JPH01299714A - Manufacture of thick-walled electric resistance welded tube - Google Patents

Abstract

PURPOSE:To drastically improve dimensional accuracy by not only giving draft by a line of vertical roll trains with hole die in a width direction of a strip steel but bending the neighborhoods of edges, rolls a thickened part and forming the shape of joining end faces with hole die. CONSTITUTION:Edge parts of a strip 1 is bent by an edge forming part composed of edge forming vertical rolls E1, roll-forming rolls E3 and pressure rolls E4 to weld joining part through common breakdown rolls, side rolls, fin rolls and squeeze rolls. The hole die forming vertical rolls E1 are formed to such a shape that the circular arc part intersects at right angles with the end faces, the edge parts in the forming vertical rolls E2 have a curvature near that of the product, then, the thickened parts in the edge parts are rolled by the forming rolls E3 and formed to a shape suitable to butt welding. Before entering a breakdown stage, the edge parts only are bent and the joining end faces, too, are formed by roll forming rolls to obtain the shape of a specified curvature. In this way, the accuracy and quality can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for manufacturing a thick-walled electric resistance welded steel pipe from a steel band, in which forming the vicinity of an edge portion is performed before bending the steel band into a tubular shape.

(Prior Art) Conventionally, electric resistance welded steel pipes are usually formed from a steel strip 1 into a tubular shape using a continuous roll forming machine consisting of breakdown, side roll, and fin pass roll rows as shown in FIG.
In the illustrated example, the steel strip 1 is manufactured in a process of butt welding, and is rolled in roll groups 2 to 5 called breakdown.
At this point, the material is bent and formed into a semicircular shape mainly by vertical reduction. Thereafter, vertical roll groups 8 to 10 called side rolls roll down in the left and right direction to form a tubular shape, and roll groups 11 to 13 called fin passes apply circumferential pressure and simultaneously bend the material. Shape to the shape of the excavated product. After the shape of the drilled product is formed in this way, the seams are welded using electric resistance welding (not shown). It is finished into a steel pipe.

In this way, the manufacturing method for ERW steel pipes can be divided into bending and welding, but when forming, the important thing is to bend it into a uniform shape all around the circumference and to create a shape that is optimal for the subsequent butt welding. The goal is to obtain an end face shape. However, the conventional technology has the following problems regarding dimensional accuracy due to bending during breakdown.

(2) When considering that bending is performed by applying vertical pressure with upper and lower rolls 15 and 16 as shown in FIG. 6 in breakdown, both ends are not sufficiently bent.

■When bending the steel strip 1, the lower roll 15 and the steel strip 1
The lower edge 17 of the is the first to start contact, and bending is performed using this point as a fulcrum. Therefore, when the bending rigidity of the steel plate increases as the Fi and thickness of the steel strip 1 increase, the thinning deformation of this portion progresses and the dimensional accuracy deteriorates. This is called edge thinning.

■Similar to the case of item (■) above, in the end contact area 18, which is the contact area between the upper roll 16 and the steel strip 1, thinning parts called indentations occur as the bending rigidity of the steel plate increases as the plate thickness increases. Dimensional accuracy deteriorates.

FIG. 7 is a graph showing the wall thickness distribution after breakdown with respect to the distance from the center of the steel strip, and a decrease in wall thickness due to edge thickness reduction and indentation can be seen.

It can be seen that within the outer circumference length 8011111, the thickness changes over the width \4011111 area. This example is data for the case where a steel strip with a plate width of 150 ff and 111 x plate thickness of 8.2 a+m is finally bent and formed into a tube with an outer diameter of 50.8 mm and a wall of r ¥8.21.

Conventionally, as a countermeasure for these items, regarding items ① and ② above, the thinning part is usually offset by increasing the thickness of the edge part that occurs when bending is formed by rolling down in the circumferential direction in the fin bath process. Because the positions of the edge thickness reduction during breakdown and the edge thickness increase during fin bathing do not completely match, a large circumferential reduction is required to offset the thickness reduction, and the inner shape deteriorates significantly due to the increase in thickness at the edge. . Further, thickening with a fin bath has the disadvantage that a difference between the two edges is likely to occur due to the rolling phenomenon of the material during molding, further deteriorating the inner shape.

FIG. 8 shows the wall thickness distribution after the fin pass with respect to the distance from the steel strip center, and the above-mentioned relationship can be seen. The thinning of the edges has been resolved, but it can be seen that the thickening of the edges is now noticeable. Note that this example is also the same as the case shown in FIG. 7, and the reduction amount at the fin pass was 2%.

Japanese Patent Application Laid-Open No. 56-1362 describes a method to fundamentally reduce insufficient bending and edge thinning due to such breakdown.
No. 30 and No. 60-72614 have been developed, but their effects are not sufficient for forming thick-walled steel pipes.

Furthermore, as a countermeasure for the above-mentioned item 0, it is common to improve the curvature of the upper roll, and Japanese Patent Application Laid-Open No. 115623/1984 has been developed, but these measures are not sufficiently effective when forming thick-walled pipes. isn't it.

On the other hand, in butt welding after forming into a tubular shape, it is desirable that both end faces are parallel, but when a steel strip with both end faces at right angles is bent and formed, both end faces are not parallel and the outside becomes open. This tendency becomes larger as the pipe becomes thicker, and t/
If D = 15% or more, butt welding will be greatly affected. Here, t is the wall thickness, and D is the outer diameter of the tube. As a countermeasure for this, edge forming is performed using a fin pass, but when the wall becomes thick, a large reduction in the circumferential direction is required and the above-mentioned inner surface shape deteriorates. Furthermore, there is a method to make the end faces of the steel strip parallel after forming into a tubular shape by cutting or rolling the end faces of the steel strip before entering the breakdown to make them parallel. The lower end of the trapezoidal cross section may come into contact with the lower roll during breakdown forming, and this portion may fold toward the end surface, which causes a butt weld failure. Furthermore, the wall thickness increases during end forming, which causes deterioration of the inner shape. For this purpose, JP-A-56
-168972 proposes a method of cutting the end faces after breakdown forming and side roll forming to ensure parallelism of the end faces during butt welding, but this method also stabilizes cutting due to rolling of the material during forming. It is difficult to ensure parallel end faces due to poor cutting.

As described above, in the past, no fundamental solution has yet been reached regarding edge forming of electric resistance welded steel pipes, especially when the pipes are thick.

(Problem to be solved by the invention) As the quality of the welded parts of ERW steel pipes has been improved, the range of applications for ERW steel pipes has expanded to include conventional seamless steel pipes. , the scope of application to high-grade steel pipes such as steel pipes for machine structures has been expanded, and thick-walled steel pipes have been adopted. However, thick-walled steel pipes have many problems in forming when manufacturing them, and in particular, dimensional accuracy is poor with conventional forming methods. There was a problem.

As already mentioned, the problems in forming thick-walled ERW steel pipes are the reduction in wall thickness due to indentation during rolling during the breakdown process, the loss of edge thickness during the breakdown process, and the problem of butt welding. This is the thickening of the edge part due to excessive circumferential reduction in the fin pass process to obtain the optimal end face shape.

Therefore, an object of the present invention is to optimize the circumferential reduction in the fin pass process by adopting an edge forming method that greatly reduces the occurrence of impressions, edge thinning, etc. in the breakdown process. It is an object of the present invention to provide a method for manufacturing thick-walled electric resistance welded steel pipes that can significantly improve accuracy.

(Means for Solving the Problems) In order to solve the problems in the prior art as described above, the present inventors have conducted various studies and found that the present inventors have developed a method to solve the problems in the prior art as described above. We learned that it is possible to manufacture thick-walled electric resistance welded steel pipes with excellent dimensional accuracy by bending both ends of a steel strip using vertical rolls with grooves and forming the joint end faces, and thus completed the present invention. It is something.

Therefore, the gist of the present invention is to provide a method for manufacturing an ERW steel pipe in which a steel strip is continuously bent into a tubular shape using a series of rolls and then electrically resistance welded. Prior to this, by a row of vertical rolls with grooves,
While rolling the steel strip in the width direction, the area near the edges is bent to a predetermined size, and then the thickened part created by rolling in the width direction is rolled using grooved vertical rolls, and a joint suitable for welding is created. This is a method of manufacturing a thick-walled electric resistance welded steel pipe, which is characterized by forming the end face shape.

The thick-walled electric resistance welded steel pipe referred to in the present invention is not limited in its wall thickness as long as the above-mentioned effects can be obtained, but - in general, t/D
= 15% or more electric resistance welded steel pipe. t and D are as described above.

(Operation) Hereinafter, the present invention will be described in further detail with reference to the accompanying drawings.

FIG. 1 is a schematic diagram showing a bending roll row according to the present invention;
Figures 2 (A), (B), (C), and (D) are schematic diagrams showing each step (process order) of the edge forming method according to the present invention, and Figure 3 shows the results of the wall thickness distribution according to the present invention. FIG. 4 is a graph also showing the curvature distribution results according to the present invention.

According to the present invention, as shown in FIG. 1, the steel strip 1 has an edge-forming vertical roll E1,
E2, rolling roll E3, and presser roll E4 (located below rolling roll E3 and not visible in Figure 1)
In the edge forming section where the steel strip is bent into a tubular shape, the edge section is bent and formed, followed by ordinary breakdown rolls 4.5, side rolls 8.9.10, It passes through each roll group of fin pass rolls 11, 12, 13 and squeeze rolls 14, is formed into a tubular shape, and the joints are welded to produce an electric resistance welded steel pipe. Note that seam welding is performed by electric resistance welding, and in the present invention, it may be performed by conventional means and is not particularly limited, and those are well known to those skilled in the art.
Explanation regarding this point will be omitted below.

FIGS. 2(A), (B), (C), and (D) are explanatory diagrams showing the edge forming method according to the present invention divided into each stage (process order).

As shown in Fig. 2 (^), the steel strip 1 used for the electric resistance welded steel pipe is cut at both ends with a slitter, but the end surfaces 19 on both sides are not at right angles and are not smooth. As the thickness increases, thinning occurs at the edges during slitting, making the edges thinner than the center. For this purpose, for the purpose of shaping the shape and bending the edge portion, a vertical roll for forming grooves as shown in FIG. 2(B) is used to apply pressure in the width direction.
The hole shape (A) of the vertical forming roll E1, which performs smoothing, recovery of the thinned edge part, and bending of the edge part, is shaped so that the arc part and the end face are perpendicular to each other. The lower part of the steel strip is supported by rolls to prevent buckling of the central part of the steel strip without any bending. The central portion is made straight in order to allow for greater bending of the edge portions, but there is no problem if the central portion is given a gentle curvature.

FIG. 2(C) shows the shape of the edge portion at the final stage of bending, with the end face bent at 90 degrees. The basic concept of the hole shape (B) is the same as that in Fig. 2 (B), but the bending of the edges is more advanced, and the curvature is close to that of the beam product. In this state, the bending of the edge portion of the steel strip 1 has been completed, and the inner side of the edge portion, which is not restrained by the rolls, is thickened due to the reduction in the width direction. Forming vertical roll E1,
Molding by E2 is not limited to two stands, and can be distributed to multiple stands as necessary. Further, it is preferable that the forming vertical roll IEL E2 be a non-driven roll if it is possible to transfer the strip by a breakdown or fin pass roll.

The copper strip whose edge portion has been bent is rolled by a rolling roll E3 in the next step shown in FIG. 2(D) to roll the thickened portion of the edge and to form a shape suitable for butt welding.

Figure 2 (D) shows the 40-1 system, which can accommodate changes in plate thickness and changes in strip width due to changes in plate thickness, but the structure is slightly inferior in terms of dimensional accuracy. It is also applicable to the simple 20-1 system.

In this way, in the present invention, only the edge portion is formed in the initial stage before entering the breakdown process, so
After this, the steel strip enters the breakdown process, but since edge forming has already been completed, the conventional first half stand of breakdown is unnecessary, and there is no need to take a large reduction in the circumferential direction of the fin path.

As detailed above, in the conventional method, especially when manufacturing thick-walled pipes with an internal thickness of 6.01 mm or more, the edge portion is formed in the tubular forming process, which may cause thinning or thickening. In addition, defects may also be observed at welded joints. The roundness near the seam was also not accurate, posing a quality problem.

However, as mentioned above, in the method of the present invention, only the edges are bent and the joint end faces are formed into a predetermined curvature shape using rolling rolls before forming into a tubular shape, so there is no thinning or thickening. Furthermore, since the joint end face is formed by rolling at the same time as the bending process, it is possible to exhibit a great effect in improving quality with excellent dimensional accuracy.

(Example) A carbon steel strip with a width of 155 mm and a plate thickness of 8.5 mm was used, and this was rolled in the width direction of the strip using vertical forming rolls E1 and E2 with the holes shown in Fig. 1 (B) and (C). After applying a rolling reduction of N: 3III and bending the strip to a range of 174 mm (longer in circumference and width) at both edges, the strip is then rolled using a 40-roll shape rolling roll E3 and a presser roll E4. Both side end portions were molded. Then, it was finally bent into a tube having an outer diameter of 50.8+wm x wall thickness of 8.5+u+ using the bending means shown in FIG. The total rolling reduction at the fin pass stand was 1%.

For comparison, a tube body was obtained by using a similar steel strip and directly bending it using the apparatus shown in FIG. 5 without forming the end portions in advance.

The joints of the molded tubes on both sides were welded by conventional electric resistance welding.

In order to see the effect of improving the wall thickness distribution of the electric resistance welded steel pipe obtained in this way by the present invention, the wall thickness distribution was measured and the results are graphed in Fig. 3 with respect to the outer circumference from the welded part. .

It can be seen that according to the present invention, there is almost no change in wall thickness near the weld, that is, near the joint. However, in the conventional example, a maximum thickness increase of about 0.5w+w is observed in the welded part.

FIG. 4 is a graph showing the curvature of the outer surface of the product and the curvature of the inner surface of the product. According to the present invention, although the inner surface of the welded portion slightly deviates from the perfect circular shape, it can be seen that not only the outer surface but also the inner surface has a fairly good shape.

In addition, here, [curvature] (ρ) is 1/R8, 1/R, assuming that the radius of curvature of the inner and outer surfaces is R and Ro, respectively.
e (within a circumferential length of 4 mm).

As can be seen from the results shown in FIGS. 3 and 4, according to the present invention, variations in both curvature and wall thickness due to thickening of the edge portion at the fin pass are suppressed, and especially on the inner surface of the product. The effect of improving the curvature distribution is large, and the dimensional accuracy is significantly improved.

(Effects of the Invention) As described in detail above, according to the present invention, it becomes easy to bend both ends of the steel strip, which is the most difficult to bend in the production of thick-walled electric resistance welded steel pipes. This eliminates the deterioration in dimensional accuracy caused by breakdown impressions and thickening of edges at fin passes, which were caused by the fin path, and has great effects such as greatly improving dimensional accuracy.

In addition, although the above description has focused on thick-walled electric resistance welded steel pipes, it goes without saying that the method of the present invention can be applied to the production of not only thick-walled electric resistance welded pipes but also thin-walled electric resistance welded steel pipes.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram showing the bending roll row of the present invention; FIGS. 2 (A), (B), (C), and (D) show the edge portion bending method of the present invention. Process chart: Figure 3 is a graph showing the effect of improving wall thickness by the method of the present invention; Figure 4 is a graph showing the effect of improving curvature distribution by the method of the present invention; Figure 5 is a row of bending rolls by the conventional method. FIG. 6 is a schematic explanatory diagram showing a conventional bending method; FIG. 7 is a graph showing wall thickness distribution after breakdown by a conventional method; and FIG. It is a graph showing wall thickness distribution after fin pass by a conventional method. 1: Steel strip 2.3, 4, 5: Breakdown roll 8.9.1
0: Side roll 11.12.13: Fin pass roll 14: Squeeze roll 17: Edge thinning portion 18: Indentation 19: End surface El, [i21 forming vertical roll E3: rolling forming roll E4: presser roll

Claims (1)

[Claims] In a method for producing an ERW steel pipe in which a steel strip is continuously bent and formed by a group of rolls and then electrically resistance welded, prior to bending and forming the steel band into a tubular shape, a vertical roll row having a hole is used to
It is characterized by applying a reduction in the width direction of the steel strip and bending the vicinity of the edge to a predetermined size, and then using a slotted roll to roll the thickened part caused by the reduction in the width direction and forming the shape of the joint end face. A method for manufacturing thick-walled ERW steel pipes.