JPS6031598B2 - All-position narrow gap single-sided MIG automatic welding method for iron pipes - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for automatically welding a circumferential joint in all positions during on-site hemming of a penstock pipe in a hydroelectric power plant or the like.

[Conventional technology]

When welding circumferential joints, the welding position changes continuously, making it more difficult to ensure sufficient penetration and a good bead surface shape for each layer during lamination than in a single position.

For this type of joint, a passing groove using the covered arc welding method has traditionally been widely used, but as the size of iron pipes increases, the cross-sectional area of the joint groove also increases, and the steel materials used also require high strength. Coupled with the use of high-quality high-strength steel, this has led to major problems such as a decrease in welding efficiency due to an increase in the amount of welding, and an increase in the burden of securing highly skilled welders and managing welding operations to ensure high quality. was. In addition, there is a welding method that uses the MIG welding method to weld a narrow gap in all positions without swinging the welding torch, moving downward from an upward position to a vertical position and then a downward position, and stacking layers in multiple passes per layer. However, in order to obtain a uniform bead appearance over all positions, relatively high-speed welding conditions are required, and the range of suitable welding conditions is also extremely narrow, considering the on-site assembly, skirting accuracy, and beveling accuracy of the iron pipe. There were problems in terms of welding stability, such as poor penetration, poor bead appearance, and blowholes.

[Object of the present invention]

The present invention was made in view of the above circumstances, and it solves the problems of the conventional technology by simple and rational means, and facilitates automatic MIG welding of iron pipes in all positions and narrow joints. The purpose is to provide a welding method that can be stably performed.

[Means for solving problems]

The automatic all-position narrow-gap single-sided MIG welding method for iron pipes of the present invention which solves the problems of the prior art is as follows: , 'b' along a direction that is inclined by a certain angle 8 with respect to the direction perpendicular to the forehead line direction of the narrow gap welded joint,
The welding torch is oscillated in a pendulum-like manner with an amplitude larger than the groove width, increasing the angle of the welding torch axis that intersects with the groove wall, generating an arc on the groove wall, and ensuring sufficient penetration range and depth. The welding torch tilt oscillation conditions were such that a high current was generated at the position where the welding torch axis intersects with the groove wall surface, and a low current was applied at the bottom of the joint to match the pendulum-like oscillation. Conditions in which high and low currents are generated alternately at
The low current applied to the bottom of the groove is lowered in the middle, and increased in the vertical position, {e} The welding speed is gradually increased from vertical to upward, and the high current applied to the groove wall is increased in the middle, and the welding speed is increased in the vicinity of the upward position. The low current to the bottom of the groove is reduced in sequence, and the conditions of [b}, 'c', 'd', and [e] above are preset in the control device, and as all-position welding progresses, each position is This is an automatic MIG welding method that performs automatic welding on one side with a narrow gap in all positions of iron pipes under the conditions of [a' In MIG automatic welding, the welding torch is oscillated in a pendulum manner with an amplitude greater than the development width along a direction that is inclined by a certain angle 0 with respect to the direction perpendicular to the axial direction of the narrow joint welding joint, Welding torch tilt oscillation conditions that increase the angle of the welding torch axis that intersects with the joint wall surface, generate an arc on the joint wall surface, and obtain sufficient penetration range and depth, {c} Welding torch A high current is generated at the position where the axis line intersects with the joint wall surface, a low current is applied at the bottom of the joint, and high current and low current are generated alternately in accordance with the pendulum-like oscillation. [d) Welding posture is The welding speed gradually decreases from the top to the vertical position, decreases near the vertical position, the high current to the groove wall is high in the middle, and the low current to the bottom of the groove increases sequentially.
e) The welding speed is gradually increased from vertical to downward.
The high current applied to the groove wall is gradually increased, the low current applied to the bottom of the groove is lowered halfway, and the downward current is slightly increased.
The present invention is characterized in that the conditions of b', 'c}, [d}, and 'd are preset in the control device, and as all-position welding progresses, automatic welding is performed under the conditions for each position. Setting of construction conditions (tilt swing angle, high current generation position, welding speed, high current condition, low current condition) and adjustment according to the welding posture can be set in advance in the control device without burdening the operator. It is also something that is certain to come true.

Table 1 summarizes the features of the present invention that enable automatic MIG welding on one side and narrow gap in all positions. Table 1 The present invention first uses {a} the MIG welding method, which has a high energy density and has a stable arc even with a relatively low current; By swinging the welding torch in a pendulum-like manner along the direction inclined by 0 with an amplitude greater than the groove width, the angle between the joint wall surface and the welding torch axis in the cross section in 8 directions is increased. death,
By generating an arc directly on the wall surface and generating a high current on the wall surface, the wall surface and the boundary between the wall surface and the previous layer are melted to a sufficient extent and depth, and a large amount of Even with regard to the amount of welding, the connection between the wall surface and the weld bead is facilitated, and the bead shape within the joint is made concave.

At the bottom of the joint, [d] the angle between the surface to be welded and the torch axis is almost a right angle, and sufficient penetration can be obtained even when welding with a low current. Welds with less current and improves the shape of the bead inside the joint (a little concave). Next, regarding high current conditions, low current conditions, and welding speed, since the negative effects of gravity appear sequentially in postures ranging from downward to vertical, the high current is gradually lowered to reduce the amount of welding, while the welding speed is In order to secure heat, the welding speed is gradually lowered, lowering the low current halfway and increasing it in the vertical position.

In postures ranging from vertical to upward, the negative effects of gravity become more apparent, so the welding speed is gradually increased, the low current is gradually lowered, the high current is increased a little in the middle, and it is lowered in the upward posture.
These adjustments must be made according to the welding position, and the voltage must also be adjusted according to the current, so if left to the operator, incorrect adjustments will occur and the welding method will no longer be viable. , {e) These conditions are set in the control device and taken out in conjunction with each posture. [Description of Examples] FIGS. 1a, 1b, and 1c each show grooves to which the present invention is applied, and show a single-sided narrow joint shape formed by a workpiece 1 to be welded.

As shown in Figure 2a, the pendulum-like swing locus of the MIG welding torch is a locus in a direction that is inclined by a certain angle 8 with respect to the direction perpendicular to the welding line, that is, the amplitude is 2, and Figure 3a ,b
, c shows an example in which high current 3 is used at both ends of the root of the root in accordance with the groove position, and b shows an example in which high current 3 is used in the center of the root [both a and b This shows the case of rhombus welding. ] c shows an example of the position where welding torch pendulum amplitude length 2 and high current 3 are used in the case of an intermediate layer, and when the welding torch moves between 3 and 3 in the figure, low current is used. This is used to form beads. As shown in Fig. 2, when the arc swings in a direction perpendicular to the welding line, as shown in c-, the arc is The bottom of the joint faces in four directions, and not only does penetration into the wall surface become small, but the distance traveled by the arc due to oscillation is also small, increasing the amount of welding heat input per unit welding length, and depending on the direction of gravity, the shape of the peed surface changes. It becomes difficult to hold it in a concave manner.

On the other hand, when it swings in a direction that is oblique by a certain angle 8 with respect to the direction perpendicular to the welding line, the angle between the groove wall surface and the welding torch axis increases, as shown in b, and the direction of the arc increases. Even if consideration is given to the characteristics, an arc will be generated on the wall surface, and the range and depth of penetration into the wall surface will be ensured.

Moreover, by generating a high current at the wall position 3 as shown in FIG. 3c, the aforementioned penetration becomes more reliable, and the connection between the wall surface and the weld bead is facilitated by a large amount of welding.

Then, the oblique oscillation locus becomes larger, the welding heat input per unit welding length decreases, and the bead becomes less susceptible to the action of gravity, so that a slightly concave bead surface shape can be easily obtained. FIG. 4 shows an example of welding conditions in all positions around the circumference, and illustrates how the conditions of the molten bale are changed as the welding position changes.

To explain the case of welding an iron pipe from the inside, each pass of welding starts from a downward position, passes through a vertical position, and is completed in an upward position. In the range from downward to vertical, the action of gravity on the molten metal has a negative effect on the bead shape, so in order to reduce the amount of deposition while ensuring the amount of welding, the welding speed and high current should be lowered. Lower the low current midway and increase it in the standing position. When it comes to voltage, it changes in the same way as the current.

In the range from vertical to upward, the action of gravity on the molten metal has a more adverse effect on the bead shape, so the melting speed is increased in ascending order. The voltage is also changed according to the current.

Similarly, the opposite side of the circumference is welded from downward to vertical to upward, completing the welding of each pass of the target circumferential joint. Next, we will explain the case where melting occurs from the outer periphery of the iron pipe.
Each pass of welding begins in the upward position, passes through the vertical position, and is completed in the downward position.

In the range from upward to vertical, the action of gravity on the molten metal has a negative effect on the bead shape, so in order to reduce the amount of welding and ensure the amount of welding heat input, the welding speed is gradually lowered and the height of the welding surface is reduced. The current is high in the middle, and the low current at the bottom of the groove gradually increases, increasing in the vertical position. The voltage is changed in the same way according to the current.

In addition, in the range from vertical to downward, the action of gravity on the molten metal takes into account the negative effect on the bead shape, so the welding speed is gradually increased, and for low currents, the welding speed is lowered in the middle and slightly increased in the downward position. , the high current is increased sequentially. Further, the voltage is also changed according to the current. Similarly, the opposite side of the circumference is welded upward, vertically, and then downward, completing the welding of each pass of the target circumferential joint. [Effects of the Invention] As described above, according to the present invention, the following effects can be obtained.

'a' By swinging the welding torch like a pendulum in a direction that is oblique by a certain angle 8 with respect to the direction perpendicular to the narrow gap welding line, the angle between the welding torch axis and the joint wall becomes larger. , an arc is generated directly on the wall surface, and in addition to generating a high current, sufficient penetration range and depth into the base metal can be obtained, and a sound narrow-open joint can be obtained.

(b) Since the welding torch is swung in a direction that is tilted by the amount a, the amplitude of the welding torch axis increases, causing a transition from a high-current arc against the groove wall to a low-current arc at the bottom of the joint. Switching is much easier than swinging in a direction perpendicular to the weld line, which stabilizes the arc and improves the bead surface shape.

Moreover, the control mechanism for the welding torch swing can be simplified. 'c} Due to the alternating generation of high and low currents, a good Uranami bead can be formed, and in all layers of the narrow groove,
Sufficient penetration into the groove wall surface is achieved.

{d) Since welding conditions for each position are set in advance in the control device and welding is performed by sequentially switching according to each position, high-quality welded joints can be easily and stably obtained.

[Brief explanation of the drawing]

Figures 1a, b, and c are explanatory diagrams showing the groove shapes targeted by the conventional method and the present invention, and Figures 2a, b, and c are explanatory diagrams of essential parts showing the single-sided narrow opening shape according to the present invention. , FIGS. 3A, 3B, and 3C are explanatory diagrams showing examples of high current insertion positions, and FIG. 4 is a chart diagram illustrating welding condition switching situations in all circumferential positions. Figure 1 Figure 2 Blinds Figure 3 Figure 4

Claims (1)

[Scope of Claims] 1 (a) In automatic all-position narrow-gap single-sided MIG welding from the inside of the penstock during on-site installation of the penstock, (b) in a direction perpendicular to the axial direction of the narrow-gap welded joint, a certain angle θ
The welding torch is oscillated in a pendulum-like direction along the direction in which the groove is tilted, with an amplitude larger than the groove width, and the angle of the welding torch axis that intersects with the groove wall is increased to generate an arc on the groove wall. (c) A high current is generated at the position where the welding torch axis intersects with the groove wall surface, and a low current is applied at the bottom of the groove. (d) As the welding position changes from downward to vertical, the welding speed gradually decreases, and the high current applied to the groove wall gradually decreases. (e) The welding speed is gradually increased from vertical to upward, and the high current applied to the groove wall is increased in the middle, and the welding speed is increased in the upward position. The conditions are such that the current decreases in the vicinity, and the low current toward the bottom of the groove decreases sequentially, (b) and (c) above.
), (d), and (e) are preset in the control device,
All-position narrow-gap single-sided M for iron pipe, characterized in that automatic welding is performed under the conditions of each position as the all-position welding progresses.
IG automatic welding method. 2 (a) In all-position narrow-gap single-sided MIG automatic welding from the outside of the penstock during on-site installation of the penstock, (b) Tilt by a certain angle θ with respect to the direction perpendicular to the axial direction of the narrow-gap welded joint. The welding torch is oscillated in a pendulum-like manner along the direction with an amplitude larger than the groove width, increasing the angle of the welding torch axis that intersects with the groove wall, generating an arc on the groove wall and ensuring sufficient penetration. (c) A high current is generated at the position where the welding torch axis intersects with the groove wall surface, and a low current is applied at the bottom of the groove. (d) As the welding position changes from upward to vertical, the welding speed gradually decreases, and the high current against the groove wall is high in the middle, then vertical. (e) The welding speed is gradually increased from the vertical position to the downward direction, and the high current applied to the groove wall is gradually increased, and the low current applied to the groove bottom is gradually increased. Conditions for lowering the low current midway and increasing it slightly in the downward direction, above (b), (
c), (d), and (e) are preset in the control device, and as all-position welding progresses, automatic welding is performed under the conditions for each position. MIG automatic welding method.