Modelling Scaling and Descaling in Hot Strip Mills

Methods are described for modelling the heat transfer during hydraulic descaling and the subsequent scale growth during rolling and cooling which in turn affects heat transfer as well as the final scale thickness of the product. The thermal effects of different descaling nozzles can be included. The heat transfer coefficient for descaling uses a standard equation based on surface temperature and water flux rate with an adjustment for additional cooling adjacent to the impingement zone. The basic scaling model shows that the scale thickness on entering the mill may be as high as 15μm but is reduced in thickness during rolling and is between 4μm and 8μm in the final product for this particular steel. The model demonstrates how the final scale thickness may be modified by processing variables such as entry, finishing and coiling temperature. Comparison with mill measurements clearly shows that no further scaling occurs after coiling in this particular mill.