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...

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...

Refractories and Classification of Refractories...

Refractories and Classification of Refractories Refractories are inorganic, nonmetallic, porous and heterogeneous materials composed of thermally stable mineral aggregates, a binder phase and additives. The principal raw materials used in the production of refractories are normally the oxides of silicon, aluminum, magnesium, calcium and zirconium. There are some non-oxide refractories like carbides, nitrides, borides, silicates and graphite. Refractories are chosen according to the conditions they face during their use. Some applications require special refractory materials. Zirconia is used when the material is required to withstand extremely high temperatures. Silicon carbide and carbon are two other refractory materials used in some very severe temperature conditions, but they cannot be used in contact with oxygen, since they oxidize and burn in atmospheres containing oxygen. Refractories are the materials which are resistant to heat and exposure to different degrees of mechanical stress and strain, thermal stress and strain, corrosion/erosion from solids, liquids and gases, gas diffusion, and mechanical abrasion at various temperatures. In simplified language, they are considered to be materials of construction which are able to withstand high temperatures. Refractories are usually inorganic non-metallic materials with refractoriness greater than 1500 deg C. They belong to coarse-grained ceramics having microstructure which is composed of large grains. The basis of body is coarse-grained grog joined by fine materials. Refractory products are a specific sort of ceramics that differs from any ‘normal’ ceramics mainly with their coarse-grained structure being formed by larger grog particles joined by finer intermediate materials (bonding). ASTM C71 defines refractories as ‘non-metallic materials having those chemical and physical properties that make them applicable for structures or as components of systems that are exposed to environments above 538 deg C’. Refractories are to be chemically and physically stable at high temperatures. Depending on the operating environment, they...

Environmental Impact Assessment and Environmental Management Plan for a Steel Project...

Environmental Impact Assessment and Environmental Management Plan for a Steel Project The environment clearance (EC) process for a steel project (Fig 1) has the following built in steps. These steps are (i) screening, (ii) scoping and consideration of alternatives, (iii) baseline data collection, (iv) impact prediction, (v) assessment of alternatives, description of mitigation measures and environmental impact statement, (vi) public hearing, (vii) environment management plan, (viii) decision making, (ix) monitoring of the clearance conditions. Fig 1 Process for obtaining environment clearance for a steel project The environmental impact assessment (EIA) and environmental management plan (EMP) is part of EC process. EIA and EMP is normally necessary for obtaining EC for (i) those projects which can significantly alter the landscape, land use pattern and lead to concentration of working and service population, (ii) those projects which need upstream development activity like assured supply of mineral products supply or downstream industrial process development, (iii) those projects which involve manufacture, handling and use of hazardous materials, and (iv) those projects which are located near ecologically sensitive areas, urban centres, hill resorts, and places of scientific and religious importance. For obtaining EC for the steel project, it is essential that a report covering the EIA and EMP) is submitted to the regulatory authorities. This report assists the process of decision making with regards to the EC for the project. In addition to getting EC for the project, the purpose of the EIA and EMP report is to take into account the environmental aspects of the project not only during its implementation but also after its commissioning. The purpose of EIA is to identify and evaluate the potential impacts (beneficial and adverse) of the steel project on the environmental system. It is a useful tool for decision making based...

Tender Technical Specification and its Contents...

Tender Technical Specification and its Contents Tender documents are prepared for the purpose of procuring materials, production unit, services, or site activities. They are used for calling the bids. A tender document (Fig 1) usually consists of three parts, namely (i) notice inviting tender, (ii) commercial specification, and (iii) technical specification. Fig 1 Components of tender document Technical specification is that part of the tender documents which provides to the bidder technical details of the materials, plant and equipment, services, or site activities which the bidder is to supply if he becomes a successful bidder. In case a plant unit is to be procured, then the technical specification is very complex since all the four types of procurements get combined into one specification. Technical specification becomes contract technical specification after incorporating the changes agreed with the bidder during the tender negotiations. The technical specification is the most important section of the tender document, both for the purchasing organization as well as for the bidders, since it is the specification which sets out precisely what characteristics are required from the materials, plant and equipment, services, or site activities being sought by the purchasing organization. Technical specification is a comprehensive document which clearly, accurately and completely describes in detail what the purchasing organization wants successful bidder to supply. A clear, accurate and complete specification is the foundation of any purchase, and ensures the best chance of getting what the purchasing organization wants. Whether the purchase is for a small simple item, or a large complex plant, or the activities to be performed at the construction site, the technical specification needs to clearly outline the requirements to the bidder. Technical specification has five mandatory requirements mainly (i) title of the specification, (ii) scope, (iii) statement of requirements, (iv) requirement for...

Synthetic Slag for Secondary Steelmaking...

Synthetic Slag for Secondary Steelmaking Synthetic slag consists of prepared mixture of several individual oxides which is used during secondary steelmaking to assist the steel treatment in the ladle from the viewpoint of effective refinement. Synthetic slag practice is normally used to obtain clean steels and also for the desulphurization of the liquid steel. Secondary steelmaking is a critical quality control step between the primary steelmaking and the continuous casting of the liquid steel. A key feature for success with the secondary steelmaking processes is the slag control. Use of synthetic slag which is specifically designed to have the required chemical composition and physical properties helps in the slag control. The  desirable properties of the synthetic slag include (i) slag is to have high sulphide capacity, (ii) it is to be basic in nature, (iii) it is to be fluid to obtain faster reaction rates, and (iv) it is not to cause excessive refractory wear. The secondary steelmaking slag is in liquid form in the ladle and floats on the surface of liquid steel which is usually at temperature of 1,600 deg or higher. It acts like a sponge to absorb the impurities consisting mainly of sulphur and non-metallic inclusions. The design of the slag is a critical step impacting the efficiency of the steel refining processes during the secondary steelmaking. Slag regime in secondary steelmaking significantly influences the final quality of the produced steel, particularly with respect to the achieved desulphurization of steel. One of the possibilities for influencing the slag regime is the application of synthetic slags to the ladle slag, formed from slag-making additions during the liquid steel tapping. Synthetic slag practice during secondary steelmaking maximizes the efficiency of the steel refining process by (i) improving steel quality, (ii) improving productivity,...