Understanding Rolling Process in Long Product Rolling Mill Nov27

Understanding Rolling Process in Long Product Rolling Mill...

Understanding Rolling Process in Long Product Rolling Mill  Steel rolling consists of passing the material, usually termed as rolling stock, between two rolls driven at the same peripheral speed in opposite directions (i.e. one clockwise and the second anti-clockwise) and so spaced that the distance between them is somewhat less than the thickness of the section entering them. In these conditions, the rolls grip the material and deliver it reduced in thickness, increased in length and probably somewhat increased in width. This is one of the most widely used processes among all the metal working processes, because of its higher productivity and lower operating cost. Rolling is able to produce a product which is having constant cross section throughout its length. Many shapes and sections are possible to roll by the steel rolling process. Steel sections are generally rolled in several passes, whose number is determined by the ratio of initial input material and final cross section of finished product. The cross section area is reduced in each pass and form and the size of the stock gradually approach to the desired profile. Rolling accounts for about 90 % of all materials produced by metal working process. It was first developed in the late 1500s. Hot Rolling is carried out at elevated temperature above the re-crystallization temperature. During this phase, the coarse-grained, brittle, and porous structure of the continuously cast steel is broken down into a wrought structure having finer grain size and improved properties. A long product rolling mill comprised of equipment for reheating, rolling and cooling. The primary objectives of the rolling stage are to reduce the cross section of the incoming stock and to produce the planned section profile, mechanical properties and microstructure of the product. Major parameters in the three...

Production of Seamless Pipes Jul26

Production of Seamless Pipes...

Production of Seamless Pipes  Pipes are either seamless or welded. The manufacturing processes for seamless pipes were developed towards the end of the nineteenth century. In spite of many earlier tests, trials and technologies, the invention of the cross roll piercing process by the Mannesmann brothers towards the end of the 1880s is widely regarded as signaling the commencement of industrial scale production of seamless pipes. In the cross roll piercing process, the roll axes were arranged parallel to the stock axis but an angle to the stock plane. With the rolls rotating in the same direction, this arrangement produced a helical passage for the stock through the roll gap. Moreover the exit speed was slower by about the power of 10 than the circumferential speed of the rolls. By introducing a piercing mandrel arranged in the roll gap, solid round materials could be pierced to produce a hollow shell in the rolling heat by the action of the cross rolls. However, it was not yet possible to produce pipes of normal wall thicknesses in usable lengths by the cross piercing process alone. It was only after development and introduction of a second forming process namely ‘the pilger rolling process’ (again by Mannesmann brothers), it became possible and economically viable to produce seamless steel pipes. The pilger process also constituted an unusual and innovative technology in that the thick walled hollow shell was elongated to the finished pipe dimension by the discontinuous forging action of the pilger rolls (or dies) on a mandrel located inside the hollow shell. Presently seamless pipe is made from round billet, which is pierced through the center to make it a hollow shell and then rolled or extruded and drawn to size. The seamless pipe manufacturing process consists of...

Roll Pass Design Jun18

Roll Pass Design

Roll Pass Design  Long products are normally rolled in several passes, whose numbers are determined by the ratio of the initial input steel material (square or round billet or bloom) and final cross section of finished product. The cross section area is reduced in each pass and form and size of the steel material being rolled gradually approach to the desired profile. Rolling is carried out between grooved rolls. Two opposite grooves in the collaborating rolls form a pass, which corresponds to a work piece’s cross section shape expected after the pass. After every pass, the cross section decreases and its shape becomes closer to a shape of the final product. Development of subsequent pass shapes and its proper location on the rolls is called the roll pass design. Roll pass design is an essential part of long product rolling process, since the long products are rolled between the shaped rolls in the long product rolling mills. Roll pass design generally means the cutting of grooves in the roll body through which steel to be rolled is made to pass sequentially to get the desired contour and size. The primary objective of the roll pass design is to ensure production of a product of correct profile within the tolerance limits, free of defects, with good surface quality and the required mechanical properties. In addition, economic condition must be achieved while rolling the product, for example, maximum productivity at the lowest cost, optimum energy utilization, easy working conditions for the rolling crew and minimum roll wear. Roll pass design is a set of methods for determining the dimensions, shape, number, and type of arrangement of rolling mill passes. Roll pass design also includes the calculation of pressing forces and their distribution on the roll passes. Several   passes are made for each section; a square or round billet or bloom acquires a specified form on each successive pass. The roll passes are designed to avoid excessive stresses in the steel being rolled, since such stresses can lead to the formation of cracks and other flaws. Roll pass design is based on the characteristics of initial input...

Main Features of a Modern Bar and Light Section Mill Feb01

Main Features of a Modern Bar and Light Section Mill...

Main Features of a Modern Bar and Light Section Mill The objective of a bar and light section mill is to reheat and roll steel billets into bars and light sections. The production of bar and light sections in these mills is subject to constant change. There is growing demands on the quality of these products as well as on the flexibility and cost effectiveness of these mills. This has necessitated the development of new and innovative technologies and processes. Modern bar and light section mills are high speed mills capable of rolling bars and light sections of special bar quality grades and engineering steels at high production rates, while keeping investments and operating costs at the reasonable levels. Modern bar and light section mills are expected to meet the following requirements. High mill availability coupled with high productivity and high yields. Meeting the need of low maintenance. Meeting the need of lower energy consumption. Close dimensional tolerances. Negative tolerances (In sectional weight). No variation in dimensions throughout the length. Uniform physical properties. For achieving these demanding requirements, many important features are incorporated in the modern bar and light section mills. Some of these are described below. Reheating furnace – Modern bar and light section mills are equipped with energy efficient walking beam furnaces which are normally computerized controlled. These reheating furnaces uniformly heat the billets to the target temperatures at the required production rates and without skid marks and without cold spots. These furnaces are capable of receiving cold or hot billets as the charge material in the furnace. The modern reheating furnaces have the features of (i) superior heated billet quality, (ii) better heating efficiency, (iii) very low fuel consumption, (iv) minimum scale loss, contributing to achieving high material yield, (v) low...

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...