Spray Cooling Unit for Heat Treatment of Stainless Steel Sheets

Abstract

Stainless steel sheets are successively heated to a temperature of 1150°C and cooled until ambient temperature during the production process. Requirements for high cooling rates of stainless steel sheets producers lead to use water as a cooling medium. The information about cooling intensity (heat transfer coefficient) of different nozzles configurations is necessary for designing cooling sections. Although many researchers deal with water spray cooling, actually a general correlation for predicting heat transfer coefficient for wide range of nozzles configurations does not exists. That is the reason why heat transfer coefficient for different nozzles configurations can be only obtained by laboratory measurements. Heat transfer coefficient is mostly influenced by water impingement density and impact velocity. However other factors e.g. water temperature and velocity of the sheet can influence the heat transfer coefficient. Optimized design of the cooling unit with high cooling intensity and low water consumption was achieved by appropriate choice of these parameters. The moving experimental sheet was cooled from a temperature of 900°C to a temperature of 50°C with various configurations of nozzles. The tests shown that heat transfer coefficient was increasing with water impingement density and impact velocity. Increasing water temperature from 20 °C to 80 °C caused a decrease of the heat transfer coefficient and Leidenfrost temperature. The effect of velocity is negligible when velocities are between 25 and 100 m/min. The cooling unit was designed according to laboratory measurements to fulfill the stainless steel producer's requirements. The measurements which were done in an industrial plant confirmed the accuracy of heat transfer coefficient obtained in the laboratory. The maximum difference between laboratory and plant measurements was 15%.

Heat treatment of thin sheets, research methodology to design a cooling system

“…Appropriate cooling regime is defined by simulations using boundary conditions obtained in previous phases. The Fives stein company designed new cooling section for heat treatment of stainless steel sheets [19]. They used boundary conditions (HTC dependence on the surface temperature) to size and produce its cooling section for stainless steel annealing.…”

Influence of Segmented Rolls on Homogeneity of Cooling in Continuous Casting

“…The second group of factors is related to the cooled surface and the geometrical conditions near the impact area. The major factors are surface temperature [4] and roughness [5], scale thickness, and geometrical conditions near the impact area. Forced convection of air with droplets mixed with vapor in the secondary cooling zone is geometrically limited by the space between the two rolls and the strand surface.…”