Patent ID: 9303668
Filing Date: 2016-04-05
CPC Classification: B21D,C21D,F16B

Claim Text:
1. A method of producing a nut-side thin joint member of a pipe coupling metal joint for coupling two pipes to each other in a manner that the two pipes are held between a circular-arc shaped surface of the nut-side thin joint member and a circular-arc shaped surface of a bolt-side thin joint member, the surfaces each following curved surfaces of the pipes to be held, and fastened by a bolt and a nut, the method comprising: preparing a thin metal sheet with thickness of 1.0 to 1.3 mm, made of boron steel, the thin metal sheet having 0.20 to 0.25 mass % of carbon and 0.001 to 0.005 mass % of boron; bending the thin metal sheet into a three-dimensionally shaped, pre-joint member having the circular-arc shaped surface; forming a cylindrical body portion in the pre-joint member by performing burring; forming a threaded part having a thread ridge comprising 3 to 3.5 ridges by performing rolling tapping on the cylindrical body, so as to make a nut; and thereafter performing quenching on the pre-joint member, the pre-joint member being heated in a furnace at a temperature of 870° C. to 900° C., thereby forming the nut-side thin joint member with the threaded part, the thickness of the thread ridge being kept 0.8 mm or more.