Abstract: A flaw detecting method and apparatus for continuously testing a strip that is continuously carried through a liquid includes features for reducing air bubble generation in a liquid. The apparatus includes a liquid, carrying rolls for passage of the strip through the liquid, and ultrasonic testing probes arranged in the liquid for testing the strip. A carrying roll in contact with the liquid is fully immersed. Air bubble generation is inhibited to improve the testing reliability by at least one of (a) shielding the liquid dropping from the portion of the strip leaving the liquid, (b) reducing the dropping force of the liquid onto the liquid surface by inclining the strip, (c) installing the fully immersed carrying roll at a depth of at least 5 mm in the liquid, and (d) using a carrying speed of less than about 200 m/min. Upon manufacturing steel strips, testing is carried out in the stage of hot-rolled steel sheet, or, preferably, in pickling equipment.

Abstract: In the present invention, in cutting the top and bottom surfaces of a hot-rolled sheet by the rotation of milling cutters holding the sheet therebetween in the thickness direction of the sheet in the running process of the hot-rolled sheet, the cutting resistance determined by the cutting conditions including the type of hot-rolled sheet, the temperature in cutting, and the cut depth is controlled by the adjustment of cut depth, and cutting is performed by making the tension produced on the hot-rolled sheet by the cutting resistance lower than the breaking strength of the joint portion to prevent the breakage of hot-rolled sheet.

Abstract: A surface cutting method for a hot-rolled steel product that includes a joint portion having a predetermined breaking strength includes a step of clamping the steel product between a pair of milling cutters that are arranged on top and bottom surfaces of the steel product, while the steel product is conveyed in a longitudinal running direction. The top and bottom surfaces of the steel product are subjected to cutting by rotating the milling cutters in a rotating direction. A cutting resistance applied to the milling cutters during the cutting is determined based on parameters including type of steel, width, thickness, surface temperature and conveying speed of the steel product, as well as circumferential speed and cutting depth of the milling cutters.

Abstract: There is provided a cleaning apparatus for a surface of a sheet steel capable of satisfactorily removing scale from a surface of a sheet steel before, for example, hot rolling. Waters (42a, 46a) are ejected from nozzles (42, 46), with an ejection pressure of 100 kg/cm.sup.2, a flow rate of 60 liters/minute and an ejection angle of 20.degree. with respect to normal of the surface (32a) of the sheet steel, toward a downward-stream end with respect to a carrying direction. On the other hand, waters (44a, 48a) are ejected also from nozzles (44, 48), with the same ejection pressure, flow rate and ejection angle as those of the nozzles (42, 46), but different in the ejecting direction. That is, waters (44a, 48a) are ejected toward an upward-stream end with respect to the carrying direction.

Abstract: Control method for preventing a breakout or/and a crack of the slab of continuous casting equipment. Heat flux waveforms or heat flux values commensurate to extracted heat values at various positions of a mold are measured by means of thin plate type surface heat flux meters (14, 14x, 14y, 14z) provided at various positions on side shell plate (11, 11c) of the mold (10). When an abnormality or a deviation from a target value is detected, pouring rate is changed, scope of supply, brands and the like of mold powder are controlled, or taper value of short sides of the mold is controlled, so that a breakout or/and a crack of the slab is prevented.

Abstract: A method of repairing a refractory lining of a vessel lined with refractory by flame gunning process, in which a patching material consisting of refractory particles and carbonaceous fuel powder is flame-gunned together with an oxygen containing gas to fuse or semi-fuse the refractory particles in a region surrounded by high-temperature flame and struck against the surface of the refractory lining to produce a deposit layer of the refractory particles, is disclosed. In this method, a patching material having a higher mixing ratio of the fuel powder or only the fuel powder is flame-gunned at an initial stage of the repairing and subsequently patching materials, in which the mixing ratio of the fuel powder is lowered stepwise, are flame-gunned in order with the progress of the repairing, during which a blow rate of the oxygen containing gas is controlled in accordance with the change of the mixing ratio of the fuel powder in the patching material.