JPH0118835B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a backing material for single-sided welding that can provide a beautiful back bead with no defects and ensure excellent slag removability. [Prior art] As a back bead forming layer of a backing material for single-sided welding,
Powder-like fluxes, solid fluxes obtained by solidifying the fluxes with water glass, inorganic fibers such as glass fibers, and composite materials combining these materials are used. Among these, the backing material with inorganic fiber as the back bead forming layer has good flexibility and has advantages such as being easy to apply to single-sided welding with uneven grooves and curved welding such as steel pipe welding. There is. By the way, in order to manufacture inorganic fibers with good productivity, raw materials and material components are severely restricted from the viewpoint of melting point, drawability, etc., but raw materials with good productivity generally melt and mix into the weld metal and cause problems in the welded area. Contains components that adversely affect the quality of the product, and often deteriorate physical properties (particularly cracking resistance) and appearance. By the way, it is believed that B ₂ O ₃ is the component that has the most negative effect on the quality of the back bead, and when the amount of B ₂ O ₃ in the inorganic fiber exceeds 6%, cracks are likely to occur in the back bead. has been confirmed. (Special Publication No. 50-35488). Therefore, B ₂ O ₃ should be reduced as much as possible, but B ₂ O ₃ was considered indispensable as a viscosity-lowering component in order to form inorganic fiber raw materials into fibers. Under these circumstances, the inventors of the present invention have conducted research to develop a technique that can be formed into a fibrous shape even when B ₂ O ₃ is reduced to zero. As a result, if the content of SiO ₂ and Al ₂ O ₃ , which are the main components of the inorganic fiber raw material, is adjusted, there will be no inconvenience when forming it into a fiber, and since this inorganic fiber does not contain B ₂ O ₃ , There is no longer any fear that the cracking resistance of the beets will deteriorate. However, as the viscosity of the welding slag increases, the air bubbles generated from the slag become difficult to escape and are left behind between the weld metal and the problem of air bubbles appearing on the back bead and poor appearance. Ta. Therefore, in order to improve the appearance of the back bead, we thought that it was necessary to take specific measures to reduce the viscosity of welding slag, and after conducting further research, we came up with the technology disclosed in Japanese Patent Publication No. 1983-4238. . This invention uses SiO ₂ , Al ₂ O ₃ , and an appropriate amount of inorganic fibers for forming the back bead of a backing material for single-sided welding.
A material containing ZrO ₂ and Na ₂ O and/or K ₂ O and substantially no B ₂ O ₃ is used. Using this backing material improves cracking resistance and improves the back bead surface. The pockmarks have also been removed. [Problems to be Solved by the Invention] However, while conducting research on the practical application of the above-mentioned prior invention, a new problem of slag removability has been encountered. In other words, slag removability refers to the removability of slag derived from the inorganic fiber for back bead formation, which is melted by welding heat and covers the back bead surface. Because the slag sticks firmly, it takes a lot of effort and time to remove it. Under these circumstances, the present invention aims to provide a backing material that also provides good results in terms of slag releasability. [Means for Solving the Problems] The present invention is a backing material for single-sided welding in which the back bead forming layer is a molded article made of inorganic fibers and having a substantially uniform composition in the width direction, wherein the inorganic fibers are SiO ₂ :40~70%
(wt%: the same below), ZrO ₂ : 10 to 25%, alkali metal oxides: 10 to 25%, alkaline earth metal oxides: 3 to 7%, and Al ₂ O ₃ is 0.9% or less. The key point is that it is limited and does not substantially contain B ₂ O ₃ . [Function] According to various experiments carried out by the present inventors, in order to improve the slag releasability, the amount of Al ₂ O ₃ among the inorganic fiber constituents in the prior invention is reduced; In addition, a new fact was confirmed that it is sufficient to contain an appropriate amount of alkaline earth metal oxides such as CaO and MgO. The present invention was completed based on this confirmed fact, and its characteristic structure is that the amount of Al ₂ O ₃ and the amount of alkaline earth metal oxide in the inorganic fiber components are limited to a specific range. . In other words, in order to improve the slag removability, the amount of Al ₂ O ₃ should be 0.9%.
It is necessary to contain 3 to 7% of alkaline earth metal oxides, and the amount of Al ₂ O ₃ must be kept below.
If it exceeds 0.9%, slag removability will not be improved.
Furthermore, if the alkaline earth metal oxide content is less than 3%, slag removability cannot be effectively prevented, while if it exceeds 7%, the surface of the back bead loses its gloss and becomes warty, resulting in a healthy back bead. Wave beads cannot be obtained. The reasons for determining the types and contents of components other than those listed above are as follows. SiO ₂ : An essential main component to increase the melting point of the generated slag and prevent it from falling out during welding, and has a content of 40%.
If it is less than this, these effects will be insufficient and shedding will occur. However, if the amount is too high, the melting point of the inorganic fibers will become too high and it will be difficult to melt them with welding heat.
Since it no longer functions as a back bead forming layer, it must be kept below 70%. ZrO ₂ : Has the function of preventing air bubble marks (pockets) generated on the back bead surface; if it is less than 10%, the viscosity of the slag produced by melting of the back bead forming layer becomes too high, making gas release difficult. Become,
Pockmarks appear on the back bead surface. Also _ZrO2
It also has the function of lowering the melting point of the material itself and making it easier to form into fibers, and for this reason it must be contained at least 10%. However, if it exceeds 25%, the melting point will become too high and it will no longer function as a back bead forming layer. Alkali metal oxides: K ₂ O, Na ₂ O, Li ₂ O, etc. can be used alone or in combination of two or more, and if it is less than 10%, long fibers with sufficient strength cannot be obtained. However, if it is too high, the hygroscopicity of the fibers will increase and the amount of bubbles generated during welding will increase, pockmarks will appear on the surface of the uranami bead and pore defects will appear in the weld metal, so it must be kept below 25%. B ₂ O ₃ : As mentioned above, it is a harmful component that significantly promotes hot cracking of weld metal, and must be limited to substantially zero. The backing material of the present invention is composed of inorganic fibers containing the above components as a back bead forming layer, and its form is not particularly limited, but it is usually in the form of a sheet, a tape, a mat, or a cloth. It is used as a molded product such as a knitted product. These inorganic fiber molded bodies may constitute the backing material by themselves, but usually the molded body is placed as the back bead forming layer in the top layer, and a fire-resistant material such as asbestos is placed below it. It is used by laminating layers and shape-retaining materials such as cardboard, and in some cases it may be covered with a heat-shrinkable film or the like. In addition, this backing material may be made into a long plate-like body of a certain size and fixed to the back side of the groove with an appropriate backing jig, or it may be made into a long band-like body and pressed against the back side of the groove with a copper plate, etc. It may also be welded. [Example] A glass fiber tape having a thickness of about 1 mm was prepared using glass fibers having the chemical components shown in Table 1. Two sheets of this tape were stacked to form a back bead forming layer, and an asbestos plate was lined to obtain a backing material for welding.
This backing material is brought into contact with the back surface of the groove as shown in Figure 1 (in the figure, 1 is the base material, 2 is the backing material, 2a is the back bead forming layer, 2b is the ceramic, and 3 is the aluminum adhesive tape). (respectively shown), single-sided welding was performed under the following conditions. (Welding conditions) Welding wire: MG-50T, 1.2mm Solid wire for gas shielded arc welding
AWS (ER70S-4) Shielding gas: CO ₂ -100%, 25/min Test steel plate: 50kg class high tensile strength steel SM50A 25mm ^t × 300mm ^w × 600mm ^l Groove shape: See Fig. 1 Welding conditions: Current... ...250A, DC (+) Voltage...28V Speed...24cm/min The results are summarized in Table 1.

[Table] From Table 1, the following can be considered. Experiment Nos. 1, 2, 5, 6, 9, 13, 14, 17, 18, and 21 are examples that meet all the requirements stipulated by the present invention, and the appearance and shape of the back bead are good, and the slag does not peel off. The quality is also excellent. On the other hand, the other experimental Nos. are comparative examples that lack any of the specified requirements, and as shown below, there are problems with the appearance, shape, and slag removability of the back bead. Experiment No. 3: Slag removability was poor because Al ₂ O ₃ exceeded the specified range. Experiment No. 4: Since no alkaline earth metal oxide is contained, the slag removability is also poor. Experiment No. 7: Due to too much alkaline earth metal oxide, the appearance of the back bead surface was poor (wart-like) and the slag removability was also somewhat poor. Experiment No. 8: Due to insufficient amount of SiO ₂ , the back bead forming layer fell off. Experiment No. 10: Due to the insufficient amount of alkaline earth metal oxide, the slag removability is poor, and the appearance and shape of the beads are not satisfactory. Experiment No. 11: If the amount of SiO ₂ is too large, the melting point of the back bead forming layer becomes high and it is difficult to melt with welding heat, so a proper back bead cannot be formed. Moreover, since the amount of alkaline earth metal oxide is insufficient, the slag removability is also poor. Experiment No. 12: Due to insufficient amount of _NrO2 , bubbles remain on the surface of the uranami bead. Experiment No. 15: The amount of ZrO ₂ is too large, the melting point of the bead forming layer becomes high, and proper Uranami beads cannot be formed. Experiment No. 16: Unable to form fibers due to insufficient amount of alkali metal oxide. Experiment No. 19: Due to too much alkali metal oxide, bubbles remain on the bead surface, and pore defects are observed inside the bead. Experiment No. 21: Although the bead appearance and slag removability were good, the weld metal suffered from high-temperature cracking because it contained B ₂ O ₃ . Experiment No. 22: Due to the insufficient amount of alkaline earth metal oxide, the slag peelability was somewhat poor, and even after impact with a hammer, etc., a portion of the slag remained unpeeled. [Effects of the Invention] The present invention is configured as described above, and by specifying the material of the back bead forming layer, all of the crack resistance of the weld metal, the appearance and shape of the back bead, and the slag removability can be improved. I was able to satisfy myself.

[Brief explanation of drawings]

FIG. 1 is an explanatory cross-sectional view showing an example of attaching the backing material of the present invention to the back surface of a groove. DESCRIPTION OF SYMBOLS 1... Base material, 2... Backing material, 2a... Back bead forming layer, 2b... Ceramics, 3... Aluminum adhesive tape.

Claims (1)

[Claims] 1 A backing material for single-sided welding in which the back bead forming layer is a molded body made of inorganic fibers and having a composition that is substantially uniform in the width direction, and the inorganic fibers are SiO ₂ :40 to 70% (weight %: the same below) , _ZrO2 : 10-25%, alkali metal oxide: 10-25%, alkaline earth metal oxide: 3
A backing material for single-sided welding, characterized in that it contains up to 7% _{of Al2O3} , is limited to 0.9% or less, and _is substantially free of _B2O3 .