Abstract: A fastening bolt fastens flanges between a bolt head and a nut attached on the threaded portion of the shaft via spherical washers. The fastening bolt has a cavity formed within the shaft. By application of pressure in the cavity with a hydraulic fluid supplied through a hydraulic pressure port in a plug, the shaft is extended and the fastening bolt becomes unfastened condition. In the unfastened condition, a gap is created between flange and nut, and the nut and the fastening bolt are free to rotate each other, therefore, the nut can be removed easily by hand from the fastening bolt, even the bolt is large in size. The fastening force is adjustable by the width of the gap before releasing hydraulic pressure in the cavity. By releasing hydraulic pressure in the cavity, the fastened condition is obtained. Conversion between fastened condition and unfastened condition can be made quickly and easily.

Abstract: The disclosure relates to a molten metal producing and refining method which does not damage the apparatus, realizes a stable and high second combustion rate, and is capable of effectively recovering heat generated by the second combustion. The method comprises introducing a metal-containing material, a carbonaceous material, a flux and O.sub.2 gas into a furnace. The carbon which dissolves into the metal bath in the furnace from the carbonaceous material is combusted with the O.sub.2 gas to generate heat and CO gas. The CO gas is subjected to the second combustion with the O.sub.2 gas to additionally generate heat, and the metal-containing material is melted and refined by both the generated heat and carbon. The method is characterized in that O.sub.2 gas or O.sub.2 -containing gas is blown into the furnace through large-diameter tuyeres installed near the bottom of the furnace and a part of the O.sub.