JPS62124031A - Production of welded pipe - Google Patents

Abstract

PURPOSE:To prevent the spring-back of a tubular body by forming a strip plate in circular or similar shape to circle after repeating the work of forming one part of the right or left side of the strip plate in the approximate radius to a product pipe and the other part in smaller radius than the product pipe in the right and left alternately at the forming finish step. CONSTITUTION:The rightside of a tubular body 2 is formed in the approximate radius to a product pipe and the left side in the smaller radius than the product pipe by passing the tubular body 2 of a strip plate through the upper and lower roll 3, 4 of a roll step I at the forming finish step of the strip plate. The left side of the tubular body 2 is then formed in the approximate radius to the product pipe and the right side in the smaller radius than the product pipe by passing through the roll step II. The tubular body 2 is further passed through in the order of the roll step II I alternately. After asymmetrical forming at the rolling step I, II it is passed through the rolling step III having the right and left symmetrical hole die in circular or similar shape to a circle. In this case the spring-back of the tubular body 2 is prevented because of the minute part having received the bend-back deformation of the tubular body 2 being formed with this bend again.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is a new welding method for suppressing spring banks and stabilizing welding when manufacturing welded pipes from strip materials such as titanium and stainless steel (carbon II). This invention relates to a method of manufacturing a tube.

(Prior art) ゛In manufacturing welded pipes, a strip material, which is a raw material, is passed between forming rolls and hole dies to form a tubular body, and the joining edges extending in the longitudinal direction on the circumference of the pipe are welded and integrated to form the pipe body. It is known how to obtain .

An example of a commonly used pipe-making line is shown in FIG. In the figure, a is an uncoiler, 1b is a breakdown roll, C is a fin pass roll, d is a sizing roll, and f
1 indicates a traveling cutting machine, g indicates a strip material, h indicates a pipe forming direction, and i indicates a welded part. There are several other types of role arrangements used, but they are essentially the same. In a normal pipe production line, 4
Forming up to welding is performed by a step-like breakdown roll, a three-step fin bath roll, and side rolls arranged between them.

In order to perform stable welding, it is necessary to minimize the springback of the tubular body during the forming process up to welding, and to suppress fluctuations in this spring huck as much as possible during pipe forming. is necessary.

If welding is performed with a large spring bank, the seam abutment becomes unstable, resulting in deterioration of the bead shape and the so-called seam misalignment problem in which the seam abutment rotates from side to side. In addition, the bead shape is easily affected by the magnitude of springback of the tubular body, and if the spring bank changes during pipe making, the bead shape will change.

In conventional pipe-making methods, springback of the strip has been mainly prevented by increasing the rolling reduction of the fin pass rolls. When the rolling force of the fin pass rolls is increased, compressive stress is generated in the circumferential direction of the tubular body 2 as shown in FIG. is suppressed. The hole shape of the fin pass roll is usually symmetrical, and fins 1 are provided at the portions that contact the edge portions of the strips to improve the butt shape of the edges. For this reason, the radius of the hole-shaped cross-section is necessarily made larger than the radius of the product tube as a whole, or the whole is made into an ellipse and only a small area is molded with a small radius. However, with these methods, it is not possible to sufficiently suppress the spring huck of the tubular body unless the reduction of the fin pass roll is increased to reduce the outer diameter. In addition,
In FIG. 5, 3 indicates an upper roll and 4 indicates a lower roll.

In addition to the method of reducing the outer diameter using fin pass rolls as described above, methods for suppressing springback during pipe making include the method of reducing the outer diameter by using fin pass rolls as described above. Some methods have been adopted to form the material to a radius of .

However, with this method, the forming area is limited to a narrow area near the edge of the strip, and the material formed at the beginning of the breakdown roll passes through the subsequent forming rolls and reaches the welding area. It cannot be said that this work is sufficiently effective in suppressing the spring bank of the tubular body before welding due to the fact that it is subjected to deformation during bending and undoing.

In forming titanium and titanium alloy tubes, since titanium is a metal with a large springback due to its material nature, it is necessary to particularly strengthen the rolling reduction with fin pass rolls. If the reduction of the fin pass roll is small, the springback of the tubular body before welding will increase, which will not only worsen the bead shape after welding, but also cause microcranks to occur in the bead due to the tensile force caused by the spring bank acting on the molten metal immediately after welding. Do it.

However, since titanium is also a metal that is very susceptible to seizure, the strong pressure of the fin pass roll to suppress springback causes seizure between the titanium tube surface and the roll, and between the strip edge and the fin.

To prevent seizure, fin pass rolls made of prepared alloy are used in titanium forming, but although these rolls can suppress seizure, the surface of the hole mold is severely abraded, resulting in the fins being damaged during pipe making. There is a problem that the reduction of the pass roll is not effective (and micro-cracks occur).In order to solve the various problems in the manufacture of titanium and titanium alloy tubes and suppress the springback of the tubular body, we have developed a band. A warm forming method in which a plate material is heated and formed during the finishing stage of forming has been proposed by the present applicant as Japanese Patent Application Laid-Open No. 57-68292.

(Problems to be Solved by the Invention) Except for the warm forming method for titanium or titanium alloy tubes, the springback of the tubular body is mainly controlled by reducing the outer diameter with fin pass rolls. In this case, as described above, it is necessary to apply a strong reduction until the tubular body is plastically deformed, and wear of the fins and roll holes becomes a problem. In addition, when forming a relatively thin tube, if the fin pass roll is used to strongly reduce the pressure, the tubular body will not conform to the roll hole shape, especially near the fins, and situations such as those shown in Figures 6 (1) and (II) will occur. This causes poor seam alignment.

Figure 7 (
1) As shown in (n), a fin roll (or roll without fins) having an elliptical or similar oval hole shape is used to roll the long axis direction from left and right ((I) in the same figure) to up and down ((I) in the same figure). A method can be considered in which each region of the tube circumference is sequentially shaped into a small radius by changing the shape shown in FIG. (II)). However, in this case, the left and right areas are molded at the stage shown in Figure (I), but when the upper and lower regions are molded at the stage shown in Figure (n), the radii of the left and right regions inevitably become larger, resulting in Since the tubular body is subjected to bending and undoing deformation, even if such forming is repeated, the spring back of the entire tubular body cannot be suppressed.

Warm forming methods for titanium or titanium alloys can suppress springback without applying strong pressure with fin bath rolls. However, this method has the economical problem of installing an additional heating furnace on the conventional pipe-making line and constantly using electricity, and the temperature of the forming rolls increases immediately after heating, resulting in roll marks. There is a problem that the number of times the roll must be polished increases.

(Means for Solving the Problems) In view of the above-mentioned problems, the present invention has been made especially for the purpose of suppressing spring banks and stabilizing welding. In a method of continuously manufacturing tubes by passing a strip material through a series of arranged roll hole molds and undergoing forming, welding, and shaping processes, the strip material is cut into a cross section perpendicular to the longitudinal direction of the forming line in the finishing stage of the forming. The shape is asymmetrical, and one of the left and right strips is formed to have a radius similar to that of the target product tube, and the other strip includes a portion having a smaller radius than the target product tube. After repeating the same molding process alternately on the left and right sides, a method was adopted in which a circular or similar symmetrical shape was formed.

(Example) Hereinafter, preferred embodiments of the present invention will be explained in detail.

A method of forming the strip to a radius smaller than the target radius of the tube in the forming and finishing stage, taking spring puncture into consideration, eliminates the springback of the tubular body without using external diameter drawing with fin bath rolls or warm forming. It was found that it is effective in preventing.

In this case, if a symmetrical hole-type roll like a conventional fin bath roll is used, it is difficult to form the strip material to a radius smaller than the tube radius in a sufficiently wide area, so the formed cross-sectional shape is asymmetrical. A method was adopted in which the left and right regions of the strip material were formed using separate rolls. The shape of the improved forming roll group of the present invention used in the new forming method and the details of the hole shape of each roll are shown in FIGS. 1 and 2, respectively. In the figure, 2 is a tubular body, 3 is an upper roll, and 4 is a tubular body.
5 indicates the lower roll, and 5 indicates the center of the forming line (center of the pipe making machine). In this method, (1) → (■) or (II
) The tubular bodies 2 are passed between the rolls 3.4 alternately in the order of -(I), and the left and right regions of the strip material are formed separately to a radius r1 smaller than the target tube radius. At this time, in order to stabilize the asymmetrical forming, it is important to keep the center 7 and edges 6, 6' of the strip material close to the center section 5 of the forming line by setting the area indicated by r2 as a radius close to the target tube radius. It turned out to be extremely effective.

Regarding the position of the strip edge portion 6 on the radius rl side,
During molding, it is necessary to avoid contact with the other molding part 6', and it is not possible to go far beyond the center of the molding line.

As a result, the radius r in the asymmetric hole cross section is r2
There exists a minute region (region indicated by a in FIG. 2) where <r≦■. In this example, in order to make the molding range of rl as wide as possible, molding was performed with this region a as a straight line, but in this minute region, the tube circumference was slightly deformed by bending back. And (1) in Figures 1 and 2,
After the asymmetric forming of step (n), the roll (III) of FIG. It was found to be effective in preventing springback in tubular bodies.

Note that it is also possible to give the a region a curvature within a range that does not significantly reduce the molding area at rl. Regarding the radius r1 in left-right asymmetric molding,
It is necessary to consider the amount of springback according to the material properties of the strip material and the dimensions of the pipe and adopt an appropriate RL.

According to the theoretically derived relational expression, the bending radius R of the thin plate,
The relationship between R and the post-springback radius R is approximately given by the following equation in the case of simple mortise.

Y: Yield strength of material (kg f/if) E: 〃
Young's modulus (〃) Also: As the bending radius r1 in thin plate thickness asymmetric forming, the bending radius r1 is such that the material becomes the target radius of the tube after springing.
If we adopt , then the theoretical rl can be obtained from equation 0 as follows.

d: Target pipe outer diameter (1 m) t: Pipe wall thickness (dragon) rl: Small diameter side radius (roll hole type radius) (1 m) Improved type of the present invention as shown in Figs. 1 and 2 As a result of conducting a forming test by changing the rl of the forming roll group, it was found that the springback of the tubular body after forming was not sufficiently reduced by the rl derived from the theoretical formula (■), and it was necessary to reduce the rl to less than the value given by the formula 0. I found that it was necessary. From the results of specific examples described later, the following results were obtained as an appropriate range of rl.

However, d/2# r 2 r2 Two large diameter side radius (roll hole type radius) (lII)
The reason for setting the lower limit of rl in the above formula 0 is that if molded with a value below this value, the tubular body will have a markedly elliptical shape after molding.
This is because not only does it interfere with welding, but also the roundness cannot be sufficiently corrected in the subsequent regular forming process.

On the other hand, if the upper limit of rl is exceeded, the spring bank of the tubular body will become large, the seam butt at the welding point will become unstable, and the bead shape will deteriorate, or (
(In the case of titanium) This shows the limit value at which microcracks and cracks occur in the weld bead.

The method of the present invention can be carried out at any position on the pipe-making line shown in FIG. 4, for example, between the conventional fin pass rolls and the welding area, but it is preferable to place it immediately before welding. In addition, asymmetric forming is shown in the above example by forming in three stages (I) to (nl), but if the forming in each stand is large (when rl is smaller than r2), the number of roll stages is added. It is also possible to perform intermediate molding. In this case, the above-mentioned intermediate forming is, for example, the forming (I) shown in FIG.
)-(II) alternately, (rlo 〉r
l) That it may be formed as shown in ((I)"-([[
)"→N)→(■))) In this case, rl of the above formula 0 gives the bending radius at the stage of maximum forming.

More specific examples of the present invention will be described below.

A non-driven upper and lower roll stand is installed between the final fin pass roll and the squeeze roll on a conventional pipe making line as shown in FIG. 4, and the improved forming roll group of the present invention as shown in FIG. (t), (n) (III) were attached and a molding test was conducted. The target outer diameter is a typical 25.4φ++
n, and the band plates were made of titanium with different strengths and wall thicknesses. Regarding the hole shape of the forming roll group, '1+ r2+ a shown in FIG. 2 was varied variously. r3 is 12
．． It was set at a constant value of 7 mm. In order to confirm the springback prevention effect of these improved forming roll groups, the rolling reduction of the finpass rolls was weakened to avoid the reduction in springback caused by the conventional method of reducing the outside diameter with the finpass rolls.

Other forming methods, welding methods, etc. were performed using conventional methods. The degree of spring bank of the tubular body after molding was evaluated by cutting out a tubular body sample before entering the squeeze roll and determining the seam opening amount δ (see FIG. 3) of this sample.

In this test, normal welding pipe production was also performed under each of the above forming conditions.

Next, the test results are shown in Tables 1 and 2.

(Effects of the Invention) In the conventional method, spring hacking of the tubular body after forming was prevented by strong pressure (outer diameter drawing) with fin pass rolls. However, the method of the present invention is completely different, and the greatest feature is that the springback can be made even smaller than the conventional method without applying strong pressure.

From the above characteristics, the following effects in terms of industrial technology were obtained.

■ Since strong pressure is not applied, the surface pressure between the strip material and the rolls is reduced, reducing wear on the rolls and fins, resulting in lower roll costs.

■ Similarly, by reducing the surface pressure, roll scratches on the product surface are reduced (improvement of M product quality).

Therefore, it is particularly effective for molding materials that are prone to seizure, such as titanium.

■ In the conventional fin-pass strong reduction method, the tubular spring bank was highly sensitive to roll wear, requiring frequent roll adjustments. However, in this method, not only the roll wear itself is small, but also the springback fluctuation due to wear is small, so the roll adjustment interval is extended and stable bead quality can be obtained for a long time.

■ Compared to conventional methods, the springback of the tubular body can be further reduced, resulting in more stable welding and improved bead quality. In addition, it is possible to prevent micro-cracks at the bead portion that occur when pipe-forming materials with large springback such as titanium at high speed, making it possible to speed up pipe-manufacturing.

[Brief explanation of drawings]

Figures 1 to 3 are drawings of forming rolls, etc. used in the method of the present invention, and Figure 1 shows the improved forming roll group.
The figure shows the hole shape of the same group of holes, and FIG. 3 shows the definition of the parameter δ representing the springback of the tubular body after molding. FIG. 4 is an explanatory diagram of one example of a pipe-making line in which the method of the present invention is implemented, and FIGS. 5 to 7 are explanatory diagrams of conventional examples. 2... Tubular body, 3... Upper roll, 4... Lower roll, 5... Center of forming line (center of pipe making machine) 6
．． 6°... hoop edge, 7. ... hoop center r1
...Small diameter side radius, r2...Large diameter side radius.

Claims (2)

[Claims] (1) In a method of continuously manufacturing tubes by passing strip material through a series of roll hole molds arranged in tandem and undergoing forming, welding, and shaping processes, the strip material is passed along the length of the forming line in the finishing stage of said forming. In a cross section perpendicular to the direction, there is a portion that is asymmetrical, and has a radius similar to that of the product tube targeting one of the left and right strips, and a radius smaller than that of the product tube targeting the other strip. Shaped to contain;
A method for manufacturing a welded pipe, which comprises repeating similar forming operations alternately on the left and right sides, and then forming a circular or similar left-right symmetrical shape. (2) The center part of the strip material and both edges thereof in a cross section perpendicular to the longitudinal direction of the forming line are in a straight line,
2. The method of manufacturing a welded pipe according to claim 1, wherein the center of the strip material and both edges thereof are located at or near the center of the forming line.