Mill Scale

Mill Scale Mill scale is the product of oxidation which takes place during hot rolling. The oxidation and scale formation of steel is an unavoidable phenomenon during the process of hot rolling which involve reheating of steel in a reheating furnace, multi-pass hot rolling and air-cooling in the inter-pass delay times and after rolling.  Mill scale is usually removed by process water used for descaling, roll and material cooling, and by other methods. It is subsequently separated by gravity separation techniques. The formation of oxide scale not only results in a significant loss of yield of steel, but also deteriorates the surface quality of the steel product caused by rolled-in scale defects or roughened surface. In addition, the presence of a hard scale layer on the steel can have an adverse effect on roll wear and working life. The amount of mill scale generated in a rolling mill depends on the type of the reheating furnace and on the practice of rolling adopted in the mill. It is generally in the range of 1 % to 3 % of the weight of the steel rolled. Mill scale mill scale is a layered and brittle material, composed of iron oxides with wustite as a predominant phase. It is normally considered as waste material. From the chemical and physical analysis performed on the mill scale, and with respect to the environmental concerns, mill scale is considered to be non-dangerous waste and normally considered as a green waste. Scale formed during the heating of steel to rolling temperatures in the reheating furnace is known as primary scale. This primary scale is removed generally by hydraulic descaling before hot rolling. The removal of the primary scale formed during the reheating operation before hot rolling is usually done for...

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...

Understanding Iron Ores and Mining of Iron Ore Apr03

Understanding Iron Ores and Mining of Iron Ore...

Understanding Iron Ores and Mining of Iron Ore Iron (Fe) is an abundant and a widely distributed element in the in the crust of the earth, constituting on an  average ranging from 2 % to 3 % in sedimentary rocks to 8.5 % in basalt and gabbro. Its supply is essentially limitless in almost all regions of the world. However, most of this iron is not in a form which can be used in current iron making practices. Hence only that part of the total iron in the crust of the earth which is available to the steel industry both economically and spatially, may correctly be termed iron ore. However, what constitutes iron ore varies widely from place to place and time to time. There are many factors which determine whether iron bearing mineral can be classified as an iron ore, but basically it is a question of economics. Keeping this concept in mind, a logical definition of iron ore for commercial purposes is ‘iron bearing material that can be economically used at a particular place and time under then current cost and market price conditions.’ Because iron is present in many areas, it is of relatively of low value and thus a deposit must have a high percentage of Fe to be considered ore grade. With the advent of improved methods of beneficiation, concentration and agglomeration, the variety of iron bearing materials that can now be used has been broadened and many low grade material types which were once considered uneconomic, are now being considered as iron ore. Typically, a deposit must contain at least 25 % Fe to be considered economically recoverable. Over 300 minerals contain iron but five minerals are the primary sources of iron ore. They are (i) magnetite (Fe3O4),...

Mining of Iron Ores Mar14

Mining of Iron Ores

Mining of Iron Ores Iron ore is a type of mineral and rock from which metallic iron is extracted economically. This ore is normally rich in iron oxides and vary in color from dark grey, bright yellow and deep purple to rusty red. The iron itself is usually found in the form of magnetite (Fe3O4), hematite (Fe2O3), goethite (FeO(OH)), limonite (FeO(OH).n(H2O)) or siderite (FeCO3). The process of mining consists of discovery of an iron ore deposit through extraction of iron ore and finally to returning the land to its natural state. It consists of several distinct steps. The first is discovery of the iron ore deposit which is carried out through prospecting or exploration to find and then define the extent, location and value of the ore body. This leads to a mathematical resource estimation of the size and grade of the deposit. Exploration and evaluation consist of identification and quantification of ore bodies by using a range of geological, geophysical and metallurgical techniques. In its simplest forms exploration involves drilling in remote areas to sample areas. The data from exploration activities is logged, mapped, analyzed and interpreted often by using models. After the ore body has been evaluated, a detailed plan for mining is developed. This detailed plan identifies which ore bodies are to be mined and in what sequence in order to deliver the required iron ore product at an appropriate cost. The process of mine planning is an important step before the start of mine development and it continues on day to day basis once the mine becomes operational. To gain access to the iron ore deposit within an area, it is often necessary to mine through or remove waste material (also known as overburden) which is not of an interest. The total movement...

Iron Ores

                               Iron Ores Iron ore is a type of minreral and rock from which metallic iron is extracted economically. This ore is normally rich in iron oxides and vary in color from dark grey, bright yellow and deep purple to rusty red. The iron itself is usually found in the form of magnetite (Fe3O4), hematite (Fe2O3), goethite (FeO(OH)), limonite (FeO(OH).n(H2O)) or siderite (FeCO3). Different types of iron ores are shown in Fig 1 Fig 1 Types of Iron ores The main ores of iron are hematite (70% iron) and magnetite (72% iron). Ores carrying very high quantities of hematite or magnetite (greater than 62% of Fe) are known as “natural ore” or “direct shipping ore”, meaning they can be fed directly into iron making furnaces. Taconite is low grade silica rich iron ore containing up to 30% magnetite and hematite. This deposit can be processed to produce a concentrate of Fe around 65%. This ore is a major source of iron in USA, Canada and China. Magnetite is also known as magnetic iron ore because it is easily attracted by a magnet. It is a heavy black mineral with metallic luster. Hematite is a steel-gray to iron- black colored mineral which is as hard as magnetite (Moh’s scale hardness is 5.5 to 6.5) but slightly less heavy (usually specific gravity varies from 5.0 to 5.3). It has also a metallic luster. The three primary sources of iron ore are banded iron formations, magmatic magnetite ore deposits, and hematite ore. Banded iron formations (BIF) – These are fine grained metamorphosed sedimentary rocks composed predominantly of magnetite and silica (as quartz). Most of the iron ore is extracted from banded iron formations, the geological structures laid down mostly between 3 and 1.2 billion years ago. Blue...