JPS6050544B2 - Narrow gap welding method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a welding method for obtaining a defect-free welded part with sufficient welding penetration in narrow gap arc welding, and a structure of an apparatus therefor.

For example, welding, particularly inert gas metal arc welding (abbreviated as MIG welding) using an inert gas as a shielding gas, is known as a means of making high-quality welded connections without defects. However, during welding, inert gas (for example, a mixture of argon gas and carbon dioxide gas) is supplied to the welding area, so the nozzle is larger than the groove size, and the movement of the welding nozzle is restricted. Narrow gap welding work that connects materials with In addition, narrow gap welding is intended for groove widths of 6 to 1 mm and base material thickness of approximately 200 to 3007 wt, making it extremely difficult to perform repairs after welding.

・In other words, these difficulties are completely new problems that must be solved when welding thick base materials with narrow grooves. Therefore, the present inventor first developed a welding wire rod (hereinafter referred to as wire i) in a narrow gap, that is, without swinging the welding nozzle itself from side to side with respect to the welding progress direction.

) proposed a means and device that can swing itself to obtain high-quality welds in narrow gaps. However, even if this wire swinging means is adopted, repeated experiments and studies were conducted to improve the quality of the welded part with fewer defects, and based on the results, the narrow gap welding method and device according to the present invention were developed. This is a proposal. In narrow gap welding, the types of defects in MIG welding and TIG (tungsten inert gas) welding are similar to those in welds made by other welding methods, such as poor penetration with the base metal groove sidewall, blowholes, slag entrainment, and There is a lack of integration with the layers. If we closely observe the melted area caused by the arc during MIG welding, the state is as shown in FIG. 1.

There is a molten pool 2 made of molten metal on the lower side of the wire 1 and slightly rearward in the welding direction a, and as welding progresses, a subsequent bead 3 is formed as a layer of metal that hardens sequentially toward the rear in the welding direction a. There are things to do. Because the surface tension of molten metal is large, its vertical cross section is close to an ellipse as shown in Figure 1, and the contact angle θ with respect to the surface of the front layer 4 is greater than 900, which is the so-called 5-wtness angle ( It has poor wettability. Furthermore, in FIG. 2 showing the A''-A'' cross section of FIG. 1, the so-called 1-wetness between the bead 3 and the base metal 5 is poor, resulting in corner parts and creating opportunities for undercuts and slag entrainment. It has become a state of being. These problems are particularly important in narrow gap welding of bead layers and baths as shown in FIG.
Conventionally, the inert gas was supplied through a passage 17 around the contact tube 6, as shown in FIG. A second inert gas passage 17a is provided surrounding the passage 17 in order to provide sufficient insulation from air.

These conventional inert gas supplies are, for example,
As described in 23461, all of them are intended to block air, and the molten pool. It is not structured to have any influence on, nor is it intended to have any influence on. The purpose of this invention is to use a shielding gas in narrow gap welding using single-layer baths, to have the effect of shielding the arc part from the air, and to more actively change the shape of the molten pool. The purpose of the present invention is to propose a welding method and device for preventing the occurrence of defects in welded parts due to pre-arc welding. Therefore, the inventor of the present application believes that in order to obtain a high-quality weld, it is necessary that the groove penetrates well into both side walls and into the bead of the previous layer, and has developed a number of methods to achieve the above object. We conducted experiments and studies.

Even in narrow gap welding of single-layer busses, it is natural that various conditions such as wire material, base material material, power supply characteristics (voltage, current), welding speed, etc. must be taken into consideration, but the above experiment and As a result of the study, it was found that narrow grooves (for example, groove widths of 6 to 1077!
00W$L) It was found that one of the most important welding conditions during welding is determining the spraying position of the shielding gas that controls the molten pool. That is, it has been found that as long as the position at which gas is blown onto the molten pool is determined, a desired weld joint can be obtained by appropriately determining the welding conditions according to the welding specifications. In short, the first feature of the present invention is that in the method of arc welding one narrow gap in a bead layer one bath using shielding gas, a molten pool formed on the rear side of the arc in the welding direction is then welded in the j direction. A secondary gas is blown onto the molten metal surface in the portion that overlaps with the subsequent bead, and the molten metal surface is pushed and spread by the wind pressure, thereby improving the wetting properties to the side walls of both grooves, and at the same time improving the wetting properties of the previous layer bead immediately before the arc. The second feature is to blow primary gas onto the surface and use the wind pressure to push back the molten metal in the front part of the molten pool to improve wetting properties with the front layer bead, and perform welding. ,
.

In addition to the first feature, the supply amount of each of the primary gas and the secondary gas is controlled. The third feature is that one narrow gap is arc welded using shielding gas.
A gas that pushes and spreads the molten metal surface of the molten pool at the rear side of the contact tube in the welding progress direction and at a position corresponding to the part where the molten pool formed at the rear of the arc overlaps with the trailing bead. A cooling water pipe is arranged between the contact tube and the secondary gas nozzle in close contact with the contact tube, and a primary gas nozzle that spouts gas for pushing back the molten metal is arranged immediately before the contact tube. This is what I have placed. An embodiment of the present invention will be described below with reference to the drawings, taking MIG welding as an example.

FIG. 3 is a diagram showing the welding apparatus viewed from the front in the direction of welding progress (a sectional view taken along the line A-A in FIG. 4). The welding nozzle usually has a long columnar shape with a rectangular cross section, and a contact tube 6 having a hole 6a through which a wire passes is disposed inside the welding nozzle. This contact tube 6 is made of a material with good thermal conductivity and high electrical conductivity, and a third wire formed in a wave shape by the device proposed earlier by the inventor is placed in the hole 6a.
In the figure, the wire is continuously supplied from above, generates an arc at the lower end, is consumed, and swings the wire ends from side to side to form a bead and weld. FIG. 4 shows a cross section taken along line BB in FIG. 3, and the primary gas nozzle 7 is attached in close contact with the contact tube 6 just before the arc 18 in the welding direction a of the contact tube 6.

The inert gas passage may have a hole with a rectangular cross section as shown in Figure 5, or it may have a hole with a rectangular cross section as shown in Figure 6, in which multiple gas passages are drilled in blocks. Furthermore, as shown in FIG. 7, a plurality of tubes may be connected to form one block.
A cooling water pipe 8 for cooling the contact tube 6 is positioned closely behind the contact tube 6 in the welding progress direction, and a secondary gas nozzle 9 is positioned further behind the cooling water pipe 8 in close contact with the outside. The shape of the gas nozzle 9 may be similar to or the same as the primary gas nozzle 7, and the shape of the gas passage may be any of those shown in FIGS. In order to confirm the properties of the material and its effect on the base material, the inventor conducted an experimental study.

The shape of the test piece is as shown in Figure 11, and x
is 300T0n, y is 30? , w is the groove width of 9 gourds.

The torch used was one that could be used for narrow grooves and had a cross section shown in FIG. 10, which is a cross-sectional view of the torch. The wall thickness of the tube material for the inert gas passage, the contact tube tube material, and the cooling water tube tube material is each 17r011, and the center-to-center distance e is 7.5? , f is 17.5? , h is 4? ，
g was set to 6=. E and f refer to the distances from the center of the arc (arc point) to the center of the primary gas nozzle and the center of the secondary gas nozzle, and are determined from the effects of pushing back, spreading, and cooling the molten pool. The welding conditions for the bead shape investigation experiment are shown in Table 1 below. Next, the shape of the molten pool when the welding apparatus according to the present invention is used will be explained.

When welding is carried out using only conventional air blocking using inert gas, the longitudinal cross-sectional shape of the molten pool is as shown by the convex surface curve 10 indicated by a dashed line in FIG. 4. In the welding apparatus according to the present invention, the position of the secondary gas nozzle 9 is at the rear of the wire end, that is, the contact progress of a set distance with respect to the arc 18, and at the rear of the entire molten pool, as is clear from FIG. It is arranged to face a position corresponding to , that is, a portion where the trailing bead 15 and a portion thereof overlap. The molten pool 11 is expanded by the wind pressure of the inert gas from the secondary gas nozzle, and its surface has a concave cross-section 9 as shown by the curve 10a in FIGS. The fused portion 14 is also sufficient to eliminate the possibility of undercutting or slag entrainment. In addition, since the primary gas nozzle is located just before the wire end in the welding direction, the primary gas is sprayed just before the arc, creating a molten pool that is expanded by the inert gas ejected from the secondary gas nozzle. The molten metal is further pushed back by the inert gas from the primary gas nozzle, so that its surface exhibits a concave surface curve 10a in cross section as shown in FIG. 4, and the arc sufficiently melts the front layer 12. Therefore, the fusion of this high-temperature molten metal and the front layer portion 12 with which it comes into contact with the melt becomes sufficiently fused as indicated by the reference numeral 13. In this way, a defect-free bead 15 is formed as the welding nozzle advances. Furthermore, in the case of a primary or secondary gas nozzle having a plurality of gas passages, as shown in FIG. The effect of pushing and spreading the molten pool can be improved.
Furthermore, by making the amount of gas ejected from the gas passages of the primary and secondary gas nozzles different for each passage, it is possible to obtain optimal conditions that enhance the effect of molten pool deformation. As mentioned above, the distance between the contact tube axis (arc position) and the forward blowing position of the primary gas (first distance) is e.
, when the distance between the contact tube axis (arc position) and the secondary gas blowing position (second distance) is f, f>e, that is, f should be greater than e for good results. I made sure that I could get it.

The optimal one is e is 7.5TfUnf is 17.5T! Un
It was hot. The cooling water pipe 8 is not limited to the illustrated arrangement, but may be arranged to surround the contact tube 6, so that the F. Dimensions of l5e! can be made appropriate. It is desirable that the primary gas nozzle, contact tube, cooling water pipe, and secondary gas nozzle be in close contact with each other in order to improve heat transfer and to minimize the structure for heat dissipation of the contact tube.
stomach. In one example, the primary gas nozzle and the secondary gas nozzle are formed into a roughly rectangular shape with a round cross section as shown in Figure 10, and the cross section has a long side of 107T$i1 and a short side of 6W
! The thickness of the n1 tube is assumed to be 1 mm.

4 The gas supply amount from this primary gas nozzle 7 is 10f
/MinlThe gas supply amount from the secondary gas nozzle 9 is also 10f.
/Min, the optimum shape of the molten pool could be achieved. In FIG. 12, A shows the relationship between the bead, the molten pool, and the torch, and B shows the molten pool related to A and the temperature state near the molten pool.

In actual measurements, the sign A is the temperature of the base material just in front of the molten pool.
At 50°C, the temperature of the molten pool under the secondary gas nozzle was approximately 1400°C, which was the temperature of the molten pool before solidification.

The reason why this mouth part has the highest temperature is because the molten pool overlaps the already formed succeeding bead (the part without diagonal lines in FIG. 12A), and the retained heat of the succeeding bead is added thereto. The mouth is where the molten metal begins to solidify from the periphery, and represents the optimal position to obtain a bead shape with good wetting properties by controlling the surface shape of the molten pool. Note that the amount of gas supplied to the primary and secondary gas nozzles is 10e/Min.
In this case, the gas velocity at the outlet is 15 rn/s.

Furthermore, as is clear from Fig. 12, since the arc position and the positional relationship between the primary gas and the secondary gas are set as in the present invention, the primary gas is blown near the tip of the molten pool and the secondary gas is blown near the rear end in the direction of welding progress. I will attach it.

Therefore, in the part of the molten pool between the two gas blowing positions, only static pressure acts on the molten pool surface due to the balance of the jetting pressures of both gases, so that the molten pool surface is not disturbed, and blowholes etc. It is possible to improve the wettability to the front layer bead and both side walls of the groove without causing defects.
As described above, the present invention specifies the spraying positions of the primary gas and the secondary gas of the shielding gas when welding a thick base material and a narrow gap in a layer-by-layer bus.

In order to perform welding as described above, various welding conditions must be determined, but in arc welding, which is the subject of the present invention, once the positions of the primary gas and secondary gas are specified, other welding conditions can be determined. can be applied to the actual machine by appropriately determining it according to the target welding specifications.

Table 2 shows examples of application to typical actual machines. By repeatedly applying this invention, the molten pool is pushed back and expanded appropriately, a concave molten metal surface is formed, and the molten metal is sufficiently melted into the base material and the front layer, preventing slag entrainment and undercuts. There are fewer defects such as blowholes, and the equipment is smaller, making it easier not only to work downwards, but also to work in all positions, such as horizontally, due to the narrow gap that holds the molten metal. It has various effects.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional view of a welding device and a bead when a narrow gap is welded by a conventional welding method and device, Fig. 2 is a cross-sectional view of the bead, and Fig. 3 is a cross-sectional view of the welding device according to the present invention. 4 is a longitudinal sectional view of the device according to the present invention, BB sectional view of FIG. 3, FIGS.
Fig. 7 is a cross-sectional view of the primary or secondary gas nozzle showing various shapes of gas passages, and Fig. 8 is a cross-sectional view of a bead showing fusion when welding with the welding device according to the present invention. , Fig. 9 is a longitudinal cross-sectional view showing an example of a case where the gas ejection directions of the plurality of gas passages of the primary or secondary gas nozzle are different from each other, Fig. 10 is a cross-sectional view of the torch, and Fig. 11 is a cross-sectional view of the torch. Perspective view showing the shape of the test piece used, Figure 12A
is a cross-sectional view schematically showing the relationship between the torch end and the weld bead,
FIG. 12B is a diagram showing the relationship with FIG. A and the temperature of the molten pool and the base material at the tip of the molten pool. 1... wire, 2... molten pool, 3...
...Subsequent bead, 4...Previous layer part, 5...
...Base material, 6...Contact tube, 6a.
... Hole, 7 ... Primary gas nozzle, 8 ...
...Cooling water pipe, 9...Secondary gas nozzle, 10
... Convex surface curve, 10a ... Concave surface curve, 11 ... Molten pool, 12 ...
Front layer part, 13... Melting part to the front layer part, 14...
... Melting part into the base material, 15... Successive bead, 161, 16.

Claims (1)

[Claims] 1. In a method of arc welding a narrow gap in one bead layer by pass using a shielding gas, a molten pool formed on the rear side of the arc overlaps a subsequent bead in the rear part in the welding direction. By blowing a secondary gas onto the molten metal surface of the part and pushing and spreading the molten metal surface by the wind pressure, at the same time improving the wettability to the side walls of both grooves,
A primary gas is blown onto the surface of the front layer bead just before the arc, and the molten metal in the front part of the molten pool is pushed back by the wind pressure to improve wetting properties with the front layer bead and welding is performed. Narrow gap welding method. 2. The narrow gap welding method according to claim 1, wherein the supply amount of each of the primary gas and the secondary gas is controlled. 3. In arc welding of a narrow gap using shielding gas, this corresponds to the rear side of the contact tube in the direction of welding progress, and corresponds to the part where the molten pool formed at the rear of the arc overlaps with the subsequent bead at the rear part. position,
A secondary gas nozzle for ejecting gas for pushing and spreading the molten metal surface of the molten pool is arranged, a cooling water pipe is arranged between the contact tube and the secondary gas nozzle in close contact with the contact tube, and immediately in front of the contact tube. A narrow gap welding device characterized by having a primary gas nozzle disposed to eject gas for pushing back molten metal.