Title

UTILIZATION AND MAINTENANCE PRACTICES OF HOT STRIP MILL BACK UP ROLLS FOR IMPROVING MILL PRODUCTIVITY

UTILIZATION AND MAINTENANCE PRACTICES OF HOT STRIP MILL BACK UP ROLLS FOR IMPROVING MILL PRODUCTIVITY

Authorship

Singh, K.K.; Verma, R.S.; Choudhary, D.; Singh, A.K.; Murty, G.M.D.

Singh, K.K.

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Verma, R.S.

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Choudhary, D.

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Singh, A.K.

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Murty, G.M.D.

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DOI

10.5151/2594-5297-0095

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Abstract

The predominant mechanisms of spalling (main failure mechanism of Hot Strip Mill back-up rolls), namely rolling contact fatigue, work hardening and roll wear, have been examined and the utilization and maintenance practices (campaign length and dressing amount) of the Hot Strip Mill back-up rolls have been evolved according to the mill-service requirements (contact stresses present on the surface and sub- surface regions of back-up rolls and number of co-rotation between back-up and work rolls for the strip geometries and steel grades rolled at Hot Strip Mill, Bokaro Steels Limited) and roll material and quality. The rolls used at Hot Strip Mill of Bokaro Steels Limited are based on 5% Cr forged alloy steel heat treated to a hardness of 60-65 Shore C. The rolls are used with a campaign length of 4000-4500 km of rolling stock with a dressing amount of 2.5-3.0 mm. The optimum utilization and maintenance practices have resulted in substantial reduction in consumption of back-up rolls and production delays. The use of portable Ultrasonic and Eddy Current flaw detectors has also been employed for inspection of back-up rolls.

The predominant mechanisms of spalling (main failure mechanism of Hot Strip Mill back-up rolls), namely rolling contact fatigue, work hardening and roll wear, have been examined and the utilization and maintenance practices (campaign length and dressing amount) of the Hot Strip Mill back-up rolls have been evolved according to the mill-service requirements (contact stresses present on the surface and sub- surface regions of back-up rolls and number of co-rotation between back-up and work rolls for the strip geometries and steel grades rolled at Hot Strip Mill, Bokaro Steels Limited) and roll material and quality. The rolls used at Hot Strip Mill of Bokaro Steels Limited are based on 5% Cr forged alloy steel heat treated to a hardness of 60-65 Shore C. The rolls are used with a campaign length of 4000-4500 km of rolling stock with a dressing amount of 2.5-3.0 mm. The optimum utilization and maintenance practices have resulted in substantial reduction in consumption of back-up rolls and production delays. The use of portable Ultrasonic and Eddy Current flaw detectors has also been employed for inspection of back-up rolls.

Keywords

Rolls; Back up rolls; Hot strip mill rolls.

Rolls; Back up rolls; Hot strip mill rolls.