JP4114667B2 - Manufacturing method and manufacturing apparatus for welded steel pipe - Google Patents

Description

  The present invention relates to a method for manufacturing a welded steel pipe that can keep the welding quality more stable when manufacturing the welded steel pipe hot, and a manufacturing apparatus that implements the manufacturing method.

  In the production of welded steel pipes, the high-frequency electric seam welding method and the forge welding method are widely used. In these methods, the heat input during welding and the steel strip at the welding point are both factors as factors determining the welding quality. The angle formed by the locus of the edge (hereinafter referred to as “V-point angle”) can be mentioned.

  That is, when the heat input at the time of welding is low, the edge end face of the steel strip cannot be sufficiently melted, resulting in a cold welding defect with insufficient welding strength. Conversely, when the heat input during welding is high, minute oxide defects called penetrators remain in the weldment.

  Therefore, when manufacturing welded steel pipes, the welding operator determines the heat input during welding empirically while actually looking at the red heat state before and after welding, and performs heat input control based on such accumulated results, etc. Is being made.

On the other hand, with respect to the V point angle, Patent Document 1 proposes a method of stabilizing the welding quality by setting the forming roll arrangement to the edge / center simultaneous deformation method and setting the V point angle to 2 to 4 degrees. ing. Note that the edge and center simultaneous deformation method means that the edge of the material is deformed by changing the distance (curvature radius) from the center line of the material at the same time that the edge of the material is formed into a circle. A method to reduce
Japanese Examined Patent Publication No. 6-98382

  However, according to the inventors' subsequent experiments, even if the V-point angle is adjusted to a range of 2 to 4 degrees, a welding failure may occur due to a short-circuit phenomenon that occurs during welding. Moreover, the edge part may wave at the time of roll shaping | molding, and the shape defect may generate | occur | produce.

  The problem to be solved by the present invention is that, in the production of welded steel pipes, conventionally, welding failure due to short-circuit phenomenon during welding cannot be completely eliminated, and the edge portion is wavy and shaped during roll forming. It is a point that a defect may occur.

The method for producing a welded steel pipe according to the present invention includes:
In order to eliminate welding defects due to short-circuit phenomenon during welding and to prevent forming defects at the edge of the steel strip,
In the manufacturing method of the welded steel pipe to be welded after continuously forming the heated steel strip by the forming roll group arranged so as to form the steel strip by the edge-center simultaneous deformation method,
While the V point angle is 3-6 degrees,
The distance which connected these steel strip edge end surfaces when each edge end surface at the time of the bending by a 1st and 2nd fin pass roll and a squeeze roll among the said forming roll group is located in 1 straight. When it is set to 0, the ratio of this distance to the distance between the end faces of the steel strip edges formed by bending with the arranged first and second fin pass rolls and squeeze rolls is 1.0 to 1.05. The main feature is to make the tube.

  In the method of the present invention, the V point angle is set to 3 to 6 degrees, according to the experiment of the inventor described later, when the V point angle is less than 3 degrees, the distance between both edges is short. This is because a short circuit occurs in front of the welding point due to speed fluctuations, tension fluctuations, and the like, which easily causes poor welding. On the other hand, if the angle exceeds 6 degrees, the trajectory of both edges becomes long and waviness is likely to occur. According to the inventor's experiment, the more desirable range of the V point angle was 4 to 6 degrees.

  In addition, it is described later that the pipe is manufactured so that the ratio of the distance between the end faces of the first and second fin pass rolls and the steel strip edge formed by squeeze rolls is 1.0 to 1.05. According to the inventors' experiment, when the distance ratio exceeds 1.05, even if the V point angle is set to 3 to 6 degrees, the edge portion may be undulated during roll forming, and a shape defect may occur. Because there is.

  Further, the fin width of the second fin pass roll is set so that the V point angle is 3 to 6 degrees, and the steel is bent by the arranged first and second fin pass rolls and the squeeze roll. The first and second fin pass rolls and the squeeze rolls are set so that the ratio of the distance connecting the band edge end faces is 1.0 to 1.05. 1 is a welded steel pipe manufacturing apparatus according to the present invention that implements a method of manufacturing a steel pipe.

  According to the present invention, by optimally setting the ratio of the V point angle and the distance between the end faces of the steel strip edge formed by bending with the first and second fin pass rolls and the squeeze roll, the short circuit phenomenon during welding It is possible to prevent both welding defects and undulations at the edge of the steel strip, and to manufacture a steel pipe having excellent welding quality (specifically, eddy current testing and flattening tests).

  The inventor investigated the cause of the fact that even when the V-point angle is set to 3 to 6 degrees, the edge portion may wave during roll forming and a shape defect may occur. As a result, the first and second fin pass roll portions that perform edge restraint and V point angle adjustment after rough forming, and a squeeze roll that further squeezes the cross section formed by the second fin pass roll into a circular shape It was found that the relative displacement of the edge position of the steel strip is related.

  Next, the inventor conducted experiments by changing the edge positions of the steel strips in these three roll portions by changing the roll diameters of the first and second fin pass rolls and the squeeze roll.

  As a result, as shown in FIG. 2 (a), when the edge end surfaces A, B, and C at the time of bending with the first and second fin pass rolls and the squeeze roll are positioned on a straight line (FIG. 2 ( If the distance L0 connecting these steel strip edge end faces A, B, and C of 1.0) is 1.0, the distance L0 is bent by these first and second fin pass rolls and squeeze rolls. Ratio (L1 + L2) / L0 (hereinafter referred to as “edge displacement”) of distance L1 (between end faces AB) + distance L2 (between end faces BC) (see FIG. 2 (c)) connecting the end faces A, B, and C of the steel strip However, it was found that the occurrence of a defective shape of the edge portion at the time of roll forming can be suppressed when it is set to 1.0 to 1.05.

The present invention has been made on the basis of this knowledge, and the best mode for carrying out the present invention based on the knowledge will be described in detail with reference to FIG.
FIG. 1 is a schematic view showing an arrangement of forming rolls constituting an apparatus for carrying out a method for manufacturing a welded steel pipe according to the present invention, and is an example in which a steel strip is formed by five-stand forming.

  The steel strip 1 has a relatively small change in the trajectory of the edge portion, the edge stretch is reduced and is smoothly deformed, and is accurate even in a pipe making process with a small number of roll stands between heat and a small deformation resistance. Forming is continuously performed by forming roll groups arranged in an edge / center simultaneous deformation system that can perform good forming.

  The bending direction at the time of molding is not particularly limited. For example, when the bending direction is downward, the scale peeled off at the time of molding, cooling water from the cutting jig, etc. can be smoothly opened in the lower part of the material during pipe production. And will not adversely affect welding stability.

  For example, after rough forming is performed by the forming roll 2, the first fin pass roll 3 is rolled down in the width direction to increase the thickness of the edge portion and restrain at the time of forming, and the second fin pass roll 4 Aperture can be applied.

  Then, after passing through the second fin pass roll 4, high-frequency resistance induction heating is performed by the high-frequency induction coil 5, and the edge portion of the strip 1 is brought into a molten state, and the squeeze roll 6 is formed into a circular cross section. . In addition, after pipe making, it is sent to the next process by the pull-out roll 7.

  And in manufacture of the above-mentioned welded steel pipe, in this invention, it is made for the V point angle at the time of welding to be 3 to 6 degree | times, for example, 4 degree | times. The V point angle can be set by the stand interval between the second fin pass roll 4 and the squeeze roll 6, the ellipticity of each roll, the neutral axis reduction ratio, etc. In the present invention, the second fin that is easy to set is used. The V point angle is set by determining the fin width of the pass roll 4.

  In addition, in the present invention, the pipe is formed so that the edge displacement is 1.0 to 1.05 at the same time as the setting of the V point angle. This is performed by the roll diameters of the two fin pass rolls 3 and 4 and the squeeze roll 6.

  In this way, the V point angle is set to 3 to 6 degrees by determining the fin width of the second fin pass roll 4, and the roll diameters of the first and second fin pass rolls 3 and 4 and the squeeze roll 6 are set. When the welded steel pipe is manufactured by the method of the present invention using the steel pipe manufacturing apparatus of the present invention in which the edge displacement is set to 1.0 to 1.05, the welding due to the short-circuit phenomenon at the time of welding is performed. It is possible to prevent both defects and undulations at the edge of the steel strip, and to manufacture steel pipes with excellent welding quality.

Hereinafter, the present invention will be described more specifically with reference to examples.
For example, when manufacturing a welded steel pipe having an outer diameter of 114 mm, the coil to be used is uncoiled, the end faces of the strip steel are flash-butt welded, and heated to 900 to 1000 ° C. in a heating furnace, and then shown in FIG. Pipe making was performed at a welding / forming stand.

  The roll to be used is determined in accordance with the distance between the squeeze roll and the first and second fin pass rolls, and the fin width of the second fin pass roll 4 is determined so that the V point angle is, for example, 5 degrees. .

  At this time, the edge displacement is minimized to suppress the undulation of the steel strip edge, and the amount of butt between each roll (the width of the base coil (periphery length at the time of forming roll) -first The circumference of the first fin pass roll, the circumference of the first fin pass roll-the circumference of the second fin pass roll, the circumference of the second fin pass roll-the circumference of the squeeze roll) The roll diameter was determined in consideration of 2.0%. In the same manner, rolls in which the V point angle was changed at a pitch of 1 degree in the range of 3 to 7 degrees were manufactured.

  Pipe making was performed using the roll thus designed. Regarding the angle of the edge butt portion at the time of pipe making, image observation was performed with a CCD camera, and it was verified whether or not the pipe was made at the designed angle.

  FIG. 3 shows the results of eddy current testing of steel pipes manufactured by changing the V point angle in the same manner. As shown in FIG. 3, the passing rate of the eddy current flaw test improved as the V point angle increased, but the passing rate of the eddy current flaw test decreased from the time when the V point angle exceeded 6 degrees.

  Next, as a result of performing an adhesion flattening test on a product that failed the eddy current flaw detection test, if the V point angle is less than 3 degrees, the scale-engaged unjoined portion that seems to be short-circuited, and the V point angle is 6 For those exceeding the degree, a wavy welded defective surface was confirmed in the seam portion.

  Table 1 below shows the results of confirming formability when the V point angle at which the passing rate of the eddy current flaw detection test was particularly good is 4 to 6 degrees and the edge displacement is varied. From this result, it was found that the molding is stable when the edge displacement is 1.05 or less.

  The present invention is not limited to the above example, and it goes without saying that the embodiment may be appropriately changed within the scope of the technical idea described in each claim.

  The present invention is not limited to pipes that are piped downward, but can also be applied to pipes that are piped upward.

It is the schematic which showed the arrangement | sequence of the forming roll which comprises the apparatus which enforces the manufacturing method of the welded steel pipe of this invention. (A) is the figure which showed the shaping | molding pattern, (b) (c) is a figure explaining edge displacement. It is the figure which showed the relationship between a V point angle and the acceptance rate of an eddy current test.

Explanation of symbols

1 Steel strip 3 First fin pass roll 4 Second fin pass roll 6 Squeeze roll

Claims (2)

In the manufacturing method of the welded steel pipe to be welded after continuously forming the heated steel strip by the forming roll group arranged so as to form the steel strip by the edge-center simultaneous deformation method,
The angle formed by the trajectories of both edges of the steel strip at the welding point is 3 to 6 degrees,
The distance which connected these steel strip edge end surfaces when each edge end surface at the time of the bending by a 1st and 2nd fin pass roll and a squeeze roll among the said forming roll group is located in 1 straight. When it is set to 0, the ratio of this distance to the distance between the end faces of the steel strip edges formed by bending with the arranged first and second fin pass rolls and squeeze rolls is 1.0 to 1.05. A method for producing a welded steel pipe, characterized in that the pipe is produced as described above. An apparatus for carrying out the method for manufacturing a welded steel pipe according to claim 1,
The fin width of the second fin pass roll is set so that the angle formed by the trajectories of both edges of the steel strip at the welding point is 3 to 6 degrees,
When the distance between the edge edges of the steel strips when the edge edges of the first and second fin pass rolls and squeeze rolls are positioned on a straight line is 1, this distance is The first and second first and second fin pass rolls and the squeeze roll bent steel strip edge end surfaces have a distance ratio of 1.0 to 1.05. An apparatus for manufacturing a welded steel pipe, wherein the roll diameters of a fin pass roll and a squeeze roll are set.

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