JPH0199724A - Manufacture of thin-gage electric resistance welded tube - Google Patents

Abstract

PURPOSE:To improve the quality of a product and to make the equipment small in size by forming metallic band sheet with a group of end working type breakdown rolls and applying nearly a square formed section. CONSTITUTION:A group of rolls for forming an electric resistance welded tube is composed of end-working type breakdown rolls having the same diameter. In this case, the band sheet is formed from a flat band sheet sequentially to shapes of band sheets 17, 18, 19. Since forming is executed with the same barrel diameter D, occurrence of the difference in the peripheral speed when these band sheets come in contact with the respective rolls is very small. In addition, since the band sheet 19 is formed finally into a square shape, rolling is restrained from occurring. Hereby, the deviation from the center of the weld zone is prevented from occurring in the formed product and the forming roll can be made small in diameter. Accordingly, qualities of the product such as strength, air-tightness, etc., are improved and the equipment is made small in size, since the forming roll becomes small in size.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for manufacturing a welded tube, particularly an electric resistance welded tube, and more particularly a thin wall electric resistance welded tube.

A thin-walled electric resistance welded tube is a metal tube with a wall thickness of 0.13 am or less, for example, and is used for applications such as heat exchangers.

[Problems to be solved by conventional technology and invention]

Figure 1 shows the manufacturing process for a typical thin-walled electric resistance welded tube.

A flat metal strip 8 wound around an uncoiler 1 is formed by a series of forming rolls 2, the end surface of the strip is heated and melted by a heating coil 3 connected to a welding power source 7, and the squeeze roll 4
After that, the outer bead is cut off with a cutting tool 5 and straightened with a group of straightening rolls 6 to produce a tube 9 (FIG. 2). In the conventional method, as shown in the cross-sectional view of forming (so-called forming flower) in FIG.
1.

Step 12 and bend it into a round shape. The roll forming state at that time is shown in FIG. The strips 10, 11 and 12 are roll formed as shown in FIGS. 3(a), 3(b) and 3(c), respectively.

The rolls used for forming are shown in Figure 3 (a) and (b).
is a breakdown roll, as shown in Figure 3(c).
In this case, it is Finbas Roll. The breakdown roll holds the strip from the thickness direction and bends it. Fin pass rolls perform bending by holding the strip from the width direction with fins that protrude circumferentially at the center of the roll. Here, the roll in (a), which is one of the breakdown rolls, is a roll that is bent only at the curved portions (R portions) at both ends of the roll, and the middle roll body has a flat cross section and the strips are formed on both sides. There is no processing involved, just press and hold.

A roll like (a) is referred to herein as an "end-processed breakdown roll." The roll (b) is a breakdown roll with a round cross section corresponding to the shape of the strip being formed, and bends the entire cross section of the roll. However, in the forming method using rolls with a round cross section as shown in FIG. 3(b), since there is a difference in circumferential speed depending on the roll contact area, the rolling causes fluctuations in Furthermore, since the stripes are thin, the holding force exerted by the fins in the width direction (circumferential direction of the round shape) is extremely small, making it impossible to prevent this rolling.

Further, after welding, in the straightening roll group 6, the center of the welded portion tends to shift as shown in FIG. 4(b) due to thermal distortion caused by welding. These two conditions cause the strip to twist between each roll as shown in Figure 5(a), and when the twist exceeds the strength limit of the strip, wrinkles 1 as shown in Figure 5(b) occur.
5 occurs, and a welding defect 16 occurs during welding as shown in FIGS. 5(c) and 5(d). As a result, the strength of the electric resistance welded pipe becomes insufficient, and in the case of an airtight pipe, defects such as leakage occur, resulting in a significant deterioration in the quality of the pipe. Furthermore, this makes the flow of the strip in the manufacturing process unstable, forcing low-speed operation, and increasing the diameter of the forming rolls to reduce the peripheral speed difference prevents the production equipment from becoming larger. I can't.

SUMMARY OF THE INVENTION Therefore, the present invention provides a method for manufacturing a high-quality thin-walled electric resistance welded pipe without welding defects due to twisting of the strip by preventing rolling of the strip during roll forming and shifting of the center of the welded part. With the goal.

[Means to solve the problem]

In order to solve the above problems, the present invention provides 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 electrically resistance welded. The group consists of edge-worked breakdown rolls, characterized in that the shaped cross section is approximately square.

〔Example〕

The present invention will be explained in more detail below with reference to Examples.

In this example, as shown in FIG. 6, the edge is formed into a strip 17 using the roll in (a), and
Parts of the strip are sequentially bent to form the strip 18 using the rolls shown in (d), and formed into a square shape like the strip 19 using the rolls shown in (d).

The roll group for performing the forming consists of edge processing type breakdown rolls (FIGS. 6(a) to 6(d)). In this point, it is completely different from the conventional method, which also uses round cross-section breakdown rolls and fin pass rolls as forming rolls.

That is, by making the diameters of the roll bodies the same as shown in FIGS. 6(a) to 6(d), the stripes are
, 19, the circumferential speed difference in the roll contact portion of the strip occurs only at the bending portion (corresponding to both ends of the roll), so the circumferential speed difference is small. Furthermore, by making the strips square, rolling as shown in FIG. 4 can be suppressed. FIG. 7 shows a cross section of the strip forming flower (forming flower) of this example.

In the roll group 6, as shown in the straightened state in FIG. 8, even if thermal strain occurs during welding, the welded portion does not shift from its center.

In the method of this embodiment, as shown in FIGS. 9 and 10, in order to improve the strength of the formed strip, each side of the quadrangular strip cross section is curved outward ( R) can also be added.

The tube obtained with the substantially rectangular cross section as described above may be used as is, depending on the application, or may be further subjected to necessary roll forming according to the final product shape.

In this example, the diameter of the forming roll was changed from the conventional 273 mm.
It can be downsized to:

〔Effect of the invention〕

The method of the present invention prevents rolling during forming by making the difference in circumferential speed of the forming rolls extremely small compared to conventional methods, and by making the forming shape approximately square, it is possible to prevent center deviation of the welded part. Since twisting of the strip does not occur, welding defects do not occur, and therefore a thin-walled electric resistance welded tube having sufficient strength, airtightness, etc. can be manufactured. Furthermore,
Since the flow of the strip during the manufacturing process is stabilized, the operating speed can be increased. Furthermore, since the forming rolls can also be made smaller, the production equipment can be made smaller.

[Brief explanation of the drawing]

Fig. 1 is a process diagram showing the manufacturing process of a general ERW pipe, Fig. 2 is a cross-sectional view of forming the conventional ERW pipe manufacturing method, and Fig. 3 (a), (b), and (c) are A front view showing the molding situation in the conventional method for performing the molding shown in FIG.
Figure 4 (a) is a front view showing the rolling that occurs during forming in Figure 3 (b), and Figure 4 (b) is a front view showing the center shift of the welded part due to thermal strain during welding. Diagram (a)
, (b), (c), and (d) are respectively (
a) A cross-sectional view showing the state of twisting of the strip and (b) a state of wrinkles caused by the twist, (c) a perspective view showing a state of defective welding due to wrinkles, and (d) an enlarged cross-sectional view of the defective welding part. , Figures 6(a), (b), (c), and (d
) is a front view showing the molding situation in an embodiment according to the method of the present invention, FIG. 7 is a cross-sectional view of molding in an embodiment according to the method of the present invention, and FIG. A front view showing the state of correction in one embodiment, FIG. 9 is a sectional view of molding in another embodiment according to the present invention, and FIG. 10 shows a state of correction when the molding shown in FIG. 9 is performed. It is a front view. 1... Uncoiler, 2... Forming roll group, 3
... Heating coil, 4... Squeeze roll, 5.
...Bite, 6...Correcting roll group, 7...
・Welding power source, 8... Flat metal strip, 9... Round electric resistance welded tube, 10, 11, 12... Formed cross section of the strip, 13...
・Welded part, 14...Twisted state, 15...
Wrinkles, 16...Poor welding areas, 17, 18
, 19... Molded cross section of strip, 20... Square electric resistance welded tube.

Claims (1)

[Claims] 1. 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 electrically resistance welded, in which the rolls consist of edge-processed breakdown rolls, and the formed cross section is approximately square. A method for manufacturing a thin-walled electric resistance welded tube.