Incline rolling equipment, inclined rolling method, and method for manufacturing metal pipes

Abstract

The purpose is to provide inclined rolling equipment, inclined rolling methods, and methods for manufacturing metal pipes. [Solution] The present invention relates to an inclined rolling mill comprising two or more rolling rolls arranged at an inclination on a circumference centered on a pass line, wherein the rolling mill has a control means for controlling the face angle of the rolling rolls, and the control means sets the exit face angle of the rolling rolls to satisfy equation (2). 6.2-(((100×Cp / D)-0.08) / 0.011) (1 / 2) ≦ N ≦ 6.2+(((100×Cp / D)-0.08) / 0.011) (1 / 2) …(2)

Description

[Technical Field]

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

[0002] In fields where seamless metal pipe products are used, particularly in areas requiring excellent corrosion resistance and high strength, seamless steel pipes made of duplex stainless steel (specifically equivalent to JIS G3459 SUS 329J1, 329J3L, 329J4L) or austenitic stainless steel (specifically equivalent to JIS G3459 SUS 301, 302, 304, 305, 309, 310, 312, 315, 316, 317, 836, 890, 321, 347) with a high amount of corrosion-enhancing elements such as Cr, Mo, and Ni added are used to improve corrosion resistance. These include seamless steel pipes made of Ni-based alloys (specifically equivalent to JIS H4552 NW4400, NW6007, NW0276, NW6022, NW6002).

[0003] These steel grades and alloys contain large amounts of alloying elements added to achieve excellent corrosion resistance. Therefore, their microstructure is either a single austenite phase or a multiphase structure with a large austenite phase. The austenite phase, with its face-centered cubic (fcc) crystalline structure, often has lower yield strength than the ferrite or martensite phases, which have body-centered cubic (bcc) crystalline structures, at low to room temperature operating environments. Therefore, when higher yield strength is required for materials containing the austenite phase, cold working is applied to the material, utilizing dislocation strengthening through processing to achieve higher yield strength.

[0004] For example, in high-strength, highly corrosion-resistant steel pipes used in oil well tubing and other applications, cold working processes such as cold drawing and cold pilgering are frequently employed, and high-strength steel pipes with a yield strength of 125 ksi or higher have been put into practical use (see Non-Patent Document 1).

[0005] The cold drawing method described in Non-Patent Document 1 is an effective technique not only for improving the strength of steel pipes in the longitudinal direction but also for uniformizing the wall thickness distribution in the longitudinal direction of steel pipes. However, it requires many processes before drawing, such as heat treatment to soften the steel pipe, pickling, chemical treatment to apply a lubricating film, and pipe end processing to create gripping parts for drawing. Furthermore, due to limitations on the pressure required for drawing and the need to prevent seizing of the tools, a wall thickness reduction of only about 20% can be achieved. Moreover, if the amount of wall thickness reduction is insufficient in a single drawing process, it is necessary to repeat the series of processes starting from the aforementioned heat treatment to soften the pipe. In addition, since the shape of the steel pipe after drawing is uniquely determined by the dimensions of the tool used for drawing, tool replacement is necessary when changing the size, making it unsuitable for small-batch, high-mix manufacturing. Furthermore, because many processes are required to perform drawing, there are problems with significant capital investment and energy consumption.

[0006] On the other hand, cold rolling eliminates the need for pre-treatment of steel pipes and allows for a high rate of wall reduction. However, the feed rate per pass is small, only a few tens of millimeters, resulting in poor production efficiency. In addition, the shape of the rolling rolls is complex, leading to a large burden on tool manufacturing (specifically, the labor and economic burden of manufacturing the rolling rolls).

[0007] One example of a technology that solves these problems is Patent Document 1. The technology described in Patent Document 1 proposes a cold rolling method in which a metal pipe is passed through the roll gap of an inclined rolling mill having two or more rolling rolls arranged at an inclination with respect to the center line of the rolling path direction of the metal pipe (hereinafter sometimes referred to as the "pass line"). This eliminates the need for pre-treatment such as applying a surface coating to the pipe to be rolled before processing or processing the pipe ends, and enables improvement of the strength of the metal pipe by cold working with high processing efficiency, resulting in environmental protection and favorable effects in industry. Furthermore, by allowing the inner surface to deform freely, it prevents excessive surface pressure on the tool and allows for the addition of desired processing distortion without the occurrence of surface defects such as seizing that occur in cold drawing, making it suitable for high-mix low-volume production. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Patent No. 6432614 [Non-patent literature]

[0009] [Non-Patent Document 1] The Iron and Steel Institute of Japan, "Current Status and Future of Steel Pipe Manufacturing Technology," The Iron and Steel Institute of Japan Publications, May 6, 1986, pp. 115-145. [Overview of the project] [Problems that the invention aims to solve]

[0010] As mentioned above, the cold rolling method described in Patent Document 1 has numerous advantages. However, the inclined rolling mill used in Patent Document 1 may cause excessive deformation of the pipe material due to the large stress applied in the circumferential direction of the pipe by the rolling load from the rolling rolls during rolling. Therefore, Patent Document 1 is not yet sufficient as a technique to bring the cross-sectional shape of the metal pipe after rolling closer to a perfect circle, that is, to improve the roundness of the metal pipe.

[0011] The provision of technology to improve the roundness of metal tubes after rolling is in demand not only for cold rolling, but also for hot rolling and warm rolling.

[0012] Furthermore, in the cold rolling method described in Patent Document 1, the metal tube is processed while rotating in the circumferential direction, which may cause the metal tube to oscillate at the exit of the inclined rolling mill. In this case, new problems may arise, such as scratches on the surface of the metal tube due to strong contact with conveying equipment or other equipment located at the exit, or interference with the equipment or other equipment located at the exit.

[0013] The present invention has been made in view of the above problems, and aims to provide an inclined rolling apparatus, an inclined rolling method, and a method for manufacturing a metal tube that can make the cross-sectional shape of the metal tube after rolling closer to a perfect circle, and further reduce the runout of the metal tube at the exit of the inclined rolling mill. [Means for solving the problem]

[0014] To solve the above problems, the inventors diligently studied an inclined rolling method and a method for manufacturing metal tubes that can improve the roundness of the metal tubes and reduce the runout of the metal tubes at the exit of the inclined rolling mill. They also diligently studied inclined rolling equipment that would enable this method. As a result, they found that by appropriately managing the contact area between the rolling rolls and the tube being rolled during rolling, and by appropriately managing the contact state between the rolling rolls and the tube being rolled at the exit of the rolling mill, the cross-sectional shape of the metal tube after rolling can be made closer to a perfect circle, and the runout of the metal tube at the exit of the inclined rolling mill can be reduced.

[0015] The inventors, through further investigation, have completed an invention comprising the following gist. [1] An inclined rolling mill comprising two or more rolling rolls arranged at an inclination on a circumference centered on a pass line, The rolling mill has control means for controlling the face angle of the rolling roll, The control means sets the exit angle of the rolling rolls to satisfy equation (2), inclined rolling equipment. 6.2-(((100×Cp / D)-0.08) / 0.011) (1 / 2) ≦ N ≦ 6.2+(((100×Cp / D)-0.08) / 0.011) (1 / 2) …(2) Here, as shown in equation (2), Cp: ​​The difference between the maximum and minimum outer diameters [mm] in the cross-section perpendicular to the axial direction of the metal pipe after rolling is complete. D: Target outer diameter [mm] of the metal pipe in a cross section perpendicular to the pipe axis after rolling is complete. N: The exit angle of the rolling roll [°]. [2] The control means further, When the distance in the vertical direction from the pass line, which indicates the allowable range of the swing of the pipe to be rolled on the outlet side during rolling, is A, based on the value of A expressed by formula (3), the outlet surface angle of the rolling roll is set to satisfy formula (4). The inclined rolling equipment according to [1] above. A = 1860 - 0.05×L …(3) N ≦ asin(A / L) …(4) Here, as shown in each formula, L: Total length of the metal pipe [mm], A: Distance in the vertical direction from the pass line, indicating the allowable range of the swing of the pipe to be rolled on the outlet side [mm], N: Outlet surface angle of the rolling roll [°]. [3] An inclined rolling method using the inclined rolling equipment according to [1] or [2] above, When rolling while rotating the plain pipe in the circumferential direction of the pipe and advancing it in the axial direction of the pipe, the outlet surface angle of the rolling roll is controlled by the control means. An inclined rolling method. [4] A method for manufacturing a metal pipe using the inclined rolling equipment according to [1] or [2] above, While rotating the plain pipe in the circumferential direction of the pipe and advancing it in the axial direction of the pipe, a rolling process of passing the plain pipe through the roll gaps of the two or more rolling rolls and performing rolling to form a metal pipe is provided. In the rolling process, the outlet surface angle of the rolling roll is controlled by the control means, and rolling is performed on the plain pipe at the outlet surface angle. A method for manufacturing a metal pipe.

Advantages of the Invention

[0016] According to the present invention, it is possible to make the cross-sectional shape of the rolled metal pipe closer to a perfect circle and reduce the swing of the metal pipe on the outlet side of the inclined rolling mill. As a result, it is possible to improve the roundness of the metal pipe and reduce the occurrence of scratches on the pipe surface.

Brief Description of the Drawings

[0017] [Figure 1] FIG. 1 is a schematic diagram for explaining an embodiment of the inclined rolling equipment of the present invention. [Figure 2] Figure 2 is a schematic side view of the inclined rolling mill shown in Figure 1. [Figure 3] Figure 3 is a schematic diagram of the inclined rolling mill shown in Figure 1, viewed from above. [Figure 4] Figures 4(A) and (B) are schematic diagrams illustrating the face angle of the rolling rolls and the contact area between the rolling rolls and the pipe being rolled in the inclined rolling equipment of the present invention. [Figure 5] Figures 5(A) and (B) are schematic diagrams illustrating the effect of the exit angle on the swing of the rolled pipe at the exit of the inclined rolling mill in the present invention. [Figure 6] Figure 6 is a schematic diagram illustrating the acceptable range of oscillation of the rolled pipe at the exit of the inclined rolling mill according to the present invention. [Figure 7] Figure 7 is a graph showing the relationship between the exit angle of the rolling roll and its roundness in the present invention. [Figure 8] Figure 8 is a schematic diagram illustrating an example of the cross-sectional shape of a metal tube after rolling. [Modes for carrying out the invention]

[0018] Embodiments of the present invention will be described with reference to the figures. Note that the following description illustrates a preferred embodiment of the present invention, and the present invention is not limited to this embodiment.

[0019] [Inclined rolling equipment] The inclined rolling mill of the present invention will be described with reference to Figures 1-4.

[0020] Figure 1 shows one embodiment of the inclined rolling equipment of the present invention, and is a front view of the inclined rolling equipment from the rolling exit side. As an example, Figure 1 shows the state in which a pipe to be rolled is being rolled by an inclined rolling equipment having two rolling rolls (i.e., a two-roll type inclined rolling equipment). Figure 2 is a schematic diagram of the inclined rolling equipment and pipe to be rolled shown in Figure 1, viewed from the side. Figure 3 is a schematic diagram of the inclined rolling equipment and pipe to be rolled shown in Figure 1, viewed from above. Figure 4 is a diagram illustrating the face angle of the rolling rolls used in the inclined rolling equipment of the present invention. For ease of understanding, in Figure 3, the lower of the two rolling rolls 3 is omitted from the illustration, and in Figures 2 to 4, the raw pipe 1 and the pipe to be rolled 2 are shown as cross-sectional views.

[0021] The inclined rolling equipment of the present invention is one type of rolling equipment used in the manufacturing process of metal pipes. Below, as an example of "rolling equipment," a 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 in which the rotation axis of the rolling rolls is inclined with respect to the center line of the rolling path direction of the raw pipe (pass line, i.e., the pipe axis direction) can be mentioned. Furthermore, 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. In this invention, "metal pipe" refers to seamless steel pipes, welded steel pipes, forge-welded steel pipes, and UOE pipes.

[0022] The inclined rolling mill 10 of the present invention is equipped with two or more rolling rolls 3 arranged at an inclination on the circumference of a circle centered on a pass line 6. This inclined rolling mill 10 has control means for controlling the face angle of the rolling rolls 3. As shown in Figure 1, two or more rolling rolls 3 are arranged in the circumferential direction of the raw pipe 1 and the pipe to be rolled 2. The raw pipe 1 is supplied to the roll gap of this inclined rolling mill 10 from the entry side of the inclined rolling mill (i.e., the rolling entry side). The raw pipe 1 is then passed through the rolling direction while being pressed between two or more rolling rolls 3, thereby subjecting the pipe material to inclined rolling (hereinafter sometimes simply referred to as "rolling") and forming a metal pipe with a desired outer diameter.

[0023] In the example of a two-roll type inclined rolling mill used for cold rolling, as shown in Figures 1 to 4, the raw pipe 1 is compressed between two rolling rolls 3 as it passes through in the rolling direction. In this example of a cold rolling mill, the metal pipe obtained after rolling is a cold-rolled pipe.

[0024] First, let me explain the rolling mill roll 3.

[0025] Figures 2 and 3 illustrate the intersection angle γ and inclination angle β of the rolling rolls 3. Figure 2 is a cross-sectional view along line AA shown in Figure 1, and shows the rolling rolls 3 and the rolled pipe 2 as viewed from the side. Figure 3 is a view along arrow BB shown in Figure 2, and shows the rolling rolls 3 and the rolled pipe 2 as viewed from above.

[0026] As shown in Figures 2 and 3, the rolling roll 3 is a roll that rolls the raw pipe 1 supplied to the inclined rolling equipment 10. The rolling roll 3 has a rolling section 3a, which performs inclined rolling on the raw pipe. The shape of the rolling roll 3 can be, for example, a barrel-shaped roll or a conical roll. Figures 1 to 4 show an example in which a barrel-shaped roll is used as the rolling roll 3.

[0027] The rolling roll 3 is positioned so that its axis of rotation 7 is inclined at an angle β with respect to the pass line 6. The angle β refers to the angle (in degrees) between the straight line in the direction of the pipe axis (pass line 6) and the axis of rotation 7 of the rolling roll 3 when the rolling roll 3 is viewed from above (i.e., in a direction perpendicular to the pipe axis and in the direction in which the rolling load is applied to the raw pipe 1), as shown in Figure 3.

[0028] In this way, by arranging two or more rolling rolls 3 at an inclination, the rolling rolls 3, which rotate around their rotation axis 7, utilize the frictional force generated by the contact between the rolling rolls 3 and the raw pipe 1 to pull the raw pipe 1 supplied to the roll gap in the rolling direction (i.e., the rolling path direction). As a result, the raw pipe 1 is rolled in a helical shape while being rotated by the rolling rolls 3. That is, the raw pipe 1 is rolled while rotating in the circumferential direction of the pipe and advancing in the axial direction of the pipe. This type of rolling can be realized by making the roll gap of the rolling rolls 3 in the inclined rolling mill smaller than the outer diameter of the raw pipe 1, and by arranging each of the rolling rolls 3 at an inclination as described above (see Figure 1).

[0029] From the viewpoint of ensuring that the raw pipe 1 and the pipe to be rolled 2 advance stably in the rolling direction, it is preferable to set the inclination angle β in the range of 0.5 to 40.0°.

[0030] In addition to having an inclination angle β, the rolling roll 3 may also be positioned with a crossing angle γ on the rolling exit side. The crossing angle γ refers to the angle (in degrees) 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 pipe axis direction and perpendicular to the direction in which the rolling load is applied to the raw pipe 1), as shown in Figure 2. The crossing angle γ is not specifically defined. From the viewpoint of preventing deterioration of the roundness of the cross-sectional shape by minimizing the change in the peripheral speed of the roll in the pipe axis direction and stabilizing the progress of the raw pipe, it is preferable to set the crossing angle γ in the range of 0 to 45.0°. Roundness will be discussed later, so the explanation is omitted here.

[0031] As shown in Figure 1, in the case of an inclined rolling mill having a pair of rolling rolls 3, the inclination angle β and intersection angle γ formed by each rolling roll may be in opposite directions relative to the pipe axis direction (pass line 6). Although not shown in the figures, even when there are three or more rolling rolls 3, the direction in which the inclination angle β and intersection angle γ are formed may be changed for each rolling roll.

[0032] Next, I will explain the control means.

[0033] The control means controls the exit angle N of each rolling roll 3. By controlling the exit angle N by the control means, the contact area between the rolling roll and the rolled pipe during rolling can be appropriately managed, and the contact state between the rolling roll and the rolled pipe at the exit side of the rolling process can be appropriately managed.

[0034] Here, with reference to Figures 4(A) and 4(B), the face angles (specifically, the entry side angle M and the exit side angle N) of the rolling roll 3, and the contact area between the rolling roll and the pipe being rolled will be explained. Figure 4(B) is an enlarged view of the area within the rectangular frame shown in Figure 4(A).

[0035] The entry angle M of the rolling roll 3 refers to the angle (in degrees) between the side of the rolling roll 3 that is on the rolling entry side relative to the rolling direction of the pipe (i.e., the tapered side 3b of the rolling roll 3, where the cross-sectional shape gradually decreases toward the rolling entry side) 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 Figure 4(A). The exit angle N of the rolling roll 3 refers to the angle (in degrees) between the side of the rolling roll 3 that is on the rolling exit side relative to the rolling direction of the pipe (i.e., the tapered side 3b of the rolling roll 3, where the cross-sectional shape gradually decreases toward the rolling exit side) and a straight line 6a parallel to the pipe axis direction when the rolling roll 3 is viewed from the side, as shown in Figure 4(A). The phrase "when the rolling roll 3 is viewed from the side" above means when viewed 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.

[0036] Furthermore, the "contact area between the rolling roll and the pipe being rolled" refers to the area where the rolling roll 3, indicated by the double-headed arrow, and the pipe surface of the pipe being rolled 2 are in contact, as shown in Figure 4(B).

[0037] Next, with reference to Figures 5 and 6, the oscillation of the rolled pipe at the exit of the inclined rolling mill will be explained.

[0038] Figure 5(A) illustrates the range of variability of the rolled pipe when the exit angle N of the rolling roll is large, and Figure 5(B) illustrates the range of variability of the rolled pipe when the exit angle N of the rolling roll is small. Figure 6 illustrates the allowable range of variability of the rolled pipe in the present invention. Figures 5 and 6 show side views of the inclined rolling equipment and pipe material.

[0039] As described above, when a pipe is rolled while rotating in the circumferential direction, the pipe may vibrate at the exit of the rolling mill, which can cause contact between the surrounding equipment at the exit and the pipe being rolled. For example, when processing a pipe using a rolling roll 3 with a large exit side angle N as shown in Figure 5(A), if the pipe being rolled vibrates at the exit of the inclined rolling mill, the inertia caused by the vibrating may cause the pipe to move rapidly in the vertical direction or elsewhere. This movement can create a difference between the peripheral speed of the rolling roll and the rotational speed of the pipe being rolled, resulting in scratches on the pipe surface due to sliding with the rolling roll.

[0040] In contrast, when processing pipe material using a rolling roll 3 with a small exit side angle N, as shown in Figure 5(B), the range in which the pipe to be rolled can swing around on the exit side is narrowly limited because the pipe to be rolled comes into contact with the rolling roll. This is because the tapered side surface 3b on the exit side comes into contact with the pipe to be rolled, preventing the pipe to swing around outside the range of "the range in which the pipe to be rolled can swing around on the exit side" shown in Figure 5(B). This prevents the pipe to be rolled from coming into strong contact with conveying equipment on the exit side, which can cause scratches on the pipe surface, and prevents the pipe to be rolled from interfering with equipment on the exit side.

[0041] From this, the inventors have found that narrowly limiting the range in which the rolled pipe can swing around on the exit side, as shown in Figures 5 and 6, specifically, appropriately managing the contact state between the rolling rolls and the rolled pipe on the exit side (i.e., the allowable range of swing of the rolled pipe), leads to the prevention of such defects. Furthermore, they have also focused on the fact that there is an appropriate range of exit side angle N to obtain this effect.

[0042] Therefore, with reference to Figure 7, we will explain in detail why the inventors focused on controlling the exit angle N of the rolling roll 3.

[0043] Figure 7 shows the results of evaluating the roundness of metal tubes after rolling using a two-roll inclined rolling mill for cold rolling, by varying only the exit side angle N of the rolling rolls. Equation (5), described later, is used to evaluate the roundness. The vertical axis of Figure 7 represents the roundness of the metal tube measured after rolling, "100 × (Cp / D) (unit: %)", and the horizontal axis represents the exit side angle "N (unit: °)" of the rolling rolls. As with the example described later, the size of the raw tube was 85 mm outer diameter (difference between maximum and minimum outer diameter: 0 mm), 5 mm wall thickness, and 250 mm length, and a barrel-shaped roll with an entry side angle M of 8.0 was used. The rolling rolls were set to an inclination angle β: 3°, a crossing angle γ: 0°, and a roll gap: 77 mm for rolling.

[0044] As can be seen from Figure 7, the roundness of the metal tube after rolling is affected by the exit angle N of the rolling roll. Roundness improves as the exit angle N increases from 0°. However, when the exit angle N exceeds 12°, the roundness deteriorates. Therefore, the inventors focused on the exit angle N and conducted further investigations.

[0045] As the exit angle N increases from 0°, the area (region) in contact between the tapered side surface 3b of the rolling roll 3 and the surface of the rolled pipe 2 at the exit side of the rolling process narrows (see Figure 4(B)). In other words, the area of ​​the surface of the raw pipe 1 and the rolled pipe 2 that is not in contact with the tapered side surface 3b of the rolling roll 3 (hereinafter referred to as the "uncontacted area") widens. A wider uncontacted area makes it more difficult for the rolled material 2 in the contact area to deform more freely. That is, it is thought that the constraint from this uncontacted area causes a force to act on the rolled pipe 2 that tries to deform it into a shape closer to a perfect circle, thus improving the roundness of the metal pipe after rolling is complete.

[0046] On the other hand, when the tapered side surface 3b of the rolling roll 3 exiting the rolling section 3a comes into contact with the surface of the pipe being rolled 2, rolling occurs with a larger roll gap than the roll gap at the rolling section 3a. As a result, the outer diameter of the pipe being rolled 2 becomes more uniform, improving its roundness. However, when the exit side angle N exceeds 12°, the area of ​​contact between the tapered side surface 3b of the rolling roll 3 exiting the rolling section 3a and the surface of the pipe being rolled 2 becomes smaller. This reduction in the area of ​​contact between the tapered side surface of the rolling roll 3 exiting the rolling section 3a and the surface of the pipe being rolled 2 reduces the effect of uniformizing the outer diameter, which is thought to have resulted in a deterioration of the roundness of the metal pipe after rolling.

[0047] From this, it was found that the difference (Cp) between the maximum and minimum outer diameters of the rolled pipe, which is used to evaluate roundness, has a high correlation with the exit angle N of the rolling roll 3. This trend was also observed when rolling was performed using a 3-roll type inclined rolling mill.

[0048] As a result of the inventors' investigation into the effects of this mechanism, it was found that the outer diameter of the metal tube after rolling and the outer surface angle N take the values ​​shown in the following equation (1). 100 × Cp / D = 0.011 × (N - 6.2) 2 +0.08 …(1) Here, as shown in equation (1), Cp: ​​The difference between the maximum and minimum outer diameters [mm] in the cross-section perpendicular to the axial direction of the metal pipe after rolling is complete. D: Target outer diameter [mm] of the metal pipe in a cross section perpendicular to the pipe axis after rolling is complete. N: Outward angle of the rolling roll [°], That is the case.

[0049] Thus, in this invention, it is important to appropriately control the exit angle N of the rolling roll 3 as a method to bring the cross-sectional shape of the metal tube after rolling (i.e., the shape of the cross-section perpendicular to the tube axis) closer to a perfect circle. This makes it possible to appropriately set the contact area between the rolling roll and the tube material during rolling, thereby preventing a decrease in roundness. At the same time, the contact state between the rolling roll and the tube material can be appropriately controlled, which reduces the runout of the tube material at the exit side during rolling.

[0050] Based on the above findings, the inventors derived the following equation (2), which defines the relationship between the difference between the maximum and minimum outer diameters of the rolled pipe (Cp) and the exit angle of the rolling roll (N).

[0051] Specifically, the control means sets the exit angle N of the rolling roll 3 so as to satisfy the following equation (2). 6.2-(((100×Cp / D)-0.08) / 0.011) (1 / 2) ≦ N ≦ 6.2+(((100×Cp / D)-0.08) / 0.011) (1 / 2) …(2) Here, as shown in equation (2), Cp: ​​The difference between the maximum and minimum outer diameters [mm] in the cross-section perpendicular to the axial direction of the metal pipe after rolling is complete. D: Target outer diameter [mm] of the metal pipe in a cross section perpendicular to the pipe axis after rolling is complete. N: The exit angle of the rolling roll [°].

[0052] The reason for the limitation in equation (2) will be explained below.

[0053] The outward angle N is less than the left-hand value of equation (2), i.e., "6.2 - (((100 × Cp / D) - 0.08) / 0.011) (1 / 2) If the value is less than the value calculated by ", the range (region) in which the tapered side surface 3b of the rolling roll 3 is in contact with the tube surface of the raw tube 1 and the rolled tube 2 becomes wider. As a result, the constraint from the area in which the rolling roll 3 is not in contact becomes smaller, and the roundness decreases. The exit side angle N is preferably "6.2 - (((100 × Cp / D) - 0.12) / 0.011)(1 / 2) It shall be as described above.

[0054] When the outlet side angle N is greater than the right side value of formula (2), that is, greater than the value calculated by "6.2 + (((100 × Cp / D) - 0.08) / 0.011)" (1 / 2) ", the contact range (area) between the tapered side surface 3b on the outlet side from the rolling part 3a of the rolling roll 3 and the tube surface of the tube to be rolled becomes narrow. As a result, due to rolling with a roll gap that is too large compared to the roll gap at the position of the rolling part 3a, the effect of equalizing the outer diameter of the tube to be rolled decreases, and the effect of improving the roundness deteriorates. The outlet side angle N is preferably "6.2 + (((100 × Cp / D) - 0.12) / 0.011)" (1 / 2) " or less.

[0055] As described above, by controlling the outlet side angle N so as to satisfy the above formula (2), the effects of the present invention can be obtained. As described using Fig. 7 above, when the outlet side angle N is controlled so that the value of "100 × (Cp / D)" shown in formula (1) is preferably within the range of 0.004 or less, the roundness can be further improved, which is preferable.

[0056] In the present invention, for the purpose of further improving the above-described operational effects, in addition to the above formula (2), it is desirable to satisfy the relational expressions defined below.

[0057] As shown in Fig. 6, it is preferable to appropriately set the range in which the tube to be rolled can swing at the rolling outlet side. Specifically, when the distance in the direction perpendicular to the tube axis direction from the pass line, which indicates the allowable range of swing at the rolling outlet side of the tube to be rolled during rolling, is A, based on the value of A represented by formula (3), the outlet side angle N of the rolling roll 3 is set so as to satisfy formula (4). This is because the swing at the outlet side of the inclined rolling equipment for the tube to be rolled can be further reduced. A = 1860 - 0.05 × L …(3) N ≦ asin(A / L)…(4) Here, as shown in each formula, L: Total length of the metal tube [mm], A: Indicates the allowable range of runout of the rolled pipe at the exit side, the distance [mm] perpendicular to the pass line. N: The exit angle of the rolling roll [°]. Note that "L" above refers to the total length of the metal tube as a final product.

[0058] The following explains the reasons for deriving equations (3) and (4), as well as the reasons for the limitations on each equation.

[0059] As described above, when the rolled pipe oscillates at the exit of the inclined rolling mill, a difference occurs between the peripheral speed of the rolling rolls and the rotational speed of the rolled pipe, causing scratches on the surface of the rolled pipe due to sliding with the rolling rolls. Therefore, the inventors conducted further intensive studies regarding these scratches and their extent, and as a result derived the above equations (3) and (4).

[0060] As shown in Figure 6, the inventors have found that defects can be prevented by setting the above distance A within the range determined by the right-hand side of equation (3) (i.e., 1860 - 0.05 × L). Distance A becomes smaller as the value of the length (i.e., total length) L of the metal pipe increases, and the larger the value of this total length L of the metal pipe, the more likely the above speed difference will occur between the rolling roll and the pipe being rolled, even if the amount of runout is small. This finding from the inventors' studies is reflected in equations (3) and (4).

[0061] If the exit side angle N is less than or equal to the value calculated by the right side of equation (4), i.e., "asin(A / L)", then the range in which the rolled pipe can swing when it hits the rolling rolls will be within the range in which the metal pipe is allowed to swing at the exit side of the rolling mill. Preferably, the exit side angle N is "0.95 × asin(A / L)" or less. Note that the "total length L of the metal pipe" used in each of the above equations may be a set value.

[0062] The exit angle N is preferably 0° or greater in order to avoid imparting excessive reduction to the rolled pipe. More preferably, the exit angle N is 0.1° or greater.

[0063] In this invention, there is no particular upper limit to the entry angle M of the rolling roll 3. When the raw pipe 1 is gripped by the rolling roll 3, if the entry angle M is large, it may be difficult to grip and the deformation may become unstable. For this reason, the entry angle M is preferably 40.0° or less, and more preferably 30.0° or less. There is also no particular lower limit to the entry angle M. If the entry angle M is small, the workpiece pipe may come into contact with the end face of the roll, making it difficult to grip and potentially resulting in unstable deformation. For this reason, the entry angle M is preferably 0.1° or more, and more preferably 0.2° or more.

[0064] As described above, the above-mentioned effects can be obtained if the exit angle N is set by the control means to satisfy equation (2). Furthermore, from the viewpoint of obtaining these effects more effectively, it is preferable to set the exit angle N to satisfy equations (3) and (4) in addition to equation (2). For example, the control means can also be controlled by a control device (not shown) of the inclined rolling equipment 10, in which case the control device can control the operation of the inclined rolling equipment 10 by command from a process computer (not shown) that manages the operation of the metal pipe manufacturing process.

[0065] Next, the roundness in the present invention will be explained with reference to Figure 8. Figure 8 shows an example of a metal tube deformed into an elliptical shape, which is perpendicular to the tube axis direction after inclined rolling.

[0066] In the cross-section perpendicular to the axial direction of the metal pipe 21 after inclined rolling, as shown in Figure 8, when the maximum value of the outer diameter of the metal pipe 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, i.e., the difference between the maximum and minimum outer diameters in the cross-section perpendicular to the axial direction of the metal pipe 21 (Dmax-Dmin), is defined as Cp. These maximum and minimum outer diameters may be measured values ​​or set values. If measured values ​​are used, they can be measured using the method described later. The target value of the outer diameter is D. Substituting the values ​​of Cp and D into equation (5), the obtained value (R) (unit: %) is called the roundness. In this invention, if the value of this roundness (R) is less than or equal to the preset value of Cp / D, it is defined as "good roundness" (i.e., "excellent roundness"). R = 100 × (Cp / D) …(5) Here, in equation (5), R is the roundness, Cp is the difference between the maximum and minimum outer diameters in the cross section perpendicular to the axial direction of the metal pipe after rolling, and D is the target outer diameter in the cross section perpendicular to the axial direction of the metal pipe after rolling.

[0067] The outer diameter of a metal pipe (in mm) can be measured using, for example, a caliper. When measuring the outer diameter of the pipe end, a ruler may also be used.

[0068] Furthermore, when measuring the outer diameter other than at the pipe ends, the metal pipe is cut perpendicular to the pipe axis at the measurement point, and the shape of the cut surface is measured. In this invention, the maximum and minimum values ​​of the outer diameter are obtained by measuring the outer diameter of the pipe at 24 equally spaced points in the circumferential direction of the pipe at the cut surface, with the maximum value being Dmax and the minimum value being Dmin. When measuring the outer diameter using calipers or a ruler, the distance in the circumferential direction between two points that serve as measurement positions (i.e., the positions where the calipers or ruler are placed) on the pipe circumference in a cross section perpendicular to the pipe axis is set to be half the pipe circumference.

[0069] The measurement position along the axial direction of the metal pipe can be any point, but since transient deformation is likely to occur in the region including the leading and trailing ends of the metal pipe, it is desirable to measure the outer diameter at points 20 mm away from each end, more preferably 40 mm away from each end. Alternatively, multiple measurement positions along the axial direction may be used, and the average value of the obtained values ​​may be used. For example, the number of measurement points may be set to 10, and the average value of the measurements taken at these 10 points may be used.

[0070] As described above, a two-roll type inclined rolling mill has been explained using Figure 1, etc., but according to the present invention, similar effects can be obtained even when rolling a raw pipe in an inclined rolling mill in which three or more rolling rolls are arranged in the circumferential direction of the pipe.

[0071] [Inclined rolling method] Next, a method for inclined rolling a metal pipe using the inclined rolling equipment of the present invention described above will be explained. Note that the explanation of the rolling rolls and control means has already been described and will therefore be omitted.

[0072] In the inclined rolling method of the present invention, an inclined rolling facility 10 is used, which is equipped with two or more rolling rolls 3, the rotation axis 7 of the rolling rolls 3 being arranged at an inclination angle β with respect to the pass line 6 (pipe axis direction). The exit side angle N is set by a control means that controls the exit side angle N of the rolling rolls 3 in the inclined rolling facility, and the raw pipe 1 is rolled while rotating in the circumferential direction of the pipe and advancing in the pipe axis direction. The rolling rolls 3 may also be arranged with an intersection angle γ.

[0073] As shown in Figure 4, a raw pipe 1 is supplied to the roll gap of the inclined rolling mill 10 from the entry side of the inclined rolling mill 10 (i.e., the right side of the paper as shown in Figure 4). The raw pipe 1 is subjected to inclined rolling by passing it through the rolling direction while being compressed between each rolling roll 3. This results in a metal pipe with a reduced outer diameter to the desired size.

[0074] During rolling, the exit angle N of the rolling roll 3 is controlled by a control means. Specifically, the control means sets the exit angle N of the rolling roll 3 based on a preset difference between the maximum and minimum outer diameters of the metal pipe after rolling is complete, and then rolls the raw pipe 1 using the rolling roll 3 set to this exit angle N.

[0075] Furthermore, from the viewpoint of improving roundness, the control means controls the outward angle N to satisfy equation (2) above. From the viewpoint of obtaining this effect more effectively, it is preferable to set the outward angle N to satisfy equations (3) and (4) in addition to equation (2).

[0076] [Method of manufacturing metal pipes] Next, a method for manufacturing metal tubes using the inclined rolling equipment of the present invention described above will be explained. That is, this manufacturing method is a method of producing metal tubes by rolling a tube to be rolled using the inclined rolling method described above. Note that the explanation of the rolling rolls and control means has already been given in the explanation of the inclined rolling equipment, so it will be omitted here.

[0077] The present invention provides a method for manufacturing a metal tube, which includes a rolling step to obtain a metal tube by inclining rolling a raw tube 1 while rotating it in the circumferential direction and advancing it in the axial direction, and passing the raw tube 1 through the roll gap of two or more rolling rolls 3.

[0078] In this rolling process, the exit angle N of the rolling roll 3 is controlled by a control means. Specifically, the control means sets the exit angle N of the rolling roll based on a preset difference between the maximum and minimum outer diameters of the metal pipe after rolling is complete, and the raw pipe 1 is rolled using the rolling roll 3 set to this exit angle. This makes it possible to suppress a decrease in the roundness of the cross-sectional shape of the metal pipe after rolling.

[0079] Furthermore, from the viewpoint of improving roundness, the control means controls the outward angle N to satisfy equation (2) above. From the viewpoint of obtaining this effect more effectively, it is preferable to set the outward angle N to satisfy equations (3) and (4) in addition to equation (2).

[0080] In the present invention's method for manufacturing metal tubes, for example, the metal tubes after the rolling process may be subjected to heat treatment. Alternatively, for example, the metal tubes after the rolling process may be pickled to remove scale from the surface of the metal tubes. The conditions for heat treatment and pickling can be set appropriately according to the composition of the metal tubes, etc.

[0081] In this invention, the manufacturing conditions for the raw tube before the rolling process described above are not particularly limited, and commonly known manufacturing conditions can be used. Furthermore, the raw tube before the rolling process is not particularly limited, and may be, for example, a hollow tube.

[0082] Furthermore, even if there is a difference between the maximum and minimum outer diameters when the raw tube is measured before the rolling process, the above-mentioned effects of the present invention can still be obtained. This is because, regardless of the roundness of the raw tube, the effects of preventing the rolled material in the contact area from deforming more freely, and the effects of making the outer diameter of the rolled tube 2 uniform by rolling on the side exiting the rolling section 3a can still be obtained.

[0083] Furthermore, from the viewpoint of obtaining the effects of the present invention more effectively, it is preferable that the raw tube before the rolling process has an elliptical or circular cross-section perpendicular to the tube axis, and that the value obtained by dividing the difference between the maximum outer diameter and the minimum outer diameter by the maximum outer diameter (i.e., ((maximum outer diameter - minimum outer diameter) / maximum outer diameter) × 100 (unit: %)) is 10% or less, and more preferably 7% or less.

[0084] As described above, according to the present invention, by performing inclined rolling on a raw pipe using an inclined rolling mill equipped with a control means that can appropriately control the exit angle N of the rolling roll, it is possible to suppress the decrease in the roundness of the cross-sectional shape of the resulting metal pipe after rolling. In particular, there is no need for pretreatment such as applying a surface coating or processing the pipe ends to the raw pipe before inclined rolling. Furthermore, it is possible to improve the hardness of the metal pipe by inclined rolling while suppressing the decrease in the roundness of the cross-sectional shape after inclined rolling. In addition, it is possible to reduce the runout of the rolled pipe at the exit side of the inclined rolling mill. [Examples]

[0085] The following describes embodiments of the present invention. However, the present invention is not limited by the embodiments described below, and can be modified as appropriate within the scope that is consistent with the spirit of the present invention.

[0086] First, a raw tube with an outer diameter of 85 mm (difference between maximum and minimum outer diameter: 0 mm) and a wall thickness of 5 mm was taken from a stainless steel rod (material: SUS329J3L) conforming to the JIS G 4303:2012 standard shown in Table 1 by machining.

[0087] [Table 1]

[0088] Next, the sampled raw pipe 1 was rolled. For this rolling, equipment with the number of rolls shown in Table 2 (i.e., a 2-roll inclined rolling mill and a 3-roll inclined rolling mill) was used as cold rolling equipment. Barrel-shaped rolls with an entry side angle M of 8.0° were used for these rolling rolls. Here, rolling was performed by changing the exit side angle N of rolling roll 3 in various ways as shown in Table 2. During rolling, the inclination angle β of the rolling rolls was set to 3°, the intersection angle γ to 0°, and the roll gap of rolling roll 3 to 77 mm. The preset Cp / D values ​​were those shown in Table 2. The total length L of the metal pipe in equations (3) and (4) was set to 9600 mm.

[0089] Next, the raw tube at room temperature was subjected to a single-pass rolling process to obtain a metal tube.

[0090] The roundness (R) of the rolled metal tube (in this case, a cold-rolled tube) was evaluated using the method described above. A 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. The value of Cp' / D was calculated using equation (5) and is shown in Table 2. In this example, if the value of Cp' / D measured after rolling was 0.004 or less, which is a predetermined value for Cp / D, it was evaluated as "pass (i.e., excellent roundness)" and the symbol "◎" was written in the evaluation result column of Table 2. On the other hand, if the value of Cp' / D exceeded 0.004, it was evaluated as "fail" and the symbol "×" was written in the evaluation result column of Table 2. The measurement position in the axial direction of the tube was the center of the metal tube (i.e., half the length of the tube from the end of the tube).

[0091] Furthermore, if defects were found on the surface of the metal tube caused by the vibration of the metal tube during the rolling process, it was evaluated as "failure," and the symbol "×" was written in the evaluation result column of Table 2. If no defects were found, it was evaluated as "pass," and the symbol "◎" was written in the evaluation result column of Table 2.

[0092] The results are shown in Table 2.

[0093] [Table 2]

[0094] The pipes No. 1 to 11 shown in Table 2 are metal pipes obtained by rolling in a two-roll type inclined rolling mill with two rolls. For pipes No. 1, 8 to 11, the value of the outer side angle N does not satisfy equation (2), and the outer side angle N was not set considering the preset Cp / D. As a result, the decrease in roundness was not suppressed. In contrast, for pipes No. 2 to 7, the outer side angle N was set considering the preset Cp / D, and as a result, the decrease in roundness was suppressed.

[0095] Furthermore, pipes No. 7 to 11 have an exit side angle N that does not satisfy equation (4). As a result, defects caused by runout have occurred. In contrast, pipes No. 1 to 6 experience only slight runout of the rolled pipes at the exit of the inclined rolling mill. There are no instances of defects caused by runout, such as scratches on the pipe surface due to strong contact with the conveying equipment at the exit, interference between the equipment at the exit and the pipe, or scratches on the pipe surface due to sliding with the rolling rolls. However, pipe No. 1 fails the evaluation of roundness.

[0096] Furthermore, pipes No. 12 to 22 shown in Table 2 are metal pipes obtained by rolling in a 3-roll type inclined rolling mill with 3 rolls. In pipes No. 12 and 19 to 22, the value of the exit side angle N did not satisfy equation (2), and the exit side angle N was not set considering the predetermined Cp / D. As a result, the decrease in roundness could not be suppressed. In contrast, in pipes No. 13 to 18, the exit side angle N was set considering the predetermined Cp / D, and as a result, the decrease in roundness could be suppressed.

[0097] Furthermore, pipes No. 18 to 22 have an exit side angle N that does not satisfy equation (4). As a result, defects caused by runout have occurred. In contrast, pipes No. 12 to 17 experience only slight runout of the rolled pipes at the exit of the inclined rolling mill. There are no instances of defects caused by runout, such as scratches on the pipe surface due to strong contact between the pipe and the conveying equipment at the exit, interference between the pipe and the equipment at the exit, or scratches on the pipe surface due to sliding with the rolling rolls. However, pipe No. 12 fails the evaluation of roundness.

[0098] From the above, it was found that in the present invention, the decrease in roundness can be suppressed, and at the same time, the runout of the rolled pipe at the exit of the inclined rolling mill can be prevented. [Explanation of symbols]

[0099] 1. Raw tube 2 Rolled pipe 3 Rolling Rolls 3a Rolling section 3b Tapered side 6 Pass Lines 7. Rotation axis of the rolling mill rolls 10. Inclined rolling mill equipment 21 Metal tube β Tilt angle γ intersection angle M Entrance angle N Exit angle Gap Roll Gap Dmax: Maximum outer diameter Dmin Minimum outer diameter

Claims

1. An inclined rolling mill comprising two or more rolling rolls arranged at an inclination on a circumference centered on a pass line, The rolling mill has control means for controlling the face angle of the rolling roll, The control means sets the exit angle of the rolling rolls to satisfy equation (2), inclined rolling equipment. 6.2-(((100×Cp / D)-0.08) / 0.011) (1 / 2) ≦ N ≦ 6.2+(((100×Cp / D)-0.08) / 0.011) (1 / 2) …(2) Here, as shown in equation (2), Cp: ​​The difference [mm] between the maximum and minimum outer diameters in a cross-section perpendicular to the axial direction of the metal pipe after rolling. D: Target outer diameter [mm] of the metal pipe in a cross section perpendicular to the pipe axis after rolling is complete. N: The exit angle of the rolling roll [°].

2. The control means further, The inclined rolling equipment according to claim 1, wherein when A is the distance perpendicular to the pass line, which indicates the allowable range of runout of the rolled pipe at the exit side of the rolling mill during rolling, the exit side angle of the rolling roll is set to satisfy equation (4) based on the value of A expressed in equation (3). A = 1860-0.05×L…(3) N≦asin(A / L)…(4) Here, as shown in each equation, L: Total length of the metal tube [mm] A: The distance [mm] perpendicular to the pass line, indicating the allowable range of runout of the rolled pipe at the exit side of the rolling mill. N: The exit angle of the rolling roll [°].

3. A method of inclined rolling using the inclined rolling equipment described in claim 1 or 2, An inclined rolling method in which, when rolling a raw pipe while rotating it in the circumferential direction and advancing it in the axial direction of the pipe, the outward angle of the rolling roll is controlled by the control means.

4. A method for manufacturing a metal tube using the inclined rolling equipment described in claim 1 or 2, The process includes a rolling step in which a raw tube is rotated in the circumferential direction and advanced in the axial direction of the tube, and the raw tube is passed through the roll gap of two or more rolling rolls to be rolled and formed into a metal tube. A method for manufacturing a metal pipe, wherein in the rolling process, the exit angle of the rolling roll is controlled by the control means, and the raw pipe is rolled at the said exit angle.

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