JPH04300031A - Manufacture of welded tube - Google Patents

Abstract

PURPOSE:To offer the means for preventing seizure of a roll at the time of forming cylindrically a metallic hoop by the roll. CONSTITUTION:The lower roll of forming rolls is divided into two. As for the lower rolls 2 divided into two, the direction being orthogonal to the advance direction of a metallic hoop and the rotation axis form an inclination angle beta, and this inclination angle beta can be adjusted. Also, as for this lower roll, the width direction of the metallic hoop and the rotation axis form a cross angle alpha in the plane being orthogonal to the advance surface of the metallic hoop. At the time of forming the metallic hoop, a relation of the inclination angle beta, a feed speed V of the metallic hoop, wall thickness T of the metallic hoop, and yield strength sigmay of the metallic hoop is set to sinbeta.V.sigmay.T<2=25000(m/min.kg/mm<2>.mm<2>). In such a way, a welded tube whose surface quality is satisfactory is obtained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a welded pipe by continuously forming a metal strip into a cylindrical shape.

0002

BACKGROUND OF THE INVENTION For example, welded pipes such as electric resistance welded pipes are manufactured by first gradually forming a flat metal strip into an arc shape in a roll forming step, and then forming the arc-shaped metal band into a tube shape in the final step.
It is manufactured by melt-welding the abutting edges in the pressure-welding step. In this step of roll forming into a tubular shape, so-called roll bending is performed, and the first step is generally called breakdown, which is forming into an arc shape, and then that arc is shaped into an even smaller radius. The final step is called the fin pass, in which a butting edge of the tubular shape is formed.

[0003] In the roll forming of such welded pipes,
In order to obtain the desired product shape, edge bending performed on both ends of the metal strip in the width direction is extremely important.
If this edge bending is not performed properly, it will cause a decrease in material yield due to quality deterioration of the welded part.

FIG. 4 shows the state of contact between the roll and the material when edge bending is performed using a normal horizontal roll stand. In the figure, 1 indicates an upper roll, 2 indicates a lower roll, and 3 indicates a metal band. Here, the contact between the lower roll 2, which is a grooved roll, and the metal strip 3 first comes into contact with both edges (points A and B) of the metal strip 3 at the roll entrance. Then, the lower roll 2 pushes the metal band 3 at points A and B, and wraps the metal band 3 around the upper roll 1.
The edge of the metal strip 3 is bent. However, when manufacturing thin-walled and thick-walled welded pipes using this method, the metal strips from thin to thick are usually formed using the same roll, so it is not possible to bend the edges of thin-walled materials. There are some difficulties. FIGS. 5(A) and 5(B) are a state diagram when forming a thin-walled material and a state diagram during forming a thick-walled material, respectively.

That is, in the case of thick-walled materials, it is possible to bend the edge of the metal strip 3 caught between the upper roll 1 and the lower roll 2, as shown in Figure (B), but for thin-walled materials, In this case, as shown in Figure (A), the edges cannot be bent. On the contrary, the edge of a thin material tends to stretch a little compared to the center of the metal band, and this stretched edge part bends and becomes wavy, resulting in poor welding. For example, if the ratio t/D between the wall thickness t and the outer diameter D is less than 1.5%, undulations will occur at the side edges of the metal band during forming. Such a phenomenon is usually called edge buckling. In addition, as a bending method for edges,
Even with the method known as the W-bending method disclosed in Publication No. 54, thin to thick materials are formed using a fixed lower roll, so it is not possible to sufficiently pre-bend the edges of thin materials. Can not.

[0006] Therefore, the present inventor has proposed an apparatus that can sufficiently perform bending on both ends of a metal strip in the width direction (Japanese Patent Laid-Open Nos. 44217-1982 and 10-1999).
No. 4419, Japanese Unexamined Patent Publication No. 2-197329). As shown in Fig. 1, this device consists of a roll 2-1 in which a lower roll of a horizontal roll is divided in the direction of the rotation axis, and these two rolls have a direction perpendicular to the direction of movement of the metal strip and a rotation axis that is inclined. This inclination angle can be adjusted, and the width direction of the metal band and the roll rotation axis form an intersecting angle α in a plane perpendicular to the plane of movement of the metal band. FIGS. 2A and 2B are state diagrams of a vertical cross section including the lower roll axis when forming a thin material (thickness: 1 mm) and a thick material (thickness: 10 mm) using the above-mentioned apparatus, respectively. In other words, by adjusting the inclination angle β of the divided lower roll 2-1, the interval between the upper and lower rolls can be adjusted to be almost the same as the wall thickness, regardless of whether the material is thin or thick. Can be done.

[0007]

However, the method of dividing the lower roll of the horizontal roll of breakdown into two and imparting an angle of inclination to the direction of movement of the metal band also has the following problems. That is, since the lower roll has an inclination angle with respect to the feeding direction of the metal strip, a speed difference ΔV is generated between the feeding speed V of the metal strip and the circumferential speed VR of the roll as shown in FIG. It has been found that roll seizure occurs when this ΔV is large. When this roll seizure occurs, it not only becomes difficult to continue molding, but also causes deterioration of the surface quality, and if the roll seizure is significant, the product becomes defective.

The present invention was made to solve the above-mentioned problems and to make it possible to manufacture high-quality welded pipes.The present invention was made to solve the above-mentioned problems and to make it possible to manufacture high-quality welded pipes. This paper attempts to propose a method for manufacturing pipes.

[0009]

[Means for Solving the Problems] The present invention comprises a group of forming rolls for continuously forming a metal strip into a cylindrical shape, and a welding means for joining both edges of the metal strip formed into a cylindrical shape. , the forming roll of at least one stand of the breakdown stand of the forming roll group consists of two or more rolls in which the lower roll of the horizontal roll is divided in the direction of the rotation axis, and at least two rolls on both sides of the rolls are formed of metal strips. A direction perpendicular to the direction of movement of the metal band and the rotation axis form an inclination angle β, and the inclination angle β is adjustable, and the width direction of the metal band and the rotation axis In a method of manufacturing a welded pipe using equipment arranged so that the angle α forms a crossing angle α, the relationship among the inclination angle β, the feeding speed V of the metal band, the thickness T of the metal band, and the yield strength σy of the metal band is determined. , sinβ・V・σy・T2≦25000(m/
The gist of this is to set the value to 1.5 kg/mm2/mm2).

0010

[Operation] In this invention, in order to prevent roll seizure, the relationship between the inclination angle β of the lower roll, the feeding speed V of the metal strip, the wall thickness T of the metal strip, and the yield strength σy of the metal strip is kept within a certain range. The reason for setting this is as follows. That is, factors that influence roll seizure are considered to be the relative speed difference between the roll and the metal band and the surface pressure applied to the roll. The relative speed difference between the metal bands is expressed as the product of the feeding speed V of the metal band and the sine of the inclination angle β. Further, the surface pressure applied to the roll is generally proportional to the product of the square of the wall thickness and the yield strength σy. Therefore, if the product of the relative speed difference and the roll surface pressure is below a certain value, it is determined that roll seizure will not occur, and as a result of the experiment, sin β・V・σy・T2 is set to 25000 (m/min・K
It was discovered that roll seizure can be prevented by setting the amount within the range of g/mm2·mm2) or less.

[0011]

[Example] Using a 2-inch electric resistance welding tube mill, roll forming was performed by applying the method of the present invention, and the presence or absence of seizure was examined at that time. The results were compared with the case where the conditions of the present invention were not met. It is shown in Table 1. In this example, carbon steel is used as the material, and the yield strength is approximately 30Kg/mm2, 40Kg/mm2, and 50Kg/mm.
I followed the second one. The presence or absence of roll seizure was determined by observing the surface of the lower roll 10 minutes after the start of pipe manufacturing. As is clear from the results in Table 1, sinβ
- There was no burn-in in all cases where V・σy・T2≦25000.

0012

[Table 1]

[0013]

[Effects of the Invention] As explained above, according to the method of the present invention, edge forming is not only carried out satisfactorily for both thick and thin materials, but it is also possible to effectively prevent roll seizure, which has been a problem in the past. Therefore, it is possible to stabilize the molding and improve the surface quality, which has a great effect on the production of welded pipes.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram showing the arrangement of upper and lower rolls of a forming device of a welded pipe manufacturing apparatus that is the object of the present invention, in which (A) is a front view, (B) is a side view, and (C) is a plan view. be.

FIG. 2 is a schematic diagram showing the state during molding of thin-walled materials and thick-walled materials by the same molding device; (A) is a state diagram during molding of thin-walled materials;
(B) is a state diagram during thick-walled material molding.

FIG. 3 is an explanatory diagram showing the difference between the feeding speed of the metal strip and the circumferential speed of the roll by the same device.

FIG. 4 is a schematic explanatory diagram showing a contact state between a roll and a molded material according to a conventional method.

FIG. 5 is a schematic diagram showing the state of forming thin-walled materials and thick-walled materials by the conventional method, (A) is a state diagram when forming thin-walled materials, (B)
is a state diagram when forming a thick-walled material.

[Explanation of symbols]

1 Top roll 2 Lower roll 3 Metal band

Claims (1)

[Claims] 1. A method comprising a forming roll group for continuously forming a metal strip into a cylindrical shape, and a welding means for joining both edges of the cylindrical metal band formed by the forming roll group, The forming roll of at least one stand of the breakdown stand of the group consists of two or more rolls in which the lower roll of the horizontal roll is divided in the direction of the rotation axis,
At least two of the rolls on both sides have an inclination angle β between a direction perpendicular to the traveling direction of the metal strip and the rotation axis,
In a method for manufacturing a welded pipe using a device in which the inclination angle β is adjustable and is arranged so that the width direction of the metal band and the rotation axis form an intersect angle in a plane perpendicular to the plane of travel of the metal band. , the relationship among the inclination angle β, the feeding speed V of the metal strip, the thickness T of the metal strip, and the yield strength σy of the metal strip is expressed as sinβ・V・σy・T2≦25000 (m/min・K
g/mm2・mm2).