# US 2017/0284570 A1 · Joint unit, magnetic rotating arc joining method, and method of manufacturing joint unit > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2017/0284570 A1 - Document ID: US20170284570A1 - Status: Published application - Kind: A1 - Application number: 15/513,583 - Filed: 2015-09-18 - Published: 2017-10-05 - Earliest claimed: 2014-09-25 - Assignees: Ntn Corporation - Applicants: Ntn Corporation - Inventors: Kohei MIZUTA; Chikara OHKI; Daisuke SATO - Web page: https://patentgrep.com/patent/US20170284570A1 ## CPC - B23K 20/028: {Butt welding} - F16L 13/02: Welded joints - B23K 9/00: Arc welding or cutting - B23K 9/028: for curved planar seams - B23K 9/0282: {for welding tube sections} - B23K 9/08: Arrangements or circuits for magnetic control of the arc - B23K 20/227: with ferrous layer - B23K 20/24: Preliminary treatment - B23K 37/08: for flash removal - B23K 2103/04: Steel {or steel} alloys - B23K: SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM - F16L: PIPES; JOINTS OR FITTINGS FOR PIPES; SUPPORTS FOR PIPES, CABLES OR PROTECTIVE TUBING; MEANS FOR THERMAL INSULATION IN GENERAL ## Abstract A joint unit includes a first metal pipe, a second metal pipe, and a joint portion (a region including a joint interface at which the end faces of the first and second metal pipes are joined to each other. At the joint portion, an outer circumferential bead portion protruding toward the outer circumference side and an inner circumferential bead portion protruding toward the inner circumference side are formed. The difference between the width of the outer circumferential bead portion (the width L1 of a grinding portion and the width L2 of the inner circumferential bead portion in a direction from the first metal pipe toward the second metal pipe is equal to or smaller than 40% with respect to the average value of the width L1 of the outer circumferential bead portion and the width L2 of the inner circumferential bead portion. ## Claims ### Claim 1 A joint unit comprising: a first metal pipe; a second metal pipe; and a joint portion at which end faces of the first and second metal pipes are joined to each other, wherein at the joint portion, an outer circumferential bead portion protruding toward an outer circumference side and an inner circumferential bead portion protruding toward an inner circumference side are formed, a difference between a width of the outer circumferential bead portion and a width of the inner circumferential bead portion in a direction from the first metal pipe toward the second metal pipe is equal to or smaller than 40% with respect to an average value of the width of the outer circumferential bead portion and the width of the inner circumferential bead portion. ### Claim 2 (depends on 1) The joint unit according to claim 1, wherein in the joint portion, the outer circumferential bead portion is removed by grinding, and the width of the outer circumferential bead portion is a width of a grinding portion formed by removing the outer circumferential bead portion by grinding. ### Claim 3 A joint unit comprising: a first metal pipe; a second metal pipe; and a joint portion at which end faces of the first and second metal pipes are joined to each other, wherein at a joint interface between the first metal pipe and the second metal pipe in the joint portion, a dendrite layer does not exist in a region inside outer circumferential surfaces of the first and second metal pipes and outside inner circumferential surfaces of the first and second metal pipes. ### Claim 4 (depends on 1) The joint unit according to claim 1, wherein a material of the joint unit is carbon steel for mechanical structures. ### Claim 5 A magnetic rotating arc joining method comprising the steps of: preparing first and second metal pipes; performing preheating until temperature at a position 2 mm away from end faces of the first and second metal pipes reaches a preheating temperature, by producing an arc discharge between the end faces of the first and second metal pipes in a state in which the end faces are disposed to be opposed to each other and applying a magnetic field between the end faces to move a position of the arc discharge in between the end faces; performing main heating until temperature at the position 2 mm away from the end faces of the first and second metal pipes reaches a joining temperature, by producing an arc discharge between the end faces of the first and second metal pipes and applying a magnetic field between the end faces to move a position of the arc discharge in between the end faces; and a step of joining the end faces by butting the end faces to each other after the step of main heating. ### Claim 6 (depends on 5) The magnetic rotating arc joining method according to claim 5, further comprising the step of feeding upset current between the end faces, after the step of main heating and before the step of joining, the upset current having a value greater than an energizing current value in the step of main heating. ### Claim 7 (depends on 5) The magnetic rotating arc joining method according to claim 5, wherein in the step of joining, a joint portion at which the end faces are butted and joined to each other is energized and heated. ### Claim 8 A magnetic rotating arc joining method comprising the steps of: preparing first and second metal pipes; performing main heating until temperature at a position 2 mm away from the end faces of the first and second metal pipes reaches a joining temperature, by producing an arc discharge between the end faces of the first and second metal pipes and applying a magnetic field between the end faces to move a position of the arc discharge in between the end faces; and joining the end faces by butting the end faces each other, after the step of main heating, wherein in the step of joining, a relative pressure welding speed of the first metal pipe to the second metal pipe in butting the end faces to each other is 20 mm/s or more. ### Claim 9 (depends on 8) The magnetic rotating arc joining method according to claim 8, wherein in the step of joining, a pressure welding force in butting the end faces to each other is 5 MPa or more. ### Claim 10 (depends on 8) The magnetic rotating arc joining method according to claim 8, wherein after the step of joining, a dendrite layer does not exist in a region inside outer circumferential surfaces of the first and second metal pipes and outside inner circumferential surfaces of the first and second metal pipes in a joint interface between the first metal pipe and the second metal pipe. ### Claim 11 (depends on 8) The magnetic rotating arc joining method according to claim 8, further comprising the step of, after the step of preparing and before the step of main heating, performing preheating until temperature at the position 2 mm away from the end faces of the first and second metal pipes reaches a preheating temperature, by producing an arc discharge between the end faces of the first and second metal pipes in a state in which the end faces are disposed to be opposed to each other and applying a magnetic field between the end faces to move a position of the arc discharge in between the end faces. ### Claim 12 (depends on 5) A method of manufacturing a joint unit, using the magnetic rotating arc joining method of claim 5. ### Claim 13 (depends on 3) The joint unit according to claim 3, wherein a material of the joint unit is carbon steel for mechanical structures. ### Claim 14 (depends on 8) A method of manufacturing a joint unit, using the magnetic rotating arc joining method of claim 8.