JP4292091B2 - Joined rebar and rebar joining method - Google Patents

Description

  The present invention relates to a bonded reinforcing bar and a reinforcing bar bonding method, and more particularly to a bonded reinforcing bar formed when a reinforcing bar for embedding concrete and the like is arranged at a construction site and the like, and a reinforcing bar bonding method thereof.

  Connecting rebars at construction sites. Examples of the joint form include a gas pressure joint, a weld joint, and a mechanical joint. A gas pressure welding joint is a joint in which two rebars are butted together at the ends, the butted portion is heated with a flame while applying a compressive force, and the heated portion that is in a red-hot state is melted without melting the joining end face It is a form. Conventionally, an oxygen-acetylene flame has been used as a heat source, and since oxygen-acetylene combustion is a strong reducing flame and is high temperature, the bonding surface (adhesion surface) is a good bonding surface with very little oxide film residue. Thus, a satisfactory pressure welded joint is obtained. In addition, in the pressure welding using an oxygen-acetylene flame, after the so-called pre-heating, in which a reducing flame is formed on a heating burner under a low oxygen ratio condition, and a butted portion is heated to form a contact surface in a red hot state, As the latter heating, the combustion oxygen ratio is increased and the reducing flame is switched to the neutral flame, and the heating burner is shaken to the left and right for further compression while performing further compression, so that the gently rounded bulge is joined. To be formed.

  However, since acetylene gas is expensive and has a strong heating power, the temperature between the surface of the bonded portion and the center portion is different, and the pressure contact performance is easily affected. In general, acetylene gas has a high risk and requires careful handling, and acetylene flame is prone to backfire. In particular, a neutral flame used in later heating has a problem that backfire is likely to occur.

  As one method for dealing with the problem, Patent Document 1 (Japanese Patent Laid-Open No. 2001-47255) discloses that acetylene gas is used for the previous heating until the butted surfaces are brought into close contact, and then propane gas is used. , LNG, ethylene gas, butane gas, methane gas, ethane gas, propylene gas, hydrogen gas and the like, or a gas pressure welding method in which late heating is performed by switching to a mixed gas thereof.

JP 2001-47255 A

  In gas pressure welding of a reinforcing bar, as described in Patent Document 1, by switching the fuel gas type between the early heating and the latter heating, several effects such as improvement of safety are brought about. However, switching the fuel gas during a series of pressure welding processes entails a large work burden and complicates the apparatus. Natural gas, propane gas, etc. are safer than acetylene gas, and produce less carbon dioxide than acetylene gas, which is preferable from the environmental point of view. The use of saturated hydrocarbon fuel is required. However, these fuel gases are weaker in reducing action than acetylene gas, and oxides are likely to be generated on the joint surfaces. Therefore, these fuel gases have not been used as a heat source for the previous heating due to problems in the joint quality. Is the current situation.

  The present invention has been made in view of the circumstances as described above, and a good joining surface is formed while using a saturated hydrocarbon fuel gas such as natural gas from the beginning as a heat source for joining. It is an object of the present invention to provide a jointed reinforcing bar and a method for joining the reinforcing bars.

  In order to solve the above-mentioned problems, the present inventors conducted an experiment in which the end surfaces of reinforcing bars were joined using a compressed natural gas (city gas) as a saturated hydrocarbon fuel gas. The oxygen ratio, the shape of the flame, and the amount of compression (referred to as the upset amount) at the time of pressure welding of the rebar where the end surfaces were in contact with each other were varied. As a result, by appropriately selecting the combustion conditions and / or the amount of compression of the reinforcing bars, even when joining using natural gas as the fuel gas from the previous heating stage, joining equivalent to joining using acetylene gas I learned that I could get a strong joint. In addition, the joint rebar made to meet that condition has a shape of the bulge part formed in the joint part, compared with the shape of the bulge part in the joint rebar made by the conventional method by acetylene gas pressure welding, I also learned that it has a so-called brim shape with a steep rise.

  The present invention has been made on the basis of the above findings, and in the joined rebar that joins the end portions according to the present invention, the length of the swollen portion of the joined portion is A, the diameter is B, and the rebar diameter is D. Sometimes, the bulging portion satisfies the conditions of A / D ≦ 1.30 and B / D ≧ 1.75. As shown in the following examples, even when the same kind of reinforcing bar is joined under the same conditions of the compressed natural gas flow rate and the oxygen flow rate, the shape of the bulge portion is A / D ≦ 1.30 and B / D ≧ 1. Those not satisfying the condition of 75 had a very low pass rate of the bending test.

  In order for the shape of the bulging part to satisfy the above conditions, the flame should be concentrated in a narrow area (joint surface area) without baking the vicinity of the joint during late heating, as in the case of pressure welding with a conventional acetylene flame. It suffices to form a bulge portion having a collar shape. Then, the compression force may be released when the shape of the bulging portion satisfies the above conditions.

  That is, the present invention is a method for joining reinforcing bars in which two reinforcing bars are brought into contact with each other and the two parts are joined by heating and softening the contacted portion and the vicinity thereof. The condition of A / D ≦ 1.30 and B / D ≧ 1.75, where A is the width of the bulge portion of the bulge portion in the rebar axis direction, B is the maximum diameter in the direction perpendicular to the axis, and D is the rebar diameter The reinforcing bar joining method is characterized in that the heating condition is controlled so as to satisfy the bulging part, and the compression amount of the reinforcing bar is controlled so that the bulging part satisfies the above conditions. There is also disclosed a reinforcing bar joining method characterized in that: It is a more preferable aspect to join the reinforcing bars by controlling both the heating conditions and the amount of compression of the reinforcing bars so that the bulging part satisfies the conditions of A / D ≦ 1.30 and B / D ≧ 1.75. . As shown in the following examples, in the case of the latter reinforcing bar joining method, when the reinforcing bar compression amount is α and the reinforcing bar diameter is D, the reinforcing bar compression amount so as to satisfy the condition of α / D ≧ 1.1. By performing the control while controlling, it is possible to reliably obtain a bonded reinforcing bar having sufficient bonding strength.

  In any case, by heating the reinforcing bar in a state where the flame is substantially fixed in a virtual plane including the contact surface between the end portions, a bonded reinforcing bar having a bulging portion that satisfies the above conditions stably is obtained. be able to.

  The reason why the bending strength of the joint portion increases due to the shape of the bulging portion satisfying the conditions of A / D ≦ 1.30 and B / D ≧ 1.75, that is, the collar shape is not necessarily clear. However, when the surface of the bonding surface is subjected to local heating by the latter heating and the red-heated surface is pressed and bulges outward, the oxide film generated on the bonding surface during the first heating is broken finely It is presumed that this is the result of gradually pushing outward, and as a result, the joining of the opposing end faces has been completed with no oxide film remaining.

  However, it is preferable that an oxide film is not formed on the joint surface in the course of the previous heating in order to obtain a joint rebar having a higher bending strength. As described above, when heating is performed with a premixed gas of oxygen and a fuel gas mainly composed of saturated hydrocarbons such as natural gas, the reducibility of the flame is weaker than that of the acetylene-oxygen flame, and the joint surface is oxidized. Easy to be. As a method for solving this problem, in a preferred embodiment of the present invention, the preheating until at least the contacted end portions are brought into close contact with each other is performed in a state where the flame and the reinforcing bar are not in contact with each other. By adopting this heating method, it is possible to suppress the formation of an oxide film on the joint surface, and it is possible to obtain a joint rebar having a greater bending strength at the joint. As shown in the following examples, the optimum value varies depending on the combustion conditions, but it is confirmed that a bonded surface with almost no oxide film can be obtained by maintaining the distance between the flame tip and the reinforcing bar surface within a range of 10 mm or less. did.

  According to the present invention, even when the reinforcing bars are joined using a saturated hydrocarbon fuel such as methane, ethane, propane, or butane, for example, compressed natural gas, as the fuel gas, the same as the joined reinforcing bars using acetylene gas as the fuel gas. It is possible to obtain a bonded reinforcing bar having a bonding strength of. Since saturated hydrocarbon fuels such as natural gas are easier to handle than acetylene, and are safer and environmentally friendly, the present invention is extremely effective as a new technique for joining reinforcing bars.

  Hereinafter, the present invention will be described based on embodiments with reference to the drawings. FIG. 1 is a schematic view of an apparatus for carrying out a reinforcing bar joining method according to the present invention, and FIGS. 2 and 3 are sectional views showing two examples of burner craters used therein. FIG. 4 is a view showing an example of the joint portion of the joint rebar according to the present invention, and FIG. 5 is a view showing the joint portion of the joint rebar made by the conventional pressure welding method.

  In FIG. 1, the two reinforcing bars 1 a and 1 b are held in a posture in which their tip surfaces are brought into contact with each other while being gripped by the clamps 3 a and 3 b of the pressure welding machine 2. A ring-shaped burner 6 is arranged so that the burner crater 5 is located in a virtual plane including the abutting surface 4, and a controlled amount of compressed natural gas and oxygen are supplied to the burner 6 from a fuel gas supply source 7. The premixed gas is supplied. The flame blowing direction of each burner crater 5 is directed to the axis L of the two reinforcing bars 1a and 1b.

  At the initial stage of joining (that is, during the previous heating), the tip of the combustion flame is not brought into contact with the surfaces of the reinforcing bars 1a and 1b by adjusting the amount of premixed gas and the shape of the burner crater. It is recommended from the viewpoint of thermal efficiency that the distance between the reinforcing bar surface and the flame tip is 10 mm or less. The burner crater 5 can have an arbitrary shape provided that the above conditions are satisfied. However, in the experiments by the present inventors, as shown in a later embodiment, the burner crater 5 is a type in which a plurality of pilot flame holes 12 are arranged around the main flame hole 11 as shown in FIG. 2 or FIG. In the case of this structure, it was confirmed that the main flame was held in the crater by the pilot flame and high stable combustion could be realized, and as a result, a good joined state was obtained. Therefore, it is recommended to use the burner 6 having the burner crater 5 of the type in which a plurality of pilot flame holes 12 are arranged around the main flame hole 11 shown in FIG. 2 or FIG.

  2 has a one-piece structure as a whole, and FIG. 3 has a two-piece structure in which the inner cylinder 5b is inserted into the outer cylinder 5a for ease of manufacture. Both functions as a burner crater.

  As shown in FIG. 1, two rebars 1 a and 1 b are set, and a required pressure is applied to the abutting surface 4 by the pressure welding machine 2. In this state, only the abutting surface 4 and its immediate vicinity are heated by the flame from the burner crater 5. The end surfaces of the two reinforcing bars 1a and 1b are preferably flat-finished, but may be a simple cut surface brought into the construction site. If flattening is performed, the abutting surface is almost a tight surface, and in the case of a simple cut surface, there is usually a gap. In either case, the rebar is heated in a state where the flame tip is not in contact with the surface of the rebar, so an oxide film is formed on the abutting surface even in the case of natural gas combustion, which is less reducible than acetylene combustion. Can be suppressed. Due to the heat from the flame, the vicinity of the contact surface becomes red hot and softens. The required pressure is applied to the abutting surface 4 of the reinforcing bar by the pressure welding machine 2, and the softened part is compressed by the amount of compression (upset amount) α, and the joint is gradually pushed outward. Then, a bulging portion 20 as shown in FIG. 4 is formed.

  In the reinforcing bar joining method of the present invention, the ring-shaped burner 6 is held at the position described with reference to FIG. 1 from the start to the end of heating. That is, as in the conventional pressure welding method using acetylene gas, the burner is not moved laterally so as to perform so-called “drawing”. Therefore, the red-hot region due to the flame becomes a narrow range, and the shape of the bulging portion 20 generated by the compression of the end surfaces becomes a brim shape with a steep rise. As a result, even if an oxide film is formed on the bonding surface in the early heating stage until the abutting surface becomes a close contact surface, the oxide film formed on the bonding surface in the later so-called later heating stage is fine. While being torn off, it is gradually pushed out toward the outside, and as a result, the joined portion without the oxide film remaining is completed. Even in the actual joining operation, the burden on the operator is reduced because no baking is required, and it is not necessary for the operator to acquire the skill of the baking. Furthermore, the fact that a good joint rebar can be obtained without performing the work process of the stake is that, in the case of automating the joining of the rebar, a mechanism or control corresponding to the stake process is not required, Compared to an automatic gas pressure welding apparatus, there is also an advantage that the apparatus can be simplified.

  As shown in the following examples, in the experiments of the present inventors, when the length of the bulge portion of the joint portion is A, the diameter is B, and the rebar diameter is D, A / D ≦ 1.30 and B When the bulging part satisfies the condition of /D≧1.75, it was confirmed that a bonded reinforcing bar having a bending strength equivalent to that required in the case of acetylene gas pressure welding can be obtained.

  Incidentally, FIG. 5 shows a joining rebar that satisfies the safety standard in acetylene gas pressure welding, and the bulge portion here has a rounded hump-like shape, A / D is about 1.14, B / D is about 1.68.

Hereinafter, the present invention will be described by way of examples.
[Example 1]
Using the gas bonding apparatus described based on FIG. 1 and the burner crater shown in FIG. 2, a bonding test was performed on 22 specimens (rebars). Table 1 shows the test conditions and results. As shown in the figure in the column of the experimental conditions in Table 1, a gap of about 5 mm is obtained when the end surfaces of the specimen are cut obliquely and the ends are brought into contact with each other for the purpose of making the test environment more severe. Was formed at the upper edge. In all tests, natural gas flow rate was 4.00Nm ³ / h, the oxygen flow rate 4.45Nm ³ / h (oxygen ratio: 0.48). The flame length was adjusted so that a gap of about 5 mm was formed between the tip of the flame and the surface of the test body at the start of the test.

  The test bodies 1 to 10 correspond to comparative examples, and the shape of the bulge portion was approximated to the shape of the bulge portion of the jointed rebar in the conventional acetylene gas pressure welding. For this purpose, after the bonded surfaces were in close contact (heating in the previous period), the ring-shaped burner was moved laterally to perform baking. The test bodies 11 to 22 correspond to the examples, and were heated by fixing the position of the ring-shaped burner from the start to the end of heating.

  The A / D in the test bodies 11 to 22 is in the range of 1.17 to 1.30, the average is 1.26, the B / D is in the range of 1.75 to 1.90, and the average is 1.83. It is. About the test bodies 11-22 after completion of joining, when the bulging part was ground and dropped and subjected to a 90 ° bending test (test according to JIS G3112), all were acceptable products (no breakage occurred in the joined part). .

  The A / D in the test bodies 1 to 10 is in the range of 1.41 to 1.55, the average is 1.45, the B / D is in the range of 1.67 to 1.72, and the average is 1.68. It is. About the test bodies 1-10 after completion of joining, when the 90 degree bending test was done similarly to the test bodies 11-22, seven were unacceptable goods (a fracture | rupture produced in the junction part).

  From the above, the shape of the bulge portion of the joint is a specific shape (when the length of the bulge portion of the joint is A, the diameter is B, and the diameter of the reinforcing bar is D, A / D ≦ 1.30 and B /D≧1.75), the joining rebar of the present invention joined by using natural gas as the fuel gas by setting the heating condition by the burner of the joining portion is acetylene gas pressure welding. It can be seen that a bonded reinforcing bar with the same bending strength can be obtained.

[Example 2]
Using the same apparatus and rebar as in Example 1, the quality of the joint surface when the flame tip was in contact with the surface of the rebar and when there was a gap was tested. The natural gas flow rate and the oxygen flow rate are the same as those in Example 1, and in three modes: a condition in which the flame tip is in contact with the reinforcing bar surface (a state of entering from −5 mm from the surface), a distance condition of 10 mm, and a distance condition of 23 mm, Heating was performed until the impingement surface was in close contact (pre-heating).

  The joint surface of each specimen was cut with a cutter, bent and fractured, the state of the fracture surface was visually observed, and the ratio of the oxide layer area was measured. The result is shown in the graph of FIG. As shown in FIG. 6, the oxide layer area is increased by the flame coming into contact with the rebar, and a more stable joint surface can be obtained by performing the joining work under the condition that the flame front does not contact the reinforcing bar surface. Show.

[Example 3]
In Example 1, a premixed gas at a ratio of natural gas flow rate: 4.00 Nm ³ / h, oxygen flow rate: 4.45 Nm ³ / h (oxygen ratio: 0.48) was used as a heating gas, and good bonding was achieved. I could get a reinforcing bar. Therefore, in order to observe the influence of the oxygen ratio on the joint surface, the ratio of (a) natural gas flow rate: 4.03 Nm ³ / h, oxygen flow rate: 3.70 Nm ³ / h (oxygen ratio: 0.40) Premixed gas, (b) natural gas flow rate: 4.03 Nm ³ / h, oxygen flow rate: 4.10 Nm ³ / h (oxygen ratio: 0.44) ratio of premixed gas, (c) natural gas flow rate: 4 0.03 Nm ³ / h, oxygen flow rate: 4.60 Nm ³ / h (oxygen ratio: 0.50) ratio of premixed gas, three premixed gases as fuel gas, and specimens 11 to 11 in Example 1 In the same manner as in No. 22, the reinforcing bars were heated in the previous period, and a joining test was conducted.

  A cut was forcibly made in the joined portion of the joined rebar after the joining was completed, the joined rebar was bent and broken, and the fracture surface was visually observed to measure the ratio of the oxide layer area. In (a), it was almost 20%, in (b) it was almost 0%, and in (c) it was almost 1% or less. In (a), since the oxygen ratio is small, the flame temperature is low and the working time is prolonged, and it is considered that the oxygen contact time in the atmosphere is increased and the oxide layer area is increased. In (b) and (c), it is almost the same as the case where the flame of Example 2 does not contact the reinforcing bar surface. From this, it can be seen that the oxygen ratio has an effect on the quality of the bonded rebar, and more preferably, a more stable bonded rebar can be obtained by carrying out the reinforcing bar bonding method according to the present invention at an oxygen ratio of about 0.44 or more. I understand that.

[Example 4]
The relationship between the bonding strength and the compression amount (upset amount) was examined. Using the same gas bonding apparatus as in Example 1, a bonding test was performed on seven groups in which three pieces were made into one group while changing the compression amount (upset amount) α of the reinforcing bars. The test conditions and results are shown in Table 2. In the same manner as in Example 1, the end face of the test body was cut obliquely so that a gap of about 5 mm was formed at the upper edge when the ends were brought into contact with each other. Reinforcing bars have an outer diameter D of 32 mm. When the total length of the two reinforcing bars whose end faces are in contact with each other is L, and the total length of the reinforcing bars after the joining process is L-α, α is the reinforcing bar. The amount of compression (upset amount) was.

In all tests, natural gas flow rate was 4.00Nm ³ / h, the oxygen flow rate 4.59Nm ³ / h (oxygen ratio: 0.50). Further, the flame length was adjusted so that a gap of about 5 mm was formed between the tip of the flame and the surface of the test body at the start of the test.

  As can be seen from Table 2, Groups 1-3 do not pass the 90 ° bending test. This is considered to be caused by the fact that the bulging part does not satisfy the conditions of A / D ≦ 1.30 and B / D ≧ 1.75. Groups 4-7 all passed the 90 ° bend test. This is presumably because the bulging portion satisfies the conditions of A / D ≦ 1.30 and B / D ≧ 1.75 in all cases, and the values of α / D are all 1. 1 or more. From this, when the reinforcing bar compression amount (upset amount) is α and the reinforcing bar diameter is D, the reinforcing bar compression amount is controlled so as to satisfy the condition of α / D ≧ 1.1. Thus, it can be seen that a bonded reinforcing bar having sufficient bonding strength can be obtained.

The schematic diagram which shows an example of the apparatus for enforcing the reinforcing bar joining method by this invention. Sectional drawing which shows an example of a burner crater. Sectional drawing which shows the other example of a burner crater. The figure which shows an example of the junction part of the joining rebar by this invention. The figure which shows the junction part of the joining rebar made by the conventional press-contact method. The graph which shows the ratio of the oxide layer area by the difference in the distance of a flame front and a reinforcing bar surface.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1a, 1b ... Rebar, 2 ... Pressure welding machine, 3a, 3b ... Clamp, 4 ... Contact surface, 5 ... Burner crater, 6 ... Burner, 7 ... Fuel gas supply source, 11 ... Main flame hole, 12 ... Pilot flame hole , Α: Rebar compression amount (upset amount)

Claims (6)

A joint rebar in which ends are joined, where A / D ≦ 1.30 and B / D ≧ 1. Where A is the length of the bulge of the joint, B is the diameter, and D is the diameter of the rebar. A jointed reinforcing bar characterized by satisfying the condition of α / D ≧ 1.1 when the bulging portion satisfies the condition of 75 and the compression amount of the reinforcing bar is α . A rebar joining method in which two rebars are brought into a state where the ends are in contact with each other, the contacted part and the vicinity thereof are heated and softened, and the two rebars are joined. the width of the axial a, the maximum diameter in a direction orthogonal to the axis B, and rebar diameter is D, the conditions of the a / D ≦ 1.30 and B / D ≧ 1.75 bulge is satisfied And the reinforcing bar joining method is characterized by controlling the heating conditions so as to satisfy the condition of α / D ≧ 1.1 when the compression amount of the reinforcing bars is α . A rebar joining method in which two rebars are brought into a state where the ends are in contact with each other, the contacted part and the vicinity thereof are heated and softened, and the two rebars are joined. the width of the axial a, the maximum diameter in a direction orthogonal to the axis B, and rebar diameter is D, the conditions of the a / D ≦ 1.30 and B / D ≧ 1.75 bulge is satisfied And the reinforcing bar joining method is characterized by controlling the amount of compression of the reinforcing bar so as to satisfy the condition of α / D ≧ 1.1, where α is the compression amount of the reinforcing bar. The reinforcing bar joining method according to claim 2 or 3 , wherein the reinforcing bar is heated in a state where the flame is substantially fixed in a virtual plane including a contact surface between end portions. Subjected to heat in the premixed gas of the saturated hydrocarbon fuel and oxygen, year heating to abutment the ends are in close contact to the claim 2 or 3, characterized in that in a state in which no contact between the flame and rebar The reinforcing bar joining method described. The reinforcing bar joining method according to claim 5 , wherein the fuel is natural gas.

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