JP4176590B2 - Closed loop type shear reinforcement - Google Patents

Description

  The present invention relates to a closed loop type shear reinforcing bar in which a closed loop is formed on a wire rod used for a reinforcing bar of a structure such as a concrete column or a beam and butt-welded.

  For reinforcing bars of concrete structures such as concrete columns and beams, hoop bars having closed loops are used as auxiliary reinforcements for shear reinforcement surrounding the main bars. For the manufacture of this hoop, for example, a wire is cut into a predetermined length and formed into a predetermined shape such as a rectangle, then the wire is gripped with an electrode, and both cut ends are pressed and energized to make butt welding. Many methods have been adopted.

  Conventional butt welding was performed by applying a welding current to the electrode holding the cut portion of the wire to heat the weld and applying pressure to the electrode to reduce the distance between the electrodes and upset the wire at once. . However, in conventional butt welding, if a high-strength wire is used for welding, the heat-affected zone at the time of welding softens, so the strength and elongation of the welded zone and the surrounding heat-affected zone are reduced. there were.

  For this reason, the high strength shear reinforcement currently on the market uses a high alloy steel to reduce the softening of the weld and to use a base material with a strength higher than the standard value. Even if the strength and elongation of the heat-affected zone decrease, the strength of the shear reinforcement is still within the standard value. However, this method unnecessarily increases the cost by using a high-alloy material with high strength, and the strength and elongation of the welded part and the surrounding heat-affected part are almost the standard value, and the fractured part is concentrated near the welded part. There is a problem.

  Also, in the conventional method of upsetting at one time and butt welding, in order to perform complete welding, the amount of upset must be increased at one time, and the outer diameter of the burr at the weld joint becomes large. There was a problem that cracks occurred on the outer periphery of the steel.

On the other hand, the present inventors previously disclosed a closed loop shear reinforcement which does not cut at the welded portion by forming a huge portion larger than the diameter of the wire near the welded portion to increase the strength (Patent Documents 1 and 2). .
JP 7-108382 A JP-A-11-151578

  The present invention solves the above problems, there is no crack in the outer periphery of the burr of the welded joint and the outer diameter is small, the strength of the welded portion is high, and the base material portion is cut instead of the welded portion when breaking, And it aims at providing the closed loop type shear reinforcement which ensures the intensity | strength and elongation which the wire had before welding.

  In order to solve the above problems, the closed loop type shear reinforcement of the present invention is a closed loop type shear reinforcement in which a wire cut to a predetermined length is formed into a loop shape and both cut ends thereof are butt welded. It is characterized by being welded so that an increased strength portion is formed at the welded joint.

  Further, the closed loop type shear reinforcement of the present invention applies electric power to the electrode holding the wire on both sides of the welded portion, heats the welded portion to the welding temperature and upset welds, and then raises the temperature of the welded joint portion to 500 ° C. or less. The temperature of the wire rod on both sides of the welded joint was raised to 500-700 ° C. by applying electric power between the electrodes again, and a predetermined amount of upsetting was performed at this temperature to form an increased strength portion in the welded joint. It is a feature.

The closed loop type shear reinforcing bar of the present invention is characterized in that the outer diameter D of the burr of the weld joint is D ≦ 2.0d, where d is the diameter of the wire, On the other hand, there is no decrease in the strength and elongation value of the welded portion, it has a yield point of 785 N / mm ² or more, and it is characterized by cutting at the base material portion at the time of fracture.

  The wire is in mass%, C: 0.40% or less, Si: 2.0% or less, Mn: 2.0% or less, carbon equivalent (C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14). It is a high-strength wire obtained by heat-treating a low alloy steel containing 8% or less.

That is, conventionally, a high alloy steel has been used in order to obtain a yield point of 785 N / mm ² or more even in a welded portion. This strength is achieved. Thereby, the cost of a shear reinforcement can be reduced. Of course, the same effect can be obtained also in the wire of high alloy steel. Further, the closed loop type shear reinforcement of the present invention has a strength increasing portion formed at the welded joints on both sides of the welded portion, and the fracture strength and elongation value of the welded portion do not decrease. A highly reliable high strength shear reinforcement is obtained.

  In addition, the closed loop type shear reinforcement of the present invention is not completed by upset welding at a time as in the prior art, but after the temperature of the welded joint is lowered to 500 ° C. or lower after welding, the both sides of the welded joint are again formed. It is characterized in that it is heated to a temperature lower than the welding temperature and strongly pressed to perform a predetermined amount of upset and to perform two-stage heating for forming a strength increasing portion at the weld joint.

In this way, by performing upset welding and upset processing after welding in two stages, the outer diameter of the burr at the weld joint can be reduced, and when the diameter of the wire is d, the outer diameter D of the burr is reduced. It is possible to prevent cracks on the outer periphery of the burr by pressing D ≦ 2.0d.
Moreover, after welding, the temperature of the welded joint is lowered to 500 ° C. or lower and then reheated to diffuse the welded molten structure. After welding, the parts on both sides of the welded portion are subjected to low temperature upsetting at 500 to 700 ° C. The effect of thermomechanical treatment is given. This restores the strength and elongation of the weld heat affected zone. In this way, an increased strength portion is formed in the weld joint, increasing the strength of the weld, and a shear reinforcement that breaks at the base material portion instead of the weld portion at the time of fracture can be obtained.
The above-mentioned welded joint means a range of distances of approximately 1d on both sides from the welding contact point, including burrs, where the diameter of the wire is d.

  The closed-loop type shear reinforcement of the present invention can be used even with an inexpensive low-alloy steel, has a burr with a small diameter and no crack on the outer periphery, and has a weld joint having strength and elongation equal to the strength of the base material. Therefore, the weight of the reinforcing bar can be reduced and the strength and safety of the concrete can be increased.

  Hereinafter, the present invention will be specifically described with reference to the best embodiment shown in the drawings. First, the butt welding apparatus used in the embodiment of the present invention will be described. FIG. 1 is a front view of a welding apparatus used for butt welding of a closed loop type shear reinforcement of the present invention, and FIG. 2 is a top view thereof.

In the figure, a moving electrode 2 and a fixed electrode 2 ′ are disposed on a frame 1 so as to face each other, and the moving electrode 2 is driven to move in the axial direction by an electrode moving cylinder 3. The position of the electrode 2 is detected by the position detection encoder 7, and the upset amount is thereby controlled. The electrodes 2, 2 'each of the grip 2a, 2b and 2a', is divided into 2b', one grip 2a, 2a 'have electrode opening cylinder 4a, is driven to move in the axial perpendicular direction by 4b, the other grip 2b and 2b ' are fixed to the frame so as to grip a wire W (hereinafter referred to as a workpiece) W of a shear reinforcement formed into a closed loop type. The set power is applied from the power transformer 30 to the electrodes 2 and 2 '.

  Using the above butt welding apparatus, butt welding was performed using a wire having a wire diameter of 13.1 mmφ, and a 785 standard shear reinforcement bar was manufactured by an example of the method of the present invention and a comparative example of the conventional method.

  Examples of the present invention will be described below. FIG. 3 is a view showing a butt welding pattern according to the embodiment of the present invention, and FIG. 4 is a view showing a shape of a weld portion formed at a time indicated by a symbol shown in FIG. FIG. 5 is a flowchart showing the welding process, the left side shows the present invention, and the right side shows the process of the comparative example. In the figure, the solid line indicates the current value applied between the electrodes, the chain line indicates the applied pressure between the electrodes, and the broken line indicates the change in the distance between the electrodes.

Based on the flowchart of the method of the present invention on the left side of FIG. 5, the welding process of the pattern of FIG. 3 of the present invention will be described. The following symbol numbers indicate the above-described element symbols of the butt welding apparatus of FIGS. First, the electrodes 2 and 2 'on both sides are placed at a standby position set at an interval of 40 mm (STEP 1), the workpiece W is set in the welding apparatus (STEP 2), and the electrodes 2 and 2' are closed by the electrode opening / closing cylinders 4a and 4b. The workpiece W is gripped (STEP 3). As shown in FIG. 3, welding pressure is applied by applying a low pressure of 10 kN between the electrodes by the electrode moving cylinder 3 (STEP 4), and a welding current of 9 kA is applied to the electrodes 2 and 2 ′ for about 2 seconds to bring the workpiece to the welding temperature. Heat (STEP 5) and upset until the distance between the electrodes is 25 mm (STEP 6). The upset amount at this time is about 15 mm.

  Here, the welding pressurization is released (STEP 7), and the welding is finished. When the welding is completed, the temperature is maintained until the temperature of the weld joint is lowered to 500 ° C. or lower. (STEP8). When the temperature of the welded joint is lowered to 500 ° C. or lower, a second current of 10 kA is applied again for about 0.5 s to heat both sides of the welded joint to 500 to 700 ° C. (STEP 9), and 60 kN between the electrodes. A second pressure is applied by applying a high pressure (STEP 10), the distance between the electrodes is brought close to 18 mm, and a second upset of 7 mm is performed (STEP 11). Thereby, the strength increasing portion W ′ is formed in the welded joint (STEP 12).

Comparative example

  The comparative example shows a conventional welding method. In the comparative example, a closed loop type shear reinforcement having the same shape was prepared using the same wire material as in Example 1. The flowchart of the process of a comparative example is shown on the right side of FIG. FIG. 6 shows a pattern of a butt welding method of a closed loop type shear reinforcement bar of a comparative example, and FIG. 7 is a diagram showing a burr form of a weld joint formed at a time indicated by a symbol in FIG.

Based on the flowchart of the comparative example on the right side of FIG. 5, the welding process of the pattern of FIG. 6 of the comparative example will be described. The following symbol numbers indicate the above-described element symbols of the butt welding apparatus of FIGS. Place the opposite electrodes 2, 2 'to the standby position set to the interval 24 mm (STEP1), set the workpiece W to the welding device (STEP2), the electrode closing cylinder 4a, closing the electrodes 2, 2' by 4b workpiece W is gripped (STEP 3). As shown in FIG. 6, welding pressure is applied by applying a pressure of 60 kN between the electrodes by the electrode moving cylinder 3 (STEP 4), and a welding current of 8 kA is applied to the electrodes 2 and 2 ′ for about 3 seconds to heat the workpiece to the welding temperature. (STEP 5), and upsetting is performed until the distance between the electrodes becomes 4 mm (STEP 6). The upset amount at this time is about 20 mm. Here, the welding pressurization was released (STEP 7), the workpiece gripping of the electrode was released (STEP 8), the electrode was returned to the standby position, and the welding was completed.

  Table 1 shows the results of the welding test. In the comparative example, the strength of the welded portion is significantly reduced with respect to the strength of the base material, the tensile strength is about 70%, the yield point is about 55%, and the elongation is about 60%. Disconnected. In contrast, in the present invention, there was no decrease in the strength of the welded portion, and the tensile strength, yield point, and elongation value were 100%, and the fracture test was cut with the base material.

  The shape of the weld in each step of the example is shown in FIGS. The welded portion by the welding method of the present invention shown in FIG. 4 has a burr outer diameter of about 26 mm (2.0 d) as shown in FIG. It was.

  On the other hand, the burr in the welded joint of the comparative example shown in FIG. 7 has a maximum outer diameter of about 30 mm, and the side surface is cracked on the outer periphery as shown in FIG. It was. For this purpose, a deburring process for scraping the outer periphery of the burr was required.

  As described above, the closed loop type shear reinforcement of the present invention has a small outer diameter and a smooth weld joint burr on the outer periphery. In addition, since the strength increasing portion is formed in the welded joint, a highly reliable closed loop shear reinforcement having high breaking strength can be obtained, and the cost of the concrete structural material can be reduced.

It is a front view of the butt welding apparatus of the closed loop type shear reinforcement used for this invention embodiment. It is a top view of the butt welding apparatus of the closed loop type shear reinforcement used for this invention embodiment. It is a figure which shows the pattern of the butt welding of the closed loop type shear reinforcement of the Example of this invention. It is a figure which shows the state of the welding part which generate | occur | produces in the process of FIG. It is a flowchart of the manufacturing process of a closed loop type shear reinforcement. It is a figure which shows the pattern of the butt welding of the closed loop type shear reinforcement of a comparative example. It is a figure which shows the state of the welding part which generate | occur | produces in the process of FIG.

Explanation of symbols

1 frame, 2 electrode, 3 electrode moving cylinder, 4 electrode open / close cylinder, 7 position detection encoder, 30 power transformer,

Claims (4)

In a closed loop type shear reinforcement where a wire cut to a predetermined length is formed into a loop shape and both cut ends are butt welded , electric power is applied to the electrode holding the wire on both sides of the weld and the weld is heated to the welding temperature. After the upset welding, the temperature of the welded joint is lowered to 500 ° C. or lower, electric power is again applied between the electrodes, and the temperature of the wire rod on both sides of the welded joint is raised to 500 to 700 ° C. A closed-loop type shear reinforcement which is characterized by having a certain amount of upset and forming an increased strength portion at the weld joint. The closed loop type shear reinforcement according to claim 1, wherein an outer diameter D of the burr of the weld joint is D≤2.0d, where d is a diameter of the wire. No decrease in strength and elongation values of the welded portion with respect to the wire base material has a 785N / mm ² or more yield point, according to claim 1 or 2, characterized in cutting with Hahazai part upon rupture Closed loop type shear reinforcement described in 1. The wire is in mass%, C: 0.40% or less, Si: 2.0% or less, Mn: 2.0% or less, carbon equivalent (C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14). The closed loop type shear reinforcement according to any one of claims 1 to 3, which is a high-strength wire obtained by heat-treating a low alloy steel containing 8% or less.

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