How to salvage welded steel pipe scrap

Abstract

To provide a scrap recovery method of a welding steel pipe which removes defects of inner surface beads by a grinder attached with an abrasive material, so as to reduce a welding steel pipe to be discarded.SOLUTION: A scrap recovery method of a welding steel pipe includes the steps of: molding a steel strip into an open tube by multistage molding roll; heating an end face weld part of the open tube by a high frequency induction heating coil; press-bonding the heated end face weld part by squeeze rolling; an inner surface inspection step by visual inspection; and removing defects of the inner surface beads by a grinder.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing welded steel pipes in which a strip of steel is bent into a cylindrical shape, heated by high-frequency induction current, and welded at both ends of the strip of steel, and relates to a scrap salvage method for welded steel pipes that involves removing the inner bead that occurs inside the pipe. [Background technology]

[0002] As one method for manufacturing metal pipes, a method for manufacturing welded steel pipes is generally known, in which a metal strip is formed into a cylindrical shape to form an open pipe, and both end faces of the open pipe are welded to form a pipe shape. The welding process in this manufacturing method is performed by raising the end faces of the open pipe to a melting temperature using a high-frequency induction heating coil, and pressure welding both end faces of the open pipe with a squeeze roll. In addition, in this welding method, when both end faces of the open pipe are pressure welded, weld beads, which are raised weld marks, are generated.

[0003] For example, Patent Document 1 discloses a method of crushing a weld bead (inner surface bead) formed on the inner surface of a welded steel pipe with a jig to smooth the inner surface of the welded steel pipe. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6058410 Summary of the Invention [Problem to be solved by the invention]

[0005] The device for smoothing the inner bead of a welded steel pipe as shown in Patent Document 1 can easily smooth the inner bead of a welded steel pipe. In addition, such inner beads may be removed by known means such as cutting, or the process of removing the inner bead may not be necessary for welded steel pipes whose product specifications permit the inner bead.

[0006] However, even after the above-mentioned inner bead removal process, there was a certain percentage of defects, such as cases where the inner bead could not be completely removed and an inner bead of a standard height or more remained, or the inner bead partially peeled off from the inner wall surface of the welded steel pipe, etc. Furthermore, when such defects in the inner bead were detected by visual inspection, it was common to discard the welded steel pipe itself, and improving the yield was an issue.

[0007] Therefore, the present invention has been made in consideration of the above-mentioned circumstances, and provides a method for salvaging welded steel pipes by removing defects in the inner bead using a grinder equipped with an abrasive material, in order to reduce the number of welded steel pipes that are discarded. [Means for solving the problem]

[0008] The present invention has been made to achieve the above object and has the following features.

[0009] The scrapping method for welded steel pipes according to the present invention includes the steps of forming a steel strip into an open pipe using multiple forming rolls, heating an end face weld of the open pipe using a high frequency induction heating coil, crimping the heated end face weld using a squeeze roll, cutting the welded steel pipe to which the end face weld is joined to a maximum length of 6 m, inspecting the inner surface by visually and / or by feeling for any steps with the fingers, and removing any inner bead defects using a grinder, the grinder being equipped with an air motor and connected to one end of a piping, The grinder has a cylindrical body, a cylindrical abrasive is attached to the grinder, the grinder body has a cylindrical housing that covers the air motor, the maximum outer diameter of the housing is smaller than the inner diameter of the welded steel pipe and the outer diameter of the abrasive and is larger than the outer diameter of the piping pipe, and the abrasive is disposed coaxially with the rotation axis of the air motor. It is characterized by:

[0011] In the method for scrapping and salvaging a welded steel pipe according to the present invention, it is preferable that a valve is connected to the other end of the piping pipe.

[0013] The above summary of the invention does not list all of the features necessary for the present invention, and any subcombination of these features may also constitute an invention. Effect of the Invention

[0014] According to the present invention, defects in the inner bead can be easily removed, and the yield in the production of welded steel pipes can be improved. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a flow chart showing a manufacturing process for a welded steel pipe according to the present embodiment. [Diagram 2] FIG. 1 is a perspective view showing a welding process according to an embodiment of the present invention; [Diagram 3] 1 is a cross-sectional view showing a process for removing an inner bead defect according to the present embodiment; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Preferred embodiments for carrying out the present invention will be described below with reference to the drawings. Note that the following embodiments do not limit the inventions according to the claims, and all of the combinations of features described in the embodiments are not necessarily essential to the solution of the invention.

[0017] FIG. 1 is a flow diagram showing the manufacturing process of a welded steel pipe according to this embodiment, FIG. 2 is a perspective view showing the welding process according to this embodiment, and FIG. 3 is a cross-sectional view showing the process of removing an inner bead defect according to this embodiment.

[0018] The method for scrapping a welded steel pipe according to the present embodiment is carried out by the steps shown in Fig. 1 and is applied to products that have been rejected by visual inspection after a welded steel pipe manufacturing process. The welded steel pipe according to the present embodiment includes stainless steel pipes, carbon steel pipes, alloy steel pipes, etc.

[0019] First, the manufacturing method of the welded steel pipe in this embodiment will be briefly described. In the following description, the terms "upstream" and "downstream" refer to the upstream and downstream directions of the steel material in the forming machine in the manufacturing process of the welded steel pipe.

[0020] In the manufacturing method of the welded steel pipe in this embodiment, first, as shown in FIG. 1, a steel plate is cut to a predetermined width according to the outer diameter of the pipe to be manufactured, to prepare a steel strip as a material for the welded steel pipe. Then, if necessary, the longitudinal end of the cut steel strip is welded to the end portion already loaded in the forming machine, to prepare a steel strip of a length that can continuously manufacture the welded steel pipe. Next, the flat steel strip is loaded into the forming machine and gradually formed into a cylindrical shape by multi-stage forming rolls. The steel strip formed into a cylindrical shape is formed into an open pipe 1 with a part open as shown in FIG. 2, with both ends in the width direction facing each other. As shown in FIG. 2, the open pipe 1 with a part open is pressed at both end faces 1a, 1b by the squeeze roll 3 to form a contact point 1c.

[0021] As shown in FIG. 2, a high-frequency induction heating coil 2 is installed upstream of the squeeze roll 3 so as to surround the outer circumference of the open pipe 1, and a high-frequency current flows through the high-frequency induction heating coil 2. Therefore, a high-frequency magnetic field is generated from the high-frequency induction heating coil 2, and an eddy current flows through the open pipe 1 along the contact point 1c. The contact point 1c is rapidly heated by the Joule heat of the eddy current generated at this time, and reaches its melting temperature. The contact point 1c heated and melted by the high-frequency induction heating coil 2 is crimped and joined when passing through the squeeze roll 3, completing the welding of both end faces 1a, 1b. When the inner surface of the welded steel pipe 1d formed in this way is crimped by the squeeze roll 3, a linear inner bead 10 is generated at the joint between both end faces 1a, 1b.

[0022] The inner bead 10 generated on the inner surface of the welded steel pipe 1d is removed by means of crushing, cutting, etc., as necessary. If the inner bead 10 is permitted in terms of the specifications of the welded steel pipe as a product, the process of removing the inner bead 10 by crushing, cutting, etc. can be omitted. The welded steel pipe is then cut to the specified length of the product, and any bends exceeding the standard dimensions are corrected, and heat treatment, etc., is performed if necessary.

[0023] After going through the above-mentioned series of manufacturing processes, the completed welded steel pipe 1e is visually inspected for appearance and checked for unevenness by the sense of touch of the fingers, and the presence or absence of scratches and defects of the inner bead are checked. In this case, if the inner bead 10 is removed but the inner bead 10 is still at a reference height or higher, or if the inner bead 10 is not removed but is partially peeled off from the inner surface of the completed welded steel pipe 1e, it has been customary to discard the pipe as a defective product. In this embodiment, a scrapping process is provided for the completed welded steel pipe 1e that is determined to be defective by visual inspection, thereby reducing the number of completed welded steel pipes 1e that are discarded as defective products.

[0024] Next, the scrap salvage process in this embodiment will be described.

[0025] As shown in FIG. 3, the correction tool 20 used in the scrap salvage process in this embodiment includes a grinder 21 driven by compressed air, an abrasive 22 attached to the rotating shaft of the grinder 21, a piping 23 connected to the grinder 21, a compressor 26 that supplies compressed air to the grinder 21 via the piping 23, an air hose 25 that connects the piping 23 and the compressor 26, and a valve 24 that controls the flow of compressed air from the compressor 26.

[0026] The grinder 21 is a straight type grinder having a cylindrical body and a rotating shaft coaxial with the body, and the outer diameter of the cylindrical body is smaller than the inner diameter of the completed welded steel pipe 1e from which the inner bead 10 is to be removed. The grinder 21 uses compressed air provided from a compressor 26 via a piping 23 to drive an air motor and rotates an abrasive material 22 attached to the rotating shaft. As an example, the air motor used in the grinder 21 may be a rotary type air motor that is composed of a rotor incorporating multiple vanes that are blade portions that receive compressed air and a housing that surrounds the rotor, and in which the rotor is eccentrically attached to the housing.

[0027] The abrasive 22 is a cylindrical grindstone attached to the rotating shaft of the grinder 21, and as an example, a grindstone with alumina or silicon carbide as abrasive grains can be used. The outer diameter of the cylindrical abrasive 22 is smaller than the inner diameter of the completed welded steel pipe 1e from which the inner bead 10 is removed, and is larger than the outer diameter of the main body of the grinder 21. In this embodiment, the abrasive 22 is described as being a grindstone with alumina or silicon carbide as abrasive grains, but the abrasive 22 is not limited to this, and a flap wheel in which abrasive cloths are radially bundled and fixed may be used. The flap wheel has a self-replenishing effect that allows grinding with a new abrasive grain surface at all times during grinding work, and since there is a large gap between the abrasive cloths, clogging is reduced, making it suitable for continuous grinding work.

[0028] The piping pipe 23 is a pipe having an outer diameter smaller than the outer diameter of the cylindrical body of the grinder 21, and various metal pipes and synthetic resin pipes can be used. The grinder 21 is connected to one end of the piping pipe 23, and the axis of the piping pipe 23 and the axis of the cylindrical body of the grinder 21 are fixed so as to be coaxial. The piping pipe 23 and the grinder 21 are connected by, for example, a piping joint having a pipe taper thread, and the connection is made using a seal tape or the like as necessary to prevent leakage of compressed air. The length of the piping pipe 23 is appropriately selected according to the length of the completed welded steel pipe 1e from which the inner bead 10 is to be removed. The piping pipe 23 also functions as a handle when performing the work of removing the inner bead 10. Therefore, the total length of the piping pipe 23 requires the length of the area where the inner bead 10 is to be removed, as well as the length of the part that serves as the handle. The length of the handle part needs to be about 50 cm, which is long enough for the worker to hold it with both hands. For example, if the area to be removed from the inner bead 10 is 3 m, the total length of the piping pipe 23, including the handle, needs to be 3.5 m. The piping pipe 23 may be a single continuous pipe, or may be made by joining multiple divided pipes together.

[0029] A valve 24 is connected to the other end of the piping pipe 23, and the compressed air supplied to the grinder 21 is controlled by opening and closing the valve 24. The valve 24 is, for example, a ball valve, butterfly valve, globe valve, or other valve capable of controlling gas. As described above, the piping pipe 23 can be used as a handle when removing the inner bead 10, so that the worker can operate the valve 24 by himself or herself during the removal of the inner bead 10 to control the grinder 21. The piping pipe 23 and the valve 24 are connected by a piping joint having, for example, a pipe taper thread, and a sealing tape or the like is used as necessary to prevent leakage of the compressed air.

[0030] The valve 24 and the compressor 26 are connected by an air hose 25. The air hose 25 is appropriately selected from those having pressure resistance corresponding to the output pressure of the compressor 26.

[0031] Next, the process of removing defects in the inner bead 10 in this embodiment will be described.

[0032] First, the completed welded steel pipe 1e, whose inner bead 10 has been determined to be defective in the visual inner surface inspection process, is fixed securely to a workbench so that it does not move or rotate during the removal of the inner bead 10. Next, a grinder 21 equipped with an abrasive 22 is inserted into the inside of the completed welded steel pipe 1e from one end. The worker holds the piping pipe 23 as a handle, opens the valve 24, and operates the grinder 21. Next, the abrasive 22, which is rotated by the supplied compressed air, is pressed against the inner bead 10 and moved back and forth to grind and remove the remaining inner bead 10. At this time, if the abrasive 22 does not reach all of the inner bead 10 by the removal work only from one end of the completed welded steel pipe 1e, the grinder 21 equipped with the abrasive 22 is inserted from the other end of the completed welded steel pipe 1e, and the removal work is performed from both ends, so that the entire inner bead 10 of the completed welded steel pipe 1e can be removed. For example, in this embodiment, when performing the work of removing the inner bead 10 of a completed welded steel pipe 1e having a maximum length of 6 m, the required length of the piping pipe 23 is 3.5 m in total, including the handle portion. By using the piping pipe 23 with such a total length to perform the work of removing the inner bead 10 from both ends of the completed welded steel pipe 1e, the work of removing the entire inner bead 10 over a maximum length of 6 m can be performed.

[0033] After the process of removing defects from the inner bead 10, the welded steel pipe is again visually inspected and checked for any unevenness by touching with the fingers, as shown in Figure 1. If no problems are found, a gauge inspection is performed to check whether the inner diameter dimension is within the standard dimensions.

[0034] As described above, in this embodiment, by providing a defect removal process for the inner bead 10 rather than immediately discarding welded steel pipes that are found to be defective by visual inspection, the number of completed welded steel pipes 1e that are discarded can be reduced.

[0035] In the above description, the grinder 21 is described as having an air motor driven by compressed air, but the grinder 21 is not limited to this and may be one having an electric motor. In that case, the compressor 26, the air hose 25, and the valve 24 are not necessary, and the power cord of the electric motor is inserted inside the piping 23. It is clear from the claims that such modified or improved embodiments are also included within the technical scope of the present invention. [Explanation of symbols]

[0036] 1 Open Tube 1a, 1b end face 1c contact point 1d Welded Steel Pipe 1e Finished welded steel pipe 2 High frequency induction heating coil 3 Squeeze Roll 10 Inner bead 20 Modification tools 21 Grinder 22 Abrasives 23 Plumbing Pipes 24 Valve 25 Air Hose 26 Compressor

Claims

1. forming the strip steel into an open tube by multiple forming rolls; Heating the end face weld of the open pipe by a high frequency induction heating coil; a step of pressing the heated end face welded portion with a squeeze roll; cutting the welded steel pipe to which the end face welds have been joined to a maximum length of 6 m; An inner surface inspection process by visually and / or by touching the inner surface of the substrate; and removing the inner bead defects by a grinder. The grinder includes an air motor and is connected to one end of a plumbing pipe; The grinder has a cylindrical body; The grinder is equipped with a cylindrical abrasive material, The main body of the grinder has a cylindrical housing that covers the air motor, The maximum outer diameter of the housing is smaller than the inner diameter of the welded steel pipe and the outer diameter of the abrasive material, and is larger than the outer diameter of the piping pipe; 13. A method for recovering scrap from welded steel pipes, comprising the steps of: (a) removing the abrasive material from the air motor;

2. The method for scrapping a welded steel pipe according to claim 1, A valve is connected to the other end of the piping.

2. A method for scrapping welded steel pipes, comprising:

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