Abstract: A knife cylinder for a rotary cutter capable to accommodate to increased cutting speed and width of a corrugated cardboard sheet in recent years and low in weight and rotatory inertia and having enough tensile strength, flexural and torsional rigidity, is provided. The cylinder body of the knife cylinder is a hollow cylindrical body consisting of layers of carbon fiber reinforced plastic and has tensile elastic modulus of 206 GPa or higher in axial direction thereof. Preferably the innermost layer is of a CFRP layer 41 with carbon fibers arranged to extend in circumferential direction of the cylinder body, and a plurality of sets of CFRP layers consisting of a layer 42 with carbon fibers arranged to extend in axial direction and layers 42, 44 with carbon fibers arranged to extend in directions inclined by ±30°˜±60° to axial direction of the cylinder are laminated on the innermost layer.

Abstract: A sodium secondary battery which assures excellent sealing and can be manufactured in a simple manner is provided. The battery includes a negative electrode chamber defined by the inside of a bottom-closed, hollow cylindrical, solid electrolyte accommodated in an outer case and a positive electrode chamber formed outside the solid electrolyte and containing a porous electrode 4 impregnated with sulfur which serves as a positive electrode active substance. A cover, which closes the opening portion of the outer case, is fastened to the outer case by use of bolts and the interposition of an insulator.

Abstract: There is disclosed a high heat resistant aluminum alloy impeller, which is suitably used as an impeller, especially for a centrifugal compressor, and for the rotor and the blade of a turbo molecular pump or the scroll of a scroll compressor. Also, a method for manufacturing this aluminum alloy impeller is disclosed. The impeller is composed of an Al--Fe rapid solidification aluminum alloy, which is produced by a spray forming process for spraying a molten metal with inert gas and rapidly solidifying the metal at a cooling speed of 10.sup.2 .degree. C./sec. or higher while simultaneously deposing the metal. The rapid solidification aluminum alloy is subjected to hot extrusion processing within a temperature range of 200.degree. C. to 600.degree. C. and further subjected to hot forging.