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...

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),...