JP3503559B2 - Manufacturing method of seamless pipe - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a seamless pipe using a piercing rolling mill of an inclined roll type. 2. Description of the Related Art As is well known, a so-called Mannesmann pipe manufacturing method widely used as a method for manufacturing a seamless metal pipe uses a solid round billet heated to a predetermined temperature as a raw material. The billet is fed to an inclined roll type piercing mill (hereinafter, referred to as a piercer), and a hole is formed in the shaft core to obtain a hollow shell. Next, the obtained raw tube is passed through an elongator or a sizer having the same configuration as that of the piercer as described above, or if necessary, is reduced in diameter by expanding or reducing the diameter thereof, followed by a plug mill, a mandrel mill, or the like. It is fed to a stretching rolling mill and stretched and rolled. Thereafter, a product tube is obtained through a refinement process of passing through a stretch reducer, a reeler, a sizer, etc. to perform a polishing tube, shape correction and sizing. FIG. 1 is a perspective view showing an example of the configuration of a piercing mill used for carrying out the above-mentioned Mannesmann pipe manufacturing method. The illustrated piercer is provided with a pair of main rolls 1, 1 arranged opposite to each other with a slant in opposite directions with respect to a pass line XX serving as a feed line of a round billet 4 as a material to be pierced. A pair of disc rolls 2 and 2 are disposed opposite to each other with the phase being 90 ° out of phase with the phases 1 and 1 and the pass line is interposed therebetween. The plug 3 is supported by a cored bar 5. However, disk roll 2,
2 may be replaced by a fixed plate. In the piercer constructed as described above, the main rolls 1 and 1 are rotated in the same direction with the inclination angle β given to the pass line XX. For this reason, the round billet 4 fed in the outline arrow direction along the pass line XX is screwed and moved after being caught between the main rolls 1, 1, and the axial center portion thereof is moved by the plug 3. Is made into a hollow shell. During this time, the disc rolls 2 and 2 serve as a guide member for the round billet 4 during rolling, and at the same time, bulge in a direction 90 ° out of phase with the opposing direction of the main rolls 1 and 1 of the hollow shell pierced by the plug 3. And serves to adjust the outer diameter shape. The disc rolls 2 and 2 are driven to rotate in the same direction as the round billet 4 in order to reduce sliding with the perforated hollow shell so that seizure does not occur. By the way, a tube piece 7 as shown in FIG. 2 is formed on the rear end face of the hollow shell 6 obtained by the piercing and rolling method as described above. The pipe piece 7 is generated when the material at the center of the rear end of the round billet 4 is extruded by the plug 3, but is extremely thin, so it is easily peeled off from the rear end of the hollow shell 6, and the inner surface of the hollow shell 6 May remain. The pipe pieces 7 remaining on the inner surface are stamped on the inner surface of the tube during rolling in the subsequent step and cause flaws, or damage the inner surface regulating tool to cause flaws on the inner surface of the subsequent rolled material. In view of the above problems, various methods for suppressing the generation of tube pieces have been proposed (for example, see Japanese Patent Laid-Open No.
No. 31753, No. 59-148102, 62
-199201, JP-A-7-214112, 4-
No. 79725). That is, all of the methods disclosed in these publications specify a method of forming a hole in the rear end face of the round billet 4 and the shape of the hole. However, according to the results of many experiments performed by the present inventors, there was a problem that the generation of the tube piece 7 could not be completely prevented by these methods. SUMMARY OF THE INVENTION An object of the present invention is to completely prevent the above-mentioned tube piece 7 from being generated, and to check whether there is any internal flaw caused by the tube piece 7 or not. It is an object of the present invention to provide a method for manufacturing a seamless tube capable of greatly reducing the rate. The gist of the present invention resides in the following seamless pipe manufacturing method. In a method for manufacturing a seamless pipe using an inclined roll type piercing mill, the following formula (1) is provided at the center of the rear end face.
And a round billet with a small hole that satisfies the formula (2) , the tip of the round billet is formed on a flat surface perpendicular to the axis of the following formula (3)
Piercing and rolling using a plug that satisfies the above conditions . 0.4 ≦ b / a ≦ 2.2 (1) c / D ≧ 0.04 (2) 0.05 ≦ a / D ≦ 0.25 (3) where, a: diameter of flat surface at plug tip (mm) b: diameter of small hole (mm) c: depth of small hole (mm) D: round billet DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The method of the present invention will be described below in detail with reference to the accompanying drawings. First, a mechanism for preventing the tube piece 7 from being generated by the method of the present invention will be described. FIGS. 3A and 3B are schematic views showing an example of the embodiment of the present invention. FIG. 3A shows a state at the end of piercing and rolling, and FIG. 3B shows a state immediately before the end of piercing and rolling. As shown in FIG. 3, in the present invention, a plug 30 having a front end formed on a flat surface 30a is used. For this reason, a shearing force acts on the periphery of the flat surface 30a. In addition, a small hole 4b is formed in the center of the rear end face 4a of the round billet 4, so that the shearing force acting on the peripheral edge of the flat face 30a is promoted. As a result, at the end of the piercing and rolling, the material 4c of the axial center portion of the round billet 4 to be a tube piece is completely sheared off from the rear end face 4a, and no tube piece is generated. On the other hand, as shown in FIG. 4, in the conventional plug 3 having a spherical tip, no matter how the shape and size of the small hole 4b is changed, the axial center portion of the round billet 4 to be a tube piece is changed. Since the material is only extruded from the rear end face 4a and is not removed by shearing, a pipe piece 7 is generated. Even if the above-mentioned plug 30 is used, as shown in FIG.
If there is no small hole in the center of the flat surface, a large shearing force does not act on the periphery of the flat surface 30a. As a result, as in the case of FIG.
The material part which becomes the tube piece of the axial center part of the round billet 4 is the rear end face 4
Since it is only extruded from a and is not removed by shearing, a pipe piece 7 is generated. The diameter a of the flat surface 30a (hereinafter simply referred to as diameter a) must be 0.05 to 0.25 times the outer diameter D of the round billet 4 (see FIG. 6 described later). Preferably, it should be 0.05 to 0.2 times. this is,
When the diameter a is less than 0.05 times the outer diameter D, the amount of the material 4c to be sheared off at the end of the rolling is too small, so that not only the tube piece 7 is easily generated, but also the tip of the plug 30 is eroded. It will be easier. On the other hand, when the diameter a exceeds 0.2 times the outer diameter D, in the case of a round billet having no small hole on the end face, it becomes difficult to form a hole on the end face of the round billet 4 at the beginning of piercing and rolling, so that the bite is not bitten. Easy to cause defects, 0.2
If it exceeds 5 times, even if a round billet provided with a small hole in the front end surface is used, poor biting often occurs. When the diameter a is 0.05 times or more the outer diameter D,
Plug erosion caused by insufficient heat capacity at the plug tip can be prevented. The diameter b of the small hole 4b is 0.4 to 2.2 of the diameter a.
Must be doubled. This is because if the diameter b does not coincide with the diameter a to some extent, the shear force acting on the periphery of the flat surface 30a is too small, and the tube piece 7 is likely to be generated. The depth c of the small hole 4b must be at least 0.04 times the outer diameter D. This means that the depth c is 0.
If the ratio is less than 04 times, the shearing force acting on the periphery of the flat surface 30a is too small, so that the material at the center of the round billet 4 is not sheared and separated, and the pipe pieces 7 are generated. The depth c may be any depth, and there is no upper limit. However, it does not make sense to make the hole too deep, and the cost of material reduction and drilling increases. Therefore, it is preferable to make the outer diameter D about 0.15 times the deep one. The shape of the small hole 4b may be either the hole A having a constant inner diameter shown in FIG. 6 or the hole B having a larger inner diameter on the end face side. Further, it is desirable that the position of the small hole 4 b is a position where its axis coincides with the axis of the round billet 4. The small hole of the shape A shown in FIG. 6A is an example of a cut hole using a drill, and the small hole of the shape B shown in FIG. 6B is an example of a hot press hole using a punch. The piercing and rolling may be performed in a conventional manner using, for example, the piercer shown in FIG. Example 1 A round billet having dimensions and materials shown in Table 1 was heated to 1230 ° C., and a piercer having a configuration shown in FIG.
In forming a hollow shell having a thickness of 23.5 mm and a length of 5500 mm, small holes having various shapes and dimensions are formed in the center of the rear end surface of the round billet, and the holes are pierced using the plugs shown in FIGS. 7 and 8. Rolling was performed. At this time, the piercer setting conditions were as shown in Table 2. Some round billets were subjected to piercing and rolling without forming a small hole on the end face. In addition, the gorge part diameter of the main roll in Table 2 is the diameter of the largest diameter part at the axial center of the main roll. [Table 1] [Table 2] Then, after the obtained hollow shell is subjected to a rolling process including a mandrel mill and a sizer to finish product tubes of various dimensions, the inner surface thereof is visually inspected, and the inner surface flaw caused by the tube piece is inspected. Was investigated. In addition, 4 to 5 product tubes were obtained from one hollow shell. The results of the investigation are shown in Table 3 together with the shapes and dimensions of the small holes and the plugs used. [Table 3] As can be seen from Table 3, in the conventional method (test number 9), the incidence of inner surface flaws caused by the pipe pieces was 3.47%.
Met. In addition, in the method of the comparative example (test number 4), the incidence of inner surface flaws caused by the pipe piece was 3.74%. further,
In the method of the comparative example (Trial No. 1), the occurrence of inner surface flaws
The birth rate is as high as 1.22%, and the plug tip melts frequently.
did. Furthermore, in the method of the comparative example (Test No. 8),
No internal flaws caused, but poor biting
did. On the other hand, in the method of the present invention (Trial Nos. 2, 3, and 5 to 7 ), the occurrence rate of the inner surface flaw caused by the pipe piece is greatly reduced to 0.09% at the maximum in Test No. 3. did. In particular, the diameter a of the flat surface at the tip of the plug is 0.
In the case of 1 or more times, no inner surface flaw caused by the pipe piece was generated at all. [0031] However, when the diameter a of more than 0.2 times the outer diameter D, the occurrence of defective biting is sometimes Mira been. [0032] Therefore, the diameter of a can, from the viewpoint of preventing the occurrence of a defective biting us go good is to 0.05 to 0.2 times the outer diameter D Togawakaru. Example 2 While using the same plug as that of Test No. 5 of Example 1, small holes having a shape A, a depth c of 20 mm, and a constant diameter b were formed on the rear end face of the round billet. Except for the above, piercing and rolling were performed under the same conditions as in Example 1, and the occurrence of internal flaws caused by the pipe pieces was examined by the same method as in Example 1. Table 4 shows the results of the survey together with the dimensions of the small holes.
It was shown to. [Table 4] [0036] As can be seen from Table 4, 0.4 to 2.2 times the present invention example of the diameter a of the flat surface of the diameter b plug tip eyelets
In the case of (Nos. 11 to 14), no inner surface flaw caused by the pipe piece was generated at all. Therefore, the diameter b of the small hole is 0.4 to 2.... Of the outer diameter D from the viewpoint of reliably preventing the generation of a tube piece.
It can be seen that it is necessary to double the value. <Example 3> While the same plug as that used in Test No. 5 of Example 1 was used, small holes having a shape A, a constant diameter 15b, and various depths c were formed on the rear end face of the round billet. Except for the above, piercing and rolling were performed under the same conditions as in Example 1, and the occurrence of internal flaws caused by the pipe pieces was examined by the same method as in Example 1. The results of the investigation are shown in Table 5 together with the dimensions of the small holes.
It was shown to. [Table 5] [0040] As can be seen from Table 5, in the case of the present invention example 0.04 times the outer diameter D of the depth c Gamal billet eyelets (Run No. 18 to 21), due to the tube piece No inner surface flaw was generated. Therefore, it is understood that the depth c of the small hole needs to be 0.04 times or more of the outer diameter D from the viewpoint of reliably preventing the generation of the pipe piece. According to the method of the present invention, it is possible to greatly reduce or eliminate the occurrence of inner surface flaws caused by pipe pieces.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing an example of a basic configuration of a piercing mill. FIG. 2 is a schematic view showing a tube piece generated at the rear end of a hollow shell after piercing and rolling. FIGS. 3A and 3B are diagrams for explaining the method of the present invention, wherein FIG. 3A shows the state at the end of piercing and rolling, and FIG. 3B shows the state immediately before the end of piercing and rolling. FIG. 4 is a schematic view showing a state in which a pipe piece is generated by a conventional method. FIG. 5 is a schematic view showing a state in which a tube piece is generated by a method of a comparative example with respect to the present invention. 6A and 6B are diagrams showing examples of the shape of a small hole, wherein FIG. 6A is a diagram showing an A shape, and FIG. 6B is a diagram showing a B shape. FIG. 7 is a schematic diagram showing plugs used in the method of the present invention and the comparative example. FIG. 8 is a schematic view showing a plug used in the conventional method of the embodiment. [Description of Signs] 1: Main roll, 2: Disc roll 3, 30: Plug,
30a: flat surface, 4: round billet, 4a: rear end surface, 4
b: small hole, 4c: material to be a tube piece, 5: core metal, 6:
Hollow shell, 7: tube piece.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-9-1210 (JP, A) JP-A-1-180711 (JP, A) JP-A-59-33011 (JP, A) JP-A-7-107 214112 (JP, A) JP-A-60-124404 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B21B 19/04 B21B 25/00

Claims (1)

(57) [Claims 1] In a method for manufacturing a seamless pipe using an inclined roll type piercing mill, the following equation (1) is provided at the center of the rear end face.
And a round billet with a small hole that satisfies the formula (2) , the tip of the round billet is formed on a flat surface perpendicular to the axis of the following formula (3)
Piercing and rolling using a plug that satisfies the above conditions . 0.4 ≦ b / a ≦ 2.2 (1) c / D ≧ 0.04 (2) 0.05 ≦ a / D ≦ 0 .25 (3) where, a: diameter of flat surface of plug tip (mm) b: diameter of small hole (mm) c: depth of small hole (mm) D: outer diameter of round billet ( mm)