Rolling of high precision bars with the reducing and sizing block

Since the introduction of the first 3-stand precision sizing block with non-adjustable 3-roll stands in 1979, 3-roll blocks have increasingly been used in new bar mills as well as for revamping of existing mills, due to the constantly growing demand for high-quality steel bars produced at lower processing costs. At the beginning of the nineties a new type of stand, a 3-roll stand without bevel gears and knock-out shafts, i.e. with 3 input shafts, was developed. At the same time the combined rolling/sizing block was developed (reducing & sizing block, RSB), which permits rolling in the roughing and intermediate mill with one pass family only. Due to the extremely large "free-size" range of up to 3 mm, a minimum number of stand changes and a very low number of roil rings and roller guides for the complete product range are sufficient. The quick stand changing system also allows so-called "chance free" rolling, i.e. the production of any dimension at any time. The design and process related characteristics of the RSB will be presented in this paper. The results achieved with a 4-stand RSB on the light section mill of Nippon Steel Corporation in Muroran, Japan, since commissioning in August 1999 for the dimension range of 19 to 70 mm dia. demonstrate the main advantages: tolerances between +/- 0.07 and +/- 0.1 mm are obtained for common as well as for temperature-controlled and thermo-mechanical rolling of corresponding materials. Yield increased by 0.5 % from 96.5 to 97.0 % and mill availability by 5 % from 85 to 90 %.