Limestone – Its Processing and Application in Iron and Steel Industry Jul07

Limestone – Its Processing and Application in Iron and Steel Industry...

Limestone – Its Processing and Application in Iron and Steel Industry Limestone is a naturally occurring and abundant sedimentary rock consisting of high levels of calcium carbonate (CaCO3) in the form of the mineral calcite. Some limestones may contain small percentage of magnesium carbonate (MgCO3). These limestones are known as dolomitic limestones. Limestone is also a very important industrial mineral. Its chemical properties make it a valuable mineral for a wide range of industrial/manufacturing uses. Limestone is also one of the vital raw materials used in production of iron and steel. Limestone, by definition, is a rock that contains at least 50 % of CaCO3 in the form of calcite by weight. There can be small particles of quartz (silica), feldspar (alumino-silicates), clay minerals, pyrite (iron sulphide), siderite (iron carbonate), and other minerals associated with the limestone. All limestones contain at least a few percent other materials. The Impurities in limestone can consists of silica (SiO2), alumina (Al2O3), iron oxide (Fe2O3), sulphur (as sulphides or sulphates), phosphorus (P2O5), potash (K2O), and soda (Na2O). Silica and alumina are the main impurities of limestone. The limestone which is used in ironmaking is required to contain at least 85 % of calcium carbonate and a low percentage of alumina. Similarly limestone which is used for steelmaking is required to contain at least 92 % of calcium carbonate and a very low percent of impurities especially the silica percentage. The main uses of limestone in iron and steel industry are (i) as a fluxing material, and (ii) other usage which consists of desulphurizing agent, coating of moulds of pig casting machine, neutralizing of acidic water, water treatment, waste water(effluent) treatment, flue gas treatment, and sludge and sewage treatment. It is also a component of synthetic slag. Limestone is...

Dolomite – Its Processing and Application in Iron and Steel Industry Jun28

Dolomite – Its Processing and Application in Iron and Steel Industry...

Dolomite – Its Processing and Application in Iron and Steel Industry Dolomite is an anhydrous carbonate mineral. It is a double carbonate of calcium and magnesium (CaCO3.MgCO3). It is one of the important raw materials used in production of iron and steel. Dolomite contains theoretically 54.35 % of CaCO3 and 45.65 % of MgCO3 or 30.41 % of CaO, 21.86 % of MgO, and 47.73 % of CO2. However, in nature, dolomite is not available in this exact proportion. Hence generally the rock containing in the range of 40 % to 45 % of MgCO3 is usually called dolomite. The main uses of dolomite in iron and steel industry are (i) as a fluxing material (ii) for protection of refractory lining, and (iii) as a refractory raw material. Dolomite in iron and steel industry is normally used in three forms. These are (i) raw dolomite which is also the natural form of dolomite, (ii) calcined dolomite, and (iii) sintered dolomite. When dolomite is used as a fluxing material then it is used as either raw dolomite or calcined dolomite. When dolomite is used for the protection of refractories, it is used in calcined form and when dolomite is being used as a refractory raw material, it is used in the form of sintered dolomite. The uses and form of dolomite in iron and steel industry is shown in Fig 1. Fig 1 Uses and form of dolomite in iron and steel industry Processing of dolomite Dolomite after its mining has to undergo several processing before it can be used in various processes. The basic processes in the production of dolomite are (i) quarrying of raw dolomite, (ii) preparing mined dolomite for its use by crushing and sizing, (iii) calcining of raw dolomite, (iv) processing...

Rolling of Steel in a Modern Long Product Rolling Mill Jun19

Rolling of Steel in a Modern Long Product Rolling Mill...

Rolling of Steel in a Modern Long Product Rolling Mill Long product is a common name for (i) reinforcement steel bars, (ii) shaped steel bar products such as rounds, flats, squares, and hexagon etc., (iii) sectional products such as angles (equal and unequal), channels, beams, tees, and special profiles etc., and (iv) wire rods. Mills which roll long products are known as long product mills. Based on the product being rolled these mills are called, merchant bar mill, bar and rod mill, light section mill, rebar mill, light merchant mill, special bar quality (SBQ) mill, and wire rod mill etc. The product range of these mills usually consists of those shaped and sectional products whose cross-section is smaller than the cross section of the products rolled in medium and heavy section rolling mills. Wire rod mills produces steel wire rods of diameters 5 mm to 12.5 mm in coil form with the weight of the coil upto 2.5 tons. The qualities of steels being rolled in these mills can range from low carbon, mild steel, medium carbon, high carbon, and micro and low alloyed steels. The design of the long product rolling mill is required to provide right solutions for the required performance requirements which include high speed production, microstructure qualities of the product, and shortest changeover time from one product to other product etc. Large amount of flexibility is available in modern long products rolling mills. These mills are normally continuous mills consisting of three sets of rolling stands namely (i) roughing group of stands, (ii) intermediate group of stands and (iii) finishing group of stands. The input material for these mills is normally billet. A billet mill can be combined with the long product rolling mill through a roller hearth furnace in...

Rolling of Steel in small and medium sized Rolling Mills Jun09

Rolling of Steel in small and medium sized Rolling Mills...

Rolling of Steel in small and medium sized Rolling Mills Rolling of steel 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 steel 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 forming processes, because of its higher productivity, close control of the rolled product, 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. Rolling of steel is a metal forming process used 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 surface of the steel material. The steel material gets squeezed between the pair of rolls mounted in a roll stand, as a result of which the thickness of the steel being rolled gets reduced and the length is increased. 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 rolling stock gradually approach to the desired profile. Mostly, rolling is done at high temperature, which is called hot rolling, because of requirement of large deformations....

Heating of Steel in Reheating Furnace Jun01

Heating of Steel in Reheating Furnace...

Heating of Steel in Reheating Furnace Reheating furnace is important equipment in the process of hot rolling. It is the heart of any hot rolling mill. Reheating of steel is a continuous process. The steel material to be rolled is charged at the entrance of the reheating furnace. The steel material is pushed forward on the hearth of the furnace by means of a pusher machine whose ram is in direct contact with the steel material. The steel material is pre-heated, heated and soaked as it passes through pre-heating, heating and soaking zone of the reheating furnace. At the end of the soaking zone of the furnace, the steel material is discharged from the furnace by ejector for rolling in the rolling mill. The temperature of the heated steel material at the time of discharged depends on several factors and it can vary in the range of 1100 deg C to 1250 deg C. The size of the reheating furnace is normally expressed as the capacity to supply the rolling mill with sufficiently hot steel, in tons per hour. Steel materials with different material compositions, dimensions, and charging temperatures can reside in the furnace simultaneously. The reheating furnace used for heating the steel materials is normally considered to be having high energy consumption. It also emits good amount pollutants in the atmosphere because the process used for heat generation is the combustion process. Reheating process has considerable influence on the economics of the working of the rolling mill. There are usually three types of continuous reheating furnaces used in the rolling mills. These are (i) pusher type furnace, (ii) walking hearth furnace, and (iii) walking beam furnace. Pusher type furnaces have some disadvantages which includes (i) frequent damage of refractory hearth, (ii) skid marks...

Scale Formation in Reheating Furnace May25

Scale Formation in Reheating Furnace...

Scale Formation in Reheating Furnace  Reheating furnaces constitute an important element in the rolling of steels, in which the semi-finished steel products are heated to a desired temperature for achieving the plastic properties in the products for rolling. The basic purposes of heating the semi-finished steel products for rolling include (i) to soften the steel for making it suitable for rolling, and (ii) to provide a sufficiently high initial temperature so that rolling process is completed in fully austenitic temperature region. During reheating in the reheating furnace, steel is passed through the furnace along which the temperature is gradually increased up to the soak zone. In there, the temperature is kept constant for thermal and chemical homogeneity of the steel. The reheating furnace is a direct fired furnace which uses either of the gaseous, liquid, or solid fuel and air. The composition of the atmosphere within the furnace generally consists mainly of nitrogen (N2), Carbon di-oxide (CO2), water vapour (H2O) and free oxygen (O2). The atmosphere composition can vary drastically during the operation. These variations are functions of the air/fuel ratio, which in turn, depends on furnace and mill operating conditions. Reheating furnace for the reheating of steel is conceptually divided into three zones. Starting from the discharge end of the reheating furnace, these zones are (i) soaking zone, (ii) heating zone/zones, and (iii) pre-heating zone. In the soaking zone, fuel and air is fired through the furnace burners at normal or reduced primary fuel stoichiometry. This zone has high furnace temperature. The temperature of steel is equalized through its cross section in this zone. The exhaust gases from this zone travel to heating zones. The heating zones, which are between preheating zone and the soaking zone, require high radiant heat transfer for increasing...