Inclined rolling facility, inclined rolling method, and method for manufacturing metal tube

Abstract

To provide an inclined rolling facility, an inclined rolling method, 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 has control means for controlling the inclination angles of the two or more rolling rolls, and the control means sets the inclination angles of the two or more rolling rolls so as to satisfy a formula (1). 0.009×(t / D)(-1.8)≤FA≤3.2+0.022×(t / D)(-2.2) ...(1)SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an inclined rolling facility for rolling metal pipes, an inclined rolling method, and a method for manufacturing metal pipes.

Background Art

[0002] In fields where seamless metal pipe products are used, especially in fields where particularly excellent corrosion resistance and high strength are required, in order to improve corrosion resistance, two-phase stainless steels (specifically equivalent to JIS G3459 SUS 329J1, 329J3L, 329J4L) or austenitic stainless steels (specifically equivalent to JIS G3459 SUS 301, 302, 304, 305, 309, 310, 312, 315, 316, 317, 836, 890, 321, 347) containing a large amount of alloying elements added to exhibit excellent corrosion resistance performance, as well as seamless steel pipes of Ni-based alloys (specifically equivalent to JIS H4552 NW4400, NW6007, NW0276, NW6022, NW6002) are used.

[0003] These steel grades and alloys contain a large amount of alloying elements added to exhibit excellent corrosion resistance performance. Therefore, as a structure, it becomes a single-phase austenite phase or a multiphase structure containing a large amount of austenite phase. The austenite phase with a face-centered cubic lattice (fcc) structure often has a lower yield strength than the ferrite phase or martensite phase with a body-centered cubic lattice (bcc) structure in a use environment of about low temperature to normal temperature. Therefore, when a higher yield strength is required for a material containing an austenite phase, cold working is added to the material, and dislocation strengthening by processing is utilized to increase the yield strength.

[0004] For example, in high-strength and high-corrosion-resistant steel pipes used for oil well pipes and the like, 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 drawing process described in Non-Patent Document 1 is an effective method not only for improving the strength in the longitudinal direction of a steel pipe but also for equalizing the wall thickness distribution in the longitudinal direction of the steel pipe. However, before the drawing process, 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 part during drawing. Also, from the perspective of limiting the pressure required for drawing and preventing seizure on the tool, a wall thickness reduction rate of only about 20% can be obtained. Furthermore, if the wall thickness reduction amount in one drawing process is insufficient, it is necessary to repeat the series of processes starting from the aforementioned softening heat treatment. In addition, since the shape of the steel pipe after drawing is uniquely determined by the tool dimensions used for drawing, tool replacement is required when changing the size, which is not suitable for manufacturing in small quantities with many varieties. Moreover, since there are many processes required when performing the drawing process, there is a problem that the facility investment and energy consumption also become large.

[0006] On the other hand, cold pilger rolling does not require pre-treatment of the steel pipe and can achieve a high wall thickness reduction rate. However, the feed amount in one pass is as small as several tens of mm, and the production efficiency is poor. Also, the shape of the rolling rolls is complex, and the tool manufacturing load (specifically, the work load and economic load for manufacturing the rolling rolls) is large.

[0007] As a technology for solving these problems, for example, Patent Document 1 can be cited. In the technology described in 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 rotation 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 for rolling. Thereby, it is possible to improve the strength of the metal pipe by cold working with high processing efficiency without requiring pre-treatment such as applying a surface film or processing the pipe ends to the metal pipe to be rolled before processing, and it is said that good effects can be obtained in terms of 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 no surface defects such as seizure generated in cold drawing occur and the desired processing strain can be added, it is also suitable for small-lot and multi-variety production.

Prior Art Documents

Patent Documents

[0008] [Patent Document 1] Japanese Patent Publication No. 6432614 [Non-Patent Document]

[0009] [Non-Patent Document 1] The Iron and Steel Institute of Japan, "Current Status and Future of Steel Pipe Manufacturing Technology", published by The Iron and Steel Institute of Japan, May 6, 1986, pp. 115-145 [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 various advantages. However, the tilt rolling mill used in Patent Document 1 may apply a large stress in the circumferential direction of the pipe due to the rolling load from the rolling rolls during rolling, and excessive deformation may be applied to the pipe material. Therefore, in Patent Document 1, the technology for making the cross-sectional shape of the rolled metal pipe closer to a perfect circle, that is, improving the roundness of the metal pipe, cannot yet be said to be sufficient.

[0011] In addition, the provision of technology for improving the roundness of the rolled metal pipe is required not only for cold rolling but also for hot rolling, warm rolling, etc.

[0012] The present invention has been made in view of the above problems, and an object thereof is to provide a tilt rolling facility, a tilt rolling method, and a method for manufacturing a metal pipe capable of making the cross-sectional shape of the rolled metal pipe 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 an inclined rolling method for improving the roundness of a metal tube and a method for manufacturing a metal tube, and have also intensively studied an inclined rolling facility capable of realizing this method. As a result, it has been found that there is a method of making the cross-sectional shape of the metal tube after rolling closer to a perfect circle by appropriately controlling the contact area between the rolling roll and the tube to be rolled during rolling. In addition to this, it has also been found that the control of the progress degree of the raw tube and the tube to be rolled advancing in the tube axis direction is more effective.

[0014] Through further studies, the inventors of the present invention have completed an invention consisting of the following gist. [1] An inclined rolling facility comprising two or more rolling rolls disposed inclined on a circumference centered on a pass line, having control means for controlling the inclination angle of the two or more rolling rolls, wherein the control means sets the inclination angle of the two or more rolling rolls so as to satisfy formula (1), the inclined rolling facility. 0.009×(t / D) (-1.8) ≦FA≦3.2 + 0.022×(t / D) (-2.2) …(1) Here, as shown in formula (1), t: The wall thickness [mm] of the raw tube before rolling set in advance, D: The outer diameter [mm] in the cross-section perpendicular to the tube axis direction of the raw tube before rolling set in advance, FA: The inclination angle [°] of the rolling roll, is. [2] The control means further when the size of the contact range between the rolling roll and the tube surface of the tube to be rolled during rolling is CA, sets the inclination angle of the two or more rolling rolls so that the value of CA represented by formula (3) satisfies formula (4), the inclined rolling facility according to [1]. CA = ((t / D) (-1.8) ) / FA …(3) CA≦50 …(4) Here, as shown in each formula, CA: A parameter [-] representing the size of the contact range, t: The wall thickness [mm] of the raw tube before rolling set in advance, D: Outer diameter [mm] in the cross-section perpendicular to the tube axis of the raw tube before rolling set in advance, FA: Inclination angle of the rolling roll [°]. [3] An inclined rolling method using the inclined rolling equipment described in [1] or [2], When rolling while rotating the raw tube in the circumferential direction of the tube and advancing it in the tube axis direction, the inclination angle of the two or more rolling rolls is controlled by the control means. [4] A method for manufacturing a metal tube using the inclined rolling equipment described in [1] or [2], While rotating the raw tube in the circumferential direction of the tube and advancing it in the tube axis direction, a rolling process is performed by passing the raw tube through the roll gap of the two or more rolling rolls to form a metal tube. In the rolling process, the inclination angle of the two or more rolling rolls is controlled by the control means, and the raw tube is rolled at the inclination angle.

Effect of the Invention

[0015] According to the present invention, since the cross-sectional shape of the rolled metal tube can be made closer to a perfect circle, a decrease in the roundness of the metal tube can be suppressed.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0017] Embodiments of the present invention will be described with reference to the respective drawings. 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〕 The inclined rolling equipment of the present invention will be described with reference to FIGS. 1 to 4.

[0019] FIG. 1 is a view showing an embodiment of the inclined rolling equipment of the present invention, and is a front view of the inclined rolling equipment from the rolling output side. Note that FIG. 1 shows, as an example, a state in which rolling is being performed on a tube to be rolled by an inclined rolling equipment having two rolling rolls (that is, a two-roll type inclined rolling equipment). FIG. 2 is a schematic diagram of the inclined rolling equipment and the tube to be rolled shown in FIG. 1 viewed from the side. FIG. 3 is a schematic diagram of the inclined rolling equipment and the tube to be rolled shown in FIG. 1 viewed from above. FIG. 4 is a diagram for explaining an example of an inclined rolling method using the inclined rolling equipment of the present invention. Note that, for ease of understanding, in FIG. 3, the illustration of the lower rolling roll among the two rolling rolls 3 is omitted, and in FIGS. 2 to 4, the plain tube 1 and the tube to be rolled 2 are shown as cross-sectional views.

[0020] The inclined rolling equipment of the present invention is one of the rolling equipment used in the manufacturing process of metal pipes. Below, as an example of "rolling equipment", cold rolling equipment for performing cold rolling on a pipe 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 (pass line, that is, the pipe axis direction) of the rolling path of the metal pipe can be cited. Also, 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 pipe" in the present invention refers to a seamless steel pipe, a welded steel pipe, a forged welded steel pipe, or a UOE pipe.

[0021] The inclined rolling equipment 10 of the present invention is an equipment including two or more rolling rolls 3 disposed inclined on a circumference centered on the pass line 6. This inclined rolling equipment 10 has control means for controlling the inclination angles of the two or more rolling rolls 3. As shown in FIG. 1 and the like, two or more rolling rolls 3 are disposed in the circumferential direction of the plain pipe 1 and the pipe to be rolled 2. The plain pipe 1 is supplied to the roll gap of this inclined rolling equipment 10 from the inlet side (that is, the rolling inlet side) of the inclined rolling equipment. Then, while sandwiching the plain pipe 1 between two or more rolling rolls 3 and passing the plain pipe 1 in the rolling direction, inclined rolling (hereinafter, may be simply referred to as "rolling") is performed on the pipe material to obtain a metal pipe having a reduced outer diameter dimension to a desired value.

[0022] In the example of a two-roll type inclined rolling equipment for performing cold rolling shown in FIGS. 1 to 4, the plain pipe 1 is sandwiched between two rolling rolls 3 and passed in the rolling direction. In this example of cold rolling equipment, the metal pipe obtained after rolling is a cold rolled pipe.

[0023] First, the rolling roll 3 will be described.

[0024] Figures 2 and 3 show diagrams for explaining the crossing angle γ, tilt angle FA, and face angles (specifically, the inlet face angle M and the outlet face angle N) of the rolling roll 3. Figure 2 is a cross-sectional view taken along line A-A shown in Figure 1, and is a view of the pipe to be rolled 2, the rolling roll 3, etc. as seen from the side. Figure 3 is a view taken in the direction of arrow B-B shown in Figure 2, and is a view of the pipe to be rolled 2, the rolling roll 3, etc. as seen from above.

[0025] As shown in Figure 2, Figure 3, etc., the rolling roll 3 is a roll for rolling the raw pipe 1 supplied to the inclined rolling facility 10. The rolling roll 3 has a rolling portion 3a, and the raw pipe is subjected to inclined rolling in this rolling portion 3a. Examples of the shape of the rolling roll 3 include a barrel-shaped roll and a conical roll. Note that Figures 1 to 4 show an example in which a barrel-shaped roll is used as the rolling roll 3.

[0026] Two or more rolling rolls 3 are arranged such that their rotation axes 7 are provided with a tilt angle FA with respect to the pass line 6. The tilt angle FA refers to the angle (unit: °) formed by a straight line in the pipe axis direction (pass line 6) and the rotation axis 7 of the rolling roll 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).

[0027] 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 7 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 direction (that is, 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 facility smaller than the outer diameter of the raw pipe 1 and arranging each of the rolling rolls 3 inclined as described above (see Figure 1). As will be described later, the present invention controls this tilt angle FA.

[0028] In addition to providing the inclination angle FA, the rolling roll 3 may be arranged with an intersection angle γ (crossing angle) 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 from the side (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). The intersection angle γ is not particularly defined. From the viewpoint of reducing the change in the roll peripheral speed in the tube axis direction and stabilizing the progress of the plain tube to prevent deterioration of the cross-sectional shape, that is, the roundness, it is preferable to set the intersection angle γ in the range of 0 to 45.0°. Note that the explanation of roundness is omitted here because it will be described later.

[0029] In the case of an inclined rolling facility having a pair of rolling rolls 3 as shown in FIG. 1 etc., each rolling roll may have the directions in which the inclination angle FA and the intersection angle γ are formed with respect to the tube axis direction (pass line 6) being opposite to each other. Although illustration is omitted, even when there are three or more rolling rolls 3, similarly, the directions in which the inclination angle FA and the intersection angle γ are formed may be changed for each rolling roll.

[0030] In the present invention, a face angle may be set for the rolling roll 3. As an example, referring to FIG. 2, the face angles (inlet face angle M and outlet face angle N) in the barrel-shaped roll will be described.

[0031] The inlet face angle M of the rolling roll 3 refers to the angle (unit: °) formed between the side surface of the rolling roll 3 on the rolling inlet side with respect to the rolling direction of the tube (that is, the tapered side surface of the rolling roll 3 whose cross-sectional shape gradually becomes smaller toward the rolling inlet side) and a straight line 6a parallel to the tube axis direction (pass line 6) when the rolling roll 3 is viewed from the side as shown in FIG. 2. Further, the outlet face angle N of the rolling roll 3 refers to the angle (unit: °) formed between the side surface of the rolling roll 3 on the rolling exit side with respect to the rolling direction of the tube (that is, the tapered side surface of the rolling roll 3 whose cross-sectional shape gradually becomes smaller toward the rolling exit side) and a straight line 6a parallel to the tube axis direction when the rolling roll 3 is viewed from the side as shown in FIG. 2.

[0032] Note that the above "when viewing the rolling roll 3 in a side view" means the case of viewing in a direction perpendicular to the tube axis direction and also perpendicular to the direction in which the rolling load is applied to the raw tube 1.

[0033] In the present invention, the face angle of the rolling roll is not particularly defined. From the viewpoints of the bite property of the raw tube and the stability of the progress of the tube to be rolled, it is preferable to set the face angle as follows. When the shape of the rolling roll 3 is a barrel-shaped roll, it is preferable to set the inlet face angle M in the range of 0.2 to 20.0° with both the inclination angle FA and the crossing angle γ being 0°, and it is also preferable to set the outlet face angle N in the range of 0.2 to 20.0° in this state.

[0034] Although illustration is omitted, when the shape of the rolling roll 3 is a conical roll, an inlet face angle M and an outlet face angle N can also be provided. From the same viewpoints as described above, it is preferable to set the inlet face angle M in the range of 0.2 to 20.0°, and it is also preferable to set the outlet face angle N in the range of 0.2 to 20.0°. Note that the definitions of the inlet face angle M and the outlet face angle N are the same as those in the above description of the barrel-shaped roll, so they are omitted.

[0035] Subsequently, with reference to FIG. 4, the control means will be described.

[0036] The control means controls the inclination angle FA of each rolling roll 3. As will be described later, the control means sets the inclination angle FA of the rolling roll 3 during rolling based on the raw tube size before the start of rolling (specifically, the dimensions of the raw tube).

[0037] Here, with reference to FIG. 5, the reason why the inventors of the present invention focused on the control of the inclination angle FA of the rolling roll 3 will be described in detail.

[0038] Figure 5 shows the results of evaluating the roundness of a metal tube after rolling by varying the tilt angle of the rolling rolls and the raw tube size of the tilt rolling equipment. The vertical axis in Figure 5 represents the tilt angle (unit: °), and the horizontal axis represents the value of "wall thickness / outer diameter (i.e., t / D)" (unit: -) of the raw tube size. The roundness evaluation is performed using Equation (2) described later. When the value of C / Dmax is 0.020 or less, it is marked as "○", and when the value of C / Dmax exceeds 0.020, it is marked as "×", and each evaluation result is marked in Figure 5.

[0039] Note that the raw tube size, the number of rolling rolls, and the tilt angle used in the evaluation of Figure 5 are as follows. a) Raw tube size: D = 80 mm, t = 7 mm, number of rolling rolls: 3, tilt angles: 0.55°, 1.50°, 4.50°, 7.87°, 11.00° b) Raw tube size: D = 60 mm, t = 12 mm, number of rolling rolls: 3, tilt angles: 0.10°, 0.15°, 1.00°, 2.50°, 3.95°, 7.00° c) Raw tube size: D = 400 mm, t = 15 mm, number of rolling rolls: 3, tilt angles: 1.00°, 12.00°, 36.00° d) Raw tube size: D = 400 mm, t = 60 mm, number of rolling rolls: 3, tilt angles: 0.10°, 3.00°, 6.00°

[0040] As shown in Equation (2), in the present invention, the roundness is evaluated based on the difference (C) between the maximum outer diameter value (Dmax) and the minimum outer diameter value (Dmin) in the cross-section perpendicular to the tube axis direction of the metal tube after rolling. This is for the following reasons. It is presumed that the change in the cross-sectional shape of the tube to be rolled is affected by the range (area) where the rolling roll and the tube to be rolled are in contact, and that range changes with the tilt angle. Also, it is presumed that the processing speed of the tube to be rolled changes with the tilt angle, thereby changing the cross-sectional shape. That is, C, which is the difference between the maximum outer diameter value and the minimum outer diameter value, is affected by the tilt angle of the rolling roll. Therefore, the present inventors focused on the tilt angle of the rolling roll and conducted further studies.

[0041] As shown in FIG. 5, when the inclination angle FA of the rolling roll 3 is large, the range (area) where the rolling roll 3 (specifically, the side surface of the rolling roll 3 on the rolling inlet side) and the pipe surface of the pipe material are in contact becomes narrow (see FIGS. 3 and 4). That is, the range where the rolling roll 3 does not contact the pipe surfaces of the raw pipe 1 and the pipe to be rolled 2 (hereinafter referred to as the "non-contact area") becomes wide. When the non-contact area is wide, it becomes more difficult for the material to be rolled in the contact area to deform freely. Due to the restraint from this non-contact area, a force that attempts to deform into a shape close to a perfect circle acts on the pipe to be rolled 2, and as a result, the difference (C) between the maximum outer diameter value and the minimum outer diameter value may be reduced. On the other hand, the larger the inclination angle FA of the rolling roll 3, the greater the distance that the raw pipe 1 and the pipe to be rolled 2 advance in the pipe axis direction during one rotation. That is, since the processing progresses rapidly, the shape of the pipe is likely to be disturbed, and due to this, the difference (C) between the maximum outer diameter value and the minimum outer diameter value may be increased.

[0042] Also, if the inclination angle FA of the rolling roll 3 is too small, the non-contact area becomes narrow. That is, the restraint from the non-contact area becomes weak, and the force that attempts to deform the pipe to be rolled 2 into a shape close to a perfect circle becomes weak. Due to this, the difference (C) between the maximum outer diameter value and the minimum outer diameter value may be increased.

[0043] Thus, it was found that the inclination angle FA of the rolling roll 3 has an opposing effect of reducing the difference (C) between the maximum outer diameter value and the minimum outer diameter value and increasing the said difference (C). Also, it was newly found that there exists a range of the inclination angle FA of the rolling roll 3 that is optimal for improving the roundness. And it was also found that the above-mentioned "range of the inclination angle FA of the optimal rolling roll 3" differs depending on the dimensions of the raw pipe before the start of rolling (specifically, the value of "t / D").

[0044] In the present invention, as a method for making the cross-sectional shape of the metal tube after rolling (i.e., the shape of the cross-section perpendicular to the tube axis direction) approach a perfect circle, it is important to appropriately set the inclination angle FA of each rolling roll 3 based on the wall thickness (t) and outer diameter (D) of the raw tube before the start of rolling. This is because it becomes possible to appropriately control the contact area between the rolling roll and the tube material (specifically, the tube to be rolled) during rolling, and it is possible to suppress a decrease in roundness. That is, in the present invention, the control means sets the inclination angle (FA) of the rolling roll so that the difference (C) between the maximum outer diameter and the minimum outer diameter of the metal tube after the rolling process becomes small.

[0045] Based on the above findings, the inventors have derived the following formula (1) that defines the relationship between the wall thickness and outer diameter of the raw tube 1 before the start of rolling and the inclination angle FA of the rolling roll 3.

[0046] Specifically, the control means sets the inclination angle FA of each rolling roll 3 so as to satisfy the following formula (1). 0.009×(t / D) (-1.8) ≦FA≦3.2 + 0.022×(t / D) (-2.2) …(1) Here, in formula (1), t: Wall thickness of the raw tube before the start of rolling set in advance [mm], D: Outer diameter in the cross-section perpendicular to the tube axis direction of the raw tube before the start of rolling set in advance [mm], FA: Inclination angle of the rolling roll [°], and it is.

[0047] Note that for the above-mentioned "wall thickness of the raw tube before the start of rolling set in advance" and "outer diameter in the cross-section perpendicular to the tube axis direction of the raw tube before the start of rolling set in advance", the actually measured values may be used, or alternatively, the values estimated from the conditions during tube manufacturing may be used, or the planned dimensions set in advance before tube manufacturing may be used.

[0048] Hereinafter, the reasons for the limitation of formula (1) will be described.

[0049] When the inclination angle FA of the rolling roll 3 is the left side value of formula (1) (i.e., "0.009×(t / D) (-1.8)If it is less than the value calculated by ")", the range (area) where the rolling roll 3 and the pipe surface of the pipe to be rolled are in contact becomes wider, and the restraint from the range where the rolling roll is not in contact becomes smaller. As a result, the roundness decreases. The inclination angle FA is preferably (0.011×(t / D) (-1.8) ) or more.

[0050] On the other hand, when the inclination angle FA of the rolling roll 3 exceeds the right side value of the formula (1) (that is, the value calculated by "3.2 + 0.022×(t / D) (-2.2) "), the distance that the plain pipe and the pipe to be rolled advance in the pipe axis direction during one rotation becomes larger. That is, since the processing progresses rapidly, the shape of the metal pipe is likely to be disturbed, and the roundness decreases. The inclination angle FA is preferably (3.0 + 0.022×(t / D) (-2.2) ) or less.

[0051] Also, as described above, the contact area between the rolling roll and the pipe to be rolled greatly affects the roundness. Therefore, in the present invention, attention is also paid to determining the inclination angle FA using a parameter representing the size of the range where the rolling roll and the pipe surface of the pipe to be rolled are in contact.

[0052] Here, the "size of the range where the rolling roll and the pipe surface of the pipe to be rolled are in contact" refers to the contact range between the rolling roll and the pipe surface of the pipe to be rolled indicated by double arrows, as shown in the partially enlarged view in FIG. 7. As a result of the study by the present inventors, it has been found that the following formula (3) is used as a parameter representing the size (CA) of the range where the pipe surface is in contact. CA = ((t / D) (-1.8) ) / FA …(3) Note that, as shown in formula (3), CA: A parameter representing the size of the contact range between the rolling roll and the pipe surface of the pipe to be rolled [-], t: The wall thickness of the plain pipe before rolling start set in advance [mm], D: The outer diameter in the cross-section perpendicular to the pipe axis direction of the plain pipe before rolling start set in advance [mm], FA: The inclination angle of the rolling roll [°], is.

[0053] The larger the value of CA represented by this formula (3), the larger the contact area. That is, the smaller the wall thickness (t) of the raw tube before the start of rolling and the larger the outer diameter (D) of the raw tube before the start of rolling, the easier it is for the tube to be flattened during rolling, and the larger the contact area. As described above, when the contact area is large, the non-contact area becomes narrow. As a result, the force that attempts to deform the tube to be rolled 2 into a shape close to a perfect circle becomes weak. The inventors have found that by setting the inclination angle FA of the rolling roll during rolling so that the value of CA satisfies formula (4), it is possible to more effectively prevent deterioration of roundness. CA ≤ 50…(4)

[0054] As described above, in the present invention, when the control means sets the size of the contact range between the rolling roll and the tube surface of the tube to be rolled during rolling as CA in addition to the provisions of the above formula (1), it is preferable to set the inclination angles of two or more rolling rolls so that the value of CA represented by formula (3) satisfies formula (4). Note that the value of CA is more preferably 48 or less. Although the lower limit of CA is not particularly defined, it is preferably 1 or more, and more preferably 2 or more.

[0055] Also, as described above, it has been found by the study of the inventors that the degree of progress of the tube to be rolled in the tube axis direction also affects the roundness. Therefore, in the present invention, in addition to the above-described control, the inclination angle FA may be determined in consideration of a parameter representing the degree of progress of the tube to be rolled in the tube axis direction.

[0056] As a result of the study by the inventors, it has been found that the following formula (5) is used as a parameter representing the degree of progress (SF) of the tube to be rolled in the tube axis direction. SF = tan(FA) …(5) Here, as shown in formula (5), SF: A parameter representing the degree of progress of the tube to be rolled in the tube axis direction [-], FA: Inclination angle of the rolling roll [°], is.

[0057] The larger the value of SF represented by this formula (5), the greater the distance the base tube and the tube to be rolled advance in the tube axis direction during one rotation. When this distance is large, the deformation progresses rapidly, and the shape of the tube to be rolled is likely to be disturbed. From this, the inventors have found that setting the inclination angle FA of the rolling roll during rolling so that the value of SF satisfies formula (6) is also preferable from the viewpoint of more effectively preventing deterioration of roundness. SF ≦ tan(3.0 + 0.022 × (t / D) (-2.2) ) …(6) Note that, as shown in formula (6), SF: A parameter [-] representing the degree of progress of the tube to be rolled advancing in the tube axis direction, t: The wall thickness [mm] of the base tube before rolling set in advance, D: The outer diameter [mm] in the cross-section perpendicular to the tube axis direction of the base tube before rolling set in advance. Note that the value of SF is more preferably (0.9 × tan(3.0 + 0.022 × (t / D) (-2.2) )) or less. Although the lower limit of SF is not particularly defined, it is preferably 0.001 or more, and more preferably 0.002 or more.

[0058] As described above, if the inclination angle FA is set by the control means so as to satisfy formula (1), the above-described operational effects can be obtained. From the viewpoint of more effectively obtaining this operational effect, it is preferable to set the inclination angle FA so as to satisfy formula (3) and formula (4) in addition to formula (1). Alternatively, it is more preferable to set the inclination angle FA so as to satisfy all of formula (1), formula (3) to formula (6). For example, the control means can also be controlled by a control device (not shown) of the inclined rolling facility 10. In this case, the control device may control the operation of the inclined rolling facility 10 according to an instruction from a process computer (not shown) that manages the operation of the metal tube manufacturing process.

[0059] Next, with reference to FIG. 6, the roundness in the present invention will be described. FIG. 6 shows an example of a cross-sectional shape perpendicular to the tube axis direction of the metal tube after inclined rolling, which is deformed into an elliptical shape.

[0060] In the cross-section perpendicular to the tube axis of the metal tube 21 after inclined rolling shown in FIG. 6, when the maximum value of the outer diameter of the metal tube 21 (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 (Dmax - Dmin) in the cross-section perpendicular to the tube axis of the metal tube 21, is defined as C. These maximum and minimum outer diameters are measured values. Then, substituting the value of C and the value of Dmax into Equation (2), the obtained value R is defined as the roundness. In the present invention, when the value of this roundness (R) is 0.020 or less, it is evaluated as having "good roundness" (i.e., "excellent roundness"). R = C / Dmax …(2) Here, in Equation (2), R: roundness, C: the difference between the maximum and minimum outer diameters in the cross-section perpendicular to the tube axis of the metal tube after rolling, Dmax: the maximum outer diameter in the cross-section perpendicular to the tube axis of the metal tube after rolling.

[0061] 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 gauge may be used.

[0062] Also, when measuring the outer diameter at locations other than the tube end, the metal tube is cut perpendicular to the tube axis at the measurement location, 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, with the maximum value being Dmax and the minimum value being Dmin. When measuring the outer diameter using calipers or a gauge, in the cross-section perpendicular to the tube axis, the circumferential distance between the two points that become the measurement positions on the tube circumference (i.e., the installation positions of the calipers or the gauge) is set to be half of the tube circumference.

[0063] The measurement position in the axial direction of the metal tube can be any location, but since unsteady part deformation is likely to occur in the regions including the head and tail ends of the metal tube, it is desirable to measure the outer diameter at locations excluding 20 mm from each of the head and tail ends, and more preferably at locations excluding 40 mm from each of the head and tail ends. Also, multiple measurement positions in the axial direction of the tube 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 value of the measurement values at these 10 points can be used.

[0064] As described above, the two-roll type inclined rolling mill has been explained with reference to FIG. 1 and the like. According to the present invention, however, even when rolling a raw tube with 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.

[0065] 〔Inclined rolling method〕 Subsequently, an inclined rolling method for a metal tube using the above-described inclined rolling equipment of the present invention will be explained. Note that the explanations regarding the rolling rolls and the control means are omitted since they have been described above.

[0066] In the inclined rolling method of the present invention, an inclined rolling equipment 10 having two or more rolling rolls 3 in which the rotation axis 7 of the rolling roll 3 is arranged at an inclination angle β with respect to the pass line 6 (axial direction of the tube) is used, and the inclination angle FA of the two or more rolling rolls 3 included in the inclined rolling equipment is set by a control means for controlling the inclination angle FA, and while rotating the raw tube 1 in the circumferential direction of the tube and advancing it in the axial direction of the tube, rolling is performed. Note that the rolling roll 3 may be further arranged with a crossing angle γ and a face angle.

[0067] As shown in FIG. 4 and the like, the raw tube 1 is supplied to the roll gap of this inclined rolling equipment 10 from the inlet side of the inclined rolling equipment 10 (that is, the right side of the paper surface shown in FIG. 4). While sandwiching the raw tube 1 with each rolling roll 3 and passing the raw tube 1 in the rolling direction, inclined rolling is performed on the raw tube 1. Thereby, a metal tube having an outer diameter dimension reduced to a desired value can be obtained.

[0068] During rolling, the inclination angle FA of each rolling roll 3 is controlled by a control means. Specifically, the control means sets the inclination angle FA of each rolling roll 3 based on the wall thickness and outer diameter of the metal tube before the start of rolling, and performs rolling on the plain tube 1 using the rolling roll 3 set to the inclination angle FA. From the viewpoint of improving the roundness, the control means controls the inclination angle FA so as to satisfy the above-mentioned formula (1). From the viewpoint of more effectively improving the roundness, it is preferable to control the inclination angle FA so as to satisfy formula (3) and formula (4) in addition to formula (1). Alternatively, it is more preferable to control the inclination angle FA so as to satisfy all of formula (1) and formula (3) to formula (6).

[0069] 〔Method for manufacturing metal tube〕 Subsequently, a method for manufacturing a metal tube using the above-described inclined rolling equipment of the present invention will be described. That is, this manufacturing method is a method for manufacturing a metal tube by performing rolling on a tube to be rolled by the above-described inclined rolling method. Note that the description of the rolling roll and the control means has been described above and will be omitted.

[0070] The method for manufacturing a metal tube of the present invention has a rolling step of obtaining a metal tube by rotating the plain tube 1 in the circumferential direction of the tube and passing the plain tube 1 through the roll gaps of two or more rolling rolls 3 while advancing in the axial direction of the tube to perform inclined rolling.

[0071] In the rolling step, the control means controls the inclination angle of the rolling roll 3 so as to be within an appropriate range. Specifically, the control means sets the inclination angle FA of the rolling roll based on the wall thickness and outer diameter of the metal tube before the start of rolling, and performs rolling on the plain tube 1 with the rolling roll 3 set to the inclination angle FA. Thereby, it is possible to suppress a decrease in roundness in the cross-sectional shape of the metal tube after rolling. From the viewpoint of improving the roundness, the control means controls the inclination angle FA of the rolling roll so as to satisfy the above-mentioned formula (1). From the viewpoint of more effectively improving the roundness, it is preferable to control the inclination angle FA so as to satisfy formula (3) and formula (4) in addition to formula (1). Alternatively, it is more preferable to control the inclination angle FA so as to satisfy all of formula (1) and formula (3) to formula (6).

[0072] In the method for manufacturing a metal tube of the present invention, for example, the metal tube after the above rolling process may be heat-treated. Further, for example, the metal tube after the above rolling process may be pickled to remove the scale on the surface of the metal tube. The conditions for the heat treatment and pickling treatment may be appropriately set according to the composition of the metal tube and the like.

[0073] In the present invention, the manufacturing conditions of the base tube before performing the above rolling process are not particularly limited, and generally known manufacturing conditions can be adopted. Further, the base tube before performing the rolling process is not particularly limited, and may be, for example, a hollow tube material.

[0074] Further, as the shape of the base tube before performing the rolling process, even if there is a difference between the maximum value of the outer diameter of the base tube and the minimum value of the outer diameter of the base tube when the actual measurement of the base tube is performed, the above-described effects of the present invention can be obtained. The reason is that the effect of preventing the material to be rolled in the contact area from being deformed more freely regardless of the roundness of the base tube can be obtained.

[0075] From the viewpoint of more effectively obtaining the effects of the present invention, the base tube before performing the rolling process has an elliptical or circular shape in the cross section perpendicular to the tube axis direction, and the difference between the maximum value of the outer diameter of the base tube and the minimum value of the outer diameter of the base tube is divided by the maximum value of the outer diameter of the base tube (that is, ((maximum value of outer diameter of base tube - minimum value of outer diameter of base tube) / maximum value of outer diameter of base tube) × 100 (unit: %)) is preferably 10% or less, and more preferably 7% or less.

[0076] As described above, according to the present invention, since the inclined rolling is performed on the base tube using the inclined rolling equipment having the control means capable of appropriately controlling the inclination angle of each rolling roll, it is possible to suppress a decrease in the roundness of the cross-sectional shape of the metal tube obtained after rolling. In particular, pretreatment such as surface coating application and end processing of the base tube before inclined rolling is not required. Further, while realizing an improvement in the hardness of the metal tube by inclined rolling, it is possible to suppress a decrease in the roundness of the cross-sectional shape after inclined rolling.

Example

[0077] 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 scope that conforms to the gist of the present invention.

[0078] [Embodiment 1] First, a raw pipe with an outer diameter (D): 80 mm (the difference between the maximum value and the minimum value of the outer diameter of the raw pipe: 0 mm), a wall thickness (t): 7 mm, and a length: 250 mm was collected from a stainless steel bar conforming to JIS G 4303:2012 standard (material: SUS329J3L) shown in Table 1 by machining.

[0079] [Table 1]

[0080] Next, the collected raw pipe was rolled. As the equipment for performing cold rolling for this rolling, the inclined rolling equipment with the number of rolls shown in Table 2 (that is, 2-roll type inclined rolling equipment and 3-roll type inclined rolling equipment) was used. For these rolling rolls, a barrel-shaped roll with an entrance side angle M of 2.5° and an exit side angle N of 3.0° was used in a state where both the inclination angle and the crossing angle were 0°. During rolling, the crossing angle γ of the rolling rolls was set to 0°, and the roll gap of rolling roll 3 was set to 70 mm. In Embodiment 1, the inclination angle FA of rolling roll 3 was variously changed as shown in Table 2, and the raw pipe at normal temperature was rolled (here, cold rolled) to obtain a metal pipe.

[0081] Using the rolled metal pipe (here, cold rolled pipe), the roundness R was evaluated by the above method. In addition, a vernier caliper was used to measure the outer diameter of the metal pipe. As described above, the difference C between the maximum outer diameter value Dmax and the minimum outer diameter value Dmin obtained by measuring the outer diameter at 24 equally spaced points in the circumferential direction of the pipe was calculated. Using the obtained values, the value of C / Dmax was calculated and shown in the column of "C / Dmax after rolling" in Table 2.

[0082] In this embodiment, the target value of C / Dmax was set to 0.020 or less, and "0.020" was recorded in the "C / Dmax (target value)" column of Table 2. That is, when the value of C / Dmax after rolling was 0.020 or less, it was evaluated as "qualified (i.e., excellent roundness)". In particular, when the value of C / Dmax after rolling was 0.011 or less, it was regarded as even more excellent roundness, and the symbol "◎" was recorded in the evaluation result column of Table 2. When the value of C / Dmax after rolling exceeded 0.011 and was 0.020 or less, the symbol "〇" was recorded in the evaluation result column of Table 2. When the value of C / Dmax after rolling exceeded 0.020, it was evaluated as "unqualified", and the symbol "×" was recorded in the evaluation result column of Table 2. The measurement position in the tube axis direction was set to the central position of the metal tube (i.e., the position at half the total length of the tube from the tube end). The evaluation results are shown in Table 2.

[0083]

Table 2

[0084] Tubes No. 1 to 9 shown in Table 2 were tubes obtained by performing inclined rolling with a two-roll type inclined rolling facility having two rolls. For tubes No. 1, 2, 8, and 9, the inclination angle FA of the rolling rolls was not set so that the difference between the maximum outer diameter value and the minimum outer diameter value of the metal tube after the rolling process was small, and the inclination angle FA did not satisfy formula (1). As a result, the measured value of C / Dmax became larger than the target value of C / Dmax (0.020), and the decrease in roundness could not be suppressed.

[0085] On the other hand, for tubes No. 3 to 7, the inclination angle FA of the rolling rolls was set so that the difference between the maximum outer diameter value and the minimum outer diameter value of the metal tube after the rolling process was small, and the inclination angle FA satisfied formula (1). As a result, the measured value of C / Dmax became smaller than the target value of C / Dmax, and the decrease in roundness could be suppressed.

[0086] In addition, the tubes numbered 10 to 17 shown in Table 2 were tubes obtained by performing rolling using a three-roll type inclined rolling facility with three rolls. For tubes No. 10, 11, 16, and 17, the inclination angle FA of the rolling rolls was not set so that the difference between the maximum outer diameter and the minimum outer diameter of the metal tube after the rolling process was small, and the inclination angle FA did not satisfy Equation (1). As a result, the measured value of C / Dmax became larger than the target value of C / Dmax, and the decrease in roundness could not be suppressed.

[0087] On the other hand, for tubes No. 12 to 15, the inclination angle FA of the rolling rolls was set so that the difference between the maximum outer diameter and the minimum outer diameter of the metal tube after the rolling process was small, and the inclination angle FA satisfied Equation (1). As a result, the measured value of C / Dmax became smaller than the target value of C / Dmax, and the decrease in roundness could be suppressed.

[0088] 〔Example 2〕 In Example 2, the case where the dimensions of the base tube were different from those in Example 1 was examined.

[0089] First, a base tube with an outer diameter (D): 60 mm (the difference between the maximum outer diameter and the minimum outer diameter of the base tube: 0 mm), a wall thickness (t): 12 mm, and a length: 250 mm was collected from a stainless steel bar of JIS G 4303:2012 standard shown in Table 1 (material: SUS329J3L) by machining.

[0090] Next, the collected base tube was rolled under the conditions shown in Table 3. The conditions such as the inclined rolling facility and the rolling rolls were the same as those in Example 1. In Example 2, the inclination angle FA of the rolling roll 3 was variously changed as shown in Table 3, and the base tube at room temperature was rolled (here, cold rolling) to obtain a metal tube.

[0091] Using the rolled metal tube (here, a cold-rolled tube), the roundness R was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 3.

[0092]

Table 3

[0093] The tubes numbered 18 to 24 shown in Table 3 were tubes obtained by performing inclined rolling with a two-roll type inclined rolling facility having two rolls. For tubes No. 18, 19, 23, and 24, the inclination angle FA of the rolling rolls was not set so that the difference between the maximum outer diameter value and the minimum outer diameter value of the metal tube after the rolling process would be small, and the inclination angle FA did not satisfy Equation (1). As a result, the measured value of C / Dmax became larger than the target value of C / Dmax (0.020), and the decrease in roundness could not be suppressed.

[0094] On the other hand, for tubes No. 20 to 22, the inclination angle FA of the rolling rolls was set so that the difference between the maximum outer diameter value and the minimum outer diameter value of the metal tube after the rolling process would be small, and the inclination angle FA satisfied Equation (1). As a result, the measured value of C / Dmax became smaller than the target value of C / Dmax, and the decrease in roundness could be suppressed.

[0095] Also, the tubes numbered 25 to 31 shown in Table 3 were tubes obtained by performing rolling with a three-roll type inclined rolling facility having three rolls. For tubes No. 25, 26, 30, and 31, the inclination angle FA of the rolling rolls was not set so that the difference between the maximum outer diameter value and the minimum outer diameter value of the metal tube after the rolling process would be small, and the inclination angle FA did not satisfy Equation (1). As a result, the measured value of C / Dmax became larger than the target value of C / Dmax, and the decrease in roundness could not be suppressed.

[0096] On the other hand, for tubes No. 27 to 29, the inclination angle FA of the rolling rolls was set so that the difference between the maximum outer diameter value and the minimum outer diameter value of the metal tube after the rolling process would be small, and the inclination angle FA satisfied Equation (1). As a result, the measured value of C / Dmax became smaller than the target value of C / Dmax, and the decrease in roundness could be suppressed.

[0097] 〔Example 3〕 In Example 3, the case where the dimensions of the plain tube were different from those in Example 1 was examined. Similarly to the above, a plain tube with an outer diameter (D): 400 mm (the difference between the maximum and minimum outer diameters of the plain tube: 0 mm), a wall thickness (t): 15 mm, and a length: 250 mm was collected by machining from a stainless steel bar conforming to JIS G 4303:2012 standard (material: SUS329J3L) shown in Table 1.

[0098] Next, the collected plain tube was rolled under the conditions shown in Table 4 to obtain a metal tube. The conditions such as the inclined rolling equipment and the rolling rolls were the same as those in Example 1. Then, using the rolled metal tube, the roundness R was evaluated in the same manner as in Example 1, and the evaluation results are shown in Table 4.

[0099]

Table 4

[0100] Tubes No. 32 to 35 shown in Table 4 were tubes produced by a two-roll type inclined rolling equipment. For tubes No. 32 and 35, since the inclination angle FA did not satisfy Equation (1), the measured value of C / Dmax became larger than the target value of C / Dmax, and the reduction in roundness could not be suppressed. On the other hand, for tubes No. 33 and 34, since the inclination angle FA satisfied Equation (1), the measured value of C / Dmax became smaller than the target value of C / Dmax, and the reduction in roundness could be suppressed.

[0101] Also, tubes No. 36 to 38 shown in Table 4 were tubes produced by a three-roll type inclined rolling equipment. For tubes No. 36 and 38, since the inclination angle FA did not satisfy Equation (1), the measured value of C / Dmax became larger than the target value of C / Dmax, and the reduction in roundness could not be suppressed. On the other hand, for tube No. 37, since the inclination angle FA satisfied Equation (1), the measured value of C / Dmax became smaller than the target value of C / Dmax, and the reduction in roundness could be suppressed.

[0102] 〔Example 4〕 In Example 4, the case where the dimensions of the plain tube were different from those in Example 1 was examined. Similarly to the above, a plain tube with an outer diameter (D): 400 mm (the difference between the maximum and minimum outer diameters of the plain tube: 0 mm), a wall thickness (t): 60 mm, and a length: 250 mm was collected by machining from a stainless steel bar conforming to JIS G 4303:2012 standard (material: SUS329J3L) shown in Table 1.

[0103] Next, the collected plain tube was rolled under the conditions shown in Table 5 to obtain a metal tube. The conditions such as the inclined rolling equipment and the rolling rolls were the same as those in Example 1. Then, using the rolled metal tube, the roundness R was evaluated in the same manner as in Example 1, and the evaluation results are shown in Table 5.

[0104]

Table 5

[0105] Tubes No. 39 to 42 shown in Table 5 were tubes produced by a two-roll type inclined rolling equipment. Tubes No. 39 and 42 had an inclined angle FA that did not satisfy Equation (1). As a result, the measured value of C / Dmax became larger than the target value of C / Dmax, and the decrease in roundness could not be suppressed. In contrast, Tubes No. 40 and 41 had an inclined angle FA that satisfied Equation (1). Therefore, the measured value of C / Dmax became smaller than the target value of C / Dmax, and the decrease in roundness could be suppressed.

[0106] Also, Tubes No. 43 to 45 shown in Table 5 were tubes produced by a three-roll type inclined rolling equipment. Tubes No. 43 and 45 had an inclined angle FA that did not satisfy Equation (1). As a result, the measured value of C / Dmax became larger than the target value of C / Dmax, and the decrease in roundness could not be suppressed. In contrast, Tube No. 44 had an inclined angle FA that satisfied Equation (1). Therefore, the measured value of C / Dmax became smaller than the target value of C / Dmax, and the decrease in roundness could be suppressed.

[0107] From Examples 1 to 4 described above, it was found that in the inventive example, the decrease in roundness can be suppressed.

Explanation of Signs

[0108] 1 Plain tube 2 Rolled tube 3 Rolling roll 3a Rolling section 6 Pass line 7 Rotation axis of the rolling roll 10 Inclined rolling equipment 21 Metal tube FA Inclination angle γ Crossing angle M Inlet side angle N Outlet side angle Gap Roll gap Dmax Maximum outer diameter Dmin Minimum outer diameter

Claims

1. An inclined rolling facility having two or more rolling rolls arranged inclined on a circumference centered on a pass line, A control means for controlling the inclination angles of the two or more rolling rolls, The control means sets the inclination angles of the two or more rolling rolls so as to satisfy formula (1). 0.009×(t / D) （－１．８） ≦FA≦3.2+0.022×(t / D) （－２．２） …(1) Here, as shown in formula (1), t: preset wall thickness of the blank pipe before rolling starts [mm], D: preset outer diameter [mm] of the blank tube in a cross section perpendicular to the tube axis direction before the start of rolling, FA: inclination angle of the rolling roll [°].

2. The control means further comprises:

2. The inclined rolling equipment according to claim 1, wherein the inclination angles of the two or more rolling rolls are set so that the value of CA expressed by formula (3) satisfies formula (4), where CA is the size of the contact area between the rolling rolls and the tube surface of the rolled tube during rolling. 324((144) （－１．８） ) / FA ...(3) CA≦50 ... (4) Here, in each formula, CA: Parameter [-] representing the size of the contact area, t: preset wall thickness of the blank pipe before rolling starts [mm], D: preset outer diameter [mm] of the blank tube in a cross section perpendicular to the tube axis direction before the start of rolling, FA: inclination angle of the rolling roll [°].

3. A tilt rolling method using the tilt rolling equipment according to claim 1 or 2, a control means for controlling the tilt angles of the two or more rolling rolls when rolling a mother tube while rotating the mother tube in a circumferential direction and advancing the mother tube in an axial direction of the mother tube.

4. A method for producing a metal tube using the tilt rolling equipment according to claim 1 or 2, comprising the steps of: a rolling process in which a blank tube is passed through a roll gap between the two or more rolling rolls while rotating the blank tube in a circumferential direction and moving the blank tube in an axial direction, thereby rolling the blank tube into a metal tube, the rolling step controls the inclination angles of the two or more rolling rolls by the control means, and rolls the blank tube at the inclination angles.

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