Continuous casting and rolling of beam blank has become a common practice in the steel beam production. Development in recent years concentrates in casting near-net-shape beam blanks. The difference between the conventional and near-net-shape beam blank is showed in Fig. 1. Conventional beam blank has a relatively thicker flange, usually over 100 mm, while the near-net shape beam blank has a flange thickness less than 100 mm, usually with a lower limit 50 mm in the practice [273]. Dozens, even a hundred beams can be produced through rolling only one beam blank.

Fig. 1: Conventional beam blank (left) and near-net shape beam blank

The plant based on the near-net shape beam blank concept is very compact, as showed in the Fig. 2. It primarily consists of beam plant casters to provide beam blank, a furnace to reach required temperature distribution for rolling, a conventional break-down stand, and a U1-E1-U2 universal stand group including an universal roughing stand, a 2-high edging stand and an universal finishing stand.

Fig. 2: Compact Beam Production (CBP)

In the following, production facilities of a plant (Nucor-Yamato) are introduced [275]. The plant started large-section beam production in 1993.
 

There are two ladle metallurgy stations: No. 1 unit located adjacent to the meltshop and No. 2 unit adjacent to the new No. 2 caster. The No. 2 caster is a curved mold machine with 2-point unbending that produces large beam blanks. Three sizes of beam blanks are produced: 465 x 550 x 150 mm(17.7x21.7x5.9in.); 400x820x110mm (15.7x32.3 x 4.3 in.); and 450x1100x120 mm (17.7x43.3x4.7 in.) in lengths between 4 and 12 metres (approximately 18 to 40 ft). Production rates of 160 to 200 tons/hr are achieved with casting speeds of 0.8 to 1.0 metre/min (approximately 31 to 39 ipm): a typical casting time is 45 min.

Approximately 90% of the products rolled on this mill are wide flange beams, with the balance being H-piling. The wide-flange product line ranges from 12x12 through 40x16 in. with footweights range from 55 to 398 lb/ft. The capacity of the mill can reach about 2 million tons. Fig. 3 illustrates major facilities in the mill.

Fig. 3: Large-section beam mill facilities [275]

Reheat furnace - The walking beam reheat furnace, is rated at 200 tonnes/hr when heating a cold charge to a dropout temperature of 2350°F. This furnace has a 40x80-ft hearth, a charge capacity of 480 tons and is fired by natural gas with low NOx burners. A metallic tube bank-type recuperator equipped with a 65,000-scfm fan provides 900°F preheated air. The furnace is controlled by a level 2 computer. A level 1 computer is also included which assists in material handling. Operator interface with the computer control system is done through a man-machine interface (MMI) that is used by furnace operator and personnel associated with the furnace.

Breakdown mill - The breakdown mill group consists of reversing breakdown mill, four manipulators (two on each side of the mill stand) each driven by its own d-c drive and working tables which consist of two table sections (one on each side of the mill). There is a 2100-psi air/water descaler ahead of the breakdown mill. The breakdown mill is a 2-h multiple groove reversing mill which has two roll positioning d-c drive systems. The mill is driven by a 6050-hp a-c reversing motor. Breakdown mill manipulator sideguards are used to shift and guide material into and out of the mill. They are located on working tables at the front and back of the mill.

For some products, improved biting in the universal roughing and edging mills needs to be achieved, so a tongue cut saw is used to cut the head (tongue) of the material.

Universal roughing and edging mill - The universal roughing and edging mills are reversing, multiple pass mills that run in tandem through computerized speed matching. This group consists of the universal roughing mill, edger mill entry and exit tilt tables, and entry and exit sideguards. The universal roughing mill is a 4-roll mill with two driven horizontal rolls and two nondriven vertical rolls. Power for the horizontal rolls is supplied by a 10,000-hp a-c reversing main motor.

Two drive systems (work side and drive side) adjust the position of the top horizontal roll. The other two drives adjust the position of the two vertical rolls.

Because of the wide range of sizes of H-beams, the passline of the universal roughing mill must be adjusted vertically for proper rolling. The mill bed plate is used for this purpose. The bed plate is driven by an a-c motor, which works in combination with solenoid actuated hydraulic cylinders to raise and lower the mill stand.

The edging mill is a 2-h, single groove mill stand driven by a 3000-hp a-c motor. The mill has two roll-positioning d-c drive systems and one bottom roll positioning hydraulic system. Roll change for the edging mill takes an average of 20 min. With an adjustable passline at the universal and edging mills, it is necessary to adjust the height of the roll tables going into and out of these stands by tilt tables.

Universal finishing mill - This group consists of the universal finishing mill, two tilt tables and four sideguards. The universal finishing mill has two driven horizontal rolls and two non-driven vertical rolls. Power for the horizontal rolls is supplied by a 4000-hp a-c main motor. It is a single-pass mill.

From the universal finishing mill group, the bar moves to the hot saw area that includes two hot saws: a stationary saw and a traveling saw. These saws are equipped with 600-hp motors and 84-in. dia blades. Also included in this area is a saw measuring gage. Bars are cut hot to customer length (25 to 120 ft) and loaded onto the cooling bed. The cooling bed is 135 ft long and 150 ft wide. It has a combination of walking beams and transfer chains to move material across the bed. Water sprays are also used on the top and bottom of bars for cooling before being moved to the finishing area.

Finishing area - The finishing area consists of a 7-roll rotary straightener, inspection bed, pilers, repair bed and a gag press. The straightener is capable of handling all sections, up to 40-in. beams. In the case the beam needs to be restraightened in the repair bed, a hydraulically operated gag press is available. It has an 800-ton press capacity and is equipped with a turning device.

The control system supplied by Allen-Bradley includes all PLC equipment, low voltage a-c and d-c drives, motor control centers and MMI systems. Toshiba supplied the mill stand main drives (cycloconverters), 34.5-kv, 4.16-kv and low voltage power distribution equipment. The PLC units currently installed are summarized in Table 1.

Table 1: Location of PLC units [275]

Proportional valves are used extensively throughout the mill. They have high reliability and dependability with a relatively low maintenance effort. One successful example is in the bottom roll positioning on the mill stands. Though the stocks cause significant disturbances in roll loads and the position of the roll, the recovery time is fast and the resultant disturbance to the product section is negligible.

[273] G. Flemming, G. Engel, M. Cygler: CBP Compact Beam Production. SMS Special writing, report on the Walzwerksausschuß des VDEh, March 1993.
[275] D.B. Adams and C.R. O'Keefe: Nucor-Yamato's large-section beam mill. Iron and Steel Engineer, Oct. 1996.