JPS643596B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a gas pressure welding method for steel materials such as reinforcing bars.
In particular, the present invention relates to a pressure welding method that can provide a sound gas pressure welded joint even when there is a gap (hereinafter referred to as butt gap) between butt end faces of steel materials to be welded.

Welding defects in gas pressure welded joints are mainly judged by the presence or absence of flat fracture surfaces and the area where they occur. A flat fracture surface is a flat, grayish-white, non-crystalline surface that is observed on the fracture surface when a joint of press-welded steel materials is fractured. It is known that the area of the gap increases as the gap increases, and solving this problem is a major factor that determines the health or failure of pressure welding joints.

Currently, a two-stage upset method or a three-stage upset method is used for gas pressure welding of steel materials, mainly reinforcing bars.

As shown in Figures 1 and 2, the above two-stage upset method involves clamping the reinforcing bars 1 and 2 to be welded to the butt part of the reinforcing bars with a chuck 6, and applying a constant pressing force a according to the cross-sectional area of the reinforcing bars 1 and 2.
(Practical pressure is a constant pressure selected in the range of 3 to 6 kgf/ ^mm2 ), heating is started from point _P1 using the ring gas burner nozzle 5, and heating progresses under the constant pressure. Butt gap 3
closes and a slight compression bulge 4 occurs, then P ₂
Once at point P, the pressure pump is stopped (initial pressure welding process), and while heating continues, pressure welding proceeds with residual pressure a', and when the pressure drops to the predetermined value at point _P3 , a constant pressure is reached. Pressure is applied again until the bulge reaches a predetermined size 4' to encourage the growth of the bulge.
This is a way to complete the task once you have obtained it.

The latter three-stage upsetting method is a method that was developed relatively recently, and as detailed in Japanese Patent Publication No. 23192/1983, after going through the same initial pressure welding process as the two-stage upsetting, the same method is used. This is a pressure welding method in which pressure welding is completed through primary repressurization and secondary repressurization under predetermined pressure control as described in the publication.

Both of the above pressure welding methods have in common that the initial pressure welding process is carried out while maintaining the initial pressure at a constant high level.

In the first place, the joining principle or joining mechanism of the welding method called gas pressure welding is thought to be similar to diffusion welding or, in the old days, forge welding. Therefore, the condition of the abutting surfaces of the base materials to be joined is such that, of course, oxides etc. on the surfaces to be joined must be completely removed in advance, and when the two end surfaces are pressed against each other, both It is most desirable that they are in close contact.

However, when joining reinforcing bars, the end faces of the reinforcing bars are not necessarily cut flat at right angles to the reinforcing bar axis when shipped from the factory by the reinforcing bar manufacturer.

In addition, when actually used in structures, reinforcing bars are cut on site by a reinforcing bar fabricator according to the design drawings, but this cutting method is the so-called push cutting method (shear cutting), and the condition of the cut surface is Usually it gets worse.

In this way, the butt state of two reinforcing bars 1 and 2 is
As it is actually quite difficult to pre-process to a state where there is no butt gap 3, the "Reinforcement Gas Pressure Welding Standard Specifications" currently adopted by the Japan Society of Civil Engineers and the Architectural Institute of Japan allows for a butt gap of up to 3 mm. . For this reason, when the end surfaces are butted and pressurized during joining, the actual contact area is extremely small, and the area that actually receives the pressing pressure applied to the abutting portion is often extremely limited. However, as mentioned above, in gas pressure welding of reinforcing bars using the two-stage and three-stage upset methods, a constant pressure a is maintained from the beginning.
Alternatively, a method is used in which a constant pressure of at least half of that pressure or more is applied in advance between the abutting end faces and then heated. This is mainly based on the idea that it is advantageous to close the butt gap 3 as quickly as possible in order to prevent the formation of a flat fracture surface, which is one of the defects in the press-welded portion. However, because of this, the initial pressure welding occurred under abnormally high pressure at a stage where the temperature had not risen sufficiently, and this actually encouraged the formation of a flat fracture surface in this area. ing.

The present invention has been provided for the purpose of improving this unreasonableness, and in the above-mentioned initial pressure welding process, the butt pressure of the steel materials is reduced to zero pressure in the presence of a gap between the end faces of the steel materials to be joined. The abutting portion is heated until it reaches the appropriate pressure welding temperature while being maintained at a temperature of The present invention is characterized by a gas pressure welding method for steel materials in which the above-mentioned initial pressure welding is performed by raising the steel materials.

EXAMPLES Examples of the present invention will be specifically described below according to experimental examples.

The reinforcing bars used were SD36.D32, and the pressurization method shown in Figure 3 was used.

The relationship between reinforcing bars and burners will be explained with reference to Figure 2.

The butt gap 3 between the end faces of the reinforcing bars 1 and 2 was targeted to be 5 mm, which is larger than the standard specifications, in order to see the effects of the present invention. Pretreatment of the end face was carried out by grinding using a hand grinder called a sander, as in the field work. In this way, reinforcing bars 1 and 2 are butted together, and pressure is applied.
A ₁ is initially kept at 0 Kgf/mm ² , and heating is started using the ring burner indicated by crater 5 (heating start point Pa ₁ ), and from the heating start point Pa ₁ the temperature of the contact area of the reinforcing bars reaches the appropriate temperature for pressure welding. The same zero pressurization or a state equal to zero pressurization (zero pressurization force a ₁ ) is maintained until reaching the temperature (nearly 900°C to 1000°C).

The time required from the initial heating start point Pa ₁ to the pressure welding appropriate temperature point Pa ₂ under zero pressure was 40 to 50 seconds. This time difference is due to the fact that the contact state is slightly different for each test piece, and the determination of the appropriate temperature is left to the operator's visual inspection.

At this optimum temperature point Pa ₂ , the pressure is increased stepwise as shown in the figure, and finally at point Pa ₃ a predetermined pressing force a (in this experiment, 5 kgf/mm ² per nominal cross-sectional area of reinforcing steel) is applied.
).

In the figure, a ₂ indicates the state of the pressurizing force a ₂ that is increased stepwise, and the stepwise pressurizing force a ₂ is obtained by operating the electric pump with pulsed energization according to a predetermined program.

The time required from the pressure welding appropriate temperature point Pa ₂ (which is also the initial pressurization start point) to the predetermined pressure point Pa ₃ was 30 to 40 seconds.

Then, the pressurized state with the predetermined pressure a is maintained until the butt gap 3 is closed (in the experiment, it is compressed to the butt gap + 1 mm just to be sure), and when the butt part is slightly compressed and bulged and the butt gap 3 is no longer recognized. , stop the operation of the electric pump according to the two-stage upset pressurization procedure described above. The process up to the initial pressurization end point _P2 corresponds to the initial press-welding process described in the two-stage and three-stage upset methods.

Although the pressure gradually decreases with the passage of time due to the stop of the pressurizing force, the compression bulge 4 continues to be encouraged to grow due to the residual pressure.

Next, when the pressurizing force a is halved, the pump is operated again to apply pressure again (repressurization start point P ₃ ), and when the compression bulge 4' reaches a predetermined amount, welding is completed.

The total time required for welding per piece based on the above is 170 ~
At 190 seconds, the total compression was 22-26 ^mm2 .

Fracture surface inspection and mechanical tests were performed on the test pieces according to the above procedure. First, for the fracture surface inspection, a notch was mechanically made in the joint, the fracture was made from the notch using a tensile tester (a bending tester may also be used), and the fracture surface was visually observed. There were no defects at all, and the crystal grains were found to be finer than those produced by conventional methods. Also, mechanical test is 1.0D
(The standard specification is 0.8D, but in this test, if there is a flat fracture surface that tends to occur along the circumference near the periphery, which is often observed in the past, it is desirable to mechanically remove it.) (because there is no such thing), it was lathed and tensile test and bending test were conducted.
In the tensile test, the base material could be cut, and in the bending test, it could be bent up to 170° without any defects.

In the experimental example, the butt gap 3 was 5 mm, but it is of course preferable that the butt gap be smaller.

Furthermore, the present application describes a heating method used in combination with the above embodiments,
That is, a second embodiment is disclosed in which the same heating method is used in combination.

The second embodiment will be described below with reference to FIGS. 3, 4, and 5.

At present, all heating flames for gas pressure welding of reinforcing bars are oxygen/acetylene flames. The heating device is a so-called ring burner, and burners for pressure welding of reinforcing bars from various companies are used. These burners have a frame surrounding the reinforcing steel as a gas passage.
Inside, a number of craters corresponding to the diameter of the reinforcing bars are arranged. Then, until the butt gap closes, reducing flames are emitted from these many craters to raise the temperature while preventing oxidation of the end face of the reinforcing steel, and at the same time, the pressure welding progresses due to the pressing pressure acting, closing the butt gap. The current gas pressure welding method for reinforcing bars then uses a neutral flame (which has a higher flame temperature) to heat the reinforcing bars to an appropriate and uniform temperature through heat conduction from the surface to the center. However, the current situation is that all of the above-mentioned ring burners used for this heating have a fixed distance from the tip of the crater to the surface of the reinforcing steel.

On the other hand, if we think about the reducing power of flame, it is true that the aforementioned reducing flame is a flame that has a higher reducing power as a whole than a neutral flame, but There are differences in the reducing power of each part. In other words, a gas flame can be broadly divided into a white core at the center and a secondary flame around it, and in the case of a reduction flame, this secondary flame is the so-called acetylene flame.
It is a white flame called a feather. The part with the strongest reducing power is 2 points from the tip of the white core.
It is thought to be ~3mm ahead. Although it is called a reducing flame, it is important to note that the reducing power varies depending on the location of the flame.

However, in pressure welding of reinforcing bars, as compression progresses, a bulge occurs at the joint, and the distance between the tip of the crater and the surface of the reinforcing steel (hereinafter referred to as the "crater spacing") gradually narrows, and even in this narrow state, backfire can occur. The essential condition is that there is no such thing. For this reason, in a ring burner with a fixed interval between the nozzles, the interval between the nozzles must be wide, and the optimum flame position is set at the time when compression has not yet occurred at the start of heating and when it is most desirable to prevent oxidation of the end face. Location is not available. In other words, it is necessary to heat the part of the flame where the reducing power is not so strong. This is considered to be another factor leading to the result that the wider the butt gap, the wider the area of the flat fracture surface, as seen in conventional experimental results.

When implementing the pressure welding method, the present invention provides a countermeasure based on the above-mentioned concept, in which the interval between the craters is continuously varied to follow the progress of compression, that is, the generation of a compression bulge, or at least two types of intervals between the craters are changed. It was decided to use a ring burner with

That is, while there is still a butt gap, the gap between the nozzles is made as small as possible, and the pressure welding proceeds while the part of the flame with the strongest reducing force is applied to the groove surface (of course, the flame is a reducing flame), and the butt gap is closed. From then on, the flame was designed to be neutral in order to effectively utilize the combustion gas energy rather than reducing power, and the flame stability (specifically, no backfire) was intended.

Below, in the pressurizing operation explained in the first embodiment,
An example will be shown in which the above heating operation concepts are combined. Description of parts that overlap with the first embodiment will be omitted. The reinforcing bars 1 and 2 used were SD35.D32 as before, and the pressurization method shown in Fig. 3 was used. 2 where the distance is 60mm and 70mm
Using a ring burner 7 having different types of burners 5a and 5b, it is possible to switch the flame between them.

The ring burner 7 has two gas supply lines 8 and 9 that communicate with the respective craters 5a and 5b, and a switching device 1 that switches between the two gas supply lines 8 and 9 in a timely manner.
has 0.

The setting of the butt gap 3 between the end faces of the reinforcing bars, the pretreatment of the end faces, etc. are carried out in the same manner as in the first embodiment, and for pressure welding, first of all, use the nozzle 5a with the interval W ₁ of 60 mm, and reduce the reducing flame as much as possible. Heating is performed by inserting it into the butt gap 3, and heating is performed under zero pressure a from the point Pa ₁ to the point P ₂ .

As mentioned above, at the initial pressurization end point _P2 where the butt gap 3 is no longer recognized, the operation of the electric pump is stopped according to the pressurization procedure of the two-stage upset, but at this stage the heating ring burner 7 is W ₂ is
Switched to 70mm crater 5b and heated with neutral flame. In the same heating state, the pressure welding process from point P ₂ onward is performed.

That is, after the pressurization is stopped at point _P2 , the pressure gradually decreases, but when the pressurization force is reduced by half, the pump is operated again and pressurization is performed again, and the joining is completed when the predetermined pressurization force and compression amount are reached.

It should be noted that both the pressurizing operation and the heating operation described above are theoretically reasonable, and experiments were conducted in which each was applied independently, and the effects of each were confirmed in separate experiments.

As described in detail above, the present invention is a new reinforcing steel gas pressure welding method that is highly adaptable to the current situation of on-site reinforcing bars, and is extremely effective in further improving the reliability of joints of reinforcing steel structures.

Although the embodiment has been described with respect to reinforcing bars, it goes without saying that the present invention may be applied to gas pressure welding of other steel materials in which a similar butt gap occurs.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between the pressurizing force, heating time, and pressurizing time in the conventional gas pressure welding method (two-stage upsetting method) for reinforcing bars, and Figures A, B, and C in Figure 2 are graphs showing the relationship between reinforcing bars in the two-stage upsetting method. A diagram explaining the pressure welding state step by step, FIG. 3 is a graph showing the relationship between the pressurizing force, heating time, and pressurizing time in the gas pressure welding method, which is an embodiment of the present invention. FIG. 4 is a graph showing the relationship between the pressurizing force and the pressurizing time, and FIG. Figure A is a side view showing the heating state of reinforcing bars in the initial pressure welding process;
Figure A' is a front view of the same, Figure B is a side view showing the reinforcing steel heating state after initial pressure welding, Figure B' is a front view of the same,
FIG. 5A is a front view of the ring burner used for the heating operation shown in FIG. 4, and FIG. 5B is a side view of the ring burner. 1, 2...Reinforcement bar, 3...Butt gap, 4...Compression bulge during initial pressure welding, 5, 5a, 5b...
... Crater, 6... Chick, Pa ₁ ... Initial heating start point, Pa ₂ ... Pressure welding appropriate temperature point (initial pressurization start point),
Pa ₃ ... Point at which the specified pressurizing force is reached, P ₂ ... Initial pressurizing end point, P ₃ ... Re-pressurizing starting point, a ₁ ... Zero pressurizing force, a ₂ ...
...Stepwise pressing force, a...Predetermined pressing force.

Claims (1)

[Claims] 1. In the initial pressure welding process in which end faces of the steel materials are butted and pressure and heat are applied to the abutting portion to eliminate the butt gap and generate a compression bulge, the steel materials are butt pressed in the presence of the abutment gap between the end faces of the steel materials. While maintaining the pressure at zero, the abutted portion is heated until the appropriate temperature for pressure welding is reached, and at the appropriate temperature for pressure welding, pressurization of the abutted portion is started, and the pressure is increased stepwise as heating progresses. A gas pressure welding method for steel materials, characterized in that initial pressure welding is performed.