Upset welding method

Abstract

To provide an upset welding method which is excellent in workability and reliability.SOLUTION: An upset welding method includes a grasping step of grasping a first bar steel B1 and a second bar steel B2 by a first clamp C1 and a second clamp C2, respectively, in a state in which shaft cores of the first bar steel B1 and the second bar steel B2 are allowed to coincide with each other, an energization step of bringing the first bar steel B1 and the second bar steel B2 into contact with each other, and energizing the first bar steel B1 and the second bar steel B2 through the first clamp C1 and the second clamp C2, and a pressing step of driving at least one of the first clamp C1 and the second clamp C2, and pressing a first end face B1a of the first bar steel B1 and a second end face B2a of the second bar steel B2 each other along the shaft core X, wherein in the gripping step a reducer K is arranged between the first end face B1a and the second end face 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 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] 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 easy to work with and can produce highly reliable welded joints. [Means for solving the problem]

[0013] (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 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; In the holding step, a reducing agent is disposed between the first end surface and the second end surface.

[0014] (effect) The upset welding method according to the present invention is particularly characterized in that a reducing agent is disposed between the first end face of the first steel bar and the second end face of the second steel bar in the holding step. The reducing agent contributes to deoxidization and purification of the weld metal, and has functions such as removing oxygen as slag and removing impurities from the surface of the base metal.

[0015] For example, in normal shielded arc welding, oxygen in the air between the base metal and the welding rod is likely to combine with the molten iron to produce iron oxide. To prevent this, adding a reducing agent to the weld prevents the oxygen component from reacting with the iron, and produces welding slag that contains oxygen, which can then be removed.

[0016] However, in a type of welding in which a first steel bar and a second steel bar are pressed against each other, such as the upset welding of the present application, the amount of air present between the first end face and the second end face is small, and oxygen and impurities present in the gap are removed by pressing the base material, so a reducing agent is not required. However, when upset welding relatively large steel bars such as D32 and D25, the effect of air present in the gap between the end faces cannot be ignored.

[0017] Therefore, by using a reducing agent in upset welding as in this configuration, oxygen and impurities present between the first end face and the second end face are reliably removed, improving the reliability of the welding work, eliminating fractures at the welded portion, and obtaining the desired joint strength.

[0018] In addition, by improving the soundness of the weld, it is possible to reduce the welding current and the pressing force between the steel bars, and to shorten the pressing distance. As a result, the welding time is also shortened. In this way, with this configuration, the welding work between steel bars becomes extremely efficient.

[0019] (Features) In the upset welding method according to the present invention, it is advantageous that the reducing agent is a synthetic resin material containing any one of polypropylene, polyethylene, and polystyrene.

[0020] (effect) These reducing agents are vaporized by the heat during welding, and can effectively remove oxygen and impurities. Furthermore, these materials are available in various forms, such as film and powder, at low cost, and can reduce the cost of welding.

[0021] (Features) In the upset welding method according to the present invention, the reducing agent can be a liquid that can be applied to at least one of the first end surface and the second end surface.

[0022] (effect) If the reducing agent is a liquid, the application of the reducing agent to the first end surface etc. can be performed quickly and easily, and therefore a reliable welding operation can be performed efficiently.

[0023] In addition, since the end face of the bar material used for upset welding is often flat, it is easy to check the application area when applying the liquid reducing agent to the end face. This makes it possible to apply the appropriate amount of reducing agent even when the application amount of the reducing agent to the end face is set.

[0024] (Features) In the upset welding method according to the present invention, the reducing agent may be a thin film that can be sandwiched between the first end surface and the second end surface.

[0025] (effect) If the reducing agent is a thin film, a predetermined area of ​​the thin film can be used depending on the area of ​​the first end face or the second end face, which means that the amount of reducing agent used is accurate and the welding conditions are stable.

[0026] Furthermore, if it is a thin film, it can easily be disposed only at the center of the first end face, and it also becomes easy to optimize the state in which reducing gas is generated when the steel bars are pressed against each other.

[0027] (Features) In the upset welding method according to the present invention, it is advantageous if the thin film has a thickness of 0.03 mm or less.

[0028] (effect) When a thin film reducing agent is used, the welding phenomenon changes depending on the thickness. For example, if the film thickness is too thick, the end faces are less likely to come into contact with each other, making it difficult to pass current to start welding. Also, if the film thickness is too thick, the thin film does not vaporize completely when the end faces are heated, and remains between the end faces, causing poor welding. In other words, by setting the thickness appropriately, the amount of gas generated in each area of ​​the end faces during heating is appropriate. In addition, when the thickness is thin, no particular problems arise even in examples where the reducing agent is liquid.

[0029] However, if the film thickness is too thick, for example, gas generated at the center of the end face may be trapped between the first end face and the second end face before being released outside the end face. Furthermore, some of the reducing agent may not vaporize and may remain in the weld. In other words, by making the film thickness of the reducing agent 0.03 mm or less as in this configuration, the reducing agent is reliably vaporized and released, and a sound weld can be obtained.

[0030] (Features) In the upset welding method according to the present invention, it is advantageous if the thin film is disposed over an area that is half or more of the area of ​​the first end face or the area of ​​the second end face.

[0031] (effect) If a thin film having an area smaller than the area of ​​the first end face or the second end face is provided, if the area is too small, the vaporized gas will not reach the entire end face, which may result in poor welding.

[0032] In addition, if the thin film is placed near the center of the end face, the vaporized gas will spread easily in the circumferential direction, making it easier to obtain a sound weld. In order to increase the yield of welding material, it is necessary to make the reducing agent small, but if the dimensions are small and the installation conditions become strict, the welding work will become complicated.

[0033] Therefore, in order to eliminate the condition related to the film thickness and the installation position, the area of ​​the thin film is set to be more than half of the area of ​​the first end face or the area of ​​the second end face in this configuration. As a result, even if the thin film is installed in a biased state toward the end of the end face, the vaporized gas spreads to the edge of the area where the thin film is not placed, and a sound weld can be obtained.

[0034] In the upset welding method of the present invention, prior to the holding step, a bending step of forming a single steel bar into a ring shape and a cutting step of simultaneously cutting the ends of the steel bar while they are overlapped, and it is convenient to carry out the holding step while the ends having both cut surfaces are designated as the first steel bar and the second steel bar, respectively.

[0035] (effect) In this configuration, first, in the bending process, for example, a straight steel bar is bent into an arbitrary ring shape using a bending machine or the like. Next, in the cutting process, the ends of the steel bar are cut at the same time while being slightly overlapped. By cutting in this way, both end faces can be set in a good parallel state.

[0036] With this method, it is possible to obtain a good abutment surface by cutting in one process, without separately processing the grooves on both end faces. As a result, both end faces abut well over the entire surface. In addition, the amorphous metal thin film can be placed between both end faces without any gaps.

[0037] When cutting, if the ends are positioned apart against the elasticity of the steel bar, then after cutting, the elasticity of the steel bar itself will press the two end faces together. This eliminates the need for a separate holder when positioning the amorphous metal, making the welding process more efficient. As a result of the two end faces being in proper contact with each other, the amorphous metal will easily diffuse into both base materials during welding, making it easier to obtain a sound weld. [Brief description of the drawings]

[0038] [Figure 1] FIG. 1 is a perspective view showing a configuration of an upset welding device according to a first embodiment; [Diagram 2] Diagram showing the specifications of the steel bars used for welding [Diagram 3] Figure showing the results of an upset welding test using a water-soluble reducing agent [Figure 4] Illustrative diagram showing tensile test results for welded joints [Diagram 5] FIG. 13 shows the results of an upset welding test using a thin film reducing agent according to the second embodiment. [Figure 6] Welding conditions diagram DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] [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. In the first embodiment, upset welding is performed while applying a water-soluble reducing agent between steel bars B to be welded.

[0040] In the upset welding device W, first, as a holding process, a first steel bar B1 and a second steel bar B2, which are steel bars B, are fixed to the upset welding device W. As shown in Fig. 1, a first clamp C1 and a second clamp C2 are provided to hold the first steel bar B1 and the second steel bar B2 separately, and the first steel bar B1 and the second steel bar B2 are held in a state where their axial centers X are aligned.

[0041] The first clamp C1 includes a lower clamp C1a that supports the lower side of the first steel bar B1 and an upper clamp C1b that supports the upper side 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.

[0042] 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.

[0043] (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 between 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. The first clamp C1 can be moved by the pressure unit 5, and 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.

[0044] 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.

[0045] (Various conditions) Various conditions for welding in this embodiment are shown below.

[0046] (steel bar) Fig. 2 shows the specifications of the steel bar B used in this example. The steel bar B used was reinforcing bar SD345 as specified in JIS G 3112. The size was D32 (nominal diameter 31.8 mm) as specified in JIS G3191. Note that similar effects can be obtained with other steel bars such as SD390, SD295A, and SD295B.

[0047] (reducing agent) Various forms of reducing agent K can be used for upset welding. In this embodiment, a welding test was performed using a water-soluble reducing agent K. FIG. 3 shows the application conditions and welding conditions (amount of heat supplied) when the water-soluble reducing agent K was used, as well as the welding test results. As the water-soluble reducing agent K, polyethylene glycol, which is widely available on the market regardless of welding, was used, and was applied to the end faces of the first steel bar B1 and the second steel bar B2 with a brush. Of course, other application methods may also be used.

[0048] The coating conditions were four types: coating on half of both end faces, coating on half of one end face, coating on the entire surface of both end faces, and coating on the entire surface of one end face. For comparison, a comparative test was also conducted with no water-soluble reducing agent.

[0049] (Welding conditions) The welding conditions for upset welding are shown in Figure 4. This shows the combination of pressure and heat supply for welding rebar SD345, size D32 using the normal method without using water-soluble reducing agent K (solid line, thick frame), and the combination of conditions using water-soluble reducing agent K this time (dashed line, thick frame).

[0050] 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. Welding is possible under any of the conditions in the solid bold frame, but the greater the pressure and heat supply, the shorter the current flow time and the more efficient it is. Appropriate values ​​for these conditions have been empirically determined, and they are set by selecting the dials on the welding equipment when welding.

[0051] The pressure conditions are the pressure and the pressing distance, which are set according to the size of the steel bar B. The pressure is the hydraulic pressing force of the first clamp C1, and is set between 0.8 Mpa and 0.4 Mpa. The pressing distance is the distance by which 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 supplied, which will be described later, and is set so that the maximum outer diameter of the bulging part after welding is 1.1 times or more the maximum outer diameter at the end of the steel bar before welding (the recommended value in the 2020 edition of the Guidelines for Reinforcement Anchorage and Joints of the Japan Society of Civil Engineers), and a sound appearance can be maintained. In the case of D32 used in this embodiment, the pressing distance is 35 mm. Note that the maximum outer diameter of the bulging part and the maximum outer diameter at the end of the steel bar before welding are the largest values ​​of the dimensions perpendicular to the longitudinal direction.

[0052] The amount of heat supplied is determined by the current value and the time for which the current is applied. As shown in Figure 4, the amount of heat supplied is set in combination for each pressure force. A dial on the welding equipment is used to select a setting value, for example, 10.0, 9.5, 9.0, 8.5, or 8.0. In the welding equipment, this dial selection determines the secondary current value (kA) applied to the first steel bar B1, etc. Specific values ​​are as shown in Figure 4.

[0053] The approximate current flow time is determined according to the settings of the pressing force and current value. The melting speed of the first steel bar B1, etc. varies depending on the current value. When the current value is large, the melting speed increases, and the deformation speed of the molten metal increases when the first steel bar B1 is pressed with a specified pressing force. Therefore, a weld of the specified shape can be obtained even with a short current flow time. On the other hand, when the current value is small, the melting speed decreases, and the deformation speed of the molten metal also decreases when the first steel bar B1 is pressed with a specified pressing force. In that case, the current flow time is extended so that a weld of the specified shape can be obtained.

[0054] The specific operation of the welding device is to bring the first steel bar B1 and the second steel bar B2 into contact with each other to the extent that electricity can be passed between them. Electricity is then started, and the contact area between the two steel bars B is heated and softened. Approximately two seconds after the start of electricity, the clamps begin to approach each other, and the first steel bar B1 and the second steel bar B2 are pressed together. The pressing distance of 35 mm at D32 is set to be approximately the same as the maximum diameter of the reinforcing bar, which is the nominal diameter of 31.8 mm plus the height of the rib.

[0055] In this embodiment, when the first steel bar B1 and the second steel bar B2 using the reinforcing bar D32 are brought into contact with each other, the water-soluble reducing agent K is brushed onto either or both of the first end face B1a and the second end face B2a.

[0056] (Welding test results) The test results of the welded parts are shown in Figures 3 and 5. Figure 3 shows the results of a welding test performed under different application conditions of the water-soluble reducing agent K under conditions where all test pieces did not break in the base metal and some test pieces broke in the welded part, i.e., conditions that were borderline conditions in the welding test results (welding conditions with thick dashed lines in Figure 4). The water-soluble reducing agent K was applied to both sides or one side, and to the entire surface or half surface. The welding test was performed three times for each welding condition. In Figures 3 and 5, the circle marks indicate conditions under which all three pieces broke in the base metal and good welded joints were obtained. The triangle marks indicate conditions under which all test pieces did not break in the base metal and some test pieces broke in the welded part. The cross marks (solid lines) indicate conditions under which the welded part broke, and the cross marks (dashed lines) indicate conditions under which the welded part had a poor appearance. The - marks indicate conditions that were not performed. The evaluation criteria for this welding test were that there was no abnormality in the appearance of the welded part and that the tensile test was passed if the welded part broke in the base metal rather than the welded part.

[0057] Figure 5 shows the results of welding rebar SD345 D32 under normal welding conditions without using water-soluble reducing agent K, as well as the results using water-soluble reducing agent K (conditions enclosed in a thick dashed line). The conditions under which a circle is obtained correspond to the welding conditions shown in Figure 4, but it can be seen that in order to obtain good results under normal welding conditions, the combination of pressure and heat supply is very limited. Incidentally, the conditions enclosed in a thick dashed line that are the subject of the present invention are the conditions under which, as shown in Figure 3, when water-soluble reducing agent K is not used, the welding test results are enclosed in a triangle.

[0058] In Fig. 5, the conditions shown in the thick dashed frame are the conditions under which the welding test results were improved by using the water-soluble reducing agent K. Details are shown in Fig. 3. According to Fig. 3, when the water-soluble reducing agent K was not used, the base metal did not fracture in all the test pieces, and some of the test pieces fractured at the welded part. However, when the water-soluble reducing agent K was applied to the entire surfaces of both sides of both steel bars B, or the entire surface of one side, or half of both sides, or half of one side, the welding test results were good when the heat supply setting value was 9.5. This condition has a smaller heat supply setting value than the conventional welding conditions.

[0059] In contrast, when the water-soluble reducing agent K was applied to half of one end face or the entire surface of one end face, a sound weld was obtained even when the heat supply setting value was 9.0. Note that no tests were conducted when the heat supply setting value was 9.0 and the water-soluble reducing agent K was applied to half or the entire surface of each of the first end face B1a and the second end face B2a. This is because, as described above, a sound weld was obtained when the water-soluble reducing agent K was applied to half of only one face or the entire surface of only one face, and therefore some tests under conditions where a larger amount of water-soluble reducing agent K was applied were omitted.

[0060] According to Figure 5, under welding conditions with a pressure of 0.8 MPa and heat supply amounts of 9.0 and 9.5, when water-soluble reducing agent K was not used, none of the test pieces broke in the base metal, and some broke in the weld (△), but by using water-soluble reducing agent K, all three pieces broke in the base metal, and good welded joints were obtained (○). In other words, the results of this welding test showed that by using water-soluble reducing agent K, a sound weld can be obtained even under conditions where the heat supply amount is set smaller than in conventional welding conditions.

[0061] It is believed that by using the water-soluble reducing agent K in the upset welding as in this configuration, oxygen and impurities present in small amounts between the first end face B1a and the second end face B2a due to the current passing through the steel bar B are reliably removed, ensuring complete penetration of the base materials. As a result, the joint strength is stabilized, and the number of cases where the welded part breaks is reduced.

[0062] In this way, by using the water-soluble reducing agent K, welding conditions that require less heat can be used. By reducing the amount of heat supplied, the maximum heating temperature of the base material is reduced, preventing deterioration of the material strength. In addition to reducing power consumption, the heating time is shortened and the pressing distance is shortened, resulting in improved welding work efficiency.

[0063] As described above, when the reducing agent K is liquid, it can be quickly, easily and reliably applied to a predetermined portion such as the first end face B1a. This allows reliable welding work to be performed without causing a decrease in work efficiency. As for the specific type of material, in addition to the above-mentioned polyethylene glycol, polypropylene, and polyethylene, propylene glycol can also be used.

[0064] Second Embodiment 6 shows the results of a welding test of the second embodiment of the upset welding method according to the present invention. Here, D32 steel bar B was used, and thin-film reducing agent K was placed between the steel bars B on half or the entire surface of the first end face B1a or the second end face B2a. Thin-film reducing agent K made of polypropylene with thicknesses of 0.03 mm and 0.04 mm, and thin-film reducing agent K made of polyethylene with a thickness of 0.009 mm were used.

[0065] When the reducing agent K was placed over the entire end face, for example, a piece cut into a size slightly larger than the area of ​​the end face was placed with tweezers or the like. On the other hand, when placing a thin film having an area smaller than the area of ​​the end face, for example, the thin film was cut into a circular shape and placed approximately in the center of the overlapping region between the first end face B1a and the second end face B2a. Note that when placing on one side, a thin film of reducing agent K having a width equivalent to the radius of the end face may be cut into a long strip and sandwiched between the first end face B1a and the second end face B2a when they are brought into contact with each other.

[0066] The pressure condition for steel bar B was 0.8 MPa, and the heat supply amount was 9.0 and 9.5. These are the same conditions as in the first embodiment. When thin film reducing agent K was not used, as shown in FIG. 3, the base metal generally fractured at both the heat supply amounts of 9.0 and 9.5, but a sound weld was not reliably obtained.

[0067] (Welding test results) As shown in Figure 6, when thin film reducing agent K was placed on half of the end face, good results were obtained at 0.009mm and 0.03mm for both heat supply amounts of 9.0 and 9.5. In Figure 6, the three pieces marked with a circle were all base metal fractures, resulting in sound welds. On the other hand, the triangle marks indicate that one of the three pieces was fractured at the weld. The cross marks indicate that welding itself was impossible due to poor current flow.

[0068] In the case of the half-surface arrangement, a sound weld was obtained when only one welding was performed with a 0.04 mm thin film of reducing agent K and a heat supply of 9.5. Since good results were obtained with a thinner 0.03 mm, no further welding tests were performed. For the heat supply of 9.0, good results were obtained with thinner 0.009 mm and 0.03 mm, so no welding tests were performed.

[0069] When the thin film reducing agent K was placed over the entire end face at 0.009 mm, a sound weld was obtained for both the heat supply amounts of 9.0 and 9.5. However, when a thin film reducing agent K with a thickness of 0.03 mm or 0.04 mm was placed over the entire first end face B1a, welding could not be performed due to poor electrical conduction for both the heat supply amounts of 9.0 and 9.5.

[0070] For this reason, a small amount of metal wire was placed as an electric current conductor between the thin film reducing agent K and the first end face B1a, or between the thin film reducing agent K and the second end face B2a. This electric current conductor locally contacts the thin film when the first end face B1a and the second end face B2a are pressed together. This breaks the thin film, ensuring that electricity flows between the first end face B1a and the second end face B2a. As a result, as shown by the dashed frame in Figure 6, when the heat supply amount was 9.5, the welding test result was (◯), and sound welds could be stably obtained.

[0071] On the other hand, when the heat supply amount was 9.0, the welding test result was (△), and welding was possible, but base metal fracture was observed in some of the test pieces. This is thought to be because, due to the thick film thickness, under the condition of 9.0, where the heat supply amount was low, some of the reducing agent K could not be vaporized, and thin film reducing agent K remained between the first end face B1a and the second end face B2a. Note that, since the reason why the welding test results improved by using the current-carrying material is thought to be because it improves the current conduction failure caused by the thin film reducing agent K, it can be understood that the improvement effect of the current-carrying material occurs even in the case of a thinner film thickness of 0.03 mm.

[0072] In this way, by using the thin film reducing agent K, the welding heat input can be reduced to 9.5 or 9.0, which reduces the thermal impact on the base material and mitigates the deterioration of the base material strength. This allows for a joint with good welding quality. Furthermore, a smaller amount of heat shortens the heating process and improves work efficiency. In addition, energy consumption is reduced, which reduces the welding work costs.

[0073] It is estimated that the thin film reducing agent K should be disposed over at least half the area of ​​the first end face B1a or the second end face B2a. In other words, even if the thin film is disposed biased toward the end of the end face, the vaporized gas spreads to the edge of the area where the thin film is not placed, and a sound weld can be obtained. In addition, if the thin film reducing agent K is disposed over at least half of the first end face B1a, etc., the attachment work to the first end face B1a, etc. does not become complicated.

[0074] On the other hand, when the reducing agent K is disposed over the entire surface of the first end face B1a or the second end face B2a, poor electrical conduction tends to occur at the start of welding. Therefore, when the thickness of the thin film-like reducing agent K is 0.03 mm or more, it is desirable to use an electrical conductive material.

[0075] If the thin film reducing agent K is a synthetic resin material containing any one of polypropylene, polyethylene, and polystyrene, it will vaporize when heated during welding, and oxygen and impurities can be effectively removed. In addition, these materials are available in various shapes, such as film and powder, at low cost, and the welding cost can be reduced.

[0076] In particular, when a thin film of reducing agent K is used, the amount of gas generated in each region of the end face during heating tends to be uniform. If the reducing agent K is in the form of a thin film, a thin film of a predetermined area can be used depending on the area of ​​the first end face B1a or the second end face B2a. In other words, the amount of reducing agent K used is accurate, and the welding conditions are stabilized. In addition, it is easy to install the reducing agent K only in the center of the first end face B1a, and the generation of reducing gas is optimized when the steel bars B are pressed against each other.

[0077] Other embodiments 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.

[0078] However, 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.

[0079] 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.

[0080] By cutting in this manner, it is possible to set both end faces in a good parallel state, and it is also possible to arrange a thin film of amorphous metal between the two without leaving any gaps.

[0081] 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]

[0082] The upset welding device of the present invention can be widely applied to welding work in areas where it is desired to suppress the expansion of the bulging part, such as the welded part of a hoop reinforcement, and to welding work to obtain a welded part with excellent bending characteristics in a specific direction. [Explanation of symbols]

[0083] 5 Pressurizing section 6. Control Unit 7 Power supply section B1 1st bar B1a 1st end surface B2 2nd 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, a reducing agent is disposed between the first end surface and the second end surface.

2. The upset welding method according to claim 1, wherein the reducing agent is a synthetic resin material containing one of polypropylene, polyethylene, and polystyrene.

3. The upset welding method according to claim 2 , wherein the reducing agent is a liquid that can be applied to at least one of the first end surface and the second end surface.

4. The upset welding method according to claim 2 , wherein the reducing agent is a thin film that can be sandwiched between the first end surface and the second end surface.

5. The upset welding method according to claim 4, wherein the thin film has a thickness of 0.03 mm or less.

6. The upset welding method according to claim 5 , wherein the thin film is disposed over an area equal to or greater than half of an area of ​​the first end surface or an area of ​​the second end surface.

7. 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 any one of claims 1 to 6, 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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