THE MANUFACTURING PROCESS

A modern high technology semi automatic manufacturing process rolls the bars of different sizes in specified diameter range and imparts high strength to the bar using the latest technique of the thermo mechanical treatment (TMT).

The raw material, steel billet/ingot is heated in a reheating furnace and rolled through a sequence of rolling stands equipped with roll sizes ranging from 460mm to 260mm which progressively reduce the billet to the final size and shape of the reinforcing bar.

The different sizes (diameter) of the bars are delivered from different roll stands at specifically controlled roll speeds. Almost all of these are finally controlled through DC drive & PLC control with well proven, sophisticated logic and sequence control, locally/remotely managed by experts.

The sizes, ribs and identification/brand marking are achieved by inscribing the same on the rolls through a CNC machine.

The QST process takes over and the bar is subjected to heat treatment in three successive stages. The first stage of ‘Quenching , supplied and licensed by H & K, under the world leading brand “Thermex” begins when the hot rolled bar leaves the final mill stands and is rapidly quenched by a special water spray system. This converts the surface layer of the bar to a hardened structure called ‘Martensite’ while the core remains “Austenitic”.

The second stage of “Self Tempering” begins when the bar leaves the quenching box with a temperature of the core being higher than that of the surface.

This allows heat to flow from the core to the surface, resulting in tempering of the surface, giving a structure called “Tempered Martensite” which is strong and tough. The Core is still “Austenitic” at this stage.

The bar travels through a set of auto controlled hydraulic twin channel which delivers the bar to a 78 mts long cooling bed for natural cooling by atmospheric air. The third stage of “Atmospheric cooling’ takes place on the cooling bed, where the Austenitic core is transformed to a ductile Ferrite-Pearlite core.

Thus, the final structure consists of a combination of strong outer layer of tempered Marten site and ductile core of Ferrite-Pearlite. This is what gives Aditya TMT bars its unique combination of strength and ductility.