RAW MATERIAL PROCESSING
The main raw material is Sponge Iron and DRI. In addition to this some selected plant revert end cuts is used in predetermined proportions. These different materials are graded and stored in a very large raw material yard. The selected raw material sample is then added into the lab furnace for the melting. The sample is tested to analyse the chemical composition. The chemical composition is checked with the help of in-house spectrometer and C & S apparatus.
STEEL MELTING SHOP (SMS)
The core less Induction furnace used for melting is composed of a refractory container capable of holding the molten bath which is surrounded by water-cooled helical coil connected to a source of alternate current. The furnace lining is made of up of silica to withstand the slag condition of mild steel or any plain carbon steel that is acidic in nature. After melting, the furnace is tilted to remove slag and other impurities that come to the surface of molten metal.
Addition of Micro Alloying Elements
Micro alloying elements are added for refining the molten metal to achieve the desired level of composition. The molten metal is fully killed with aluminium, Ferro Silicon and Ferro Manganese. Throughout the melting process and micro alloying elements addition process, samples are chemically analysed to ensure accurate and desired composition
Purging is done to the molten metal tapped to the ladle to achieve homogenous chemistry and temperature throughout the ladle. In order to avoid thermal stratification that leads to undesirable varying steel compositions, gas purging is done. Purging is conducted by generating bath turbulence to retain thermal homogeneity. This process also helps in removing excessive non-metallic inclusions.
After purging, the ladle is taken to Continuous Casting set up where it is placed on the tundish. The material then passes from ladle to tundish and tundish to moulds. Liquid steel is continuously poured into the mould to replenish the withdrawn steel at an equal rate. The withdrawal rate depends on the cross section grade and quality of steel is being produced. Casting time is typically 45 – 60 minutes per heat to avoid excessive ladle heat losses.
Upon exiting the mould, strand enters a roller containment section and secondary cooling chamber in which the solidifying strand is sprayed with water or air mist for solidification. This area preserves cast shape integrity and product quality.
HOT CHARGING & REHEATING FURNACE
After the Casting of billet, an online billet shear cuts the billet into PLC controlled lengths as per rolling requirements, post the cut, the billets are straight away transferred to the roughing mill for rolling using conveyors. Whereas when some excess production of billet is there its charged into the reheating furnace for recrystallization temperature (1150 C). The re-crystallization temperature is important because at this temperature the rolling process can be started effectively without destroying the bonding. Reheating with the producer gas is very eco-friendly and ensures uniform temperature of billet from one end to other. Billet are pushed into the reheating furnace with the help of pusher and then reheated to temperature of 1150 C.
Once the billets reach the desired rolling temperature, they are brought outside the furnace. With the help of rolling conveyor, these billet are made to pass through the first stand i.e. Roughing mill. With this, the process of gradual size reduction of billets begins. Following roughing mill, the size is further reduced in intermediate and finishing mill. This gradual reduction is an important factor to ensure finer grain structure of the bar. The rolling continues until the desired size is obtained. With help of roller bearings fitted on the roll neck any unnecessary deformation of the bar is prevented. The loop scanner in the flow of the bar ensures perfectly tensionless rolling process that ensures perfect round shape of the bars. The rolling mill technology is from Danieli – Morgårdshammar, Italy.
TEMPCORE QUENCHING SYSTEM
After the Final Finishing stand has imparted it impression on the re-bar, they enter the Tempcore Quenching System to establish their strength, where they can be made in a grade ranging Fe 415 to Fe 550 as per requirement. The process is carried out by extremely high pressure RO water and compressed air. After the box the Bars are cut into 60m sizes by the dividing shear.
Self-tempering & cooling
At the cooling bed, the core that is still hot transfers heat outside to the case thereby tempering it. Due to this self-tempering, the martensitic case becomes. Tempered Martensite, which has more strength and very corrosion resistance properties. Quenching as well as self-tempering leads to typical micro-structure of TMT bar, i.e. fine grained Ferrite-Pearlite structure at the Core (Soft) and tempered Martensite Case (Hard).
Subsequently, normalizing process starts where the bar cools down in atmospheric temperature and gradually attaining the same.
CUTTING, BENDING & BUNDLING
The Rolling Mill is connected to a set of on-line Master bundling and Bend bundle making PLC controlled automatic machines from Sund Brista, Sweden. this enables us to bind bundles of Variable sizes and length as per Customer requirement both straight & bended, without the need of physical labour which has its limitations pertaining to weight of bundles and Bundle quality.
STORAGE AND DISPATCHES
Once the Bars are cooled and Packed into bundles they are stored in our covered indoor warehouse according to their Sizes, Lot numbers and/or any other distinguishing factors. We have our ware houses at strategic locations in Chennai & Bangalore also where the Tirumala TMT steel is readily available for dispatch as per Customer requirements. Having Covered and Controlled warehouses keep our material always fresh and rust free.