JP2010162579A - Method for manufacturing forge-welded steel tube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a forge-welded steel tube, capable of remarkably reducing the occurrence frequency of crushing of the front edge of the tube when rotationally straightening a forge-welded steel tube stock. <P>SOLUTION: In the method for manufacturing the forge-welded steel tube, an inlet side guide and an outlet side guide of tapered tube type, the inner diameters of which are tapered at their ends closely to the outer diameter of a forge-welded steel tube stock 5, are installed in the inlet side and the outlet side of a rotary straightening machine respectively to guide the tube stock, for correcting the bending, the outer diameter dimension, and the outer diameter shape of the tube stock by means of the rotary straightening machine. Two or more stages of inlet side guides 1 are installed in series with predetermined interstage distances. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a forged steel pipe, and in particular, a method for manufacturing a forged steel pipe including a step of correcting the bending, outer diameter, and shape of a forged steel pipe cut into a predetermined length after forging with a rotary straightening machine. Regarding the method.

Steel pipes used as household gas pipes and water pipes are mainly classified into electric welded pipes and forged welded pipes, and forged welded steel pipes that can be provided at low cost are widespread.
In the forged steel pipe manufacturing process, the steel strip is hot-rolled, so temperature unevenness is likely to occur in the circumferential and longitudinal directions of the pipe. Longitudinal bending and radial flattening are occurring. Therefore, with respect to the forged steel pipe base tube formed by cutting this to a predetermined length, the bend and flatness are corrected with a rotation straightening machine combining a plurality of drum-shaped rolls up and down, so that the outer diameter size and shape are good. The trouble of the next process is prevented, the work is smoothed, and the yield is improved.

  For example, Patent Documents 1 and 2 are given as conventional techniques related to straightening rotation of a tube material. In Patent Document 1, a tubular guide for guiding pipe material is provided on the inlet side of the straightening machine and on the outlet side thereof in two stages. Moreover, in patent document 2, the cylindrical guide for pipe material guidance is provided in the entrance side and the exit side of the roll straightening device one step each. As for such a cylindrical guide, it is known that a tapered cylindrical type in which the inner diameter of the cylinder tip is close to the outer diameter of the pipe material is a preferred form.

JP-A-57-184515 JP-A-5-325

  However, the prior art has a problem that the yield of the product is not good because there are not a few cases where the pipe tip is crushed and becomes a defective material when the rotation of the forged steel pipe base pipe is corrected.

The present invention provides a method for producing a forged steel pipe that solves the above-mentioned problems and can significantly reduce the occurrence frequency of crushing of the tip of the pipe during rotation correction of the forged steel pipe elementary pipe. It is as follows.
(1) While continuously feeding the steel strip, after heating in a heating furnace, it is formed into a tubular shape, and both ends in the circumferential direction of the formed body are heated to below the melting point, and a tubular body is formed by pressure welding and forging. Cut into length to make a forged steel pipe elemental tube, and bend the outer diameter and shape of the elemental tube with a rotation straightening machine. A method of manufacturing a forged steel pipe in which a tapered tube-shaped inlet side guide and outlet side guide having an inner diameter close to the outer diameter of the raw pipe are installed to guide the raw pipe, and the inlet guide is installed in two or more stages in series. A method for producing a forged steel pipe, characterized in that:
(2) The method for manufacturing a forged steel pipe according to (1) above, wherein an interstage distance of the entry-side guide is 150 to 300 mm.
(3) The method for manufacturing a forged steel pipe according to (1) or (2) above, wherein a distance between the entry side guide and the rotation straightening machine is 150 to 350 mm.
(4) Any one of (1) to (3) above, wherein a ratio of the outer diameter of the tube to the difference between the inner diameter of the cylinder end of the inlet guide and the outer diameter of the raw tube is set to more than 0 and 15% or less. The manufacturing method of the forged steel pipe of description.

  According to the present invention, when manufacturing a forged steel pipe, when the forged steel pipe base pipe enters the rotation straightening machine, the vertical and horizontal run-out of the raw pipe is suppressed to be small and stably in the central part in the rotational correction roll width direction. By making it enter, it is possible to prevent the tube tip from being crushed due to the collision between the rotation correction roll width end and the tube tip, and it becomes possible to manufacture a forged steel tube having a good outer diameter and shape. As a result, the forged steel pipe can be manufactured stably with a high yield.

Schematic plan sectional view showing an example of a conventional rotation correction method Schematic plan sectional view showing an example of an embodiment of the present invention Schematic front sectional view showing normal correction progress Schematic front sectional view showing the progress of correction leading to the occurrence of steel pipe tip crushing Explanatory drawing showing the ratio of the outer diameter of the inlet pipe to the difference between the inner diameter of the inlet guide tip and the outer diameter of the pipe

  Conventionally, in the straightening of raw pipes (forged steel pipes), tapered pipe-type inlet guides and outlet guides with the cylinder tip inner diameter approaching the pipe outer diameter on the inlet and outlet sides of the rotation straightener, respectively. Is installed to guide the raw tube. FIG. 1 is a schematic plan sectional view showing an example of a conventional rotation correction method, in which 1 is an entrance guide, 2 is a guide tube, and 3 and 4 are rotation straighteners 1 and 2 respectively. Hourglass rotation correction roll, 5 is a raw pipe (forged steel pipe base pipe), 9 is a pipe material traveling direction, and Ψ is a deflection angle of the raw pipe 5. Conventionally, the entrance guide 1 is installed in one stage as shown in FIG. In the study by the present inventors, the following knowledge was obtained. That is, when the entry side guide 1 has one stage, the upper and lower sides and the left and right sides of the element tube 5 are supported with the entry side guide 1 as a fulcrum until the tip of the element tube 5 reaches the exit side guide (not shown) of the rotation corrector. Vibration is likely to occur. As shown in FIG. 3, if the normal correction progress is present, the horizontal deflection of the tube 5 is small, and the tube 5 is composed of the upper drum rotation correction roll 6 and the lower rotation rotation lower roll 7 of the same stand. The tube tip is not crushed by passing through the central portion in the roll width direction. However, when the horizontal deflection of the pipe 5 is large, as shown in FIG. 4, the tip of the pipe 5 comes from the center in the roll width direction between the upper and lower hourglass rotation correction rolls 6 and 7 of the same stand. Since the end portion (the roll gap in the cross section orthogonal to the tube material traveling direction is smaller) passes through the portion that is largely biased, the end of the base tube 5 is the wide end portion of the upper and lower hourglass rotation correction rolls 6, 7. The tip of the tube will be crushed.

However, after the tip of the pipe reaches the outlet guide, the shake of the pipe is significantly reduced.
From these findings, it is possible to support the pipe at two points on the inlet side of the rotation straightener, or at three or more points, especially from the reduction of the fluctuation of the pipe after the tip of the pipe reaches the outlet guide. The inventors have come up with the idea that the vertical and horizontal deflections of the pipe can be sufficiently suppressed even before the tip of the pipe reaches the exit guide. Then, it was confirmed by experiments that this was actually the case, and the present invention was made. FIG. 2 shows an example in which the entrance guide 1 is installed in two stages in series. The pipe 5 is supported at two points at the inner diameter of the cylindrical tip of the inlet guides 1 and 1 installed in two stages in series on the inlet side of the rotation straightening machine, and the pipe 5 before the tip reaches the outlet guide. The deflection angle Ψ can be kept small. The same applies when three or more entry-side guides are installed in series.

In the present invention, the difference between the tube tip inner diameter D and the tube outer diameter d of the entry side guide shown in FIG. 5 is greater than 0 against the outer tube diameter ratio η = {(D−d) / d} × 100 (%). If it is 15% or less, an appropriate gap can be secured between the outer diameter surface of the blank tube and the inner diameter surface of the cylinder tip, and the deflection of the blank tube can be more effectively suppressed.
Moreover, in this invention, it is preferable that the interstage distance L of the entrance guides 1 and 1 whose definition is shown in FIG. L <150 mm means that the distance between the two points of support is too small, and the effect of suppressing the shake of the raw tube is slightly reduced. On the other hand, L> 300 mm is a restriction that interference with other equipment on the upstream side occurs. This makes it difficult to install.

  Moreover, in this invention, it is preferable that the distance M between the entrance side guide 1 and the roll of a rotation correction machine 1st stand which show a definition in FIG. 2 shall be 150-350 mm. The reason why M> 350 mm is that even if the deflection angle Ψ of the blank tube is the same, the deflection width at the tip of the blank tube is increased, and the deflection suppression effect of the blank tube is slightly reduced. This is because installation becomes difficult due to the equipment constraints of the machine.

When manufacturing a forged steel pipe by rotating the forged steel pipe with a rotary straightening machine, the guide installation conditions of the rotary straightened machine are changed as shown in Table 1, and 1000 straight pipes are rotated for each condition. The number of tube tip crushing was investigated. The results are shown in Table 1.
From Table 1, it can be seen that in the present invention example, the number of occurrences of crushing of the tube tip is significantly smaller than in the comparative example, and the effect of the present invention is evident. In addition, No. 1 and No. 2 in which rotation correction is performed in the best embodiment (conditions in which η, L, and M are all within a preferable range) among the examples of the present invention have the strongest action for suppressing the collapse of the tube tip I understand that there was.

DESCRIPTION OF SYMBOLS 1 Entrance side guide 2 Guide tube 3 Hourglass rotation correction roll of rotation straightener 1st stand 4 Hourglass rotation correction roll 5 of rotation straightener 2nd stand (forged steel pipe blank)
6 Upper hourglass rotation correction roll 7 Lower hourglass rotation forcing roll 9 Tube travel direction L Distance between entry guides M Distance between entry guide and rotation corrector η The ratio of the pipe outer diameter to the outer pipe diameter ratio Ψ

Claims (4)

  While continuously feeding the steel strip, after heating it in a heating furnace, it is formed into a tubular shape, both ends in the circumferential direction of the formed body are heated to below the melting point, and pressed and welded to a predetermined length. Cut and form a forged steel pipe, and correct the bend, outer diameter size and shape of the pipe with a rotary straightener. A method of manufacturing a forged steel pipe in which a tapered tube-shaped inlet guide and outlet guide that are close to the outer diameter of the pipe are installed to guide the raw pipe, wherein the inlet guide is installed in two or more stages in series. A method for producing a forged steel pipe characterized by the above.   The method for producing a forged steel pipe according to claim 1, wherein an interstage distance of the entry side guide is set to 150 to 300 mm.   The method for manufacturing a forged steel pipe according to claim 1 or 2, wherein a distance between the entrance guide and the rotation straightening machine is 150 to 350 mm.   The forged welded steel pipe production according to any one of claims 1 to 3, wherein a ratio of the outer diameter of the raw pipe to the difference between the inner diameter of the pipe tip of the entry side guide and the outer diameter of the raw pipe is set to more than 0 and 15% or less. Method.

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