Hot rolling forming method for thick-walled square steel pipes with improved corner forming quality

Abstract

The invention discloses a hot rolling forming method for thick-walled square steel pipes capable of improving corner forming quality, and solves the problem of how to improve the corner forming quality when hot rolling square pipes are formed by hot rolling using hot rolled seamless steel pipes as blanks. The hot rolled seamless steel pipes are used as blanks for hot rolled square pipes or rectangular pipes, and after preheating the hot rolled seamless steel pipe blanks to 800° C.-1000° C., continuous and gradual roll bending is performed under the joint rolling of an outer roll group and an inner roll group of a roll bending forming device. The roll bending forming device comprises a blank feeding device, a roll bending frame, a mandrel device, a mandrel supporting device and a roll holding device. The various devices cooperate with each other to roll the hot rolled seamless steel pipe blanks into square steel pipes or rectangular steel pipes. The continuous and gradual roll bending of the seamless round pipes under the joint action of the outer roll group and the inner roll group is achieved, thereby improving the forming accuracy of the corners of the square or rectangular steel pipes.

Description

Technical Field

[0001] The present invention relates to the technical field of hot-rolled seamless steel pipes, and in particular to a hot-rolling forming method for thick-walled square steel pipes capable of improving corner forming quality. Background Art

[0002] Square steel tubes or rectangular steel tubes are widely used in construction fields such as steel structure, machinery manufacturing, and building frame construction. At present, the forming processes of square steel tubes or rectangular steel tubes include hot rolling forming process, cold drawing forming process, and welded square tube process. Among them, the cold drawing forming process has the defects of many steps, small deformation per pass, long production cycle and low forming efficiency. The welded square tube process uses hot-rolled strip steel as raw material, and is formed by multiple extrusion passes and welding. No heat treatment is performed during the entire process, and the stress generated during the extrusion forming process cannot be eliminated. For the welded square tube process, the cold-bent square and rectangular tubes produced by this forming method, except for the limited area of ​​the bending angle, the material properties of the remaining parts of the tube body are basically similar to those of the parent body. In particular, the closure of the weld seam is not ideal, the forming process is unstable, and it is difficult to obtain high-quality products.

[0003] Hot-rolled seamless square tubes are suitable for mass production and have high production efficiency. Hot-rolled square steel tubes can destroy the casting structure of steel ingots, refine the grains of steel, and eliminate defects in microstructure, thereby making the steel structure denser and greatly improving the mechanical properties. However, during the hot rolling process, square or rectangular steel tubes are prone to low forming accuracy, especially the problem of many corner forming defects. The defects include: asymmetry and fullness problems of corner forming, forming limit and internal corner cracking. If hot-rolled seamless steel tubes are used as billets, hot-rolled seamless square or rectangular steel tubes can be formed, which can greatly improve the forming efficiency of square and rectangular steel tubes. However, how to improve the overall forming accuracy of square or rectangular steel tubes during hot rolling, especially to improve the quality of corner forming, has become a difficult problem that needs to be solved on site. Summary of the Invention

[0004] The present invention provides a hot rolling forming method for thick-walled square steel pipes capable of improving the corner forming quality, which solves the technical problem of how to improve the corner forming quality when hot rolling square pipes are formed using hot-rolled seamless steel pipes as blanks.

[0005] The present invention solves the above technical problems through the following technical solutions:

[0006] The overall concept of the present invention is: using a hot-rolled seamless steel pipe as a blank for hot-rolled square steel pipe or rectangular steel pipe, preheating the hot-rolled seamless steel pipe blank to 800°C-1000°C, and then performing continuous and gradual roll bending under the joint rolling of an outer roll group and an inner roll group of a roll bending forming device; the roll bending forming device includes a blank feeding device, a roll bending frame, a mandrel device, a mandrel supporting device and a roll holding device; each device cooperates to roll the hot-rolled seamless steel pipe blank into a square steel pipe or a rectangular steel pipe.

[0007] A hot rolling forming method for thick-walled square steel pipes capable of improving the quality of corner forming comprises a seamless round pipe blank feeding mechanism, a blank conveying roller, a seamless round pipe blank, a roll bending machine frame, a mandrel supporting device, a mandrel holding roller device and a mandrel; a seamless round pipe blank feeding mechanism is provided at the left end of the blank conveying roller, and a mandrel holding roller device is provided at the right end of the blank conveying roller; a first roll bending machine frame, a second roll bending machine frame, a third roll bending machine frame and a fourth roll bending machine frame are provided at intervals from left to right on the blank conveying roller. The frame comprises a first roll bending frame having a biting outer roll group, a second roll bending frame having a first outer roll group, a third roll bending frame having a second outer roll group, and a fourth roll bending frame having a third outer roll group. The biting outer roll group, the first outer roll group, the second outer roll group and the third outer roll group are all arranged in a "mouth" shape, and the roll surfaces of the outer roll groups from left to right gradually transition from arc-shaped roll surfaces to flat roll surfaces. The frame is characterized by the following steps:

[0008] The first step is to determine the diameter of the seamless round tube billet according to the circumference of the pre-rolled thick-walled square steel tube; according to the diameter of the seamless round tube billet, select the mandrel;

[0009] The second step is to determine the installation positions of the four outer rollers of the bite outer roller group, the installation positions of the four outer rollers of the first group of outer rollers, the installation positions of the four outer rollers of the second group of outer rollers, and the installation positions of the four outer rollers of the third group of outer rollers according to the outer roller design drawing of the pre-rolled thick-walled square steel pipe;

[0010] Step 3: On the mandrel, respectively set the first set of guide rollers, the first set of inner angle forming rollers, the second set of inner angle forming rollers and the third set of inner angle forming rollers; and determine the installation position of each set of inner angle forming rollers according to the inner roller design drawing of the pre-rolled thick-walled square steel pipe;

[0011] Step 4: After the left end of the mandrel passes through the third group of outer rollers, the second group of outer rollers, the first group of outer rollers and the bite outer roller group from right to left, it is arranged on the left side of the first roll bending machine frame, so that the first group of inner angle forming rollers is arranged corresponding to the first group of outer rollers, and each inner angle forming roller in the first group of inner angle forming rollers is arranged on the bisector of the right angle formed by the two adjacent outer rollers; the second group of inner angle forming rollers is arranged corresponding to the second group of outer rollers, and the third group of inner angle forming rollers is arranged corresponding to the third group of outer rollers;

[0012] Step 5: Preheat the seamless round tube billet to 800-1000℃. Then, through the seamless round tube billet feeding mechanism and the billet conveying roller, the right end of the preheated seamless round tube billet is guided by the first set of guide rollers and then bitten by the biting outer roller group in the first roll bending stand.

[0013] Step 6: The seamless round tube billet bitten by the outer roller group is fed into the second roll bending stand. Under the joint rolling action of the first outer roller group and the first inner angle forming roller group, the seamless round tube billet is rolled and formed in the first pass.

[0014] Step 7: After the seamless round tube billet is rolled and formed in the first pass, it is continuously transported to the right and enters the third roll bending stand. Under the joint action of the second set of outer rolls and the second set of inner angle forming rolls, it is rolled and formed in the second pass.

[0015] Step 8: After being rolled and formed in the second pass, the seamless round tube billet continues to be transported to the right and enters the fourth roller bending machine frame. Under the joint action of the third group of outer rolling rollers and the third group of inner angle forming rollers, the third rolling and forming is carried out.

[0016] The central axis of the "mouth"-shaped rolling mouth formed by the four outer rollers in each group of outer roller groups coincides with the central axis of the mandrel; the central axis of the rhombus formed by the four guide rollers in each group of guide roller groups coincides with the central axis of the mandrel, and a spring is arranged between the guide roller and the mandrel to make the guide roller surface fit together with the inner surface of the seamless round tube blank; a second group of guide rollers is arranged in the middle of the mandrel, and a third group of guide rollers is arranged at the right end of the mandrel.

[0017] The core rod is cylindrical, and a guide roller is respectively provided at the 0°, 90°, 180° and 270° angle phases on the section perpendicular to the central axis of the core rod. These four guide rollers constitute the first group of guide rollers; an inner angle forming roller is respectively provided at the 45°, 135°, 225° and 315° square angle phases of the circular radial section of the cylindrical core rod. These four inner angle forming rollers constitute the first group of inner angle forming rollers.

[0018] On the billet conveying roller on the right side of the fourth roll bending stand, the fifth roll bending stand, the sixth roll bending stand and the seventh roll bending stand are arranged at intervals respectively; in the fifth roll bending stand, the fourth group of outer roll groups is arranged; in the sixth roll bending stand, the fifth group of outer roll groups is arranged; in the seventh roll bending stand, the sixth group of outer roll groups is arranged; on the mandrel passing through the fourth group of outer roll groups, the fourth group of inner angle forming roll groups is arranged; on the mandrel passing through the fifth group of outer roll groups, the fifth group of inner angle forming roll groups is arranged; on the mandrel passing through the sixth group of outer roll groups, the sixth group of inner angle forming roll groups is arranged.

[0019] A first mandrel support device is provided between the first roll bending stand and the second roll bending stand, and a second mandrel support device is provided between the third roll bending stand and the fourth roll bending stand. Before the seamless round tube billet is conveyed from left to right, the first mandrel support device, the second mandrel support device and the mandrel roller device are in a mandrel-holding working state. When the seamless round tube billet is conveyed from left to right, the first mandrel support device, the second mandrel support device and the mandrel roller device are in a mandrel-releasing working state in sequence. After the seamless round tube billet is conveyed from left to right, the first mandrel support device, the second mandrel support device and the mandrel roller device are in a mandrel-holding working state in sequence. The first mandrel support device, the second mandrel support device and the mandrel roller device cooperate with each other to ensure the passability of the seamless round tube billet while ensuring that the mandrel does not move.

[0020] The present invention uses hot-rolled seamless round tubes as blanks to roll-form hot-rolled seamless square or rectangular steel tubes, which can greatly improve the forming efficiency of square steel tubes; the blanks are kept at a relatively high temperature and can be subjected to a small amount of supplementary heating to reach the temperature required for rolling, thereby reducing the energy consumption required for heating the blanks; the mandrel device of the present invention realizes continuous gradual roll bending of seamless round tubes under the joint action of the outer roller group and the inner roller group, thereby improving the forming accuracy of the corners of square or rectangular steel tubes; the inner rollers arranged on the mandrel device of the present invention can adjust their radial heights through pads, thereby realizing multiple uses of one core, and realizing the forming of square tubes or torch-shaped tubes of different sizes. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a structural schematic diagram of the present invention;

[0022] Figure 2 It is a schematic structural diagram of the mandrel 4 of the present invention;

[0023] Figure 3 This is a diagram showing the relationship between the mandrel 4 and the outer roller assembly of the present invention;

[0024] Figure 4This is a diagram showing the coordination relationship between the inner angle forming roller group and the outer roller group of the present invention. DETAILED DESCRIPTION

[0025] The present invention is described in detail below with reference to the accompanying drawings:

[0026] A hot rolling forming method for thick-walled square steel pipes capable of improving corner forming quality, comprising a seamless round tube billet feeding mechanism 1, a billet conveying roller 2, a seamless round tube billet 3, a roll bending machine frame, a mandrel supporting device, a mandrel holding roller device 5 and a mandrel 4; at the left end of the billet conveying roller 2, a seamless round tube billet feeding mechanism 1 is provided, and at the right end of the billet conveying roller 2, a mandrel holding roller device 5 is provided; between the seamless round tube billet feeding mechanism 1 and the mandrel holding roller device 5, from left to right, a first roll bending machine frame 6, a second roll bending machine frame 7, a third roll bending machine frame 8 and a fourth roll bending machine frame 9 are provided at intervals. The roll bending frame 9 is provided with a biting outer roll group 21 in the first roll bending frame 6, a first outer roll group 22 in the second roll bending frame 7, a second outer roll group 23 in the third roll bending frame 8, and a third outer roll group 24 in the fourth roll bending frame 9. The biting outer roll group 21, the first outer roll group 22, the second outer roll group 23 and the third outer roll group 24 are all arranged in a "mouth" shape, and the roll surfaces of the outer roll groups from left to right gradually transition from arc-shaped roll surfaces to flat roll surfaces; it is characterized by the following steps:

[0027] The first step is to determine the diameter of the seamless round tube blank 3 according to the circumference of the pre-rolled thick-walled square steel tube; and select the mandrel 4 according to the diameter of the seamless round tube blank 3;

[0028] The second step is to determine the installation positions of the four outer rollers of the bite outer roller group 21, the installation positions of the four outer rollers of the first outer roller group 22, the installation positions of the four outer rollers of the second outer roller group 23, and the installation positions of the four outer rollers of the third outer roller group 24 according to the outer roller design drawing of the pre-rolled thick-walled square steel pipe;

[0029] Step 3: On the mandrel 4, a first set of guide rollers 12, a first set of inner angle forming rollers 15, a second set of inner angle forming rollers 16, and a third set of inner angle forming rollers 17 are respectively arranged; and the installation position of each set of inner angle forming rollers is determined according to the inner roller design drawing of the pre-rolled thick-walled square steel pipe;

[0030] Step 4: The left end of the mandrel 4 is passed through the third group of outer rollers 24, the second group of outer rollers 23, the first group of outer rollers 22 and the bite outer roller group 21 from right to left in sequence, and then arranged on the left side of the first roll bending stand 6, so that the first group of inner angle forming rollers 15 is arranged corresponding to the first group of outer rollers 22, and each inner angle forming roller in the first group of inner angle forming rollers 15 is arranged on the bisector of the right angle formed by the two adjacent outer rollers; the second group of inner angle forming rollers 16 is arranged corresponding to the second group of outer rollers 23, and the third group of inner angle forming rollers 17 is arranged corresponding to the third group of outer rollers 24;

[0031] Step 5: Preheat the seamless round tube billet 3 to 800-1000°C. Then, the right end of the preheated seamless round tube billet 3 is guided by the first set of guide rollers 12 and then bitten by the biting outer roller group 21 in the first roll bending stand 6 through the seamless round tube billet feeding mechanism 1 and the billet conveying roller 2.

[0032] Step 6: The seamless round tube billet 3 bitten by the outer roller group 21 is conveyed to the right into the second roll bending stand 7. Under the joint rolling action of the first group of outer rollers 22 and the first group of inner angle forming rollers 15, the seamless round tube billet 3 is rolled and formed in the first pass.

[0033] Step 7: After being rolled and formed in the first pass, the seamless round tube billet 3 is continuously conveyed to the right and enters the third roll bending stand 8. Under the joint action of the second set of outer rolls 23 and the second set of inner angle forming rolls 16, the seamless round tube billet 3 is rolled and formed in the second pass.

[0034] Step 8: After being rolled and formed in the second pass, the seamless round tube billet 3 continues to be transported to the right and enters the fourth roller bending machine frame 9. Under the joint action of the third group of outer rollers 24 and the third group of inner angle forming rollers 17, it is rolled and formed in the third pass.

[0035] A first mandrel support device 10 is installed between the first and second roll bending stands 6 and 7, and a second mandrel support device 11 is installed between the third and fourth roll bending stands 8 and 9. Before the seamless round tube 3 is conveyed from left to right, the first and second mandrel support devices 10, 11, and mandrel roller device 5 are in a state of tightening the mandrel 4. As the seamless round tube 3 is conveyed from left to right, the first and second mandrel support devices 10, 11, and mandrel roller device 5 are in a state of loosening the mandrel 4. After the seamless round tube 3 has been conveyed from left to right, the first and second mandrel support devices 10, 11, and mandrel roller device 5 are in a state of tightening the mandrel 4. The first and second mandrel support devices 10, 11, and mandrel roller device 5 work together to ensure the seamless round tube 3 can pass through while preventing the mandrel 4 from moving.

[0036] A hot rolling forming tool for thick-walled square steel pipes that can improve the quality of corner forming, comprising a seamless round tube blank feeding mechanism 1, a blank conveying roller 2, a seamless round tube blank 3, a roll bending machine frame, a mandrel supporting device, a mandrel holding roller device 5 and a mandrel 4; at the left end of the blank conveying roller 2, a seamless round tube blank feeding mechanism 1 is provided, at the right end of the blank conveying roller 2, a mandrel holding roller device 5 is provided, between the seamless round tube blank feeding mechanism 1 and the mandrel holding roller device 5, from left to right, a first roll bending machine frame 6, a second roll bending machine frame 7, a third roll bending machine frame 8 and a fourth roll bending machine frame 9 are provided at intervals. The bending frame 9 is provided with a biting outer roller group 21 in the first roller bending frame 6, a first group of outer roller group 22 in the second roller bending frame 7, a second group of outer roller group 23 in the third roller bending frame 8, and a third group of outer roller group 24 in the fourth roller bending frame 9. The biting outer roller group 21, the first group of outer roller group 22, the second group of outer roller group 23 and the third group of outer roller group 24 are all arranged in the shape of a "mouth", and the roller surface of the outer roller group from left to right gradually transitions from a circular arc roller surface to a flat roller surface; the left end of the mandrel 4, from right to left, After passing through the third group of outer rollers 24, the second group of outer rollers 23, the first group of outer rollers 22 and the bite outer roller group 21 in sequence, it is arranged on the left side of the first roll bending machine frame 6, and the right end of the mandrel 4 is arranged in the mandrel holding roller device 5; on the billet conveying roller 2, a seamless round tube billet 3 is movably arranged, and the right end of the seamless round tube billet 3 is fed in and sleeved on the left end of the mandrel 4, and the seamless round tube billet 3 is fed to the right by the seamless round tube billet feeding mechanism 1; on the mandrel 4, a first group of inner angle forming rollers 15 and a second group of inner angle forming rollers 16 are arranged at intervals from left to right. and the third group of inner angle forming roller groups 17. In each inner angle forming roller group, four inner angle forming rollers are arranged at equal intervals on the section perpendicular to the central axis of the core rod 4; the first group of inner angle forming roller groups 15 and the first group of outer roller groups 22 are arranged correspondingly, and each inner angle forming roller in the first group of inner angle forming roller groups 15 is arranged on the bisector of the right angle formed by the two outer rollers in the first group of outer roller groups 22 adjacent to it; a seamless round tube blank 3 is rolled between the first group of inner angle forming roller groups 15 and the first group of outer roller groups 22.

[0037] A first set of guide rollers 12 is provided at the left end of the mandrel 4. The first set of guide rollers 12 is composed of four guide rollers. These four guide rollers are arranged at equal intervals of arc on a section perpendicular to the central axis of the mandrel 4. The left end of the seamless round tube blank 3 is guided by the first set of guide rollers 12 and enters the biting outer rolling roller group 21 on the first roll bending frame 6; a second set of guide rollers 13 is provided in the middle of the mandrel 4, and a third set of guide rollers 14 is provided at the right end of the mandrel 4; a first mandrel support device 10 is provided between the first roll bending frame 6 and the second roll bending frame 7, and a second mandrel support device 11 is provided between the third roll bending frame 8 and the fourth roll bending frame 9.

[0038] The central axis of the "mouth"-shaped rolling mouth formed by the four outer rollers in each group of outer roller groups coincides with the central axis of the mandrel 4; the central axis of the rhombus formed by the four guide rollers in each group of guide roller groups coincides with the central axis of the mandrel 4, and a spring is provided between the guide roller and the mandrel 4 to enable the guide roller to be movably connected to the inner side surface of the seamless round tube blank 3.

[0039] The core rod 4 is cylindrical, and a guide roller is respectively provided at the 0°, 90°, 180° and 270° angle phases on the cross section perpendicular to the central axis of the core rod 4. These four guide rollers constitute the first group of guide rollers 12; an inner angle forming roller is respectively provided at the 45°, 135°, 225° and 315° square angle phases of the circular radial cross section of the cylindrical core rod. These four inner angle forming rollers constitute the first group of inner angle forming rollers 15.

[0040] On the billet conveying roller 2 on the right side of the fourth roll bending stand 9, the fifth roll bending stand, the sixth roll bending stand and the seventh roll bending stand are respectively arranged at intervals. In the fifth roll bending stand, the fourth group of outer roll groups 25 are arranged, in the sixth roll bending stand, the fifth group of outer roll groups 26 are arranged, and in the seventh roll bending stand, the sixth group of outer roll groups 27 are arranged; on the core rod 4 passing through the fourth group of outer roll groups 25, the fourth group of inner angle forming roll groups 18 are arranged, on the core rod 4 passing through the fifth group of outer roll groups 26, the fifth group of inner angle forming roll groups 19 are arranged, and on the core rod 4 passing through the sixth group of outer roll groups 27, the sixth group of inner angle forming roll groups 20 are arranged; arranging six or more groups of roll groups can further improve the quality of square tube rolling forming.

Claims

1. A hot rolling forming method for thick-walled square steel pipes capable of improving the quality of corner forming, comprising a seamless round tube blank feeding mechanism (1), a blank conveying roller (2), a seamless round tube blank (3), a roll bending machine frame, a mandrel supporting device, a mandrel holding roller device (5) and a mandrel (4); a seamless round tube blank feeding mechanism (1) is provided at the left end of the blank conveying roller (2), and a mandrel holding roller device (5) is provided at the right end of the blank conveying roller (2); a first roll bending machine frame (6), a second roll bending machine frame (7), a third roll bending machine frame (8) and a fourth roll bending machine frame (9) are provided on the blank conveying roller (2) from left to right. The roll bending frame (9) is provided with a bite outer roll group (21) in the first roll bending frame (6), a first outer roll group (22) in the second roll bending frame (7), a second outer roll group (23) in the third roll bending frame (8), and a third outer roll group (24) in the fourth roll bending frame (9), wherein the bite outer roll group (21), the first outer roll group (22), the second outer roll group (23) and the third outer roll group (24) are all arranged in a "mouth" shape, and the roll surfaces of the outer roll groups from left to right gradually transition from arc-shaped roll surfaces to flat roll surfaces; It is characterized by the following steps: The first step is to determine the diameter of the seamless round tube blank (3) according to the circumference of the pre-rolled thick-walled square steel tube; and select the mandrel (4) according to the diameter of the seamless round tube blank (3); Step 2: According to the outer roller design drawing of the pre-rolled thick-walled square steel pipe, the installation positions of the four outer rollers of the bite outer roller group (21), the installation positions of the four outer rollers of the first outer roller group (22), the installation positions of the four outer rollers of the second outer roller group (23), and the installation positions of the four outer rollers of the third outer roller group (24) are determined respectively; Step 3: On the mandrel (4), a first group of guide rollers (12), a first group of inner angle forming rollers (15), a second group of inner angle forming rollers (16), and a third group of inner angle forming rollers (17) are respectively arranged; and the installation positions of the inner angle forming rollers of each group are respectively determined according to the inner roller design drawing of the pre-rolled thick-walled square steel tube; Step 4: After the left end of the mandrel (4) passes through the third group of outer rollers (24), the second group of outer rollers (23), the first group of outer rollers (22) and the bite outer rollers (21) from right to left, it is set on the left side of the first roll bending machine frame (6), so that the first group of inner angle forming rollers (15) and the first group of outer rollers (22) are set correspondingly, and each inner angle forming roller in the first group of inner angle forming rollers (15) is set on the bisector of the right angle formed by the two adjacent outer rollers; the second group of inner angle forming rollers (16) and the second group of outer rollers (23) are set correspondingly, and the third group of inner angle forming rollers (17) and the third group of outer rollers (24) are set correspondingly; Step 5: preheat the seamless round tube billet (3) to 800°C-1000°C, and then, through the seamless round tube billet feeding mechanism (1) and the billet conveying roller (2), the right end of the preheated seamless round tube billet (3) is guided by the first set of guide rollers (12) and then bitten by the biting outer roller group (21) in the first roller bending frame (6); Step 6: The seamless round tube billet (3) bitten by the outer roller group (21) is fed into the second roller bending stand (7), and the seamless round tube billet (3) is rolled and formed in the first pass under the joint rolling action of the first outer roller group (22) and the first inner angle forming roller group (15); Step 7: After the seamless round tube billet (3) is formed by the first rolling process, it is continuously conveyed to the right and enters the third roller bending machine (8), and is rolled and formed by the second outer roller group (23) and the second inner angle forming roller group (16). In the eighth step, the seamless round tube billet (3) formed by the second rolling process is continuously conveyed to the right and enters the fourth roller bending machine frame (9), and is subjected to the third rolling process under the joint action of the third group of outer rollers (24) and the third group of inner angle forming rollers (17).

2. A hot rolling forming method for thick-walled square steel pipes capable of improving corner forming quality according to claim 1, characterized in that: The central axis of the "mouth"-shaped rolling mouth formed by the four outer rollers in each group of outer roller groups coincides with the central axis of the mandrel (4); the central axis of the rhombus formed by the four guide rollers in each group of guide roller groups coincides with the central axis of the mandrel (4), and a spring is provided between the guide roller and the mandrel (4) so ​​that the guide roller and the inner side surface of the seamless round tube blank (3) are movably connected together; a second group of guide rollers (13) is provided in the middle of the mandrel (4), and a third group of guide rollers (14) is provided at the right end of the mandrel (4).

3. A hot rolling forming method for thick-walled square steel pipes capable of improving corner forming quality according to claim 1 or 2, characterized in that: The core rod (4) is cylindrical, and a guide roller is respectively provided at the 0°, 90°, 180° and 270° angle phases on the cross section perpendicular to the central axis of the core rod (4), and these four guide rollers constitute a first group of guide rollers (12); and an inner angle forming roller is respectively provided at the 45°, 135°, 225° and 315° angle phases of the circular radial cross section of the cylindrical core rod, and these four inner angle forming rollers constitute a first group of inner angle forming rollers (15).

4. The hot rolling forming method of thick-walled square steel pipe capable of improving corner forming quality according to claim 3, characterized in that: On the billet conveying roller (2) on the right side of the fourth roll bending frame (9), a fifth roll bending frame, a sixth roll bending frame and a seventh roll bending frame are respectively arranged at intervals. The fifth roll bending frame is provided with a fourth group of outer roll groups (25), the sixth roll bending frame is provided with a fifth group of outer roll groups (26), and the seventh roll bending frame is provided with a sixth group of outer roll groups (27). On the mandrel (4) passing through the fourth group of outer roll groups (25), a fourth group of inner angle forming roll groups (18) is provided, on the mandrel (4) passing through the fifth group of outer roll groups (26), a fifth group of inner angle forming roll groups (19) is provided, and on the mandrel (4) passing through the sixth group of outer roll groups (27), a sixth group of inner angle forming roll groups (20) is provided.

5. The hot rolling forming method of thick-walled square steel pipe capable of improving corner forming quality according to claim 4, characterized in that: A first mandrel support device (10) is provided between the first roll bending frame (6) and the second roll bending frame (7), and a second mandrel support device (11) is provided between the third roll bending frame (8) and the fourth roll bending frame (9); before the seamless round tube blank (3) is conveyed from left to right, the first mandrel support device (10), the second mandrel support device (11) and the mandrel roller holding device (5) are in a working state of holding the mandrel (4); when the seamless round tube blank (3) is conveyed from left to right, the first mandrel support device (10) The first mandrel support device (10), the second mandrel support device (11) and the mandrel holding roller device (5) are in a state of loosening the mandrel (4) in sequence; after the seamless round tube blank (3) is conveyed from left to right, the first mandrel support device (10), the second mandrel support device (11) and the mandrel holding roller device (5) are in a state of tightening the mandrel (4) in sequence; the first mandrel support device (10), the second mandrel support device (11) and the mandrel holding roller device (5) cooperate with each other to ensure the passability of the seamless round tube blank (3) and at the same time ensure that the mandrel (4) does not move.

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