Process for production of seamless metal pipe by cold rolling

A technology of seamless metal pipes and cold rolling mills, applied in the direction of metal rolling, etc., can solve the problems of unproposed high-quality seamless steel pipes, and achieve the effect of suppressing inner surface defects

Inactive Publication Date: 2011-11-16
NIPPON STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, no method has been proposed to manufacture high-quality seamless steel pipes free from inner surface defects by cold rolling using a pilger cold rolling mill.

Method used

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  • Process for production of seamless metal pipe by cold rolling
  • Process for production of seamless metal pipe by cold rolling
  • Process for production of seamless metal pipe by cold rolling

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0045] The 25Cr-30Ni-3Mo high-alloy steel pipe with an outer diameter of 50.8mm and a wall thickness of 5.5mm produced by hot extrusion was used as the test tube billet, and the test tube billet was reduced in diameter and rolled into an outer tube billet by a Pilger cold rolling mill. The diameter is 38.1mm and the wall thickness is 2.4mm. Feed and turn angles are assigned at the start of the stroke. The experimental conditions are summarized as follows.

[0046] Diameter of conical mandrel: dm=39.6~33.1mm (with conical surface)

[0047] Feed to the stroke (feed): f = 8.0mm

[0048] Rotation angle (rotation angle) of the stroke: θ=60°

[0049] Tube blank size: do×to=50.8mm×5.5mm

[0050] Processing size: d×t=38.1mm×2.4mm

[0051] Diameter reduction ratio: d / do=0.75

[0052] Stretch ratio: to(do-to) / t(d-t)=2.91

[0053] Wall thickness / outer diameter ratio: t / d=0.063

[0054] Outer diameter reduction rate / wall thickness reduction rate ratio: Rd / Rt=0.46<1 / 2

[0055] Amo...

Embodiment 2

[0059] 25Cr-30Ni- The 3Mo high-alloy steel pipe was used as the test tube billet, and the test tube billet was reduced and rolled to an outer diameter of 41.0mm and a wall thickness of 2.2mm by using a Pilger cold rolling mill. The outer diameter reduction rate of the stretching and shrinking mill was 77% or less. The experimental conditions are summarized as follows.

[0060] The diameter of the tapered mandrel: dm=36.4mm (no tapered surface)

[0061] Feed to stroke: f=8.0mm

[0062] Rotation angle of forward stroke: θ=60°

[0063] Tube size: do×to=48.6mm×6.0mm

[0064] Processing size: d×t=41.0mm×2.2mm

[0065] Diameter reduction ratio: d / do=0.84

[0066] Stretch ratio: to(do-to) / t(d-t)=3.0

[0067] Wall thickness / outer diameter ratio: t / d=0.054

[0068] Outer diameter reduction rate / wall thickness reduction rate ratio: Rd / Rt=0.25<1 / 2

[0069] Among them, the outer diameter reduction rate: Rd={1-(do / d)}×100(%)

[0070] Wall thickness reduction rate: Rt={1-(to / t)}×1...

Embodiment 3

[0073] The 25Cr-30Ni-3Mo with an outer diameter of 101.6mm and a wall thickness of 7.0mm will be produced by a cross piercer, a mandrel mill and a sizing machine using the Mannesmann mandrel rolling process. The high-alloy steel pipe is used as the test tube billet, and the test tube billet is reduced and rolled to an outer diameter of 88.9mm and a wall thickness of 2.8mm by using a Pilger cold rolling mill. The outer diameter reduction rate of the sizing machine is 33% or less. The experimental conditions are summarized as follows.

[0074] The diameter of the tapered mandrel: dm=83.8mm (no tapered surface)

[0075] Feed to stroke: f=10.0mm

[0076] Rotation angle of forward stroke: θ=60°

[0077] Tube blank size: do×to=101.6mm×7.0mm

[0078] Processing size: d×t=88.9mm×2.8mm

[0079] Diameter reduction ratio: d / do=0.88

[0080] Stretch ratio: to(do-to) / t(d-t)=2.8

[0081] Wall thickness / outer diameter ratio: t / d=0.032

[0082] Outer diameter reduction rate / wall thick...

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Abstract

In cold-rolling a seamless metal pipe by means of a cold pilger mill, too great an outer-diameter reduction as compared with wall thickness reduction creates too great a circumferential strain on the flange sides to result in too great a circumferential compressive stress, whereby wrinkles occur on the inner surface of the pipe. Further, the wrinkles are folded on the groove bottom sides to create cold shut folds. Repetition of these phenomena causes flaws on the inner surface. Unlike a tube stock produced by an extrusion process, a tube stock produced by a Mannesmann-mandrel process has, on the inner surface, wrinkles which have occurred during the sizing (using a stretch reducer or a sizer), and the wrinkles are further encouraged by cold-rolling. Therefore, attention must be paid to this problem. In view of these facts, the ratio of outer-diameter reduction to wall thickness reduction in cold-rolling using a cold pilger mill is adjusted to 1 / 2 or below, whereby the occurrence of flaws on the inner surface is prevented in the cold rolling, and a high-quality seamless metal pipe having few flaws on the inner surface can be obtained.

Description

technical field [0001] The present invention relates to a cold-rolling method for seamless metal pipes, and in particular to a method for manufacturing high-quality seamless metal pipes by cold rolling in order to ensure the inner surface quality of high-grade special pipes in view of suppressing wrinkle defects on the inner surface of the pipes method. Background technique [0002] If the seamless metal pipe cannot meet the quality, strength or dimensional accuracy requirements in the hot working state, it will be sent to the cold working process. As the cold working process, a cold drawing method using a die and a plug or a die and a mandrel, and a cold rolling method using a Pilger cold rolling mill are generally used. [0003] In the cold rolling using the pilger cold rolling mill, the degree of processing of the pipe is extremely high, and it can be stretched by about 10 times through rolling processing, and the correction effect of the uneven wall thickness of the pip...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): B21B21/00B21B23/00
CPCB21B17/14B21B2261/04B21B2265/14B21B3/02B21B3/00B21B2261/08B21B21/005B21B19/10B21B21/02B21B21/00B21B23/00
Inventor 林千博
Owner NIPPON STEEL CORP
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