JPH07100652A - Welding method for galvanized steel - Google Patents

Abstract

PURPOSE:To obtain a high quality welded steel tube by arc heating the weld zone of galvanized steel in an inert gas flow or a reducing gas flow and in the specified temp. range, dispersing zinc on steel surface and executing arc welding. CONSTITUTION:The weld zone of galvanized steel 1a, 1b is arc heated in an inert gas flow or a reducing gas flow with using non comsumable electrode so as to obtain 900-1500 deg.C, dispersing zinc on steel surface, a galvanization 2 is efficiently removed as compared with galvanized film removal with using a conventional tool, etc., pretreatment of welding is simplified. Also, by using automatic welding device, removal of galvanized layer and welding are successively and automatically executed. Accordingly, a welded steel tube of low defect and high quality is efficiently produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for welding a galvanized steel material, in which the zinc layer on the surface of the steel material can be easily removed without removing the zinc layer by using a special apparatus before welding and welding without defects. Regarding how to do.

[0002]

2. Description of the Related Art Galvanized steel pipes are excellent in corrosion resistance against water and are widely used for water supply, cooling water, fire extinguishing pipes and the like in construction equipment. When welding this galvanized steel material, unless the zinc layer in the welded part and its vicinity is peeled off beforehand, zinc will evaporate due to arc heat during welding,
Since this is caught in the weld metal, welding defects such as blow holes and pits occur, and good weld joint performance cannot be obtained. Therefore, conventionally, before welding the galvanized steel material, a step of removing the zinc coating on the surface with a dedicated tool or a grinder has been required in advance.

[0003]

However, the zinc film removal using the conventional tool or the like has a poor work efficiency, and this peeling work requires a lot of time and manpower. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a welding method for galvanized steel material capable of performing defect-free welding without using special zinc stripping equipment.

[0004]

The welding method for galvanized steel material of the present invention comprises a non-consumable electrode so that the welded portion of the galvanized steel material is heated to 900 to 1500 ° C. in an inert gas or reducing gas flow. It is characterized in that it is used for arc heating to dissipate zinc on the surface of the steel material, and then arc welding is performed using a non-consumable electrode or a consumable electrode.

[0005]

[Operation] By arc-heating the welded part of the galvanized steel material in an inert gas or reducing gas stream at a temperature of 900 to 1500 ° C. by using a non-consumable electrode to disperse zinc on the surface of the steel material. The zinc plating can be removed more efficiently than the conventional zinc film removal using a tool or the like. Further, by using the automatic welding device, it is possible to continuously and automatically remove the galvanized layer and perform welding.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of a welding method for galvanized steel material according to the present invention will be described below with reference to the drawings. In addition, this example shows an example in which the method of the present invention is applied to TIG welding of an end surface of a galvanized steel pipe. Figure 1 shows two galvanized steel pipes 1a, 1b to be welded. These galvanized steel pipes 1
The a and 1b are obtained by forming a galvanized layer on the surface of a base steel pipe made of carbon steel or the like. These galvanized steel pipes 1
The end faces to be welded a and 1b are preferably subjected to desired end face processing using an end face processing machine or the like.

Two galvanized steel pipes with end face processing 1
The end faces of a and 1b are abutted against each other and temporarily attached by the tack welding portion 3 as shown in FIG. Figure 3 shows the temporarily attached steel pipe 1.
As shown in (a) and (b), it is set on the welding head 4 for automatic TIG welding. This automatic TIG welding machine is for automatically welding circular pipes, in which the temporarily attached steel pipe 1 is inserted into the welding head 4 and the tungsten electrode tip 9 which is the non-consumable electrode of the welding head 4 is temporarily attached to the steel pipe 1. Attached part (joint line)
While fixing the steel pipe 1 with the clamp 6 so that it is directly above, a fine adjustment is made so that the gap between the surface of the steel pipe 1 and the tip 9 of the tungsten electrode becomes a predetermined distance, and either the steel pipe 1 or the welding head 4 is The surface of the steel pipe 1 is arc-welded while rotating.

When the steel pipe 1 is fixed to the welding head 4,
The welding line of the steel pipe 1 is set to 9 in an inert gas or reducing gas flow.
Arc heating is performed using a non-consumable electrode so that the temperature becomes 00 to 1500 ° C. to dissipate the zinc plating layer 2 on the surface of the steel pipe 1,
As shown in FIG. 3 (a), a zinc peeling portion 7 having zinc removed is formed along the welding line. In this heat treatment for stripping zinc, only the arc is generated in an inert gas such as Ar or a reducing shield gas such as Ar + 5% H ₂ without supplying a wire, and the entire circumference of the welding line is heat treated. The guideline for setting the heating current is to set the steel pipe surface temperature to 900 to 1500 ° C. The boiling point of zinc is 930 ° C., and heating to at least 900 ° C., which is the closest to the boiling point, is indispensable in order to rapidly dissipate heat. Further, the maximum heating temperature is a temperature just before the melting point of the steel pipe material, and if it is heated to a temperature higher than this, complete welding will proceed. When heated to the maximum temperature, only the surface may be melted, but a slight melting does not particularly affect welding.

Next, as shown in FIGS. 4 (a) and 4 (b),
While the wire 5 made of carbon steel of the same quality as the steel pipe 1 is supplied near the tip 9 of the tungsten electrode, the welding line of the steel pipe 1 is arc-heated in an inert gas or reducing gas flow to remove the welding line of the steel pipe 1. Heat to 1500 ° C or higher and weld. As a result, as shown in FIG. 4 (a), a weld bead 8 is formed on the weld line to obtain an integrated steel pipe. The welded portion of the steel pipe is made to have the same corrosion resistance as other portions by painting or plating, if necessary. As the inert gas used during the welding, in addition to the shielding gas, the He, Ar + the He, and a gas containing O ₂ and CO ₂ of about 1000ppm of these gases can be used. further,
In the above example, the case where TIG welding is used for both zinc plating removal and welding is shown. In the case of welding, in addition to TIG welding using non-consumable electrodes, MIG welding and MAG welding using consumable electrodes are also used. You may use and weld. When welding with these consumable electrodes, the shielding gas is A
Gas mainly containing r and mixed with O ₂ and CO ₂ or Ar +
It is performed using a gas in which He is mixed with O ₂ or CO ₂ .

According to this welding method, the welded portion of the galvanized steel pipes 1a, 1b is heated to 900 to 900 in an inert gas or reducing gas stream.
By arc heating using a non-consumable electrode to 1500 ° C and dissipating zinc on the surface of the steel pipe, the zinc plating can be removed more efficiently than the conventional zinc film removal using tools. it can. Further, by using the automatic welding device, it is possible to continuously and automatically remove the galvanized layer and perform welding. Therefore, according to this method, a high-quality welded steel pipe with few defects can be efficiently manufactured.

(Experimental example) Test material: Carbon steel pipe for piping (SGP) White tube 100A (φ
114.3mm, t4.5mm) Pretreatment: Galvanized steel pipes 1a, 1b for butt welding
Was cut into a predetermined length, and then an I-open front end surface was processed by an end surface processing machine. The galvanized part 2 remains the same. Welding preparation: Steel pipes whose end surfaces were processed were butted, and tack welding 3 was performed to fix them. Next, the automatic welding head 4 was fixed to the steel pipe with the fixing clamp 6, and the fine adjustment was performed so that the tip 9 of the tungsten electrode at the tip of the torch was directly above the welding line, and then the head was fixed. The gap between the base material and the electrode was 2 mm. Heat treatment: The heating rate is 5 mm / sec and the heating current is Ar.
120A for shield gas, 1 for Ar + 5% H ₂
It was set to 00A, and the entire circumference of the welding line was heated. Welding: After completion of the heat treatment, the same shield gas as that used for the heat treatment is continuously used to set the welding speed to 1 mm / sec, and the average welding current is 120 A when Ar shield gas is used.
When r + 5% H _{2 was} used, the welding bead was set to 100 A, and while the wire 5 was being supplied, complete penetration welding of the entire circumference of the welding line was performed, and a weld bead 8 was formed on the zinc peeling portion 7.

Three sets of welding samples were prepared under the same conditions,
A radiation transmission test of the welded portion was performed on these samples according to JIS Z3104. The shooting was done in two places. The results are shown in Table 1. For comparison, the results of the radiation transmission test when the zinc coating was performed without heat treatment and welding was also shown in the table.

[0013]

[Table 1]

As is clear from the results in the table, most of the heat treatments were of the first grade or the second grade. On the other hand, most of the samples that were not heat-treated were grade 4, and could not be put to practical use as welded joints.

[0015]

As described above, according to the present invention, the welded part of the galvanized steel material is subjected to an inert gas or reducing gas flow,
Arc heating is performed using a non-consumable electrode so that the temperature is 900 to 1500 ° C. to evaporate zinc on the surface of the steel material, and then that portion is arc-welded using the non-consumable electrode or consumable electrode. The zinc layer in the part can be removed very efficiently, and the pretreatment for welding can be simplified. Further, by using the automatic welding device, it is possible to continuously and automatically remove the galvanized layer and perform welding. Therefore, according to this method, a high-quality welded steel pipe with few defects can be efficiently manufactured.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing two steel pipes to be welded for explaining an example of a welding method of the present invention.

FIG. 2 is a cross-sectional view showing a state in which a steel pipe is temporarily fixed.

FIG. 3 is a view showing a heat treatment step, (a) is a front view,
(B) is a side view.

4 (a) is a front view and FIG. 4 (b) is a side view showing a welding process.

[Explanation of symbols]

1a, 1b ... Galvanized steel pipe, 2 ... Galvanized layer,
3 ... Temporary welded portion, 4 ... Welding head, 5 ... Welding wire, 6 ... Fixing clamp, 7 ... Zinc peeling portion, 8 ...
Weld beads, 9 ... Tungsten electrodes.

Claims (1)

[Claims] 1. A welded portion of a galvanized steel material is arc-heated in an inert gas or reducing gas stream at a temperature of 900 to 1500 ° C. by using a non-consumable electrode to disperse zinc on the surface of the steel material. Then, a method of welding galvanized steel material, characterized by performing arc welding using a non-consumable electrode or a consumable electrode.