Abstract: The present invention relates to a method for removing clogging dust in gas passing holes in a honeycomb catalyst. A honeycomb catalyst whose gas passing holes are clogged with dust in exhaust gas is immersed in water in a vessel, and then the vessel is closed and vacuum suction is exerted, by which water is allowed to flow in the gas passing holes in the honeycomb catalyst to remove dust in the gas passing holes.

Abstract: A method and apparatus for grinding a roll in a rolling mill on an on-line grinding basis, are improved in that a freely rotatable grinding body such and is a grindstone is pressed against a surface of the roll to be ground as directed in the direction making a predetermined angle with respect to the axis of the roll. The roll is rotated so that the surface of the roll may be ground by a relative slip between the grinding body and the roll caused by their different circumferential velocities.

Abstract: A device for detecting the surface level of molten metal in a mold, in which a thermo-sensitive magnetic element the relative magnetic permeability of which varies depending upon temperature is provided on an outer wall surface of the mold, and a coil connected to an A. C. power supply is mounted so as to leave a gap between the thermo-sensitive magnetic element and the coil, so that variation in electromagnetic coupling between the coil and the thermo-sensitive magnetic element due to temperature increase of the mold according to the rise of molten metal level can be detected.