Abstract: An atomization roasting furnace for producing ferrite raw material powder includes an elongated roasting furnace body with a center burner located at the top end thereof. At least three liquid spray nozzles are located in an expansion slope portion below the center burner circumferentially with respect to the center burner. A quencher, located below the elongated roasting furnace body, has a top end connected to a bottom end of the elongated roasting furnace body. Quencher nozzles are located adjacent the top end of the quencher.

Abstract: This invention provides an atomization roasting method which can easily obtain a soft ferrite sintered body, for example, a sintered body having a crystal particle size of not greater than 2 .mu.m, by using as a raw material an ultra-fine powder having a mean particle size of not greater than 0.1 .mu.m obtained by atomization roasting and which can obtain a soft ferrite raw material powder subjected to an oxidation reaction, having an extremely small residual chlorine content, and having and extremely small deviation of high vapor pressure components such as zinc between the atomized raw material solution and the oxide as the product and which can economically produce a soft ferrite core having an excellent power loss characteristic in a high frequency range, particularly in a MHz range, and is extremely effective for reducing the size of a high frequency transformer.

Abstract: Hot steel plate as hot-rolled is passed forward longitudinally through pairs of top and bottom rollers disposed in the direction of the plate travel. The steel plate is cooled with water supplied to its top and bottom surfaces from the nozzles on a plurality of cooling units disposed in the same longitudinal direction. Each cooling unit is disposed between adjoining pairs of the top and bottom rollers. Before cooling is started, the temperature distribution in the steel plate is determined and the desired mean cooling rate is set. The distance from the plate edge over which the supply of the cooling water at least to the bottom side of the plate is to be cut off is determined for each cooling unit on the basis of the determined temperature distribution and preset mean cooling rate. By so doing, the temperature of the inner edge portion of the steel plate is kept above the temperature of the middle portion, thereby allowing the Ar.sub.