JPH01148469A - Narrow gap submerged arc welding method - Google Patents

Abstract

PURPOSE:To improve welding efficiency and to reduce the welding cost by regulating the quantity of deposition per unit weld length at the time of submerged arc welding where materials to be welded having a narrow gap are rotated and a consumable electrode is shifted for every rotation between groove walls to perform multi-pass and multi-layer welding. CONSTITUTION:The materials 1 and 2 to be welded to form the narrow gap 3 are subjected to submerged arc welding while the tip of a welding wire 4, namely, the consumable electrode being shifted between both walls of the narrow gap 3 with a point P as a center. While the materials 1 and 2 to be welded being rotated, the narrow gap 3 at one wall side is subjected to one rotation welding and continuously, the welding wire 4 is shifted to the other wall side of the narrow gap 3 by a holder 5 and it is subjected to one-rotation girth welding and its part is overlapped and laminated and the narrow gap is filled with weld beads 6. In this case, a welding current at the time of shifting is set at a lower value than that at the stationary time and it is regulated so that the quantity of deposition per unit weld length is made to 2.5g/cm.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a narrow gap submerged arc welding method, and more particularly, to a relatively large-diameter ring-shaped or cylindrical workpiece,
For example, multi-pass/multi-pass welding large crankshafts, etc.
The present invention relates to a narrow gap submerged arc welding method suitable for use in IT9 welding.

[Conventional technology]

As is well known, in submerged arc welding, high current welding can be performed stably by automatic welding, and penetration is deep.
It is applied to narrow gap welding of relatively large diameter workpieces.

In order to perform narrow-gap submerged arc welding on large-diameter ring-shaped or thick-walled cylindrical objects, it is common to perform multi-pass welding, in which the objects to be welded are automatically welded continuously while rotating.
A multilayer welding method, in which a melting electrode is placed between one wall and the other wall of a groove formed between opposing surfaces of a pair of workpieces, and the workpieces are rotated. There is a method of welding by circumferentially welding, shifting the melt electrode between both groove walls with each rotation, and welding continuously by filling the groove with a multi-pass, multi-layer weld bead that is laminated inside the groove. It is used.

Figures 2 and 3 are conceptual explanatory diagrams of the conventional multi-pass/multilayer welding method. FIG. 3 is a cross-sectional view of the tip, and FIG. 3 is a partial plan view of the groove portion illustrating the formation of a weld bead due to the shift of the melt electrode.

In FIGS. 2 and 3, (1) and (2) are a pair of objects to be welded, and here the vicinity of the welded portion is shown.

(3) is a narrow gap, and the narrow gap (3) is formed between the opposing weld surfaces of the pair of welded proboscis (1) and (2). (4) is a welding wire, the welding wire (
4) is continuously supplied from the welding machine main body (not shown).

(5) is a holder, and the holder (5) holds the welding wire (4) and supplies power to the welding wire (4).
), that is, the melt electrode, is shifted between both walls of the narrow groove (3) around point (P) in the figure.

(6) is a weld bead, and FIG. 2 schematically shows the cross-sectional layered state of the weld bead (6), and FIG. 3 shows the elevated state of the shifted part. An example using multilayer welding is shown.

The narrow gap (3) is made by welding one wall side of the narrow gap (3) one turn while rotating the objects to be welded (1) and (2), and then welding with the retainer (5). By shifting the wire (4) to the other wall side of the narrow gap (3) and welding it around one turn, weld beads are layered with some overlap (
6). Note that the shift portion shifts the phase in the circumferential direction every rotation, and is set so as not to completely overlap the bead caused by the previous shift.

[Problem that the invention seeks to solve]

The present inventor has developed a method for performing narrow gap submerged arc welding on relatively large thick-walled cylindrical objects using automatic multi-pass, multi-layer welding.
When the welding current increases, the welding rate (g
r/m1n), that is, the amount of groove filling per unit time increases and the welding time can be shortened.We aimed to improve the welding efficiency by increasing the welding current, which is relatively easy to control.

However, although increasing the welding current and increasing the welding speed (gr/m1n) shortens the welding time and improves the welding efficiency, when the quality of the welded part of the resulting product is confirmed by an ultrasonic flaw detection test, It has been found that when the welding current is increased beyond a certain value, the number of defects detected increases as the welding current increases.

When these defects were investigated, it was found that the defect was caused by the shift region, especially the weld bead during the shift, being formed close to one of the walls of the groove, and a groove-like recess between the bead and the groove wall. It has been found that the welding occurs in the areas where the welding current is formed (the areas indicated by A and B in FIG. 3), and that its size also corresponds to the increase in welding current.

Based on the above investigation results, the present inventor has determined that these defects are caused by the groove-like recess formed in the area being completely dissolved by the welding heat during the next welding process in which a weld bead is laminated on top of the groove-like recess. The welding is not carried out and remains as a defect due to poor welding.
Moreover, when the welding current is increased beyond a certain value, the number of defects increases due to the amount of welding per unit length (
gr/cm), the height of the weld bead increases, and the groove-like recess formed between the weld bead and the groove wall becomes deeper (which promotes poor penetration). I've come to a conclusion.

In view of the above problems, the present invention increases the welding current during steady state,
The purpose of the present invention is to provide a narrow gap submerged arc welding method that can suppress the occurrence of defects in the shift part even if the overall welding speed (gr/l1in) is increased, maintain quality, and increase welding efficiency. It is.

[Means for solving problems]

In order to achieve the above object, the present invention has the following configuration. That is, the narrow gap submerged arc welding method according to the present invention rotates a pair of axial or cylindrical workpieces having narrow grooves, and connects the groove wall of one of the workpieces to the groove wall of the other workpiece. In the narrow gap submerged arc welding method, in which the welding electrode is continuously welded in multiple passes and in multiple layers by shifting the melt electrode between each revolution and the wall, the welding current during shifting is lower than that during steady state, and unit welding Welding length per length is 2.5 gr
This feature is set to a value not exceeding /cm.

[Effect]

A ring-shaped or cylindrical workpiece having a narrow groove is rotated, and the melt electrode is continuously shifted between one groove wall and the other groove wall of the workpiece every rotation. In the narrow gap submerged arc welding method that performs multi-pass, multi-layer welding, the welding current is increased to increase the welding speed (gr/+win) as described above.
In order to increase the welding efficiency by increasing the welding current, increasing the welding current beyond a certain value increases the rate of occurrence of defects at the shift site as the welding current increases. The welding current is set to be lower than that during steady state, the amount of welding per unit welding length is set to a value not exceeding 2.5g/am, and the bead height at the shift part is controlled to be relatively low. This can suppress the occurrence of defects in the region, and increase the overall welding rate (gr/m1n) by increasing the welding current in the steady region.

The amount of welding during shifting was limited to a value not exceeding 2.5gr/cm based on the unit of welding current (A) and welding speed (gr/5in) divided by welding speed (c++/m1n). This is based on test results that investigated the relationship between the amount of welding per length (gr/cm) and the presence or absence of defects.

Figure 1 is a graph showing the results of this test.The graph plotted with an X indicates an example in which a defect was detected by ultrasonic flaw detection, and the one plotted with an ○ indicates an example in which a defect was detected by ultrasonic flaw detection. Examples are shown below in which no defects were detected.

As shown in Figure 1, at various current values, the welding! (gr/cm) does not exceed 2.5 gr/cna, the occurrence of defects can be reliably suppressed.

The amount of welding (gr/cm) is normally controlled by controlling the welding current or welding speed, but in the present invention, welding can be achieved by controlling the welding current value! (gr.
/cm), and compared to welding speed control that is performed by adjusting the rotation of the workpiece or the moving speed of the welding electrode by mechanical means, it reduces the inertia effect of the workpiece and equipment and the operation time lag. The control can be made reliable and easy without being affected by such factors.

〔Example〕

A forged carbon steel material with a diameter of 680 mm was prepared, many narrow grooves were formed in it, and it was subjected to a submerged arc welding test using two-pass multilayer welding.

Comparison ■ The groove of the sample material was automatically welded using a 3.21 diameter welding wire and molten flux while varying the welding current and welding speed.

In addition, in this comparative example, the welding current and welding speed in each welding example were set to constant values, and continuous automatic welding was performed without changing them even during shifts.

Then, the welded portion of each welded sample material was subjected to ultrasonic flaw detection with a defect detection sensitivity of 0.81 in terms of flat bottom hole diameter, and the presence or absence of defects was investigated at this detection sensitivity.

After examining these ultrasonic flaw detection inspection results, we found that in the welding examples where defects were detected, the defect detection location corresponded to the shift part, and no defect was detected in the circumferential weld part, that is, the steady part, and The number is the welding speed (gr/n+in
) was increased in proportion to the amount of welding per unit length (gr/cm) divided by the welding speed (am/m1n).

Further, when the detected defective portions were inspected by cutting, all of these defects were found in positions extremely close to one of the walls of the groove in the shift portion.

Regarding these results, welding current (A) and welding amount (g
r/cm) and the presence or absence of defects, and
This is illustrated by plotting it in the graph of the figure.

An x mark on the plot in the graph of FIG. 1 indicates that there is a defect, and an O mark indicates that there is no defect.

As shown in Figure 1, in all welding examples where the amount of welding exceeds 2.5gr/cm, defects are detected by ultrasonic testing, while on the other hand, in cases where the amount of welding is less than 2.5gr/cm. No defects were detected in the welding example.

From this result, these defects occur in locations where the weld bead during shifting is formed close to one of the walls of the groove, forming a groove-like recess between the bead and the groove wall. As a result, these groove-shaped recesses were not completely melted by the welding heat during the next welding process when a weld bead was laminated on top of them, and the weld was in a poor state and remained as a defect. , the number and size of these defects increase as the amount of welding per unit length (gr/cm) increases, because the height of the weld bead increases as the amount of welding per unit length (gr/cm) increases. This is because the groove-like recess formed between the weld bead and the groove wall becomes deeper and promotes poor penetration.
It has been found that when the thickness is less than m, the groove-like recesses of the shift portion are melted during the next welding and do not remain as defects.

Note that Fig. 1 shows an example of a welding current in the range of 350A to 600A, but this is because if the welding current is less than 350A, the welding current is too low and penetration into the groove wall is insufficient; A range exceeding this range is not normally applied because the penetration is excessive and causes cracking, so it is omitted here.

Implementation ■ Based on the results of the comparative example above, in the narrow gap submerged arc welding method that continuously performs multi-pass and multi-layer welding, if the amount of welding during shifting is suppressed to 2.5 gr/cm or less, no defects occur. It was found that the welding speed during steady state could be increased, so using the above sample material, the amount of welding during shifting was increased by 2.
．． A welding test was conducted within a range that satisfied the condition of 5 gr/cm or less.

Table 1 shows the conditions for these welding tests.

In addition, in order to control the welding current (A) during shifting in these welding tests, the welding current was controlled by an activation signal of a mechanism that operates a welding wire holder that shifts the welding electrode every rotation of the test material. The solution was to install an electric circuit that controls the value to a predetermined value.

For each sample material welded under the conditions shown in Table 1, the flat-bottomed hole diameter conversion value was 0. When ultrasonic flaw detection was performed with defect detection sensitivity of hm diameter, welding current (A) in the steady part
No defects were detected in all welding test examples, including those where the welding strength was increased to 60OA.

In the above example, the welding voltage (v) is selected and set at a value that stabilizes the welding arc in accordance with the welding current in the steady section, and the welding speed (am/5in) is set according to the submerged arc. The speed was selected from the speed range (30 to 60 am/m1n) normally applied to welding.

〔Effect of the invention〕

As described above, the present invention enables multi-pass, multi-layer welding of relatively large-diameter axial or cylindrical workpieces with high efficiency and without sacrificing quality. It has a great practical effect, making it possible to improve the efficiency of submerged arc welding of relatively large objects to be welded, and contributing to cost reduction.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the welding current, the amount of welding, and the occurrence of defects in a comparative example of the embodiment of the present invention. FIGS. 2 and 3 are conceptual explanatory diagrams of a conventional multi-pass/multi-layer welding method. (1) (2) - Work to be welded, (3) - Narrow gap, (4) -
Welding wire, (5) - retainer, (6) - welding bead. Patent applicant: Kobe Steel, Ltd. Representative Patent attorney: Akira Kanemaru - Figure 1 Welding current (^) Figure 2

Claims (1)

[Claims] A pair of shaft-like or cylindrical objects to be welded having a narrow groove are rotated, and a melt electrode is shifted between one groove wall and the other groove wall of the weld objects every rotation. Continuously multiple passes/
A narrow gap submerged arc welding method for multi-layer welding, characterized in that the welding current during shifting is lower than that during steady state, and the amount of welding per unit welding length is set to a value not exceeding 2.5 gr/cm. Narrow gap submerged arc welding method.