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2Investigation of physical mechanisms of laser cleaning applicable for cleaning rolled metal from mill scale
D.V. Zhurba1'2*. V.M. Zhurba2, V.P. Veiko1
1-ITMO University, Russia, Saint Petersburg, Sablinskaya Street, 14 2- NPP VOLO LLC, Russia, Saint Petersburg, 17th line V.O., 4-6
A cleaning of rolled metal from scale is a very important for industry and at the same time very complicated and ambitious aim. The most demanded and, at the same time, the most difficult task here is the removal of oxide layers from the surface of hot-rolled carbon steels (mill scale). Well known methods such as mechanical, chemical and evaporative laser cleaning of rolling scale is an insufficiently efficient and low-productivity processes [1]. A new approach to realize this process by means of the mechanisms of scale destruction due to phase change of the surface layers with appearance of the wustit phase with its small adhesion to the main metal followed by thermal stresses has been suggested. This approach was realized be means of continuous laser radiation of fiber laser [2].
The possibility of destruction of mill scale due to thermochemical reactions in the scale and subsequent thermomechanical destruction has been identified and substantiated. The search and optimization of laser exposure modes has been carried out to increase the cleaning efficiency. For a more complete description of the laser cleaning process, attention is paid to the structure of rolled scale and the features of its formation and probable phase transformations under the action of laser heating are described (fig).
The structure of the scale in the rolling proccss
Fe.O. Fe,0( Laser treatment T > 570 "C
FeO ^mM.
Steel FeO Steel
Mill scale on the finished rolled metal after cooling
Fe.O.
S Q^cfi
FeO ~
Steel
Thermochemical transformation of mill scale as a result of laser heating and cooling
Fig. The formation of rolling scale and its transformation during laser heating and subsequent cooling.
The field of modes of exposure to continuous laser radiation, which leads to thermomechanical destruction of scale, without the contribution of evaporation, is investigated. The studied range of exposure durations is 10-5 - 10-4 s. The studied range of power densities is 50 - 1000 kW/cm2. A method of two-stage roughing and finishing laser cleaning is proposed, which allows to increase the productivity and quality of cleaning.
[1] J.M. Deschênes and A. Fraser, Empirical Study of Laser Cleaning of Rust, Paint, and Mill Scale from Steel Surface. In: J. Lee, S. Wagstaff, G. Lambotte, A. Allanore, F. Tesfaye (eds), Materials Processing Fundamentals. The Minerals, Metals & Materials Series. Springer, Cham (2020).
[2] D.V. Zhurba, V.M. Zhurba, A.E. Puisha, Laser cleaning of surfaces of structures of pipeline transportation of hydrocarbons, Drilling and oil, № S2. pp. 61-67, (2023).
