Application of Hot Rolling Lubrication on a Reversing Coil/Plate Mill

key account business analyst, Quaker Chemical Corp., Conshohocken, Pa., USA [email protected] Nucor Steel Tuscaloosa Inc. is the first U.S. mill to employ Steckel mill technology for producing high-quality wide coiled plates and discrete plates. Since 1985, the Steckel mill has consistently demonstrated product versatility, quality and cost advantage over traditional plate mills. The single stand of a 4-high reversing Steckel mill carries out both roughing and finishing passes. With the increase of market demand on high-strength low-alloy (HSLA) steels, the mill needs to extend its roughing pass schedule to roll the steels due to the limit of torque. However, an extensive pass schedule does not meet the requirements of mechanical properties, since the strain rate is reduced. To resolve the contradiction of the pass reduction rate with the mill torque limit that was rated at 1.25 million ft-lbs, application of roll lubrication was discussed, since the technique showed the advantage in reducing the torque of tandem mills. In addition, it was recognized that the roll wear in rolling HSLA steels is much faster than that in rolling carbon steels due to the increase of separating force. Application of roll lubrication could bring another benefit to the mill, i.e., reduction of roll wear. Most HSLA steels require thermomechanical control rolling to achieve the mechanical properties and high toughness under a low service temperature. Since the precipitation of microalloys occurs in rolling, the separating force increases sharply due to the raised flow stress of metal, which also creates difficulty for mill operators in controlling the shape of the strip. In 2011, a portable lubricant mixer was used to spray the oil solution on the bottom backup roll. The initial trial result showed that the mill torque was reduced by about 8% on average over all passes. Furthermore, additional spray headers were installed permanently in 2012, as shown in Figure 1. The top backup roll allows one spray header to be installed due to the limited space, and the bottom allows for two headers to be installed. Six flat-fan spray nozzles were mounted on each header. The top and bottom spray distances from the roll surface are 12 inches and 18 inches, respectively. In the application of roll lubrication technology to the reversing hot rolling mills, several concerns arise, i.e., bite and roll slippage and effectiveness. This paper studies the mechanism of roll lubrication of the reversing hot rolling mill theoretically and investigates the effect of the roll lubrication on mill separating force, torque, and backup roll profile and roll wear practically. It’s what’s inside that counts.