MERCHANT MILL:

          In the merchant mill mainly rods and bars generally made. Merchant mill was commissioned in the year 1961. It has been modernized with a capacity of 280000 MT/yr of plain rounded and thermo-mechanically treated (TMT) bars.

          Here a special process known as Thermax Process (after modernization) makes tore steel or structural steel with ribs and lugs. Previously it was seen that structural steel made by twisting failed in case of fire accidents. In the Thermax process the steel rod is passed through tubes and water sprayed on it as a result of which the outer side gets hardened due to formation of martensite while the inner core remains ductile as tempered marensite is formed. The steel prepared by this process was seen to withstand high temperature without failing. Rounds less than 10mm diameter are called rods and greater than 10mm diameter are called bars. They are prepared from the rolled billets from the billet mills. The process is explained below.

          The billets of 100 sq. mm and 9m lengths from the billet mill are stacked quality wise in the billet stockyard. They are then transferred by cranes to the aspirating skid table which automatically de-piles batches of product into single layer.

          First the billets are reheated in a reheating furnace. The furnace is two zones fired type, and also side charged and side discharged. The capacity of the reheating furnace is 70 tons/hr. It is fired with the help of a mixed gas (CO gas + blast furnace gas). Its calorific value is 300 BTU/cu. Ft. It has got dual burners.

MILL STANDS:

The mill consists of total 13 rolling mills. Of these there are 7 roughing stands, 2 intermediate stands, 4 looping stands and the arrangement of which is given below.

·        Roughing stands – 1 to7

·        Intermediate stands – 8 to 9

·        Looping stands – 10, 11, 12 and 14.

Each stand is driven through pinion housing and reduction gearing by individual DC motor.

·        400 HP for stands 3, 4, 5.

·        500 HP for stands 1, 2, 6 and 9.

·        600 HP for stands 10 and 11.

·        800 HP for stands 12 and 14.

Four 180⁰ repeaters are provided between stands 9-10, 10-11, 11-12, & 12-14 to handle sections up to 25 mm diameter rounds & ribbed bars, beyond the finishing stands. There is drum type rotary shear, which cuts the bar to such length that can be accommodated on the cooling beds, and finally the bars are packed and automatically packed and bundled in the dispatch bay. The bars produced generally are 16, 18 and 20 mm diameter.

The major features envisaged after the modernization:

Ñ     Rapid quenching by Thermax process to produce TMT bars of high strength combined with toughness and ductility.

Ñ     CROP cums COBBLE SHEAR to crop the front end of the bar and also cropping in pieces, which is to be cobbled.

Ñ     DOUBLED STRAND ROOLING of 12–16 mm round by slit rolling process, which slits a single billet into two parts longitudinally.

AUTOMATIC BUNDLING & BINDING facilities for bar counting, weighing, bundling and binding.