OPTIMAL HYDRAULIC DESCALING

conference paper

en

Hydraulic descaling is an inherent part of the hot rolling process but can sometimes also be applied in the heat treatment process, continuous casting and other processes. The need for optimal descaling is linked with the quality of the final product. The goal is usually simplified to the complete removal of the scale layer from the hot surface. The descaled surfaces are often wide and a number of nozzles must be used. The quality problems are almost exclusively connected with the overlap of water jets. An experimental study of overlap optimization is presented in this paper. A new approach using in-line configuration of jets is introduced and discussed. This paper also describes why even the completely oxide-free surface achieved after descaling the unit can be a far from optimal solution. Thermal strips on the hot surface cause much more intensive oxidation of the hot part and much slower oxidation in the cold strips on the descaled surface. The speed of oxide formation on the steel surface is exponentially dependent on the surface temperature. Temperature non-homogeneity after descaling in the rolling process can cause the same defects on the surface of the final product as poor descaling. Temperature aspects with links to heat loss and secondary oxidation are discussed.

Hydraulic descaling is an inherent part of the hot rolling process but can sometimes also be applied in the heat treatment process, continuous casting and other processes. The need for optimal descaling is linked with the quality of the final product. The goal is usually simplified to the complete removal of the scale layer from the hot surface. The descaled surfaces are often wide and a number of nozzles must be used. The quality problems are almost exclusively connected with the overlap of water jets. An experimental study of overlap optimization is presented in this paper. A new approach using in-line configuration of jets is introduced and discussed. This paper also describes why even the completely oxide-free surface achieved after descaling the unit can be a far from optimal solution. Thermal strips on the hot surface cause much more intensive oxidation of the hot part and much slower oxidation in the cold strips on the descaled surface. The speed of oxide formation on the steel surface is exponentially dependent on the surface temperature. Temperature non-homogeneity after descaling in the rolling process can cause the same defects on the surface of the final product as poor descaling. Temperature aspects with links to heat loss and secondary oxidation are discussed.

Descaling, hydraulic, nozzle, hot rolling, overlap

27.07.2020

978-80-87294-97-0

Metal 2020

118–125

8