JPH021564B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an apparatus for forming an ERW steel pipe whose seam line extends parallel to the pipe axis, and more specifically, to an apparatus for forming an electric resistance welded steel pipe in which a seam line extends parallel to the pipe axis, and more specifically, a forming apparatus for forming an electric resistance welded steel pipe in which a seam line extends parallel to the pipe axis. In the process of forming ERW steel pipes, in which the edges of the raw pipe are welded through finpass rolls, the cross-sectional shape of the strip is bent into a U-shape.
Next, it relates to a molding device for processing and molding into a circular cross section.

[Conventional technology]

In general, for ERW steel pipes whose seam lines extend parallel to the pipe axis, strips are cut in advance to the developed dimensions of the ERW steel pipe to be manufactured, and are sequentially shaped into a predetermined shape using various forming rolls during rough and intermediate forming processes. The joint edges are stably formed using fine pass rolls in the final forming process, and after final forming into a blank pipe of the specified shape and dimensions, the joint edges are pressure welded using squeeze rolls. It is manufactured there.

In a conventional electric resistance welded steel pipe forming apparatus, forming rolls are arranged according to the forming flower. For example, coarse,
In the intermediate forming process, there is (a) a device that bends the entire strip (b) a center bend roll type device, and in the final forming process, there is (c) a Yoder and Matsukei type flower forming device (d) an Etna type flower forming device. There is a molding device.

The equipment that bends the entire strip in the rough and intermediate forming processes is a circular bending method or a combination forming equipment such as edge bending. Although it has the advantage of being able to reduce the molding load, it has problems such as an increase in the number of molding rolls, an increase in the length of the molding line, an increase in roll adjustment and replacement time, and a narrowing of the range in which the rolls can be used together.

In addition, conventional center bend roll forming equipment only bends the center of the strip and does not form the edges during the rough and intermediate forming processes, so edge bending is required during the subsequent fine pass roll forming. As a result, the load for forming the fin pass roll increases, and edge forming with the fin pass roll becomes extremely difficult. In addition, with this forming device, the spatial locus length of the strip edge is the longest in the rough and intermediate forming processes compared to other forming methods, and the edge stretch is large, and furthermore, because the edge part is not bent, buckling occurs. Low resistance. Therefore, there is a problem in that edge waves are likely to occur between the roll stands. Due to the occurrence of such problems, center bend roll forming apparatuses have not been put to practical use in the past.

In the final forming process, that is, in the fine pass roll forming apparatus, the above-mentioned Yoder and Matsukei type flower forming apparatuses have a relatively large fine pass forming load, and roll defects are likely to occur, and edge sparks and edge There are problems in that waves are likely to occur and the edges are likely to thicken.

In addition, although the above-mentioned Etna type molding flour forming equipment reduces the fine pass forming load and suppresses the occurrence of roll defects compared to the Yoder and Matsukei types, it is difficult to bend the entire strip in the rough and intermediate forming processes, especially , finishing bending of the lower half of the raw tube is required, making it difficult to perform the forming process in the rough and intermediate forming processes. Furthermore, the problem of the narrowing of the weld V-shape angle due to the narrowing of the edge interval after the final fin pass, as well as the occurrence of thickening of the edge due to the increase in the fin angle in the upstream fin pass, are the same problems as Yoder and Matsukei molded flowers. In particular, there is a danger that Etsuji's increased flesh will become larger than Yoder and Matsukei types.

As mentioned above, in conventional molding equipment,
Increase in the number of forming roll stands due to the bending of the entire strip in the rough and intermediate forming processes, narrowing of the range of rolls that can be used together, increased roll adjustment and replacement time, poor cross-sectional bending shape of the raw pipe and increased fine pass forming load, final There are many problems such as a decrease in the weld V-shape angle due to the narrowing of the fin width, increased thickness at the edge of the raw pipe, the need to adjust the fin pass reduction due to changes in plate thickness and grade, and an increase in residual stress in the circumferential direction of the raw pipe. There's a problem.

JP-A-57-70028 proposes a pipe forming method and apparatus in which so-called cassettes are arranged in which a plurality of upper and lower roll groups are assembled into shapes corresponding to the progressing stages of forming. This proposal makes it easy to rearrange the roll groups, but there are problems in terms of roll strength and cassette frame strength when forming thick strips, and the roughness and intermediate forming rolls are not driven. , it becomes difficult to insert the strip, it is difficult to obtain sufficient driving force even in the stationary part, and furthermore,
Roll flaws are likely to occur.

Special Publication No. 56-53448 and Special Publication No. 57-1328, the rough and intermediate forming of the raw pipe was performed by sequentially bending the strip into a cylindrical shape while restraining the edges of the strip using a non-driven truncated conical vertical roll with a flange. A technique to do this is shown.
With this forming device, the strip is not formed into a smooth arc shape, and there is angularity due to local bending.
Also, when the strip rolls, the edges are severely damaged. Furthermore, when forming the tip of the strip, the edges tend to collapse and roll, resulting in edge waves.

Additionally, multiple edge bend rolls are used to bend the strip from the edge to the center of the strip, and in the middle to final stage of rough forming, multiple cage rolls are used to perform arc-shaped O-forming. There is a molding device (Special Publication No. 57-56409, USP
No.4339938). This device requires large breakdown rolls, which are prone to roll flaws, and it is difficult to form arc-shaped blank tubes in the upstream forming process, and furthermore, it is difficult to adjust the cage rolls.

As a discontinuous two-dimensional forming device for welded steel pipes,
UOE pipe manufacturing equipment is known. UOE pipe is made by bending a flat plate of a predetermined length into a U-shape using a mold with the same cross section in the longitudinal direction.
Manufactured by pressing with a shaped die. UOE pipe is a plastic processing technology with deformation behavior that is completely different from the forming of ERW steel pipes in which strips are continuously formed three-dimensionally using hole-shaped rolls. It cannot be used for this purpose, and there is no such practical example to date. Moreover, the O-forming press hole shape is a simple perfect circle shape, and complicated forming processing cannot be performed with the O-forming press.

In order to solve the above-mentioned problems, the inventors of the present invention solved the above problem by () bending the central part of the strip by using a roll that continuously restrains and supports the edge of the strip and a complex center bend roll that restrains and forms the central part of the strip; Only the forming process is performed, and the remaining widthwise part of the strip is not bent, but roll forming is performed to obtain a U-shaped shaped flower. In addition to suppressing the forming process and bending the edge part of the raw pipe to a curvature of 80% or more of the curvature of the final formed pipe, each side part of the raw pipe and the edge part of the raw pipe, and the side part of the raw pipe and the bottom part of the raw pipe are By overbending the boundary part to a degree greater than the final pipe curvature, and () applying a reduction mainly in the direction of reducing the vertical diameter of the raw pipe using the subsequent fine pass rolls, the side of the raw pipe whose bending is suppressed in () above is applied. The parts are sequentially stretched in the width direction, and the lateral diameter of the raw pipe is formed in a direction that gradually increases. Through this stretch forming process, the side parts of the raw pipe are bent and formed, and the raw material that has been overbended in () above is formed. A new type of electric resistance welded steel pipe that is characterized by unbending the boundaries between the pipe side and the raw pipe edge, and between the raw pipe side and the raw pipe bottom, and which exhibits excellent forming in thin-walled strips. We have proposed a forming method (Japanese Patent Application No. 58-131938), but for products that exceed this method, that is, thick-walled strips, it is difficult to carry out the forming processes () to () with stable quality. There was a problem.

[Problem that the invention seeks to solve]

An object of the present invention is to provide a forming apparatus which can suitably carry out the above-mentioned Japanese Patent Application No. 58-131938 even when forming a relatively thick band plate, and which makes the forming of the band plate stable and easy. It is something.

The second object of the present invention is to reduce the number of forming rolls, shorten the length of the forming line, be inexpensive, have a wide range of common uses for the rolls, make it possible to manufacture tubes with a large number of wall thicknesses and dimensions using the same roll, and The purpose is to provide a device with short adjustment and roll exchange time and high mill operation rate.

A third object of the present invention is to provide an apparatus that prevents thickening of the edge portion and obtains an electric resistance welded steel pipe having an excellent welded portion shape.

A fourth object of the present invention is to reduce the molding load by reducing fin pass reduction and to eliminate the need for reduction adjustment by changing the plate thickness grade.

A fifth object of the present invention is to provide an apparatus that can improve edge bendability, increase the fin width of the final fin pass roll, and expand the weld V-shape angle. It is in.

The sixth object of the present invention is to reduce the residual stress in the circumferential direction of the raw tube, thereby increasing the material yield and
The purpose is to make it possible to manufacture electric resistance welded steel pipes with excellent pipe shape and welded part quality.

[Means for solving problems]

The apparatus of the present invention for achieving the above object includes: (a) An edge forming roll for inwardly bending the edge portion of the strip is installed upstream of the roll forming section. This edge forming roll is composed of a pair of upper and lower rolls arranged above and below the strip.

(b) Multiple sets of center bend rolls are arranged downstream in the longitudinal direction of the strip. This center bend roll consists of twin rolls arranged symmetrically and coaxially at intervals in the width direction of the strip, and these are arranged in pairs above and below the strip.

(c) A pair of upper and lower single roll center bend rolls are arranged at the center in the width direction of the strip downstream thereof.

(d) Cage rolls are continuously disposed on the lower surface of the strip edge from upstream of the most upstream roll of the plurality of center bend roll groups to downstream of the center bend roll of the most downstream single roll.

(e) Place a group of fine pass rolls downstream.

The present invention will be explained in detail below with reference to the drawings.

FIG. 1 shows a plan view of an embodiment of the apparatus of the present invention together with a strip being bent. −, −, −, −, −, − in Figure 1
, -, -, - The cross sections of the strips in the direction of the arrows are respectively a, b, c, d, e, f, g, h,
Shown in i.

In the apparatus of the present invention, the edge forming rolls EF are installed in an upper and lower pair, and the center bend rolls 1CB and 2 are arranged downstream of the upper and lower pairs.
CB, 3CB, and 4CB are arranged at intervals in the traveling direction of the strip S, and the strip S passes between the upper and lower rolls, and cage rolls are placed on the back side of both edges of the strip S.
A CR is arranged, and fin pass roll groups 1F, 2F, and 3F are arranged downstream of it.

The edge-forming roll EF consists of a roll installed on the upper surface of the strip S and having a convex profile, and a roll installed on the lower surface of the strip S and having a concave profile, which are arranged in a pair to face each other. There is. Front views of the edge forming roll stand are illustrated in FIGS. 5a, b, and c.

No matter which of the apparatuses shown in FIGS. 5a, b, and c is used, the desired molding can be obtained.

Center bend roll 1CB, 2CB, 3CB,
4CB has a pair of rolls having a convex profile disposed on the upper surface of the strip S and a roll having a concave profile disposed on the lower surface of the strip S, facing each other. center bend roll 1
A front view of the stand for CB and 2CB is shown in FIG. 6, and a front view of the stand for center bend roll 3CB is shown in FIG. 7. In addition, if a single roll is installed instead of the twin roll in Fig. 7, the center bend roll 4CB will be obtained.

Above center bend rolls 1CB, 2CB, 3
As shown in Figures 6 and 7, CB has 2 left and right sides.
The center bend roll 4CB on the downstream side consists of a single roll.

Center bend roll 1 consisting of twin rolls
CB, 2CB, and 3CB are arranged in the longitudinal direction of the strip S, and are provided with symmetrical coaxial twin rolls spaced apart at a constant interval in the center of the strip S in the width direction. Each of the twin rolls is arranged in the center of the strip S in the width direction at a position separated by about 1/3 of the strip width.

Center bend rolls 1CB, 2CB, and 3CB have a convex profile on the top side of the strip S and a concave profile on the bottom side. The uneven profile is made to have a curvature larger than that of the product steel pipe as the forming progresses.

The cage rolls CR are arranged from the upstream side of the most upstream center bend roll 1CB of the strip plate to the downstream side of the most downstream center bend roll 4CB.

In Fig. 1, the cage roll CR is schematically shown as a circular shape, but in reality, the cylindrical surface of the roll is placed on the back side of the edge of the strip S, as seen in the front views of Figs. 6 and 7. It is arranged so as to come into contact with the edge portion of the strip S.

In the process of bending the strip S into a trough-shaped cross section and then forming it into a U-shaped cross section, center bend rolls 1CB, 2CB, 3CB, 4CB and a large number of cage rolls CR are arranged, and their interaction allows continuous bending. The band plate S is formed and processed.

That is, the edge part is inwardly bent using the edge forming roll EF, and then the center bend rolls 1CB, 2CB, 3CB and the cage roll CR are used.
The strip S is formed into a trough-shaped cross section by the cooperation of the center bend roll 4CB and the cage roll CR.

Unlike the conventional forming apparatus, the apparatus of the present invention performs forming by locally curving only a part of the strip in the width direction by cooperation of the center bend roll and the cage roll.
For CB, 3CB, and 4CB, it is sufficient to use fewer rolls than conventional center bend rolls, which are smaller than conventional center bend rolls that curve the entire strip widthwise to a uniform curvature, and cage roll CR is the most upstream center bend roll. By arranging it from upstream of 1CB, it effectively contributes to local bending of the strip.

FIG. 3 schematically shows a plan view of a strip forming apparatus using a conventional cage roll forming mill for comparison.
08, six sets of inner rolls 110, accessory rolls for performing partial processing such as edge forming rolls EF, and a cage roll CR. In conventional cage roll molding, the cage roll CR is not arranged in the molding machine of the preforming roll or breakdown roll 102 or upstream thereof due to the concept of the molding method.

Compared to conventional cage roll forming mills, the device of the present invention requires a shorter forming line and can significantly reduce the number and size of accessory rolls, resulting in lower equipment costs and easier roll adjustment. becomes.

FIG. 4 is a perspective view comparing the apparatuses shown in FIGS. 1 and 3 with respect to changes in the profile of the strip during the tube forming process.

Figure 4b shows the molding process using a conventional device,
FIG. 4a shows the molding process using the apparatus of the invention.
Figures a and b respectively show the deformed state of the strip from the flat state at the upper right to the completion of fin pass forming at the upper left end. In one example, the line lengths in FIGS. 4b and 4a are 1:0.7 in the same tube forming apparatus, and the line length in the gauge forming area excluding the fin pass forming section is 1:0.6.

FIG. 8 is an explanatory diagram comparing the sizes of a conventional forming breakdown roll and a center bend roll of the present invention. The sizes of rolls 1CB to 3CB are shown with diagonal lines.

As described above, the bending roll of the present invention may be small in size, and the rolling device may also be small and light equipment.

Further, as shown in FIG. 9, the distance between the twin rolls of the center bend rolls 1CB, 2CB, and 3CB of the present invention is made variable by the distance piece 20, and the position of the cage roll CR is made variable. By adjusting the position and rolling down, it is possible to manufacture a wide range of ERW steel pipes with different diameters and thicknesses without changing rolls, and the size of rough and intermediate forming rolls can be adjusted. Dual use is achieved.

This means that while the center part of the strip S is kept straight, the twin roll center bend roll 1CB,
This was made possible by local bending using 2CB, 3CB and cage roll CR.
This was not possible with conventional ERW steel pipe forming.

Next, the molding process using the apparatus of the present invention will be explained.

The strip S whose width has been appropriately trimmed upstream is continuously supplied to the forming device, and first,
As shown in Figure 3, the edge portion is inwardly bent using an edge forming roll, and then its cross-sectional shape is locally bent into a trapezoidal trough shape with its open side widened.
This trough-shaped cross section, as shown in Figure 2d,
It consists of a total of three straight parts, ie, the side lines 11, 11a on both sides and the flat bottom part 12, and two local bent parts 13, 13a connecting these straight lines.

Figures 2b, c, and d show the cross-sectional profile of the strip S showing the process of forming this trough-shaped cross section. They are located at two positions separated by a distance of 15, which is 1/3 of the width. The curvature of the circular arc of the local bent portions 13, 13a is bent so as to have a larger curvature (therefore, the radius of curvature is smaller) than the curvature of the electric resistance welded steel pipe to be manufactured as the forming progresses. By doing so, the portions 13, 13a are processed in the direction of reducing the curvature during fin pass forming in the subsequent process, and a preferable forming effect is produced.

Next, as shown in FIG. 2e, the flat bottom portion of the trough-shaped cross section formed in steps b, c, and d, that is, the central portion 12 of the strip S, is bent into a semicircle. The radius of curvature of this semicircle is greater than the radius of curvature of the electric resistance welded steel pipe to be manufactured. The progress of bending of the semicircular part of the central part 12 of the strip in the process shown in Fig. 2e is carried out by the cage roll group after 4CB, and at the end of the U-shaped forming process, as shown in Fig. 2f, Both side lines of the cross section of the band plate S are approximately parallel or have a U-shape that is slightly narrower at the top, and at the same time, the width of the U-shaped blank tube is made to be equal to or less than the lateral diameter of the roll hole shape of the subsequent first fin pass. do. FIG. 10 shows an example of the roll map in the rough and intermediate forming steps according to the present invention. The above description will be fully understood from this figure.

In the rough and intermediate forming process, as described above, by bending only the center part of the strip and forming without processing the both sides, rough and intermediate forming can be carried out very easily and rationally, and the second As shown in Figures g, h, and i, in the next step, the upper edge (edge part) of the U-shaped cross section is bent inward by fin pass forming, and the vertical diameter of the U-shape is reduced by overhang forming. The side lines 11, 11a of the U-shaped cross section of the strip plate bulge out laterally, so that a circular cross section can be formed reasonably easily.

According to such a forming apparatus, it is possible to most rationally and easily improve edge bendability, improve edge wrap and thickness increase, and obtain a good electrical resistance welded tube shape.

According to the apparatus of the present invention, in the rough and intermediate forming steps, a U-shaped blank tube is formed by bending the central part of the strip into a semicircular shape having a curvature greater than the finished tube curvature, and
By forming the lateral diameter of the formed raw pipe to a size smaller than the roll hole lateral diameter of the subsequent first fine pass roll, and when forming the U-shaped raw pipe with the first fine pass roll, By overbending the boundary between the pipe edge and the side part and between the base pipe side part and the bottom part to a degree greater than the product pipe curvature, and by performing processing to suppress bending of the base pipe side part, The contact between the side position of the raw tube (corresponding to the roll flange position in a two-roll type fine pass roll) and the roll is extremely weak compared to the conventional forming method.

In addition, in the second fin pass or third fin pass roll after the first fin pass, the part that was overbend-formed in the first fin pass roll is bent back and the side part of the raw pipe whose bending is suppressed is formed. Stretch molding is performed, but in this molding, the overbend part still has a bending curvature higher than the product curvature, so the first
As with the fine pass roll, the contact between the side position of the raw tube and the roll is extremely weak. Therefore, in this forming apparatus, roll flange flaws do not occur in the two-roll type fin pass roll.

In the case of a two-roll type fine pass roll in conventional forming equipment, roll flange flaws are likely to occur due to the strong contact between the side position of the raw pipe and the flange of the fine pass roll, and the occurrence of roll flange flaws is particularly difficult when the outside diameter of the pipe increases. It was becoming noticeable. For this reason, in the case of large-diameter sizes, a four-roll type fine pass roll is put into practical use.

In the case of a four-roll finpass, the stand structure is complicated, so it takes time to change and adjust the rolls, leading to a decrease in operating efficiency. However, with this forming device, for the reasons mentioned above, it is possible to use a two-roll type fine pass roll regardless of the outer diameter size of the production tube, and the simplified stand structure makes it easier to change and adjust the rolls. Improved availability is achieved.

〔Effect of the invention〕

As detailed above, the apparatus of the present invention is constructed with a small number of center bend rolls and cage rolls, can easily sequentially form a strip into the desired shape for each process, and has a simple structure. It is small, inexpensive, and easy to maintain. Moreover, it can be used for manufacturing many types of pipes.

Further, according to the device of the present invention, it is possible to average out the fin pass neutral axis reduction under load.
Figure 11 shows each Finpass stand 1F, 2F, 3.
A comparison of the allowable range of fin pass reduction in F is shown. In conventional molding equipment, a large reduction is required on the fin pass stand 1F to prevent edge waves, while on the other hand, the fin pass stand 3
With F, there is a problem that the fin pass reduction is extremely small, making it impossible to firmly grip the pipe.
And their range was also limited to an extremely small range. According to the apparatus of the present invention, as shown in FIG. 11, the reductions in each of the fin pass stands 1F, 2F, and 3F are averaged, their maximum values are lowered, and their ranges are further expanded.

Averaging the above fine pass appropriate reductions,
As a result of the reduction and the expansion of the appropriate tolerance range, automatic setting of the reduction becomes easily possible, and the required strength of the stand can be reduced. Furthermore, welding stability is achieved by increasing the gripping force of the final fin pass stand 3F.

Further, according to the present invention, the bendability of the edges of the raw pipe is improved, and when the edges are butted during welding, the edge end faces are in an I-shaped ideal butting state, and the occurrence of edge lapping is extremely reduced. FIG. 12 is a distribution diagram of the bending curvature in the circumferential direction of the tube after final fin pass forming, showing this fact. As is clear from Fig. 12, in the molding of the present invention, there is insufficient overhang at the side parts of the tube, but the edge part has an extremely good shape. The defect has been resolved.

Therefore, the drawbacks of conventional forming apparatuses, such as peaking phenomenon caused in the welding process due to insufficient edge bending, V-shaped butting phenomenon of edge end faces, and defective edge wrap caused by these, are completely overcome. .

Further, in the present invention, the increase in thickness at the edge portion during fine pass molding is reduced.

Furthermore, in the present invention, edge bending and overbending of the boundary between the edge part and the side part of the raw pipe are performed in the first fin pass forming, so it is necessary to proceed with edge bending in the final fin pass as in conventional forming. There is no. As a result, the width of the fin in the final fin pass forming can be increased, and the V-shape angle of the welded portion can be increased. Therefore, the generation of sparks at the edge portion in the pressure welding process can be significantly reduced, and the occurrence of welding defects due to this can be greatly reduced. In addition, the residual stress in the circumferential direction of the welded pipe is reduced by bending back the overbend portion in the first fin pass with a subsequent fin pass roll. For example, the measured value of the amount of spring back after squeezing when no welding was performed on the same pipe was as follows.

That is, when the width of the conventional device is W, the fin width of the final fin pass roll is as follows in the device of the present invention.
At this time, the opening width of the edge of the blank tube after forming, that is, the amount of spring back, was 3.1W in the conventional device and 2.4W in the device of the present invention. Therefore, the ratio (difference between spring back amount and fin width)/(fin width) is (3.1W-W)/W=2.1 in the conventional device, whereas it is (2.4W-W) in the device of the present invention. 1.7W)/1.7W=0.38.

In addition, in the present invention, since the contact between the tube side part and the flange part of the fine pass roll is weak in fine pass forming, a two-roll type fine pass roll can be applied to forming steel pipes with large outer diameters, and in that case, the roll flange No defects occur.
The ability to make two rolls makes it easy to adjust and preset the rolls.

[Brief explanation of drawings]

FIG. 1 is a plan view of an embodiment of the forming apparatus of the present invention, FIG. 2 is a cross-sectional view of a strip showing the process of forming a strip according to the method of the present invention, and FIG. 3 is a plan view of a conventional forming apparatus. , FIG. 4 is a perspective view showing changes in the profile of the strip during the tube forming process in the conventional forming apparatus and the forming apparatus of the present invention, and FIGS. 5 a, b, and c respectively show the edge forming roll stand of the present invention. A front view of the embodiment, FIGS. 6 and 7 are respectively front views of an embodiment of the center bend roll stand of the present invention, and FIG. 8 is a comparison of the sizes of the conventional breakdown roll and the center bend roll of the present invention. 9 is a front view of the center bend roll of the present invention, FIG. 10 is a roll map of an embodiment of the present invention, FIG. 11 is a graph showing fin pass reduction, and FIG. 12 is a tube circle of fin pass. It is a graph of bending curvature in the circumferential direction. S...Strip plate, 1CB, 2CB, 3CB, 4CB...
Center bend roll, 1F, 2F, 3F...fin pass roll, CR...cage roll, EF...
Edge Forming Roll.

Claims (1)

[Scope of Claims] 1. In an electric resistance welded pipe manufacturing apparatus that continuously roll-forms a strip and welds the formed end face through a fine pass roll, an edge portion of the strip is attached to the upper end of the roll-formed part. Edge forming rolls for inward bending are installed, and downstream there are center bend rolls that are equipped with twin rolls arranged symmetrically and coaxially at intervals in the strip width direction in pairs above and below the strip. A plurality of sets of center bend rolls are arranged in the longitudinal direction of the strip, and a pair of upper and lower center bend rolls of a single roll arranged at the center in the width direction of the strip is disposed downstream thereof, and A cage roll is continuously arranged on the lower surface of the strip edge from upstream of the upstream roll to downstream of the center bend roll of the most downstream single roll, and a group of fine pass rolls are arranged downstream of the cage roll. Forming equipment for ERW steel pipes. 2. The electric resistance welded steel pipe according to claim 1, wherein the distance between the twin rolls of the center bend roll made of the twin rolls is variable, and the arrangement position and height of the cage roll are variable. Molding equipment. 3. The electric resistance welded steel pipe forming apparatus according to claim 1 or 2, wherein the fin pass rolls include two upper and lower rolls.