JP2016179484A - Welding method of galvanized steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a welding method of a galvanized steel sheet capable of reducing a zinc fume amount.SOLUTION: A welding method of a galvanized steel sheet includes: a process (S10) for preparing a galvanized steel sheet; a process (S20) for forming an arc between the galvanized steel sheet and a welding wire, heating and melting the galvanized steel sheet and the welding wire while performing shielding with shield gas, and forming a molten pool; and a process (S30) for solidifying the molten pool. The welding wire is copper-plated and has a diameter of 0.9 mm or less. The shield gas is a mixed gas which comprises carbon dioxide, argon and the remainder consisting of inevitable impurities. Carbon dioxide contained in the shield gas is 1 to 4 vol.%.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for welding galvanized steel sheets.

  A galvanized steel sheet having excellent corrosion resistance and weather resistance is a steel material that is being used in the fields of automobiles, buildings, and the like. For joining steel materials, for example, arc welding is used. However, when arc welding is performed on a galvanized steel sheet, zinc having a lower boiling point than the melting point of steel becomes zinc vapor. And it may become difficult to realize a good welding state due to zinc vapor. Specifically, a blow hole or the like may be formed in the bead due to zinc vapor. In addition, the formation state of the arc may be unstable due to zinc vapor, and the generation of spatter may increase. Furthermore, in the welding of galvanized steel sheets, there are cases where slag remaining on the beads and slag (edge slag) remaining on the bead toes are increased. As a result, good formation of a rust preventive film or the like formed in a coating process performed after welding may be hindered, or the rust preventive film or the like may be peeled off due to secular change. On the other hand, a technique for realizing a good welding state by arc welding has been proposed (see, for example, Patent Documents 1 and 2).

JP 2013-1111597 A JP 2013-248621 A

  In welding galvanized steel sheets, in addition to the welded state, generation of zinc fume caused by zinc vapor is also a problem. In the welding operation of the galvanized steel sheet, zinc fume is recovered by a recovery device (fume collector). Thereby, an appropriate working environment can be ensured. However, when the amount of zinc fume generated is large and the filter replacement frequency of the fume collector increases, not only the consumption of the filter increases, but also the work efficiency decreases due to the stop of the welding work. Therefore, reduction of the amount of zinc fume has become an important issue in the use of galvanized steel sheets. The objective of this invention is providing the welding method of the galvanized steel plate which can reduce the amount of zinc fume.

  The method of welding a galvanized steel sheet according to the present invention includes a step of preparing a galvanized steel sheet, and forming an arc between the galvanized steel sheet and the welding wire while shielding with a shielding gas, A step of heating and melting to form a molten pool; and a step of solidifying the molten pool. The welding wire is copper-plated and has a diameter of 0.9 mm or less. The shield gas is a mixed gas containing carbon dioxide and argon, with the balance being inevitable impurities. Carbon dioxide contained in the shield gas is 1% by volume or more and 4% by volume or less.

  The inventors of the present invention have examined factors that affect the amount of zinc fume in welding work of galvanized steel sheets. As a result, it has been found that the ratio of carbon dioxide contained in the shielding gas and the structure of the welding wire have a great influence on the amount of zinc fume. Specifically, in general GMA (Gas Metal Arc) welding, a mixed gas of carbon dioxide and argon containing about 20% by volume of carbon dioxide is used as a shielding gas. However, in the welding of galvanized steel sheets, with such a shield gas composition, the amount of zinc fume generated increases, and the frequency of replacement of the filter of the fume collector increases. On the other hand, the amount of zinc fume generated can be reduced by significantly reducing the proportion of carbon dioxide to 4% by volume or less. On the other hand, when the proportion of carbon dioxide is reduced to less than 1% by volume, the arc is not stable and welding becomes difficult. Therefore, in order to achieve welding in which the amount of zinc fume is reduced, the proportion of carbon dioxide contained in the shielding gas needs to be 1% by volume or more and 4% by volume or less.

  Moreover, the amount of zinc fume in welding galvanized steel sheets is extremely sensitive to the structure of the welding wire. Specifically, when the diameter of the welding wire exceeds 0.9 mm, it is difficult to sufficiently reduce the amount of zinc fume even when the composition of the shielding gas is adjusted as described above. Therefore, the diameter of the welding wire needs to be 0.9 mm or less.

  Furthermore, it is important that the welding wire is copper plated. That is, it is important that a copper plating layer is formed on the outer peripheral surface of the welding wire. This can be considered due to the following reasons. When the welding wire is not plated with copper, the arc tends to be generated from a wide range in the longitudinal direction of the tip of the welding wire. As a result, even when the diameter of the welding wire is reduced to 0.9 mm or less, the spread of the arc is increased, the range of galvanization that receives the heat of the arc is increased, and the amount of zinc fume is increased. When the welding wire is copper-plated, the amount of zinc fume is reduced because the arc is generated from a narrow range at the tip of the welding wire. Then, the amount of zinc fume can be reduced by appropriately adjusting the composition of the shield gas as described above and appropriately selecting the structure of the welding wire.

  Specifically, the amount of zinc fume is obtained by adopting a copper-plated welding wire having a diameter of 0.9 mm or less and a ratio of carbon dioxide in the shield gas of 1% by volume to 4% by volume. Can be effectively reduced.

  In the welding method of the galvanized steel sheet of the present invention, the welding wire is copper-plated, and the diameter thereof is 0.9 mm or less. Furthermore, carbon dioxide contained in the shielding gas is 1% by volume or more and 4% by volume or less. Therefore, according to the welding method of the galvanized steel sheet of the present invention, the amount of zinc fume can be reduced. In addition, when the diameter of a welding wire becomes small, since the current density of a welding wire will become large and the melting rate of a wire will become high, control of welding will become difficult. Therefore, the diameter of the welding wire is preferably 0.8 mm or more.

  In the welding method of the galvanized steel sheet, in the step of forming the molten pool, the current between the galvanized steel sheet and the welding wire is repeatedly a base value and a peak value higher than the base value. May be. By controlling the current between such a galvanized steel sheet and the welding wire, it becomes easy to reduce the amount of zinc fume.

  In the welding method for the galvanized steel sheet, carbon dioxide contained in the shielding gas may be 3% by volume or less. By doing in this way, the amount of zinc fume can be reduced more reliably.

  As apparent from the above description, according to the method for welding galvanized steel sheets of the present invention, a method for welding galvanized steel sheets capable of reducing the amount of zinc fume can be provided.

It is a flowchart which shows the outline of the procedure of welding. It is a schematic sectional drawing for demonstrating the procedure of welding. It is a figure which shows the relationship between the ratio of the carbon dioxide contained in shielding gas, and the amount of zinc fume.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. With reference to FIG. 1, in the welding method of the galvanized steel sheet according to the present embodiment, first, a galvanized steel sheet as a workpiece is prepared (S10). In this step (S10), referring to FIG. 2, for example, a pair of galvanized steel sheets (galvanized steel sheets 21, 22) is prepared. The galvanized steel sheet 21 and the galvanized steel sheet 22 are such that a part of one main surface 21A of the galvanized steel sheet 21 and a part of one main surface 22A of the galvanized steel sheet 22 are in contact with each other (adhere). Be placed.

  Next, a weld pool is formed using a welding torch (S20). Referring to FIG. 2, a welding torch 10 includes a welding nozzle 11 having a hollow cylindrical shape, a contact tip 12 disposed so as to be partially surrounded by the welding nozzle 11, and connected to a power source (not shown). including. A part of the contact tip 12 protrudes toward the front end side of the welding nozzle 11 outside the space surrounded by the welding nozzle 11. While contacting the contact tip 12, the welding wire 13 is continuously supplied to the distal end side of the welding nozzle 11. As the welding wire 13, from the viewpoint of reducing the generation of slag, it is possible to employ a mild steel wire with low Mn (manganese; for example, 1.4% by mass or less) and low Si (silicon; for example, 0.7% by mass or less). it can. Specifically, YGW16 and G43A0C16 of JIS (Japan Industrial Standards) Z3312, such as DD50A manufactured by Daido Special Steel Co., Ltd., MG-SOFT manufactured by Kobe Steel Co., Ltd., and the like can be employed.

  The gap between the welding nozzle 11 and the contact tip 12 is a shield gas flow path. The shield gas flowing through the flow path is discharged from the tip of the welding nozzle 11. The step (S20) can be performed using the welding torch 10 having such a structure.

  When a voltage is applied between the galvanized steel plates 21 and 22 and the welding wire 13 with the galvanized steel plates 21 and 22 as one electrode and the welding wire 13 as the other electrode, the welding wire 13 and the galvanized steel plates 21 and 22 Arc β is formed during The arc β is shielded from the surrounding air by the shielding gas discharged along the arrow α from the tip of the welding nozzle 11. Part of the galvanized steel plates 21 and 22 and the tip of the welding wire 13 are melted by the heat of the arc β. The droplet formed by melting the tip of the welding wire 13 moves to the molten region of the galvanized steel plates 21 and 22. Thereby, the molten pool 31 which is the liquid area | region where the molten galvanized steel plates 21 and 22 and the welding wire 13 were mixed is formed.

  Next, the process (S30) of solidifying the previously formed molten pool while moving the formation area of the molten pool is performed. In this step (S30), the welding torch 10 is moved relative to the galvanized steel plates 21 and 22 along the extending direction of the beads to be formed. As a result, the region where the molten pool 31 is formed sequentially moves, and the previously formed molten pool 31 is solidified to form a bead. And welding is completed by forming a bead along the field which should be joined.

Here, in the welding method of the galvanized steel sheet according to the present embodiment, the welding wire 13 is copper-plated and has a diameter of 0.9 mm or less. Further, in the present embodiment, the shielding gas includes carbon dioxide (CO ₂₎ and argon (Ar), the remainder being mixed gas comprising unavoidable impurities. Then, CO ₂ contained in the shielding gas is 4 vol% or more 1% by volume. By employing the welding wire 13 having the above-described structure and setting the composition of the shielding gas within such a range, the generation of zinc fume can be suppressed. Thus, according to the welding method of the galvanized steel sheet of the present embodiment, the amount of zinc fume can be reduced. As a result, it is possible to reduce the replacement frequency of the filter of the fume collector, and it is possible to reduce the consumption of the filter and increase the efficiency of the welding operation.

  When the diameter of the welding wire 13 is reduced, the current density of the welding wire 13 is increased and the melting rate of the wire is increased, so that it is difficult to control the welding. Therefore, the diameter of the welding wire 13 is 0.8 mm or more. It is preferable to do. In the step (S20), it is preferable that the current between the galvanized steel plates 21 and 22 and the welding wire 13 repeats a state where the current is a base value and a state where the current is a peak value higher than the base value. That is, in this embodiment, it is preferable to employ pulse welding. Thereby, it becomes easy to reduce the amount of zinc fume.

  Furthermore, in the method for welding galvanized steel sheets of the present embodiment, the carbon dioxide contained in the shield gas is preferably 3% by volume or less. Thereby, the amount of zinc fume can be reduced more reliably.

  We conducted actual welding of galvanized steel sheets and conducted experiments to confirm the effects of the proportion of carbon dioxide contained in the shielding gas and the structure of the welding wire (wire diameter and copper plating) on the amount of zinc fume. The experimental procedure is as follows.

  Welding of the galvanized steel sheet was performed according to the method described in the above embodiment. As the galvanized steel sheets 21 and 22, steel sheets having a thickness of 2.3 mm were prepared. The galvanized steel sheet 21 and the galvanized steel sheet 22 are arranged such that a part of one main surface 21A of the galvanized steel sheet 21 and a part of one main surface 22A of the galvanized steel sheet 22 are in close contact with each other. Welding was performed so as to form a bead of a certain length. At this time, as the shielding gas, a mixed gas containing carbon dioxide and argon and the balance consisting of inevitable impurities was employed. The proportion of carbon dioxide was changed in the range of 1 to 20% by volume. As welding wire 13, DD50A (wire A) manufactured by Daido Steel Co., Ltd. having a diameter of 0.9 mm and having an outer peripheral surface plated with copper, Co., Ltd. having a structure having a diameter of 1.0 mm and having an outer peripheral surface plated with copper. Three types of wires were used: Kobe Steel MG-SOFT (Wire B) and Kobe Steel SE-A50 (Wire C) having a structure with a diameter of 0.9 mm and an outer peripheral surface not plated with copper. For each wire, the amount of zinc fume generated when the ratio of carbon dioxide in the shielding gas was changed was measured. The experimental results are shown in FIG.

  In FIG. 3, the horizontal axis indicates the ratio of carbon dioxide in the shield gas. The vertical axis indicates the amount of zinc fume generated when beads having a certain length are formed. In the case of the bead length employed in this experimental condition, it can be determined that the amount of zinc fume is sufficiently reduced if the amount of zinc fume is 40 mg or less.

  Referring to FIG. 3, wire B whose outer peripheral surface is copper-plated and having a diameter of 1.0 mm exceeding 0.9 mm and wire C whose diameter is 0.9 mm and whose outer peripheral surface is not copper-plated are shown. Was used as a welding wire, the region where the amount of zinc fume was suppressed to 40 mg or less was not confirmed even when the proportion of carbon dioxide was changed. On the other hand, when the wire A having a diameter of 0.9 mm and having an outer peripheral surface plated with copper is used, the amount of zinc fume is drastically reduced by setting the ratio of carbon dioxide to 4% by volume or less. Zinc fume amounts below 40 mg have been achieved. Furthermore, the amount of zinc fume is further reduced by setting the ratio of carbon dioxide contained in the shielding gas to 3% by volume or less.

  Further, according to the study by the present inventors, when the welding wire 13 whose outer peripheral surface is copper-plated and whose diameter is 0.8 mm is employed, the same result as that of the wire A can be obtained. That is, when the outer peripheral surface of the welding wire 13 is copper-plated and the diameter is 0.9 mm or less, the proportion of carbon dioxide contained in the shield gas is 1% by volume to 4% by volume, preferably 1% by volume to 3%. By setting the volume% or less, the amount of zinc fume can be effectively reduced. However, when the diameter of the welding wire 13 is less than 0.8 mm, the resistance of the welding wire 13 increases, and the welding control itself becomes difficult. Therefore, the diameter of the welding wire 13 is preferably 0.8 mm or more. Moreover, when the ratio of carbon dioxide contained in the shielding gas is less than 1% by volume, the arc is not stable and welding becomes difficult. Therefore, in order to achieve welding with a reduced amount of zinc fume, the proportion of carbon dioxide contained in the shielding gas needs to be 1% by volume or more and 4% by volume or less.

  From the above experimental results, it is confirmed that according to the method for welding galvanized steel sheets of the present invention, a method for welding galvanized steel sheets capable of reducing the amount of zinc fume can be provided.

  It should be understood that the embodiments and examples disclosed herein are illustrative in all respects and are not restrictive in any respect. The scope of the present invention is defined by the scope of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the scope of the claims.

  The welding method of the galvanized steel sheet of the present invention can be particularly advantageously applied to welding of a galvanized steel sheet that requires a reduction in the amount of zinc fume.

  DESCRIPTION OF SYMBOLS 10 welding torch, 11 welding nozzle, 12 contact tip, 13 welding wire, 21,22 galvanized steel sheet, 21A, 22A main surface, 31 molten pool.

Claims (3)

Preparing a galvanized steel sheet;
Forming an arc between the galvanized steel sheet and the welding wire while shielding with a shielding gas to heat and melt the galvanized steel sheet and the welding wire to form a molten pool;
Solidifying the molten pool, and
The welding wire is copper plated and has a diameter of 0.9 mm or less,
The shielding gas includes carbon dioxide and argon, and the balance is a mixed gas composed of inevitable impurities,
The method for welding galvanized steel sheets, wherein carbon dioxide contained in the shielding gas is 1% by volume or more and 4% by volume or less.   The step of forming the molten pool repeats a state where a current between the galvanized steel sheet and the welding wire is a base value and a state where the current is a peak value higher than the base value. A method for welding the galvanized steel sheet according to 1.   The method for welding a galvanized steel sheet according to claim 1 or 2, wherein carbon dioxide contained in the shield gas is 3% by volume or less.

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