JPS5813269B2 - DC gas shield arc welding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a DC gas shielded arc welding method for steel materials other than non-ferrous metals.

Arc welding methods using shielding gas, such as MIG welding and carbon dioxide gas welding, are known as welding methods for large-diameter steel pipes, tanks, and other steel materials and structures. When welding, Si, M
So-called deoxidizing elements such as n, Ti, B, and Zr react with carbon dioxide and oxygen in the shielding gas to generate deoxidizing products separate from the molten metal, and also to prevent rust and other adhesion within the groove. Deoxidation products from the kimono are also produced.

In particular, when the base material itself is a non-ferrous metal, depending on the type of shielding gas used, the amount of deoxidized products generated may be extremely large or there may be a danger of explosion. This shows the shield arc welding situation, in which the torch 9 is moved along the groove 31 of the base metal 3, the shield gas 91 is flowed out from the outer periphery of the core wire 92, and an arc 93 is generated between the core wire 92 and the base metal 3. This heat is then used to weld.

At this time, the deoxidized product, that is, the molten slag 8, generated for the above reasons, as shown by the arrow in FIG.
(molten metal) 10 to the front and back in the welding direction.

Among such deoxidized products 8, the deoxidized products 8a that have moved to the rear surface in the welding progress direction float up from the molten pool 10 and adhere to the surface of the bead 101, so there is no problem.

However, the deoxidized product 8b that has moved to the front in the welding direction shows a behavior that gradually accumulates in front of the arc 93 as welding progresses, and this is because, for example, when tacking is done by spotting, The points are often collected intensively in the scoring section.

When there is a mechanical change or physical change (magnetic change) in the groove, the deoxidized product 8b accumulated at the front of the arc
The arc 93 moves from the front of the arc, passes directly under the arc, and moves toward the rear of the arc. At this time, the arc 93 is generated, albeit temporarily, on the deoxidized product, and as a result, the arc The arc becomes more unstable than if it were generated on metal, and this arc instability causes local bead defects.

However, the gas shielded arc welding method as described above is
Regardless of the type of shielding gas, welding has generally been carried out in a small current range of 500 A or less with a core wire diameter of 2.4 mmφ or less, and in this case, the amount of deoxidation products generated is small. The frequency of occurrence of bead defects due to this is low, and the degree of bead defects is relatively minor.

However, welding under the above-mentioned welding conditions has the drawback that the absolute value of the welding amount is small, and especially when the base metal is thick, welding becomes very multi-bus welding, resulting in poor welding efficiency.

On the other hand, as a recently developed gas-shielded arc welding method, there is a MIG welding method disclosed in Patent Application No. 135559 filed in 1972.

This MIG welding method uses a large diameter solid wire of 3.2 to 6.4 snφ and a welding current of 600 to 1500 Amps.
, arc voltage 23~36 volts, welding speed 300
~1500mm/min under a mixed shielding gas atmosphere with a total flow rate of 50~200l/min, consisting mainly of inert gas and to which carbon dioxide gas of 30% or less or oxygen of 5% or less is added, single electrode or multielectrode. It involves welding.

This method has the advantage of being able to weld very efficiently compared to the conventional method using a small-diameter core wire and a small current, but it also uses a large-diameter core wire, a large current, and a slightly oxidizing atmosphere. Because of this, a large amount of deoxidation products are generated, which increases the frequency of bead defects caused by deoxidation products as described above, and the degree of bead defects also poses a problem in terms of bead appearance. It has the disadvantage that it is more likely to cause defects than normal.

If this method is used for welding non-ferrous metals such as aluminum, the above disadvantages will become even more pronounced as the shielding gas will contain active gas, and there is also the risk of explosion.
It is usually not used for welding aluminum, etc.

The present invention was developed through research to eliminate the disadvantages and shortcomings of the conventional gas shielded arc welding method as described above, and its purpose is to Direct current gas-shielded arc welding is applicable to welding methods and can produce welds with extremely high welding efficiency, without defects such as bead defects caused by deoxidation products, and with good mechanical properties such as impact value. The purpose is to provide a method.

Another object of the present invention is to provide a DC gas-shielded arc welding method that can easily prevent the magnetic blow phenomenon and fusion failure caused by the magnetic blow, which has been a problem in DC welding technology, especially for steel materials. There is a particular thing.

Therefore, in order to achieve this object, the present invention performs gas-shielded arc welding on a base material such as steel using two or more multi-electrodes, and at the same time, performs welding using specific welding conditions for each electrode. This is how it was done.

That is, in the present invention, the first electrode (preceding electrode) is mainly made of an inert gas such as pure argon or helium, and carbon dioxide gas of 30 parts or less and/or oxygen of 5 parts or less is added to the gas at a total flow rate of 15 to 100 tons. /min in a mixed shielding gas atmosphere, using a core wire with a diameter of 0.6 to 1.6 mm, a welding current of 100 to 500 A, and the second electrode and subsequent electrodes (trailing electrodes) to pure argon or Mainly composed of inert gas such as helium, and carbon dioxide gas of 7.5 to 50% and/or
Or a total flow rate of 50l/min with 1-10% oxygen added.
Under the above mixed shielding gas atmosphere, the diameter is 3.0 to 6.
Using a large diameter core wire of 4 mmφ, welding current is 600 to 150.
Welding is performed along the groove line under welding conditions with a large current of 0A and a distance between each electrode after the first and second electrodes of at least 100 mm, and a shallow weld is formed with the first electrode. This is then welded while melting at the second and subsequent electrodes, and the wall action of the welded portion of the first electrode prevents the deoxidized product from moving to the front of the arc.

The DC gas shielded arc welding method according to the present invention will be specifically explained below.The present invention performs gas shielded arc welding using two or more multiple electrodes when welding a base material such as a grooved steel material. However, at that time, the first
The welding conditions for the electrode and the welding conditions for the second and subsequent electrodes are not the same, but the composition of the shielding gas, the core wire, and the welding current are changed, and the electrode spacing is specified.

That is, to describe it specifically, first, for the first electrode, a core wire with a diameter of 0.6 to 1.6 gates, b a welding current of 100 to 500 A, c a shielding gas inert such as pure argon or helium. A total flow rate of 15 to 100, consisting mainly of gas, with the addition of carbon dioxide gas of 30 parts or less and/or oxygen of 5 parts or less
, 17 min of mixed gas.

The reason why a small-diameter core wire is used here is to reduce the amount of deoxidation products generated when the core wire itself, the base material, or oxides in the groove react with oxygen and carbon dioxide gas in the shielding gas. This is to reduce the number of welds, and because the first electrode and subsequent electrodes are not synchronized in terms of efficiency, the first electrode is used to form a temporary weld with shallow penetration.To achieve these purposes, This is because it is appropriate to use a diameter of 0.6 to 1.6 mφ.

Next, the welding current is limited to 100 to 500 A because the above range is appropriate for preventing the generation of spatter, ensuring favorable spray transfer of droplets, and preventing clogging of the torch.

Table 1 below shows specific core wire diameters and appropriate welding current ranges.

By taking the welding current values shown in Table 1, it is possible to prevent the occurrence of spatter and also to prevent clogging of the torch.
It is necessary to prevent the torch from clogging. If the torch becomes clogged, it will require maintenance, and not only will welding become impossible for a long period of time, but a clogged torch will also result in an incomplete seal by the shielding gas, which will cause oxygen in the air to leak out. This is because nitrogen and nitrogen are drawn into the welded part and remain in the welded part after the second electrode, deteriorating the mechanical properties and impact value of the welded part.

Next, we limited the composition of the shielding gas because, in general, in order to suppress the generation of deoxidation products, it is necessary to reduce the amount of carbon dioxide and oxygen as much as possible (particularly for gas-shielded arcs of non-ferrous metals such as aluminum). However, in gas-shielded arc welding of steel materials, etc., the stability of the arc must be considered, and from the viewpoint of these considerations, inert gas such as pure argon or helium should be used as the main material. This is because it is appropriate to add and mix carbon dioxide with a coefficient of 30 or less and/or active gas with oxygen of a coefficient of 5 or less.If the carbon dioxide or oxygen is increased to a value higher than that, the droplet transfer phenomenon that increases spatter may occur. deoxidation is more likely to occur, and more deoxidation products are produced.

In addition, the lower limit of the shielding gas flow rate was set to 15 t/min because this flow rate is required at least to completely seal the arc, and the upper limit was set to 100 t/min.
The reason for setting n was due to economic considerations.

Next, for the second and subsequent electrodes, ■' diameter is 3
．． 0 to 6. 4m++φ core wire, ■' Large welding current of 600A to 1500A, ■' Shielding gas mainly composed of inert gas such as pure argon or helium, and carbon dioxide gas of 7.5 to 50% and/or 1 ~Total flow rate 50t with addition of 10 units of oxygen
The condition is to use a mixed gas of /min or more.

Under the above welding conditions, the core wire and welding current are made larger in diameter and larger in current than the first electrode, but this is due to the fact that the
This is because it is necessary to melt the tack welded part formed by the electrode and to improve welding efficiency.

First, the lower limit of the core wire diameter was set to 3.0 mmφ because welding efficiency was poor if the thickness was smaller than this, and the upper limit was set to 6.4 mm.
The reason why the diameter is mmφ is that if it exceeds this value, the core wire feedability becomes unreasonable, so from the viewpoint of efficiency and actual work, the above range, that is, the diameter of 3.0 to 6.4 Mφ is appropriate.

In addition, the welding current is specified as above because there is an optimal welding current range depending on the diameter of the core wire used, and beyond that range, even if the core wire used is appropriate, an unstable arc or spatter may occur. This may result in a droplet transfer form with many
This is because the electrode will not be able to properly melt the welded part. Table 2 below shows the core wire diameter and the appropriate welding current range for it.

In addition, in welding after the second electrode, the composition and flow rate of the shielding gas are different from those of the first electrode, and the amount of carbon dioxide added is 7.5 to 50% and the amount of oxygen added is 1 to 10%. The reason is that when carbon dioxide gas is less than 7.5 parts and/or oxygen is less than 1 part, the plasma air flow is too strong and defects such as poor fusion are likely to occur. This is because if the amount of oxygen exceeds 10% or the oxygen content exceeds 10%, droplet transfer phenomenon that increases spatter is likely to occur.

On the other hand, the reason why the lower limit of the gas flow rate is set to 5 0 1 /min is that less than this will result in insufficient shielding.

It is desirable that the upper limit is 2001/min. This is because if the gas flow rate exceeds this value, the bead will have a concave appearance, which is unfavorable in terms of appearance.

In addition, the above upper limit flow rate refers to that of the final electrode, and in the case of two electrodes, the gas flow rate of the second electrode is 200 l/rnl.
n or less.

Next, regarding the issue of polarity, since the first electrode is so-called tack welding, it can be either DC reverse polarity or DC positive polarity, but from the second electrode onwards, it is necessary to form penetration, magnetic blowing and Considering the prevention of spatter, it can be said that DC reverse polarity is desirable.

However, in internal welding of a cylindrical structure such as a steel pipe, it is preferable to use positive polarity for the first electrode because DC reverse polarity is used as the electrode polarity for the second and subsequent electrodes.

That is, in this way, magnetic blowing and resulting poor fusion, which have been a problem during multi-electrode welding, can be avoided by utilizing the effect of the welding lead wires to cancel each other's magnetic fields, without requiring any special magnetic blowing treatment. This can be easily prevented.

The present invention can be applied to various types of multi-electrode DC gas shielded arc welding with two or more electrodes;
Specific preferable conditions in the case of more than an electrode are as follows.

First of all, in the case of 3 electrodes, the first electrode is
The conditions of ■ are as follows, and for the second electrode,
Among the conditions mentioned above, the shielding gas composition should be 20 to 50 parts carbon dioxide and/or 3 to 10 parts oxygen, and by keeping it in this range, a good bead with no fusion defects can be formed. .

Regarding the third electrode, among the conditions of ■'■'■' mentioned above, in the shield gas composition, carbon dioxide gas is 7.5 to 7.5
The conditions should be 30 parts and/or 1 to 5 parts oxygen.

This shielding gas composition is effective in preventing poor fusion and preventing deoxidation products on the bead surface.

Further, the polarity of the third electrode should be reversed regardless of the polarity of the first and second electrodes.

This has advantages in terms of preventing spatter and increasing the angle of rise of the bead appearance.

Next, in the case of welding with four or more electrodes, apply the conditions for the second electrode in the three-electrode case described above to intermediate electrodes such as the second and third electrodes, and apply the conditions for the third electrode in the three-electrode case. should be the final electrode condition.

In any case, the distances between each electrode, that is, between the first and second electrodes, between the second and third electrodes, between the third and fourth electrodes, etc., are the distances of the arc. The distance must be at least 100 mm to avoid mutual interference.

Another reason is that the weld formed by welding the preceding electrode becomes a wall that can effectively restrict the forward movement of deoxidized products, as described below, so a certain degree of temperature drop is required. The distance between the electrodes must be at least 100 mm.

FIG. 24 shows an example in which the DC gas shielded arc welding of the present invention is performed using the first electrode 1 and the second electrode 2.

In the drawing, 11 is the nozzle of the first electrode 1, and 12 is the nozzle of the first electrode 1.
The core wire of the electrode, 13 is the arc of the first electrode, 21 is the nozzle of the second electrode 2, 22 is the core wire of the second electrode, and 23 is the arc of the second electrode.
1 and the nozzle 21 of the second electrode as described above.
00 mm or more, and the welding conditions for the first electrode 1 and the second electrode 2 are set within the shield gas atmosphere, core wire, and welding current ranges as described above, and the first electrode 1 and the second electrode 2 are
and are moved along the groove 31 of the base material 3 at a predetermined speed.

In this way, the inside of the groove 31 can be welded with the thin core wire 12 of the preceding first electrode 1 using a small current, and a proper gas shielding state can be maintained, so that spatter and oxygen caused by clogging of the torch can be prevented. The droplets fall in a stable spray transfer form without any entrainment of nitrogen or nitrogen, and a tack welded part 5 is formed by the molten pool 4 with shallow penetration.

Due to the above-mentioned welding conditions, the amount of deoxidation products generated in this welded portion 5 is small, and the bead defects generated are minor.

Then, following such tack welding by the first electrode 1, the second electrode 2 moves within the groove 31 after a required time;
In this second electrode 2, a stable arc and a preferable spray transfer state can be obtained under the above-mentioned welding conditions, and the core wire 2 has a large diameter.
Since welding is carried out using a large current as shown in FIG. 2, the tack welded portion 5 formed by the first electrode 1 is sequentially melted, and the weld metal 7 is efficiently formed by a large molten pool 6 as shown in the figure.

When welding with the second electrode 2, the nozzle 21
The first
There is a weld 5 by the electrode 1, and a wall 51 of this weld 5
The welding of the second electrode 2 progresses by breaking down one after another, so to speak.

Therefore, even if a deoxidized product 8 is generated during welding by the second electrode 2, the deoxidized product 8 is transferred to the wall 5 of the welded portion 5 of the first electrode.
The stopper action of 1 prevents the arc 23 from moving to the front, so that the deoxidized product 8
moves only toward the rear of the molten pool 6, that is, toward the rear surface of the arc 23, and the arc 23 is no longer generated on the deoxidized product 8, thereby eliminating bead defects caused by this.

At the same time, since the generation and concentration of deoxidized products are prevented during welding using the first electrode 1, bead defects such as roughness on the groove surface and intermittent bead portions during tacking occur when welding using the second electrode 2. do not.

In addition, although the welding situation using two electrodes, the first electrode 1 and the second electrode 2, has been described above, this also applies to the case where three or more electrodes are used.

That is, welding is performed while melting the welded part of the first electrode with the second electrode, and then welding is performed while melting the welded part made with the second electrode 2 with the third electrode, and so on. In each case, the deoxidizing product is moved only backward in the welding direction by the action of the wall of the welding part of the preceding electrode as described above, and no bead defects occur.
In either case, the resulting weld is free from entrainment of oxygen, nitrogen, etc., and when securing the same amount of welding, the amount of welding at the trailing electrode can be reduced by the amount of the preceding electrode.
Less heat input is required, which allows for good mechanical properties of the weld.

Next, specific examples of the present invention will be shown.

Example 1 Large-diameter steel pipes were butt-seam welded by the present invention and the conventional gas-shielded arc welding method using a large-diameter core wire.

A comparison of the welding conditions and bead failure occurrence rate at that time is shown in Table 3 below.

As is clear from Table 3, according to the present invention, it is possible to obtain a good welded part without bead defects while maintaining high efficiency.

This is because the welding of the leading electrode creates a wall that restricts the forward movement of deoxidation products generated during welding of the trailing electrode, and the leading electrode prevents the generation and accumulation of deoxidation products.
This is due to the fact that roughness of the groove surface and intermittent beads during tack-welding do not occur during welding with the trailing electrode.Example 2 By using the present invention and the conventional method, a thick plate base material (3. 5Ni steel) was butt welded.

The welding conditions at this time and the impact test results of each welded part are shown in Table 4 below.

In addition, as for the core wire, in both the method of the present invention and the conventional method, N i
-Mo-Ti type material was used.

As is clear from Table 4, in the case of the present invention, the impact characteristics can be improved compared to the conventional large current gas shielded arc welding method.

This is because, in the case of the present invention, the amount of welding at the trailing electrode can be reduced by the amount of welding at the leading electrode, which reduces the amount of heat required by the welder, and also reduces the amount of oxygen, nitrogen, etc. in the air caused by a clogged torch. This is clearly due to the fact that there is no winding.

According to the present invention as described above, there is no occurrence of defects such as bead defects caused by deoxidation products in DC gas shielded arc welding of thick plates of steel materials other than non-ferrous metals, and mechanical properties such as impact value are good. It has the excellent effect of being able to obtain a welded part with extremely high welding efficiency.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing the conventional gas-shielded arc welding state and the movement of the deoxidized products at that time, and Fig. 2 shows the state in which the welding method of the present invention is carried out and the movement of the deoxidized products at this time. It is an explanatory diagram. In the drawings, 1...first electrode, 2...second electrode, 12
... Core wire of the first electrode, 22 ... Core wire of the second electrode, 5 ...
Welded part (welded metal) formed by the first electrode, 7...
Welded part (welded metal) 8 by the second electrode...deoxidation products are shown.

Claims (1)

[Claims] 1. When performing DC gas shielded arc welding of steel materials, etc. using two or more electrodes and using an inert gas with carbon dioxide and/or oxygen gas added as a shielding gas, the welding conditions for the first electrode are pure Diameter 0.6 to 1 in a mixed shielding gas atmosphere with a total flow rate of 15 to 100 l/min, consisting mainly of inert gas such as argon or helium, to which carbon dioxide gas of 30 parts or less and/or oxygen of 5 parts or less is added. .6mmφ core wire and welding current 100~50
Using 0A, the welding conditions after the second electrode are mainly inert gas such as pure argon or helium, and 75~
Welding a core wire with a diameter of 3.0 to 6.4 mφ and a welding current of 600 mφ in a mixed shielding gas atmosphere with a total flow rate of 50 t/min or more containing carbon dioxide gas and/or 1 to % oxygen.
Using a large current of ~1500A, and setting each electrode spacing to 100
mm or more, create a shallow weld zone with the first electrode, melt this in sequence with the trailing electrode, and weld while preventing the deoxidation product from moving to the front of the arc with the wall of the weld zone created by the leading electrode. A DC gas-shielded arc welding method featuring: