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...

Management of Re-rolling mills in SME sector...

Management of Re-rolling mills in SME sector Re-rolling mills in SME sector play a very important role towards the steel economy of the country. There are around 1800 re-rolling mills in small and medium enterprise (SME) sector in India. The rolling capacities of these mills are mostly in the range of 8,000 tons per year to 80,000 tons per year. These mills are crucial to the national economy since they are not only making available a large amount of finished steel in the market but many of these mills are also converting a substantial amount of steel scrap into finished steel thus serving the overall cause of steel recycling. Since the conversion of steel scrap is taking place without its melting in these re-rolling mills, it is helping towards the cause of the conservation of raw materials and energy as well as saving the generation of green-house gases. The technology adoption level of these mills is rather low and many of these mills operate with technologies which are 50 years to 60 years old. Most of these re-rolling mills do not have practices to keep systematic data in different areas of their functioning. These mills operate at low level of productivities and high level of energy consumptions. They have some special problems and challenges. Re-rolling mills in SME sector practically do not have even simple control systems. They work with a low degree of standardization. The work force is having high experience in limited area. There is increased focus on the experience of the people and there is practically no effort to enhance the knowledge of the work force. The approach to all the issues is informal leading to decisions which does not often bring improvements in the working of the mills. Re-rolling mills...

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...

Bearings for Rolling mill Rolls...

Bearings for Rolling mill Rolls Rolling mills for rolling of steel differ in many aspects with each other. The rolling mills are of different sizes and capacities. The mills roll steel materials of different cross-sections, sizes and qualities and in material conditions which are either hot or cold. The mills have different configurations and speeds of rolling. The configurations of the mills can vary from cross country, reversing, semi continuous to continuous. The equipments of rolling mills can have manual operations, mechanical operations, electro-mechanical operations, pneumatic operations, hydraulic operations, or a combination of all of these. The controls provided in the mills can be manual controls, remote controls, instrumented controls, or fully automated controls. Further in many types of mills even heat treatment processes are integrated. In spite of the so many differences, all the rolling mills have in common some basic technologies and equipments. All the rolling mills have rolls for the rolling of materials which are fitted in roll stands. Rolls are either driven by electric power or friction driven and are to resist many forces for normal rolling. The roll stands can have two rolls, three rolls, four rolls, six rolls, or a set of multiple rolls mounted on them depending on the types of mills. During rolling, the load on the rolls gets transferred to the roll neck bearings and their assembly (chocks). Rolls for their smooth rotation as well as for resistance to different forces need ‘bearings’.  Roll bearings are to meet the basic need of the rolling mill which is the smooth rolling of the steel products. They are friction reducing devices which provide support to the rolls for effective rolling with minimum of energy loss. The bearings are designed to withstand high rolling loads, heavy shocks, varying...

Importance of Housekeeping and Cleanliness at Workplace...

Importance of Housekeeping and Cleanliness at Workplace Housekeeping and cleanliness at the workplace are closely linked to the industrial safety. The degree, to which these activities are effectively managed, is an indicator of the safety culture of the organization. Housekeeping and cleanliness not only make the organization a safer place to work in but also provide a big boost to the image of the organization. These activities also (i) improve efficiency and productivity, (ii) helps in maintaining good control over the processes, and (iii) assist in maintaining the quality of the product. These important aspects of housekeeping and cleanliness are shown in Fig 1. Fig1 Important aspects of housekeeping and cleanliness There are several signs which reflect poor housekeeping and cleanliness at the workplace in the organization. Some of these signs are (i) cluttered and poorly arranged work areas, (ii) untidy or dangerous storage of materials (such as materials stuffed in corners and overcrowded shelves etc.), (iii) dusty and dirty floors and work surfaces, (iv) items lying on the shop floor which are in excess or no longer needed, (v) blocked or cluttered aisles and exits, (vi) tools and equipment left in work areas instead of being returned to proper storage places, (vii) broken containers and damaged materials, (vii) overflowing waste bins and containers, and (viii) spills and leaks etc. Housekeeping and cleanliness refer to the processes which ensure facilities, equipment, work areas and access routes are kept in good condition. This condition is required for supporting safe and reliable operation and maintenance during normal plant operation. Additionally, during the emergency, housekeeping and cleanliness ensure that the plant operations are not inhibited. Further, the housekeeping and cleanliness both are interrelated. Reaching a good standard in one of them is difficult without reaching a good...