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| Galvanizing Line |
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Ispat Industries Limited pioneered the manufacture of thin, medium and thick gauge galvanized steel sheets in India. The company currently has four galvanizing lines at the Kalmeshwar unit, with a total installed production capacity of over 0.325 million tonnes per annum.
Ispat's philosophy is to bring to its consumers the foremost technology relevant to galvanized sheets. Consequently, the Galvanizing Line at Kalmeshwar produces coils and galvanized plain/corrugated sheets that match international standards.
The unit is accredited with QS-9000 and ISO-14000 certifications and is equipped with computerised quality checks at every stage, including an x-ray thickness gauge and other contemporary systems.
A noteworthy feature of the galvanizing unit at Kalmeshwar is its self-sufficiency in raw material - cold rolled (CR) coils, which facilitates versatility in its product range. Until the last quarter of 1988, CR coils were imported, as is still done by other galvanizers. However, Ispat planned its backward integration in the form of a Cold Rolling Mill to ensure its own raw material for the Galvanizing Line. The company's computer controlled 6-hi reversible combination Cold Rolling Mill began production in 1988.
Quality control at the galvanizing unit is aided by up-to-date laboratories, both chemical and physical, that ensure tests of inputs and process results. In fact, quality control begins right from the selection of raw material and goes through the entire operation, ending finally with the rigorous testing of the finished products. |
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Manufacturing Process |
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The CR coils which serve as raw materials are transferred directly from the Cold Rolling Mill to the Continuous Galvanizing Lines. The coils then pass through various processes to remove defects.
As the galvanizing line is a continuous line, the coils are passed through a looper. Continuous annealing takes place in an in-line annealing furnace. This cleans the coils and helps achieve the desired hardness. The temperature of the strip in this pre-heating oxidising furnace is between 460oC to 480oC.
After this, the coils are passed through a zinc pot where zinc coating is carried out using a technologically advanced hot-dip process. Zinc and antimony of the highest purity are used for coating the sheets. This operation is performed under precise temperature conditions, with the bath temperature maintained within a range of 440oC to 460oC.
Due care is taken for pretreatment of the substrate on which the zinc coating takes place, as this increases the life and performance of the galvanized sheets. The percentage of aluminium, antimony and tin in the batch is 2 to 3 per cent, 0.35 to 0.45 per cent and 0.3 to 0.4 per cent respectively.
The zinc-coated coils are then passed through a chromate solution to safeguard the coils against white rusting and other atmospheric reactions. The chromic acid concentration is 20 to 25 gm/ltr, and the temperature is kept at 40oC to 45oC. Lastly, the coils are passed through a Tension Leveller to improve the shape of the product and ensure perfect flatness. |
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