Prior to its partial demolition, the 48" Mill consisted of several open-air slab yards, a reheating building, a shipping building, and the 48" mill building. These structures were laid out to fit a triangular shaped marshy depression on the upstream end of the plant. Extensive fill and foundation work was needed to support the weight of the complex.
Remarkably well preserved, the 48" universal plate mill and reversing engine are extremely rare. It has always been driven by its steam engine, and operated without substantial modification from 1899 to December 29,1979. When construction plans were announced, the mill was to be the largest of its class ever built. Comparison of the machinery with surviving blueprints, and with photographs of the mill when it was installed suggests that minor changes were made in the 1930s, 1940s,and early 1970s. The horizontal screwdown gear system probably date to the first set of changes; the current pulpit, the hydraulic manipulator , an emergency steam cut-off valve, and the safety platform are part of the latter modifications. The slab yards, reheating furnaces, shear building, and shipping building constructed in 1899 are no longer extant.
The 48" Universal Plate Mill was originally designed to roll universal plate 46" to 20" wide, 5/16" to 2" thick, and up to 150' long direct from slab ingots. Subsequent modifications permitted the mill to roll substantially narrower and a bit wider plate. The steel was worked by a set of horizontal rolls and two sets of vertical rolls (vertical rolls are the distinguishing feature of a universal mill). The horizontal rolls were 48" long and 31" in diameter. They were coupled to the pinion stand via spindles. An electric-driven belt powered the horizontal screwdowns. Counterweights under the stand kept the top roll against the screws. The 17-1/2" diameter vertical rolls had 25-1/8" long bodies and were mounted in bearing boxes. Power for the vertical rolls was taken off a gear extending from the engine side of the upper pinion. A set of gears divided this power and transmitted it to the vertical rolls via horizontal shafts and miter gears. Two electric motors, one for each set of vertical rolls, open and closed the rolls. THe motor shafts rotate a series of interlocking gears which in turn rotate two horizontal screws for each bearing box. A hydraulic system maintained contact between the bearing boxes and the screws. The approach table has a hydraulic manipulator. Extensive safety railings and platforms cover much of the top of the mill housing.
As with the roll stand, the steam engine was manufactured by Mackintosh-Hemphill and is a horizonatal, non-condensing, double-acting, twin-cylinder, direct-connected reversing engine. Steam is admitted to the cylinders via piston valves, and the engine uses a Stephenson reversing mechanism. A weighted wheel located betweent the eccentrics balances the reciprocating mass. The 50"x60" bore and stroke developed 5,850 maximum horespower under test. Contract costs were $57,000 and $43,750 for the mill and the engine respectively. Between 1911 and 1922 the mill rolled an average 167, 697 gross tons of plate per year.
Sources:
Harbord F.W. and J.W. Hall. The Metallurgy of Steel. Fourth edition, Volume II. London : Charles Griffin and Co.,1911, 674.
"Homestead Mill Updated." Iron and Steel Engineer 48 (June 1971): 96.
Mackintosh-Hemphill CO. Rolling Mills, Engines and Machinery for Iron and Steel Works.
"Mammoth Plate Mill to be Built at Homestead." Iron Trade Review 30 (December 23, 1897): 10.