Upset welding method

Abstract

To provide an upset welding technology which is excellent in workability, has a small welding swelling part, and is capable of welding of high quality.SOLUTION: An upset welding method has: a gripping step which grips a first bar steel B1 and a second bar steel B2 with a first clamp C1 and a second clamp C2, respectively in the state that shaft cores X of the first bar steel B1 and the second bar steel B2 are matched; a conduction step which contacts the first bar steel B1 and the second bar steel B2, and conducts the first bar steel B1 and the second bar steel B2 via the first clamp C1 and the second clamp C2; and a pressing step which drives at least either the first clamp C1 or the second clamp C2 and presses a first end surface B1a of the first bar steel B1 against a second end surface B2a of the second bar steel B2 along the shaft core X. In the gripping step, an amorphous metal is arranged between the first end surface B1a and the second end surface B2a.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an upset welding method in which two steel bars are held separately by clamps and pressed against each other while passing an electric current through them, thereby welding the steel bars together. [Background technology]

[0002] Upset welding is a method of connecting steel bars by applying electric current while pressing them together and using resistance heating. For example, in the fields of architecture and civil engineering, it is used to connect rebars that reinforce reinforced concrete structures. However, there have traditionally been limitations on the size of rebars that can be welded. For example, the Japan Society of Civil Engineers' Guidelines for Reinforcement Bar Anchorages and Joints (2020 edition) stipulates that only relatively small diameter rebars can be upset welded, ranging from D10 (nominal diameter 9.53 mm) to D16 (nominal diameter 15.9 mm).

[0003] In upset welding, the ends must fuse together properly to obtain a sound weld. Therefore, it is very important to set the pressure welding conditions and current conditions so that impurities present on the ends are expelled to the outside of the weld.

[0004] However, as the cross-sectional area of ​​the reinforcing bar increases, it becomes more difficult to shape the weld end surface, and poor welding or insufficient strength can easily occur due to changes in the electrical current flow between the end surfaces.

[0005] In view of such problems, a conventional technique for improving the reliability of welded parts is disclosed in, for example, Patent Document 1 (see

[0012] to

[0011] and FIG. 2).

[0006] In this conventional upset welding method, a first pressure is applied to the two rods to be joined so that they are in light contact with each other, and electricity is passed through to heat the weld.Then, the power supply is increased while the pressure applied between the rods is increased to a second pressure to join the rods.

[0007] In this method, when the first pressure is applied, the most protruding convex parts on the end faces come into contact with each other, then they separate due to local melting, and the current flow point moves. This causes the unevenness of the end face to be smoothed out, and the molten part is distributed over the entire end face, resulting in an appropriate melting state.

[0008] The method according to the conventional technology does not require any additional mechanisms, such as a mechanism for moving the electrode to grip the rod or a reactance circuit to generate an arc, making the welding equipment inexpensive. In addition, contamination caused by welding is unlikely to occur regardless of the end face shape or area of ​​the rod, and a stable and strong weld with a regular nodular weld shape can be obtained. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2013-75314 A Summary of the Invention [Problem to be solved by the invention]

[0010] In the welding technique of Patent Document 1, the convex part on the end surface gradually disappears and the entire surface becomes molten, so there is a possibility that the shaping work of the end surface prior to welding can be made more efficient. However, there is an appropriate value for the pressing force between the rods, and the appropriate value may differ depending on the shape of the end surface. For example, in the case of a cone-shaped convex surface, the molten part gradually spreads, and impurities are easily discharged to the surrounding area.

[0011] However, if there are protrusions scattered all over the end face, the melting of the areas between the protrusions may be delayed, and impurities present there may be left behind in the weld. In such a case, it is necessary to set the first pressure to a small value and allow a long time for the protrusions to disappear. This operation becomes more difficult as the cross-sectional area of ​​the bar material increases.

[0012] In addition, in conventional upset welding, in order to ensure the fusion of the end faces and to expel impurities present on the end faces, it was necessary to keep the pressing distance between the two faces long. This meant that the outer diameter of the weld had to be much larger than the outer diameter of the base material, which required a certain amount of work time for pressing, and there was a certain limit to how much welding efficiency could be improved.

[0013] Furthermore, when embedding the welded reinforcing bars in concrete, it is necessary to ensure that the concrete covers the reinforcing bars to a certain thickness, which requires time-consuming post-weld construction, such as retracting the weld bulge a certain distance from the surface of the concrete.

[0014] As described above, there are still areas that need improvement in conventional upset welding techniques, and there is a demand for an upset welding method that is excellent in workability and can produce high-quality welded joints with small weld bulges. [Means for solving the problem]

[0015] (Features) The characteristic configuration of the upset welding method according to the present invention is as follows: a clamping step of clamping the first steel bar and the second steel bar with a first clamp and a second clamp, respectively, while axial centers of the first steel bar and the second steel bar are aligned; a current application step of abutting a first steel bar B1 and a second steel bar B2 and applying current to the first steel bar B1 and the second steel bar B2 via the first clamp B1 and the second clamp B2; a pressing step of driving at least one of the first clamp and the second clamp to press a first end surface of the first steel bar and a second end surface of the second steel bar against each other along the axis; In the holding step, an amorphous metal is disposed between the first end surface and the second end surface.

[0016] (effect) By placing an amorphous metal between the first steel bar and the second steel bar in upset welding as in this configuration, the amorphous metal is diffused into the base material, improving welding performance even in the case of upset welding.

[0017] In particular, by using the upset welding method, the contact surface between the first steel bar and the second steel bar is heated quickly and evenly, making it possible to activate the diffusion phenomenon of the amorphous metal from the beginning of the current application.

[0018] (Features) In the upset welding method according to the present invention, the amorphous metal may contain an Fe-based material.

[0019] (effect) Fe-based amorphous metals have good diffusion properties when used in, for example, steel bars, making it possible to obtain welds with sufficient tensile strength. In addition, Fe-based amorphous metals can be welded at low cost.

[0020] (Features) In the upset welding method according to the present invention, the amorphous metal may be in the form of a thin film.

[0021] (effect) If the amorphous metal is a thin film, it is extremely easy to place it between the first steel bar and the second steel bar.

[0022] Furthermore, since the size of the thin film can be set arbitrarily prior to placement, the supply amount of the amorphous metal can be set accurately.

[0023] (Features) In the upset welding method of the present invention, it is advantageous to place a synthetic resin material containing one of polypropylene, polyethylene, and polystyrene between the amorphous metal and at least one of the amorphous metal and the second end surface.

[0024] (effect) By disposing a synthetic resin material between the first end face and the second end face, the synthetic resin material is vaporized by the electrical heating during welding, and the air remaining between both end faces is expelled. This prevents the weld from being oxidized, reduces the occurrence of welding defects, and improves the reliability of the weld.

[0025] (Features) In the upset welding method of the present invention, the relative movement distance between the first end face and the second end face in the pressing process can be set so that the bulging outer diameter of the welded portion after welding is completed is an outer diameter within 130% of the larger outer diameter of the first steel bar and the second steel bar.

[0026] (effect) In this method, amorphous metal, which has inherent diffusibility, is interposed between steel bars, so there is no need to press the steel bars together as in conventional upset welding. By applying a certain pressing force to the amorphous metal and base material while heating, the fluidity of the base material is increased, activating the diffusion of amorphous metal molecules into the base material.

[0027] Therefore, the outer diameter of the bulge formed in the pressing portion is extremely small compared to the bulge formed by conventional upset welding. In particular, when the steel bar size is D32, D25, D22, or D19 as specified in JIS G3191, a sufficiently strong weld can be obtained even if the outer diameter of the bulge is kept within 130% of the outer diameter of the steel bar.

[0028] (Features) In the upset welding method of the present invention, prior to the holding step, a bending step is performed to shape a single steel bar into a ring shape, and a cutting step is performed to simultaneously cut the ends of the steel bar while they are overlapped, and the holding step can be performed while the ends having the cut surfaces of both steel bars are designated as the first steel bar and the second steel bar, respectively.

[0029] (effect) For example, hoop reinforcement bars used in construction are initially straight and then bent into a ring shape, after which both end faces are shaped with a grinder or the like and then upset welded. However, in this type of upset welding, it is preferable to place the amorphous metal between both end faces with no gaps.

[0030] In order to form the butt end surfaces, the wire is first formed into an annular shape, and then the two ends are overlapped and cut in one cutting operation. After that, the wire is set in an upset welding machine so that the cut surfaces are aligned, allowing the end surfaces to abut against each other properly.

[0031] This method is efficient because it is possible to obtain a good abutment surface without separately preparing the grooves on both end faces, and moreover, it is possible to obtain a sound weld because the amorphous metal is easily diffused into both base materials during welding. [Brief description of the drawings]

[0032] [Figure 1] FIG. 1 is a perspective view showing a configuration of an upset welding device. [Diagram 2] Diagram showing the specifications of the steel bars used for welding [Diagram 3] Figure showing welding test results using Fe-based amorphous metal D32 [Figure 4] Figure showing welding test results using Fe-based amorphous metal D25 [Diagram 5] Photograph showing the appearance of welds made with Fe-based amorphous metals D32 and D25 [Figure 6] Figure showing the results of welding tests using D32 Fe-based amorphous metal and a reducing agent [Figure 7] Figure showing the results of welding tests using D25 Fe-based amorphous metal and a reducing agent [Figure 8] Figure showing the results of welding tests using D22 Fe-based amorphous metal and a reducing agent [Figure 9] Figure showing the results of welding tests using D19 Fe-based amorphous metal and reducing agent [Figure 10]Figure showing the results of welding tests using D16 Fe-based amorphous metal and reducing agent [Figure 11] Figure showing the results of welding tests using D32 Ni-based amorphous metal and a reducing agent [Figure 12] Figure showing the results of welding tests using D32 Ni-based amorphous metal and a reducing agent [Figure 13] A diagram showing the results of welding tests using D25 Ni-based amorphous metal and a reducing agent. [Figure 14] A diagram showing the results of welding tests using D25 Ni-based amorphous metal and a reducing agent. [Figure 15] An explanatory diagram showing the results of a welding test using Fe-based amorphous metal [Figure 16] An explanatory diagram showing the results of a welding test using Ni-based amorphous metal DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] [First embodiment] (overview) A first embodiment of an upset welding method according to the present invention will be described with reference to Figures 1 to 5 and 15. The upset welding method of the present invention involves disposing an amorphous metal between steel bars B to be welded together, and utilizing the diffusion of the amorphous metal into the base material during welding. As shown in Figure 1, the upset welding device W includes a first clamp C1 and a second clamp C2 that respectively grip the first steel bar B1 and the second steel bar B2, which are steel bars B of the same size, with the axial centers X of the first steel bar B1 and the second steel bar B2 aligned.

[0034] For example, the first clamp C1 includes a lower clamp C1a that supports the lower part of the first steel bar B1 and an upper clamp C1b that supports the upper part of the first steel bar B1. The lower clamp C1a does not move vertically, but the upper clamp C1b can move vertically, for example, by a hydraulic cylinder not shown. In order to stabilize the gripping state of the steel bar B according to the thickness of the steel bar B to be welded, the chuck member 3 is replaceable in both the upper clamp C1b and the lower clamp C1a.

[0035] The chuck member 3 attached to the lower clamp C1a is formed with a V-shaped groove 3a that matches the size of the steel bar B, and is capable of clamping the steel bar B at a predetermined position. This groove 3a may be formed in the upper clamp C1b, but if it is formed at least in the lower clamp C1a, the gripping position of the steel bar B is determined.

[0036] (Control unit / Electrical unit) During welding, the first steel bar B1 and the second steel bar B2 are brought into contact with each other, and while current is being applied to the first steel bar B1 and the second steel bar B2 (current application process), the first clamp C1 and the second clamp C2 are brought close to each other, and the first end face B1a of the first steel bar B1 and the second end face B2a of the second steel bar B2 are pressed against each other along the axis X (pressing process). The second clamp C2 does not move in the direction of approach, and only the first clamp C1 can be moved by the pressure unit 5. The movement of the first clamp C1 can be achieved by using various driving methods, such as a hydraulic cylinder, an air cylinder, or an electric motor.

[0037] The clamping action of the steel bar B in the first clamp C1 and the second clamp C2 and the pressing action of the first clamp C1 are performed by a switch operation by an operator and an automatic operation by the control unit 6. During welding, a current according to the size of the steel bar B is applied from the power supply unit 7 to the first steel bar B1 and the second steel bar B2, and this current application work is also controlled by the control unit 6.

[0038] The welding conditions in this embodiment are as follows.

[0039] (steel bar) Figure 2 shows the specifications of steel bar B to be welded. Reinforcing bar SD345 specified in JIS G 3112 was used for steel bar B. There are five sizes specified in JIS G3191: D32 (nominal diameter 31.8 mm), D25 (nominal diameter 25.4 mm), D22 (nominal diameter 22.2 mm), D19 (nominal diameter 19.1 mm), and D16 (nominal diameter 15.9 mm). Note that other steel bars such as SD390, SD295A, and SD295B can also be used in the same way.

[0040] (Pressure and pressing distance) The welding conditions for upset welding are shown in Figure 3 and Figure 4 onwards. The main parameters to be set are the pressure conditions and heat supply for the first steel bar B1 and the second steel bar B2. Appropriate values ​​for these conditions are empirically determined according to the size of the steel bar B.

[0041] The pressure conditions are the pressure force and the pressing distance. The pressure force is the hydraulic pressing force of the first clamp C1, and is set between 0.8 MPa and 0.5 MPa, for example. The pressing distance is the distance that the first clamp C1 presses the first steel bar B1 from the state in which the first steel bar B1 and the second steel bar B2 are in contact. The pressing distance is also related to the amount of heat supply described below, and is set so that the outer diameter of the bulging portion after welding remains within 1.4 times the initial outer diameter and a sound appearance can be maintained.

[0042] The amount of heat supplied is determined by the current value and the time for which the current is applied. The current value is determined by the secondary current value (kA) applied to the first steel bar B1, etc., by dial selection on the welding device. Specific values ​​are as shown in each figure from Figure 3 onwards.

[0043] The current application time is roughly determined by the settings of the pressure and current value. In other words, the pressing distance is preset for each size of the steel bar B, but the melting speed of the first steel bar B1, etc. varies depending on the current value. Thus, when the current value is large, the melting speed increases and the current application time becomes short, and when the current value is small, the melting speed decreases and the current application time becomes long. In the case of the device used in this test, the pressing operation and current application are synchronized, and the device is configured to end the current application when the pressing ends.

[0044] Another parameter is the type of amorphous metal to be placed between the first steel bar B1 and the second steel bar B2. In this embodiment, an Fe-based amorphous metal having a film shape and a thickness of 25 μm was used. Various conditions were set, and welding tests were performed on three pieces for each condition.

[0045] The specific operation of the upset welding device W is to bring the first steel bar B1 and the second steel bar B2 into contact to the extent that electricity can be passed between them, and then start passing electricity. Prior to passing electricity, a thin film of amorphous metal is placed between the two steel bars. The contact area between the two steel bars B is heated and softened by passing electricity. About two seconds after the start of passing electricity, the clamps start to approach each other, and pressure is applied to the first steel bar B1 and the second steel bar B2 according to the conditions in each figure.

[0046] The current settings for the upset welding device W were the same for each size of steel bar B, but the actual current value applied varied slightly. Also, the end of energization coincides with the end of the pressing action of first clamp C1, but although the pressing distance was set to the same value using the setting dial of the welding machine, there was an error of about 1 second in the actual energization time.

[0047] (Types of amorphous metals) Amorphous metals are produced by quenching metal materials with various main components from a high-temperature molten state and solidifying them before a crystal structure is formed. Rolling and sputtering methods are used for production. In this embodiment, HB1M / SA1 (25 μm) manufactured by Metglas is used as the Fe-based amorphous metal.

[0048] (Number of amorphous metals placed) In the first embodiment, one to four thin films of an Fe-based amorphous metal were used for the steel bars B of D32 and D25.

[0049] (Welding test results under basic conditions using Fe-based amorphous metal) The test results of the welds for D32 are shown in Figure 3, and those for D25 are shown in Figure 4. D32 was tested under two conditions, with a pressing distance of 11 mm and 8 mm. D25 was tested under two conditions, with a pressing distance of 8 mm and 6 mm. The current value and current flow time differ depending on the pressing distance. For D32, when the pressing distance is 11 mm, the current value is about 10.5 kA and the current flow time is about 34 seconds. When the pressing distance is 8 mm, the current value is about 13.5 kA and the current flow time is about 21 seconds. For D25, when the pressing distance is 8 mm, the current value is about 12 kA and the current flow time is about 9 seconds. When the pressing distance is 6 mm, the current value is about 13 kA and the current flow time is about 9 seconds.

[0050] The evaluation criteria were that there were no abnormalities in the appearance of the welded parts, and that the tensile test failed at the base metal, not the welded parts. Three welding tests were carried out under each condition. Those in which all three parts failed in the base metal were rated ○, those in which one failed in the welded parts were rated △, and those in which all failed in the welded parts were rated ×. Each figure shows the tensile strength at the time of failure, but there was no significant difference between the tensile strength of those judged to have failed in the welded parts and the tensile strength of those in which the base metal failed.

[0051] Figure 5 shows photographs of the appearance of the welds for D32 and D25. Figure 5(a) is for D32. The left is a weld using amorphous metal, and is the appearance after welding of test piece 9b in Figure 3. The pressure was 0.8 MPa, the pressing distance was 8 mm, the current was 13.5 kA, and the current flow time was 21.2 seconds. It can be seen that the outer diameter of the bulge is extremely small at 40.59 mm. In contrast, the right is a conventional weld that does not use amorphous metal. The pressure was 0.8 MPa, the pressing distance was 35 mm, the current was 11.6 kA, and the current flow time was 45 seconds.

[0052] Figure 5(b) relates to D25. On the left is a welded part using amorphous metal, and is the appearance after welding of test piece 9b in Figure 4. The pressure was 0.8 MPa, the pressing distance was 6 mm, the current was 12.8 kA, and the current flow time was 9.1 seconds. It can be seen that the outer diameter of the bulge is extremely small at 32.04 mm. In contrast, on the right is a conventional welded part that does not use amorphous metal. The pressure was 0.8 MPa, the pressing distance was 29 mm, the current was 10.5 kA, and the current flow time was 18 seconds.

[0053] The reason why the conditions are different between the two is that the method of the present invention utilizes the principle of diffusion bonding with amorphous metals and does not require strong pressing of the steel bars B together. Therefore, in both D32 and D25, the pressing distance is about one-fourth of the conventional method, and the current application time is about half. This makes it possible to keep the outer diameter of the bulging portion extremely small.

[0054] The bulge size was calculated by (maximum outer diameter of the bulge after welding / maximum outer diameter at the end of the steel bar before welding). When the pressing distance for D32 was 11 mm, the bulge size was 122-125%, and when the pressing distance was 8 mm, the bulge size was 118-125%. In the case of conventional welding methods for D32, the bulge size was, for example, 160-170%. The maximum outer diameter of the bulge and the maximum outer diameter at the end of the steel bar before welding were determined as the largest value of the dimension perpendicular to the longitudinal direction.

[0055] As shown in Figures 3 and 15, in the case of D32 and a pressing distance of 11 mm, all specimens (specimen 1) that did not use Fe-based amorphous metal failed. In contrast, when Fe-based amorphous metal was used, good results were obtained, but one specimen (specimen 3c) that used two sheets failed. On the other hand, in the case of a pressing distance of 8 mm, all specimens (specimen 9) that used four sheets of amorphous metal passed, but one specimen with two and three sheets failed (specimens 7b and 8c), and all specimens with zero and one sheet failed (specimens 5 and 6). The tensile strength of the failed specimens was 10 to 20 N / mm lower than those that passed. 2 The result was low.

[0056] Regarding the test results for D25 (Figure 4), the bulge size of the welded part was 125-130% when the pressing distance was 8 mm, and 116-124% when the pressing distance was 6 mm.

[0057] In D25, when no amorphous metal was used, all tests (test pieces 1 and 5) failed at both the 8mm and 6mm pressing distances, but good results were obtained when amorphous metal was used. Furthermore, when one sheet of amorphous metal was used at a pressing distance of 6mm, one test piece (test piece 6a) broke at the welded part. It was confirmed that welding is possible when two or more sheets of amorphous metal are used when the pressing distance is short.

[0058] Figure 15 shows the results of welding tests using Fe-based amorphous metals for D32 and D25. When the pressing distance for D25 was 6 mm, good results were obtained with 2 to 4 sheets of amorphous metal, and when the pressing distance was 8 mm, good results were obtained with 1 to 3 sheets of amorphous metal. Also, for D32, when the pressing distance was 8 mm, good results were obtained with 4 sheets of amorphous metal, and when the pressing distance was 11 mm, good results were obtained with 1 and 3 sheets of amorphous metal.

[0059] Thus, it was confirmed that upset welding using a thin film of Fe-based amorphous metal is sufficiently practical by appropriately setting the welding current, pressing distance, and number of amorphous metal sheets. In general, diffusion welding is a method of diffusing major elements such as Fe into the base metal by maintaining a relatively low temperature bonding condition for a long period of time. In contrast, the upset welding of the present invention is a method of welding in a short period of time by applying a relatively large heat input while using amorphous metal, which is significantly different from the concept of conventional diffusion bonding. However, by setting specific conditions, it was possible to obtain a weld with extremely small bulge dimensions that satisfies the conditions for base metal fracture.

[0060] Second Embodiment (Welding test results using Fe-based amorphous metal and reducing agent) In this embodiment, amorphous metal was used, and a water-soluble reducing agent was applied to the end faces of the first steel bar B1 and the second steel bar B2. The steel bars B used were D32, D25, D22, D19, and D16. The test results for D32 to D16 are shown in Figures 6 to 10 and 15, respectively.

[0061] The pressing distances of the welding conditions were 11 mm and 8 mm for D32, 8 mm and 6 mm for D25, 5 mm for D22, and 4 mm for D19 and D16. The amount of heat supplied was about 10.5 kA and about 34 seconds for a pressing distance of 11 mm for D32. It was about 14 kA and about 21 seconds for a pressing distance of 8 mm for D25. It was about 12 kA and about 9 seconds for a pressing distance of 8 mm for D25, and about 13 kA and about 9 seconds for a pressing distance of 6 mm for D22. It was about 13 kA and about 5.5 seconds for D22, about 11.3 kA and about 3.7 seconds for D19, and about 10 kA and about 2.5 seconds for D16. The Fe-based amorphous metal thin film was set to 1 to 4 sheets with a thickness of 25 μm.

[0062] By using a reducing agent in upset welding, the reducing agent is vaporized by heating during welding, and oxygen and impurities are effectively removed. In this embodiment, a water-soluble liquid reducing agent is applied to the entire end faces of the first steel bar B1 and the second steel bar B2 with a brush. If the reducing agent is liquid, it can be quickly, easily, and reliably applied to a predetermined location such as the first end face B1a. Therefore, reliable welding work can be performed without causing a deterioration in work efficiency. Polyethylene glycol was used as the water-soluble reducing agent. Note that polypropylene, polyethylene, polystyrene, polyethylene, propylene glycol, etc. can also be used.

[0063] The evaluation criteria for the welding test results shown in Figs. 6 to 10 were the same as those for the first embodiment, and a specimen was deemed to have passed if there was no abnormality in the appearance of the weld and if the fracture occurred not at the weld but at the base material in the tensile test.

[0064] The welding conditions for D32 and D25 were the same as those in the first embodiment except that a reducing agent was used, so the bulge size of the welded portion was also the same as that in the first embodiment, as shown in Figs.

[0065] Regarding the fracture location, in the case of D32 (Fig. 6, Fig. 15), at both pressing distances of 11 mm and 8 mm, the test failed when no amorphous metal was used (test pieces 1 and 5 in Fig. 6), even when a reducing agent was used. On the other hand, the test results improved when amorphous metal and a reducing agent were used. In particular, the base material fractured when 1 to 3 sheets of amorphous metal were used at a pressing distance of 11 mm, and when 1 to 4 sheets of amorphous metal were used at a pressing distance of 8 mm.

[0066] In D25 (Fig. 7, Fig. 15), when no amorphous metal was used, even when a reducing agent was used, the fracture occurred at the welded portion and the test was unsuccessful (test specimens 1 and 5). When there was one amorphous metal sheet, all fractures occurred in the base metal when the pressing distance was 8 mm (test specimen 2), and when the pressing distance was 6 mm, some fractured at the welded portion (test specimen 6c). However, when there were two or three amorphous metal sheets, the fracture occurred in the base metal at both pressing distances of 8 mm and 6 mm, and good results were obtained. Furthermore, when the pressing distance was 6 mm, the fracture occurred in the base metal even when four amorphous metal sheets were used, and good results were obtained (test specimen 9).

[0067] For D22 (Fig. 8), D19 (Fig. 9), and D16 (Fig. 10), welding tests were basically conducted using a reducing agent. First, in the case of not using Fe-based amorphous metal, as shown in Fig. 8 and Fig. 15, D22 failed regardless of whether a reducing agent was used or not, just like D32 and D25 (specimens 1 and 2). However, for D19 and D16, although they failed when a reducing agent was not used (specimen 1 in each case), good welds were obtained by using a reducing agent, even without using an amorphous metal (specimen 2 in each case).

[0068] Furthermore, when Fe-based amorphous metal was used, good results were obtained for almost all of D16 to D22, as shown in Figure 15. However, in D22, only one of the four amorphous metal sheets (specimen 6b in Figure 8) broke at the weld. The bulge size of the weld was 117-125% for D22, 121-126% for D19, and 130-137% for D16. There is a tendency for the bulge size to increase as the diameter becomes smaller.

[0069] From these, it can be seen that in the case of D16 to D22, which are relatively thin rebars, good results can be obtained by placing one to three sheets of Fe-based amorphous metal. Considering the effort and cost of the welding work, it is preferable to place one sheet of amorphous metal. On the other hand, in D25, good results were obtained without using a reducing agent at both pressing distances of 8 mm and 6 mm, and the effect of the reducing agent was not observed. In addition, in D32, the welding test results were very good when a reducing agent was used at both pressing distances of 11 mm and 8 mm. In particular, in D25 and D32, good welds were obtained in all cases where two or three sheets of Fe-based amorphous metal were used.

[0070] As described above, it was found that upset welding using amorphous metal and reducing agent in combination can produce a sound weld by specifying the welding current, pressing distance, and the manner in which the amorphous metal and reducing agent are used. In particular, the effect of the reducing agent was remarkable in the case of D32. This is thought to be because the larger the cross-sectional area of ​​the end face, the more likely it is that impurities such as oxygen will remain between the end face and the amorphous metal when pressed, but the use of a reducing agent can effectively remove oxygen and other impurities.

[0071] Third Embodiment (Welding test results using Ni-based amorphous metal and reducing agent) Here, Ni-based amorphous metal was used, and D32 and D25 were used as steel bar B. MBF20 (25μm) manufactured by Metglas was used as Ni-based amorphous metal. The welding conditions for D32 and D25 were the same as those shown in paragraph

[0046] . One to four sheets of this thin-film Ni-based amorphous metal were placed between the first steel bar B1 and the second steel bar B2, and welding was performed both without and with a water-soluble reducing agent. The welding test results for D32 are shown in Figs. 11 and 12, and the welding test results for D25 are shown in Figs. 13 and 14. These results are also summarized in Fig. 16.

[0072] For D32, the detailed results for a pressing distance of 11 mm are shown in Fig. 11, and the detailed results for a pressing distance of 8 mm are shown in Fig. 12. As is clear from Fig. 16, the test results when Ni-based amorphous metal was used were not so good, and only when three sheets of amorphous metal were used with a pressing distance of 11 mm (specimen 4 in Fig. 11) did good welds be obtained for all three specimens.

[0073] As for D25, as shown in FIG. 16, when no Ni-based amorphous metal was used, good results were not obtained regardless of whether a reducing agent was used or not (specimens 1 and 6 in FIG. 13 and specimens 1 and 6 in FIG. 14). Also, when the number of Ni-based amorphous metal sheets was 1 to 3, many specimens broke at the welded part regardless of whether a reducing agent was used or not. However, when the number of Ni-based amorphous metal sheets was increased to 4 when the pressing distance was 8 mm, good results were obtained regardless of whether a reducing agent was used or not (specimens 5 and 9 in FIG. 13). The size of this bulge was 121 to 128%, and it was confirmed that the bulge size was small.

[0074] The size of the bulge in the test piece that broke at the weld was 120-126%, which is not a significant difference from the passed product. However, the tensile strength of the passed product was 550N / mm 2 The failure rate was about 500N / mm 2The difference in the welding conditions between these passed and failed products was the number of amorphous metal sheets. Therefore, it was confirmed that when using Ni-based amorphous metal, sound welding is possible by limiting the size of the steel bar B to be welded and appropriately setting the number of amorphous metal sheets used.

[0075] [Fourth embodiment] In the above embodiment, a straight steel bar B is used, and before placing two steel bars B in the upset welding machine, the end faces of each are cut to form welded end faces perpendicular to the longitudinal direction. However, in construction work, hoop reinforcement bars and the like to be installed inside columns and beams are initially bent into a ring shape from the straight steel bar B, and then both ends are welded together.

[0076] In upset welding, if the abutment state between the end faces is not appropriate, the possibility of welding defects increases, so the formation of both end faces is important. In particular, in the method of the present application, since amorphous metal is placed between the end faces, the abutment state of both end faces before welding is particularly important.

[0077] Therefore, in this embodiment, prior to the gripping process in the upset welding machine, a bending process is performed in which one steel bar B is formed into a ring shape, and a cutting process is performed in which the ends of the steel bar B are overlapped and cut simultaneously. Specifically, the straight steel bar B is bent into an arbitrary ring shape by a bending machine (not shown) so that the ends of the steel bar B are slightly overlapped. In this state, both overlapped ends are fixed to various jigs and cut at the same time. For example, a disc-shaped cutting wheel or a band saw is used for cutting.

[0078] By cutting in this manner, both end faces can be set in a good parallel state, and a thin film of amorphous metal can be disposed between the two without any gaps.

[0079] This method is efficient because it is possible to obtain a good abutment surface by a single cutting process without separately preparing the grooves on both end faces. Moreover, if the ends of both pieces are positioned in a state where they are separated from each other against the elasticity of the steel bar B during cutting, then after cutting, the elasticity of the steel bar B itself will press both end faces against each other. Therefore, there is no need to prepare a separate holding tool when positioning the amorphous metal, making the welding work even more efficient. As a result of the appropriate abutment state of both end faces, the amorphous metal is more likely to diffuse into both base materials during welding, making it easier to obtain a sound weld. [Industrial Applicability]

[0080] The upset welding method according to the present invention can be widely applied to welding operations in areas where it is desired to suppress the expansion of the bulging portion, such as the welded portions of various steel bars B and hoop reinforcement. [Explanation of symbols]

[0081] 5 Pressurizing section 6. Control Unit 7 Power supply section B1 1st bar B1a 1st end surface B2 2nd steel bar B2a 2nd end surface C1 First clamp C2 Second clamp K reducing agent X-axis center

Claims

1. a clamping step of clamping the first steel bar and the second steel bar with a first clamp and a second clamp, respectively, in a state in which the axial centers of the first steel bar and the second steel bar are aligned; a current application step of contacting the first steel bar and the second steel bar and applying current to the first steel bar and the second steel bar via the first clamp and the second clamp; a pressing step of driving at least one of the first clamp and the second clamp to press a first end surface of the first steel bar and a second end surface of the second steel bar against each other along the axis; An upset welding method, wherein in the holding step, an amorphous metal is disposed between the first end face and the second end face.

2. The upset welding method of claim 1 , wherein the amorphous metal includes an Fe-based material.

3. The upset welding method according to claim 2 , wherein the amorphous metal is a thin film.

4. 2. The upset welding method according to claim 1, wherein a synthetic resin material containing one of polypropylene, polyethylene, and polystyrene is disposed between the amorphous metal and the first end surface and / or between the amorphous metal and the second end surface.

5. An upset welding method as described in any one of claims 1 to 4, wherein the relative movement distance between the first end face and the second end face in the pressing process is set so that the bulging outer diameter of the welded portion after welding is completed is within 130% of the outer diameter of the larger of the first steel bar and the second steel bar.

6. Prior to the holding step, A bending process for forming a single steel bar into a ring shape; A cutting process for cutting the ends of the steel bars simultaneously in a state where the ends are overlapped with each other, The upset welding method according to claim 1 , wherein the holding step is performed while both ends having the cut surfaces are the first steel bar and the second steel bar, respectively.

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