Heating of Cold Stock One of the prequisites of the hot ROLLING PRACTICE is heating the input bloom/billet/slab from the room temperature to the rollable temperature. Hot ROLLING permits large deformations of the metal to be achieved with a small number of ROLLING cycles. to the distance between the rolls, and if the rolls are grooved it is shaped according to the groove design. Steel is, thus, reduced to a thickness equal 1. A mechanism, commonly called a roller table, directs the work piece to the rolls, and another roller table for handling the pieces emerging out of the roll.Ħ The table in front of the rolls forces the steel against the rolls which grip and pull the steel between them. The layout of a ROLLING mill varies, from a simple single stand mill to several stands positioned either side by side or in a line. The rolls run on massive neck bearings mounted in housings of enormous strength and driven by powerful electric motors. To achieve this, rolls exert forces of tens of millions of Newton - equivalent to a weight of thousands of tonnes. In hot- ROLLING of steel, the temperature in the ultimate finishing stand varies from 8500 C 9000 C, and is always above the upper critical temperature of steel.ĥ Steel is squeezed between rolls until the final thickness and shapes are achieved. The blooms/slabs are heated initially at 11000 C -13000 C. The objective is to breakdown the cast ingot into blooms or slabs for subsequent finishing into bars, plate or a number of rolled sections. These mills are normally two-high reversing mills with metres diameter rolls (designated by size). The initial hot-working operation for most steel products is done on the primary roughing mill (blooming, slabbing or cogging mills).
These rolls can either be flat or grooved (contoured) for the hot ROLLING of rods or shapes.Ĥ Under these conditions, the rolls grip the piece of metal and deliver it, reduced in cross-sectional area and therefore, increased in length. The distance between them is spaced, which is somewhat less than the height of the metal stock entering them. ROLLING involves passing the material between two rolls revolving more or less at the same peripheral speed but in opposite directions,, clockwise and counterclockwise. The metal stock is subjected to high compressive stresses as a result of the friction between the rolls and the metal surface. ģ For hot working processes, large deformation can be successively repeated, as the metal remains soft and ductile. If the temperature of the metal is above its recrystallization temperature, then the process is termed as hot ROLLING. Hot ROLLING Technology ROLLING is classified according to the temperature of work piece rolled.
This is particularly important in the manufacture of steel for use in construction and other industries. ROLLING is the most widely used method of forming / shaping metals, which provides high production, higher productivity and close control of final product than other forming processes. The process involves plastically deforming a metal work piece by passing it between rolls. In profile ROLLING, the final product is either a round rod or other cross sections shaped products such as structural sections (beam, channel, joist, rails, etc).Ģ The initial breakdown of ingots into blooms and billets is done by hot- ROLLING. In flat ROLLING the final shape of the product is either classed as sheet, also called "strip" (thickness less than 3 mm,) or plate (thickness more than 3 mm). There are two types of ROLLING process - flat and profile ROLLING. ROLLING is a metal forming process in which metal stock is passed through a pair of rolls. (Hons.), Executive Director, ISP & RMD, SAIL (Retired). 1 HOT ROLLING PRACTICE An Attempted Recollection Saral Dutta.