Steel pipe preparation device and steel pipe preparation method

Abstract

The invention provides a steel pipe preparation device and a steel pipe preparation method. The steel pipe preparation device comprises a first fixed diameter reducing device and a second fixed diameter reducing device, the first fixed diameter reducing device comprises a plurality of first racks and a plurality of second racks, the first racks and the second racks are sequentially arranged in the conveying direction of pierced billets, the diameter reducing rates of the first racks are gradually increased in the conveying direction of the pierced billets, and the diameter reducing rates of the second racks are equal; the second sizing and reducing device comprises a plurality of third racks and a plurality of fourth racks, the third racks and the fourth racks are sequentially arranged in the conveying direction of the pierced billet, the reducing rates of the third racks are equal, the reducing rates of the fourth racks are gradually reduced in the conveying direction of the pierced billet, and the reducing rates of the second racks are equal to the reducing rates of the third racks. According to the technical scheme, the problem that a steel pipe prepared by an existing preparation device is low in size precision can be solved.

Description

Technical Field

[0001] This invention relates to the field of seamless steel pipe technology, and more specifically, to a steel pipe preparation apparatus and a steel pipe preparation method. Background Technology

[0002] The main production processes for hot-rolled seamless steel pipes include piercing, rolling, and sizing (reduction). The sizing (reduction) process, as the final link in the hot-rolling production chain, reduces the outer diameter of the rough pipe (i.e., the rolled steel pipe) to the required specifications by passing it through a series of stands, ensuring the finished steel pipe has high-precision dimensions and good ovality. During the sizing (reduction) process, the steel pipe passes through the stands without a mandrel and is subjected to radial compression, thereby achieving precise control of the outer diameter. In the sizing (reduction) process, equipment configuration and parameter settings have a direct impact on the quality of the finished product. The number of working stands on the sizing mill is relatively small, generally between 3 and 14.

[0003] However, when producing small-diameter thick-walled steel pipes using existing manufacturing equipment, it is often necessary to reduce the diameter of the large-diameter rough pipe to the finished size in one step, which means that the reduction rate per stand must be increased. Although this approach can achieve the production of small-diameter thick-walled steel pipes, it will bring about a serious internal hexagonal defect, that is, the inner hole of the steel pipe cross-section is hexagonal rather than circular, resulting in lower dimensional accuracy of the steel pipe. Summary of the Invention

[0004] The main objective of this invention is to provide a steel pipe preparation apparatus and a steel pipe preparation method, which can solve the problem of low dimensional accuracy of steel pipes prepared by existing preparation apparatuses.

[0005] To achieve the above objectives, one aspect of the present invention provides a steel pipe manufacturing apparatus, comprising: a first diameter reduction device, including a plurality of first frames and a plurality of second frames, the plurality of first frames and the plurality of second frames being configured to be arranged sequentially along the conveying direction of the raw pipe, the diameter reduction rate of the plurality of first frames gradually increasing along the conveying direction of the raw pipe, the diameter reduction rate of the plurality of second frames being equal, and the diameter reduction rate of the plurality of second frames being greater than or equal to the diameter reduction rate of the adjacent first frame; and a second diameter reduction device, including a plurality of third frames and a plurality of fourth frames, the plurality of third frames and the plurality of fourth frames being arranged sequentially along the conveying direction of the raw pipe, the diameter reduction rate of the plurality of third frames being equal, the diameter reduction rate of the plurality of fourth frames gradually decreasing along the conveying direction of the raw pipe, and the diameter reduction rate of the plurality of third frames being greater than or equal to the diameter reduction rate of the adjacent fourth frame, and the diameter reduction rate of each second frame being equal to that of each third frame.

[0006] Furthermore, the number of the first and fourth racks ranges from 1 to 5, and the number of the second and third racks ranges from 6 to 13.

[0007] Furthermore, the diameter reduction rate of the first and fourth frames is in the range of 0 to 2%, and the diameter reduction rate of the second and third frames is in the range of 2% to 3%.

[0008] Furthermore, the first frame, second frame, third frame, and fourth frame all include a roll assembly, which includes three rolls arranged sequentially along the circumference of the rough tube. Each roll is rotatable relative to its own central axis. Each roll includes: a first roll segment with a first rolling surface; and two second roll segments symmetrically arranged at opposite ends of the first roll segment along a first direction and connected to the first roll segment. Each second roll segment has a second rolling surface. In a longitudinal section passing through the central axis of the roll, the first rolling surface includes two first arc-shaped segments spaced apart and axially symmetrically arranged along a second direction. Each second rolling surface includes two second arc-shaped segments spaced apart and axially symmetrically arranged along the second direction. Along the second direction, the first arc-shaped segments and second arc-shaped segments on the same side of the roll are connected. The ellipticity of the first arc-shaped segment is smaller than that of the second arc-shaped segment. The first direction is perpendicular to the second direction.

[0009] In another aspect, the present invention provides a method for manufacturing steel pipes, utilizing the steel pipe manufacturing apparatus as described above. The method includes: manufacturing a rough pipe; passing the rough pipe through a first diameter reduction device to perform a first diameter reduction operation and obtain a first processed part; and passing the first processed part through a second diameter reduction device to perform a second diameter reduction operation.

[0010] Furthermore, the steps after preparing the rough tube and before passing it through the first diameter reduction device include: heating the rough tube to a first preset temperature T1, wherein the value of the first preset temperature T1 is in the range of Ac3+50℃≤T1≤Ac3. + The steps for performing the first diameter reduction operation on the raw pipe at 60℃ through the first diameter reduction device include: waiting for the raw pipe to cool to a second preset temperature T2, then performing the first diameter reduction operation on the raw pipe. The second preset temperature T2 is less than the first preset temperature T1, and the range of the second preset temperature T2 is Ac3+20℃≤T2≤Ac3. + 30℃, where Ac3 refers to the temperature at which steel completely transforms from the ferrite phase to the austenite phase.

[0011] Further, the steps for preparing the rough tube include: preparing a billet; preheating the billet for the first time at a temperature of 150℃~400℃ for 15min~20min; preheating the billet for the second time at a temperature of 400℃~650℃ for 20min~25min; heating the billet for the first time at a temperature of 650℃~850℃ for 25min~30min; heating the billet for the second time at a temperature of 850℃~1120℃ for 25min~30min; heating the billet for the third time at a temperature of 1120℃~1300℃ for 25min~30min; heating the billet for the fourth time at a temperature of 1210℃~1300℃ for 20min~25min; and stopping the heating of the billet when its temperature reaches 1200℃~1290℃ to obtain the workpiece to be processed.

[0012] Furthermore, the steps for preparing the rough tube also include: piercing the workpiece to obtain a rough tube; and rolling the rough tube to obtain the raw tube.

[0013] Furthermore, when piercing the workpiece, the temperature of the workpiece is 1170℃~1270℃; when rolling the tube, the temperature of the tube is 960℃~1160℃; and / or, after the step of rolling the tube, the blank tube is cooled to a temperature of 450℃~600℃.

[0014] Furthermore, in the step of piercing the workpiece, a conical piercing machine is used for the piercing operation.

[0015] When preparing steel pipes using the steel pipe preparation apparatus and method of this application, the diameter of the rough pipe is gradually reduced and the initial shape is corrected by multiple first stands. Subsequently, the shape and size are further adjusted by multiple second and third stands based on increasing the reduction rate, so as to achieve preliminary precise control of the steel pipe. The reduction rates of the second and third stands are equal, which can stabilize the reduction rate and ensure that the rough pipe can be reduced in size uniformly. The fourth stand is used to fine-tune the shape and size of the rough pipe in the final stage to prevent excessive reduction from causing dimensional errors or defects. This achieves a smooth transition in the reduction process of the rough pipe and reduces the non-uniformity of metal flow that may be caused by a single large reduction, thereby significantly improving the dimensional accuracy of the rough pipe and finally realizing the production of hot-rolled small-diameter thick-walled seamless steel pipes with uniform wall thickness and no internal hexagonal defects.

[0016] The steel pipe manufacturing apparatus and method of this application have the following advantages: They solve the problem that when using a three-roll sizing mill, the limited number of working stands makes it impossible to produce smaller diameter finished pipes from large-diameter rough pipes; they solve the problem of internal hexagonal defects appearing in thick-walled steel pipes during large diameter reduction, ultimately achieving the goal of producing smaller diameter finished pipes from large-diameter rough pipes, avoiding the increased costs associated with secondary sizing (reduction) processes; they significantly reduce the reduction rate per stand of the sizing mill, reduce the ellipticity of the sizing mill in the main deformation zone, greatly reduce the degree of internal hexagonal defects in small-diameter thick-walled steel pipes, improve the dimensional accuracy of the steel pipes, significantly reduce production costs, and improve production efficiency; they can be used on conventional hot-rolling production lines to produce small-diameter thick-walled seamless steel pipes without adding any existing processes or complex equipment, requiring only modifications to existing equipment. With minor modifications, the production of hot-rolled small-diameter thick-walled seamless steel pipes with uniform wall thickness and no severe internal hexagonal defects can be achieved online in batches, greatly reducing production costs and improving production efficiency. Large-diameter rough pipes can be sized into a wider range of small-diameter thick-walled hot-rolled seamless steel pipes, overcoming the limitations of piercing and rolling mill production on pipe specifications. During regular production, the first sizing / reducing device is used for daily sizing, while the second sizing / reducing device is used as a transport frame. When it is necessary to reduce the diameter of large-diameter rough pipes into small-diameter finished pipes, the first and second sizing / reducing devices are used together to reduce the reduction rate per stand, thereby obtaining finished pipes with high dimensional accuracy and no internal hexagonal defects. The first and second sizing / reducing devices of this application can easily switch between two production modes, greatly reducing production equipment investment and production costs. Attached Figure Description

[0017] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0018] Figure 1 A partial structural schematic diagram of a steel pipe manufacturing apparatus according to an embodiment of the present invention is shown;

[0019] Figure 2 A schematic diagram of the structure of the rolls according to an embodiment of the present invention is shown;

[0020] Figure 3 A flowchart illustrating a steel pipe manufacturing method according to an embodiment of the present invention is shown.

[0021] The above figures include the following reference numerals:

[0022] 10. First roll section; 11. First arc section; 20. Second roll section; 21. Second arc section; 40. First diameter reduction device; 41. First frame; 50. Roll; 60. Second diameter reduction device; 61. Third frame. Detailed Implementation

[0023] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0024] Currently, the actual production process usually uses a three-roll sizing (reducing) mill. However, in the actual hot rolling process, when the reduction ratio is large, the wall thickness is thick, or the tension reduction ratio is greater than 60%, even if the wall thickness is small, despite the adoption of various measures such as optimized die design, deformation redistribution, speed distribution and tension control, there is still uneven circumferential deformation of the steel pipe in the sizing (reducing) mill stand, which causes different degrees of "inner hexagonal" defects on the cross-section of the steel pipe.

[0025] To solve the above problems, see [reference] Figure 1 and Figure 2 As shown, the present invention provides a steel pipe manufacturing apparatus, which includes: a first diameter reduction device 40, comprising a plurality of first frames 41 and a plurality of second frames, the plurality of first frames 41 and the plurality of second frames being arranged sequentially along the conveying direction of the raw pipe, the diameter reduction rate of the plurality of first frames 41 gradually increasing along the conveying direction of the raw pipe, the diameter reduction rate of the plurality of second frames being equal, and the diameter reduction rate of the plurality of second frames being greater than or equal to the diameter reduction rate of the adjacent first frame 41; and a second diameter reduction device 60, comprising a plurality of third frames 61 and a plurality of fourth frames, the plurality of third frames 61 and the plurality of fourth frames being arranged sequentially along the conveying direction of the raw pipe, the diameter reduction rate of the plurality of third frames 61 being equal, the diameter reduction rate of the plurality of fourth frames gradually decreasing along the conveying direction of the raw pipe, and the diameter reduction rate of the plurality of third frames 61 being greater than or equal to the diameter reduction rate of the adjacent fourth frame, and the diameter reduction rate of each second frame being equal to that of each third frame 61.

[0026] In this embodiment, the first frame 41, the second frame, the third frame 61 and the fourth frame can all perform diameter reduction operations on the rough pipe. When preparing the steel pipe, the rough pipe first passes through multiple first frames 41, multiple second frames, multiple third frames 61 in sequence, and finally passes through multiple fourth frames.

[0027] The reduction ratio of the multiple first frames 41 gradually increases along the conveying direction of the raw tube. The reduction ratio of the first frame 41 adjacent to the second frame is the largest among the multiple first frames 41. The reduction ratio of the first frame 41 at the front end is smaller, mainly serving as the initial bite of the raw tube for fixed reduction operation. When the raw tube reaches the location of the multiple second frames, the reduction ratio of the second frames is generally greater than that of most of the first frames 41, in order to reduce the diameter of the raw tube. The reduction ratios of the multiple second frames are equal, ensuring that after the raw tube undergoes initial deformation, it can be further corrected in size and shape under stable deformation conditions, avoiding dimensional fluctuations caused by frequent and large adjustments to the reduction ratio. When the raw tube reaches the location of the multiple third frames 61, the reduction ratio of the multiple third frames 61 remains unchanged and is equal to that of the multiple second frames, further providing a stable and continuous dimensional reduction environment for the raw tube. This is beneficial for maintaining the dimensional consistency of the raw tube at this stage and reducing errors caused by unstable reduction. When the raw pipe reaches the location of multiple fourth frames, the fourth frame adjacent to the third frame 61 has the largest reduction rate. Along the conveying direction of the raw pipe, the reduction rate of the other fourth frames gradually decreases to slow down the reduction of the raw pipe and to finely adjust the shape and size of the raw pipe (mainly the function of rounding), so as to avoid the drastic reduction in the final stage affecting the dimensional accuracy of the final steel pipe.

[0028] As described above, using the steel pipe preparation apparatus of this application, the diameter of the rough pipe is gradually reduced and the initial shape is corrected by multiple first stands 41. Subsequently, the shape and size are further adjusted by multiple second and third stands 61 on the basis of increasing the reduction rate, so as to achieve preliminary precise control of the steel pipe. The reduction rates of the second and third stands 61 are equal, which can stabilize the reduction rate and ensure that the rough pipe can achieve uniform size reduction. The fourth stand is used to fine-tune the shape and size of the rough pipe in the final stage (mainly the function of rounding), to prevent excessive reduction from causing dimensional errors or defects. The steel pipe preparation apparatus of this application realizes a smooth transition in the rough pipe reduction process, reduces the non-uniformity of metal flow that may be caused by a single large reduction, thereby significantly improving the dimensional accuracy of the rough pipe, and finally realizing the production of hot-rolled small-diameter thick-walled seamless steel pipes with uniform wall thickness and no internal hexagonal defects.

[0029] It should be noted that "multiple" refers to two or more. In conventional production, the first sizing and reducing device is used for daily sizing production, and the second sizing and reducing device is used as a transport frame. When it is necessary to reduce the diameter of large-diameter rough pipes into small-diameter finished pipes, the first and second sizing and reducing devices are used together to reduce the reduction rate per frame, thereby obtaining finished pipes with high dimensional accuracy and no internal hexagonal edges. The first and second sizing and reducing devices of this application can easily switch between the two production modes, greatly reducing the investment in production equipment and production costs.

[0030] In one embodiment of the present invention, the number of the first rack 41 and the fourth rack are both in the range of 1 to 5, and the number of the second rack and the third rack 61 are both in the range of 6 to 13.

[0031] In this embodiment, the number of first frames 41 is relatively small, mainly for biting into the raw tube. The number of fourth frames is also relatively small, used to fine-tune the shape and size of the raw tube at the end of the production line, so as to accurately control the shape and size of the raw tube in the finished product stage, avoid excessive deformation, and reduce wall thickness deviation and shape defects. The number of second and third frames 61 is relatively large, used for stabilizing and correcting the size and shape, and reducing the wall thickness fluctuation of the raw tube.

[0032] It should be noted that the above value ranges all include endpoint values.

[0033] In one embodiment of the present invention, the diameter reduction rate of the first frame 41 and the fourth frame is in the range of 0 to 2%, and the diameter reduction rate of the second frame and the third frame 61 is in the range of 2% to 3%.

[0034] In this embodiment, the reduction rates of the first and fourth frames are set at a relatively low range of 0-2%. This prevents excessive friction caused by an excessively high reduction rate in the initial processing stage, which would hinder pipe insertion, lead to uneven wall thickness, and cause internal stress concentration. Similarly, in the final processing stage, a gradually decreasing reduction rate allows for precise control of the shape and size of the raw pipe. The reduction rates of the second and third frames are both in the range of 2%-3%, enabling effective size reduction and shape correction of the raw pipe in the middle of the processing.

[0035] It should be noted that the above value ranges all include endpoint values.

[0036] See also Figure 1 and Figure 2As shown, in one embodiment of the present invention, the first frame 41, the second frame, the third frame 61, and the fourth frame all include a roll assembly. The roll assembly includes three rolls arranged sequentially along the circumference of the rough tube. Each roll is rotatable relative to its own central axis. Each roll includes: a first roll segment 10 having a first rolling surface; and two second roll segments 20 symmetrically arranged at opposite ends of the first roll segment 10 along a first direction, and both second roll segments 20 being connected to the first roll segment 10. Each second roll segment 20 has a second roll pressing surface. On the longitudinal section passing through the central axis of the roll, the first roll pressing surface includes two first arc-shaped segments 11 arranged at intervals along the second direction and symmetrically arranged. Each second roll pressing surface includes two second arc-shaped segments 21 arranged at intervals along the second direction and symmetrically arranged. Along the second direction, the first arc-shaped segments 11 and the second arc-shaped segments 21 located on the same side of the roll are connected. The ellipticity of the first arc-shaped segment 11 is smaller than that of the second arc-shaped segment 21. The first direction is perpendicular to the second direction.

[0037] In this embodiment, the first direction refers to Figure 2 The horizontal direction in the middle, the second direction refers to Figure 2 The vertical direction is specified. The rolls in this application are rotating bodies. Both the first and second roll surfaces can contact the outer wall surface of the rough tube and apply force to the rough tube in the radial direction. The three rolls of the roll assembly are arranged circumferentially along the rough tube, and the first arc segment 11 and the second arc segment 21 of the three rolls of the roll assembly together form a rolling hole. The rolling hole is neither a standard circle nor a standard ellipse, but approximately circular, and the rough tube is located inside the rolling hole.

[0038] The first rolling surface includes a first arc-shaped segment 11, and the second rolling surface includes a second arc-shaped segment 21. The ellipticity of the first arc-shaped segment 11 is smaller than that of the second arc-shaped segment 21. The second arc-shaped segment 21 is gentler than the first arc-shaped segment 11, which can reduce the ellipticity of the rolling hole and thus reduce the degree of "inner hexagonal" defects in the finished steel pipe. At the same time, the second arc-shaped segment 21 is connected to the first arc-shaped segment 11, providing a gentler transition zone for metal flow, which increases the width coefficient of the rolling hole and expands the lateral flow space of the metal. The increased size prevents the lateral flow of metal from the pipe wall into the roll gap during the rolling process, thus effectively preventing the metal from spreading to the roll gap during the sizing process. This prevents the formation of blue lines and ensures the dimensional accuracy of the steel pipe. It solves the problems of severe internal hexagonal defects and low dimensional accuracy in the current production of large-diameter, small-diameter, thick-walled hot-rolled seamless steel pipes. It can be used in conventional hot-rolling production lines to produce small-diameter, thick-walled seamless steel pipes, ultimately achieving the production of hot-rolled small-diameter, thick-walled seamless steel pipes with uniform wall thickness and no severe internal hexagonal defects.

[0039] On the longitudinal section passing through the central axis of the roll, the first roll pressing surface includes two first arc-shaped segments 11 arranged at intervals along the second direction and symmetrically arranged. Each second roll pressing surface includes two second arc-shaped segments 21 arranged at intervals along the second direction and symmetrically arranged. This symmetrical layout ensures that the rough tube is subjected to uniform pressure distribution when passing through the roll, whether from above, below, or to the side. The axial symmetry helps to balance the metal flow, reduces the possibility of metal being squeezed in a certain lateral roll gap, and thus reduces the probability of blue line formation.

[0040] It should be noted that the aforementioned blue lines refer to the deformation of the pipe wall metal under the rolling force from the rolls during the processing of the steel pipe. When the space formed by the rolls is insufficient along the deformation direction, the pipe wall metal fills the roll gap under the pressure of the rolls, resulting in several marks appearing on the outer surface of the steel pipe at the corresponding locations of the roll gaps.

[0041] In one embodiment of the present invention, the first diameter reduction device 40 is a separate drive, and the second diameter reduction device 60 is a centralized differential drive or a separate drive.

[0042] In this embodiment, the first sizing and reducing device 40 is a separate drive, that is, each frame has an independent power source and control unit, and each frame can be independently and precisely adjusted in speed. The speed of each frame can be adjusted in a timely manner to ensure that the rough pipe can be smoothly bitten in and uniformly reduced in diameter, and to meet the deformation requirements of steel pipes with different outer diameters and wall thicknesses.

[0043] The second sizing and reducing device 60 is a centralized differential transmission, meaning multiple frames share a single power source, but through the design of gears, sprockets, or other transmission components, speed differences can be maintained between different frames, thus achieving different frame rotation speeds. This reduces the number of power sources and lowers the complexity of the device. Alternatively, the second sizing and reducing device 60 can be an individual transmission, meaning each frame has an independent power source and control unit. Each frame can be independently and precisely adjusted in speed, allowing for timely and individual speed adjustments to ensure that the rough pipe can be smoothly engaged and uniformly reduced in diameter, meeting the deformation requirements of steel pipes with different outer diameters and wall thicknesses.

[0044] It should be noted that the power source and control unit of the first diameter reduction device 40 can adopt existing technology, and the power source, gears, sprockets and other transmission elements for realizing transmission of the second diameter reduction device 60 can also adopt existing technology, and their structures will not be described in detail here.

[0045] Currently, limited by the specifications of existing piercing mills and rolling mills, the production of small-diameter thick-walled steel pipes involves a single-stage reduction process using large-diameter rough pipes, followed by increasing the reduction rate on a single stand of the sizing mill or a two-stage reduction process. However, these two processes still have drawbacks. First, the secondary heating in the two-stage reduction process results in higher energy consumption per unit product compared to conventional processes, significantly increasing production costs. Second, regardless of increasing the reduction rate on a single stand or using existing sizing mill pass profiles, large deviations in finished wall thickness and severe internal defects occur, especially for small-diameter thick-walled pipes with a small diameter-to-sizing (D / S) ratio.

[0046] To solve the above problems, see [reference] Figures 1 to 3 As shown, the present invention also provides a steel pipe manufacturing method, which utilizes the steel pipe manufacturing apparatus described above. The steel pipe manufacturing method includes: preparing a rough pipe; passing the rough pipe through a first diameter reduction device 40 to perform a first diameter reduction operation and obtain a first processed part; and passing the first processed part through a second diameter reduction device 60 to perform a second diameter reduction operation.

[0047] In this embodiment, the steel pipe preparation device has all the technical solutions and effects of the above-mentioned steel pipe preparation device, which will not be repeated here.

[0048] After the raw tube is prepared, it passes through the first sizing and reducing device 40. The first stand 41 has a relatively small reduction rate, mainly serving as an initial bite for the raw tube to facilitate the sizing and reducing operation. The raw tube then reaches multiple second stands, where the reduction rate is generally greater than that of most of the first stands 41, to further reduce the diameter of the raw tube. The reduction rates of the multiple second stands are equal, ensuring that after the initial deformation, the raw tube can be further corrected in size and shape under stable deformation conditions, avoiding dimensional fluctuations caused by frequent and large adjustments to the reduction rate, thus obtaining the first processed part. Then, the raw tube is moved to... At the locations of multiple third stands 61, the reduction rate of the multiple third stands 61 remains constant and is equal to that of the multiple second stands, further providing a stable and continuous dimensional reduction environment for the rough tube. This helps maintain the dimensional consistency of the rough tube at this stage and reduces errors caused by unstable reduction. Finally, the rough tube reaches the locations of multiple fourth stands, which can fine-tune the shape and size of the rough tube, avoiding the impact of the drastic reduction in the final stage on the shape and dimensional accuracy of the final finished tube, thus realizing the second fixed reduction operation on the rough tube.

[0049] As can be seen from the above, the first and second diameter reduction operations achieve a smooth transition in the diameter reduction process of the rough tube, reducing the non-uniformity of metal flow that may be caused by a single large diameter reduction, thereby significantly improving the dimensional accuracy of the rough tube, and ultimately achieving the production of hot-rolled small-diameter thick-walled seamless steel pipes with uniform wall thickness and no internal hexagonal defects.

[0050] In one embodiment of the present invention, the step of passing the raw tube through the first diameter reduction device 40 after the raw tube is prepared includes: heating the raw tube to a first preset temperature T1, wherein the value of the first preset temperature T1 is in the range of Ac3+50℃≤T1≤Ac3. + The steps for performing the first diameter reduction operation on the raw pipe at 60℃ through the first diameter reduction device 40 include: waiting for the raw pipe to cool to a second preset temperature T2, then performing the first diameter reduction operation on the raw pipe. The second preset temperature T2 is less than the first preset temperature T1, and the range of the second preset temperature T2 is Ac3+20℃≤T2≤Ac3. + 30℃, where Ac3 refers to the temperature at which steel completely transforms from the ferrite phase to the austenite phase.

[0051] In this embodiment, the steel pipe is first heated in a walking beam furnace to 50-60°C above Ac3. After exiting the furnace, the cooling is controlled so that the steel pipe undergoes the first diameter reduction operation at 20-30°C above Ac3. The steel pipe exhibits optimal plastic deformation during diameter reduction at this temperature. The rough pipe is heated to the range of Ac3+50°C to Ac3+60°C, which is the high-temperature range of austenitic phase transformation. At this temperature, the steel is in a soft state, which is conducive to achieving a large amount of deformation without causing cracks or fractures, ensuring that the rough pipe has good plasticity. After the rough pipe is cooled to the temperature range of Ac3+20°C to Ac3+30°C, the first diameter reduction operation is performed. At this time, the steel still maintains good plasticity, but the plasticity is reduced compared to T1. This is beneficial for controlling the fluidity and deformation of the metal, preventing excessive widening (i.e., excessive radial outward flow of metal) during the diameter reduction process, thereby reducing defects such as blue lines that may appear in the finished steel pipe.

[0052] In one embodiment of the present invention, the steps for preparing the rough tube include: preparing a billet; preheating the billet for the first time at a temperature of 150℃~400℃ for 15min~20min; preheating the billet for the second time at a temperature of 400℃~650℃ for 20min~25min; heating the billet for the first time at a temperature of 650℃~850℃ for 25min~30min; heating the billet for the second time at a temperature of 850℃~1120℃ for 25min~30min; heating the billet for the third time at a temperature of 1120℃~1300℃ for 25min~30min; heating the billet for the fourth time at a temperature of 1210℃~1300℃ for 20min~25min; and stopping the heating of the billet when the temperature of the billet reaches 1200℃~1290℃ to obtain the workpiece to be processed.

[0053] In this embodiment, the first preheating lasts 15-20 minutes, primarily to eliminate the temperature difference between the surface and interior of the billet, ensuring uniform heating in subsequent stages and preventing uneven deformation and internal stress caused by temperature inconsistencies. The second preheating, and subsequent heatings up to the fourth, operate at temperatures ranging from 400℃ to 650℃, 650℃ to 850℃, 850℃ to 1120℃, and then to 1120℃ to 1300℃, with heating times of 20-25 minutes, 25-30 minutes, 25-30 minutes, and 25-30 minutes respectively. This gradual heating from low to high temperatures progressively improves the plasticity of the steel while avoiding oxidation losses and surface defects caused by excessively high temperatures, as well as internal cracks caused by rapid temperature increases. Furthermore, these heating conditions ensure sufficient heating of the billet, which is beneficial for piercing and rolling processes.

[0054] It should be noted that the above value ranges all include endpoint values.

[0055] In one embodiment of the present invention, the step of preparing the rough tube further includes: piercing the workpiece to obtain a rough tube; and rolling the rough tube to obtain the raw tube.

[0056] In this embodiment, a hole is formed in the center of the billet using a piercing mill. Compared to directly rolled tubes, the pierced tube utilizes material more effectively and reduces waste. Piercing also allows for more flexible adjustment of the tube wall thickness and diameter. The subsequent rolling process is easier after the hole is formed in the billet. The piercing operation transforms the billet from a solid state to a hollow state, reducing deformation resistance in subsequent processes, decreasing the load on processing equipment, and thus improving production efficiency.

[0057] In one embodiment, rolling is performed using a conventional continuous rolling mill or Assel mill to roll the tube blank into a rough tube, thereby obtaining a rough tube with excellent dimensional accuracy.

[0058] In one embodiment of the present invention, when the workpiece is pierced, the temperature of the workpiece is 1170°C to 1270°C, and when the tube is rolled, the temperature of the tube is 960°C to 1160°C.

[0059] In this embodiment, within the temperature range of 1170℃ to 1270℃, the steel material is in a fully austenitic state, at which point the material's plasticity reaches its maximum, facilitating penetration by the piercing machine head to form a hollow capillary. The material at high temperatures exhibits lower deformation resistance, thus making the piercing process easier and reducing mechanical wear and energy consumption. Simultaneously, piercing within this temperature range effectively prevents cracking during the piercing process.

[0060] The temperature of the capillary tube is 960℃~1160℃. On the one hand, it can ensure that the material has sufficient plasticity, so as to achieve the required size reduction and shape correction, while avoiding the difficulty of size control caused by excessive softening. On the other hand, it can effectively reduce work hardening, that is, the increase in hardness and strength of the material due to plastic deformation during cold working. This helps to maintain the processing performance of the material and reduce energy consumption and equipment wear in subsequent processes.

[0061] It should be noted that the above value ranges all include endpoint values.

[0062] In one embodiment of the present invention, after the step of rolling the tube to obtain a rough tube, the method further includes: cooling the rough tube until the temperature of the rough tube drops below 600°C.

[0063] Specifically, the above-mentioned cooling operation can be performed using a small cooling bed based on existing technology.

[0064] In one embodiment of the present invention, after the step of passing the first workpiece through the second diameter reduction device to perform the second diameter reduction operation, the method further includes: first, transporting the rough tube to a large cooling bed for air cooling, and then sequentially performing operations such as cutting the head and tail, straightening, physical and chemical testing, non-destructive testing, manual inspection, spraying lettering, and packaging and warehousing.

[0065] It should be noted that existing technology can be used for the large cooling bed, and the specific structure will not be described in detail here.

[0066] In one embodiment of the present invention, after the step of rolling the tube, the method includes: cooling the raw tube to a temperature of 450°C to 600°C.

[0067] Through the above settings, on the one hand, it can promote the transformation of steel from the austenitic state to a low-energy state such as ferrite + pearlite, which helps to refine the grains, eliminate internal stress, and optimize the mechanical properties of steel. On the other hand, it can also effectively reduce surface oxidation, control the formation of oxide scale, improve the surface condition of finished products, and reduce the need for subsequent surface treatment steps such as pickling, thereby reducing production costs and improving production efficiency.

[0068] In one embodiment of the present invention, a conical piercing machine is used to perform the piercing operation on the workpiece.

[0069] In this embodiment, the tube is pierced with a tapered diameter expansion, and then rolled with a certain deformation to reduce the diameter and wall thickness, thereby providing a rough tube with excellent dimensional accuracy for subsequent sizing, and thus obtaining a finished tube with excellent dimensional accuracy. At the same time, the tapered diameter expansion piercing can achieve a large total deformation, allowing for flexible adjustment of the deformation amount in each process such as piercing and rolling.

[0070] In one embodiment of the present invention, the steel pipe preparation method further includes a smelting process of metallurgical raw materials to obtain a billet.

[0071] In one embodiment of the present invention, the first arc segment 11 is located at the top or bottom of the rolling hole, and the second arc segment 21 is located at the roll gap of the rolling hole.

[0072] Example

[0073] The steel pipe sizing machine of this application is used for pipes with a diameter of 121mm. A 20mm rough tube is reduced in diameter to form an 80mm diameter tube. The 20mm small-diameter thick-walled seamless steel pipe is provided, wherein the number of the first frame 41, the second frame, the third frame 61 and the fourth frame are 3, 7, 7 and 3 respectively. The first frame 41, the second frame, the third frame 61 and the fourth frame are arranged sequentially along the conveying direction of the raw pipe. The diameter reduction rates of the three first frames 41 are 0.51%, 1.24% and 1.62% respectively, the diameter reduction rates of the second frame and the third frame 61 are both 2.5%, and the diameter reduction rates of the three fourth frames are 1.93%, 1.25% and 0.76% respectively. The three rolls installed on the first frame 41 and the fourth frame are rolls of the prior art, and the rolls on the other frames all include a first roll section 10 and a second roll section 20.

[0074] Comparative Example

[0075] The existing three-roll sizing (reducing) mill is used for 121mm diameter diameters. A 20mm rough tube is reduced in diameter to form an 80mm diameter tube. 20mm small-diameter thick-walled seamless steel pipe, of which the number of frames of the three-roll sizing (reducing) mill is 20.

[0076] The shape and dimensional accuracy of the small-diameter thick-walled seamless steel pipes prepared in the examples and comparative examples were inspected by visual inspection, vernier calipers and ultrasonic thickness gauge respectively. The results are shown in Table 1.

[0077] Table 1. External shape and dimensional measurement results of the small-diameter thick-walled tubes in the examples and comparative examples.

[0078]

[0079] It should be noted that the PN value is generally used to measure the degree of defects in the hexagonal inner surface of the steel pipe. It is generally believed that when PN≤10, the hexagonal inner surface of the steel pipe meets the requirements.

[0080] The formula for calculating the PN value is as follows: .

[0081] In the formula, SA represents the six wall thickness values ​​(thickest points) at the top of the corresponding die or at the roll gap.

[0082] SB represents the six wall thickness values ​​(thinnest points) at the midpoint between the top of the corresponding die and the roll gap.

[0083] Da is the outer diameter of the steel pipe after reduction.

[0084] As can be seen from the above description, the above embodiments of the present invention achieve the following technical effects: When preparing steel pipes using the steel pipe preparation apparatus and method of this application, the diameter of the rough pipe is gradually reduced and the initial shape is corrected by multiple first stands. Subsequently, the shape and size are further adjusted by multiple second and third stands on the basis of increasing the reduction rate, so as to achieve preliminary precise control of the steel pipe. The reduction rates of the second and third stands are equal, which can stabilize the reduction rate and ensure that the rough pipe can achieve uniform size reduction. The fourth stand is used to fine-tune the shape and size of the rough pipe in the final stage to prevent excessive reduction from causing size errors or defects. This achieves a smooth transition in the rough pipe reduction process, reduces the non-uniformity of metal flow that may be caused by a single large reduction, thereby significantly improving the size accuracy of the rough pipe, and finally realizing the production of hot-rolled small-diameter thick-walled seamless steel pipes with uniform wall thickness and no internal hexagonal defects.

[0085] Obviously, the embodiments described above are merely some, not all, embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0086] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0087] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A steel pipe manufacturing apparatus, characterized in that, Comprise: The first reducing device (40) comprises a plurality of first racks (41) and a plurality of second racks, the plurality of first racks (41) and the plurality of second racks are arranged in sequence along the conveying direction of the hollow pipe, the reducing rate of the plurality of first racks (41) gradually increases along the conveying direction of the hollow pipe, the reducing rate of the plurality of second racks is equal, and the reducing rate of the plurality of second racks is greater than or equal to the reducing rate of the first rack (41) adjacent thereto; The second reducing device (60) comprises a plurality of third racks (61) and a plurality of fourth racks, the plurality of third racks (61) and the plurality of fourth racks are arranged in sequence along the conveying direction of the hollow pipe, the reducing rate of the plurality of third racks (61) is equal, the reducing rate of the plurality of fourth racks gradually decreases along the conveying direction of the hollow pipe, and the reducing rate of the plurality of third racks (61) is greater than or equal to the reducing rate of the fourth rack adjacent thereto, and the reducing rate of each second rack and each third rack (61) is equal.

2. The steel pipe production apparatus according to claim 1, characterized by The number of the first rack (41) and the fourth rack ranges from 1 to 5, and the number of the second rack and the third rack (61) ranges from 6 to 13.

3. The steel pipe production apparatus according to claim 1, characterized by The reducing rate of the first rack (41) and the fourth rack ranges from 0 to 2%, and the reducing rate of the second rack and the third rack (61) ranges from 2% to 3%.

4. The steel pipe production apparatus according to any one of claims 1 to 3, characterized by The first rack (41), the second rack, the third rack (61) and the fourth rack all comprise a roller assembly, the roller assembly comprises three rollers (50), the three rollers (50) are arranged in sequence along the circumference of the hollow pipe, each roller (50) can rotate relative to its central axis, and the roller (50) comprises: A first roller segment (10) has a first roller pressure surface; Two second roller segments (20) are symmetrically arranged at opposite ends of the first roller segment (10) along a first direction, and the two second roller segments (20) are connected with the first roller segment (10), each second roller segment (20) has a second roller pressure surface, in a longitudinal section passing through the central axis of the roller (50), the first roller pressure surface comprises two first arc segments (11) which are arranged in a second direction and are axially symmetric, each second roller pressure surface comprises two second arc segments (21) which are arranged in the second direction and are axially symmetric, the first arc segment (11) and the second arc segment (21) are connected on the same side of the roller (50) along the second direction, the ellipticity of the first arc segment (11) is less than the ellipticity of the second arc segment (21), and the first direction is perpendicular to the second direction.

5. A method of producing a steel pipe, characterized by, The steel pipe preparation device according to any one of claims 1 to 4, the steel pipe preparation method comprises: Preparation of a hollow pipe; Passing the hollow pipe through the first reducing device (40) to perform a first reducing operation and obtain a first processed part; The first workpiece is passed through the second sizing device (60) to perform a second sizing operation.

6. The steel pipe production method according to claim 5, characterized by After the preparation of the hollow pipe, the step of passing the hollow pipe through the first sizing device (40) before the first sizing operation includes heating the hollow pipe to a first preset temperature T1, wherein the first preset temperature T1 is in a range of Ac3+50℃≤T1≤Ac3 + 60℃, the step of passing the hollow pipe through the first sizing device (40) to perform the first sizing operation includes: when the temperature of the hollow pipe cools to a second preset temperature T2, performing the first sizing operation on the hollow pipe, wherein the second preset temperature T2 is less than the first preset temperature T1, and the second preset temperature T2 is in a range of Ac3+20℃≤T2≤Ac3 + 30℃, wherein Ac3 represents the temperature at which the steel material completely transforms from the ferrite phase to the austenite phase.

7. The steel pipe production method according to claim 5, characterized by, The step of preparing the hollow pipe comprises: preparing a blank; preheating the blank for the first time at a temperature of 150-400 DEG C for 15-20 minutes; preheating the blank for the second time at a temperature of 400-650 DEG C for 20-25 minutes; heating the blank for the first time at a temperature of 650-850 DEG C for 25-30 minutes; heating the blank for the second time at a temperature of 850-1120 DEG C for 25-30 minutes; heating the blank for the third time at a temperature of 1120-1300 DEG C for 25-30 minutes; heating the blank for the fourth time at a temperature of 1210-1300 DEG C for 20-25 minutes; stopping heating the blank when the temperature of the blank is 1200-1290 DEG C to obtain a workpiece to be processed.

8. The steel pipe production method according to claim 7, characterized by, The step of preparing the hollow pipe further comprises: performing a piercing operation on the workpiece to be processed to obtain a rough pipe; performing rolling on the rough pipe to obtain the hollow pipe.

9. The steel pipe production method according to claim 8, characterized by When performing the piercing operation on the workpiece to be processed, the temperature of the workpiece to be processed is 1170-1270 DEG C, and when performing the rolling operation on the rough pipe, the temperature of the rough pipe is 960-1160 DEG C. And / or, after the step of performing rolling on the rough pipe, the step of cooling the hollow pipe to a temperature of 450-600 DEG C is performed.

10. The steel pipe production method according to claim 8, characterized by, In the step of performing the piercing operation on the workpiece to be processed, a conical piercer is used to perform the piercing operation.

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