Inclined rolling facility and method for manufacturing metal tube

Abstract

To provide an inclined rolling facility and a method for manufacturing a metal tube.SOLUTION: An inclined rolling facility of the present invention includes two or more rolling rolls arranged in an inclined manner on a circumference around a pass line, and the rolling rolls are provided with a parallel portion on a rolling roll inlet side and an inlet side face angle on the terminal end side of the parallel portion.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to an inclined rolling facility and a method for manufacturing a metal tube, which are excellent in the circumferential cross-sectional shape of the metal tube after rolling.

Background Art

[0002] In fields where seamless metal tubes are used, especially in fields where excellent corrosion resistance and high strength are required, many elements that improve corrosion resistance, such as Cr and Ni, are added to obtain high corrosion resistance performance. For example, duplex stainless steels (specifically equivalent to JIS G3459 SUS 329J1, 329J3L, 329J4L), austenitic stainless steels (specifically equivalent to JIS G3459 SUS 301, 302, 304, 305, 309, 310, 312, 315, 316, 317, 836, 890, 321, 347), and Ni-based alloys (specifically equivalent to JIS H4552 NW4400, NW6007, NW0276, NW6022, NW6002) can be mentioned.

[0003] As a result of containing a large amount of alloying elements in these steel grades and alloys to improve corrosion resistance, they have a single austenite phase or a multiphase structure containing a large amount of austenite phase. The austenite phase often has a lower yield strength than the ferrite phase or the martensite phase. Therefore, when high yield strength is required for materials containing the austenite phase, dislocation strengthening by cold working is used to increase the yield strength.

[0004] For example, in high-strength and high-corrosion-resistant steel pipes with an outer diameter of 3-1 / 2 inches or more used for oil well pipes, etc., cold working such as cold drawing and cold pilgering is frequently used, and high-strength steel pipes with a yield strength of 125 ksi or more have been put into practical use (see Non-Patent Document 1).

[0005] The cold working method described in Non-Patent Document 1 is an effective technique not only for improving the strength in the longitudinal direction of the steel pipe but also for equalizing the wall thickness distribution in the longitudinal direction of the steel pipe. However, before cold working, many processes are required, such as softening heat treatment of the steel pipe, pickling, chemical conversion treatment for applying a lubricating film, and pipe end processing for creating a gripping portion during drawing. Also, from the perspective of limiting the pressure required for cold working and preventing seizure on the tool, the wall thickness reduction rate can only be obtained to about 20%. Furthermore, if the wall thickness reduction amount is insufficient in one cold working, it is necessary to repeat the series of processes from the softening heat treatment again. Also, since the shape of the steel pipe after cold working is uniquely determined by the tool dimensions used for drawing, tool replacement is required when changing the size, and it is not suitable for manufacturing small quantities of multiple varieties. Furthermore, since there are many processes required when performing cold working, there is a problem that the equipment investment and energy consumption also become large.

[0006] On the other hand, the cold pilger rolling described in Non-Patent Document 1 does not require pre-treatment of the steel pipe and can obtain a high wall thickness reduction rate. However, the feed amount in one pass is as small as several tens of millimeters, and the production efficiency is poor. Also, it is known that there is a problem that the shape of the rolling roll is complex and the tool manufacturing load (specifically, the work load and economic load for manufacturing the rolling roll) is large.

[0007] As a technique for solving the above problems, for example, the technique of Patent Document 1 can be cited. In the technique of Patent Document 1, a cold rolling method is proposed in which a metal pipe is passed through the roll gap of an inclined rolling mill having two or more rolling rolls whose rotating axes are arranged inclined with respect to the rolling pass direction center line (hereinafter, may also be referred to as the "pass line") of the metal pipe and rolled. Thereby, it becomes possible to improve the strength of the metal pipe by cold working with high processing efficiency without requiring pre-treatment such as surface film application and pipe end processing on the pipe to be rolled before processing, and it is said that good effects can be obtained in environmental protection and industry. Also, by making the inner surface freely deformable, it is possible to prevent the surface pressure generated on the tool from becoming excessive, and since it is possible to add the desired processing strain without generating surface defects such as seizure generated in cold drawing, it is also suitable for small batch production of multiple varieties.

Prior Art Documents

Patent Document

[0008]

Patent Document 1

Non-Patent Document

[0009]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] As described above, the cold rolling method described in Patent Document 1 has many advantages. The inclined rolling mill used in the cold rolling method described in this Patent Document 1 passes a pipe to be rolled through the roll gap of the inclined rolling mill to perform rolling (referred to as diameter reduction rolling in the same document 1) to obtain a metal pipe. However, during the rolling, there is a risk that excessive deformation may be applied to the pipe material due to the pipe material protruding between the rolling rolls. Therefore, in Patent Document 1, as a technique for making the circumferential cross-sectional shape of the metal pipe after rolling closer to a perfect circle, that is, improving the roundness of the metal pipe, it cannot be said that it is sufficient yet.

[0011] In addition, the provision of a technique for improving the roundness of the metal pipe after rolling is required not only for cold rolling but also for hot rolling and warm rolling.

[0012] This invention has been made in view of the above problems, and an object thereof is to provide an inclined rolling facility and a method for manufacturing a metal pipe capable of making the circumferential cross-sectional shape of the metal pipe after rolling closer to a perfect circle.

Means for Solving the Problems

[0013] In order to solve the above problems, the inventors of the present invention have intensively studied a manufacturing method for improving the roundness of a metal tube. As a result, it has been found that there is a method of making the circumferential cross-sectional shape of the metal tube after rolling closer to a true circular shape by optimizing the roll shape of the rolling roll.

[0014] Then, through further studies, the inventors of the present invention have completed a manufacturing method for a metal tube consisting of the following gist and an inclined rolling facility for realizing this manufacturing method. [1] It is provided with two or more rolling rolls arranged obliquely on the circumference centered on the pass line, The rolling roll is an inclined rolling facility provided with a parallel portion on the inlet side of the rolling roll and an inlet surface angle on the terminal side of the parallel portion. [2] The length of the parallel portion of the rolling roll satisfies formula (1), and the inclined rolling facility according to [1]. 1.45×(t / D) -0.95 ≦L≦1.98×(t / D) -1.6 …(1) Here, D: outer diameter of the raw tube before rolling (mm), t: wall thickness of the raw tube before rolling (mm), L: length of the parallel portion of the rolling roll (mm). [3] The inlet surface angle of the rolling roll satisfies formula (2), and the inclined rolling facility according to [1] or [2]. ((t / D) / 0.009) 0.71 ≦M≦((t / D) / 0.02) 3.3 …(2) Here, D: outer diameter of the raw tube before rolling (mm), t: wall thickness of the raw tube before rolling (mm), M: inlet surface angle (°). [4] A manufacturing method for a metal tube using the inclined rolling facility according to any one of [1] to [3], A manufacturing method for a metal tube having a rolling process of passing the raw tube through the roll gap of two or more of the rolling rolls and rolling it while rotating the raw tube in the circumferential direction of the tube and advancing it in the tube axis direction to form a metal tube.

Effects of the Invention

[0015] According to the present invention, it is possible to make the circumferential cross-sectional shape of the metal tube after rolling closer to a perfect circular shape, so that the roundness of the metal tube can be improved.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0017] With reference to each figure, the inclined rolling equipment of the present invention and the method for manufacturing a metal tube using the inclined rolling equipment will be described. Note that the following description shows a preferred embodiment of the present invention, and the present invention is not limited to this embodiment.

[0018] 〔Inclined Rolling Equipment〕 With reference to FIGS. 1 to 7, the inclined rolling equipment of the present invention will be described.

[0019] FIG. 1 is a view showing an embodiment of the inclined rolling equipment of the present invention, which is a front view of the inclined rolling equipment from the rolling output side. For the sake of understanding, FIG. 1 shows, as an example, a state in which a metal tube to be rolled is being rolled by an inclined rolling equipment having two rolling rolls (i.e., a two-roll type inclined rolling equipment). FIG. 2 is a schematic view of the inclined rolling equipment and the metal tube to be rolled shown in FIG. 1 as viewed from the side. FIG. 3 is a schematic view of the inclined rolling equipment and the metal tube to be rolled shown in FIG. 1 as viewed from above. For the sake of easy understanding, in FIG. 3, the illustration of the lower rolling roll among the two rolling rolls 3 is omitted. FIGS. 4 and 5 are views for explaining the shape of the rolling roll used in the inclined rolling equipment of the present invention.

[0020] The inclined rolling equipment of the present invention is one of the rolling equipment used in the manufacturing process of metal tubes. Hereinafter, as an example of the "rolling equipment", a cold rolling equipment for performing cold working on a metal tube to be rolled will be described. For example, an inclined rolling equipment having two or more rolling rolls whose rotation axes are inclined with respect to the center line (path line, i.e., the tube axis direction) of the rolling path of the raw tube can be mentioned. Further, as an example of "rolling", the case of performing cold rolling will be described, but the present invention is applicable not only to cold rolling but also to hot rolling and warm rolling. Note that the "metal tube" in the present invention refers to seamless steel tubes, electric welded tubes, forged tubes, and UOE tubes.

[0021] As shown in FIG. 1 and the like, the inclined rolling equipment 10 of the present invention includes two or more rolling rolls 3 disposed obliquely on a circumference centered on the path line 6. That is, two or more rolling rolls 3 are arranged in the circumferential direction of the raw tube 1 and the metal tube 2 to be rolled. The raw tube 1 is supplied to the roll gap of the inclined rolling equipment 10 from the input side (i.e., the rolling input side) of the inclined rolling equipment. Then, while sandwiching the raw tube 1 between two or more rolling rolls 3, the raw tube 1 is passed in the rolling direction (the advancing direction shown in FIG. 2 and the like), so that inclined rolling is performed on the tube material to obtain a metal tube whose outer diameter is reduced to a desired outer diameter dimension.

[0022] In the example of the two-roll type inclined rolling equipment shown in FIGS. 1 and 2, the inclined rolling equipment includes two rolling rolls 3, and the raw pipe 1 is passed in the rolling direction while being sandwiched between a pair of rolling rolls 3. In this example of the cold rolling equipment, the obtained metal pipe is a cold rolled pipe.

[0023] Next, the rolling roll 3 of the present invention will be described.

[0024] First, with reference to FIGS. 2 and 3, the crossing angle γ and the inclination angle β of the rolling roll 3 will be described. FIG. 2 is a cross-sectional view taken along line A-A shown in FIG. 1, and is a view of the rolling roll 3, the pipe to be rolled 2, etc. seen from the side. FIG. 3 is a view seen in the direction of arrow B-B shown in FIG. 2, and is a view of the rolling roll 3, the pipe to be rolled 2, etc. seen from above.

[0025] As shown in FIG. 2 and the like, the rolling roll 3 is a roll for rolling the raw pipe 1 supplied to the inclined rolling equipment 10. The rotation axis 7 of the rolling roll 3 is arranged with an inclination angle β with respect to the pass line 6. The inclination angle β is, as shown in FIG. 3, when the rolling roll 3 is viewed from above (that is, in a direction perpendicular to the pipe axis direction and in the direction in which the rolling load is applied to the raw pipe 1), the angle (unit: °) formed by the straight line in the pipe axis direction (pass line 6) and the rotation axis 7 of the rolling roll 3.

[0026] In this way, by arranging two or more rolling rolls 3 in an inclined manner, the rolling roll 3 that rotates about the rotation axis of the rolling roll 3 utilizes the frictional force generated by the contact between the rolling roll 3 and the raw pipe 1, and draws the raw pipe 1 supplied to the roll gap in the rolling pass direction. Therefore, the raw pipe 1 is rolled in a spiral shape while being rotated by the rolling roll 3. That is, the raw pipe 1 is rolled while rotating in the pipe circumferential direction and advancing in the pipe axis direction. Such a rolling form can be realized by making the roll gap of the rolling roll 3 of the inclined rolling equipment smaller than the outer diameter of the raw pipe 1 and arranging each of the rolling rolls 3 inclined as described above.

[0027] The inclination angle β is not particularly defined. From the viewpoint of controlling the roundness of the metal tube after rolling to a better shape, it is preferable to set the inclination angle β in the range of 2° to 5°.

[0028] In addition to providing the inclination angle β, the rolling roll 3 may be arranged with an intersection angle (crossing angle) γ on the rolling exit side. The intersection angle γ refers to the angle (unit: °) formed between the pass line 6 and the rotation axis 7 of the rolling roll 3 when the rolling roll 3 is viewed in a side view (that is, in a direction perpendicular to the tube axis direction and perpendicular to the direction in which the rolling load is applied to the plain tube 1), as shown in FIG. 2. The intersection angle γ is not particularly defined. From the viewpoint of suppressing additional circumferential shear strain, it is preferable to set the intersection angle γ in the range of 0 to 45.0°.

[0029] In the above two or more rolling rolls 3, the directions in which the inclination angle β and the intersection angle γ are formed with respect to the tube axis direction may be opposite to each other.

[0030] Subsequently, with reference to FIGS. 4 and 5, the shape of the rolling roll 3 of the present invention will be described in detail. Each figure shows an example of the appearance of the rolling roll of the present invention, FIG. 4 is a perspective view, and FIG. 5 is a side view. Note that FIG. 5 also shows a partially enlarged view of the parallel portion and its periphery enlarged.

[0031] In the present invention, in order not to deteriorate the roundness of the circumferential cross-section of the metal tube after rolling, it is important to adopt a roll shape in which a parallel portion 3a and an entrance side angle 3b are provided in a specific region of the rolling roll 3 (see FIGS. 4 and 5).

[0032] As shown in Fig. 5, the parallel portion 3a is a portion parallel to the rotation axis 7 of the rolling roll 3. The inlet surface angle 3b refers to the angle (M1, unit: °) formed between the side surface of the rolling roll 3 on the rolling inlet side (i.e., the tapered side surface of the rolling roll 3 whose cross-sectional shape gradually decreases toward the rolling inlet side) with respect to the traveling direction of the pipe and a straight line 6a parallel to the pipe axis direction (pass line). The rolling roll 3 of the present invention is provided with a parallel portion 3a in the region between the roll end on the rolling inlet side and the surface angle portion, and an inlet surface angle 3b is provided following the end of the parallel portion 3a.

[0033] First, the action and effect of the parallel portion 3a of the present invention will be described.

[0034] Fig. 9 shows a state in which a raw pipe 23 is being rolled using a rolling roll 22 having a barrel-shaped roll as a conventional example of a two-roll type inclined rolling facility 21. As shown in Fig. 9, the rolling roll 22 has a tapered shape in the roll region for rolling the raw pipe 23 and does not have a parallel portion as in the present invention. In the case of such a conventional rolling roll having such a roll shape, since the raw pipe is reduced in diameter in a state where its bending rigidity is low, it cannot withstand large bending, local buckling occurs, and the roundness of the rolled metal pipe deteriorates.

[0035] On the other hand, as shown in Figs. 2 and 5, in the case of the rolling roll 3 of the present invention provided with a parallel portion 3a on the rolling inlet side of the rolling roll, the raw pipe 1 to which strain is imparted by the parallel portion 3a undergoes work hardening. Due to the work hardening, the raw pipe 1 improves its bending rigidity, becomes able to withstand large bending, and local buckling is suppressed. Thereby, the roundness of the rolled metal pipe is improved.

[0036] Through further investigation by the inventors of the present invention, it was found that the parallel portion 3a has a high correlation with roundness.

[0037] A specific description will be given with reference to FIG. 6. FIG. 6 shows a correlation diagram between the length (L) of the parallel portion 3a and the roundness (R) of the metal tube after rolling when the inlet surface angle 3b(M) of the rolling roll 3 is fixed at 10°. The vertical axis represents the roundness (unit: %), and the horizontal axis represents the length of the parallel portion (unit: mm). Note that the conditions other than the inlet surface angle (M) are the same as those in the examples described later, and single-pass rolling is performed on the plain tube using a two-roll type inclined rolling facility arranged at an inclination angle (β): 3° and an intersection angle (γ): 0°. Also, as will be described later, in the present invention, when the value of the roundness (R) is 1.30% or less, it is defined as "excellent roundness". As can be seen from FIG. 6, the roundness (R) improves as the length (L) of the parallel portion increases, but it was found that the roundness deteriorates when the length of the parallel portion exceeds 200 mm. This is because by lightly reducing the diameter of the plain tube with the parallel portion 3a, the plain tube undergoes work hardening without deteriorating the roundness. As a result, it is considered that the roundness is improved because the diameter is reduced by the inlet surface angle 3b while the bending rigidity of the tube being rolled during rolling increases. That is, it was found that there is an appropriate range for the length (L) of the parallel portion 3a.

[0038] From this, it was noted that providing a flat parallel portion 3a, which is a portion parallel to the rotation axis 7 of the rolling roll 3, and appropriately controlling the length (L) of the parallel portion 3a are effective for improving the roundness.

[0039] Subsequently, the action and effect of the inlet surface angle 3b of the present invention will be described.

[0040] Even in the case of a conventional two-roll type inclined rolling facility 21 as shown in FIG. 9, an inlet surface angle may be provided on the rolling roll 22. However, the conventional rolling roll 22 does not have a parallel portion adjacent to the inlet surface angle as in the present invention. Therefore, in the case of a conventional rolling roll having such a roll shape, the plain tube cannot undergo work hardening by the parallel portion of the present invention described above, so the bending rigidity cannot be improved. As a result, it cannot withstand the large bending during diameter reduction by the inlet surface angle.

[0041] Furthermore, through further studies by the present inventors, it was also found that the inlet surface angle 3b has a high correlation with the roundness.

[0042] This will be specifically described with reference to FIG. 7. FIG. 7 shows a correlation diagram between the entrance side surface angle 3b (M) and the roundness (R) of the metal tube after rolling when the length (L) of the parallel portion 4a of the rolling roll 3 is fixed at 40 mm. The vertical axis represents the roundness (unit: %), and the horizontal axis represents the entrance side surface angle (unit: mm). Note that conditions other than the parallel portion length (L) are the same as those in the examples described later, and single-pass rolling is performed on the plain tube using a two-roll type inclined rolling facility arranged at an inclination angle (β): 3° and an intersection angle (γ): 0°. Also, as described above, when the value of the roundness (R) is 1.30% or less, it is defined as "excellent roundness". As shown in FIG. 7, up to an entrance side surface angle of 8°, the roundness improved as the entrance side surface angle increased. Also, from an entrance side surface angle of 8° to 25°, the roundness was substantially constant even as the entrance side surface angle increased, and after an entrance side surface angle of 30°, the roundness deteriorated as the entrance side surface angle increased. The following was found from FIG. 7. By optimizing the entrance side surface angle (M), the timing at which the entrance side surface angle (M) and the diameter reduction of the tube to be rolled are optimized, and as a result, the material flow rate on the entrance side of the rolling roll is increased. Thereby, it is possible to suppress the circumferential expansion of the tube to be rolled during rolling, so that the tube material (tube to be rolled) does not protrude between the rolling rolls, which is considered to be the reason for the improvement of the roundness (R). That is, it was found that there is an appropriate range for the entrance side surface angle (M).

[0043] From this, it was noted that providing the entrance side surface angle 3b adjacent to the terminal side of the flat parallel portion 3a and appropriately managing the entrance side surface angle (M) are also effective for improving the roundness.

[0044] Then, the inventors found that the outer diameter and wall thickness of the plain tube before rolling are respectively affected by the length (L) of the parallel portion 3a of the rolling roll 3 and the entrance side surface angle 3b (M), and arrived at the following formulas (1) and (2).

[0045] Specifically, as shown in FIG. 5, the rolling roll 3 is provided with a parallel portion 3a on the inlet side of the rolling roll, and an inlet surface angle 3b(M) is provided following the end of the parallel portion 3a. The length (L) of the parallel portion 3a is preferably set to satisfy the following formula (1). 1.45×(t / D) -0.95 ≦L≦1.98×(t / D) -1.6 …(1) In addition to this condition, it is more preferable that the inlet surface angle 3b(M) is set to satisfy the following formula (2). ((t / D) / 0.009) 0.71 ≦M≦((t / D) / 0.02) 3.3 …(2) Here, in formulas (1) and (2), D: outer diameter of the raw tube before rolling (mm), t: wall thickness of the raw tube before rolling (mm), L: length of the parallel portion (mm), M: inlet surface angle (°).

[0046] The reason for the limitation of formula (1) will be described below.

[0047] When the length (L) of the parallel portion 3a is less than the left side value of formula (1) (that is, the value of "1.45×(t / D)" -0.95 ), the work hardening by the parallel portion becomes insufficient, and the diameter reduction is performed in a state where the bending rigidity is low, so local buckling is likely to occur. Therefore, the length of the parallel portion 3a is preferably set to be equal to or greater than the value of "1.45×(t / D)" -0.95 , and more preferably set to be equal to or greater than the value of "1.14×(t / D)" -0.99 .

[0048] On the other hand, when the length (L) of the parallel portion 3a exceeds the right side value of formula (1) (that is, the value of "1.98×(t / D)" -1.6 ), the reduction amount by the parallel portion 3a becomes large, and the roundness of the raw tube 1 deteriorates before the diameter reduction by the inlet surface angle 3b, so that the roundness of the metal tube also deteriorates as it is. Therefore, the length of the parallel portion 3a is preferably set to be equal to or less than the value of "1.98×(t / D)" -1.6 , and more preferably set to be equal to or less than the value of "2.31×(t / D)" -1.14 .

[0049] In addition, when the value of t / D, which is the ratio of the wall thickness of the raw tube to the outer diameter of the raw tube, is small, the bending rigidity of the raw tube itself is low. Therefore, when the rigidity of the raw tube is low, increasing the amount of improvement in bending rigidity by preprocessing by extending the parallel portion 3a is considered in Equation (1).

[0050] The reason for the limitation of Equation (2) will be described below.

[0051] When the inlet side angle 3b(M) is less than the value on the left side of Equation (2) (that is, the value of "((t / D) / 0.009) 0.71 "), the taper of the rolling roll becomes gentle, so the contact time between the tube to be rolled and the rolling roll during rolling becomes faster, and the timing at which the tube material is reduced in diameter by the inlet side angle 3b also becomes earlier. As a result, the material flow rate due to diameter reduction becomes excessive. Therefore, the inlet side angle 3b is preferably set to be equal to or greater than the value of "((t / D) / 0.009) 0.71 ", and more preferably set to be equal to or greater than the value of "((t / D) / 0.02) 1.9 ".

[0052] On the other hand, when the inlet side angle 3b(M) exceeds the value on the right side of Equation (2) (that is, the value of "((t / D) / 0.02) 3.3 "), the taper of the rolling roll becomes steep, so the distance by which the tube to be rolled is reduced in diameter by the inlet side angle 3b of the rolling roll during rolling becomes short, and as a result, the amount of diameter reduction per unit distance in the rolling direction becomes excessive and the tube to be rolled protrudes between the rolling rolls. As a result, local buckling occurs. Therefore, the inlet side angle M is preferably set to be equal to or less than the value of "((t / D) / 0.02) 3.3 ", and more preferably set to be equal to or less than the value of "((t / D) / 0.018) 2.9 ".

[0053] Note that as described above, the parallel portion 3a of the present invention is preferably located in the region on the inlet side of the rolling roll with respect to the entire length of the rolling roll 3. By providing the parallel portion within this range, the bending rigidity is improved by work hardening without impairing the roundness of the raw tube.

[0054] Next, with reference to FIG. 8, the roundness in the present invention will be described. FIG. 8 shows an example of a cross-sectional shape perpendicular to the tube axis direction of a metal tube after inclined rolling, which is deformed into an elliptical shape.

[0055] In the cross-section perpendicular to the tube axis direction of the metal tube 20 after inclined rolling shown in FIG. 8, when the maximum value of the outer diameter of the metal tube 20 (i.e., the major axis of the ellipse) is Dmax and the minimum value of the outer diameter (i.e., the minor axis of the ellipse) is Dmin, the difference between the two, that is, the difference between the maximum outer diameter and the minimum outer diameter in the cross-section perpendicular to the tube axis direction of the metal tube 20 (Dmax - Dmin) is defined as Cp. Also, the average value of the outer diameter (average outer diameter) of the metal tube 20 is defined as Dave.

[0056] Then, the value of Cp and the value of Dave are substituted into Equation (3), and the obtained value R is defined as the roundness. In the present invention, when the value of this roundness (R) is 1.30% or less, it is defined as "good roundness" (i.e., "excellent roundness"). R = (Cp / Dave) × 100 …(3) Here, in Equation (3), R: roundness (%), Cp: difference between the maximum and minimum outer diameters in the cross-section perpendicular to the tube axis direction (mm), Dave: average value of the outer diameter in the cross-section perpendicular to the tube axis direction (mm).

[0057] Note that the outer diameter of the metal tube (unit: mm) can be measured using, for example, calipers. When measuring the outer diameter of the tube end, a straightedge may be used.

[0058] Also, when measuring the outer diameter other than the tube end, the metal tube is cut at the measurement location so as to be perpendicular to the tube axis direction, and the shape of the cut surface is measured. In the present invention, the above-mentioned maximum and minimum outer diameters are obtained by measuring the outer diameter of the tube at 24 equally spaced points in the circumferential direction of the cut surface, taking the maximum value as Dmax and the minimum value as Dmin. Also, the above-mentioned average outer diameter (Dave) is the average of the values obtained by measuring these 24 points.

[0059] When measuring the outer diameter using a caliper or a ruler, in the cross-section perpendicular to the tube axis direction, the distance in the circumferential direction of the tube between two points that become the measurement positions on the tube circumference (that is, the installation positions of the caliper or the ruler) is set to be 1 / 2 of the tube circumference.

[0060] Also, the measurement position in the tube axis direction of the metal tube can be at any location. However, since the regions including the tip and tail ends of the metal tube cause non-steady part deformation, it is desirable to measure the outer diameter at locations excluding 20 mm from each of the tip and tail ends, and more preferably at locations excluding 40 mm from each of the tip and tail ends. Also, multiple measurement positions in the tube axis direction can be set, and the average value of the obtained values can be used. For example, the number of measurement locations can be 10 points, and the average of the measurement values at these 10 points can be used.

[0061] In the above description, a two-roll type inclined rolling mill was shown using FIG. 1. However, according to the present invention, even in an inclined rolling mill in which three or more rolling rolls are arranged in the circumferential direction of the tube, the same operational effects can be obtained, so that the tube to be rolled (raw tube) can be rolled.

[0062] 〔Manufacturing method of metal tube〕 Hereinafter, a manufacturing method of a metal tube for manufacturing a metal tube using the above-described inclined rolling equipment of the present invention will be described. Note that the description regarding the rolling roll is omitted since it has already been made in the description of the inclined rolling equipment.

[0063] The manufacturing method of the metal tube of the present invention has a rolling step of obtaining a metal tube by passing the raw tube 1 through the roll gaps of two or more rolling rolls while rotating the raw tube in the circumferential direction and advancing it in the tube axis direction for inclined rolling.

[0064] In the manufacturing method of the metal tube of the present invention, for example, heat treatment may be performed on the metal tube after the above rolling step. Also, for example, a treatment may be performed to remove the scale on the surface of the metal tube by pickling the metal tube after the above rolling step. The conditions for the heat treatment and pickling treatment may be appropriately set according to the composition of the metal tube and the like.

[0065] In the present invention, the manufacturing conditions of the base pipe before performing the above rolling process are not particularly limited, and generally known manufacturing conditions can be adopted. Also, the base pipe before performing the rolling process is not particularly limited, and a hollow pipe may be used.

[0066] Also, even if there is a difference between the maximum outer diameter value and the minimum outer diameter value in the shape of the base pipe before performing the rolling process, the above effects of the present invention can be obtained. From the viewpoint of more effectively obtaining the operational effects of the present invention, the base pipe before performing the rolling process has an elliptical or circular cross-section perpendicular to the pipe axis direction, and the value obtained by dividing the difference between the maximum outer diameter value and the minimum outer diameter value by the maximum outer diameter value (i.e., ((maximum outer diameter value - minimum outer diameter value) / maximum outer diameter value)×100) is preferably 10% or less, and more preferably 7% or less.

[0067] As described above, by rolling the base pipe with the inclined rolling equipment of the present invention, the bending rigidity during rolling due to work hardening in the parallel portion 3a increases, and the pipe to be rolled can be reduced in diameter by the inlet side angle 3b following the parallel portion. Therefore, regardless of the component composition of the base pipe, the yield strength of the rolled metal pipe can be 700 MPa or more. Also, from the viewpoint of preferably using the present invention in the manufacture of metal pipes for the above applications (for example, oil wells), the outer diameter of the metal pipe is preferably 8 to 600 mm, and the wall thickness of the metal pipe is preferably 0.2 to 40.0 mm. The wall thickness is more preferably 1.0 to 32.0 mm.

[0068] As described above, according to the present invention, by using inclined rolling equipment having a rolling roll provided with a parallel portion of an appropriate length on the inlet side of the rolling roll and an inlet side angle with an appropriately provided face angle on the terminal side of the parallel portion, rolling can be performed in a state where the roundness of the cross-sectional shape of the rolled metal pipe is good. In particular, in the present invention, pretreatment such as surface coating application and pipe end processing is not required for the base pipe before inclined rolling. Also, while realizing an improvement in the hardness of the metal pipe by inclined rolling, it is possible to suppress a decrease in the roundness of the cross-sectional shape after inclined rolling.

Examples

[0069] Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited by the following embodiments, and can be appropriately modified within the range that conforms to the gist of the present invention.

[0070] First, a raw pipe with an outer diameter of 88 mm (the difference between the maximum outer diameter and the minimum outer diameter: 0 mm), a wall thickness of 5 mm, and a length of 250 mm was taken from a stainless steel bar (material: SUS329J3L) conforming to JIS G 4303:2012 standard by machining. Next, one-pass rolling was performed on the raw pipe at room temperature.

[0071] For this rolling, as equipment for performing cold rolling, two-roll type inclined rolling equipment or three-roll type inclined rolling equipment was used. The shape of the rolling rolls of these inclined rolling equipment was the roll shape shown in Table 2. In addition, during rolling, the inclination angle β of the rolling roll 3 was set to 3°, the crossing angle γ was set to 0°, and the roll gap of the rolling roll 3 was set to 76 mm.

[0072] Then, using the rolled metal pipe (here, a cold-rolled pipe), the roundness R was evaluated by the above method. A vernier caliper was used to measure the outer diameter of the metal pipe. As described above, the difference Cp between the maximum outer diameter Dmax and the minimum outer diameter Dmin obtained by measuring the outer diameter at 24 equally spaced points in the circumferential direction of the pipe was calculated, and the average outer diameter Dave was also obtained. The roundness R was calculated using the obtained values and the above formula (3), and the roundness was evaluated.

[0073] Based on the calculated value of the roundness R, A to D were assigned to the remarks column in Table 1. A was when the value of the roundness R was 1.10% or less, B was when the value of the roundness R exceeded 1.10% to 1.20%, C was when the value of the roundness R exceeded 1.20% to 1.30%, and D was when the value of the roundness R exceeded 1.30%. Here, when the calculated value of the roundness R was 1.30% or less, it was evaluated as "excellent roundness". The measurement position in the pipe axis direction was the central position of the metal pipe (that is, the position corresponding to half of the total length of the pipe).

[0074]

Table 1

[0075] From Table 1, it was confirmed that by rolling the tube to be rolled with the inclined rolling equipment equipped with the rolling roll having the roll shape of the present invention, the metal tube can be rolled without deterioration of the roundness.

Explanation of Signs

[0076] 1 Plain tube 2 Tube to be rolled 3 Rolling roll 3a Parallel part 3b Inlet surface angle 6 Pass line 7 Rotation axis of rolling roll 10 Inclined rolling equipment 20 Metal tube 21 Inclined rolling equipment 22 Rolling roll 23 Plain tube 24 Tube to be rolled β Inclination angle γ Crossing angle L Length of parallel part M Inlet surface angle Dmax Maximum outer diameter Dmin Minimum outer diameter

Claims

1. comprising two or more rolling rolls disposed obliquely on a circumference centered on a pass line, wherein the rolling roll is an inclined rolling facility provided with a parallel portion on the inlet side of the rolling roll and an inlet surface angle on the terminal side of the parallel portion.

2. The inclined rolling facility according to claim 1, wherein the length of the parallel portion of the rolling roll satisfies formula (1). 1.45×(t / D) －０．９５ ≦ L ≦ 1.98×(t / D) －１．６ …(1) Here, D is the outer diameter of the raw pipe before rolling (mm), t is the wall thickness of the raw pipe before rolling (mm), and L is the length of the parallel portion of the rolling roll (mm).

3. The inclined rolling facility according to claim 1, wherein the inlet surface angle of the rolling roll satisfies formula (2). ((t / D) / 0.009) ０．７１ ≦ M ≦ ((t / D) / 0.02) ３．３ …(2) Here, D is the outer diameter of the raw pipe before rolling (mm), t is the wall thickness of the raw pipe before rolling (mm), and M is the inlet surface angle (°).

4. The inclined rolling facility according to claim 2, wherein the inlet surface angle of the rolling roll satisfies formula (2). ((t / D) / 0.009) ０．７１ ≦ M ≦ ((t / D) / 0.02) ３．３ …(2) Here, D is the outer diameter of the raw pipe before rolling (mm), t is the wall thickness of the raw pipe before rolling (mm), and M is the inlet surface angle (°).

5. A method for manufacturing a metal tube using the inclined rolling facility according to any one of claims 1 to 4, the method for manufacturing a metal tube having a rolling step of rotating the raw tube in the circumferential direction of the tube and passing the raw tube through the roll gap of two or more of the rolling rolls while advancing in the axial direction of the tube to form a metal tube.

Images