JP2007196233A - Method for manufacturing backing flux for submerged arc welding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a backing flux for submerged arc welding by which the coating of a thermosetting synthetic resin on the surface side is unnecessary and both flux slag and excess backing flux are useable for the recycled material of the backing flux of the submerged arc welding. <P>SOLUTION: When recycling the melt type backing flux 14A on and after the second time, not only a sinter type surface flux slag 15 but the melt type backing flux slag 16A and the unused melt type backing flux 14A are also recovered and made into the recycled raw material. Then, each material which comprises the recycled raw material becomes the same composition system as that of the sinter type surface flux slag 15. As a result, the coating of a thermosetting synthetic resin on the surface side is unnecessary and both the flux slag 15, 16A and the excess backing flux 14A are useable as the recycled raw material for a new melt type backing flux 14A. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a backing flux for submerged arc welding, and more particularly, to a method for producing a backing flux for submerged arc welding by melting a used sintered surface flux slag and regenerating it as a backing flux for submerged arc welding. .

The submerged arc welding method (Submerged Arc Welding (SAW)) is a method of performing welding while feeding a flux having a particle shape and a wire separately. The submerged arc welding method was developed in the United States around 1934, and it was possible to automate the welding and increase the current as compared with the conventional welding using a coated arc welding rod.
Flux used for single-sided backside welding such as large plate joint butt welding has different compositions on the front side (front flux) and backside (backing flux) of the steel plate to be welded. Only the sintered backing flux is coated with a thermosetting resin on the front side.

At the time of welding, a front flux slag as a residue is generated from the front flux, and a backing flux slag is also generated from the backing flux.
In addition, during welding, the backing flux is heated non-uniformly, so that the disappearance portion and the residual portion of the coated thermosetting resin are mixed in the backing flux. Therefore, it is impossible to form a weld bead having a good surface shape at the time of reuse. As a result, the surplus of the backing flux was not reusable unlike the surplus surface flux, and was discarded together with both flux slags.

For example, Patent Document 1 and Patent Document 2 are known as conventional techniques for solving this problem. Patent Document 1 is a backing flux for single-sided welding using a slag pulverized material generated during welding of a sintered (bond) type flux as a raw material. In Patent Document 1, a backing flux is manufactured by granulating and firing a backing flux and coating the surface of the obtained fired particles with a thermosetting synthetic resin.
Patent Document 2 discloses a one-sided submerged arc welding in which a used (surplus) backing flux is heated to remove the thermosetting synthetic resin, and then the powder is recovered and coated again with the thermosetting synthetic resin. It is a manufacturing method of the reproduction | regeneration backing flux.
JP 2002-331389 A JP 2005-34877 A

However, according to Patent Document 1 and Patent Document 2, when the flux slag and the excess backing flux are regenerated to the backing flux, a special process of coating the front side of the powder with the thermosetting synthetic resin as described above. Had to be given.
Conventionally, a method has been developed in which the surface flux slag and the backing flux slag, which are residues of both fluxes having different compositions from each other, are collected together with the excess backing flux and used as a raw material for the backing flux in a lump. It wasn't.

  The present invention does not require a thermosetting synthetic resin coating on the front side, and can be used as a recycling material for the backing flux in a lump without discarding both flux slag and the excess backing flux. It aims at providing the backing flux manufacturing method for arc welding.

The invention according to claim 1 is a first recovery step for recovering only the sintered type surface flux slag after use of the submerged arc welding, and coke is mixed and melted in the recovered sintered type surface flux slag. In the melted sintered type surface flux slag, at least one of CO gas and CO ₂ gas is solid-dissolved, and the metal component contained in the melted sintered type surface flux slag is settled. A first melting step to remove from the sintered mold surface flux slag, and the sintered mold surface flux slag dissolved in the melting process is granulated in a foamed or dense state by granulation or air crushing, and then dried. The first dry crushing step and the crushing surface flux slag obtained in the dry crushing step are further pulverized to adjust to a predetermined particle size range, and then the obtained pulverized surface flux slag remains after magnetic separation. A first pulverizing and sizing step to obtain a molten type backing flux for submerged arc welding, and after the submerged arc welding using the molten type backing flux, the sintered type surface flux slag, A second recovery step of recovering a recycled raw material comprising the molten type backing flux slag and an excess of the molten type backing flux; and coke mixed with the recovered recycled raw material and dissolved; A second melting step in which at least one of CO gas and CO ₂ gas is solid-dissolved therein, and a metal component contained in the dissolved recycled raw material is settled and removed from the recycled raw material; The regenerated raw material dissolved in the process is granulated or blown into a foamed or dense state, and then dried, and then dried, and the crushed regenerated raw material obtained in the dry crushing step is further pulverized. Crushing to adjust to a predetermined particle size range, and then removing the remaining metal by subjecting the obtained pulverized and regenerated raw material to a magnetic separation treatment, and a second pulverizing preparation as a melting type backing flux for submerged arc welding. A method for producing a backing flux for submerged arc welding comprising a grain process.

According to the first aspect of the present invention, first, the first submerged arc welding is performed using the sintered type surface flux and the sintered type backing flux having different compositions. Thereafter, only the sintered type surface flux slag is recovered and regenerated as a molten type backing flux. By using the melt type, it is not necessary to coat the front side of the backing flux with a thermosetting synthetic resin.
Next, the regenerated molten backing flux is used as the backing flux, and the second submerged arc welding is performed. Similarly, after each subsequent arc welding, the melting type backing flux is sequentially regenerated. However, after the second time, not only the sintered type surface flux slag but also the molten type backing flux slag and the surplus molten type backing flux are collected, and a mixture of these three types is used as a recycled material.

In spite of both fluxes having different compositions, these three types of materials can be used as the reclaimed raw material because the sintered type surface flux slag is regenerated one time before the corresponding recycle. This is because the melt-type backing flux regenerated as a raw material is used as the backing flux. As a result, each of the three materials constituting the recycled raw material has the same composition system as the sintered type surface flux slag. Therefore, even if a mixture of these three types is used as a recycled material, the regenerated molten backing flux does not cause any problem in its welding characteristics.
This eliminates the need for a coating of thermosetting synthetic resin on the front side of the backing flux, and without discarding both flux slag and excess backing flux, the above three types of materials can be used together for the backing flux. It can be used as a recycled material.

The submerged arc welding method to which the present invention is applied is not limited. Examples thereof include a flux backing method (RF) and a flux copper backing method (FCB).
The sintered mold surface flux may be a low-temperature sintered mold (sintered at 350 to 600 ° C.) or a high-temperature sintered mold (sintered at 700 ° C. or higher) in which no oxide film is formed.
The composition of the sintered type surface flux is not limited. For example, PFI-55E manufactured by Kobe Steel (MnO is 0.9 wt%, SiO ₂ is 11.2 wt%, Al ₂ O ₃ is 5.7 wt%, CaO is 7.6 wt%, and MgO is 19 wt%. 0.0 wt%, TiO ₂ 10.4 wt%, and iron powder 30 wt%). Further, Nippon Steel Sumitomo Metals Welding Industries, Ltd. NSH-50 (MnO 6.8 wt%, SiO ₂ is 15.9 wt%, _Al 2 _{O 3} is 3.9 wt%, CaO 6.1 wt%, MgO may be 18.2 wt%, TiO ₂ may be 3.9 wt%, and iron powder may be 30 wt%).

The backing flux used during the first welding may be a sintered type or a molten type. The composition of the backing flux for the first welding is not limited. For example, PFI-50R manufactured by Kobe Steel (FeO 5.2% by weight, MnO 1.2% by weight, SiO ₂ 27.6% by weight, Al ₂ O ₃ 6.1% by weight, CaO 16% 0.1 wt%, MgO 32.6 wt%, and TiO ₂ 0.1 wt%). NSH-1R manufactured by Nippon Steel & Sumikin Welding Co., Ltd. (FeO is 6.9% by weight, MnO is 6.8% by weight, SiO ₂ is 15.9% by weight, Al ₂ O ₃ is 3.9% by weight, (CaO is 6.1% by weight, MgO is 18.2% by weight, TiO ₂ is 3.9% by weight). A thermosetting resin (phenol resin, furan resin, xylene resin, etc.) is coated on the front side of each particle of the backing flux.

The bulk density of the backing flux used during the first welding is not limited. For example, 0.8 to 1.3 g / cm ³ (preferably around 1.1 g / cm ³ ). When the bulk density is less than 0.8 g / cm ³ , the arc shielding property during welding is lowered, and there is a possibility that the bead appearance defect, the occurrence of blowholes, and the slag peelability from the base metal and the weld metal may be lowered. On the other hand, when the bulk density exceeds 1.3 g / cm ³ , the slag is easily seized onto the base material and the weld metal, the peelability is lowered, and the workability is deteriorated.

The coke material added to the sintered surface flux slag is not limited. For example, a carbon stamp material (a material obtained by mechanically compacting and compacting carbon), a material mainly composed of carbon (carbon) such as lump coke and powdered coke can be used.
The particle size of coke is, for example, 0.1 to 1 mm. However, coke finer than 0.1 mm or coke coarser than 1 mm may be used in consideration of the amount and components of flux slag to be dissolved, reaction rate, and the like.

The amount of coke added to the sintered surface flux slag is not limited. For example, it is 2 to 3 parts by weight with respect to 100 parts by weight of the sintered type surface flux slag. The amount of coke added may be less than 2 parts by weight or more than 3 parts by weight in consideration of the amount and components of the flux slag to be dissolved and the reaction rate.
The mixing method of the sintered type surface flux slag and coke is not limited. For example, sintered type surface flux slag and coke may be charged into a mixer and stirred and mixed for a predetermined time.

In the melting of the sintered type surface flux slag and coke, both materials may be stirred and mixed in advance, and then the mixture may be put into a melting furnace, or both materials may be put into a stirring and melting furnace (for example, an arc furnace). You may stir and mix in a furnace.
The heating temperature (average temperature) of the sintered type surface flux slag and coke is, for example, 1400 to 2000 ° C. Depending on the melting point and viscosity of the flux slag, the heating temperature may be less than 1400 ° C or may exceed 2000 ° C.

CO gas, CO ₂ gas, or both of these gases are dissolved in the melted sintered surface flux slag. In order to dissolve the sintered flux slag in such a reducing atmosphere, the iron content contained in the melted flux slag is reduced to be metalized and settled on the furnace bottom. At this time, the residual amount of the alloy element added at the time of manufacturing the surplus sintered type flux slag and the residual amount of the alloy element added at the time of manufacturing the sintered type flux slag after using the submerged arc welding are also the iron content. In the same manner as above, it is reduced to be metalized and settled to the furnace bottom. As a result, the sintered type surface flux slag from which the metal component (iron component, remaining alloy element and metal component) has been removed floats and separates in the furnace and is discharged from the upper part of the furnace.

The granulation of the melted sintered surface flux slag means that the sintered surface flux slag is crushed into particles of a predetermined size by introducing the sintered surface flux slag into a large amount of flowing water.
By air blowing, for example, air or an inert gas is blown to the flux slag that has been subjected to the melting treatment, and by the action of the gas, the sintered surface flux slag is foamed and crushed into particles of a predetermined size. Say.
The particle size of the sintered type surface flux slag after water granulation or air granulation is mainly 5 mm or less.

The crushed surface flux slag which has been granulated or air-pulverized and granulated in this way is inserted into a drying device such as a rotary kiln or a band dryer and dried. Drying conditions are not limited.
The crushing surface flux slag is pulverized by a known pulverizer (roll crusher, hammark crusher, etc.). The grinding conditions are not limited.
Here, the reason why the particle size of the pulverized surface flux slag magnetically treated in the first pulverizing step is limited to a range of 2.36 mm or less will be described below. When the particle size of the flux slag is larger than 2.36 mm, the bead appearance becomes rough and the aesthetic appearance is impaired. Therefore, the particle size of the pulverized surface flux slag was set to 2.36 mm or less. However, it is preferably 0.85 mm or less.

The preferable particle size of the pulverized surface flux slag is 0.85 mm or less.
The ground surface flux slag is subjected to magnetic separation by a known magnetic separator. As a result, the metal component that could not be removed from the flux slag during the melting process in the melting process is removed, and the molten backing flux for submerged arc welding is regenerated.

The molten type backing flux thus regenerated is used in accordance with a known submerged arc welding method.
After the second welding, the sintered type surface flux slag, the molten type backing flux slag and the surplus (used) molten type backing flux are recovered, and these are mixed to obtain a recycled material.
The obtained regenerated raw material is regenerated into a melt-type backing flux through the same steps as in the first recycle. That is, coke is mixed and dissolved in the recovered recycled material, at least one of CO gas and CO ₂ gas is dissolved in the dissolved recycled material, and the metal contained in the dissolved recycled material is further dissolved. Minutes are allowed to settle and removed from the recycled material (second dissolution step). Next, the recycled raw material dissolved in the dissolving step is subjected to water granulation or air crushing to foam and granulate, and then dried (second drying crushing step). Then, after further crushing the crushing and recycling raw material obtained in the dry crushing step, the crushing and recycling raw material is adjusted to a predetermined particle size range, and the obtained crushing and recycling raw material is subjected to magnetic separation to remove the remaining metal component, A melting type backing flux for submerged arc welding is used (second pulverizing step).

  According to the first aspect of the present invention, when the backing flux is regenerated for the second and subsequent times, not only the sintered type surface flux slag as the first material but also the molten type backing flux slag and unused The melting type backing flux is also collected, and a mixture of these three types is used as a recycled material. As a result, all the materials constituting the recycled raw material have the same composition system as the sintered type surface flux slag. Therefore, no thermosetting synthetic resin coating on the front side of the backing flux is required, and both flux slag and surplus backing flux can be used together as a recycling raw material for the backing flux without being discarded. it can.

  Examples of the present invention will be specifically described below.

With reference to FIGS. 1-3, the manufacturing method of the backing flux for submerged arc welding which concerns on Example 1 of this invention is demonstrated.
First, the first submerged arc welding is performed by the flux copper backing method (FCB method) (FIG. 3). Specifically, the sintered surface flux 12 is raised on the groove portion (welding line) 11 a of the base material (steel plate) 11. And the sintering type | mold backing flux 14 is arrange | positioned under the groove part 11a through the copper plate 13. FIG. At this time, the air hose H disposed immediately below the copper plate 13 is inflated to lift the copper plate 13, and the sintered backing flux 14 is pressed below the weld line of the base material 11. In this state, a tip portion of an electrode wire (not shown) is inserted into the sintered surface flux 12 and an arc is generated between the electrode wire and the base material 11 to be welded. As a result, the groove portion 11a of the base material 11 is welded by the molten metal, while the sintered type surface flux slag 15 is generated on the front side of the base material 11, and the sintered type back flux slag is formed on the back side of the base material 11. 16 is generated.

  The surplus sintered type surface flux 12 is sucked and collected by a suction nozzle (not shown) and then reused. On the other hand, the sintered type surface flux slag 15 is recovered and used as a raw material for regeneration of the molten type backing flux 14A. The remaining surplus sintered type backing flux 14 and sintered type backing flux slag 16 are greatly different from the sintered type surface flux slag 15 in composition. As a result, it cannot be adopted as a material for recycling the molten type backing flux 14A and is discarded.

Next, a method for regenerating the first melting type backing flux 14A will be described with reference to FIG.
First, a 1st melt | dissolution process is demonstrated. Coke powder (particle size of about 0.1 to 1 mm) is mixed with, for example, 2 to 3 wt% of the sintered type surface flux slag 15 (500 kg) after use of the submerged arc welding. Thereafter, the mixture is dissolved in a reducing atmosphere by using an arc furnace using a carbon stamp material. Here, the heating temperature of the sintered type surface flux slag 15 is, for example, about 1400 to 2000 ° C., and the sintered type surface flux slag 15 is completely dissolved. As a result, CO gas, CO ₂ gas, or these gases are dissolved in the melted sintered type surface flux slag 15.

  Thus, since the sintered type surface flux slag 15 is melted in a reducing atmosphere, iron contained in the melted sintered type surface flux slag 15 is reduced and metalized, and settles on the furnace bottom. At this time, the remaining alloy element added at the time of manufacturing the unused sintered type surface flux slag 15 and the metal content generated by melting the sintered type surface flux slag 15 after use of the submerged arc welding are also included. As with iron, it is reduced to metal and settles to the furnace bottom. In this way, the molten surface flux slag from which the metal component, that is, the iron component, the remaining alloy element, and the metal component have been removed floats and separates in the furnace and is discharged from the upper part of the furnace.

Next, the first dry granulation step will be described. Here, melt-type surface flux slag that has been melted in the melting step and discharged from the upper part of the furnace is put into a large amount of running water. At this time, the CO gas, CO ₂ gas, or these _two gases dissolved in the melt type surface flux slag, or the metal slightly remaining (for example, about 0.1 to 2% by weight) in the melt type surface flux slag Hydrogen gas in the slag generated by the reaction between the water and the water causes the molten surface flux slag to foam. As a result, the melt-type surface flux slag is reduced in specific gravity and is water-crushed into granules mainly having a particle size of 5 mm or less. The molten surface flux slag that has been granulated and granulated in this way is dried using a drying device such as an electric furnace. Thereafter, the dried granular molten type surface flux slag is subjected to magnetic separation. As a result, the remaining metal component that could not be removed from the molten flux slag during the melting process in the melting step is removed.

Next, the first pulverizing and sizing step will be described. The granulated surface flux slag mainly having a particle size of 5 mm or less obtained in the dry granulation step is pulverized using a pulverizer such as a roll crusher or a hammark crusher. Then, the obtained pulverized surface flux slag is classified through a classifying (sieving) device, and adjusted to a predetermined particle size range (here, 2.36 mm or less).
In this way, the pulverized surface flux slag is adjusted to a predetermined particle size range, and then further subjected to magnetic separation. Therefore, it is possible to remove the remaining metal that could not be removed from the surface flux slag during the magnetic separation in the first dry water granulation step. As a result, the molten surface flux slag whose particle size is adjusted to 2.36 mm or less and from which the metal component in the slag has been removed can be regenerated as the molten backing flux 14A.

Of the pulverized surface flux slag, those having a particle size exceeding 2.36 mm are pulverized again by the pulverizer in the first pulverizing step until the particle size becomes 2.36 mm or less. Adjust to a range of 2.36 mm or less by using a classification device. Then, the remaining metal portion that could not be removed from the surface flux slag during the magnetic separation process in the first dry granulation process is removed by the magnetic separation process. The molten surface flux slag, which is adjusted to 2.36 mm or less by the above method and from which the metal content in the slag is removed, is used as the molten backing flux 14A. In addition, the bulk density of the grinding | pulverization surface flux slag which adjusted the particle size at the said 1st grinding | pulverization sizing process becomes 0.8-1.3g / cm < ³ > by firing at a dry water granulation process.

Next, with reference to the flow sheet of FIG. 2, a second method of regenerating the melting type backing flux 14A will be described. In addition, the reproduction | regeneration method of 14 A of fusion | melting type backing flux after the 3rd time is also the same.
After the use of the melting type backing flux 14A, the second melting type backing flux 14A is regenerated. First, after the submerged arc welding using the regenerated molten type backing flux 14A, the recycled raw materials comprising the sintered type surface flux slag 15, the molten type backing flux slag 16A, and the excess molten type backing flux 14A are respectively recovered. To do.

Thereafter, in the second melting step, the sintered flux slag 15 (500 kg) after use of the submerged arc welding, the molten type backing flux slag 16A (500 kg), or the excess molten type backing flux 14A (500 kg) or Coke powder (particle size of about 0.1 to 1 mm) is mixed with these mixtures, for example, 2 to 3% by weight. This is melted in a reducing atmosphere by an arc furnace using a carbon stamp material. Here, the heating temperature of the sintered type surface flux slag 15 is, for example, about 1400 to 2000 ° C., and the sintered type surface flux slag 15, the molten type backing flux slag 16 A, the excess molten type backing flux (hereinafter, regenerated). Raw material) 14A is completely dissolved. As a result, CO gas, CO ₂ gas, or these gases are dissolved in the dissolved recycled material. The recycled material from which the metal has been removed floats and separates in the furnace and is discharged from the top of the furnace.

Next, the second dry water granulation step will be described. Here, the regenerated raw material discharged from the upper part of the arc furnace is put into a large amount of running water. At this time, the reaction between the CO gas, CO ₂ gas or these _two gases dissolved in the regenerated raw material, or the metal content slightly remaining (for example, about 0.1 to 2% by weight) in the regenerated raw material and water The hydrogen gas generated in the step causes the dissolved recycled material to foam. As a result, the recycled material has a reduced specific gravity and is water-crushed into granules mainly having a particle size of 5 mm or less. The granulated reclaimed raw material that has been granulated and granulated in this way is dried by an electric furnace or the like and then subjected to magnetic separation. As a result, the metal component that could not be removed from the recycled material during the melting process in the melting step is removed.

Next, the second pulverizing and sizing step will be described. The granulated regenerated raw material mainly having a particle size of 5 mm or less is pulverized by a roll crusher or the like, and the obtained pulverized regenerated raw material is classified through a classifier to adjust it to 2.36 mm or less.
Thus, after adjusting the pulverized regenerated raw material to a predetermined particle size range, the magnetic separation process is further performed, so that the remaining metal component that could not be removed from the regenerated raw material during the magnetic separation in the second dry granulation step is removed. be able to. As a result, the molten regenerated raw material whose particle size is adjusted to 2.36 mm or less and from which the metal content has been removed can be regenerated as a molten backing flux.

  As in the case of regeneration of the first backing flux, among the regenerated raw materials pulverized in the second pulverization and sizing process, those whose particle size exceeds 2.36 mm In the process, pulverization is performed by a pulverizer until the particle size becomes 2.36 mm or less. After pulverization, a classification (sieving) device is used to adjust the range to 2.36 mm or less. Then, the remaining metal component that could not be removed from the recycled material by the magnetic separation process in the second dry granulation process is removed by the magnetic separation process. A recycled raw material that is adjusted to 2.36 mm or less by the above method and from which the metal content in the slag has been removed is used as the molten backing flux 14A.

  Thus, at the time of regeneration of the molten backing flux 14A for the second and subsequent times, not only the sintered-type surface flux slag 15 that is the raw material for the first time, but also the molten backing flux slag 16A and unused (surplus) melting. The mold backing flux 14A is also collected, and a mixture of these three types is used as a recycled material. As a result, all the materials constituting the recycled material are of the same composition system as the sintered surface flux slag 15. Therefore, no coating of the thermosetting synthetic resin on the front side of the backing flux is required, and a new melt-type backing flux is collectively obtained without discarding both flux slags 15 and 16A and the excess backing flux 14A. 14A can be used as a recycled material.

It is a flow sheet which shows the 1st backing flux reproduction | regeneration process in the backing flux manufacturing method for submerged arc welding which concerns on Example 1 of this invention. It is a flow sheet which shows the backing flux reproduction | regeneration process after the 2nd in the backing flux manufacturing method for the submerged arc welding which concerns on Example 1 of this invention. It is a principal part expanded sectional view which shows the submerged arc welding operation state which concerns on Example 1 of this invention.

Explanation of symbols

15 Sintered type surface flux slag,
14A melting type backing flux,
16A Melting type backing flux slag.

Claims (1)

A first recovery step of recovering only the sintered type surface flux slag after use of submerged arc welding;
Coke is mixed and dissolved in the recovered sintered type surface flux slag, and at least one of CO gas and CO ₂ gas is dissolved in the dissolved sintered type surface flux slag, and further dissolved. A first melting step of sinking and removing the metal component contained in the sintered type surface flux slag from the sintered type surface flux slag;
A first dry crushing step in which the sintered surface flux slag dissolved in the dissolution step is granulated in a foamed or dense state by water granulation or air crushing, and then dried;
The crushing surface flux slag obtained in the dry crushing step is further pulverized and adjusted to a predetermined particle size range, and then the obtained crushing surface flux slag is magnetically treated to remove the remaining metal, and the latent arc A first pulverizing and sizing step for a melting type backing flux for welding;
A second recovery step of recovering a regenerated raw material comprising the sintered type surface flux slag, the molten type backing flux slag and an excess of the molten type backing flux after the submerged arc welding using the molten type backing flux When,
Coke is mixed and dissolved in the recovered recycled material, and at least one of CO gas and CO ₂ gas is dissolved in the dissolved recycled material, and the metal contained in the dissolved recycled material is further dissolved. A second dissolving step of sedimenting and removing from the recycled material;
A second dry crushing step in which the recycled raw material dissolved in the dissolution step is granulated in a foamed or dense state by water granulation or air crushing, and then dried;
The crushed and regenerated raw material obtained in the dry crushing step is further pulverized and adjusted to a predetermined particle size range, and then the obtained pulverized and regenerated raw material is subjected to magnetic separation to remove the remaining metal, and for submerged arc welding. A method for producing a backing flux for submerged arc welding, comprising: a second pulverizing and sizing step of using a molten type backing flux.

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