Hot rolling lubrication for improved product properties

The application of a hot rolling lubrication is connected to various benefits. The achievable reduction of the friction between the work rolls and the rolled strip leads to two essential effects. One effect is the reduction of the rolling power and rolling load what can be used for an improvement of the hot rolling process. The other one deals with an improvement of the rolled product. The lubrication has a positive influence on the hot strip properties at the strip surface and through that also on the mechanical features of the final product. The reduction of the rolling power which can be measured by the reductions of the global quantities rolling force and torque, can in the simplest case be used for energy savings which is generally positive for the environment. It also involves the possibility to reduce or eliminate oscillations of the hot strip mill, which sometimes occur when mills work near their maximum power level. These oscillations can have a bad influence on the control system and on the regularity of the produced strip. The power savings can also be used for the optimisation of rolling schedules, for the extension of the product range of a hot strip mill or for a further reduction of the final strip thickness. These items are very interesting especially for elder hot strip mills which are limited in these features but they also fit the general demand for the production of thin hot strip < 1 mm e.g. for direct application or the relief of the cold roll shop. In addition, the reduction of the rolling load together with the reduction of friction leads to a decrease of work roll wear, so that the rolls can in practice be used for longer production times. The reduction of the friction goes together with a reduction of the shear texture at the strip surface. It is known that the shear texture is detrimental for the drawing properties. Because of that, the textures throughout the whole strip thickness are equalised which correspond to an optimal status. This fact is especially important for ferritically hot rolled material. At rolling temperatures below ca. 850°C this material does not fully re-crystallise and the texture property is transmitted to the final cold rolled and annealed product. An improved texture leads to a better deep-draw-behaviour of the final product. Besides that, an improvement of the strip surface quality (roughness) can be assumed. While the purpose for a rolling power reduction can be realised by a relatively rough setting of the lubrication parameters the demand for a material property improvement requires very well adjusted parameters (e.g. a constant very low friction coefficient <= 0,1). Because the product characteristics are influenced in every production step it is necessary to lubricate at nearly every stand of a hot strip mill. The lubrication has to be adjusted very carefully at every rolling stand and because of the different structural circumstances on every side of it individually. For a production line it is also very important that the lubrication is controllable to achieve constantly and reproducibility and that it is easily integrate-able into the overall mill control.