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: The present invention relates to an inclined rolling facility including two or more rolling rolls arranged in an inclined manner on a circumference around a pass line, where the inclined rolling facility includes control means for controlling the inlet side face angle of the rolling roll, and the control means sets the inlet side face angle of the rolling roll so as to satisfy a formula (2). M≥(0.07 / (Cp / D))(1 / 0.9) ...(2)SELECTED DRAWING: Figure 4

Description

Technical Field

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

Background Art

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

[0003] These steel types and alloys contain a large amount of alloying elements added to exhibit excellent corrosion resistance performance. Therefore, as the structure, it becomes a single austenite phase or a multiphase structure containing a large amount of austenite phase. The austenite phase with a face-centered cubic lattice (fcc) structure generally has a lower yield strength than the ferrite phase or martensite phase with a body-centered cubic lattice (bcc) structure in a use environment from low temperature to normal temperature. Therefore, when higher yield strength is required for materials containing the austenite phase, cold working is added to the material, and dislocation strengthening by the working is utilized 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 drawing process described in Non-Patent Document 1 is an effective method 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 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 sticking to the tool, the wall thickness reduction rate can only be about 20%. Furthermore, if the wall thickness reduction amount in one drawing process is insufficient, it is necessary to repeat the series of processes from the softening heat treatment again. 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 small quantities of multiple varieties. Furthermore, since there are many processes required when performing the drawing process, there is a problem that the equipment 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 millimeters, 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 rotating axes are arranged inclined with respect to the center line in the rolling pass direction of the metal pipe (hereinafter, may also be referred to as the "pass line") and rolled. 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 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 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 it is possible to add the desired processing strain without generating surface defects such as sticking that occur in cold drawing, it is also suitable for small-lot production of multiple varieties.

Prior Art Documents

Patent Documents

[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. However, the inclined 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, as a technique for making the 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 yet be said to be sufficient.

[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] The present invention has been made in view of the above problems, and an object thereof is to provide an inclined rolling facility, an inclined rolling method, and a method for manufacturing a metal pipe capable of making the 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 present inventors 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 that enables 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.

[0014] As a result of further studies, the present inventors have completed an invention consisting of the following gist. [1] An inclined rolling facility comprising two or more rolling rolls disposed obliquely on the circumference centered on the pass line, comprising control means for controlling the entrance side surface angle of the rolling roll, The control means sets the entrance side surface angle of the rolling roll so as to satisfy formula (2), an inclined rolling facility. M ≧ (0.07 / (Cp / D)) (1 / 0.9) …(2) Here, as shown in formula (2), Cp: The difference [mm] between the maximum outer diameter value and the minimum outer diameter value in the cross section perpendicular to the tube axis direction of the metal tube after rolling, D: The target outer diameter value [mm] in the cross section perpendicular to the tube axis direction of the metal tube after rolling, M: The entrance side surface angle [°] of the rolling roll, is. [2] An inclined rolling method using the inclined rolling facility according to [1], When rolling while rotating the raw tube in the circumferential direction of the tube and advancing it in the tube axis direction, the entrance side surface angle of the rolling roll is controlled by the control means, an inclined rolling method. [3] A method for manufacturing a metal tube using the inclined rolling facility according to [1] to manufacture a metal tube, having a rolling process of passing the raw tube through the roll gap of the two or more rolling rolls while rotating the raw tube in the circumferential direction of the tube and advancing it in the tube axis direction to perform rolling to obtain a metal tube, In the rolling process, the entrance side surface angle of the rolling roll is controlled by the control means, and rolling is performed on the raw tube at the entrance side surface angle, a method for manufacturing a metal tube.

Effect of the Invention

[0015] According to the present invention, since the cross-sectional shape of the metal tube after rolling 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

Embodiments for Carrying Out the Invention

[0017] Referring to each figure, embodiments of the present invention 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〕 Referring to FIGS. 1 to 4, 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-out side. For the sake of easy understanding, in FIG. 1, as an example, a state in which a pipe to be rolled is being rolled by inclined rolling equipment having two rolling rolls (that is, two-roll type inclined rolling equipment) is shown. FIG. 2 is a schematic view of the inclined rolling equipment and the pipe 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 pipe to be rolled shown in FIG. 1 as viewed from above. FIG. 4 is a view for explaining the face angle of the rolling roll used in the inclined rolling equipment of the present invention. For the sake of easy understanding, in FIG. 3, the illustration of the lower rolling roll among the two rolling rolls 3 is omitted, and the plain pipe 1 and the pipe 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. Hereinafter, as an example of the "rolling equipment", cold rolling equipment for performing cold rolling on a material 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 plain pipe can be mentioned. 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 equipment including two or more rolling rolls 3 inclined and arranged on a circumference centered on the pass line 6. This inclined rolling equipment 10 has control means for controlling the entrance side face angle of the rolling roll 3. As shown in FIG. 1 and the like, two or more rolling rolls 3 are arranged 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 entrance side (that is, the rolling entrance side) of the inclined rolling equipment. Then, by passing the plain pipe 1 through the two or more rolling rolls 3 while sandwiching it, inclined rolling (hereinafter, may also be simply referred to as "rolling") is performed on the pipe material to obtain a metal pipe having a reduced diameter to a desired outer diameter dimension.

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

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

[0024] FIGS. 2 and 3 show diagrams for explaining the crossing angle γ and the inclination angle β of the rolling roll 3. FIG. 2 is a 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. as seen from the side. FIG. 3 is a view taken 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. as seen from above.

[0025] As shown in FIGS. 2 and 3 etc., the rolling roll 3 is a roll for rolling the raw pipe 1 supplied to the inclined rolling equipment 10. The rolling roll 3 has a rolling part 3a, and inclined rolling is performed on the raw pipe by this rolling part 3a. Examples of the shape of the rolling roll 3 include a barrel-shaped roll and a conical roll. In addition, FIGS. 1 to 4 show an example in which a barrel-shaped roll is used as the rolling roll 3.

[0026] The rolling roll 3 is arranged such that its rotation axis 7 is provided with an inclination angle β with respect to the pass line 6. The inclination angle β means, 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.

[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 tube 1 to draw the raw tube 1 supplied to the roll gap into the rolling direction (i.e., the rolling pass direction). Therefore, the raw tube 1 is rolled in a spiral shape while being rotated by the rolling roll 3. That is, the raw tube 1 is rolled while rotating in the circumferential direction of the tube and advancing in the tube 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 tube 1 and arranging each of the rolling rolls 3 in an inclined manner as described above (see Fig. 1).

[0028] From the viewpoint of stably advancing the raw tube 1 and the tube to be rolled 2 in the rolling direction, it is preferable to set the inclination angle β in the range of 0.5 to 40.0°.

[0029] 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 from the side (i.e., in a direction perpendicular to the tube axis direction and perpendicular to the direction in which the rolling load is applied to the raw tube 1), as shown in Fig. 2. The intersection angle γ is not particularly specified. From the viewpoint of reducing the change in the roll peripheral speed in the tube axis direction and stabilizing the advancement of the raw tube to prevent deterioration of the roundness of the cross-sectional shape, 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.

[0030] In the case of an inclined rolling equipment 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 β and the intersection angle γ are formed opposite to each other with respect to the tube axis direction (pass line 6). Although the illustration is omitted, even when there are three or more rolling rolls 3, similarly, the directions in which the inclination angle β and the intersection angle γ are formed may be changed for each rolling roll.

[0031] Subsequently, the control means will be described.

[0032] The control means controls the inlet side surface angle M of each rolling roll 3. By controlling the inlet side surface angle M by the control means, the contact area between the rolling roll and the pipe material during rolling can be appropriately managed.

[0033] Here, with reference to FIG. 4, the surface angles (specifically, the inlet side surface angle M and the outlet side surface angle N) of the rolling roll 3 will be described.

[0034] The inlet side surface angle M of the rolling roll 3 refers to the angle (unit: °) formed between the side surface of the rolling roll 3 on the inlet side of rolling (that is, the tapered side surface of the rolling roll 3 whose cross-sectional shape gradually becomes smaller toward the inlet side of rolling) and a straight line 6a parallel to the pipe axis direction (pass line 6) when the rolling roll 3 is viewed from the side as shown in FIG. 4. Further, the outlet side surface angle N of the rolling roll 3 refers to the angle (unit: °) formed between the side surface of the rolling roll 3 on the outlet side of rolling (that is, the tapered side surface of the rolling roll 3 whose cross-sectional shape gradually becomes smaller toward the outlet side of rolling) and a straight line 6a parallel to the pipe axis direction when the rolling roll 3 is viewed from the side as shown in FIG. 4. The above-mentioned "when the rolling roll 3 is viewed from the side" means the case of viewing in a direction perpendicular to the pipe axis direction and perpendicular to the direction in which the rolling load is applied to the raw pipe 1.

[0035] Subsequently, with reference to FIG. 5, the reason why the inventors focused on the control of the inlet side surface angle M of the rolling roll 3 will be described in detail.

[0036] Fig. 5 shows the results of evaluating the roundness of a metal tube after rolling by using a two-roll type inclined rolling facility for cold rolling and performing rolling on a plain tube while variously changing only the entrance side angle of the rolling rolls. Equation (3) described later is used for the evaluation of roundness. In Fig. 5, the preset value of Cp / D is set to 0.020, and when the value of "Cp / D" representing roundness is 0.020 or less, it is defined as "excellent roundness". The vertical axis of Fig. 5 is the roundness (Cp / D) of the metal tube measured after rolling (unit: -), and the horizontal axis is the entrance side angle of the rolling roll (unit: °). Note that, similar to the examples described later, the size of the plain tube is an outer diameter of 100 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, and a barrel-shaped roll with an exit side angle N of 4.0° is used, and the rolling roll is set with an inclination angle β: 3°, a crossing angle γ: 0°, and a roll gap: 85 mm for rolling.

[0037] As can be seen from Fig. 5, the roundness of the metal tube after rolling is affected by the entrance side angle of the rolling roll. The roundness is evaluated based on the outer diameter of the tube as shown in Equation (3). From this, 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 it can be seen that this range changes depending on the entrance side angle of the rolling roll. Therefore, the present inventors focused on the entrance side angle and conducted further studies.

[0038] When the entrance side angle M is large, the range (area) where the tapered side surface of the rolling roll 3 contacts the tube surface of the tube to be rolled on the entrance side of rolling becomes narrow (see Fig. 4). In other words, the range where the tapered side surface of the rolling roll 3 does not contact the tube surfaces of the plain tube 1 and the tube 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 2 to be rolled in the contact area to deform freely. That is, due to the restraint from this non-contact area, a force that tries to deform into a more circular shape acts on the tube to be rolled 2, so it is considered that the roundness of the metal tube after rolling is improved. From this, it was found that there is a high correlation between the entrance side angle M of the rolling roll 3 and the difference (Cp) between the maximum outer diameter and the minimum outer diameter of the tube after rolling, which is used for the evaluation of roundness. Note that this tendency was the same even when rolling was performed using a three-roll type inclined rolling facility.

[0039] As a result of the inventors' examination of this effect, it was found that the outer diameter of the metal tube after rolling and the entrance side angle take the values shown in the following formula (1). Cp / D = 0.07 / (M 0.9 ) … Formula (1) Here, as shown in formula (1), Cp: The difference [mm] between the maximum outer diameter and the minimum outer diameter in the cross-section perpendicular to the tube axis of the metal tube after rolling, D: The target outer diameter [mm] in the cross-section perpendicular to the tube axis of the metal tube after rolling, M: The entrance side angle [°] of the rolling roll, That is.

[0040] Note that the above maximum outer diameter, minimum outer diameter, and target outer diameter can be determined based on, for example, the product specifications of the metal tube.

[0041] Thus, in the present invention, as a method for making the cross-sectional shape of the metal tube after rolling (that is, the shape of the cross-section perpendicular to the tube axis) approach a perfect circle, it is important to appropriately control the entrance side angle M of the rolling roll 3 based on the difference (Cp) between the maximum outer diameter and the minimum outer diameter of the metal tube after rolling preset before the start of rolling. This makes it possible to appropriately set the contact area between the rolling roll and the pipe material during rolling, and thus prevent a decrease in roundness.

[0042] Based on the above findings, the inventors derived the following formula (2) that defines the relationship between the difference: Cp between the maximum outer diameter and the minimum outer diameter of the tube after rolling and the entrance side angle: M of the rolling roll.

[0043] Specifically, the control means sets the entrance side angle M of the rolling roll 3 so as to satisfy the following formula (2). M ≧ (0.07 / (Cp / D)) (1 / 0.9) …(2) Here, as shown in formula (2), Cp: The difference [mm] between the maximum outer diameter and the minimum outer diameter in the cross-section perpendicular to the tube axis of the metal tube after rolling, D: Outer diameter target value [mm] in the cross-section perpendicular to the tube axis of the metal tube after rolling M: Inlet side surface angle of the rolling roll [°].

[0044] The reasons for the limitation of Equation (2) will be described below.

[0045] When the inlet side surface angle M is less than the right side value of Equation (2) (i.e., the value calculated by (0.07 / (Cp / D)) (1 / 0.9) , the range (area) where the tapered side surface of the rolling roll 3 contacts the tube surfaces of the raw tube 1 and the tube to be rolled 2 becomes wider. As a result, the restraint from the range where the rolling roll 3 does not contact becomes smaller, so the roundness decreases. The inlet side surface angle M is preferably (0.09 / (Cp / D)) (1 / 0.9) or more.

[0046] In the present invention, the upper limit of the inlet side surface angle M is not particularly defined. When the raw tube 1 bites into the rolling roll 3, if the inlet side surface angle M is large, it may be difficult to bite and the deformation may become unstable. Therefore, the inlet side surface angle M is preferably 40.0° or less, and more preferably 30.0° or less.

[0047] In the present invention, the outlet side surface angle N of the rolling roll 3 is not particularly defined. From the viewpoint of the stability of the progress of the tube to be rolled 2, the outlet side surface angle N of the rolling roll 3 is preferably set in the range of 0.2 to 10.0°.

[0048] As described above, if the inlet side surface angle is set by the control means so as to satisfy Equation (2), the above-described operational effects can be obtained. For example, the control means can also be controlled by a control device (not shown) of the inclined rolling equipment 10. In this case, the control device may control the operation of the inclined rolling equipment 10 according to an instruction from a process computer (not shown) that manages the operation of the manufacturing process of the metal tube.

[0049] Next, with reference to FIG. 6, the roundness in the present invention will be described. FIG. 6 shows an example of the cross-sectional shape perpendicular to the tube axis of the metal tube after inclined rolling, which is deformed into an elliptical shape.

[0050] 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 denoted as Dmax and the minimum value of the outer diameter (i.e., the minor axis of the ellipse) is denoted as 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 denoted as Cp. The maximum and minimum outer diameters may be measured values or set values. When they are measured values, they can be measured by the method described later. Note that the target value of the outer diameter is denoted as D. Then, the values of Cp and D are substituted into Equation (3), and the obtained value (R) is referred to as the roundness. In the present invention, when the value of this roundness (R) is equal to or less than the value of Cp / D set in advance, it is defined as "good roundness" (i.e., "excellent roundness"). R = Cp / D …(3) Here, in Equation (3), R: roundness, Cp: the difference between the maximum and minimum outer diameters in the cross-section perpendicular to the tube axis of the metal tube after rolling, D: the target value of the outer diameter in the cross-section perpendicular to the tube axis of the metal tube after rolling.

[0051] 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 scale may be used.

[0052] 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 maximum and minimum outer diameters are obtained by measuring the outer diameter of the tube at 24 equally spaced points in the tube circumferential direction on the cut surface, with the maximum value being Dmax and the minimum value being Dmin. When measuring the outer diameter using calipers or a scale, in the cross-section perpendicular to the tube axis, the distance in the tube circumferential direction between two points that become the measurement positions on the tube circumference (i.e., the installation positions of the calipers or the scale) is set to be half of the tube circumference.

[0053] The measurement position in the axial direction of the metal tube can be anywhere, but since unsteady part deformation is likely to occur in the regions including the tip and tail ends of the metal tube, it is desirable to measure the outer diameter at positions excluding 20 mm from each of the tip and tail ends, and more preferably at positions excluding 40 mm from each of the tip 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 points can be set to 10, and the average value of the measurement values at these 10 points can be used.

[0054] 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.

[0055] 〔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.

[0056] 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 with an inclination angle β with respect to the pass line 6 (axial direction of the tube) is used, and the entrance side angle M of the rolling roll 3 included in the inclined rolling equipment is set by a control means for controlling the entrance side angle M, 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 an intersection angle γ.

[0057] As shown in FIG. 4 and the like, the raw tube 1 is supplied to the roll gap of the inclined rolling equipment 10 from the entrance 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.

[0058] During rolling, the inlet side angle M of the rolling roll 3 is controlled by the control means. Specifically, the control means sets the inlet side angle M of the rolling roll 3 based on the difference between the maximum outer diameter value and the minimum outer diameter value of the metal tube after rolling, which are preset, and performs rolling on the plain tube 1 using the rolling roll 3 set to the inlet side angle. From the viewpoint of improving the roundness, the control means controls the inlet side angle M so as to satisfy the above-mentioned formula (2).

[0059] 〔Method for manufacturing a 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 subjecting a tube to be rolled to rolling by the above-described inclined rolling method. Note that the description of the rolling roll and the control means is omitted because it has already been described in the description of the inclined rolling equipment.

[0060] 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 advancing it in the axial direction of the tube, and passing the plain tube 1 through the roll gaps of two or more rolling rolls 3 for inclined rolling.

[0061] In the rolling step, the inlet side angle M of the rolling roll 3 is controlled by the control means. Specifically, the control means sets the inlet side angle M of the rolling roll based on the difference between the maximum outer diameter value and the minimum outer diameter value of the metal tube after rolling, which are preset, and performs rolling on the plain tube 1 with the rolling roll 3 set to the inlet side angle. Thereby, a decrease in roundness in the cross-sectional shape of the metal tube after rolling can be suppressed. From the viewpoint of improving the roundness, the control means controls the inlet side angle M so as to satisfy the above-mentioned formula (2).

[0062] In the method for manufacturing a 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 scale on the surface of the metal tube by pickling the metal tube after the above rolling step. The conditions for heat treatment and pickling treatment may be appropriately set according to the composition of the metal tube and the like.

[0063] In the present invention, the manufacturing conditions of the base tube before performing the above-described rolling process are not particularly limited, and generally known manufacturing conditions can be adopted. Also, the base tube before performing the rolling process is not particularly limited, and for example, it may be a hollow pipe material.

[0064] Further, as the shape of the base tube before performing the rolling process, even if there is a difference between the maximum outer diameter value and the minimum outer diameter value 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 regardless of the roundness of the base tube, an effect of preventing the material to be rolled in the contact area from being deformed more freely can be obtained.

[0065] From the viewpoint of more effectively obtaining the effects of the present invention, the base tube before performing the rolling process preferably has an elliptical or circular shape in the cross-section perpendicular to the tube 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 (that is, ((maximum outer diameter value - minimum outer diameter value) / maximum outer diameter value)×100 (unit: %)) is 10% or less, and more preferably, the value is 7% or less.

[0066] As described above, according to the present invention, by performing inclined rolling on a base tube using inclined rolling equipment having control means capable of appropriately controlling the entrance side surface angle of the rolling roll, it is possible to suppress a decrease in the roundness of the cross-sectional shape of the obtained metal tube after rolling. In particular, pretreatment such as surface coating application and end processing of the base tube before inclined rolling is not required. Also, 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

[0067] Hereinafter, examples of the present invention will be described. However, the present invention is not limited by the following examples, and it is also possible to appropriately change within the range that can conform to the gist of the present invention.

[0068] First, a plain tube with an outer diameter of 100 mm (the difference between the maximum and minimum outer diameters: 0 mm), a wall thickness of 5 mm, and a length of 250 mm was taken by machining from a stainless steel bar conforming to JIS G 4303:2012 standard (material: SUS329J3L) shown in Table 1.

[0069]

Table 1

[0070] Next, the taken plain tube 1 was rolled. For this rolling, as equipment for cold 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, barrel-shaped rolls with an exit side angle N of 4.0° were used. Here, the entry side angle M of rolling roll 3 was variously changed and rolled as shown in Table 2. At the time of rolling, the inclination angle β of the rolling roll was set to 3°, the crossing angle γ was set to 0°, and the roll gap of rolling roll 3 was set to 85 mm. The preset Cp / D was set to the value shown in Table 2.

[0071] Next, one-pass rolling was performed on the plain tube at room temperature to obtain a metal tube.

[0072] Using the rolled metal tube (here, a cold-rolled tube), roundness (R) was evaluated by the above method. In addition, a vernier caliper was used to measure the outer diameter of the metal tube. As described above, the difference Cp´ between the maximum outer diameter Dmax´ (measured value) and the minimum outer diameter Dmin´ (measured value) obtained by measuring the outer diameter at 24 equally spaced points in the circumferential direction of the tube was calculated. Using Equation (3), the value of Cp´ / D was calculated and shown in Table 2. In this example, when the value of Cp´ / D measured after rolling was 0.012 or less, which was the preset value of Cp / D, it was evaluated as "qualified (that is, excellent roundness)", and the symbol "◎" was marked in the evaluation result column of Table 2. On the other hand, when the value of Cp´ / D exceeded 0.012, it was evaluated as "unqualified", and the symbol "×" was marked in the evaluation result column of Table 2. In addition, the measurement position in the tube axis direction was set to the central position of the metal tube (that is, the position at half the total length of the tube from the tube end).

[0073] The results are shown in Table 2.

[0074]

Table 2

[0075] The tubes numbered 1 to 11 shown in Table 2 are tubes obtained by performing rolling on a two-roll type inclined rolling facility with two rolls. For tubes numbered 1 to 3, the setting of the inlet surface angle considering the preset Cp / D has not been performed, and the value of the inlet surface angle M does not satisfy Equation (2). As a result, the decrease in roundness could not be suppressed. On the other hand, for tubes numbered 4 to 11, the setting of the inlet surface angle M considering the preset Cp / D has been performed, and as a result, the decrease in roundness could be suppressed.

[0076] Also, the tubes numbered 12 to 22 shown in Table 2 are tubes obtained by performing rolling on a three-roll type inclined rolling facility with three rolls. For tubes numbered 12 to 14, the setting of the inlet surface angle considering the preset Cp / D has not been performed, and the value of the inlet surface angle M does not satisfy Equation (2). As a result, the decrease in roundness could not be suppressed. On the other hand, for tubes numbered 15 to 22, the setting of the inlet surface angle M considering the preset Cp / D has been performed, and as a result, the decrease in roundness could be suppressed.

[0077] From the above, it was found that in the example of the present invention, the decrease in roundness can be suppressed.

Explanation of Signs

[0078] 1 Plain tube 2 Tube to be rolled 3 Rolling roll 3a Rolling part 6 Pass line 7 Rotation axis of rolling roll 10 Inclined rolling facility 21 Metal tube β Inclination angle γ Crossing angle M Inlet surface angle N Outlet surface angle Gap Roll gap Dmax Maximum outer diameter Dmin Minimum outer diameter

Claims

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 entrance side surface angle of the rolling roll, wherein the control means sets the entrance side surface angle of the rolling roll so as to satisfy formula (2). The inclined rolling facility. M ≥ (0.07 / (Cp / D)) （１／０．９） …(2) Here, as shown in formula (2), Cp: The difference [mm] between the maximum outer diameter value and the minimum outer diameter value in the cross section perpendicular to the tube axis direction of the metal tube after rolling, D: The target outer diameter value [mm] in the cross section perpendicular to the tube axis direction of the metal tube after rolling, M: The entrance side surface angle [°] of the rolling roll.

2. An inclined rolling method using the inclined rolling facility according to Claim 1, wherein when rolling while rotating the raw tube in the circumferential direction of the tube and advancing it in the tube axis direction, the control means controls the entrance side surface angle of the rolling roll. The inclined rolling method.

3. A method for manufacturing a metal tube using the inclined rolling facility according to Claim 1, having a rolling process of passing the raw tube through the roll gap of the two or more rolling rolls while rotating the raw tube in the circumferential direction of the tube and advancing it in the tube axis direction to perform rolling to obtain a metal tube, wherein in the rolling process, the control means controls the entrance side surface angle of the rolling roll and performs rolling on the raw tube at the entrance side surface angle. The method for manufacturing a metal tube.

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