JPS6072689A - Gas press welding method of steel material - Google Patents

Abstract

PURPOSE:To improve reliability of a joint by butting the end faces of steel materials, increasing stepwise or gradually the pressurizing force to be exerted on the butt part thereof in accordance with progression of heating and subjecting the butt part to initial press welding. CONSTITUTION:Reinforcing steel bars 1, 2 are butted and are heated by ring burners 5 initially under zero pressurizing force. The zero pressurization is maintained until the temp. in the contact part of the reinforcing steel bars attain the temp. adequate for the press welding temp. The pressurizing force is stepwise or gradually increased upon attainment of the adequate temp. until finally the prescribed pressurizing force is attained. The prescribed pressurizing force is maintained until the butt space is closed to generate some compressive bulge in the butt part. The operation of an electrically driven pump is stopped in accordance with the precedure for pressurizing in two-stage upsetting where the butt space is no more observed. The pressure decreases gradually after stoppage of the pressurizing force and the bulge 4 is kept accelerated to grow by the residual pressure. When the pressurizing force is reduced by half, the pump is again operated to pressurize the butt part again and where the compressed bulge 4 attains a prescribed extent, the joining is completed.

Description

[Detailed description of the invention] The invention relates to a gas pressure welding method for steel materials such as reinforcing bars, and in particular to obtain a sound gas pressure welded joint even when there is a gap between butt end faces of the steel materials to be joined (hereinafter referred to as butt gap). This relates to a pressure mounting method that produces

Welding defects in gas pressure welded joints are mainly determined by the presence or absence of flat fracture surfaces and the area where they occur. A flat fracture surface refers to the flat, grayish-white, non-crystalline surface that is observed on the fracture surface when a joint of press-welded steel materials is fractured.This flat fracture surface is likely to occur when the above-mentioned butt gap exists. It is known that the 11ili product increases as the gap increases, and the solution to this problem is a major factor that determines the health or failure of pressure welding joints.

Two-stage upsetting or three-stage upsetting methods are currently used for welding steel materials, mainly reinforcing bars.

As shown in Figures 1 and 2, the above-mentioned two-stage upsetting method involves clamping the reinforcing bars 1 and 2 to be welded with chucks 6 to the protruding edges of the reinforcing bars, and applying a constant pressure a (a practical stone) depending on the cross-sectional area. While applying a constant pressure (selected in the range of 3 to 6 kgf/mm2), heating is fully started from the nozzle 5 of the cylinder gas burner at point 21, and as the heating progresses under the constant pressure, the butt gap is increased. 3 closes and a slight compression bulge 4 occurs, 1) the pressure pump is stopped at 2 points (initial pressure welding process), and while heating continues, pressure welding is progressed by the residual pressure a', and the pressure is increased. Once the predetermined value of 28 points has been obtained, the pressure reaches a certain level and the pressure is reapplied at 1 to encourage the growth of the bulge, resulting in a predetermined bulge 4' and completing the work at 1 point. The latter three-stage upsetting method is a method that was developed relatively recently, and as detailed in Japanese Patent Publication No. 58-23192, the initial pressing method is similar to the two-stage upsetting method described above. After that, a pressure welding method is used in which the pressure welding is completed by performing primary repressurization and secondary repressurization under predetermined pressure control as described in the same publication.

All of the surface pressure welding methods described above 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 past, forge welding. Of course, it is best to completely remove oxides etc. on the surfaces to be joined in advance, and in the state T/c2 where the two end surfaces are pressed against each other, it is most desirable that they are in close contact. be.

However, the end faces of the reinforcing bars are not necessarily cut flat and 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 (/yaar cutting), and the condition of the cut surface is As a practical matter, it is quite difficult to pre-process the butt condition of two reinforcing bars 1.2 to a condition where there is no butt gap 3, as shown here, where it is normal for the situation to worsen, so currently the Japan Society of Civil Engineers and Adopted by the Architectural Institute of Japan! In the standard specification for reinforcing steel gas pressure welding work, the butt gap is 3 mm and they intersect tolerably. For this reason, when the end faces are erected and pressure is applied during joining, the actual contact area is extremely small, and the actual pressure receiving area of the pressure applied to the abutting part may be extremely limited. However, as mentioned above, in gas pressure welding of reinforcing bars using the two-stage and three-stage upsetting methods, a constant pressure a, or at least a constant pressure of at least half of that pressure, is applied between the abutting end surfaces in advance and then heated. A method is being taken. This is mainly based on the idea that it would be 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. .

The invention was provided with the entire purpose of improving the absurdity of this point, and its gist is to butt the ends of the steel materials l'fj, apply pressure and heat to the butt part, and eliminate the butt gap. Copper phase gas pressure welding in which the entire initial pressure welding is performed through a process of increasing the pressure applied to the abutting portion stepwise or gradually as the heating progresses in the initial pressure welding step of generating a compression bulge. Method VrC has characteristics.

Hereinafter, an example of the present invention will be described as an experiment f! According to IIJ, specifically explain F! A.

The reinforcing bar used is 5D35. D32 was used, and the pressurization method shown in FIG. 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, for the purpose of seeing the effect of non-invention. The pretreatment of the end faces was carried out by grinding using a hand grinder called a ring, as in the field work, and the reinforcing bars 1 and 2 were butted together, and the pressurizing force a1 was initially set to Okgf/mm2, as shown by the crater 5. Start heating with a ring burner (heating start point Pa1) L, the heating start point pa1
The temperature of the contact part of the reinforcing steel is the appropriate temperature for pressure welding (900'C-10
The same volume pressurization or the state equivalent to zero pressurization (zero pressurization a+) is maintained until reaching 00'C (near 00'C).

The time required from the initial heating start point pa+ to the pressure welding appropriate humidity point Pa2 under zero pressure was 40 to 50 seconds. This time difference tfi contact state is slightly different for each test piece, and the variation is due to leaving judgment of the appropriate temperature to the operator's visual observation.

At this optimum temperature point Pa2, the pressurizing force is increased stepwise or gradually as shown in the figure, and finally at point pa3 a predetermined pressurizing force a (in this experiment, 95 kg f per nominal cross-sectional area of the reinforcing steel) is applied.
/'mrn2 and sita).

In the figure, a2U shows the state of the pressurizing force a2 that is increased in stages, and the stepwise pressurizing force a2 [obtained by operating the electric pump by energizing pulses according to a predetermined program.

The above pressure welding and heating point Pa2 (also the initial pressurization start point)
The time required to reach the specified pressure point Pa3t is 30 to 4
It was 0 seconds.

Then, the pressurized state with a predetermined pressure a is maintained until the butt gap 3 is closed (in the experiment, the butt gap is compressed to +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 absent pressurization procedure described above. The initial pressure end point P2 corresponds to the initial pressure welding process described in the two-stage and three-stage abselination methods.

Although the pressure gradually decreases as 9 hours pass due to the stop of the pressurizing force, the compressed 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 P3), and the joining is completed when the compression bulge 4' reaches a predetermined amount.

The total time required for welding per piece according to the above is 170 to 190 minutes.
seconds, the total compression amount was 22-26 mm2.

After performing a fracture surface inspection and mechanical test on the test piece according to the above procedure, first, for the fracture surface inspection, mechanical cuts () and 1) are made in the joint, and a tensile tester is used (a bending tester may also be used). No. 1. The fracture surface was visually observed after being fractured from the edge, and it was found that there were no flat fracture surfaces or other defects, and the crystal grains were found to be finer than those produced by conventional methods. Also mechanical test c″ff1
．． OD (The standard specification is 0.8D, but in this test, the flat fracture surface, which is often observed in the past and tends to occur around the circumference near the periphery, was The test train was machined using a lathe (because we did not want to cut it), and a tensile test and a bending test were conducted, but the base material was cut in the tensile test, and the bending test was able to bend the fl170"E without any defects. In this case, the butt gap 3 was set at 5 mm, but
Of course, it is desirable that this butt gap be smaller.

Further, Fuwa discloses a heating method that can be used in combination with the above embodiment, ie, a second embodiment that uses the same heating method in combination.

Below, the same second example is shown in Figures 3 and 4, and ``5''.
This will be explained with reference to all the figures.

At present, all heating charcoal for gas pressure welding of reinforcing bars uses oxygen/acetylene flame. The heating device is a so-called cylinder burner, and burners for pressure welding of reinforcing bars from various companies are used.

These burners have a frame that serves as a gas passage that goes around the reinforcing steel, and a number of craters corresponding to the diameter of the reinforcing steel are arranged inside the frame. A reducing flame is emitted from the reinforcing steel, which rises and mixes while preventing oxidation of the end face of the reinforcing steel. At the same time, the pressing force that is acting on the pressure advances the pressure welding and closes the butt gap. After that, a neutral flame (this flame temperature is lower) The current gas pressure welding method for reinforcing steel is to heat the central part 1 of the reinforcing steel to an appropriate and uniform temperature by heat conduction from the surface. 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 The reducing power of each part is different. Gas flames are roughly divided into a white core at the center and secondary flames around it.In the case of reduction flames, this secondary flame is a white flame called acetylene feather. It has become a flame.

And the part with the strongest reducing power is the tip of the white heart! l1
It is thought to be 2 to 3 mm ahead. Although it is called a reducing flame, it is important to note that the reducing power differs depending on the part of the flame, but on the other hand, in pressure welding of reinforcing steel, as the compression progresses, a bulge occurs at the joint, causing a bulge in the crater. It is essential that the distance between the tip and the surface of the reinforcing steel (hereinafter referred to as the crater distance) gradually narrows, and that no backfire occurs even in this narrowed state. For this reason, in a ring burner with fixed nozzle spacing, the nozzle spacing must be wide, and the optimal flame is set at the point when compression has not yet occurred at the start of heating and when it is most desirable to prevent oxidation of the end surface. As can be seen in previous experimental results, the wider the butt gap, the more the flame is forced to heat in areas where the flame's reducing power is not strong. It is thought that there are other factors that lead to the result that the area of the flat fracture surface becomes wider.

When implementing the pressure welding method, as a countermeasure based on the above-mentioned idea, the invention is to continuously vary the spark gap to follow the progress of compression, that is, the generation of a compression bulge, or to use at least two types of spark holes. It was decided to use all ring burners with intervals.

In other words, while there is still a butt gap, the gap between the nozzles should be made as small as possible so that pressure welding can proceed without hitting the fully grooved surface where the reducing force of the flame is strongest (of course, the flame is a reducing flame).
, After the butt gap is closed, the flame should be neutral in order to effectively utilize the combustion gas energy rather than reducing force, and the stability of the flame (specifically, no flashback) should be maintained. One implementation f+lJ is shown in which the heating operation described above is perfectly combined with the pressurizing operation described in the first example.
Explanation of parts that overlap with the 81st embodiment will be omitted. The reinforcing bars 1 and 2 used are 5D35. D32 and the pressurization method shown in Figure 3 was used in this experiment.
As shown in the figure, there are two types of craters 5a and 5b, the distance between the craters facing each other in the reinforcing bar diameter direction is 60 mm and 7 Qrnm.
Using separate ring burners 7, it was possible to switch the flame between them.

The ring burner 7id has two gas supply pipes 8.9 that communicate with each of the above-mentioned populations 5a and 5biC, and both gas supply pipes 8.9
It has a switching circuit 10 for switching the timing.

The setting of the butt gap 3 between the end faces of the reinforcing bars, the pretreatment of the end faces, etc. were carried out in the same manner as in the first embodiment, and for pressure welding, first of all, the cracker 5a with a spacing of 60 mm was used, and the restoring flame was butted as much as possible. It is heated while being inserted into the gap 3, and initial pressure welding is performed from the Pa+ point to the 22nd point.

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 completely stopped in accordance with the pressurization procedure in step 7 of the two-stage uptake, but at this stage, the heating ring burner 7 is The interval W2 was switched to the nozzle 5b of 7 (1 mm) and heated with a neutral flame. In the same heating state, the pressure welding process from the 22nd point onwards was performed.

That is, the pressure gradually decreases during the pressurization at 22 points, but when the pressurization force is halved, the pump is operated again.
When the pressure is fully applied again and the predetermined pressure and compression amount are reached, the joining is completed.

It should be noted that both the above-mentioned pressurizing operation and heating operation are theoretically reasonable, and experiments in which each was applied independently were also conducted, and the effect of each was determined to be 82 G n in separate experiments.

As detailed above, the invention is extremely effective in further improving the reliability of joints of reinforced structures by using a new reinforcing steel gas pressure welding method that is highly adaptable to the current state of reinforcing bars on site.

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 welding force, heating time, and pressurization time in the conventional gas pressure welding method (two-stage upsetting method) for reinforcing bars. 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 that is an implementation of the present invention, and FIG. 4 is a heating operation used in combination with the invention. Fig. 8 is a diagram illustrating work 8, and Fig. A shows the heating state in the initial pressure welding process of reinforcing bars, and a side view of "31";
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, Figure 5A is a ring used in the heating operation shown in Figure 4 above. Front view of the burner,
Figure B is a side view of the same. 1.2・Reinforcement bar, 3・Butt gap, 4 Compression bulge during initial pressure welding, 5, 5a, 5b Crater, 6...Chuck, pa+・Initial heating start point, pa2...Point of pressure welding appropriate temperature reached (initial pressure start point), pa3...Predetermined pressurization force attainment point, P2 initial pressurization end point, P3 repressurization start point, al
Zero pressure, a2 Stepwise pressure, a - Predetermined pressure. 1.ゝ(ε−

Claims (1)

[Claims] In the initial pressure welding process in which the end faces of the copper phase are abutted and pressure and heat are applied to the abutting portion to eliminate the abutment gap and generate a compression bulge, the pressure applied to the abutting portion is gradually applied as the heating progresses. A method for gas pressure welding of steel materials, characterized in that the above-mentioned initial pressure welding is entirely performed through a process of raising or gradually raising the material.