Basics of Rolling of Steel Nov21

Basics of Rolling of Steel...

Basics of Rolling of Steel  Liquid steel is usually cast in continuous casting machines in the shape of billets, blooms, or slabs. In some plants, it is also being cast in continuous casting machines in the shape of thin slabs or dog bone sections. These shapes are processed by hot rolling by passing them through plain or grooved cylindrical rotating rolls to produce plates, sheets, rods, structural sections, and tubes etc. Rolling process is one of the most important and widely used industrial metal forming operations. It provides high production and close control of the final product. It was developed in late 1500s. It accounts for 90 % of all metals produced by metal working processes. Rolling of steel is a metal forming process in which steel is passed through a pair of rotating rolls for plastic deformation of the steel. Plastic deformation is caused by the compressive forces applied through the rotating rolls. High compressive stresses are as a result of the friction between the rolls and the steel stock surface. The steel material gets squeezed between the pair of rolls, as a result of which the thickness gets reduced and the length gets increased. Rolling is classified according to the temperature of the steel rolled. If the temperature of the steel is above its recrystallization temperature, then the process is termed as hot rolling. If the temperature of the steel is below its recrystallization temperature, the process is termed as cold rolling. The rolls run on massive neck bearings mounted in housings of enormous strength and driven by powerful electric motors. These are known as mill stands. A rolling mill stand contains two or more rolls for plastic deformation of steel between rotating rolls. It basically consists of (i) rolls, (ii) bearings,...

Cold Rolling of Steels Oct08

Cold Rolling of Steels...

Cold Rolling of Steels  The primary purpose of cold rolling of steels is to reduce the thickness of the hot rolled steel strips (normally in the range of 1.5 mm to 5 mm) into thinner thicknesses (usually in the range of 0.12 mm to 2.5 mm) which cannot be normally achieved during hot rolling in a hot strip mill. Besides reduction in thickness cold rolling is done for improving the surface finish of steels, for improving the thickness tolerances, for offering a range of ‘tempers’, for improving the physical characteristics, and for preparing the strip for surface coating. Cold rolling makes the cold rolled sheets a much improved product. Cold rolled steel products offer good control of thickness, shape, width, surface finish, and other special quality features that compliment the need for highly engineered end user applications.  To meet the various end user requirements, cold rolled sheets are metallurgically designed to provide specific attributes such as high formability, deep drawability, high strength, high dent resistance, good magnetic properties, weldability, enamelability, and paintability etc. Cold rolling of hot rolled steel strips is done below the recrystallization temperature normally at room temperature. In cold rolling process, usually no heat is applied to the hot rolled strip before rolling.  However, frictional energy at the contact surfaces of the strip being rolled gets converted into heat. This heat may increase temperature of the strip being rolled in rapid adiabatic process to a level of 50 deg C to around 250 deg C. During cold rolling process the reduction in thickness is due to the plastic deformation which occurs by means of dislocation movement. Steel gets hardened because of the buildup of these dislocations. This increases strength and strain hardening upto 20 %. These dislocations reduce the ductility of the...

Production of Tin Plates and Tin Free Steel Oct04

Production of Tin Plates and Tin Free Steel...

Production of Tin Plates and Tin Free Steel  Tin coating is the process of thinly coating sheets of steel with tin (Sn), and the resulting product is known as tinplate. It is most often used to prevent rust. The sheet of steel on which the tin coating is done is known as black plate. When chromium (Cr) and chromium oxides is used for coating in place of tin then the coated sheet is known as tin free steel. Tin free steel is produced by applying electrolytic chromic acid treatment over steel sheets. On tin free steel sometimes polyethylene terephthalate (PET) or polypropylene films are laminated in order to eliminate the painting and cleaning processes when using tin free steel. History The tinplate industry is founded on the invention of the process of preserving sterilized food for long periods of time by Nicolas Appert in 1810. The Appert process was adapted to the preservation of food in tinplate containers by John Hall in 1812 in London. By the 1820s, canned foods were widely sold in UK and France, and by 1839, foods were being canned in the USA. Starting in the 1880s, a series of technical innovations which took place has transformed the tinplate industry. These included the replacement of wrought iron with steel black plate in about 1880, the development of continuous cold reduction in 1927 that eliminated hot pack rolling, the introduction of continuous electro tinning on a small scale in Germany in 1934 and on a commercial scale in the USA in 1937 which replaced the hot dip process, the invention of double cold reduction in 1960, and the invention of tin free steel in the early 1960s in Japan and the USA. Presently there are two processes for the tinning of the black plates namely...