Page:EB1922 - Volume 31.djvu/631

Rh REHEATING FURNACE

ARMOUR PLATE MILL

SPECIAL USE OUTSIDE OF REGULAR INDUSTRY

SLABBINQ MILL

BLOOMING MILL

BLOOMS

FORGE

> [ FORGE ^.

I FURNACES

v!V

-HAMMER

AIR STEAM

-PRESS HYDRAULIC

-BULLDOZER

MOTOR DRIVEN

SEAMLESS TUBES HOT FINISHED A

I

POLISHING MILL

t

REDUCING MILLS

ROUGH SEAMLESS TUBES

t ,

I ""

UNIVERSAL MILL

\

UNIVERSAL PLATES (rf TO 6rf WIDE *"TO f THICK)

PLATE MILL

1

SHEARED PLATES

SPECI/ (QREY. PU

'

H-GIRDERS.SP


 * ir

BIG SHAPE MILL OR RAIL MILL

SHAPES. RAILS /SHI LARGE SECTIONS / , 1 Pt

r \FURN

L MILL \^^ >PE.SACK) SHEE

J

=CIAL SECTIONS

1 BILLET MILL SHEET BAR MILL

- < T >

MEDIUM SHAPE MILL

-^ Y / \MEDIUM SHAPES

/ BILLET \

"rXSBF Blu f s


 * w ' 1 ^

ACES/ ^FURNACES/

r MILL ^ 1

f SHEET MILLS 2O TO 10 DIA. WIRE MILL ETS f t SMALL SHAPES. SQUARES. ROUNDS WIRE BANDS, ETC.

FIG. I. Steps in the Process of Making Various Forms of Steel.

guards ; they roll either blooms or slabs. Plate-mills carry cylindrical rolls to produce sheared plates (or plates which are subsequently sheared to required width), but may have in addition two sets of vertical rolls driven from the main pinion housing, to produce universal plates which require no shearing, both sides of the slabs being rolled. Both forms may be of the three-high continuous run- ning or the two-high reversing type. Their roll diameters are 24 up to 42 in. The three-high or Fritz form of plate-mill is often called the Lauth type and is characterized by the fact that the middle roll is smaller and not direct-driven, but rotated by friction from the upper or lower roll. For large blooming-mills preference for the reversing drive was shown in the decade 1910-20. Three-high bloom- ing-mills were seldom built in the larger units because of clumsy accessories. For the heavy plate-mills, also, the two-high reversing type was preferred. For small knocking-down or cogging-mills and the smaller plate-mills, the two types were in competition, with no apparent superiority of either system.

For driving continuous mills electricity was preferred to the steam-engine. The uniflow steam-engine found favour up to 3,000- H.P. units, but installations were few. Where the effort was to bring about a complete electrification of the plant, steam-engines proved unpopular, possible economy being counterbalanced by complica- tion of maintenance and other administrative considerations. For the reversing drive of large units, requiring loads up to 20,000 or 25,000 H.P., the electrical drive was not necessarily in the ascen- dency. The high initial cost of the motor generator flywheel set with direct-current motor directly connected to pinion and mill was made the chief argument against universal adoption of electricity, and numbers of old plants were reluctant to change their somewhat obsolete steam equipment. In America only a few engines as large as 25,000 to 30,000 H.P. (Weirton and Lukens) were installed in new work, and in England large vertical engines were built. The electrical units, however, increased considerably in number and size and considerable progress was realized in the matter of mano3uvring capacity, in standardization of winding and accessories, in records of output and efficiency of running. In 1920 the electrical industry was aggressively working on betterments, while the partisans of the steam-engine rested on past laurels. Parity existed on all points except first cost of installation. Even for smaller mills of the reversing type electrical drives were built, such as 24-in. mill (Mark, Indiana Harbor), 26-in. mill (Atlanta, Ga.). Two-high reversing plate-mills also disputed the field with the three-high type in the medium-sized equipment, and latest universal-mill installations were of the revers- ing type electrically driven. The largest mill for plates, 192 in. wide, at Lukens, Pa., which was completed in 1918, was of special design, reversing, and steam-driven. (Iron Age, Jan. 2 1919.)

In shape, billet and smaller mills no revolutionary change was

made. In shape- or rail-mills great subdivision of rolling-passes into individually driven stands proved to be an exaggeration, and later installations concentrated the drives. The use of a second reversing roughing-mill, however, bade fair to become standard, in relieving the burden of the first blooming-mill and in preparing quickly for the finishing stands. Billet and sheet-bar mills, usually of the continuous type, were standardized into two units, the 24-in. mill of four to six stands and the 2i-in. mill of six stands. Patented mills for special beam shapes having wide flanges were built under Grey patents in Differdange, Luxemburg, in 1904, and in Bethlehem, Pa., 1908 and 1915, and under Puppe patents in Peine, Germany, in 1914, and Sack patents in Rombach, Lorraine, in 1912. Mechanical solutions of the reversing problem were attempted by the Lamberton mill or the Fawell mill but were not put into any wide use. Sheet-mill construc- tion changed little except that the electric drive became universal. The design with two overhung flywheels on pinion shaft proved efficient and final. The reduction ratio showed a tendency to in- crease from 8 to i to 12 to I.

Billets (in.) 5x5 to 2x2

Bars (in.) below ijwi

Bloom ingots(in.) 12x12 to 24x24

Blooms (in.) 6x6 to 12x12

Sheet bars (in.) 15x2 to 8xJ

Slab ingots (in.) 20x8 to 40x16

Slabs (in.) 10x3 to 36x10

Plates up to 190 in. wide

The concentration of production in large well-balanced plants with adequate resources and sales organization permitted a logical subdivision of the rolling-mill programme with a subsequent reduc- tion of production cost. The smallest bloom section, 6x6 in., had a tendency to grow toward 8x8 in., as some experts claimed that 50 sq. in. was the economic limit of the range of a large mill. To reduce the time required for roll changing, complete spare housings, com- pletely mounted, came to be good mill practice, these being dropped on the shoeplates by the cranes. In some specialty plants sometimes two or three housings were changed together.

Furnaces. The development of soaking, reheating and annealing furnaces was influenced by the increasing price of fuel and consider- able efforts were made to boost heating efficiencies. In Europe gas- firing with recuperation and regeneration of waste heat was the favourite, especially because producer-gas firing was much used and remarkable results achieved. In America continuing shortage of natural gas for industrial purposes in regions such as the Pittsburgh district made a substitute market for crude oils, coke-oven gas and powdered coal. Especially since 1915, the use of powdered coal developed to a surprising degree for all kinds of metal-heating appli-