JP2015150572A - Method of welding multi-electrode single-sided submerged arc, method of manufacturing weldment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce poor appearance of penetration beads obtained through multi-electrode single-sided submerged arcs.SOLUTION: The welding device 1 performs single-sided submerge arc weldment on a steel sheet with the use of a first welding unit 10 that uses a first wire 110, a second welding unit 20 that uses a second wire 120, a third welding unit 30 that uses a third wire 130 and a fourth welding unit 40 that uses a fourth wire 140. At that time, the first welding unit 10 regulates a feeding speed of the first wire 110 at a constant rate with the use of a first feeding device 11, and supplies electric power to the first wire 110 with the use of a first welding power source 12 whose method of electric power supply is direct-current and whose external characteristic is set as constant voltage characteristic.

Description

  The present invention relates to a multi-electrode single-sided submerged arc welding method and a method for manufacturing a welded article.

  As a type of consumable electrode arc welding method, a flux composed of powdered metal, artificial oxide, or mineral is sprayed on the surface of the groove provided in the steel plate, and the flux deposited on the groove of the steel plate In particular, there is known a submerged arc welding method in which an electric current is supplied to an electrode wire that is fed to generate an arc from the electrode wire so that the electrode wire and the steel plate are melt-mixed and integrated. This submerged arc welding method has features of deep penetration and high efficiency due to the use of a large current, compared to other arc welding methods such as the covering arc welding method, the TIG arc welding method, and the gas shielded arc welding method.

  Here, in Patent Document 1, in the submerged arc welding method, the electrode wire is fed using a welding power source having a drooping characteristic or a constant current characteristic as an external characteristic, and a welding voltage setting signal and a welding voltage feedback signal are used. It is described that the electrode wire feeding speed is controlled by the magnitude of the difference signal.

  In Cited Document 2, a plurality of electrode wires are arranged side by side along the groove, and a backing material is arranged on the back surface side of the steel plate, so that a plurality of electrode wires are provided from the front surface side to the back surface side of the steel plate. A multi-electrode single-sided submerged arc welding method is described in which welding is performed in a single run using a wire. In this multi-electrode single-sided submerged welding method, the entire thickness of the steel sheet can be completely penetrated by one run (this is called one run), and there is no need to reverse the steel sheet. Widely used.

JP 2000-117442 A JP 2007-268551 A

  In the multi-electrode single-sided submerged arc welding described above, a back bead is formed on the back surface side of the steel plate mainly by the electrode wire (leading electrode) that is first welded to the steel plate among the plurality of electrode wires.

  However, when a configuration is adopted in which power is supplied to a leading electrode electrode wire using a welding power source having drooping characteristics or constant current characteristics, and the feed rate is feedback controlled based on the arc voltage, the obtained background is obtained. In some cases, the appearance of the wave bead was poor.

  An object of this invention is to reduce the appearance defect of the back bead obtained by multi-electrode single-sided submerged arc welding.

The present invention is a multi-electrode single-sided submerged arc welding method using a leading electrode and a trailing electrode following the leading electrode, and each of the leading electrode and the trailing electrode uses a wire having a diameter of 2.4 mm or more. The power supply method and the external characteristic of the power supply for supplying power to each wire, and the speed control method of the feeding speed of each wire are the direct current, the power supply method is DC, the external characteristic is a constant voltage characteristic, The speed control method is set to constant speed control, and in the trailing pole,
(A) The power feeding method is DC, the external characteristic is constant voltage characteristic, the speed control method is constant speed control (b) The power feeding method is AC, the external characteristic is constant voltage characteristic, and the speed control method is constant speed control (C) The power feeding method is AC, the external characteristic is a constant current characteristic, and the speed control method is voltage feedback control based on an arc voltage. (D) The power feeding method is AC, the external characteristic is a drooping characteristic, and the speed control method is Voltage feedback control based on arc voltage (e) The feeding system is set to DC, the external characteristic is constant current characteristic, and the speed control system is set to voltage feedback control based on arc voltage.
In such a multi-electrode single-sided submerged arc welding method, the trailing electrode is configured to include a plurality of electrodes following the leading electrode, and each of the plurality of electrodes constituting the trailing electrode includes the feeding method. The external characteristics and the speed control method are set to any one of (a) to (e).
Further, among the plurality of electrodes constituting the trailing electrode, the power feeding method, the external characteristic, and the speed control method are the above (c) or the last electrode located at the rearmost side when viewed from the leading electrode. It can be characterized in that it is set to (d).
Further, when the power supply having the constant voltage characteristic is used, a differential value dV / dI that is a slope of a voltage with respect to a current at an operating point is −12.0 × 10 ⁻³ (V / A) or more. It can be.
Furthermore, when the power supply having the constant current characteristic or the drooping characteristic is used, a differential value dV / dI that is a slope of a voltage with respect to a current at an operating point is −24.0 × 10 ⁻³ (V / A) or less. It can be characterized by being.
Further, from another point of view, the present invention is a method for manufacturing a welded material obtained by welding a base material by single-sided submerged arc welding using a leading electrode and a trailing electrode following the leading electrode. The leading electrode and the trailing electrode each use a wire having a diameter of 2.4 mm or more, and a power supply method and an external characteristic of a power source for supplying power to each wire, and a speed control method of the feeding speed of each wire In the leading electrode, the power feeding method is set to DC, the external characteristic is set to a constant voltage characteristic, the speed control method is set to constant speed control, and in the trailing electrode,
(A) The power feeding method is DC, the external characteristic is constant voltage characteristic, the speed control method is constant speed control (b) The power feeding method is AC, the external characteristic is constant voltage characteristic, and the speed control method is constant speed control (C) The power feeding method is AC, the external characteristic is a constant current characteristic, and the speed control method is voltage feedback control based on an arc voltage. (D) The power feeding method is AC, the external characteristic is a drooping characteristic, and the speed control method is Voltage feedback control based on arc voltage (e) The feeding system is set to DC, the external characteristic is constant current characteristic, and the speed control system is set to voltage feedback control based on arc voltage.

  ADVANTAGE OF THE INVENTION According to this invention, the external appearance defect of the back bead obtained by multi-electrode single-sided submerged arc welding can be reduced.

It is a figure which shows schematic structure of the welding apparatus which concerns on embodiment of this invention. It is a figure for demonstrating the structure of the welding power supply and feeding apparatus in each of a 1st welding unit-a 4th welding unit. (A)-(c) is a figure for demonstrating the external characteristic of a welding power supply. It is a figure for demonstrating the structure of the experimental apparatus in a 1st Example and a 1st comparative example. It is a figure for demonstrating the structure of the experimental apparatus in a 2nd Example and a 2nd comparative example. It is a figure for demonstrating the structure of the experimental apparatus in a 3rd Example and a 3rd comparative example. (A) is the size of each steel plate and groove in the first example and the first comparative example, (b) is the size of each steel plate and groove in the second example and the second comparative example, (c) is It is a figure for demonstrating each steel plate and the dimension of a groove | channel in a 3rd Example and a 3rd comparative example, respectively.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a diagram showing a schematic configuration of a welding apparatus 1 according to the present embodiment. This welding apparatus 1 performs one-sided submerged arc welding (four-electrode one-sided submerged arc welding) on a workpiece (not shown) made of a steel plate using four electrodes (wires).

  The welding apparatus 1 includes a first welding unit 10 that performs welding using the first wire 110, a second welding unit 20 that performs welding using the second wire 120, and a first welding unit that performs welding using the third wire 130. 3 welding units 30 and a fourth welding unit 40 that performs welding using a fourth wire 140. In addition, the welding apparatus 1 is equipped with the first welding unit 10 to the fourth welding unit 40 and travels along a moving direction A from the right side to the left side in the drawing, and a truck driving device 50 that drives the carriage 90. And a control device 60 for controlling the operations of the first welding unit 10 to the fourth welding unit 40 and the cart driving device 50. Furthermore, the welding apparatus 1 includes a first flux supply device 70 and a second flux supply device 80 that house a surface flux (not shown) therein and supply the surface flux downward in the drawing. In this example, the control device 60, the first flux supply device 70, and the second flux supply device 80 are also mounted on the carriage 90.

  Among these, the first welding unit 10 includes a first feeding device 11 including a first feeding roller 11a that feeds the first wire 110 along a feeding direction B from the upper side to the lower side in the drawing, and a feeding unit. The first welding power source 12 is connected to a first contact tip 12a that contacts the supplied first wire 110 and supplies a welding current (first welding current). The first welding unit 10 further includes a reel (not shown) that is a supply source of the first wire 110 while the first wire 110 is wound thereon.

  Further, the second welding unit 20 is fed with a second feeding device 21 provided with a second feeding roller 21a for feeding the second wire 120 along a feeding direction B from the upper side to the lower side in the figure. A second welding power source 22 connected to a second contact tip 22a for supplying a welding current (second welding current) in contact with the incoming second wire 120 is provided. The second welding unit 20 further includes a reel (not shown) that is a supply source of the second wire 120 while the second wire 120 is wound around.

  Further, the third welding unit 30 is fed with a third feeding device 31 provided with a third feeding roller 31a that feeds the third wire 130 along the feeding direction B from the upper side to the lower side in the drawing. A third welding power source 32 connected to a third contact tip 32a for supplying a welding current (third welding current) in contact with the coming third wire 130 is provided. The third welding unit 30 further includes a reel (not shown) that is a supply source of the third wire 130 while the third wire 130 is wound.

  Furthermore, the fourth welding unit 40 includes a fourth feeding device 41 including a fourth feeding roller 41a that feeds the fourth wire 140 along the feeding direction B from the upper side to the lower side in the drawing, A fourth welding power source 42 connected to a fourth contact tip 42a for supplying a welding current (fourth welding current) in contact with the incoming fourth wire 140 is provided. The fourth welding unit 40 further includes a reel (not shown) that is a supply source of the fourth wire 140 while the fourth wire 140 is wound thereon.

  In welding apparatus 1 of the present embodiment, first welding power source 12, second welding power source 22, third welding power source 32, and fourth welding power source 42 are mounted on cart 90, and these first welding power sources are combined with cart 90. Although the power supply 12 to the fourth welding power supply 42 are configured to travel, the present invention is not limited to this. For example, the first welding power source 12 to the fourth welding power source 42 are fixed and arranged outside the carriage 90, and each component on the first welding power source 12 to the fourth welding power source 42 and the carriage 90 is used by using a cable or the like. It does not matter if they are connected to each other.

  Moreover, the 1st flux supply apparatus 70 is provided with the 1st flux supply port 70a which supplies the surface flux accommodated in the inside toward the downward direction in the figure. The amount of surface flux supplied by the first flux supply device 70 is adjusted by a valve (not shown) provided in the first flux supply device 70.

  Furthermore, the second flux supply device 80 is provided with a second flux supply port 80a for supplying the surface flux accommodated in the inside downward in the drawing. The amount of surface flux supplied by the second flux supply device 80 is adjusted by a valve (not shown) provided in the second flux supply device 80.

  In this welding apparatus 1, when viewed from the moving direction A, the first wire 110 that is the first electrode on the most downstream side, and the second wire 120 that is the second electrode on the upstream side of the first wire 110 is the second wire. A third wire 130 serving as the third electrode is disposed upstream of 120, and a fourth wire 140 serving as the fourth electrode is disposed downstream of the third wire 130 and on the most upstream side. In the welding apparatus 1, the first flux supply device 70 is on the downstream side of the first wire 110 when viewed from the moving direction A, and the second flux supply device 80 is on the upstream side of the second wire 120 when viewed from the moving direction A. In addition, they are disposed downstream of the third wire 130. When the welding apparatus 1 is viewed from above in the drawing, the first flux supply port 70a, the first wire 110, the second wire 120, the second flux supply port 80a, the third wire 130, and the fourth wire 140 move. They are arranged in this order along a straight line along the direction A.

  Moreover, in this welding apparatus 1, as the 1st wire 110-the 4th wire 140, each diameter is 2.4 mm or more and 6.4 mm or less. Here, all of the first wire 110 to the fourth wire 140 may have the same diameter, or three may have the same diameter, while one may have a different diameter, and the two may have the same diameter. While one may have a diameter, two may have another same diameter, or all four may have different diameters.

  Furthermore, each of the first wire 110 to the fourth wire 140 used in the welding apparatus 1 is basically composed of a solid wire having no flux. However, one or more of these may be configured with a flux-cored wire.

  In the following description, the first welding unit 10 including the first wire 110 may be referred to as a “leading electrode”. In addition, the second welding unit 20 including the second wire 120, the third welding unit 30 including the third wire 130, and the fourth welding unit 40 including the fourth wire 140 may be collectively referred to as “following electrodes”. . Further, the second welding unit 20 including the second wire 120 is referred to as a “first intermediate pole”, the third welding unit 30 including the third wire 130 as a “second intermediate pole”, and the fourth welding unit including the fourth wire 140. 40 may be referred to as a “final pole”.

  FIG. 2 shows a welding power source (first welding power source 12 to fourth welding power source 42) and a feeding device (first feeding device 11) in each of the first welding unit 10 to the fourth welding unit 40 constituting the welding device 1. FIG. 4 is a diagram for explaining a configuration of a fourth feeding device 41). Here, FIG. 2 shows the relationship between each welding unit, the power feeding method and external characteristics in each welding power source, and the wire speed control method in each feeding device.

First, the first welding unit 10 will be described.
The first welding power source 12 constituting the first welding unit 10 is a direct current power source adopting DC (Direct Current) as a power feeding method, and its external characteristic is a constant voltage characteristic. In addition, the first feeding device 11 performs constant speed control for feeding the first wire 110 at a constant speed as a wire speed control method.

  Next, the second welding unit 20 will be described. In this Embodiment, the 2nd welding unit 20 is comprised by any one of the five combinations (1st structure-5th structure) demonstrated below.

(A) First Configuration The second welding power source 22 in the first configuration is a DC power source that employs DC (Direct Current) as a power feeding method, and its external characteristic is a constant voltage characteristic. In addition, the second feeding device 21 in the first configuration performs constant speed control for feeding the second wire 120 at a constant speed as a wire speed control method. Thus, the first configuration is the same combination as the first welding unit 10.

(B) Second Configuration The second welding power source 22 in the second configuration is an AC power source that employs AC as a power feeding method, and its external characteristic is a constant voltage characteristic. In addition, the second feeding device 21 in the second configuration performs constant speed control for feeding the second wire 120 at a constant speed as a wire speed control method.

(C) Third Configuration The second welding power source 22 in the third configuration is an AC power source that employs AC as a power feeding method, and its external characteristic is a constant current characteristic. Further, the second feeding device 21 in the third configuration performs voltage FB (Feed Back) shift control for feeding the second wire 120 at an appropriate speed sequentially by feedback control based on the arc voltage as a wire speed control method. .

(D) Fourth Configuration The second welding power source 22 in the fourth configuration is an AC power source that employs AC as a power feeding method, and its external characteristic is a drooping characteristic. Moreover, the 2nd feeder 21 in a 4th structure performs the voltage FB shift control which feeds the 2nd wire 120 at an appropriate speed one by one by the feedback control based on an arc voltage as a wire speed control system.

(E) Fifth Configuration The second welding power source 22 in the fifth configuration is a DC power source that employs DC as a power feeding method, and its external characteristic is a constant current characteristic. Moreover, the 2nd feeder 21 in a 5th structure performs the voltage FB shift control which feeds the 2nd wire 120 at an appropriate speed one by one by the feedback control based on an arc voltage as a wire speed control system.

  Moreover, about the 3rd welding unit 30 and the 4th welding unit 40, similarly to the 2nd welding unit 20, it comprises by any one of the 1st structure (a)-5th structure (e) mentioned above. be able to. Here, as for the 2nd welding unit 20, the 3rd welding unit 30, and the 4th welding unit 40, all three may be made into the same structure, and it is good also considering one as a different structure while making two into the same structure. All of the three may be configured differently.

  The feeding speed of the first wire 110 to the fourth wire 140 can be determined based on the moving speed (welding speed) of the carriage 90 in the moving direction A. For example, in the case of constant speed control, the operator determines a reference value for the feed speed based on the welding speed, and the constant speed control is performed so as to maintain the reference value for the feed speed. For example, in the case of the voltage FB shift control, the operator determines a reference value for the feed rate based on the welding speed, and the shift control is performed by feeding back the arc voltage to the reference value for the feed rate.

Next, the external characteristics of each welding power source described above will be described.
FIG. 3 is a diagram for explaining the external characteristics of the welding power source. Here, FIG. 3A illustrates a constant voltage characteristic, FIG. 3B illustrates a constant current characteristic, and FIG. 3C illustrates a drooping characteristic. In each of FIGS. 3A to 3C, the horizontal axis represents the output current I (A), and the vertical axis represents the output voltage V (V). The external characteristic curve moves (changes) in response to a current or voltage instruction input to the welding power source. FIG. 3A illustrates an external characteristic curve corresponding to the four-step command voltage, and FIGS. 3B to 3C illustrate external characteristic curves corresponding to the four-step command current. Yes. In the case of the welding power source, the output current I corresponds to the welding current, and the output voltage V corresponds to the total value obtained by adding other voltage loss factors (consumption in the cable, contact resistance, etc.) to the arc voltage.

First, the constant voltage characteristic shown in FIG.
In the case of the constant voltage characteristic, the fluctuation of the output voltage V is small with respect to the fluctuation of the output current I.

Next, the constant current characteristic shown in FIG.
In the case of the constant current characteristic, the fluctuation of the output voltage V is larger than the fluctuation of the output current I. From the opposite viewpoint, in the constant current characteristic, even if the output voltage V fluctuates greatly, the fluctuation of the output current I is small.

Next, the drooping characteristic shown in FIG.
In the case of the drooping characteristic, as in the case of the constant current characteristic, the fluctuation of the output voltage V is large with respect to the fluctuation of the output current I. However, in the drooping characteristic, the fluctuation of the output voltage V is more gradual and changes depending on the current value than in the case of the constant current characteristic.

  Here, FIGS. 3A to 3C show arc characteristics for generating an arc having an arc length L as well as the respective external characteristics. In each case, the intersection of one of the external characteristic curve and the arc characteristic curve is an operating point P (a specific output current I and a specific output voltage V corresponding thereto) that generates an arc having a target arc length L. ) In the following description, the slope of the voltage with respect to the current at the operating point P for generating an arc having the target arc length L is referred to as a differential value dV / dI.

  Here, a welding power source having drooping characteristics and constant current characteristics is considered to have little penetration depth fluctuation, and is suitable for submerged arc welding. However, in a welding power source having drooping characteristics and constant current characteristics, since the arc voltage is likely to change, it is common to combine with wire feeding by voltage FB shift control. When the welding power source having drooping characteristics or constant current characteristics and the voltage FB shift control are combined, if the arc length L is shortened, the arc length L is reduced by lowering the wire feed speed in accordance with the decrease in the arc voltage. When the arc length L is increased, the arc length L is returned to the original length by increasing the wire feeding speed in accordance with the increase of the arc voltage.

  On the other hand, a welding power source having constant voltage characteristics is suitable for mag welding and MIG welding using a thin wire. Moreover, the welding power supply which has a constant voltage characteristic may be used for the submerged arc welding using the wire of diameter 2.0mm or less. However, since a welding current easily changes in a welding power source having a constant voltage characteristic, it is generally combined with wire feeding by constant speed control. When the welding power source having constant voltage characteristics and constant speed control are combined, if the arc length L is shortened, the welding current is automatically increased to return the arc length L to the original length, If the arc length is increased, the welding current is automatically reduced, so that the arc length L returns to the original length.

  Here, the characteristics of the welding conditions in the multi-electrode single-sided submerged arc welding method of the present embodiment will be described.

<About the diameter of each wire>
In the single-sided submerged arc welding method, it is necessary to melt the groove with a strong arc force to form a back bead. However, it is not just a high welding current, and if a lot of wires are melted by high-speed feeding, a pool of hot water is formed immediately below the arc, and the arc force is buffered by itself and the penetration is reduced. Therefore, it is desirable to increase the welding current but not to increase the amount of wire melt. This condition is suitable for low current density (A / mm ² ) conditions, that is, the wire diameter is increased and the wire is operated at low speed. It is preferable to feed. In gas shielded arc welding, a thin wire having a diameter of 1.6 mm or less is generally used. For single-sided submerged arc welding, a wire having a diameter of 2.4 mm or more is suitable. More preferably, it is desirable to use a wire having a diameter of 3.2 mm or more, more preferably 4.8 mm or more. There is no particular technical limitation on the upper limit, but a diameter of 6.4 mm or less is practical from the viewpoint of wire feedability and cutability.

<About the number of electrodes>
The leading electrode melts the groove deeply to form a weld pool and a back bead, and the welding conditions are specialized for this role.For example, the base metal is thin and the weld pool is the base metal. Even if the surface is reached, the appearance of the front bead is not improved with a single electrode. On the other hand, since the final electrode mainly has a role for adjusting the appearance of the front bead, the welding conditions are different from those of the preceding electrode. As described above, since it is necessary to share roles in single-sided submerged arc welding, it is essential to form a plurality of electrodes using two or more wires. Generally, the number of wires increases as the thickness of the steel plate increases. Although there is no technical limitation in particular to provide an upper limit for the number of electrodes, for example, a four-electrode system shown in FIG.

  An appropriate interval is provided between each pole. It is not unconditionally adjusted by the plate thickness, welding speed, various types of control of the welding machine to be used and wire feeding, but is adjusted as appropriate. Depending on the gap, a flux supply port (a first flux supply port 70a or a second flux supply port 80a shown in FIG. 1) may be provided.

<Wire speed control method, external characteristics, and power supply method at the leading electrode>
[About the wire speed control system in the leading electrode]
In multi-electrode single-sided submerged arc welding, the leading electrode is mainly used to form a back bead. The inventors of the present invention have found that the penetration driving force significantly affects the quality of the back wave in back wave welding, and the back wave bead tends to be excessive or insufficient. The inventors have repeated experiments on the driving force of penetration, and in general joints, the current and voltage factors are correct, but in single-sided welding, these are not, but the wire feed speed has the greatest influence. I found it.

  That is, if the wire feeding speed is excessive, the wire easily pushes down the molten pool supported mainly by the surface tension on the back surface of the steel sheet, and forms an excessive back wave. Furthermore, if the feeding speed is high, the wire may break through the molten pool.

  Conversely, if the wire feeding speed is insufficient, the molten pool is not pushed from the back surface of the steel sheet, and the back wave is insufficient. These phenomena should theoretically not occur if the wire feed speed reacts to the change in the arc length L that inevitably occurs without time loss and the arc length L can be restored. However, in reality, a wire motor for feeding a wire is an industrial product, and a certain delay occurs in the reaction. With respect to this reaction time delay, the height of the back bead does not have a robust property and is easily affected by the change.

  In view of this problem, the leading electrode that influences the formation of back welding does not affect the feed speed even if the current or voltage changes, and the feed speed is constant (constant speed control). Clarified that is desirable. As described above, the wire feed constant control is a control method that has conventionally been unsuitable for large-diameter submerged arc welding. The reason for this is that a large-diameter wire is difficult to melt uniformly in the entire cross section, and as a result, the wire melting rate becomes unstable, and consequently the arc length L cannot be expected to stabilize. However, only in the case where the back bead is formed by single-sided welding, rather than stabilizing the arc length L, the feed speed stabilization has a higher shape stabilization effect.

[External characteristics at the leading electrode]
Next, regarding the external characteristics of the leading electrode, the drooping characteristics are common sense as a conventional technique. As described above, the drooping characteristic has a small fluctuation in current value with respect to a fluctuation in voltage value. As a welding machine structure that is simple, inexpensive, and easy to maintain, iron core movable welding machines that use leakage reactance have been used for a long time without using electronic elements, but only drooping characteristics could be created with this method. There is also a historical situation.

  While it is effective for stabilization of penetration in non-back wave welding where the current value has the greatest effect on the penetration depth, fluctuations in the current value are important for stabilizing the shape of the back wave bead in back wave welding. It is not high rank as an influencing factor. On the other hand, although the arc length L is not greatly affected by the stabilization of the back wave as compared with the fluctuation of the feeding speed, if the arc length L is suddenly changed, an adverse effect is brought about. For example, when the arc length L is zero, that is, when the arc disappears, the welding itself stops, or an arc is generated explosively at the time of re-ignition, so that the back bead cannot be normally formed by that force. On the other hand, if the arc length L is excessive, the arc cannot be maintained, and the arc disappears immediately afterwards, or the arc force per unit area decreases, and the back bead cannot be formed.

  Furthermore, defects such as an irregular weld bead shape, meandering affected by magnetic blowing, and undercut that causes the base material to be crushed are brought about. That is, stabilization control of the arc length L is necessary.

  Assuming that the feed speed is constant for stabilizing the back wave, a control object other than the feed speed control is required as means for stabilizing the arc length L. It is known that the melting rate of the consumable electrode type welding wire is expressed by the formula (1), and it is suggested that the current value (welding current I) which is a square has the greatest influence.

Mw = K1 · I + K2 · I 2 · ρ · L ... (1)
Mw: Wire melting speed I: Welding current ρ: Electric resistivity L: Wire protrusion length K1, K2: Constant

  Accordingly, it is effective to positively change the welding current I as a means for stabilizing the arc length L on the premise of a constant feed speed. For example, if the arc length L is shortened, the wire melting rate Mw is decreased by rapidly increasing the welding current I, and the arc length L is restored. On the other hand, if the arc length L is increased, the wire melting rate Mw is increased by rapidly decreasing the current, and the arc length L is returned. This phenomenon is generally called a self-control action of the arc length. The self-control action of the arc length requires a steep change in current, and the only external characteristic that realizes this is the constant voltage characteristic. Therefore, in order to realize the constant wire feed speed necessary for stabilizing the back wave welding, the external characteristic of the welding power source corresponding to the leading electrode needs to be a constant voltage characteristic as an indirect factor.

  Such a combination of “wire speed control: constant speed” and “external characteristic: constant voltage characteristic” is used in a gas shield arc welding method using a thin wire having a diameter of 1.6 mm or less. This is because the meltability is excellent because the wire is thin, so that the self-control action of the arc length is very effective. However, since a wire with a diameter of 2.4 mm or more is inferior in meltability compared to a wire thinner than this, the arc length self-control action does not act agility when used for non-single-sided welding, and the arc and bead shape. It causes instability.

[About the power feeding method at the leading electrode]
Subsequently, as for the leading electrode power feeding method, direct current is essential for the leading electrode of single-sided welding. In alternating current, the current is always zero, that is, the arc extinction state occurs periodically. For non-single-sided welding or the trailing electrode in single-sided welding, that is, after the second electrode, short-time arc disappearance has a minor effect on welding quality, but the leading electrode has a strong effect on stabilization of the back wave. Will cause destabilization. If the arc does not re-ignite quickly, the solid wire pushes down the molten pool, resulting in a back wave overload condition.

  For the reasons described above, the leading electrode employs a combination of “wire speed control: constant speed”, “external characteristics: constant voltage characteristics”, and “feeding method: direct current”.

  The most popular high current submerged arc welding machine is an inexpensive AC core type AC machine. In this method, the external characteristic is necessarily a drooping characteristic. On the other hand, if a thyristor element is used to generate a direct current, a large direct current can be obtained, and the external characteristics can be constant voltage characteristics. Furthermore, recently, an inverter type welder that is weak against heat and difficult to output a large current has also been developed, which features a large current output. By using this, it is possible to obtain a very excellent DC characteristic.

<Wire speed control method, external characteristics, and power supply method at the trailing electrode>
Although it cannot be seen with multi-electrode single-sided submerged arc welding, the molten pool formed in the surface flux deposited on the steel plate is basically a long one called a one pool where all the molten metals of the wires are connected. Liquid metal. As described above, the leading electrode has the greatest influence on the shape of the back bead, but if it is one pool, the influence is relatively small, but the trailing electrode also has the shape of the back bead. Will be affected. For example, even if the first electrode serving as the leading electrode can form a well-shaped back bead in a liquid state, the molten pool formed by the first electrode after the second electrode serving as the trailing electrode is pushed out to the back surface side. In this way, the final solidified bead in the solidified state becomes irregular. Therefore, “wire speed control: constant speed” and “external characteristics: constant voltage characteristics”, which are the same as those of the leading electrode, can be applied to the second and subsequent electrodes. Here, direct current is desirable as the power feeding method, as in the case of the leading electrode. However, since the degree of influence of the polarity after the second electrode is relatively small with respect to the first electrode, it is practical even with alternating current.

  On the other hand, when the plate thickness of the steel plate is increased and the number of electrodes is increased, even if the pressure of the molten pool formed in the trailing electrode changes slightly even though it is one pool, Will no longer have a significant effect. In such a case, conventionally used “wire speed control: voltage FB shift control” and “external characteristic: drooping characteristic” can be applied. It is obvious that there is no problem even if a welding power source of “external characteristic: constant current characteristic” having the same target property is used instead of the drooping characteristic. As the role of the trailing electrode, it is also necessary to arrange the shape of the front bead. For this purpose, it may be more effective to prioritize and stabilize the current value and arc length L even if the feeding speed changes. . To meet such demands, “Wire speed control: voltage FB shift control”, “External characteristics: drooping characteristics or constant current characteristics”, and deflection due to arc interference and magnetic blowing are less likely to occur. This combination is preferred.

<Others>
[About backing]
In single-sided welding, a grooved copper or solid oxide backing material is generally used to receive the back bead. The solid oxide specifically corresponds to ceramic or glass. In the case of glass, a tape-like material in which glass fibers are knitted is generally used. Without any backing material, when excessive arc force acts on the first layer, the molten pool is dropped, the arc disappears, and welding cannot be continued. If some sort of backing material is used, this worst situation can be prevented.

  If the bottom surface of the steel plate that is the base metal is in close contact, the shape of the back bead should stabilize even when the arc force is unstable, but in reality, a large steel plate is not flat and is slightly curved or wavy. Since it is often done, it does not necessarily adhere. Therefore, in order to fill the gap between the steel plate bottom and the backing material, which is unavoidable, the backing flux may be dispersed in advance. Then, it becomes possible to some extent to prevent the molten pool on the back side from dripping. Further, there is a method in which the backing flux is thickly spread without lining the backing material, and the backing flux is pushed up by injecting gas into an air hose laid under the backing flux to improve the adhesion. In this case, the backing flux may have a powder laminated structure with a curable resin in order to prevent molten pool dripping.

[About table flux]
Since it is the minimum basic configuration for submerged arc welding, there is no need for explanation, but the flux is a container called a hopper with a hose underneath (first flux supply device 70 and second flux supply device 80 shown in FIG. 1). As the welding progresses, it is sprayed at a constant speed from the flux supply port at the tip of the hose provided immediately before the leading electrode or, if necessary, between the electrodes.

[About groove filler]
When powdered steel or steel alloy is sprayed in the groove, it melts during welding to form part of the molten metal. In addition to the effect of high efficiency, when the route gap is partially excessive, it makes it difficult to escape the back wave. Further, there is an effect of increasing the cooling rate in the vicinity of the weld and suppressing the quality deterioration of the base metal heat affected zone. In addition, there is an effect of relieving wire feeding and arc instability of the trailing electrode after the first electrode during back wave welding. However, if the amount of application is too large, it will not melt and will remain solid, which may lead to defects, so do not overspray. The optimum amount is determined by the balance between current and groove shape. As the material of the powder, a so-called fine iron powder or a coarse particle obtained by cutting a fine welding wire is used.

[Differential value of welding voltage with constant voltage characteristics]
Generally, since specifications are described in nominal terms such as a constant voltage characteristic, a drooping characteristic, and a constant current characteristic in a welding machine, the user side rarely scrutinizes the characteristics. However, the names of these external characteristics are conceptual and do not have a quantitative definition. Recently, there are models that allow users to adjust external characteristics. The slope of the desired voltage-current characteristic as the constant voltage characteristic at the operating point current, that is, the differential value dV / dI is on the horizontal side of -12.0 × 10 ⁻³ (V / A). In other words, the desirable differential value dV / dI is −12.0 × 10 ⁻³ (V / A) or more. If the differential value dV / dI is equal to or greater than −12.0 × 10 ⁻³ (V / A), the current greatly changes in response to the change in the arc length L, and the self-control action of the arc length L is effectively performed. Desirable for working. More desirably, if the differential value dV / dI is −8.0 × 10 ⁻³ (V / A) or more, the back wave shape is further stabilized. In addition, as a general characteristic of external characteristics including a constant voltage characteristic, since it cannot be a positive slope, 0 is the upper limit in effect for the differential value dV / dI.

[Differential value of welding voltage with constant current characteristics or drooping characteristics]
There is no quantitative definition of constant current characteristics and drooping characteristics. It can be said that the constant current characteristic and the drooping characteristic are generated using a rectifying element or using leakage magnetic flux due to iron core operation, but in terms of directing constant current even when the arc length L changes. The same. The desired slope of the voltage-current characteristic in common with the constant current characteristic and the drooping characteristic, that is, the differential value dV / dI at the operating point current is on the vertical side with respect to −24.0 × 10 ⁻³ (V / A). In other words, the desirable differential value dV / dI is −24.0 × 10 ⁻³ (V / A) or less. If the differential value dV / dI is less than −24.0 × 10 ⁻³ (V / A) and the voltage feedback control of the feeding speed is combined, the change in the arc voltage is detected and the feeding speed is changed. By doing so, the arc length L can be stabilized, which contributes to the stabilization of the front bead shape. In addition, as a general characteristic of external characteristics including a constant current characteristic and a drooping characteristic, there cannot be a slope on the + side, so −∞ (infinity) is a practical lower limit.

  Hereinafter, the present invention will be described in more detail based on examples. However, the present invention is not limited to the following examples unless it exceeds the gist.

(First Example and First Comparative Example)
FIG. 4 is a diagram for explaining the configuration of the experimental apparatus in the first example and the first comparative example. The basic configuration of the experimental apparatus shown in FIG. 4 is the same as that of the welding apparatus 1 shown in FIG. Here, in FIG. 4, together with the experimental apparatus, the workpiece 200 including the first steel plate 201 and the second steel plate 202, the front flux 300 supplied to the surface side of the workpiece 200, and the backing disposed on the back surface side of the workpiece 200 The weld metal 500 formed on the workpiece 200 along with the part 400 and welding is also shown.

  Moreover, Fig.7 (a) has shown the dimension of each steel plate and groove | channel in a 1st Example and a 1st comparative example. In this example, the first steel plate 201 and the second steel plate 202 were each subjected to an open tip surface treatment using a 35 mm thick, 500 mm wide × 3000 mm long steel plate having a tensile strength of 490 MPa class carbon steel to form butt joints. The groove shape was a 45 ° V type from the surface to 29 mm, and the remaining plate thickness of 6 mm was vertical as the root face. The root gap was 0 mm at which the steel plates on both sides were in contact with each other at the shortest portion, but there was a portion where a gap of 2 mm at the maximum was inevitably generated due to distortion of the steel plate. Each wire (the 1st wire 110-the 4th wire 140) used JIS Z3351 YS-S6 applicable goods, and the surface flux 300 used JIS Z3352 SACI1 applicable goods. An appropriate amount of the front flux 300 is automatically continuously distributed before the first electrode (leading electrode) and between the second electrode and the third electrode.

  A grooved backing copper plate 402 with a small amount of backing flux 401 dispersed thereon was pressed as a backing portion 400 on the back side of the steel plate groove. For each electrode, an independent welding power source was connected between the corresponding contact tip and the steel plate. Each wire is sent to the welded portion by a feed roller provided immediately above each contact tip.

  And the test of the 4-electrode single-sided submerged arc welding method was performed using the experimental apparatus shown in FIG. More specifically, by using the test apparatus shown in FIG. 4, the wire diameter, power feeding method, external characteristics, wire speed control, welding current, and arc voltage were changed for each electrode, and the influence was confirmed. In the experimental apparatus shown in FIG. 4, the distance between the tip of the first wire 110 and the tip of the second wire 120 is 40 mm, the distance between the tip of the second wire 120 and the tip of the third wire 130 is 120 mm, The distance between the tips of the third wire 130 and the tip of the fourth wire 140 was 30 mm. And the welding speed in this example was 44 (cm / min), and was made common.

  Moreover, as a test result, a back bead shape, a front bead shape, and an internal defect were evaluated. Ideally, the back bead shape should have a width of 10 mm or more and a back wave height of 2 mm or more and 6 mm or less, and the meandering is small and the variation in width is very good. Those that did not need to be repaired due to defects in the back bead shape were marked as B, and those that needed to be reworked as C. The front bead shape was also evaluated in the same manner as the back bead shape. As for internal defects, “none” was indicated when no defect was found even after ultrasonic testing or cross-sectional macro cut test, and “existing” was indicated when fusion failure was confirmed.

  Tables 1 and 2 show manufacturing conditions and test results in the first example and the first comparative example. Here, No. 1 shown in Table 1. 1-1-No. No. 1-5 is the first embodiment, and No. 1 shown in Table 2 was used. 1-6 to No. Reference numeral 1-11 denotes a first comparative example.

  In the power feeding methods shown in Table 1 and Table 2, “AC” means alternating current, “DC (EP)” means “Electrode Plus” which is direct current and has a wire, that is, the electrode side as a positive electrode, “DC (EN)” means “Electrode Negative” which is a direct current and has a wire, that is, an electrode side as a negative electrode. This notation is the same in Tables 3 to 6 described later.

First, the first embodiment will be described.
No. 1-1 uses DC / constant voltage characteristics / constant speed control for the first electrode, and uses conventional AC / droop characteristics / voltage FB shift control for the second and subsequent electrodes. The shape is obtained. On the other hand, the fourth electrode, which is the final pass, is set to AC / droop characteristics / voltage FB shift control, so that the front bead shape is also very good.

  No. 1-2 is No. This is a case where the differential value dV / dI of the external characteristic in the welding power source of the first electrode is smaller than that of 1-1, that is, the constant voltage characteristic is weakened. Since the control action is weakened and destabilized, the back bead shape is no. It is slightly inferior to 1-1. Nevertheless, since the DC / constant speed control is adopted, a back bead shape which is an allowable range is obtained.

  No. 1-3 is No. 1-3. Although it is similar to 1-1, the power polarity of the first electrode is DC positive polarity, that is, the electrode side minus (minus). In general, the DC power supply polarity is often DC reverse polarity, that is, the electrode side + (plus) is often used, but there is no problem in the welding quality, indicating that either method can be used in this construction method.

  No. 1-4 uses DC / constant voltage characteristics / constant speed control for all electrodes. By adopting control to reduce the pressure change in the molten pool after the second electrode, a very good back bead shape can be obtained. ing. On the other hand, although it is within an allowable range, the surface bead shape is slightly inferior when using direct current that is easily affected by inter-arc interference and magnetic blow, compared to when using alternating current.

  No. 1-5 has constant voltage characteristics / constant speed control for all the electrodes, and only the first electrode is DC, but the others are AC. By adopting alternating current on the trailing pole side, the arc is less susceptible to magnetic blowing, and as a result, not only the back bead shape but also the front bead shape is very good.

Subsequently, the first comparative example will be described.
No. 1-6 is a typical one currently used. AC, drooping characteristics and voltage FB shift control are adopted for all electrodes. Fluctuation in feed speed and periodic arc disappearance peculiar to alternating currents cause instability of the backside molten pool, and although internal defects and surface bead shape are not particularly problematic, they are unsuitable for backside welding. Defect in bead shape was remarkable.

  No. 1-7 is No.1. In contrast to 1-6, constant voltage characteristics and constant speed control are applied to the fourth electrode, but even if control is performed to reduce the pressure change in the molten pool only at the fourth electrode, which is the final electrode, the contribution ratio Was lower than that of the first electrode, and the back bead shape was not improved.

  No. 1-8 is No.1. Although it is similar to 1-7, the constant voltage characteristic / constant speed control is applied to the second electrode instead of the fourth electrode. However, the second electrode serving as the first intermediate electrode has a lower contribution to stabilizing the pressure applied to the molten pool forming the back bead than the first electrode, and the effect of improving the back bead shape was not obtained.

  No. In 1-9, the first electrode and the second electrode both have a conventional AC / dripping welding power source and the wire feed is controlled at a constant speed. In the drooping characteristic, in principle, the arc length must be stabilized by wire feed control, but since the speed is constant, the arc length stabilizing action is not working at all. Therefore, the arc length always fluctuated greatly and stable welding could not be performed. As a result, both the back bead shape and the front bead shape were largely rough and unstable, and poor fusion occurred inside.

  No. 1-10 has a DC / constant current characteristic for the first electrode, while the wire speed control is made constant speed control. Welding power sources with direct current and constant current characteristics are generally non-melting electrodes, that is, power sources used in TIG welding and plasma welding methods that generate arcs from non-consumable tungsten electrodes, not consumable wires. This control is the same as the drooping characteristic, and the upper and lower sides on the electrode side are necessary. Even if this power source is used as a melting electrode type, when the wire is controlled at a constant speed, the arc length stabilizing action does not work at all. Therefore, no. As with 1-9, the arc length always fluctuated greatly, and stable welding was not possible. Both the back bead shape and the front bead shape were largely rough and unstable, and poor fusion occurred inside.

  No. Reference numeral 1-11 is a change from the AC / droop characteristic / voltage FB shift control to the DC / constant current characteristic / voltage FB shift control for all the conventional electrodes. As a result, the back bead shape was not stabilized. As for the table bead shape, constant current characteristics / voltage FB shift control was acting, and although instability due to arc mutual interference peculiar to DC was observed, it was within an allowable range.

(Second Example and Second Comparative Example)
FIG. 5 is a diagram for explaining the configuration of the experimental apparatus in the second embodiment and the second comparative example. The basic configuration of the experimental apparatus shown in FIG. 5 is obtained by removing the fourth welding unit 40 from the welding apparatus 1 shown in FIG. Here, in FIG. 5, together with the experimental apparatus, the workpiece 200 including the first steel plate 201 and the second steel plate 202, the front flux 300 supplied to the surface side of the workpiece 200, and the backing disposed on the back surface side of the workpiece 200 The weld metal 500 formed on the workpiece 200 along with the part 400 and welding is also shown.

  Moreover, FIG.7 (b) has shown the dimension of each steel plate and groove | channel in a 2nd Example and a 2nd comparative example. In this example, the first steel plate 201 and the second steel plate 202 were subjected to an open tip surface treatment using a tensile strength 400 MPa class carbon steel plate with a thickness of 30 mm, a width of 500 mm × a length of 3000 mm, to form butt joints. The groove shape was a 45 ° V shape from the surface to 25 mm, and the remaining plate thickness of 5 mm was vertical as the root face. The root gap was 0 mm at which the steel plates on both sides were in contact with each other at the shortest portion, but there was a portion where a gap of 2 mm at the maximum was inevitably generated due to distortion of the steel plate. Each wire (the 1st wire 110-the 3rd wire 130) used JIS Z3351 YS-S6 applicable goods, and the surface flux 300 used JIS Z3352 SACI1 applicable goods. An appropriate amount of the front flux 300 is automatically and continuously sprayed before the first electrode (leading electrode) and between the second electrode and the third electrode.

  On the back side of the steel plate groove, a small amount of backing flux 412 containing a curable resin component is spread on the underlay flux 411 as the backing portion 400 without using a molding solid such as a copper plate or a ceramic plate. The backing flux 412 was pressed against the back surface of the steel sheet by injecting gas from an air hose 413 passed through the inside. For each electrode, an independent welding power source was connected between the corresponding contact tip and the steel plate. Each wire is sent to the welded portion by a feed roller provided immediately above each contact tip.

  And the test of the three-electrode single-sided submerged arc welding method was performed using the experimental apparatus shown in FIG. More specifically, using the test apparatus shown in FIG. 5, the wire diameter, power feeding method, external characteristics, wire speed control, welding current, and welding voltage were changed for each electrode, and the effects were confirmed. In the experimental apparatus shown in FIG. 5, the distance between the tip of the first wire 110 and the tip of the second wire 120 was 40 mm, and the distance between the tip of the second wire 120 and the tip of the third wire 130 was 120 mm. The welding speed in this example is 47 (cm / min) and is common.

  As test results, the back bead shape, the front bead shape, and internal defects were evaluated. Ideally, the back bead shape should be 9 mm or more in width and 2 mm or more and 5 mm or less in back wave height. Furthermore, it is very good if the meandering is small and the variation in width is very small. A. Those that did not need to be repaired due to defects in the back bead shape were marked as B, and those that needed to be reworked as C. The front bead shape was also evaluated in the same manner as the back bead shape. As for internal defects, “none” was indicated when no defect was found even after ultrasonic testing or cross-sectional macro cut test, and “existing” was indicated when fusion failure was confirmed.

  Tables 3 and 4 show manufacturing conditions and test results in the second example and the second comparative example. Here, No. 2 shown in Table 3 was used. 2-1. No. 2-4 is the second embodiment. 2-5-No. Reference numeral 2-10 denotes a second comparative example.

First, the second embodiment will be described.
No. 2-1 uses DC / constant voltage characteristics / constant speed control for the first electrode, and uses conventional AC / droop characteristics / voltage FB shift control for the second and subsequent electrodes. The shape is obtained. Further, the outer electrode of the front bead shape is very good because the third electrode, which is the final pass, is subjected to AC / droop characteristics / voltage FB shift control.

  No. No. 2-2 is No.2. This is a case where the differential value dV / dI of the external characteristic in the second and third electrode welding power sources is larger than that of 2-1, that is, the constant current characteristic is weakened. When the constant current characteristic is weakened, the arc voltage is less likely to change, and the feedback control of the arc length is also less effective. Accordingly, although it is within an allowable range, the surface bead shape is more affected by the stability of the arc length than the backside bead shape. That is, it is suggested that the voltage FB shift control with a small differential value dV / dI is more preferable in order to improve the surface bead shape.

  No. 2-3 has DC / constant voltage characteristics / constant speed control for all electrodes. By adopting control to reduce the pressure change in the molten pool after the second electrode, it has a very good back bead shape. Is obtained. On the other hand, although it is within the allowable range, the front bead shape is somewhat inferior to the case where alternating current is adopted because it is somewhat disturbed by inter-arc interference caused by direct currents arranged.

  No. 2-4 adopts DC / constant voltage characteristics / constant speed control for the first electrode, while DC / constant current characteristics / voltage FB shift control for the second electrode, AC / constant current characteristics / voltage FB for the third electrode. Shift control is used. Inter-arc interference occurs due to the direct current lined up on the first and second electrodes, so the back bead shape is slightly inferior although it is within the allowable range. On the other hand, the arc length is more stable and the excellent surface bead shape is obtained by adopting the constant current characteristic that is more excellent in the constant current characteristic than the drooping characteristic for the trailing electrode that forms the surface layer side. .

Subsequently, the second comparative example will be described.
No. 2-5 is No.2. In contrast to 2-1, the first electrode is not a direct current but an alternating current. Constant voltage characteristics and constant speed control are within the scope of the present invention. However, since alternating current is used, periodic arc disappearance unique to alternating current causes instability of the backside molten pool, and a stable backside bead shape is obtained. I couldn't.

  No. 2-6 is a typical one currently used. AC, drooping characteristics and voltage FB shift control are adopted for all electrodes. Although the internal defect and the front bead shape are not particularly problematic, both alternating current and shift control are unsuitable for back wave welding, and the back bead shape is defective.

  No. 2-7 is the first electrode and the third electrode is within the scope of the present invention, but the second electrode is combined with AC, drooping characteristics and current FB shift control. In the drooping characteristic, since the current does not move much with respect to the movement of the arc length, the feedback control that monitors the current is inferior as the arc length control means than the arc voltage feedback. The control of the arc length did not work well and the wire feeding was not constant, so that not only the back bead shape defect, but also the internal defect due to poor fusion and the surface bead shape defect occurred.

  No. No. 2-8 is a combination of constant current characteristics and current FB speed control, in which the constant current characteristics are further enhanced with respect to the drooping characteristics for all electrodes. Since the control of the arc length does not work well and the wire feeding is not constant, not only the defect of the back bead shape but also the internal defect of the fusion defect and the defect of the front bead shape occur. Overall quality was inferior to 2-7.

  No. 2-9 is a combination of constant voltage characteristics and voltage FB shift control as the first electrode. In the constant voltage characteristic, the voltage does not move very much with respect to the movement of the arc length. Therefore, the feedback control that monitors the voltage has low performance as an arc length control means, and the first electrode forming the back bead is the wire feed speed. Is the most important for shape stabilization, so that a good back bead shape could not be obtained with this configuration. Also, due to the remarkable instability of the first layer due to the first electrode, poor fusion occurred at the meeting point with the second electrode.

  No. 2-10 combines DC / constant current characteristics / constant speed control as the first electrode, but this combination does not work to stabilize the arc length, so the welding is unstable and the back bead shape is poor. In addition, due to the remarkable instability of the first layer due to the first electrode, poor fusion occurred at the meeting point with the second electrode.

(Third Example and Third Comparative Example)
FIG. 6 is a diagram for explaining the configuration of the experimental apparatus in the third example and the third comparative example. The basic configuration of the experimental apparatus shown in FIG. 6 is obtained by removing the third welding unit 30, the fourth welding unit 40, and the second flux supply apparatus 80 from the welding apparatus 1 shown in FIG. Here, in FIG. 6, together with the experimental apparatus, the workpiece 200 including the first steel plate 201 and the second steel plate 202, the front flux 300 supplied to the surface side of the workpiece 200, and the backing disposed on the back surface side of the workpiece 200 A part 400, a weld metal 500 formed on the workpiece 200 along with welding, and a groove filler 600 supplied in advance to the groove are also shown.

  Moreover, FIG.7 (c) has shown the dimension of each steel plate and groove | channel in a 3rd Example and a 3rd comparative example. In this example, the first steel plate 201 and the second steel plate 202 were subjected to an open tip surface treatment using a tensile strength 520 MPa class carbon steel plate having a thickness of 14 mm, a width of 500 mm and a length of 3000 mm, thereby forming a butt joint. The groove shape was a 50 ° V type without a root face. The root gap was 0 mm at which the steel plates on both sides were in contact with each other at the shortest portion, but there was a portion where a gap of 2 mm at the maximum was inevitably generated due to distortion of the steel plate. Each wire (the 1st wire 110 and the 2nd wire 120) used JIS Z3351 YS-S6 applicable goods, and the surface flux 300 used JIS Z3352 SACI1 applicable goods. A proper amount of the front flux 300 is continuously continuously sprayed before the first electrode (leading electrode). Separately from the surface flux 300, a groove filler 600 made of iron powder was manually dispersed in the groove in advance. The filling height of the groove filler 600 was controlled at 3 mm from the steel sheet surface position. The groove filler 600 is melted together with each wire and the surface flux 300 at the time of welding to form a molten pool.

  On the back side of the steel plate groove, a soft backing material 421 called a glass tape made of glass fiber woven to a thickness of several mm is used as the backing portion 400 without using a molding solid such as a copper plate or a ceramic plate or a backing flux. It was. Since the glass tape is soft, it is not affected by the corrugation of the steel sheet and can be adhered to the back surface. Although the vicinity of the arc melts at the time of welding, the non-molten portion serves as a cushion to prevent excessive spilling of the back wave. For each electrode, an independent welding power source was connected between the corresponding contact tip and the steel plate. Each wire is sent to the welded portion by a feed roller provided immediately above each contact tip.

  Then, using the experimental apparatus shown in FIG. 6, a two-electrode single-sided submerged arc welding method was tested except for a part (No. 3-8 described later). More specifically, using the test apparatus shown in FIG. 6, the wire diameter, power feeding method, external characteristics, wire speed control, welding current, and arc voltage were changed for each electrode, and the effects were confirmed. In the experimental apparatus shown in FIG. 6, the distance between the tip of the first wire 110 and the tip of the second wire 120 was 70 mm. And although the welding speed in this example was constant in each manufacturing condition, it varied according to manufacturing conditions. In addition, No. 3-8 is a test by a single electrode single-sided submerged arc welding method using only the first wire 110.

  As test results, the back bead shape, the front bead shape, and internal defects were evaluated. Ideally, the back bead shape should be 6 mm or more in width and 1 mm or more and 4 mm or less in back wave height. Furthermore, it is very good if the meander is small and the variation in width is very small. A. Those that did not need to be repaired due to defects in the back bead shape were treated as B, and those that did not need to be repaired as C. The front bead shape was also evaluated in the same manner as the back bead shape. As for internal defects, “none” was indicated when no defect was found even after ultrasonic testing or cross-sectional macro cut test, and “existing” was indicated when fusion failure was confirmed.

  Tables 5 and 6 show manufacturing conditions and test results in the third example and the third comparative example. Here, No. 1 shown in Table 5 was obtained. 3-1. 3-4 is the third embodiment and No. 3 shown in Table 6. 3-5-No. 3-14 is a third comparative example.

First, the third embodiment will be described.
No. 3-1 uses DC / constant voltage characteristics / constant speed control for the first electrode, and the second electrode uses conventional AC / droop characteristics / voltage FB shift control. A bead shape is obtained.

  No. 3-2 is No.3. Although the first electrode is a direct current on the electrode side with respect to 3-1, no. The quality equivalent to that of 3-1 is obtained.

  No. 3-3 uses DC / constant voltage characteristics / constant speed control of both electrodes on the electrode side. No. 3-1. As in 3-2, the stability of the back bead shape is originally superior to the constant speed control rather than the speed change control at the second pole, but by using the groove filler 600, the There was no effect on the back bead shape. On the other hand, in the case of the two-electrode method, the second electrode, which is the final electrode, is the dominant electrode having a surface bead shape, and although within the allowable range, the shape stability is affected by the influence of inter-arc interference due to the direct current lined up. Somewhat inferior.

  No. 3-4 is a constant voltage characteristic / constant speed control for both electrodes, and the first electrode is DC and the second electrode is AC. The wire feed control that most strongly influences the back bead shape is controlled at a constant speed, and the first electrode is direct current with no periodic arc break, while the second electrode that dominates the front bead shape is inter-arc interference. Since the AC was not affected by the magnetic blow and the magnetic blow, the best front / back quality of the third example was obtained.

Subsequently, the third comparative example will be described.
No. 3-5 is a typical currently used. Both poles adopt AC, drooping characteristics and voltage FB shift control. Although the internal defect and the front bead shape are not particularly problematic, both AC and shift control are unsuitable for the back wave welding, and the back bead shape is very bad. Moreover, since the plate | board thickness of the steel plate was small with respect to Example 1 and 2 mentioned above, the defect of a back bead shape also affected the surface bead shape and caused it to deteriorate a little.

  No. 3-6 combines AC / constant current characteristics / constant speed control as the first electrode. In this combination, periodic arc breaks peculiar to AC not only adversely affect the back bead shape, but also the arc length. Since the stabilization control does not work, welding is unstable, and not only the back bead shape is defective, but also the first electrode has significant instability in the first layer, resulting in poor fusion at the meeting point with the second electrode. did. If the number of electrodes is large as in the first example and the second example, the back bead shape defect due to the first electrode does not affect the front bead shape much, but this example is a two-electrode construction, The instability of the back bead shape affected the front bead shape and caused deterioration.

  No. In the case of 3-7, the combination of the first electrode having constant voltage characteristics and constant speed control is within the scope of the present invention, but the wire diameter is as thin as 2.0 mm. As a result, a back bead could not be formed, and a dent was formed on the back side of the steel plate. In order to form the back bead, it is necessary to achieve both a strong arc force and a thickness reduction of the molten pool that does not obstruct it. In order to make this combination suitable, it is effective to reduce the current density, and the larger the wire diameter, the more advantageous. That is, it can be said that a wire diameter of 2.0 mm is insufficient.

  No. The combination of constant voltage characteristics and constant speed control 3-8 is within the scope of the present invention, but the challenge is to finish the backside bead formation and the front bead formation simultaneously with only one electrode. However, although a good shape was obtained for the backside bead, the front bead shape could not be made good. Since the role of the first electrode is specialized to form a back bead, the welding conditions are limited, and the front bead shape must be a narrow convex shape. If there are two or more electrodes, the thin and convex molten pool shape formed at the leading electrode can be adjusted using welding conditions for improving the surface bead shape at the trailing electrode (particularly the final electrode). This role sharing is not possible with one electrode construction, so it is unsuitable for back wave welding.

  No. 3-9 adopts AC / constant current characteristics / voltage FB shift control as the leading electrode. Although internal defects and front bead shape are not particularly problematic, alternating current and speed change control is unsuitable for back wave welding, and the back bead shape is notoriously defective.

  No. 3-10, leading electrode, No. 3-10. 3-11, no. The trailing pole of 3-12 has constant voltage characteristics and voltage FB shift control, but the voltage does not move very much with respect to the movement of arc length regardless of direct current or alternating current. Since the control has low performance as an arc length control means, welding is unstable, appearance defects occur in both the back bead shape and the front bead shape, and poor fusion occurs in the meeting portion.

  No. 3-13, no. The trailing electrode of 3-14 has constant current characteristics and constant speed control. Regardless of direct current or alternating current, the arc length stabilization control does not work with this combination, so welding is unstable and the back bead shape In addition, the appearance of the front bead shape was poor, and poor fusion occurred at the meeting part.

  In the first embodiment, the case where the backing flux 401 and the backing copper plate 402 are used as the backing portion 400 in the four-electrode single-sided submerged arc welding has been described. In the second embodiment, the case where the underlay flux 411, the backing flux 412 and the air hose 413 are used as the backing portion 400 in the three-electrode single-sided submerged arc welding has been described. Furthermore, in the third embodiment, the case where the soft backing material 421 is used as the backing portion 400 in the two-electrode single-sided submerged arc welding has been described. However, the number of electrodes and the configuration of the backing portion 400 in multi-electrode single-sided submerged welding are not limited to the above-described combinations, and the combinations may be changed as appropriate.

DESCRIPTION OF SYMBOLS 1 ... Welding apparatus, 10 ... 1st welding unit, 11 ... 1st feeding apparatus, 12 ... 1st welding power supply, 20 ... 2nd welding unit, 21 ... 2nd feeding apparatus, 22 ... 2nd welding power supply, 30 ... 3rd welding unit, 31 ... 3rd feeding device, 32 ... 3rd welding power source, 40 ... 4th welding unit, 41 ... 4th feeding device, 42 ... 4th welding power source, 50 ... cart drive device, 60 ... Control device, 70 ... First flux supply device, 80 ... Second flux supply device, 90 ... Cart, 110 ... First wire, 120 ... Second wire, 130 ... Third wire, 140 ... Fourth wire, 200 ... Workpiece 201 ... first steel plate 202 ... second steel plate 300 ... surface flux 400 ... backing portion 500 ... welded metal 600 ... groove filler

Claims (6)

A multi-electrode single-sided submerged arc welding method using a leading electrode and a trailing electrode following the leading electrode,
Each of the leading electrode and the trailing electrode uses a wire having a diameter of 2.4 mm or more,
The power supply method and the external characteristics of the power source that supplies power to each wire, and the speed control method of the feeding speed of each wire,
In the leading electrode, the power feeding method is set to DC, the external characteristic is a constant voltage characteristic, and the speed control method is set to constant speed control,
In the trailing electrode,
(A) The power feeding method is DC, the external characteristic is constant voltage characteristic, the speed control method is constant speed control (b) The power feeding method is AC, the external characteristic is constant voltage characteristic, and the speed control method is constant speed control (C) The power feeding method is AC, the external characteristic is a constant current characteristic, and the speed control method is voltage feedback control based on an arc voltage. (D) The power feeding method is AC, the external characteristic is a drooping characteristic, and the speed control method is Voltage feedback control based on arc voltage (e) The multi-electrode, wherein the power feeding method is set to DC, the external characteristic is constant current characteristic, and the speed control method is set to voltage feedback control based on arc voltage Single-sided submerged arc welding method. The trailing electrode includes a plurality of electrodes following the leading electrode,
The power supply method, the external characteristic, and the speed control method are set to any one of (a) to (e) for each of the plurality of electrodes constituting the trailing electrode. Item 2. The multi-electrode single-sided submerged arc welding method according to Item 1. Among the plurality of electrodes constituting the trailing electrode, in the final pole located on the rearmost side when viewed from the leading electrode, the power feeding method, the external characteristic, and the speed control method are the (c) or (( The multi-electrode single-sided submerged arc welding method according to claim 2, which is set to d). When using the power supply having the constant voltage characteristic, a differential value dV / dI which is a slope of a voltage with respect to a current at an operating point is −12.0 × 10 ⁻³ (V / A) or more. The multi-electrode single-sided submerged arc welding method according to any one of claims 1 to 3. When the power supply having the constant current characteristic or the drooping characteristic is used, a differential value dV / dI that is a slope of a voltage with respect to a current at an operating point is −24.0 × 10 ⁻³ (V / A) or less. The multi-electrode single-sided submerged arc welding method according to any one of claims 1 to 4. It is a method for manufacturing a welded product obtained by welding a base material by single-sided submerged arc welding using a leading electrode and a trailing electrode following the leading electrode,
Each of the leading electrode and the trailing electrode uses a wire having a diameter of 2.4 mm or more,
The power supply method and the external characteristics of the power source that supplies power to each wire, and the speed control method of the feeding speed of each wire,
In the leading electrode, the power feeding method is set to DC, the external characteristic is a constant voltage characteristic, and the speed control method is set to constant speed control,
In the trailing electrode,
(A) The power feeding method is DC, the external characteristic is constant voltage characteristic, the speed control method is constant speed control (b) The power feeding method is AC, the external characteristic is constant voltage characteristic, and the speed control method is constant speed control (C) The power feeding method is AC, the external characteristic is a constant current characteristic, and the speed control method is voltage feedback control based on an arc voltage. (D) The power feeding method is AC, the external characteristic is a drooping characteristic, and the speed control method is Voltage feedback control based on arc voltage (e) The welded product wherein the power feeding method is set to DC, the external characteristic is a constant current characteristic, and the speed control method is set to voltage feedback control based on the arc voltage Manufacturing method.

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