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The basic characteristics of pipe nozzle cooling with retaining water on a plate has been studied in a laboratory test by using a moving hot plate.The cooling ability of pipe nozzle flow changes with the amount of retaining water. It was found that maximum cooling ability can be obtained when the depth of retaining water is approximately 50 mm. The cooling ability with retaining water increases slightly as the nozzle is raised, while the cooling ability without retaining water decreases as the nozzle height increases.The influence of the cooling conditions, such as flow-type and plate temperature, on the cooling ability with retaining water was also investigated and the cooling ability of pipe nozzle flow was compared with that of slit nozzle flow with a large gap. It was found that the slit nozzle flow has less cooling efficiency than the pipe one in the high water flux, though no difference can be seen when the water flux is low.

The factors affecting the descaling property of reheated steel slabs have been studied in the plate rolling shop. The frequency of scale defects is closely related to the amount of residual scale on the steel slabs after descaling by the hydraulic scale breaker. It is found in the rolling shop that the amount of the residual scale depends remarkably on the following two factors.1) Degree of overheating in the furnace2) Surface temperature of the scale on slabs immediately before descalingOn the other hand, it has been pointed out by many workers that the descaling property of Si-killed steels are worse than semi-killed steels. It is well known that fayalite is formed in the scale of Si-killed steels. In this study, the effect of surface temperature of scale on the descaling property is mainly examined. It is found experimentally that the existence of fayalite causes the cracks in the scale during cooling.It could be concluded that the descaling property tends to be bad for the Si-killed steels when the cracks are formed in the scale before descaling.