The production facilities of GPH Ispat Limited consist of three major units, namely: (1) Steel Melting Shop, (2) Steel Re-Rolling Mills and (3) Captive Power Plant. These units are arranged in a semi-integrated pattern. The Steel Re-Rolling Mills uses billets, products of the Steel Melting Shop, to manufacture bars (deformed & plain) of various sizes. Billets are produced through Induction Furnace, Ladle Refining Furnace and Continuous Casting Machine route. Raw materials of billet production are mild steel scrap, ferroalloys, direct-reduced iron, carburizers, de-carburizers and fluxes & additives. Bars are produced in fully automated Re-Rolling Mills. The Captive Power Plant of 12MW (synchronized with PDB grid) and the National Grid are the sources of electricity of the factory.
Fig: Production Flow Chart
Once the bars are cooled, they are cut into desired length by means of cold shearing. Different sized bars are then packed in intact sealed bundles with strips. Later these bundles are stored in Finished Goods Yard according to their Grade, Size, Lot No., and any other extinguishing factor for onward dispatch.
Features of GPH TMT 500W Rebar: GPH TMT 500W bar can be described as new-generation-high-strength steel having superior properties such as fire resistance, corrosion resistance, weld-ability, strength, ductility and bend-ability meeting highest quality standards at international level.
- Fire Resistance: Withstands temperatures up to 5000 degrees Celsius.
- Corrosion Resistance: The TMT process gives the bar superior strength and good anti-corrosive properties.
- Earthquake Resistance: The soft ferrite-pearlite core enables the bar to bear dynamic and seismic loading.
- Superior Malleability: TMT bars are most preferred because of its flexible nature.
- Better Weldability: They have fine welding features.
- Excellent Bonding strength: External ribs running across the entire length of TMT bar give superior bonding strength between the bar and the concrete.
- Cost-effective: A high tensile strength and better elongation value gives great savings
Production Process of GPH TMT 500W Rebar:
GPH TMT 500W bar is produced by fully automatic, computerized machines based on sophisticated and accurate advanced technology and design. The thoroughly tested billets are reheated under controlled temperature in automatic reheating furnace at 1100-1200°C and are subsequently rolled through a sequence of rolling stands progressively reducing to the required size. After rolling the bars are allowed to be cool naturally in the cooling bed, which are then tied into small bundle. After cooling the ribbed bars are tied in small bundles of 12 meters length for easy handling.
With the help of rolling conveyor, the billets are made to pass through Roughing Stand. This begins the process of gradual size reduction of billets. 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 till the required size is achieved.
The bar after leaving the last rolling mill stand is fed to quenching box at a very high speed. In this section, a rapid and controlled water quenching is performed reducing the temperature of surface drastically from around 950°C to 600°C. Due to higher speed, only outer portion of bar gets quenched. The inner part remains hot only. The case due to rapid quenching gets converted in Martensite form. The Microstructure is fine-grained Ferrite-Pearlite structure at the Core and Martensite at the case. Then the bar is cut with automatic Flying Shear and fed into the cooling bed.
At cooling bed, the core that is still hot transfers heat outside to the case thereby tempering it. Due to this self-tempering, the Martensite Case becomes tempered Martensite that has more strength and very high Corrosion Resistance Properties. Both quenching and self-tempering, lead to typical micro-structure of TMT bar i.e. Fine grained Ferrite-Pearlite structure at the Core (soft) and Tempered Martensite Case (hard). After this Normalizing process starts where the bar cools down in atmospheric temperature and gradually attaining the same.