Method for reducing bending degree of pipe end of pierced seamless pipe

Abstract

The invention discloses a method for reducing the bending degree of the pipe end of a seamless steel pipe billet. The method comprises the steps of perforating, continuous rolling or longitudinal rolling / skew rolling, pipe removing or rod removing / flattening and diameter fixing / reducing. Wherein the pipe end necking processing procedure is arranged before the sizing / reducing procedure, and the pipe end of the pierced billet is processed into an approximately conical shape. After the pierced billet with the inclined stubbles is processed by a necking process, the pipe end or the pipe tail of the pierced billet is processed into an approximately conical shape or other shapes smaller than the outer diameter of the pipe body, the pipe body part in contact with a roller in the subsequent deformation process is uniformly stressed and cannot be bent, and the bending degree of the pipe end in the traditional process is greatly improved; according to the method, the bending degree of the pipe end is reduced, the cutting length caused by the fact that the bending degree exceeds the standard is greatly reduced, and the product yield can be increased; in addition, the pipe end is machined before sizing / reducing, so that the bending degree of the pipe end after sizing / reducing is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of seamless pipe production, in particular to a method for reducing the pipe end bending degree of a seamless steel pipe blank. BACKGROUND

[0002] At present, in the production of seamless steel pipes, especially in the production of large-diameter seamless steel pipes, pipe ends often have bevels (or chamfers, horseshoe openings, etc.). After deformation by the sizing / reducing mill set, the blanks with bevels are prone to bending at the pipe end. The distance between the bending point and the pipe end is related to the distance between the adjacent racks of the sizing / reducing mill. It is roughly one or two times the distance between the racks of the sizing / reducing mill. In many standards (such as "National Standard GB / T 8163-2018 Seamless Steel Pipes for Transporting Fluids"), the bending degree per meter is specified (for example, the bending degree per meter of steel pipes with a wall thickness of less than 15 mm is not greater than 1.5 mm, etc.), and exceeding the standard will be judged as a defective defect. This defect generally needs to be cut off. Therefore, the bending of the pipe end of the blank increases the cutting loss of the pipe end of the blank, reduces the first pass rate and the yield rate, increases the ton steel consumption, and raises the ton steel cost.

[0003] Chinese patent CN113714297B discloses a processing method for reducing the tail cutting length of a steel pipe. After the elongation process of the steel pipe in the hot rolling seamless steel pipe production process and before the sizing process, a tail end cutting process or a tail end reducing process is added to cut off the horseshoe of the blank pipe end after the elongation process, thereby obtaining a basically flush blank pipe tail end, reducing the tail cutting length of the steel pipe, and reducing the tail cutting size of the steel pipe. However, this process has metal loss during hot cutting, low yield, and environmental pollution caused by sawdust splashing.

[0004] The paper "Large-diameter seamless steel pipe bending degree control process practice" (Modern Metallurgy, Li Jinrong, Long Jinhua, Li Bowang, December 2019, Vol. 47, No. 6) discloses that by increasing the heating temperature of the 4th to 6th zones of the ring furnace, stabilizing the discharge rhythm at 140 s to ensure uniform heating of the blank, and adjusting the piercing, continuous rolling and stretching / reducing, the reducing bending is reduced, which has a certain effect; but the energy consumption is high, the cost is high, and the bending problem cannot be completely solved. SUMMARY

[0005] The purpose of the present application is to provide a method for reducing the bending degree of the pipe end of a seamless steel pipe blank, which processes the pipe end before sizing / reducing to reduce the bending degree of the pipe end after sizing / reducing.

[0006] To achieve the above-mentioned purpose, the technical scheme of the present application is as follows:

[0007] A method for reducing the bending degree of the pipe end of seamless steel pipe blank, comprising piercing, continuous rolling or longitudinal rolling / oblique rolling, pipe or rod drawing / straightening and sizing / reducing; wherein a pipe end necking processing procedure is arranged before the sizing / reducing procedure to process the pipe end of the blank into a conical shape.

[0008] Preferably, the pipe end necking processing equipment is arranged at a position before the sizing / reducing machine, including the following position selection:

[0009] on the roller table before the sizing / reducing machine;

[0010] on the roller table after the pipe / rod drawing / straightening machine;

[0011] on the blank transverse moving chain / fork before the sizing / reducing machine;

[0012] on the roller table and the rack between the pipe / rod drawing / straightening machine and the sizing / reducing machine.

[0013] Preferably, the pipe end necking processing equipment adopts necking tongs and clamping tongs; the pass of the necking tongs is a structure with gradually reduced inner hole size, or an overall conical structure, or a local conical structure.

[0014] Preferably, the pass diameter of the clamping tongs is 80% to 200% of the outer diameter of the blank.

[0015] Preferably, the surface of the pass of the clamping tongs in contact with the blank is a circular ring structure, and the edge part is chamfered / rounded; preferably, the circular ring structure is composed of at least two arc-shaped parts.

[0016] Preferably, the clamping tongs and the necking tongs each have three opening degrees:

[0017] large opening degree D 大 : opening value D 大 10 to 500 mm larger than the hot state diameter of the blank;

[0018] small opening degree D 小 : opening value 10 to 300 mm larger than the hot state diameter of the blank;

[0019] closed opening degree D 闭合 : opening value D 闭合 ±300 mm of the hot state diameter of the blank.

[0020] Preferably, the large opening D 大 of the necking tongs and the clamping tongs is defined as:

[0021] large opening degree of the necking tongs: 1 to 2 times the distance from the center line to the surface of the groove bottom at the position of the side edge of the groove bottom close to the pipe body at the section B position of the necking tongs;

[0022] The maximum opening of the clamping pliers: 1 to 2 times the distance between the bottom surface of the groove at position C of the clamping pliers and the center line;

[0023] in:

[0024] Section A is defined as the section located at the point closest to the pipe body where the pipe end bevel is;

[0025] Section B defines the section containing the end face of the necking pliers located near the pipe body;

[0026] Section C is defined as the section that is perpendicular to the axis of the tube and in contact with the working surface of the clamping forceps.

[0027] Preferred,

[0028] The formula for calculating the maximum opening of clamping pliers and reducing pliers is as follows:

[0029] D 大 =K0, where K0 is the equipment limit opening of the clamping pliers and the reducing pliers, in mm;

[0030] The formula for calculating the minimum opening size of mouth-reducing pliers and clamping pliers is as follows:

[0031]

[0032] D 小_夹持 =D 前 +K2,

[0033] In the formula: D 小_缩口 : Minimum opening size of the necking pliers, mm;

[0034] D 小_夹持 : Minimum opening of the clamping pliers, mm;

[0035] D 前 : The hot diameter of the rough tube before the sizing reduction, in mm;

[0036] D nom : Hot outer diameter of the finished pipe after sizing and reduction, mm;

[0037] S nom : Hot wall thickness of the finished pipe after sizing and reduction, mm;

[0038] K1: Correction factor for diameter-to-wall ratio, -1 to 1;

[0039] K2: Outer diameter correction factor, 0~50mm;

[0040] The formula for calculating the closing opening degree of clamping pliers and reducing pliers is as follows:

[0041] D 闭合_缩口 =D nom (1-K3),

[0042] D 闭合_夹持 =D 前 -K4;

[0043] In the formula: D 闭合_缩口 : Closure opening of the shrinking pliers, mm;

[0044] D 闭合_夹持 : Clamping opening degree, mm;

[0045] K3: Correction coefficient for the closing opening degree of the clamping pliers, -0.1 to 0.2;

[0046] K4: Clamping clamp closure opening correction coefficient, 0~(D 前 -D nom )mm.

[0047] Preferably, the length of the constricted end of the rough pipe is 10 to 2000 mm, and the diameter reduction range is calculated based on the reduction in outer diameter at the end of the slanted cut of the rough pipe, with a minimum of 10 mm and a maximum of half the hot outer diameter of the rough pipe before the diameter reduction is determined.

[0048] Preferably, from the end of the rough cut to the end of the pipe, the outer diameter of the steel pipe after the necking shows a trend of gradually decreasing in all or part of the pipe, such as a conical shape, a stepped shape, or a polygonal shape.

[0049] The mechanism by which the pipe tail bends is as follows:

[0050] During the sizing and reducing process, the steel pipe is bitten into and reduced in diameter by the rollers of each stand of the sizing mill. During this reduction process, the outer diameter of the steel pipe decreases under the pressure of the rollers, resulting in symmetrical stress on the rough pipe. When the pipe end with a slanted end enters the sizing mill pass and is pressed down, it is subjected to the pressure of the rollers, such as... Figure 1 Point E, as shown, is pressed down. On the opposite side of the beveled end of the tube, the force is smaller, or even nonexistent, resulting in asymmetrical force. The beveled portion of the tube will move in the opposite direction, and the tube at the adjacent stand roll will bend due to radial pressure. Figure 1 The support point F shown creates a depression. The outer diameter of the beveled section experiences only a small reduction or no reduction due to the pipe's bending. Each time the beveled section passes a stand, the bending value of the outer diameter pipe end further increases.

[0051] See Figure 2 The diagram shows the shape of the rough tube with a bevel before the necking process in this invention. Before necking, the tube end has a raised tail, the distance from the tail end to the tube body axis is greater than the tube body radius, and metal is missing on the other side. This easily leads to a difference in the pressure of the rollers on both sides of the tube end during the subsequent diameter reduction process. One side is subjected to roller pressure, while the other side is not subjected to force due to the missing metal, and the difference in force causes bending.

[0052] See Figure 3The diagram shows the shape of a rough tube with a beveled end after processing in the tapering process according to the present invention. The purpose of the tapering process is to process the end or tail of the rough tube into an approximately conical shape or another shape smaller than the outer diameter of the tube body. After tapering, the tube end presents a conical shape, and the part of the tube body in contact with the rolls is subjected to balanced force during subsequent deformation, preventing bending.

[0053] The pipe end reduction processing equipment of this invention can be used in combination with reduction clamps and raw pipe clamping clamps. The reduction clamps process the pipe end to reduce its outer diameter and are the main deformation equipment in the pipe end reduction process. To avoid bending, flattening, and other defects in the raw pipe body during the reduction process, the clamping clamps are installed. This device mainly serves to clamp and stabilize the raw pipe and prevent excessive deformation of the raw pipe body. The clamping and stabilizing device is located near the reduction clamps, close to the side of the pipe body.

[0054] Pipe end reduction processing equipment (such as reduction pliers) has a hole shape that is generally near-conical, or partially near-conical. The purpose is to facilitate the reduction of the outer diameter of the rough pipe end. The processed pipe end will be conical or other shapes with an outer diameter smaller than the pipe body. That is, from the end of the bevel cut of the rough pipe to the pipe end, the outer diameter of the steel pipe after reduction shows a trend of gradually decreasing, either entirely or partially, such as a conical shape, a stepped shape, or a polygonal shape.

[0055] The surface of the clamping pliers that contacts the rough tube is annular, with its edges chamfered / rounded. Preferably, the annular part is composed of at least two arc-shaped segments, which ensures that the hole can be opened and closed.

[0056] The clamping pliers and the reducing pliers each have three opening sizes: large opening size, small opening size, and closed opening size.

[0057] (1) Maximum Opening Degree: The maximum opening degree setting for the clamping and reducing clamps is to ensure the rough pipe can smoothly enter the reducing and clamping clamps, facilitating subsequent positioning and adjustment of the opening degree for smaller openings and closures. Opening Degree Value D 大 It is 10 to 500 mm larger than the diameter of the raw tube when it is hot.

[0058] Narrowing pliers and clamping pliers D 大 Defined as:

[0059] The maximum opening angle of the mouth-reducing pliers: 1 to 2 times the distance between the bottom surface of the mouth-reducing pliers at position B (near the side of the pipe body) and the centerline. (See [reference]). Figure 8 ;

[0060] The maximum opening of the clamping pliers is 1 to 2 times the distance between the bottom surface of the groove at position C of the clamping pliers and the center line.

[0061] Wherein, section A is defined as the section where the pipe end bevel is closest to the pipe body;

[0062] Section B defines the section containing the end face of the necking pliers located near the pipe body;

[0063] Section C is defined as the section that is perpendicular to the axis of the tube and in contact with the working surface of the clamping forceps.

[0064] (2) Small opening degree D 小 This is to reduce the time it takes for the clamping pliers and necking pliers to reach the closed opening, thereby reducing the temperature drop of the rough tube. The opening value is 10-300 mm larger than the hot diameter of the rough tube. This value is defined in the same way as the definition of the maximum opening.

[0065] (3) Closure degree: Opening degree value D 闭合 The diameter of the raw tube in its hot state is ±300mm.

[0066] This value is defined as 1 to 2 times the distance from the centerline at section A, i.e., the distance from the bottom surface of the groove inside the constricting clamp at the end of the pipe end bevel. The degree of closure determines the geometry of the pipe end. A larger value results in less pipe end deformation and less impact on the curvature, leading to a larger curvature at the pipe end; a smaller value results in greater pipe end deformation and a greater impact on the curvature, leading to a smaller curvature at the pipe end.

[0067] The large opening angle, small opening angle, and closed opening angle of the clamping pliers and reducing pliers described in this invention are calculated using formulas:

[0068] Large opening angle of clamping pliers and grippers:

[0069] D 大 =K0, where K0 is the limit opening of the clamping pliers and the reducing pliers, in mm.

[0070] The small opening of the necking pliers and clamps is designed to reduce the opening size of the raw pipe as it passes through them, thereby minimizing the total necking time. The calculation formula is:

[0071]

[0072] D 小_夹持 =D 前 +K2

[0073] In the formula: D 小_缩口 : Minimum opening size of the necking pliers, mm;

[0074] D 小_夹持 : Minimum opening of the clamping pliers, mm;

[0075] D 前 : The hot diameter of the rough tube before the sizing reduction, in mm;

[0076] Dnom : Hot outer diameter of the finished pipe after sizing and reduction, mm;

[0077] S nom : Hot wall thickness of the finished pipe after sizing and reduction, mm;

[0078] K1: Correction factor for diameter-to-wall ratio, -1 to 1;

[0079] K2: Outer diameter correction factor, 0~50mm.

[0080] The closing opening degree of the clamping pliers and reducing pliers is closely related to the diameter of the rough tube after sizing and reduction. The smaller the diameter of the rough tube, the smaller the closing opening degree of the reducing pliers, which is more conducive to reducing the curvature of the finished tube. The opening degree of the clamping pliers is related to the hot outer diameter of the rough tube before sizing and reduction, and mainly plays a role in stabilizing the rough tube. The calculation formula is:

[0081] D 闭合_缩口 =D nom (1-K3)

[0082] D 闭合_夹持 =D 前 -K4

[0083] In the formula: D 闭合_缩口 : Closure opening of the shrinking pliers, mm;

[0084] D 闭合_夹持 : Clamping opening degree, mm;

[0085] K3: Correction coefficient for the closing opening degree of the clamping pliers, -0.1 to 0.2;

[0086] K4: Clamping clamp closure opening correction coefficient, 0~(D 前 -D nom )mm.

[0087] Traditional processes often result in tubes with a raised tail, where the distance from the tail to the tube's axis is greater than the tube's radius, and metal is missing on the other side. This can easily lead to a difference in pressure exerted by the rollers on both sides of the tube during subsequent diameter reduction. One side experiences roller pressure, while the other side, lacking metal, is unaffected, causing this pressure difference to result in bending.

[0088] Compared with traditional processes, the beneficial effects of this invention are as follows:

[0089] In this invention, after the rough tube with slanted cut is processed by the necking process, the end or tail of the rough tube is processed into an approximately conical shape or other shape smaller than the outer diameter of the tube body. During the subsequent deformation process, the part of the tube body in contact with the roll is subjected to balanced force and will not bend, which greatly improves the tube end bending degree of the traditional process.

[0090] The production process employed in this invention reduces the curvature of the pipe end, significantly decreasing the cutting length caused by excessive curvature and thus improving the product yield. Attached Figure Description

[0091] Figure 1 Explanation of the pipe end bending mechanism;

[0092] Figure 2 , Figure 3 This is a schematic diagram showing the shape of the rough pipe with a beveled end before and after the pipe end narrowing process in this invention.

[0093] Figure 4 This is a perspective view of the pipe end reduction clamp used in the pipe end reduction process of the present invention;

[0094] Figure 5 This is a perspective view of the clamping pliers used in the pipe end reduction process of the present invention;

[0095] Figure 6 The positional relationship between the rough pipe, the necking pliers, and the clamping pliers during the processing of the pipe tail end;

[0096] Figure 7 The positional relationship between the rough pipe, the reducing pliers, and the clamping pliers during pipe end processing;

[0097] Figure 8 This document describes the large opening, small opening, and closed opening of the clamping pliers described in this invention, as well as the measurement positions for each opening degree of the clamping pliers. Detailed Implementation

[0098] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0099] The method for reducing the curvature of the end of a seamless steel pipe rough tube according to the present invention includes piercing, continuous rolling or longitudinal / skew rolling, tube removal or bar removal / smoothing and sizing / reducing diameter; wherein, a tube end shrinking process is set before the sizing / reducing diameter process to process the end of the rough tube into a conical shape.

[0100] Preferably, the pipe end reduction processing equipment is located in front of the sizing / reducing machine, including the following location options:

[0101] Located on the roller conveyor in front of the sizing / reducing mill;

[0102] Located on the roller conveyor after the tube / bar removal / leveling machine;

[0103] Located on the rough pipe transverse transfer chain / fork in front of the sizing / reducing machine;

[0104] Located on the roller conveyor and frame between the tube / rod / sizing machine and the sizing / reducing machine.

[0105] See Figures 4-7The pipe end reduction processing equipment uses reduction clamps 1 and clamping clamps 2; the hole type of reduction clamps 1 is a structure with gradually decreasing inner hole size, or an overall conical structure, or a partially conical structure.

[0106] Preferably, the diameter of the hole in the clamping clamp 2 is 80% to 200% of the outer diameter of the rough tube 100.

[0107] Preferably, the surface of the clamping clamp 2 that contacts the rough tube 100 is a ring-shaped structure, and its edge is chamfered / rounded; preferably, the ring-shaped structure is composed of at least two arc-shaped segments.

[0108] Production The hot rolling process for thin-walled tubes includes piercing, continuous rolling, tube removal, and diameter reduction; the diameter of the rough tube 100 before sizing is 436mm. Among them, a tube end reduction process is set before the sizing / reduction process to process the end of the rough tube 100 into an approximately conical shape.

[0109] The diameter of the orifice of clamping pliers 2 is 100% of the outer diameter of the rough pipe 100, which is 436 mm. Clamping pliers 2 and reducing pliers 1 have three opening sizes:

[0110] Maximum opening degree: opening value D 大 It is 200mm larger than the diameter of the raw tube in its hot state, i.e., 636mm;

[0111] The minimum opening degree of the reducing pliers 1 and the clamping pliers 2 is calculated as follows:

[0112] (K1 takes the value of 1).

[0113] D 小_夹持 =D 前 +K2=436+30=466mm, (K2 is 30).

[0114] The closing opening degree of clamping pliers 2 and reducing pliers 1 is calculated as follows:

[0115] D 闭合_缩口 =D nom (1-K3) = 399.3, (K3 takes the value 0.1)

[0116] D 闭合_夹持 =D 前 -K4 = 436 - 0 × (436 - 377) = 436; (K4 takes the value 0)

[0117] The rough tube has a conical neck and a length of 100mm.

[0118] This invention utilizes a pipe end reducing machine installed between the pipe removal / rod removal / sizing machine and the sizing / reducing machine to process the pipe end into an approximately conical shape or other shape smaller than the outer diameter of the pipe body. This reduces the degree of pipe end bending after the sizing / reducing machine, ensuring that the pipe end bending meets standard requirements (such as GB / T 8163-2018 requiring a bending degree of 1.5mm / M for steel pipes with a wall thickness of less than 15mm) or the bending degree requirements negotiated with the user.

[0119] The method described in this invention can solve the problem of excessive bending at the pipe ends in the existing seamless steel pipe production process, thus achieving good results in reducing the end-cutting length of seamless pipes and improving the yield of steel pipes. This invention innovates the existing continuous rolling pipe production process, and the process method adopted is environmentally friendly, which can improve product quality and yield, and reduce end-cutting damage and rolling costs per ton of steel.

[0120] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Therefore, all equivalent variations made to the content described in the claims of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A method for reducing the bending degree of the pipe end of seamless steel pipe rough pipe, comprising piercing, continuous rolling or longitudinal / oblique rolling, pipe or rod breaking / leveling and sizing / reducing; characterized in that: The pipe end necking processing device is arranged before the sizing / reducing machine, and includes the following position selection:

2. The method of claim 1 wherein: on the roller table before the sizing / reducing machine; on the roller table after the pipe / rod removing / straightening machine; on the pipe transverse moving chain / fork before the sizing / reducing machine; on the roller table and the rack between the pipe / rod removing / straightening machine and the sizing / reducing machine. The pipe end necking processing device adopts the necking tongs and the clamping tongs; the hole type of the necking tongs is gradually reduced in size, or is an overall conical structure, or is a local conical structure.

3. The method of claim 1 wherein: The hole type diameter of the clamping tongs is 80% to 200% of the outer diameter of the pipe.

4. The method of claim 3 wherein: The hole type of the clamping tongs is a circular ring structure, and the edge part is chamfered / rounded; preferably, the circular ring structure is composed of at least two arc-shaped parts.

5. A method of reducing the crookedness of the pipe ends of seamless steel pipe blooms as claimed in claim 3 or 4, characterized in that: The necking tongs and the clamping tongs each have three opening degrees:

6. A method of reducing the crookedness of the pipe ends of seamless steel pipe rough pipes as set forth in claim 3 or 4 or 5, characterized by: The large opening degree of the necking tongs: the distance between the groove bottom surface at the position of the section B of the necking tongs close to the side edge of the pipe body and the center line is 1 to 2 times; Large opening degree D 大 : Opening degree value D 大 10-500 mm larger than the hot state diameter of the rough pipe; Small opening degree D 小 : opening degree value is 10-300mm larger than hot state diameter of the blank pipe; The opening degree D 闭合 The opening degree D 闭合 The hot diameter of the hollow pipe is ±300 mm.

7. The method of claim 6 wherein: Large opening D of pinch and clamp tongs 大 is defined as: The large opening degree of the clamping tongs: the distance between the groove bottom surface at the position of the section C of the clamping tongs and the center line is 1 to 2 times; Wherein: The section A is defined as the section where the pipe end bevel is closest to the pipe body; The section B is defined as the section where the end surface of the necking tongs close to the pipe body is located; The section C is defined as the section perpendicular to the pipe body axis and in contact with the working surface of the clamping tongs.

8. The method for reducing the bending degree of the pipe end of the seamless steel pipe blank according to claim 6, characterized in that: The calculation formula of the large opening degree of the clamping tongs and the necking tongs is: The calculation formula of the small opening degree of the clamping tongs and the necking tongs is: D 大 = K0, where K0 is the device limit opening of the clamping jaw and the necking jaw, mm; K1: diameter-wall ratio correction coefficient, -1 to 1; D 小_夹持 = D 前 + K2, In the formula: D 小_缩口 : small opening opening degree of the pinch pliers, mm; D 小_夹持 : small opening of the clamp forceps, mm; D 前 : hot pipe body diameter before sizing, mm D nom : hot outside diameter of finished pipe after reducing, mm; S nom : hot wall thickness after sizing, mm K2: outer diameter correction coefficient, 0 to 50 mm; The calculation formula of the closed opening degree of the clamping tongs and the necking tongs is: K3: necking tongs closed opening degree correction coefficient, -0.1 to 0.2; D 闭合_缩口 = D nom (1-K3), D 闭合_夹持 = D 前 - K4; In the formula: D 闭合_缩口 : closed opening of the constrictor, mm; D 闭合_夹持 : Closed opening of the clamp, mm; The length of the pipe blank necking is 10 to 2000 mm, and the reducing amount is calculated based on the outer diameter reduction at the end of the pipe blank bevel, which is at least 10 mm and at most half of the hot state outer diameter of the pipe blank before sizing / reducing. K4: pinch clamp closed opening correction factor, 0~(D 前 - D nom ) mm.

9. The method of claim 1 wherein: From the end of the pipe blank bevel to the pipe end, the outer diameter of the necked steel pipe gradually decreases in whole or in part.

10. The method of claim 9 wherein: From the end of the pipe blank bevel to the pipe end, the outer diameter of the necked steel pipe is in a conical shape, a stepped shape or a polygonal shape.

11. The method of claim 9 wherein: ​

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