Study of the Tractive Forces Applied to Galvanized Strip on a Straightening Machine in a Continuous Hot-Galvanizing Unit

Abstract

Relations are presented to determine the tractive force exerted on strip by a straightening machine in a continuous hot-galvanizing unit. The working rollers of the machine have different radii. The relations take this difference into account along with the coefficient of rolling friction in the bearings of the rollers, the number of rollers in the straightening machine, the curvature of the strip, unit back tension, and the strip's mechanical properties and geometric dimensions. Results are presented from a study of how the tractive forces are affected by the cross-sectional area of the strip and the unit back tension. The results are Most of the flat-rolled products made with metallic coatings are strips and sheets with zinc and zinc-bearing coatings. In world practice, rolled strip is galvanized with the use of various types of machines and methods which differ mainly in the processes used for annealing and degreasing the metal (1-4). The accuracy of the geometry of galvanized strip is appreciably influenced by the adjustment of the straightening machine. The goal of present investigation is to examine the tractive forces applied to the strip by a straightening machine in a continuous hot-galvanizing unit (CHGU) and to develop efficient regimes for subjecting the strip to tension. The CHGU at the Mariupol Metallurgical Combine applies a wide range of coatings to strip in a broad range of widths and thicknesses. The unit controls coating thickness through the use of jets, subjects the strip to non-oxidative heat- ing, rapidly cools it in a controlled manner with a protective gas, and is equipped with an automated system that controls the overall production process (4). Among the pieces of equipment in the CHGU: uncoilers; twin shears for cropping the ends of the strip; centering rollers; welding machine; shears for trimming the sides of the strip; a horizontal storage unit that receives incoming strip; preheating furnace, high-speed heating furnace, and soaking unit; sections for rapid, slow, and final cooling of the metal; a sloping trough and a galvanizing bath; a gas cutter to control the thickness of the coating; air cooling section; a vertical unit for storing outgoing strip; temper stand; straightening machine; lubricating unit; coilers; a unit for transverse cutting of the strip; packaging machine. After the strip has been coated, it is straightened to obtain a smooth surface without shape defects. Steel strip with a thick- ness in the range 0.16-0.32 mm is straightened in straightening machines with 40-46-mm-diam. work rollers, while strip thicker than 0.32 mm is sent through straightening machines with work rollers 50-60 mm in diameter. The speed of the rollers is syn- chronized with the overall speed of the hot-galvanizing unit. Tension devices are positioned on both sides of the straightening