# US 11,305,320 B2 · Method for producing seamless metal pipe

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- Number: US 11,305,320 B2
- Document ID: US11305320B2
- Status: Granted
- Kind: B2
- Application number: 16/619,631
- Filed: 2018-06-08
- Published: 2020-05-21
- Granted: 2022-04-19
- Earliest claimed: 2017-06-12
- Assignees: Nippon Steel Corporation
- Applicants: Nippon Steel Corporation
- Inventors: Kouji Yamane; Kazuhiro Shimoda; Yuji Inoue; Shusuke Shimooka; Yuichi Yamanari
- Web page: https://patentgrep.com/patent/US11305320B2

## CPC

- B21C 23/085: {Making tubes (B21C23/10 take precedence)}
- B21B 19/04: Rolling basic material of solid, i.e. non-hollow, structure; Piercing {, e.g. rotary piercing mills}
- B21B 23/00: Tube-rolling not restricted to methods provided for in only one of groups B21B17/00, B21B19/00, B21B21/00, e.g. combined processes {planetary tube rolling, auxiliary arrangements, e.g. lubricating, special tube blanks, continuous casting combined with tube rolling}(B21B25/00 takes precedence)
- B21C 25/08: Dies or mandrels with section variable during extruding, e.g. for making tapered work; Controlling variation
- B21C: MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES, PROFILES OR LIKE SEMI-MANUFACTURED PRODUCTS OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
- B21B: ROLLING OF METAL (auxiliary operations used in connection with metal-working operations covered in B21, see B21C; bending by rolling B21D; manufacture of particular objects, e.g. screws, wheels, rings, barrels, balls, by rolling B21H; pressure welding by means of a rolling mill B23K20/04)

## Abstract

A method for producing a seamless metal pipe includes the steps of: preparing a billet having a diameter (B); heating the billet; forming, in a center part of a rear end of the heated billet, a hole including four grooves extending in an axial direction of the billet, the grooves each having a groove width (D) satisfying Formula (1), a groove height (H) satisfying Formula (2), and a groove depth (L1) satisfying Formula (3); and subjecting the billet provided with the hole to piercing-rolling from a front end thereof by means of a piercing machine. By this means, the generation of burrs and internal defects at the rear end of a hollow shell after piercing-rolling can be suppressed. 0.12≤D/B≤0.25 (1) 0.10≤H/B≤0.20 (2) 0.05≤L1/B≤0.10 (3)

## Claims

### Claim 1

A method for producing a seamless metal pipe using a piercing machine including a plurality of skew rolls and a plug arranged between the plurality of skew rolls, the method comprising the steps of:
preparing a billet having a diameter B (mm),
heating the billet,
forming, in a center part of a rear end of the heated billet, a hole including four grooves extending in an axial direction of the billet, the grooves each having a groove width D (mm) satisfying Formula (1), a groove height H (mm) satisfying Formula (2) and a groove depth L1 (mm) satisfying Formula (3), and
subjecting the billet provided with the hole to piercing-rolling from a front end by means of the piercing machine, wherein
the four grooves are provided in a cross shape as seen from an axial direction of the billet,
the four grooves extend from the rear end face of the billet,
the grooves are disposed at equal intervals around the axial centerline of the billet, and two grooves that are adjacent in the circumferential direction are orthogonal, and wherein
each groove side-face of the groove is parallel with the radial direction of the billet, and among the two ends of the groove side-face, an end that is nearer to a rear end center connects with an end that is nearer to the rear end center of the groove side-face of another groove that is adjacent thereto:
0.12≤D/B≤0.25 (1)
0.10≤H/B≤0.20 (2)
0.05≤L1/B≤0.10 (3).

### Claim 2 (depends on 1)

The method for producing a seamless metal pipe according to claim 1, wherein:
L2 (mm) satisfies Formula (4), where L2 is a distance that is twice a maximum distance from a rear end center of the billet to a groove bottom face on a rear end face of the billet;
0.30≤L2/B≤0.60 (4).