Industrial Heating Furnaces and their Types...

Industrial Heating Furnaces and their Types A furnace is equipment which is used as a reactor, or for melting of metals for casting, or to heat materials to change their shape (e.g. rolling, forging etc.) or properties (heat treatment). Industrial furnaces are mainly used for carrying out the process or for the purpose of heating. Furnaces which are used for carrying out the processes are sometimes known as reactors. Industrial furnaces which do not ‘show colour’, that is, in which the temperature is below 650 deg C are sometimes called ‘ovens’. However, the dividing line between ovens and furnaces is not very sharp. As an example, coke ovens operate at temperatures above 1400 deg C. In the ceramic industry, furnaces are called ‘kilns’. In the petrochemical and chemical process industries, furnaces are termed ‘heaters’, ‘kilns’, ‘afterburners’, ‘incinerators’, or ‘destructors’. The furnace of a boiler is known as its ‘firebox’ or ‘combustion chamber. Industrial heating furnaces are insulated enclosures designed to deliver heat to loads for many forms of heat processing. Furnaces used as reactors, and melting furnaces require very high temperatures and can involve erosive and corrosive conditions. Shaping operations need high temperatures to soften materials for processes such as forging, swaging, rolling, pressing, bending, and extruding etc. Heat treating operations need midrange temperatures to physically change crystalline structures or chemically (metallurgically) alter surface compounds, including hardening or relieving strains in metals, or modifying their ductility. These include aging, annealing, normalizing, tempering, austenitizing, carburizing, hardening, malleabilizing, nitriding, sintering, spheroidizing, and stress relieving etc. Industrial processes which use low temperatures include drying, coating, polymerizing, and chemical changes etc. Industrial heating operations encompass a wide range of temperatures, which depend partly on the material being heated and partly on the purpose of the heating process and...

Pickling of scale formed on hot rolled strip of carbon steel Apr23

Pickling of scale formed on hot rolled strip of carbon steel...

Pickling of scale formed on hot rolled strip of carbon steel During the hot rolling or heat treatment of steel, oxygen from the atmosphere reacts with the surface iron to form a crust that is made up of oxides of iron. This crust is known as scale and need to be removed before steel is further processed in cold rolling mill. Non removal of scale will have the following detrimental effects. Scale not only give bad appearance to the product but also accelerate corrosion During cold rolling of the strip scale patches affects the reduction with the possibility of the skidding of rolls. Effective scale removal is essential for the success of not only for cold rolling but also of subsequent annealing and coating operations. During cold rolling and annealing the scale will produce a dirty surface and cause the rusting of the strip During coating of the strip, presence of scale causes poor to total adhesion failure. Fig 1 shows hot rolled strip surface as well as pickled surface.   Fig 1 hot rolled surface and pickled surface Scale and its origin The normal scale found on hot rolled strip is blue/grey in colour and covers the entire strip surface. This scale is generated during rolling in the last stands of the finishing mill, across the run out table (ROT) and during cooling of the coil. It is composed of three well defined layers of iron oxides. Adjacent to the steel is the thickest layer consisting of wustite having an approximate composition of FeO. The intermediate layer consists of magnetite (Fe3O4) while the outermost layer is hematite (Fe2O3). The thickness of these layers will depend on the temperature of the strip at the exit of the finishing mill, temperature of the coiling and...