Reduction in Roll Wear Through Technological Interventions at CRM & SSM of Rourkela Steel Plant

Abstract

Cold Rolling Mill (CRM) complex of Rourkela Steel Plant (RSP) was set up in 1968. The CRM has two pickling lines which use sulphuric acid as pickling medium. Under-pickling is inherent problem with sulphuric acid pickling line. Under-pickled coils processed at tandem mill leads to contamination of emulsion leading to increased roll wear and poor surface quality of cold rolled coils. Also, the deficient roll cooling system aggravates the situation, leading to higher occurrence of strip breakage and inferior shape of the coils. Technological measures were taken both at the Pickling Line and at the Tandem Mill to improve their operating conditions. These measures include introduction of improved scale washing system at Pickling Line and heat exchanger in acid regeneration plant to improve pickling bath condition. New generation ‘tantalum shell and tube heat exchanger’ introduced in pickling lines to reduce the under-pickling. Roll cooling system at Tandem Mill was modified to reduce thermal- crown of work rolls, which helped in reduction in roll wear by 20%. With these measures, diversion of CR coils due to bad shape reduce by 30%.

Electrical grade of steel produced at Silicon Steel Mill (SSM) is one of the major revenue- earners for RSP. Electrical steel is cold rolled in four high cold reversing mill at SSM. The thermal crown of the work rolls in the mill found to be high, leading to higher specific roll consumption, lower campaign size and poor surface quality of electrical steel rolled in this mill. A modified roll cooling system with differential flow density along the work roll barrel in accordance to the roll thermal profile was introduced at reversing mill to improve shape of the cold rolled coils. The headers have been divided into three zones depending on the intensity of the cooling required with the central zone having the highest flow density followed by the intermediate and the end zones. A self-cleaning wedge type auto filter capable of filtration of 300 micron level was introduced for supply of continuous emulsion flow to roll cooling headers. The improved roll cooling system has led to reduction in roll wear and the specific roll consumption has reduced by 20%.