Method for welding steel bar and method for manufacturing closed annular reinforcement

Abstract

To provide a welding method of a steel bar in which the setting of welding conditions is relatively easy, the scattering of high temperature spatters can be suppressed, and sufficient welding strength can be obtained.SOLUTION: The rod steel welding method includes setting the first deformed bar steel 11 and the second deformed bar steel 12 such that end faces thereof are brought into contact with each other, energizing the first deformed bar steel 11 and the second deformed bar steel 12 to heat and melt the end face of the first deformed bar steel 11, the end face of the second deformed bar steel 12 and vicinities thereof, instantaneously joining the first deformed bar steel 11 and the second deformed bar steel 12 by making a compression pressure in an axial direction act on the first deformed bar steel 11 and the second deformed bar steel 12 after elapse of a first predetermined time from start of energization, and stopping energization to the first deformed bar steel 11 and the second deformed bar steel 12 and holding the joined first deformed bar steel 11 and second deformed bar steel 12 as they are for a second predetermined time.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for welding steel bars and a method for manufacturing a closed annular reinforcement. [Background technology]

[0002] Closed circular reinforcement bars used in reinforced concrete structures are manufactured by bending steel bars (reinforcing bars), especially deformed steel bars (deformed reinforcing bars) with irregularities on the surface to increase the bond strength with concrete, into a ring shape and joining both ends. The ends of such deformed steel bars are generally joined by butt welding, especially flash butt welding, which can provide a relatively high joint (weld) strength. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-126875 Summary of the Invention [Problem to be solved by the invention]

[0004] In flash butt welding, the end faces of steel bars, to which a large current is applied during the flash process, repeatedly come into contact and then go out of contact, causing a large amount of high-temperature spatter to fly from the end faces of the steel bars. Therefore, the installation of shutters or sheets to protect the workers and the area around the welding machine from the flying spatter has been required. Furthermore, some of the flying spatter adheres to and accumulates on the welding machine's electrodes, etc. This requires frequent removal of the accumulated spatter, which has been one of the factors hindering productivity improvements for products manufactured using flash butt welding (e.g., closed-loop annular reinforcement). Furthermore, it is difficult to set the conditions for maintaining the appropriate flashing state with flash butt welding, which has also posed a problem in terms of the yield of products manufactured using flash butt welding.

[0005] Therefore, an object of the present invention is to provide a method for welding steel bars in which the welding conditions can be set relatively easily, the scattering of high-temperature spatter can be suppressed, and sufficient weld strength can be obtained.

[0006] Another object of the present invention is to provide a method for manufacturing closed circular muscles that can improve productivity and yield compared to conventional methods. [Means for solving the problem]

[0007] One aspect of the present invention provides a novel method for welding steel bars, comprising: a first step of setting a first steel bar and a second steel bar so that their end faces are in contact with each other; a second step of passing current through the first steel bar and the second steel bar while maintaining the end faces in contact with each other, thereby heating and melting the end faces of the first steel bar, the end faces of the second steel bar, and their vicinities; a third step of, after a first predetermined time has elapsed since the start of current passage, applying axial compressive pressure to the first steel bar and the second steel bar while maintaining the current passage through the first steel bar and the second steel bar, thereby instantaneously joining the first steel bar and the second steel bar; and a fourth step of stopping the current passage through the first steel bar and the second steel bar and holding the joined first steel bar and the second steel bar in this state for a second predetermined time.

[0008] According to another aspect of the present invention, there is provided a novel method for manufacturing a closed annular steel bar, which includes a bending process for bending a predetermined length of deformed steel bar into a ring shape, a welding process for welding both ends of the bent deformed steel bar to be processed, and a scraping process for scraping off bulges generated at the welded portions of the deformed steel bar to be processed. The welding process includes clamping one end portion of the deformed steel bar to be processed, including the one end face, with a fixed electrode so that the one end face and the other end face of the deformed steel bar to be processed are in contact, and clamping the other end portion of the deformed steel bar to be processed, including the other end face, with a movable electrode; holding the movable electrode so that the one end face and the other end face do not separate, and passing electricity through the fixed electrode and the movable electrode to the one end portion and the other end portion, thereby heating and melting the one end face, the other end face and their vicinity; after a first predetermined time has elapsed from the start of current flow, applying a driving force to the movable electrode while maintaining current flow to the one end portion and the other end portion, thereby instantaneously moving the movable electrode toward the fixed electrode, thereby instantaneously joining the one end portion and the other end portion; and stopping current flow to the one end portion and the other end portion and holding the movable electrode in the moved position for a second predetermined time. [Effects of the Invention]

[0009] According to one aspect of the present invention, it is possible to provide a method for welding steel bars in which the welding conditions can be set relatively easily, the scattering of high-temperature spatter can be suppressed, and sufficient weld strength can be obtained.

[0010] According to another aspect of the present invention, a method for manufacturing a closed circular muscle can be provided that can improve productivity and yield compared to conventional techniques. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram illustrating a configuration of a main part of an example of a welding machine. [Figure 2] 3A to 3C are diagrams for explaining a method for welding steel bars using the welding machine. [Figure 3] 3A to 3C are diagrams for explaining a method for welding steel bars using the welding machine. [Figure 4] 3A to 3C are diagrams for explaining a method for welding steel bars using the welding machine. [Figure 5] 3A to 3C are diagrams for explaining a method for welding steel bars using the welding machine. [Figure 6] 3A to 3C are diagrams for explaining a method for welding steel bars using the welding machine. [Figure 7] FIG. 4 is a diagram showing the results of a tensile test on joined (welded) first and second steel bars. [Figure 8] FIG. 1 is a diagram showing a closed shear reinforcement bar, which is an example of a closed annular reinforcement bar. [Figure 9] FIG. 1 is a diagram showing an example of a deformed steel bar (a processed deformed steel bar) bent into a ring shape. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0013] Fig. 1 is a diagram showing the essential configuration of an example of a welding machine 1 used to weld together the ends of steel bars, particularly deformed steel bars. The welding machine 1 shown in Fig. 1 is a so-called butt welding machine, which is configured to weld the first deformed steel bar 11 and the second deformed steel bar 12 by passing current through the end faces of the first deformed steel bar 11 and the second deformed steel bar 12 while they are butted together and applying axial pressure (applying axial compressive pressure to both). Here, the first deformed steel bar 11 and the second deformed steel bar 12 may be two separate deformed steel bars, or may be, for example, one end portion including one end face and the other end portion including the other end face of a single deformed steel bar (a deformed steel bar to be processed) that has been bent into an annular (hoop) shape.

[0014] Referring to FIG. 1, a welding machine 1 includes a fixed electrode 2, a movable electrode 3, a driving device 4, a welding power source 5, and a control device 6.

[0015] The fixed electrode 2 is configured to be able to clamp the first deformed steel bar 11. The fixed electrode 2 includes a first lower electrode 21 having a first steel bar placing portion 21a and a first upper electrode 22 having a first steel bar pressing portion 22a. The first lower electrode 21 is fixed. The first upper electrode 22 is configured to be movable in a direction toward the first lower electrode 21 and a direction away from the first lower electrode 21 by a first actuator (not shown). The fixed electrode 2 is configured so that the first deformed steel bar 11 is placed sideways (horizontally) on the first steel bar placing portion 21a of the first lower electrode 21, and then the first upper electrode 22 moves toward the first lower electrode 21, and the first steel bar pressing portion 22a of the first upper electrode 22 presses the upper part of the outer peripheral surface of the first deformed steel bar 11, thereby clamping the first deformed steel bar 11. The fixed electrode 2 is configured so that the clamping of the first deformed steel bar 11 is released when the first upper electrode 22 moves in a direction away from the first lower electrode 21 .

[0016] The movable electrode 3 is disposed at a distance from the fixed electrode 2, is movable, and is configured to be able to clamp the second deformed steel bar 12. The movable electrode 3 has a configuration similar to that of the fixed electrode 2. The movable electrode 3 includes a second lower electrode 31 having a second steel bar placing portion 31a, and a second upper electrode 32 having a second steel bar pressing portion 32a. The second upper electrode 32 is configured to be movable toward and away from the second lower electrode 31 by a second actuator (not shown). The movable electrode 3 is configured so that the second deformed steel bar 12 is placed horizontally (horizontally) on the second steel bar placing portion 31a of the second lower electrode 31, and then the second upper electrode 32 moves toward the second lower electrode 31, and the second steel bar pressing portion 32a of the second upper electrode 32 presses the upper part of the outer peripheral surface of the second deformed steel bar 12, thereby clamping the second deformed steel bar 12. The movable electrode 3 is configured so that the second upper electrode 32 moves in a direction away from the second lower electrode 31, thereby releasing the clamping of the second deformed steel bar 12.

[0017] Here, in the welding machine 1, the axis of the first deformed steel bar 11 clamped by the fixed electrode 2 and the axis of the second deformed steel bar 12 clamped by the movable electrode 3 are positioned on the same straight line.

[0018] The driving device 4 is configured to be able to move the movable electrode 3 along the same straight line in a direction toward the fixed electrode 2 and a direction away from the fixed electrode 2. More specifically, the driving device 4 is configured to be able to hold the position of the movable electrode 3, apply a force to the movable electrode 3 in a direction toward the fixed electrode 2 to move the movable electrode 3 toward the fixed electrode 2, adjust the force acting on the movable electrode 3 in the direction toward the fixed electrode 2, and return the moved movable electrode 3 to a predetermined position.

[0019] The welding power source 5 is configured to supply welding power (low voltage, large current) to the first deformed steel bar 11 and the second deformed steel bar 12 via the fixed electrode 2 and the movable electrode 3, in other words, to pass electricity through the first deformed steel bar 11 and the second deformed steel bar 12 via the fixed electrode 2 and the movable electrode 3.

[0020] The control device 6 controls the overall operation of the welding machine 1. In this embodiment, the control device 6 is configured to be able to control the first actuator, the second actuator, and the drive device 4, and to supply welding power to the first deformed steel bar 11 and the second deformed steel bar 12 from the welding power source 5, based on operations by an operator via an operation unit (not shown).

[0021] Next, an example of a method for welding steel bars (here, deformed steel bars) using the welding machine 1 will be described with reference to FIGS.

[0022] Fig. 2 shows the standby state of the welding machine 1. As shown in Fig. 2, when the welding machine 1 is in the standby state, the movable electrode 3 is in an initial position spaced apart from the fixed electrode 2. In addition, the first upper electrode 22 of the fixed electrode 2 is spaced apart from the first lower electrode 21, and the second upper electrode 32 of the movable electrode 3 is spaced apart from the second lower electrode 31.

[0023] When welding a first deformed steel bar 11 and a second deformed steel bar 12, as shown in Figure 3, the operator first places the first deformed steel bar 11 on the first steel bar mounting portion 21a of the first lower electrode 21 of the fixed electrode 2, and places the second deformed steel bar 12 on the second steel bar mounting portion 31a of the second lower electrode 31 of the movable electrode 3, so that the end faces of the first deformed steel bar 11 and the second deformed steel bar 12 are in contact, i.e., so that the end faces of the first deformed steel bar 11 and the second deformed steel bar 12 are butted together without any gaps.

[0024] Next, the operator operates a first operating unit (not shown) of the welding machine 1. When the first operating unit is operated, the control device 6 operates the first actuator to move the first upper electrode 22 in a direction approaching the first lower electrode 21, and operates the second actuator to move the second upper electrode 32 in a direction approaching the second lower electrode 31. As a result, as shown in FIG. 4 , the first deformed steel bar 11 is clamped by the fixed electrode 2 and the second deformed steel bar 12 is clamped by the movable electrode 3 with the end faces of the first deformed steel bar 11 and the second deformed steel bar 12 in contact (butting together without any gaps). In other words, in the welding machine 1, the first deformed steel bar 11 and the second deformed steel bar 12 are set so that their end faces contact each other (butting together without any gaps). Note that in this example, the control device 6 moves the first upper electrode 22 and the second upper electrode 32. However, this is not limited to this. The first upper electrode 22 may be moved in a direction approaching the first lower electrode 21 by an operator operating a lever, etc., to clamp the first deformed steel bar 11 by the fixed electrode 2, and the second upper electrode 32 may be moved in a direction approaching the second lower electrode 31 to clamp the second deformed steel bar 12 by the movable electrode 3.

[0025] Next, the operator operates a second operating unit (not shown) of the welding machine 1. When the second operating unit is operated, the control device 6 performs welding of the first deformed steel bar 11 and the second deformed steel bar 12. Specifically, the control device 6 performs the "preheating process," "joining process," and "holding process" described below.

[0026] [Preheating process] The preheating process is a process in which current is passed through the first deformed steel bar 11 and the second deformed steel bar 12 while maintaining a contact state (butt state) between the end faces of the first deformed steel bar 11 and the second deformed steel bar 12, causing the end faces of the first deformed steel bar 11, the end faces of the second deformed steel bar 12 and their vicinity to heat and melt.

[0027] In this embodiment, the control device 6 is configured to perform the preheating step when the second operating unit is operated. Specifically, the control device 6 uses the driving device 4 to hold the movable electrode 3 so that the end faces of the first deformed steel bar 11 and the second deformed steel bar 12 do not separate, while the welding power source 5 passes current through the fixed electrode 2 and the movable electrode 3 to the first deformed steel bar 11 and the second deformed steel bar 12. As a result, a large current flows through the contact area between the end faces of the first deformed steel bar 11 and the second deformed steel bar 12, and the end faces of the first deformed steel bar 11 and the second deformed steel bar 12 and their vicinities are heated and melted, as shown by hatching in Fig. 5.

[0028] Here, holding the movable electrode 3 so that the end faces of the first deformed steel bar 11 and the second deformed steel bar 12 do not separate includes locking the movable electrode 3 and applying a predetermined holding force to the movable electrode 3. The predetermined holding force is a force in a direction toward the fixed electrode 2, and may be a force that is strong enough to prevent the movable electrode 3 from being pushed back by thermal expansion of the first deformed steel bar 11 and the second deformed steel bar 12.

[0029] While not particularly limited, for example, when the nominal diameters of the first deformed steel bar 11 and the second deformed steel bar 12 are D10 to D16, an axial compressive pressure of 0.03 to 0.10 MPa may be applied to the first deformed steel bar 11 and the second deformed steel bar 12 in the preheating step. Furthermore, the time required from the start of current application to the first deformed steel bar 11 and the second deformed steel bar 12 until the end faces of the first deformed steel bar 11 and the second deformed steel bar 12 and their vicinity reach a suitable molten state, i.e., the time required for the preheating step, may be 2.5 to 4.0 seconds. Furthermore, when the predetermined holding force is applied to the movable electrode 3, the movable electrode 3 may move slightly toward the fixed electrode 2. In this case, the amount of movement of the movable electrode 3 may be 0.5 mm or less, for example, 0.1 to 0.3 mm.

[0030] [Joining process] The joining process is a process in which, after the end faces of the first deformed steel bar 11, the end faces of the second deformed steel bar 12 and their vicinity have reached an appropriate molten state through the preheating process, in other words, after the time required for the preheating process has elapsed since the start of current flow through the first deformed steel bar 11 and the second deformed steel bar 12, the first deformed steel bar 11 and the second deformed steel bar 12 are instantaneously joined by applying a relatively large axial compressive pressure to the first deformed steel bar 11 and the second deformed steel bar 12 while maintaining current flow through the first deformed steel bar 11 and the second deformed steel bar 12.

[0031] In this embodiment, the control device 6 performs the joining process when the time required for the preheating process has elapsed since the welding power source 5 started to pass current through the fixed electrode 2 and the movable electrode 3 to the first deformed steel bar 11 and the second deformed steel bar 12. Specifically, without stopping the passage of current through the first deformed steel bar 11 and the second deformed steel bar 12, the control device 6 causes the drive device 4 to apply a predetermined driving force to the movable electrode 3, as shown in FIG. 6 , thereby instantaneously moving the movable electrode 3 a predetermined distance toward the fixed electrode 2, thereby instantaneously joining the first deformed steel bar 11 and the second deformed steel bar 12. The predetermined driving force is a force directed toward the fixed electrode 2 and is greater than the predetermined holding force.

[0032] Although not particularly limited, for example, when the nominal diameters of the first deformed steel bar 11 and the second deformed steel bar 12 are D10 to D16, an axial compressive pressure of 0.35 to 0.55 MPa may act on the first deformed steel bar 11 and the second deformed steel bar 12 in the joining process. The time required for the joining process, in other words, the time required for moving the movable electrode 3, may be about 1 second. Furthermore, the amount of movement of the movable electrode 3 in the joining process (the predetermined distance) may be 12 to 15 mm.

[0033] [Holding process] The holding process is a process in which the current flow to the first deformed steel bar 11 and the second deformed steel bar 12 is stopped, and the first deformed steel bar 11 and the second deformed steel bar 12 joined by the joining process are held in their current state for a predetermined holding time.

[0034] In this embodiment, the control device 6 performs the holding step after instantaneously moving the movable electrode 3 toward the fixed electrode 2. Specifically, the control device 6 stops the current flow from the welding power source 5 to the first deformed steel bar 11 and the second deformed steel bar 12 via the fixed electrode 2 and the movable electrode 3, and causes the drive device 4 to hold the movable electrode 3 in the position to which it was moved in the joining step for the predetermined holding time.

[0035] Although not particularly limited, when the nominal diameters of the first deformed steel bar 11 and the second deformed steel bar 12 are D10 to D16, the predetermined holding time in the holding step may be 1 to 2 seconds.

[0036] When the holding step is completed, that is, when the predetermined holding time has elapsed after the movable electrode 3 was instantaneously moved toward the fixed electrode 2, the control device 6 first operates the second actuator to move the second upper electrode 32 in a direction away from the second lower electrode 31. This releases the clamping of the second deformed steel bar 12 by the movable electrode 3. Next, the control device 6 moves (returns) the movable electrode 3 to the initial position using the drive device 4. Next, the control device 6 operates the first actuator to move the first upper electrode 22 in a direction away from the first lower electrode 21. This releases the clamping of the first deformed steel bar 11 by the fixed electrode 2. Then, when the clamping of the first deformed steel bar 11 by the fixed electrode 2 is released, the operator can remove the joined (welded) first deformed steel bar 11 and second deformed steel bar 12 from the welding machine 1.

[0037] When the first deformed steel bar 11 and the second deformed steel bar 12 are joined (welded) as described above, a bulge 13 consisting of a bump (weld bump) and a burr (weld burr) is formed at the joint (weld) between the first deformed steel bar 11 and the second deformed steel bar 12, as shown in Fig. 6 , and this bulge 13 may have a size that is 1.5 or more times the nominal diameter of the first deformed steel bar 11 and the second deformed steel bar 12. Therefore, the bulge 13 formed at the joint (weld) is scraped off after the joined (welded) first deformed steel bar 11 and the second deformed steel bar 12 are removed from the welding machine 1. Although not particularly limited, the bulge 13 is scraped off until it becomes approximately 1.1 to 1.3 times the nominal diameter of the first deformed steel bar 11 and the second deformed steel bar 12, preferably until it becomes approximately 1.1 times the nominal diameter. That is, the bulge 13 formed at the joint (welded portion) is scraped off so as to leave a part of it.

[0038] The inventors conducted a tensile test on the joined (welded) first deformed steel bar 11 and second deformed steel bar 12. The results are shown in Figure 7. Figure 7(a) shows the result of the tensile test before the bulge 13 was removed, and Figure 7(b) shows the result of the tensile test after the bulge 13 was removed. As shown in Figures 7(a) and (b), none of the multiple samples broke at the joint (weld), confirming that the above-mentioned steel bar welding method can provide sufficient joint (weld) strength, and more specifically, can provide joint (weld) strength equivalent to that obtained when flash butt welding is used.

[0039] According to the above-described method for welding steel bars, the following effects can be obtained.

[0040] The above-mentioned steel bar welding method includes setting the first deformed steel bar 11 and the second deformed steel bar 12 so that their end faces are in contact with each other (first step), passing current through the first deformed steel bar 11 and the second deformed steel bar 12 while maintaining the contact state between the end face of the first deformed steel bar 11 and the end face of the second deformed steel bar 12, thereby heating and melting the end faces of the first deformed steel bar 11 and the second deformed steel bar 12 and their vicinity (second step, preheating step), and determining the time required for the preheating step from the start of passing current through the first deformed steel bar 11 and the second deformed steel bar 12 (first predetermined time). ) has elapsed, applying axial compressive pressure to the first deformed steel bar 11 and the second deformed steel bar 12 while maintaining the flow of electricity to the first deformed steel bar 11 and the second deformed steel bar 12 to instantly join the first deformed steel bar 11 and the second deformed steel bar 12 (third step, joining step), and stopping the flow of electricity to the first deformed steel bar 11 and the second deformed steel bar 12 and holding the joined first deformed steel bar 11 and second deformed steel bar 12 in that state for the predetermined holding time (second predetermined time<first predetermined time) (fourth step, holding step).

[0041] In the above-described steel bar welding method, the end faces of the first deformed steel bar 11 and the second deformed steel bar 12 do not separate when current is applied, thereby suppressing the scattering of high-temperature spatter. Furthermore, there is no need to control unstable phenomena such as flashing. The current, the time required for the preheating process, the axial compression pressure, and the predetermined holding time can be appropriately set according to the steel type and diameter of the first deformed steel bar 11 and the second deformed steel bar 12. Therefore, compared to conventional techniques, setting welding conditions is relatively easy, and stable weld quality can be obtained. Furthermore, sufficient joint (weld) strength, i.e., joint (weld) strength comparable to that of flash butt welding, can be obtained.

[0042] Next, a method for manufacturing a closed annular reinforcement using the above-mentioned steel bar welding method will be described.

[0043] Fig. 8 is a diagram showing a welded closed type shear reinforcement, which is an example of a closed type annular reinforcement. As shown in Fig. 8, the welded closed type shear reinforcement 50 is arranged so as to surround the main reinforcement 60 in a column or beam of a reinforced concrete structure. The welded closed type shear reinforcement 50 (i.e., the closed type annular reinforcement) is manufactured mainly through bending, welding, and cutting processes.

[0044] [Bending process] The bending process is a process in which a steel bar, particularly a deformed steel bar, which has been cut to a predetermined length in advance, is bent into a ring shape (a circular hoop shape or a polygonal hoop shape). Here, as shown in Figure 9, the deformed steel bar is bent into a square hoop shape. The bending process can be performed using a known hydraulic rebar bender (not shown) or the like.

[0045] [Welding process] The welding process is a process of welding both ends of the deformed steel bar that has been bent into an annular shape in the bending process, i.e., the deformed steel bar to be processed, and can be performed using the above-mentioned welding machine 1. Basically, the welding process is performed by replacing the "first deformed steel bar 11" in the above-mentioned steel bar welding method with "one end portion 54 including one end face 52 of the deformed steel bar to be processed 51," and by replacing the "second deformed steel bar 12" in the above-mentioned butt welding of deformed steel bars with "the other end portion 55 including the other end face 53 of the deformed steel bar to be processed 51." The welding process includes the following steps (1) to (4).

[0046] (1) One end portion 54 of the processed deformed steel bar 51, including one end face 52, is clamped by a fixed electrode 2 so that one end face 52 and the other end face 53 of the processed deformed steel bar 51 are in contact (butted together without any gaps), and the other end portion 55 of the processed deformed steel bar 51, including the other end face 53, is clamped by a movable electrode 3.

[0047] (2) While the movable electrode 3 is held by the drive device 4 so that one end face 52 and the other end face 53 of the processed deformed steel bar 51 do not separate, electricity is passed through the fixed electrode 2 and the movable electrode 3 to one end portion 54 and the other end portion 55 of the processed deformed steel bar 51, causing the one end face 52, the other end face 53 of the processed deformed steel bar 51 and their vicinity to heat up and melt (this corresponds to the ``preheating process'' mentioned above).

[0048] (3) After the time required for the preheating process has elapsed since the start of current flow to the one end portion 54 and the other end portion 55 of the deformed steel bar 51 to be processed, the welding power source 5 maintains current flow to the one end portion 54 and the other end portion 55 of the deformed steel bar 51 to be processed, while the driving device 4 applies a predetermined driving force to the movable electrode 3, thereby instantly moving the movable electrode 3 a predetermined distance toward the fixed electrode 2, thereby instantly welding the one end portion 54 and the other end portion 55 of the deformed steel bar 51 to be processed (corresponding to the above-mentioned ``joining process'').

[0049] (4) The welding power source 5 stops supplying current to one end portion 54 and the other end portion 55 of the deformed steel bar 51 to be processed, and the drive device 4 holds the movable electrode 3 in the position to which it was moved in (3) above for the specified holding time (corresponding to the above-mentioned ``holding process'').

[0050] [Machining process] The cutting process is a process of cutting away bulges (see reference numeral 13 in FIG. 6) consisting of bumps (weld bumps) and / or burrs (weld burrs) formed at the joints (weld portions) of the deformed steel bar 51 to be processed. In this embodiment, the bulges are cut away so that a portion of the bulges remains. Specifically, the bulges are cut away until they become approximately 1.1 to 1.3 times the nominal diameter of the deformed steel bar, preferably until they become approximately 1.1 times the nominal diameter.

[0051] In the above-mentioned manufacturing method of closed annular reinforcement, one end face 52 and the other end face 53 of the deformed steel bar 51 to be processed do not separate during the welding process when current is applied, and scattering of high-temperature spatter can be suppressed, so frequent spatter removal work is not required. In addition, it is easier to set welding conditions compared to flash butt welding, and stable welding quality can be obtained. Therefore, the above-mentioned manufacturing method of closed annular reinforcement can improve the productivity and yield of closed annular reinforcement compared to conventional techniques.

[0052] In the above-described embodiment, the ends of the deformed steel bars are mainly joined (welded) together. However, this is not limited to this. Ends of steel bars other than the deformed steel bars may also be joined (welded) together.

[0053] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and it goes without saying that modifications and changes can be made based on the technical concept of the present invention. [Explanation of symbols]

[0054] 1...welding machine, 2...fixed electrode, 3...movable electrode, 4...driving device, 5...welding power source, 6...control device, 11...first deformed steel bar, 12...second deformed steel bar, 13...bulge portion, 21...first lower electrode, 21a...first steel bar placing portion, 22...first upper electrode, 22a...first steel bar holding portion, 31...second lower electrode, 31a...second steel bar placing portion, 32...second upper electrode, 32a...second steel bar holding portion, 50...closed shear reinforcement (closed annular reinforcement), 51...processed deformed steel bar, 52...one end face, 53...other end face, 54...one end portion, 55...other end portion, 60...main reinforcement

Claims

1. a first step of setting a first steel bar and a second steel bar so that their end surfaces are in contact with each other; A second step of applying current to the first steel bar and the second steel bar while maintaining the contact state between the end surfaces of the first steel bar and the second steel bar to heat and melt the end surfaces of the first steel bar, the end surfaces of the second steel bar, and their vicinities; a third step of applying an axial compressive pressure to the first steel bar and the second steel bar while maintaining the current flow through the first steel bar and the second steel bar after a first predetermined time has elapsed since the start of the current flow, thereby instantly joining the first steel bar and the second steel bar; a fourth step of stopping the application of current to the first steel bar and the second steel bar and holding the joined first steel bar and second steel bar in that state for a second predetermined time; A method for welding steel bars, including:

2. The first step includes clamping the first steel bar with a fixed electrode and clamping the second steel bar with a movable electrode spaced apart from the fixed electrode, the second step includes passing a current through the first steel bar and the second steel bar via the fixed electrode and the movable electrode while holding the movable electrode so that the end surfaces of the first steel bar and the second steel bar do not separate from each other, the third step includes applying a driving force to the movable electrode to instantaneously move the movable electrode toward the fixed electrode; the fourth step includes holding the movable electrode at the moved position; The method for welding steel bars according to claim 1.

3. 3. A method for welding steel bars as described in claim 1 or 2, wherein the first steel bar is one end portion of the processed deformed steel bar, which includes one end face of the processed deformed steel bar, obtained by bending a predetermined length of deformed steel bar into a ring shape, and the second steel bar is the other end portion of the processed deformed steel bar, which includes the other end face of the processed deformed steel bar.

4. a bending process for bending a predetermined length of deformed steel bar into a ring shape; a welding process of welding both ends of the deformed steel bar to be processed that has been bent into an annular shape; A cutting process step of cutting off a bulge formed at the welded portion of the processed deformed steel bar; Including, The welding step includes: Clamping one end portion of the deformed steel bar to be processed, including the one end surface, with a fixed electrode so that one end surface and the other end surface of the deformed steel bar to be processed are in contact with each other, and clamping the other end portion of the deformed steel bar to be processed, including the other end surface, with a movable electrode; While holding the movable electrode so that the one end surface and the other end surface do not separate, current is passed through the fixed electrode and the movable electrode to the one end portion and the other end portion, thereby heating and melting the one end surface, the other end surface, and their vicinities; After a first predetermined time has elapsed since the start of energization, applying a driving force to the movable electrode while maintaining the energization of the one end portion and the other end portion, thereby instantaneously moving the movable electrode toward the fixed electrode, thereby instantaneously joining the one end portion and the other end portion; stopping the current supply to the one end portion and the other end portion and holding the movable electrode at the moved position for a second predetermined time; A method for producing a closed circular muscle, comprising:

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