Rolling Process for Steel Mar27

Rolling Process for Steel...

Rolling Process for Steel Rolling is the process of plastically deforming steel by passing it between rolls. Rolling is defined as the reduction of the cross sectional area of the steel piece being rolled, or the general shaping of the steel products, through the use of the rotating rolls. Rolling of steel is one of the most important manufacturing processes for steel. It is usually the first step in the processing of steel after it is made and cast either in Ingot or continuous cast product in a steel melting shop. The initial rolling of steel is done in a hot rolling mill where blooms and slabs are rolled down to various rolled products such as plate, sheet, strip, coil, billet, structures, rails, bars and rods. Cold rolling of steel is also carried out for some products. Many of these rolled products such as rails and reinforcement bars etc. are directly used by the consumers while the other rolled products are the starting raw materials for subsequent manufacturing operations such as forging, sheet metal working, wire drawing, extrusion, machining, and fabrication industry. Steel rolling can produce a wide range of products. The width of a rolled product can vary from a few millimeters to several meters while the thickness can vary from 0.1 mm to more than 200 mm. The rolled section can be square, rectangular, round or shaped sections. Different rolling processes for steel are shown in Fig 1 Fig 1 Rolling processes of steels Principle of rolling steel During rolling, steel work piece is subjected to high compressive stresses as a result of the friction between the rolls and the surface of work piece being rolled. The work piece is plastically deformed by the compressive forces between two constantly rotating rolls. These...

Rolling Mills Rolls

Rolling Mills Rolls Rolling had assumed importance in the industrialized world during the nineteenth century. Profiles and flats are hot rolled while some flat products are also cold rolled. Rolls are tools in the rolling mill. The weight of the rolls can vary from a few kilograms to as high as 250 tons. Rolls are required to carry out the heavy work of reduction of the cross section of the steel being rolled.  Rolls have to take all kind of stresses, loads from normal and abnormal rolling and which are changing with the roll wear during a rolling campaign. Roll should never break, spall or wear. They are expected to give excellent performance without causing any problems. Under the conditions of rolling, the contact area of the roll that comes in contact with the steel suffers wear, while other parts of the roll body and roll necks does not experience plastic deformation or fatigue but are under high loads. In the recent past rolling technology was improved and changed but rolls have always remained the critical part of the rolling mills. Hence the development of roll quality and roll making technology had followed the development of rolling technology. Historical developments In the nineteenth century basically non alloy grey iron and forged steel was used for rolls. The cast iron grades varied from mild hard to clear chill, where the barrel showed a white iron layer with grey iron core and necks. These rolls were used for flat rolling without any roll cooling in the sheet mills. Later cast steel rolls were developed. These rolls are still produced today. Around 1930 ICDP (Indefinite chill double pour) rolls were developed for hot rolling. In late 1990s ICDP enhanced with carbide rolls were developed. Around 1950 nodular...

Classification of Rolling mills...

Classification of Rolling mills Rolling is the process of plastically deforming metal by passing it between rolls. It is the most widely used forming process, which provides high production and close control of final product. Leonardo da Vinci invented the first rolling mills but only after a few centuries rolling mills became important for the steel industry. In its simplest form, a rolling mill (Fig 1) consists of two driven rolls in a mill stand with a screw down. The work piece to be rolled is passed through the rotating rolls to get the desired shape. Fig 1 A simple rolling mill But in practice rolling mills are not that simple. They are quite complicated and they are of several types. Though all the rolling mills utilize the same principle of rolling but they differ in many ways. The classification of mills can be done in many ways. These are described below. Classification based on temperature of rolling Under this classification, rolling mills are classified according to the temperature of the metal to be rolled. Based on this classification rolling mills are basically of two types: (i) hot rolling mill (ii) cold rolling mill. Hot rolling mills – In these mills, rolling is done above the recrystallization temperature of the metal. During rolling in these mills the grains, which deform during the process of rolling, recrystallize, maintain an equiaxed microstructure and prevent the metal from work hardening. In this type of rolling hot rolled metals have very little directionality in the mechanical properties and deformation induced residual stresses. Cold rolling mills – In these mills, rolling is done below the recrystallization temperature of the metal. Rolling in these mills which is normally done at the room temperature, increases the strength of the metal through...

Some Basics of Rolling and Rolling Mills...

Some Basics of Rolling and Rolling Mills Rolling is the process of plastically deforming metal by passing it between rolls. It is the most widely used forming process, which provides high production and close control of final product. During rolling metal is subjected to high compressive stresses as a result of the friction between the roll and the metal surface. Leonardo da Vinci invented the first rolling mills but only after a few centuries rolling mills became important for the steel industry. Modern rolling practice is attributed to Henry Cort who got a patent for use of grooved rolls for rolling iron bars. Henry Cort is also called “father of modern rolling”. The first rail mill was established in 1820 while the first plate mill was exhibited in 1851. Three high mills for rolling heavy sections were introduced in 1853. Hot strip mill were developed in America in the first half of the twentieth century. Basic concept of the rolling The arc of contact between the rolls and the metal is a part of a circle. The coefficient of friction is constant in theory, but in reality it varies along the arc of contact. The metal is considered to deform plastically during rolling. The volume of metal is constant before and after rolling. In practice the volume might decrease a little bit due to close up of pores. The velocity of the rolls is assumed to be constant. The metal only extends in the rolling direction and there is no extension in the width of the material. The cross sectional area normal to the rolling direction is not distorted. Factors influencing rolling The major factors which influences the rolling process are given below The diameters of the rolls The amount of reduction in a...