A die for expanding the end of a seamless steel pipe with a small diameter and its usage method

Abstract

The present invention discloses a small-diameter seamless steel pipe end expanding die and a using method thereof, which comprise a die body and a die core cone. The die core cone includes a cone head. The die body includes single-piece dies and mounting holes. A plurality of groups of single-piece dies are arranged and surround to form mounting holes on the opposite side. One end of each group of single-piece dies is adapted to be installed inside the end of the steel pipe, and the cone head is adapted to be installed inside the mounting hole and extrude each group of single-piece dies to expand radially. The present invention realizes rapid hole expansion for the end of the steel pipe, avoiding the complex structure of the hole-expanding device in the prior art, which leads to an increase in processes and costs.

Description

Technical Field

[0001] The present invention belongs to the technical field of expanding dies, and specifically relates to an expanding die for the end of a seamless steel pipe with a small diameter and a using method thereof. Background Art

[0002] In the steel pipe installation project, for the butt joint connection between steel pipes, it is required that the pipe end diameter and roundness must meet certain technical requirements. However, for the currently directly manufactured steel pipes, their ends need to be processed to make the port diameter and roundness meet the usage requirements. Currently, for the known expanding of the ends of steel pipes, only large-diameter steel pipes are available. The ends of small-diameter steel pipes are all processed by machining, but the machining of the ends of steel pipes has low efficiency and reduces the strength of the ends of steel pipes.

[0003] Reference document CN201710913924.4, a method for improving the efficiency and reducing the cost of pipe end expansion and a special expanding die, mentions an expanding method, which uses a fixed expanding die to be extruded by a moving placement. First, its structure is complex and the installation is cumbersome, resulting in too high actual expanding cost. Second, the different forming hole diameters of the expanding die have different effects, resulting in the need to remove the whole or at least all the expanding dies for the change of the expanding hole diameter, leading to cumbersome processes.

[0004] In view of this, the present invention is specifically proposed. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to achieve rapid hole expansion for the ends of steel pipes and avoid the increase of processes and costs caused by the complex structure of the existing hole-expanding devices.

[0006] To solve the above technical problem, the inventor has obtained the technical solution of the present invention through practice and summary. The present invention discloses an expanding die for the end of a seamless steel pipe with a small diameter, including a die body and a die core cone. The die core cone includes a cone head. The die body includes single-piece dies and an installation hole. There are multiple groups of the single-piece dies, and they surround and form the installation hole on the opposite side. One end of each group of the single-piece dies is adapted to be installed inside the end of the steel pipe, and the cone head is adapted to be installed inside the installation hole and extrude each group of single-piece dies to expand radially.

[0007] Further, the die core cone further includes a cylinder. The cylinder is integrally provided with the cone head. A push-pull disk is installed at one end of the cylinder away from the cone head. The push-pull disk is fixedly connected to the cylinder. A driving member is installed on the side of the push-pull disk facing away from the cylinder. The driving member is adapted to be connected to the push-pull disk and push the push-pull disk to move.

[0008] Further, the die body includes a large end portion and a pointed end portion. A circumferential groove is provided outside the large end portion formed by multiple groups of the single-piece dies. A locking ring is installed in the circumferential groove, and the locking ring is adapted to relatively fix multiple groups of the single-piece dies.

[0009] Further, a main body disc is installed outside the die body. The main body disc includes a rear cover, a washer, and a front cover. Intermediate holes are provided in both the rear cover and the front cover, and the diameters of the intermediate holes are both larger than the diameters of the cylinder and the pointed end portion. The rear cover and the front cover are arranged in parallel. The large end portion of the die body is installed between the front cover and the rear cover, and the diameter of the large end portion is smaller than the inner diameter of the washer.

[0010] Further, an oil injection nozzle is provided at the upper end of the washer. The oil injection nozzle is in the shape of a stepped hole and is adapted to inject oil from the outside to the inside.

[0011] Further, a first positioning hole is provided on one side of each group of the single-piece dies facing away from the steel pipe end. A second positioning hole is provided on the rear cover. The first positioning hole is adapted to the second positioning hole. A guiding pin is installed between the first positioning hole and the second positioning hole, and the guiding pin is adapted to relatively fix the rear cover and the single-piece die.

[0012] Further, a first screw counterbore is provided on the rear cover, a second screw counterbore is provided on the front cover, and a transition hole is provided on the washer. The first screw counterbore and the second screw counterbore are symmetrically distributed and are adapted to install countersunk head screws. The countersunk head screws are adapted to be installed in the first screw counterbore or the second screw counterbore respectively and are connected in the transition hole.

[0013] Further, the die body includes six groups of single-piece dies. The cone head is a six-sided cone, the installation hole is a six-sided tapered hole, the diameter of the pointed end portion is adapted to the inner diameter of the steel pipe end, and the taper of the cone head and the installation hole is the same.

[0014] A method for using a small-diameter seamless steel pipe end expanding die includes the following steps:

[0015] S1. According to the design of the drawing, the driving member includes a hydraulic cylinder. The moving range of the output piston rod of the hydraulic cylinder is set to a preset value, and the size of the preset value is the same as the moving range of the cone head. When the output piston rod reaches the preset value, the extrusion of the cone head causes the diameter of the pointed end portion to expand radially and be adapted to the required inner diameter of the steel pipe end for expansion;

[0016] Install the die body: Symmetrically install six groups of single-piece die combinations, install them on the circumferential groove through the locking ring. The locking ring has elasticity and is adapted to install and lock six groups of single-piece dies. Then install the die body formed by six groups of single-piece die combinations inside the washer, and relatively limit the positions of the die body and the rear cover through the guiding pin;

[0017] The front cover and the rear cover are successively distributed on both sides of the gasket. Countersunk screws are installed in both the first screw countersunk hole and the second screw countersunk hole. The countersunk screws connect the front cover or the rear cover to the gasket respectively. The center lines of the cone head, the middle hole and the tip end are aligned in sequence to ensure that the working extrusion paths of the cone head for each single flap die are the same;

[0018] S2. Before the diameter expansion, the output piston rod of the hydraulic cylinder is connected to the push-pull disk. The retraction of the push-pull disk drives the die core cone to retract. The large end composed of six groups of single flap dies of the die body is relatively fixed under the clamping force of the locking ring. The conical surface of the installation hole in the die body fits tightly against the conical surface of the cone head and contracts, so that the tip end is in a contracted state to facilitate the insertion of the tip end into the inner diameter of the steel pipe end;

[0019] Lubricating oil is injected along the oil injection nozzle to ensure the locking effect of the locking ring and reduce the friction during diameter expansion;

[0020] S3. During the diameter expansion, the output piston rod of the hydraulic cylinder extends, pushing the push-pull disk and driving the die core cone to move axially along the installation hole. Under the action of the conical surface of the cone head, each single flap die expands radially outward, that is, the steel pipe end is expanded in diameter. After the stroke of the output piston rod of the hydraulic cylinder reaches the preset value, the pressure is maintained and the operation stops;

[0021] S3. After the diameter expansion, the output piston rod of the hydraulic cylinder retracts, the push-pull disk retracts and drives the cone head to retract. The large end composed of six groups of single flap dies of the die body is relatively fixed under the clamping force of the locking ring. The conical surface of the installation hole in the die body fits tightly against the conical surface of the cone head and contracts, so that the tip end is in a contracted state to facilitate the withdrawal of the tip end from the steel pipe end.

[0022] Compared with the prior art, the present invention can achieve the following technical effects:

[0023] By adopting the method of equal-spacing expansion after the die is extruded, the present invention aims at the problems of excessive cost caused by using a fixed diameter-expanding die to extrude and expand the hole in the existing method, and the need to frequently replace the diameter-expanding die to meet the diameter-expanding requirements of different steel pipe ends.

[0024] The present invention first uses a locking ring to limit the die body at the large end, and then adopts the method of pushing in and sending out the cone head to perform head extrusion on the tip end to achieve diameter expansion. The cone head does not need to directly contact the steel pipe end, avoiding the quality problem of damaging the steel pipe end and ensuring the connection effect of the steel pipe in the later stage.

[0025] The present invention limits the positions of the die core cone and the die body through the installation of the main body disk, ensuring the coaxial effect between the two to guarantee the actual diameter expansion quality. The vertical effect of the connection is ensured by installing the alignment pin to eliminate the error generated when the die core cone enters and exits. Then, countersunk screws are installed in the first screw counterbore and the second screw counterbore for limit installation to achieve the effect of fixed connection. An oil injection nozzle is provided to be suitable for adding lubricating oil to ensure the high-frequency repeated effect of the overall entry and exit.

[0026] The structure of the present invention is simple and novel, with strong safety and reliability. Moreover, the setting cost is relatively low compared with the prior art, and the response speed is fast, which can effectively improve the work efficiency. Brief Description of the Drawings

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0028] Figure 1 It is a working schematic diagram of the die core cone in the die body in Embodiment 1 of the present invention;

[0029] Figure 2 It is a cross-sectional view of the die body in Embodiment 2 of the present invention;

[0030] Figure 3 It is a side view of the die core cone in Embodiment 2 of the present invention;

[0031] Figure 4 It is a side view of the rear cover in Embodiment 2 of the present invention;

[0032] Figure 5 It is a state diagram of the un-expanded state in Embodiment 2 of the present invention;

[0033] Figure 6 It is a state diagram during the diameter expansion in Embodiment 2 of the present invention.

[0034] In the figure: 1. Die body; 11. Single-piece die; 12. Installation hole; 13. Tip end; 14. Large end; 2. Die core cone; 21. Cone head; 22. Cylinder; 23. Push-pull disk; 3. Steel pipe end; 4. Locking ring; 5. Main body disk; 51. Rear cover; 52. Washer; 53. Front cover; 54. Middle hole; 55. Oil injection nozzle; 56. First screw counterbore; 57. Second screw counterbore; 6. Alignment pin; 7. Output piston rod. Detailed Embodiments

[0035] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0036] The application principle of the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0037] Embodiment 1

[0038] As Figures 1 to 3 shown, an implementation scheme of the present invention is a die for expanding the end of a seamless steel pipe with a small diameter, which includes a die body 1 and a die core cone 2. The die core cone 2 includes a cone head 21. The die body 1 includes single-segment dies 11 and an installation hole 12. There are multiple groups of single-segment dies 11, and one side of the single-segment dies 11 opposite to each other surrounds to form the installation hole 12. One end of multiple groups of single-segment dies 11 is adapted to be installed in the end of the steel pipe 3, and the cone head 21 is adapted to be installed in the installation hole 12 and squeeze each group of single-segment dies 11 to expand radially.

[0039] As Figure 2 shown, the die body 1 includes a large end portion 14 and a pointed end portion 13. A circumferential groove is provided outside the large end portion 14 formed by multiple groups of single-segment dies 11. The circumferential groove is the upper concave portion in Figure 2 and surrounds its outer side surface. A locking ring 4 is installed in the circumferential groove. The locking ring 4 is adapted to relatively fix multiple groups of single-segment dies 11. The locking ring 4 is multiple groups of juxtaposed snap rings, which ensures that the movement and splitting effect of the large end portion 14 is restricted.

[0040] The die core cone 2 further includes a cylinder 22. The cylinder 22 is integrally provided with the cone head 21. A push-pull disc 23 is installed at one end of the cylinder 22 away from the cone head 21. The push-pull disc 23 is fixedly connected to the cylinder 22. A driving member is installed on the side of the push-pull disc 23 facing away from the cylinder 22. The driving member is adapted to connect to the push-pull disc 23 and push the push-pull disc 23 to move.

[0041] The outer end of the push-pull disc 23 is installed with the output piston rod 7 of a hydraulic cylinder. The output effect of the hydraulic cylinder can, on the one hand, limit the output time of the hydraulic cylinder through electronic control time, or provide a hydraulic circuit to limit the output time of the output piston rod 7, so as to further control the range of the output piston rod 7 to reach a preset value. This can be solved by traditional technical methods and will not be elaborated here.

[0042] Before the diameter expansion, the output piston rod 7 retracts, the push-pull disc 23 drives the die core cone 2 to retract. Under the clamping force of the locking ring 4, the inner conical surface of each single-segment die 11 of the die body 1 is tightly attached to the conical surface of the die core cone 2 and contracts, so that the diameter expansion die is in a contracted state, which is beneficial for the working part of the diameter expansion die body 1 to enter the inner diameter of the steel pipe.

[0043] When the diameter is expanded, the output piston rod 7 extends to push the push-pull disc 23, and the push-pull disc 23 pushes the die core cone 2 to move axially. Under the action of the conical surface of the die core cone 2, the single-piece die 11 moves radially outward to expand the end of the steel pipe 3. After the stroke of the output piston rod 7 reaches the preset value, the pressure is maintained and stopped;

[0044] Embodiment 2

[0045] As Figures 4 to 6 shown, this is another implementation of the present invention. On the basis of Embodiment 1, it is defined that the die body 1 is composed of six single-piece dies 11, the cone head 21 is a six-sided cone, the mounting hole 12 is a six-cone hole, the diameter of the pointed end 13 is adapted to the inner diameter of the end of the steel pipe 3, and the taper of the cone head 21 and the mounting hole 12 is the same. A main body disc 5 is installed outside the die body 1. The main body disc 5 includes a rear cover 51, a washer 52 and a front cover 53. Intermediate holes 54 are provided on both the rear cover 51 and the front cover 53, and the aperture of the intermediate holes 54 is larger than the diameters of the cylinder 22 and the pointed end 13. The rear cover 51 and the front cover 53 are arranged in parallel. The large end 14 of the die body 1 is installed between the front cover 53 and the rear cover 51, and the diameter of the large end 14 is smaller than the inner diameter of the washer 52.

[0046] In order to reduce the problem of excessive friction during the entry and exit of the cone head 21, an oil injection nozzle 55 is provided at the upper end of the washer 52. The oil injection nozzle 55 is in the shape of a stepped hole and is suitable for injecting oil from the outside to the inside.

[0047] A first positioning hole is provided on the side of each single-piece die 11 facing away from the end of the steel pipe 3, and a second positioning hole is provided on the rear cover 51. The first positioning hole is adapted to the second positioning hole, and a guide pin 6 is installed between the first positioning hole and the second positioning hole. The guide pin 6 is suitable for relatively fixing the rear cover 51 and the single-piece die 11.

[0048] Furthermore, a first countersunk screw hole 56 is provided on the rear cover 51, a second countersunk screw hole 57 is provided on the front cover 53, a transition hole is provided on the washer 52, the first countersunk screw hole 56 and the second countersunk screw hole 57 are symmetrically distributed and are suitable for installing countersunk screws. The countersunk screws are suitable for being installed in the first countersunk screw hole 56 or the second countersunk screw hole 57 respectively and connected in the transition hole.

[0049] A method for using a small-diameter seamless steel pipe end expanding die includes the following steps:

[0050] S1. According to the design of the drawing, the driving member includes a hydraulic cylinder. The moving range of the output piston rod 7 of the hydraulic cylinder is set as a preset value. The size of the preset value is the same as the moving range of the cone head 21, and when the output piston rod 7 reaches the preset value, the extrusion of the cone head 21 causes the diameter of the pointed end 13 to expand radially to be adapted to the inner diameter required for expanding the end of the steel pipe 3;

[0051] Installation of the die body 1: Assemble and symmetrically install the six groups of single-segment dies 11. Install them on the circumferential groove through the locking ring 4. The locking ring 4 has elasticity and is suitable for installing and locking the six groups of single-segment dies 11. Then install the die body 1 composed of the six groups of single-segment dies 11 into the washer 52, and relatively limit the positions of the die body 1 and the rear cover 51 through the alignment pins 6.

[0052] Arrange the front cover 53 and the rear cover 51 on both sides of the washer 52 in sequence. Install countersunk screws in both the first countersunk screw hole 56 and the second countersunk screw hole 57. The countersunk screws connect the front cover 53 or the rear cover 51 with the washer 52 respectively. Then determine the installation in sequence to make the center lines of the cone head 21, the middle hole 54, and the tip part 13 coincide, ensuring that the working extrusion paths of the cone head 21 for each single-segment die 11 are the same.

[0053] S2. Before expanding the diameter, the output piston rod 7 of the hydraulic cylinder is connected to the push-pull disk 23. The retraction of the push-pull disk 23 drives the die core cone 2 to retract. The large end part 14 composed of the six groups of single-segment dies 11 of the die body 1 is relatively fixed under the clamping force of the locking ring 4. The conical surface of the installation hole 12 in the die body 1 closely adheres to the conical surface of the cone head 21 and contracts, making the tip part 13 in a contracted state to facilitate the insertion of the tip part 13 into the inner diameter of the steel pipe end 3.

[0054] Inject lubricating oil along the oil injection nozzle 55 to ensure the locking effect of the locking ring 4 and reduce the friction during diameter expansion.

[0055] S3. During diameter expansion, the output piston rod 7 of the hydraulic cylinder extends, pushing the push-pull disk 23 and driving the die core cone 2 to move axially along the installation hole 12. Under the action of the conical surface of the cone head 21, each single-segment die 11 expands radially outward, that is, expands the diameter of the steel pipe end 3. After the stroke of the output piston rod 7 of the hydraulic cylinder reaches the preset value, stop and maintain pressure.

[0056] S3. After diameter expansion, the output piston rod 7 of the hydraulic cylinder retracts, the push-pull disk 23 retracts and drives the cone head 21 to retract. The large end part 14 composed of the six groups of single-segment dies 11 of the die body 1 is relatively fixed under the clamping force of the locking ring 4. The conical surface of the installation hole 12 in the die body 1 closely adheres to the conical surface of the cone head 21 and contracts, making the tip part 13 in a contracted state to facilitate the withdrawal of the tip part 13 from the steel pipe end 3.

[0057] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention.

[0058] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only includes an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A die for expanding the end of a seamless steel pipe with a small diameter, characterized in that: It includes a mold body (1) and a mold core cone (2). The mold core cone (2) includes a cone head (21). The mold body (1) includes single-piece molds (11) and mounting holes (12). Multiple groups of the single-piece molds (11) are provided and surround to form the mounting hole (12) on the opposite side. One end of multiple groups of the single-piece molds (11) is adapted to be installed in the steel pipe end (3), and the cone head (21) is adapted to be installed in the mounting hole (12) and extrude each group of single-piece molds (11) to expand radially; The mold core cone (2) further includes a cylinder (22). The cylinder (22) is integrally provided with the cone head (21). A push-pull disk (23) is installed at one end of the cylinder (22) away from the cone head (21). The push-pull disk (23) is fixedly connected to the cylinder (22). A driving member is installed on the side of the push-pull disk (23) facing away from the cylinder (22). The driving member is adapted to connect to the push-pull disk (23) and push the push-pull disk (23) to move; The mold body (1) includes a large end portion (14) and a pointed end portion (13). A circumferential groove is provided outside the large end portion (14) formed by multiple groups of the single-piece molds (11). A locking ring (4) is installed in the circumferential groove. The locking ring (4) is adapted to relatively fix multiple groups of the single-piece molds (11); A main body disk (5) is installed outside the mold body (1). The main body disk (5) includes a rear cover (51), a gasket (52) and a front cover (53). Intermediate holes (54) are provided on both the rear cover (51) and the front cover (53). The diameters of the intermediate holes (54) are both larger than the diameters of the cylinder (22) and the pointed end portion (13). The rear cover (51) and the front cover (53) are arranged in parallel. The large end portion (14) of the mold body (1) is installed between the front cover (53) and the rear cover (51). The diameter of the large end portion (14) is smaller than the inner diameter of the gasket (52); An oil injection nozzle (55) is provided at the upper end of the gasket (52). The oil injection nozzle (55) is in the shape of a stepped hole and is adapted to inject oil from the outside to the inside; A first positioning hole is provided on the side of each group of single-piece molds (11) facing away from the steel pipe end (3). A second positioning hole is provided on the rear cover (51). The first positioning hole is adapted to the second positioning hole. A guiding pin (6) is installed between the first positioning hole and the second positioning hole. The guiding pin (6) is adapted to relatively fix the rear cover (51) and the single-piece molds (11); A first screw counterbore (56) is provided on the rear cover (51). A second screw counterbore (57) is provided on the front cover (53). A transition hole is provided on the gasket (52). The first screw counterbore (56) and the second screw counterbore (57) are symmetrically distributed and are adapted to install countersunk head screws. The countersunk head screws are adapted to be installed in the first screw counterbore (56) or the second screw counterbore (57) respectively and connected in the transition hole; The mold body (1) includes six groups of single-piece molds (11). The cone head (21) is a six-sided cone, the mounting hole (12) is a six-cone hole, the diameter of the pointed end (13) is adapted to the inner diameter of the steel pipe end (3), and the taper of the cone head (21) is consistent with that of the mounting hole (12).

2. A method for using a die for expanding the end of a seamless steel pipe with a small diameter as described in claim 1, characterized in that: It includes the following steps: S1. According to the design of the drawing, the driving part includes a hydraulic cylinder. The moving range of the output piston rod (7) of the hydraulic cylinder is set to a preset value. The size of the preset value is the same as the moving range of the cone head (21). When the output piston rod (7) reaches the preset value, the extrusion of the cone head (21) causes the diameter of the pointed end (13) expanding radially to be adapted to the required inner diameter of the expanded diameter of the steel pipe end (3). Install the mold body (1): Assemble and symmetrically install the six groups of single-piece molds (11), install them on the circumferential groove through the locking ring (4). The locking ring (4) has elasticity and is suitable for installing and locking the six groups of single-piece molds (11), and install the mold body (1) composed of the six groups of single-piece molds (11) in the washer (52), and then relatively limit the positions of the mold body (1) and the rear cover (51) through the alignment pin (6). Arrange the front cover (53) and the rear cover (51) on both sides of the washer (52) in sequence. Install countersunk head screws in both the first screw counterbore (56) and the second screw counterbore (57). The countersunk head screws connect the front cover (53) or the rear cover (51) to the washer (52) respectively, and sequentially determine the installation to make the center lines of the cone head (21), the middle hole (54) and the pointed end (13) coincide, ensuring that the working extrusion of the cone head (21) has the same expansion path for each single-piece mold (11). S2. Before expanding the diameter, the output piston rod (7) of the hydraulic cylinder is connected to the push-pull disk (23). The retraction of the push-pull disk (23) drives the die core cone (2) to retract. The large end (14) composed of the six groups of single-piece molds (11) of the mold body (1) is relatively fixed under the clamping force of the locking ring (4). The conical surface of the mounting hole (12) in the mold body (1) fits tightly against the conical surface of the cone head (21) and contracts, so that the pointed end (13) is in a contracted state to facilitate the insertion of the pointed end (13) into the inner diameter of the steel pipe end (3). Inject lubricating oil along the oil injection nozzle (55) to ensure the locking effect of the locking ring (4) and reduce the friction during diameter expansion. S3. When expanding the diameter, the output piston rod (7) of the hydraulic cylinder extends, pushes the push-pull disk (23) and pushes the die core cone (2) to move axially along the mounting hole (12). Under the action of the conical surface of the cone head (21), each single-piece mold (11) moves radially outward to expand the diameter of the steel pipe end (3). After the stroke of the output piston rod (7) of the hydraulic cylinder reaches the preset value, stop and hold the pressure. After the diameter expansion, the output piston rod (7) of the hydraulic cylinder retracts, the push-pull disc (23) retracts and drives the cone head (21) to retract. The large end (14) composed of six groups of single-piece dies (11) of the die body (1) is relatively fixed under the clamping force of the locking ring (4). The conical surface of the mounting hole (12) in the die body (1) closely adheres to the conical surface of the cone head (21) and contracts, so that the pointed end (13) is in a contracted state, which is conducive to the withdrawal of the pointed end (13) from the steel pipe end (3).

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