate is rolled from 12 to 20 inches in width, 

 and of thickness required for different sizes of nails, so 

 that the plate can be sheared transversely into bars 

 which are fed into machines which cut nails, preserv- 

 ing the grain of the iron. 



Plate-iron for boilers or ships is made in smooth 

 three-high trains of large diameter, and as the weight 

 of some of the plates is great the pile is of correspond- 

 ing size. The best brands of boiler plate-iron are 

 known as " C. H. No. 1," and "flange" iron C. H. 

 being an abbreviation for charcoal hammered, and in- 

 dicating that the iron was mado witli charcoal in sink- 

 ing fires, hammered into blooms, and rolled out into 

 bars which were piled for plate-iron. The U. S. secre- 

 tary of the treasury publishes in the rules governing 

 the construction of boilers for steam-vessels provisions 

 that the tensile strength shall be stamped on plate, and 

 that the ductility shall be as follows: "Iron of 45,000 

 pounds per square inch tensile strength shall show a 

 reduction of area of 15 percent., and each 1000 Ibs. 

 tensile strength shall show 1 per cent, additional con- 

 traction of area up to and including 55,000 Ibs. tensile 

 strength. Iron of 55,000 Ibs. tensile strength and up- 

 wards showing 25 per cent, reduction of area shall be 

 deemed to have the lawful ductility." 



Sheet-iron has been rolled to such small gauje as to 

 be thinner than paper ; this was merely experimental 

 and required a superior quality of iron. Most of the 

 sheet-iron is made from metal above the ordinary 

 character. There is no defining line between sheet- 

 and plate-iron, the terms being affected as much by 

 the purpose for which the product is used as by its 

 thickness; but iron under 3-lGth inch is generally 

 considered as sheet- and above that thickness as 

 plate-iron. 



Skelp-iron is a term applied to long, narrow sheets 

 of iron rolled for the purpose of making wrought-iron 

 tubing or flues, of which large quantities are demanded 

 for plumbing, gas-fitting, water or gas supply, oU or 

 gas wells, etc. 



The manufacture of beams, channels, angles, and 

 special shapes is rapidly extending, and demands a 



flant of large proportions and powerful machinery, 

 'ire-proof construction, bridge-and roof-building, ship- 

 building, and modern architecture constantly call for 

 new shapes and sizes. I beams up to 20 inches in 

 height have been rolled. . The development of this 

 specialty is the growth of but a few years, but it 

 promises to continue to increase both in quantity and 

 variety of product. 



For the statistics of the production of Rolled Iron in 

 the United States see the end of article Ino.\. 



Wire Rods. The general features of puddling, 

 heating, and regenerative furnaces, squeezers, ham- 

 mers, roll-trains, etc., are given in the ENCYCLOPEDIA 

 BRITANNICA. There are numerous improvements pe- 

 culiar to American practice which apply to various 

 specialties, but the advance has been more marked in 

 the rolling of rails, particularly in connection with the 

 Bessemer steel-works. In another specialty American 

 practice has been remarkably progressive, viz., the rolling 

 of wire. The requirements of this country arc not less 

 than 350,000 tons of wire rods per annum. Since on 

 an average 125,000 to 150,000 tons fire imported, there 

 is a balance of at least 200,000 to 225,000 tons to be 

 provided for by American works. These possess about 

 30 trains of roll, some of which roll small iron and 

 merchant shapes during a part of the time. Steel wire 

 rods are made a specialty by about a dozen firms. 



The iron wire rod trains and modern steel rod mills 

 do not work under the same conditions. For both rapid 

 rolling is desirable, but for different reasons. With the 

 first it is aimed at on account of its influence upon the 

 character of the product ; with the second, for the 

 effect it has upon the cost. In order to reduce the 

 number of passages through the wire draw-plate, rods 

 for wire-drawing must be rolled to small dimensions, 

 while avoiding anything that injures the quality of the 

 iron. Speed in rolling tends to completely utilize the 

 welding and to allow of making the small sizes aimed 

 at before the wire grows too cool. If this temperature 

 should be reached before the last pass, the transforma- 

 tion of the previous oval into round cannot be effected 

 without affecting the molecular structure of the metal 

 and robbing it of certain properties. The iron will be 

 hardened, and in cooling will not be covered by the 

 blue oxide but by reddish oxides. In order to manu- 

 facture No. 7 and No. 8 B. W. gauge, it is therefore 

 try to increase the speed of rolling and to be 

 content to roll pieces of moderate length, according to 

 the softness of the metal treated. 



It is a different matter with steel wire rods, which 

 are rarely smaller than No. 5 B. W. gauge. With 

 them the question of maintaining quality is not the 

 ruling one. Steel is more easily rolled than iron, and 

 in this ease high speed is aimed at chiefly to reduce 

 cost of labor and general expenses. 



The oldest wire rod mill, the English train, consists 

 of five stands of rolls in a line, viz., an 8J- to 10-inch 

 three-high roughing set and four sets of 7- to 8-inch 

 continuous rolls. In this system the speed of the rolls 

 is limited by the skill of the workman. Its defects 

 have led to its being generally replaced by what the 

 Americans call the "Belgian" system. In it the 

 roughing train is separate, having a speed below 200 

 revolutions, being a set of three 12- or 13-inch rolls, 

 with the pinions placed at the outer end, in order to 

 interfere less with the finishing train. The latter, 

 placed parallel to it and 40 to 50 feet from it, consists 

 of a stand of pinions and five to seven two-high sets, 

 which may be driven at greater speed. 



In some mills a further step has been taken. In- 

 stead of increasing regularly the size of all the finish- 

 ing rolls, those or the two last sets have been 

 increased half an inch, by which the corresponding 

 passes, leaving injurious loops of wire between the 

 last two, have been diminished. 



An essentially American train is arranged to roll 

 4-inch blooms about 4 feet long, which are directly 

 converted into rolls of wire several hundred feet in 

 length. It suppresses one reheating, the loss, the cost 

 and the waste of oxidation which that implies. This 

 idea necessitates certain special arrangements. The 

 passage from one set of rolls to the next must be 

 prompt. Two to three blooms pass per minute, and 

 00 to 100 seconds suffice for the complete reduction 

 of each one of them. 



A train resembling the above, running since 1884, 

 used 4-inch steel blooms weighing from 125 to 130 Ibs. 

 In one week, making 11 single turns, the mill rolled 



