JP2788911B2 - Manufacturing method of thin wall ERW pipe - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a welded pipe, particularly an electric resistance welded pipe, and more particularly, to a thin wall electric resistance welded pipe.

A thin-walled electric resistance welded tube is, for example, a metal tube having a thickness of 0.13 mm or less.
Used for applications such as heat exchangers.

[Conventional technology]

FIG. 4 shows a manufacturing process of a general thin-walled electric resistance welded tube. The flat metal strip 2 wound around the uncoiler 1 is formed by a series of forming rolls consisting of a breakdown roll group 3 and a fin pass roll group 4, and the end face of the strip is heated by a heating coil 6 connected to a welding power source 5. It is heated and melted and pressurized by a squeeze roll 7 to perform end face butt welding. Thereafter, the outer surface bead is cut off by the cutting tool 8 and corrected by the sizing roll group 9 to manufacture an electric resistance welded tube having a predetermined sectional shape.
Fig. 5 Molded sectional view (so-called forming flower)
As shown in (1), the flat strip 2 is sequentially bent into a round shape as shown in (a), (b) or (c) by the breakdown rolls 17 and 18 and the fin pass roll 19. The breakdown roll performs bending by holding the strip in the thickness direction. The fin pass roll performs bending by holding the strip in the width direction with fins projecting circumferentially at the center of the roll.

In roll forming in which a flat metal strip is formed into a tubular shape, the springback of the metal strip increases as the sheet thickness decreases, and the welding of the end face of the metal strip becomes unstable. As methods for suppressing springback, there are known a method in which the pressing force of the fin pass roll is increased and an outer diameter is reduced, and a method in which the end portion of the metal strip is overformed in advance by forming a breakdown roll. However, in the latter case, the springback suppression is weak, so the former method is employed when the plate thickness is 0.4 mm or less. However, the thickness is even thinner
In the case of 0.15 mm or less, springback cannot be suppressed unless the pressing force of the fin pass roll is further increased. Therefore, by the pressure of the fin pass roll,
Buckling 20 shown in FIG. 9 is likely to occur at the end of the metal strip. When buckling occurs, subsequent welding becomes unstable.
Heretofore, the present inventors have proposed a method of making the fins of a fin pass roll rotatable as a method of preventing buckling (Japanese Patent Application No.
No. 266556) and a method of locally bending only a breakdown roll without using a fin pass roll (Japanese Patent Application No. 62-256376). In the latter method, buckling does not occur, so welding is possible, but since the drawing force that applies a pressing force with the fin pass roll does not work on the metal strip, the spring back is smaller than when using the fin pass roll. Control becomes insufficient. Also, the rigidity of the metal strip is poor. Therefore, welding becomes unstable. In general, roll forming in the production of an electric resistance welded pipe employs a forming method as shown in FIGS. 5 (a) to 5 (c). (A) of the figure shows edge forming by bending from the material end. (B) Center forming in which the material is bent from the center. (C) is a circular forming in which the entire material is bent at a single curvature. As the rolls, breakdown rolls (a) and (b) and a fin pass roll (c) shown in FIG. 6 are used. As can be seen from this, in general, in ERW pipe manufacturing,
First, a round tubular body is formed, and then a flat tube, an elliptical tube, a square tube, or a predetermined sectional shape is obtained. That is, when welding is performed, it is general to perform the welding with a round tubular body. Here, as the thickness becomes thinner, another problem occurs in addition to the problem described above. For example,
Even when it is desired to obtain a predetermined cross-sectional shape and a large outer diameter, the welding butt portion of the round tubular body has a large radius of curvature because the round tubular body is used for welding. Therefore, the rigidity of the welding butt portion decreases (the stiffness force is inversely proportional to the cube of the radius of curvature), and the welding butt portion is deformed by the pressing force during welding, as shown in FIG. Deformed weld butt 10b
Causes a step of butt to lower welding strength and deteriorate welding quality. In addition, the thinner the material, the lower the rigidity of the round tubular body (generally, it is inversely proportional to the double thickness), so the round tubular body is easily twisted and the welded portion 10a moves left and right with respect to the traveling direction. Cause rolling. For this reason, the relative height of both ends of the metal strip at the butt portion changes, causing a butt step, which also has the problem of reducing welding strength and deteriorating welding quality.

[Problems to be solved by the invention]

The present invention is based on the buckling of the end of the metal strip at the time of fin pass molding, the deformation of the end of the metal strip due to welding pressure during welding,
An object of the present invention is to provide a method for manufacturing a thin-walled electric resistance welded pipe in which rolling of a welded portion due to twisting of a metal strip formed into a tubular body is prevented.

[Means for solving the problem]

According to the present invention, there is provided a method for manufacturing a thin-walled electric resistance welded tube in which a metal strip is formed by a series of rolls and then subjected to electric resistance welding, wherein the rolls include a breakdown roll and a fin path downstream thereof. Rolls are formed, and by this fin pass roll, forming including drawing is performed before welding so that the end of the metal strip has a smaller radius of curvature than the other parts, and both ends are welded in that state This is achieved by a method for manufacturing a thin-walled electric resistance welded tube characterized by the following.

In the present invention, when forming a fin pass roll, a drawing process is performed by applying a pressing force to a metal strip to prevent springback. At that time, if the rigidity of the metal strip is small,
Buckling occurs at the end of the strip. Therefore, in order to increase the rigidity of the end portion of the metal strip, the radius of curvature of the end portion is reduced as compared with other portions.

According to the method of Japanese Patent Application No. 62-256376, since the forming is performed only by the breakdown roll, the suppression of the springback is insufficient and the rigidity of the end portion of the metal strip is relatively low.

The present invention is performed using a breakdown roll and a fin pass roll, and forming a metal strip end with a smaller radius of curvature than other portions in the fin pass roll forming,
By welding both ends in this state, the above-mentioned drawbacks are eliminated.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

An example of the arrangement of an apparatus for carrying out the method of the present invention will be described with reference to FIG.

In the figure, 1 is an uncoiler wound with a thin (thickness of 0.13 mm or less) flat metal strip, 2 is a thin flat metal strip, and 3 is a conventional thin metal strip formed into a tubular body. A group of breakdown rolls, in which the back surface of the metal strip is bent while making direct surface contact with the rolls. 4 is
This is a group of fin pass rolls for forming the metal strip formed by the breakdown rolls in accordance with the present invention, wherein the outer surface of the metal strip is subjected to bending while being brought into direct surface contact with the roll. 5 is a welding power source (high-frequency oscillator), and 6 is a high-frequency induction heating coil. Reference numeral 7 denotes a squeeze roll, which extrudes molten metal generated by heating and melting the edge end surface of the metal band formed into a tubular body by the heating coil 6. Reference numeral 8 denotes a cutting tool for cutting a weld bead, and reference numeral 9 denotes a group of sizing rolls for forming a tubular welded pipe into a predetermined sectional shape.

In FIG. 3, reference numeral 11 denotes a squeeze roll according to the present invention, in which the radius of curvature of the welding butt portion is reduced.
In the drawing, reference numeral 12 denotes an elliptic tube having a reduced radius of curvature at the butt portion, 12a a welded portion, and 12b a welded butt portion. (In the conventional method, a round tubular squeeze roll as shown in FIG. 7 was used.) FIGS. 1 (a) and 1 (b) show examples of the cross-sectional shape of the fin pass roll formed according to the present invention. ) And (c).

16A to 16C, reference numeral 16a denotes a fin pass roll formed into an elliptical shape having a reduced radius of curvature r of the welding butt portion, and 16b forms a shell shape having a reduced radius of curvature r at the welding butt portion. The fin pass roll 16c is a fin pass roll for forming into a square with a small radius of curvature r of the welding butted portion.

After the metal flat strip 2 is formed into a required tubular body by a group of breakdown rolls, the flat metal strip 2 is formed according to the present invention by a fin pass roll disposed downstream thereof. That is, they are formed into the shapes shown in FIGS. 2 (a), (b) and (c) by the fin pass rolls shown in FIGS. 1 (a), (b) and (c), respectively. It is welded at a butt portion having a radius of curvature (r).

FIG. 3 shows an arrangement state when welding is performed in an elliptical shape as a typical case. By the squeeze roll 11, the pressing force F
Is applied, the force F is transmitted to the elliptical tube 12, and the welding bead 12
a is formed. In order to form an elliptical tube at the time of welding, the squeeze roll 11 must be formed into an almost elliptical shape at the time of roll forming, or the squeeze roll 11 will not fit the formed material. As shown in (1), the edge portion is formed into a shape close to an elliptical shape with a small curvature r. Fin pass roll forming in a shape close to an elliptical shape suppresses springback in thin roll forming, so that a drawing force is applied to the formed material to suppress buckling of edges. Next, welding is performed with this elliptical shape. Since the elliptical minimum radius of curvature is used as the welded portion, the rigidity of the welded portion is increased. Therefore, the edge portion is not deformed by the pressing force, the distortion due to the welding heat is prevented, and the minimum radius of curvature exists at the upper and lower two points, which serves as a position for preventing the pipe from being twisted. And a high-quality thin-walled electric resistance welded tube free from poor butting can be obtained.

According to the test results performed by the inventor, 10
When using a round tube with a diameter of about mm, the plate thickness is 0.075 to 0.100 mm
In the brass material, buckling occurred when the radius of curvature of the end of the metal strip was 4 mm or more, and no buckling occurred when the radius of curvature was 3 mm or less. or,
As a result of welding the shapes of (a), (b) and (c) of FIG. 1 in the shapes of (a), (b) and (c) of FIG.
Since the minimum radius of curvature plays a role in positioning to prevent twisting, no rolling of the welded portion occurred. Then, the deformation 10b of the end portion of the metal strip shown in FIG. 8 did not occur at all.

The present invention is particularly advantageous when applied to the manufacture of an electric resistance welded tube having a wall thickness of 0.13 mm or less, and is particularly suitable when the wall thickness is 0.075 mm or more.

〔The invention's effect〕

As described above, according to the present invention, it is possible to manufacture a high-quality thin-walled electric resistance welded tube by preventing buckling and deformation of the end portion of the metal strip and twisting of the metal strip.

[Brief description of the drawings]

1 (a), 1 (b) and 1 (c) are partial cross-sectional views showing an example of performing a fin pass roll forming according to the present invention, and FIGS. 2 (a), 2 (b) and 2 (c) are , Each first
FIG. 3 is a cross-sectional view showing the shape of the fin pass roll formed by the fin pass roll forming shown in FIGS. 3 (a), 3 (b) and 3 (c). FIG. FIG. 4 is a process diagram showing a general manufacturing process of an electric resistance welded tube, and FIGS. 5 (a), (b) and (c) are moldings in a conventional method of manufacturing an electric resistance welded tube. FIGS. 6 (a), 6 (b) and 6 (c) show a breakdown roll forming ((a) and (b)) and a fin pass roll forming ((c 7) FIG. 7 is a front view showing an example of pressing a conventional strip formed into a round shape with a squeeze roll, and FIG. 8 is generated during the pressing shown in FIG. FIG. 9 is a partial cross-sectional view showing the deformation of the end portion of the metal strip, and FIG. It is a fragmentary sectional view showing the buckling of the metal strip end which occurs. DESCRIPTION OF SYMBOLS 1 ... Uncoiler, 2 ... Metal strip, 3 ... Breakdown roll (group), 4 ... Fin pass roll (group), 5 ... High frequency power supply for welding, 6 ... High frequency induction heating coil, 7 ... … Squeeze roll, 8… bite, 9… straightening roll (group), 10… round metal strip, 10 a… squeeze roll pressed butted part, 10 b… metal generated at butt Deformation of the end of the strip, 11… oval squeeze roll, 12… oval shaped metal strip, 12 a… butt, 12 b… end of metal strip, 13… round squeeze roll 14 metal shell strips, 15 metal strip strips, 16a oval fin path rolls, 16b shell fin path rolls, 16c square fin path rolls Roll, 17,18 ... Breakdown roll, 19 ... Round type Roll.

Continued on the front page (72) Inventor Fumio Kasai 1-1-1, Showa-cho, Kariya-shi, Aichi Japan Inside Denso Co., Ltd. (72) Inventor Yoshimitsu Yamaguchi 1-1-1, Showa-cho, Kariya-shi, Aichi Japan Nihon Denso Corporation Inventor Takayuki Suzuki 1-1-1 Showa-cho, Kariya-shi, Aichi Japan Inside Denso Co., Ltd. (56) References JP-A-63-286220 (JP, A) JP-A-58-196181 (JP, A) JP-A Sho 55-30327 (JP, A)

Claims (1)

(57) [Claims] 1. A method of manufacturing a thin-walled electric resistance welded tube in which a metal strip is formed by a series of rolls and then subjected to electric resistance welding, wherein the rolls comprise a breakdown roll and a fin pass roll downstream thereof. The fin pass roll is composed of a pair of opposed rollers, one of which is composed of a portion having a predetermined radius of curvature and a portion having a smaller radius of curvature. A method for producing a thin-walled electric resistance welded tube, comprising: performing drawing before welding so that an end portion has a smaller radius of curvature than other portions; and welding both ends in that state.