Hyundai Steel tasked Primetals Technologies with the supply of a large bar mill and a small bar and wire rod mill for its Dangjin plant. The two multi-line rolling mills are capable of producing an annual one million tons of special steel billets as well as straight and coiled bars, with dimensions from 5.5 to 350 millimeters. The products are used in the manufacture of engine and transmission components used by Hyundai-Kia Automotive Group. The processed grades include carbon, special alloy, spring, bearing, and free-cutting steel. Sensors and electronics integrate with mechatronic packages, thus equipping the mill for Industry 4.0 applications and constituting the next step in long rolling for automotive at Hyundai Steel.
FIRST MILL: LARGE BAR MILL
The first mill is a large bar mill (LBM) that rolls blooms into finished large round and square products, as well as into intermediate billets. A 2-high reversing breakdown stand is followed by a finishing and sizing train with continuous-gap-adjustment stands equipped with an under-load roll-parting system for automatic gap control.
The mill’s capacity of one million tons per year is split into some 800,000 tons of billets that serve the second mill, and 200,000 tons of other large bars. The product mix includes 150 mm and 180 mm billets, 80-350 mm rounds and 85-180 mm finished squares that are 10-12 meters in length.
The starting bloom is 530×390 mm with lengths of 3.5-8 meters, weighing 5.7-13 tons. The mill runs at a maximum speed of 1.1 meters per second with a maximum production rate of 200 t/h. The produced bars measure 4-12 meters in length, with bundles weighing 2-10 tons.
This mill comprises a 2-high housing-type reversing stand, with rolls having a maximum diameter of 1,200 mm and a barrel length of 2,600 mm. At both sides of the mill, lineals with tilting fingers operate the pass change of the rolling stock. Complete with hydraulic capsules for the positioning of the bottom roll, the mill is designed for fully automatic operation and ease of maintenance.
The continuous finishing and sizing train allows for the whole range of sizes and shapes to be rolled using feeds that were prepared in a uniform pass sequence in the break-down mill, with only a few variants required for square products and larger rounds. The train features Red Ring Series 5 stands and Continuous Gap Adjustment technology.
Round bars up to 140 mm are divided by the start-stop flying crank shear with a 270-ton nominal cutting force. The shear also provides front and tail-end crop cuts, which are collected in a bucket below mill floor level. A software program optimizes the cut lengths according to the actual bar weight and size, compensating for differences in bloom weight and crop amounts, while ensuring that only multiples of commercial length are processed by the subsequent cut-off station.
Bars grouped in layers are processed at the cut-off station for commercial length cutting. The station comprises two horizontal saws equipped with a 1,800-mm-diameter metallic disk. The disk is appropriately encased to avoid spilling cooling water onto the bar, thereby preventing bar-surface damage or undesired hardening effects. The cut-off process is fully automated, including the position/speed recalculation required to compensate for disk wear.
SECOND MILL: SMALL BAR AND WIRE ROD MILL
The second mill—a small bar and wire rod mill (SBWRM)—combines lines of small bars, rods, and bars-in-coil. Billets are rolled in a continuous rolling mill with original Red Ring Series 5 stands. The rod outlet features Morgan equipment such as No-Twist Mills and Reducing/Sizing Mills, High-Speed Laying Head, and Stelmor Conveyor.
With an annual capacity of 800,000 tons, the SBWRM produces some 400,000 tons of wire rod, 300,000 of small bars, and 100,000 tons of bars-in-coil. The product mix includes 5.5-26 mm wire rod, 16-100 mm rounds, and 16-60 mm bars-in-coil. The starting materials are 150 mm and 180 mm billets produced by the large bar mill; 200 mm billets can also be used.
The mill runs at a maximum speed of 110 meters per second for wire rod and 18 for bar, with a maximum production rate of 160 tons per hour. Straight bars are finished-sized by a Kocks block and produced in 4-10 meter lengths in 1-5 ton bundles. Finalized coils of wire rod have an inner diameter of 900 mm and an outer diameter of 1,250 mm.
The bars-in-coil are finished-sized by a Kocks block and have a diameter of 1,000 (inner) and 1,350 mm (outer). Coils from both the wire rod and the bar-in-coil lines weigh 1.7-3 tons, and are handled by a common combined vertical and horizontal conveyor system.
Hyundai plans to produce 400,000 tons of wire rod and 600,000 tons of straight bar and bar-in-coil per year.
The continuous rolling train comprises 18 Red Ring Series 5 stands, arranged in alternating horizontal and vertical configuration. Three sizes of stands are used, with full interchangeability within each size.
Bars-in-coil are conveyed by a turndown into the pouring reels, with a high-speed switch alternately directing bars into the two pouring reels. The turndown is equipped with cluster rollers to prevent scratching of the bar. Pinch rolls facilitate the entrance of the bar to the reels, which are equipped with wear strips on the outer rotating drum.
Using a Vee configuration, the finishing mill features an 8-stand Morgan No-Twist Mill with 230 mm ultra-heavy-duty interchangeable roll housings. This design ensures the optimum configuration for the size range required as well as reduced roll cost and improved section control, allowing a wide range of grades to be rolled.
The Morgan Stelmor Conveyor incorporates a wide range of processing conditions in a single system, including fast, slow, or hybrid cooling, to produce a broad spectrum of carbon and alloy steel grades. This flexibility, coupled with controlled temperature rolling, allows more grades to be produced in a directly useable condition, thus eliminating or accelerating downstream processes such as recrystallization and solution treatment.
