The full form of TMT Bar/Rebar is Thermo Mechanically Treated bars. We all know that TMT Bars are essential for all type of construction purposes but it is also important to know how it is made.
Best Quality TMT Bars pass through series of processes that determines the strength & flexibility of it. The manufacturing process of TMT Bar involves series of processes like rolling, water quenching, heat treatment, cooling at various stages of manufacturing.
The Thermo Mechanical Treatment involves 3 essential steps that are:
- Self Tempering
- Atmospheric cooling
The quality of TMT Bar depends on three major factors
- Quality of raw materials
- Quality rolling mill that gives the uniform and proper shape for all rebars
- Quality system for quenching and tempering
Iron Ore to Steel
Raw material for manufacturing the TMT Bar are iron ore, coal, dolomite. In this process raw materials are piled, recovered and mixed in required proportion.
The iron ore experiences beneficiation procedure to raise the iron substance. At this point metal fines are gathered to shape a mass of pellets and sinter to improve efficiency. The coal is changed to coke for future purpose.
Now limestone accompanies with the existing are deployed to the furnace. Hot air being supplied to the furnace through its nozzle that results melting the raw materials and come out from a pool that is on the bottom of the furnace. In this process when limestone molts a liquid because of its impurity comes out that is knows as slag it is lighter in nature that is why it floats on the surface of the molten metal.
Primary Steel Making
During the initial stage of primary steel making, in oxygen furnace combining oxygen with carbon in the iron and that eliminates carbon dioxide is known as pre-treatment.
Then, the steel once again passes through the EAF (Electric Arc Furnace) for refining the composition of steel.
Now molten steel from EAF (Electric Arc Furnace) is transferred to a ladle and it transferred to the continuous casting machine. Liquid steel flows out of the ladle into the casting ladle and then into water cooled mold.
Solidification begins in the mold. Continuous Billets coming out from the CCM is sized according to the length required.
Thermo Mechanical Treatment
Quenching – Once the hot rolled bars releases from finished mill it enters to the water spray system that is known as ‘Thermex System’. The best quality tmt bars manufacturing process uses Thermex Technology that cool down the outer core rapidly and ensure the ductility of TMT Rebars. Rapid cooling hardens the outer core of the TMT Rebars to a depth optimized for each section, forming a martensitic rim while the core remains hot & Austenitic.
This cooling technology is known as Quenching.
Self Tempering – Once the rebars is out of the Thermex Quenching box, the core remains hot compared to the surface allowing heat to flow from the core to the surface causing Tempering of the outer Martensite layer thus forming a structure called ‘Tempered Martensite’.
Atmospheric Cooling – Once the self tempering is over the bars get ready for atmospheric cooling. This is done on cooling bed on normal temperature. In this step the austenitic core turns as ferrite-pearlite structure. Thus the final structure consists of strong outer layer with ductile core. This process increases the tensile strength that makes it highly ductile and weldable.