JP2002153912A - Method for manufacturing welded tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a welded tube for dissolving instability when bending a metallic strip and forming it into an open tube by suppressing the production of defective products just after changing rolls and also suppressing the generation of rolling in a method for manufacturing the welded tube by bending the heated metallic strip, forming it into the open tube and performing electric resistance welding to the bent and formed open tube, furthermore, to provide the manufacturing method of the welded tube by which the generation of edge waves is suppressed. SOLUTION: By continuously arranging a plurality of stands having a pair of side rolls having a circular-arcuate rolling face respectively and using flanged rolls having the flange parts which are continued to the rolling face for the side rolls of at least the most upstream stand, the metallic strip is bent and formed into the open tube. The formation rate α at the most upstream stand is controlled to <=35 %. α=R0/R1×100 (%), where, R0 is the radius of curvature of the welded tube and R1 is the radius of curvature of the rolling face of the side roll at the most upstream stand.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for manufacturing a welded pipe. More specifically, the present invention relates to a method for manufacturing a welded pipe by hot forming and electric resistance welding.

[0002]

2. Description of the Related Art For example, as a method of manufacturing a steel pipe having a relatively small diameter from a steel strip as a raw material, there are a wrought pipe manufacturing method in which a pipe is formed hot and an electric resistance welding pipe method in which a pipe is formed cold.

[0003] The wrought tube method has the advantages of high productivity because it is formed by hot working, and has the advantage that the hardened abnormal structure is not retained in the welded portion and the metal structure in the circumferential direction is made uniform. Since it is molding, there is an advantage that processing is easy and the number of stands used for molding is small. However, on the other hand,
There is a disadvantage that the strength of the weld is weak.

[0004] On the other hand, the electric resistance welding pipe forming method has an advantage that the strength of the welded portion is high because it is formed in a cold state.
There is a disadvantage in that an abnormally hardened structure is retained in the welded portion and the metal structure in the circumferential direction tends to be non-uniform.

[0005] Therefore, as a pipe manufacturing method capable of making use of the respective advantages of the forged pipe manufacturing method and the electric resistance welding pipe manufacturing method and compensating for the disadvantages, Japanese Patent Publication No. 2-246 is disclosed.
No. 06 discloses that a steel strip heated to a temperature of 500 to 900 ° C. is formed into an open pipe by an electric resistance welding pipe forming apparatus including a breakdown roll, a side roll, a fin pass roll, a high frequency induction coil, and a squeeze roll. , welded to the main pipe, then the method for producing a steel pipe of the main pipe and the product pipe was rolled in by heating to a ₃ transformation point or above the temperature pipe reducing rolling apparatus is disclosed. The publication also states that
It is described that a mandrel having an inner bead cutting blade or a bead press roller attached to the tip is inserted from an intermediate position between breakdown and a side roll to remove the inner bead.

[0006]

[Problems to be Solved by the Invention] Japanese Patent Publication No. 2-24606
In the method disclosed in the above-mentioned publication, when manufacturing steel pipes of a plurality of sizes from a mother pipe of one size, the transfer of the steel strip is stopped and the rolls of the pipe drawing rolling device are replaced, but immediately after the start of the transfer. Since the temperature of the steel strip has decreased, bending by a breakdown roll is required. At this time, as described in Japanese Patent Publication No. 2-24606, a mandrel is inserted from an intermediate position between the breakdown roll and the side roll to remove the inner surface bead.
However, since the insertion of the mandrel requires a length of about 5 m or more, the distance between the breakdown roll and the side roll is long, and the molding of the side roll into an open pipe tends to be unstable. .

[0007] Therefore, usually, during the period in which the temperature of the steel strip is lowered immediately after the roll change, the mandrel is not inserted and the open pipe is formed using the breakdown roll, the side roll, and the fin pass roll. And then
When the temperature of the steel strip reaches a predetermined value or higher, the mandrel is inserted with the breakdown roll removed, and the open pipe is formed using only the side roll and the fin pass roll. However, when a steel pipe is manufactured by this method, there are the following problems a to c.

A. During the period in which the temperature of the steel strip immediately after the roll replacement is low, since the mandrel is not inserted, the inner surface bead cannot be removed, and defective products are generated. b. When the breakdown roll is not used, the so-called rolling, in which the steel strip slides in the width direction, occurs during the bending forming by the side roll, and the forming may be unstable.

C. The phenomenon that both edges of the steel strip undulate in the longitudinal direction during forming with side rolls (hereinafter referred to as edge waves)
In particular, it may occur when forming a thin steel strip.

An object of the present invention is to provide a method for manufacturing a welded pipe by bending a heated metal strip into an open pipe and subjecting the bent-formed open pipe to electric resistance welding to suppress the occurrence of defective products immediately after a roll change. Another object of the present invention is to provide a method for manufacturing a welded pipe that suppresses the occurrence of rolling and eliminates instability when bending and forming an open pipe. Also,
An object of the present invention is to provide a method for manufacturing a welded pipe, which can further suppress the generation of edge waves.

[0011]

Means for Solving the Problems In order to solve the above problems, the present inventors have studied a method of forming an open pipe without using a breakdown roll, and have obtained the following findings.

A. A plurality of stands each having a pair of side rolls having an arc-shaped pressing surface are continuously arranged, and at least as a side roll of the most upstream stand, a brim having a brim portion continuously formed on the pressing surface is provided. By using a roll and restraining both edges of the metal strip with the collar, the steel strip can be stably formed into an open pipe without using a breakdown roll.

B. In other words, by using the flanged roll at least at the most upstream stand, both edges of the metal band are restrained by the brim portion, the biting property when the metal band is bitten by the side roll is stabilized, and furthermore, the bending forming Also in the process, the occurrence of so-called rolling, in which the metal band slides on the pressing surface, is suppressed, and the forming into an open pipe is stabilized.

C. In forming with a brim roll, new problems such as a biting out of material from a roll gap portion and an increase in thickness at both edges of a metal band may occur. The parameters L1 and L2 defined by the following equation are determined according to the shape of the flanged roll, the dimensions of the metal band, the roll gap, etc., by L1 ≧
By adjusting the factors that affect the values of the parameters L1 and L2 so as to satisfy the relationship of L2, it is possible to suppress the occurrence of biting that causes surface defects and the occurrence of thickening that causes welding defects. Can be.

L1 = πRP (α + β) / 90 L2 = B · RP / (RP−t / 2) where β = Arcsin (G1 / RP) −Arcsin ｛(G1-G) / RP｝, α: pressure surface G1: the distance between the straight line passing through the center of curvature of the pressing surface and parallel to the roll axis and the flange end of the pressing surface, G: 1/2 of the roll gap B: the width of the metal band, RP: the pressing surface Radius of curvature, t: thickness of the metal strip.

D. The edge wave is generated when both edges elongate and deform in the longitudinal direction at a stage prior to the bending process, and at the stage subsequent to the bending process, the both edges which have been stretched and deformed cannot be reduced to the original length and buckle. The edge wave can be suppressed by setting the forming rate α in the most upstream stand to 35% or less. Here, the forming ratio α is defined by the following equation.

Α = R0 / R1 × 100 (%) where R0 is the radius of curvature of the welded pipe, and R1: the radius of curvature of the pressing surface of the side roll in the most upstream stand.

The present invention has been completed based on the above findings, and the gist thereof is as follows. (1) A heated metal strip is bent into an open pipe by a hot forming apparatus having a plurality of stands each having a pair of side rolls each having an arcuate pressing surface, and then the open pipe is electrically connected to the open pipe. A method for performing resistance welding to form a welded pipe, wherein a flanged roll having a flange portion continuous on the pressing surface is used as a side roll of at least the most upstream stand of the plurality of stands. Manufacturing method.

(2) The method for manufacturing a welded pipe according to the above item (1), wherein a forming ratio α of the most upstream stand defined by the following equation is 35% or less. α = R0 / R1 × 100 (%) where R0 is the radius of curvature of the welded pipe, and R1 is the radius of curvature of the pressing surface of the side roll in the most upstream stand.

(3) In the stand having the above-mentioned flanged roll, the parameters L1 and L2 defined by the following equations are L
(1) wherein the relationship of 1 ≧ L2 is satisfied.
Item or the method for producing a welded pipe according to item (2).

L1 = πRP (α + β) / 90 L2 = B · RP / (RP−t / 2) where β = Arcsin (G1 / RP) -Arcsin {(G1-G) / RP}, α: pressure surface G1: the distance between the straight line passing through the center of curvature of the pressing surface and parallel to the roll axis and the flange end of the pressing surface, G: 1/2 of the roll gap B: the width of the metal band, RP: the pressing surface Radius of curvature, t: thickness of the metal strip.

(4) The method for manufacturing a welded pipe according to the above item (3), wherein the roll gap of the stand having the flanged roll is adjusted so that the above relationship is satisfied.

[0023]

Embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, the metal strip is a steel strip, and the hot forming apparatus has two stands each having a pair of side rolls, that is, a first stand which is the most upstream stand and a downstream of the first stand. 2nd arranged in
The case where a stand is provided is taken as an example.

FIG. 1 is a schematic diagram showing an example of a production line for a welded pipe according to an embodiment of the present invention. Symbol 10 is a steel strip,
11 is a heating furnace, 12 is a hot forming apparatus, 13 is a first stand, 13a is a roll with a collar, 14 is a second stand, 1
4a is a collarless roll, 15 is a fin pass roll, 16
Denotes a high frequency induction coil, 17 denotes a squeeze roll, 18 denotes an open pipe, and 19 denotes a welded pipe.

As shown in FIG. 1, the welding pipe manufacturing line includes a heating furnace 11, a hot forming apparatus 12, a high-frequency induction coil 16, and a squeeze roll 17 sequentially from upstream to downstream. .

The heating furnace 11 has a function of heating the steel strip 10 to a predetermined temperature at which the steel strip 10 can be formed. The heating method is not particularly limited, but usually a gas heating method is used. The hot forming apparatus 12 includes a first stand 13, a second stand 14,
The first stand 13 includes a pair of flanged rolls 13a that are vertical rolls, and the second stand 14 includes a pair of collarless rolls 1 that are vertical rolls.
4a.

FIG. 2 is a front view schematically showing an example of the shape of the flanged roll 13a. Reference numeral 21 denotes a pressing surface, 22 denotes a flange portion, and 23 denotes a flange end. Α is the center angle of the pressing surface with respect to the arc, RP is the radius of curvature of the pressing surface, O is the center of curvature, G1 is the distance between the straight line passing through the center of curvature O and parallel to the roll axis and the flange end 23, β is the flange end The angle formed between the straight line connecting the center of curvature 23 and the center of curvature O and the straight line parallel to the roll axis, γ is the angle of inclination of the flange, and the angle formed between the portion contacting the edge of the steel strip and the direction perpendicular to the roll axis. Represents

As shown in FIG. 2, the rimmed roll 13a
Has an arc-shaped pressing surface 21 having a radius of curvature: RP and a central angle: α, and a linear flange 22. Collar part 22
Is formed following the pressing surface, and when bending the steel strip,
It acts to constrain the edge of the steel strip so that the steel strip does not slide along the pressing surface. In other words, the shape is not limited to a specific shape as long as such an effect is exhibited. For example, the inclination angle γ
May have a contact portion where the angle is 0 degrees or more and 60 degrees or less. FIG. 2 shows the brim portion having a linear shape, but may have an arc shape.

The radius of curvature RP and the central angle α in FIG.
It is appropriately determined according to conditions such as the outer diameter and the wall thickness of the welded pipe.
Usually, (α + β) is set to 30 degrees or more and 90 degrees or less. FIG. 3 is a schematic diagram showing a state in which a pair of flanged rolls are arranged in a stand and a cross section of a steel strip as a material to be formed. Reference numeral 10 is a steel strip, G is １ ／ of the roll gap, and the same elements as those in FIG. 2 are represented by the same reference numerals.

As shown in FIG.
a, 13a are provided with their respective rotation axes perpendicular to the width direction of the steel strip. The steel strip 10 has a predetermined roll gap G.
Then, the brim portions 22, 22 of the brim rolls 13a, 13a
The pressing surfaces 21 and 21 are bent into a shape substantially along the pressing surface.

FIG. 4 is a front view schematically showing an example of the shape of the brimless roll 14a. 2 are denoted by the same reference numerals. As shown in FIG.
Has a substantially semi-circular pressure surface having a radius of curvature: RN.
The radius of curvature RN is appropriately determined depending on conditions such as the outer diameter and wall thickness of the welded pipe. The rotation axis of the collarless roll is provided in parallel with the rotation axis of the collared roll.

The fin pass roll 15 is a horizontal roll at the end of the open tube forming, and has a function of performing angle adjustment, finish forming, and centering of both edges of the steel strip by using a fin plate attached to the upper roll.

The high-frequency induction coil 16 is used to heat both edges of the steel strip formed into an open pipe at a temperature equal to or higher than the electric resistance welding temperature, for example, 13
It has a function of heating to a temperature of 00 ° C or higher. The squeeze roll 17 adjusts the upset amount and the butt shape of both edges heated to a temperature equal to or higher than the electric resistance welding temperature,
Has the function of butt welding.

Next, the method of the present invention will be described with reference to FIGS. The steel strip 10 heated to a predetermined temperature capable of being formed by the heating furnace is sent to a hot forming apparatus 12, and a first stand 13 having a pair of flanged rolls 13a and a second stand having a pair of flangeless rolls 14a. The open tube 18 is formed by the stand 14 and the fin pass roll 15. That is, as shown in FIG. 3, the steel strip 10 is pressed from the width direction in a state where both edges of the steel strip are restrained by the brim portions of the brim rolls 13a, 13a. It is shaped into a curved shape in the width direction, and further pressurized by a brimless roll, the bending deformation in the width direction progresses, and the tube becomes an open pipe after being pressed by the fin pass roll 15.

If the degree of bending of the steel strip in the first stand is excessive, edge waves are likely to occur. Therefore,
In the first stand, the molding rate represented by the following equation (1) is set to 3
It is desirable that the content be 5% or less. More preferably, 30%
It is as follows.

Α = R0 / R1 × 100 (%) (1) where R0 is the outer radius of the welded pipe, and R1 is the radius of curvature of the pressing surface of the side roll in the first stand.

The lower limit of the molding ratio is not particularly limited.
If it is too small, the number of side roll stands will increase.
It is better to be 5% or more. In addition, in the forming by the rimmed roll, if the pressing force in the width direction is excessive, the material is entangled from the roll gap and the thickness of both edges is increased, which may cause surface defects and welding defects. . Therefore,
Parameters L1 and L defined by the following equations (2) and (3)
2 satisfy the relationship L1 ≧ L2,
It is preferable to adjust factors such as the shape of the flanged roll, the width of the steel strip, and the roll gap that affect the values of 1 and L2. It is more preferable to adjust the roll gap so that the relationship of L1 ≧ L2 is satisfied.

L1 = πRP (α + β) / 90 (2) L2 = B · RP / (RP−t / 2) (3) where β = Arcsin (G1 / RP) −Arcsin ｛(G1-G) / RP ｝, Α: central angle of the pressing surface with respect to the arc, G1: distance between a straight line passing through the center of curvature of the pressing surface and parallel to the roll axis and the flange end of the pressing surface, G: 1/2 of the roll gap B: metal band Width, RP: radius of curvature of the pressing surface, t: thickness of the metal band.

By satisfying the relationship of L1 ≧ L2, the pressing force in the width direction at the time of forming by the flanged roll is optimized, and the biting and the increase in the thickness of both edges are suppressed. When the steel strip formed into the open tube passes through the high-frequency induction coil, both edges are intensively heated by high-frequency current, and are pressed by the squeeze roll provided on the exit side of the high-frequency induction coil to join the two edges. It becomes a welded pipe. Beads formed on the inner and outer surfaces of the welded pipe are removed before entering the heat treatment furnace.
The bead generated on the outer surface is removed by a bead cutter (not shown), and the bead generated on the inner surface is removed by a cutting blade or a bead pressure roller mounted on the tip of a mandrel inserted from the entry side of the first stand. Usually, the welded pipe from which the beads on the inner and outer surfaces have been removed is transferred to a heat treatment furnace,
After being heated to a predetermined temperature, it is rolled by a reduction rolling device including a plurality of stands to form a product tube having a predetermined size.

In the method of the present invention, a plurality of stands each having a pair of side rolls are continuously arranged, and a flanged roll is used as a side roll of the most upstream stand. Therefore, a breakdown roll is used. Without this, the open pipe can be formed stably. Further, conventionally, it was necessary to extract and reinsert a mandrel having an inner bead cutting blade every time the roll of the rolling mill was replaced, but the method of the present invention eliminates the need to use a breakdown roll. In addition, the roll of the rolling mill can be replaced while the mandrel is inserted, the time required for adjusting the mandrel can be shortened, the occurrence of defective products during adjustment is reduced, and the yield is improved.

Further, in the method of the present invention, since the relationship of L1 ≧ L2 is satisfied and the forming is performed by the roll with the flange, an excessive pressing force does not act in the width direction of the steel strip, which causes the surface flaw. Squeezing and the increase in the thickness of the edge which causes welding defects are suppressed.

Further, in the method of the present invention, since the molding rate at the most upstream stand is set to 35% or less, generation of edge waves can be suppressed. In particular, it is suitable for manufacturing a welded pipe having a ratio (t / D) of the thickness t of the welded pipe to the outer diameter D of the welded pipe of 0.02 or less.

[0043]

(Embodiment 1) A heating furnace having the structure shown in FIG. 1, two stands (first and second stands) each having a pair of side rolls, a fin pass roll, and a high-frequency induction coil And a device equipped with a squeeze roll,
Outer diameter 125m from steel strip of 396mm width and 3.0mm thickness
m were manufactured. The side surface roll of the first stand, which is the most upstream stand, has a curvature radius RP:
A 79 mm flanged roll (see FIG. 2) is used, and the side roll of the second stand has a radius of curvature RN:
A 04 mm non-collar roll (see FIG. 4) was used. Therefore, the forming ratio in the first stand was set to 34.9%.

The steel strip heated to 850 ° C. in the heating furnace is
After forming the open pipe with the stand, the second stand and the fin pass roll, heat both edges of the pipe to 1400 ° C or more with a high frequency induction coil, and immediately afterwards, press down with a squeeze roll to make a welded pipe (test No. A1) was performed. At that time, in the first stand, the roll gap was set such that the difference (L1-L2) between L2 and L1 was 0 mm.

For comparison, a test (test) was carried out under the condition that the first stand was provided with a brimless roll having a radius of curvature RN: 179 mm, and the second stand was provided with a brimless roll having a radius of curvature RN: 104 mm. No. A2), the second stand was not used, and the first stand was provided with a radius of curvature RN: 104
test under the condition that a roll without a brim (mm)
o. A3) was also performed. Test No. A2 and Test No. A
Other than the above conditions of Test No. 3, Test No. 3 Same as A1.

Observation of the rolling condition of the steel strip at the time of shaping the open pipe by the side rolls was carried out, and the stability of the shaping was investigated. No rolling occurred and the stability was good: O, rolling occurred and stability was poor. : Evaluated by x mark, and shown in Table 1 together with test conditions.

[0047]

[Table 1]

As shown in Table 1, in the test No. 1 in which the first stand was provided with a rimmed roll and the second stand was provided with a rimless roll. In A1, a good quality weld pipe was obtained without rolling, and good quality was obtained. On the other hand, Test No. A
In No. 2, rolling occurred, molding became unstable, and the shape of the open tube became poor. Test No. In A3,
Test No. Rolling occurred similarly to A2, and the shape of the open tube became poor, and further, edge waves were generated. (Example 2) The first stand and the second stand of the apparatus shown in Fig. 1 were provided with a roll with a brim and a roll without a brim, respectively. (L1-L2) of the first stand: 0 mm, molding ratio:
34.9% (RP = 179 mm) (Test N
o. B1) and (L1-L2): -2 mm, molding ratio 3
4.9% (RP = 179 mm) (Test No.
B2), (L1-L2): 0 mm, molding ratio: 45.0
% (RP = 139 mm) (Test No. B3)
And (L1-L2): 2 mm, molding ratio: 30.0% (R
A welded pipe was manufactured under four conditions (test No. B4) under which P = 208 mm). Other conditions were the same as in Example 1.
Test No. Same as A1. (L1-L2)
Was adjusted by the roll gap of the first stand.

Observing the rolling condition of the steel strip when forming the open pipe by the side rolls, investigating the stability of the forming, and examining the state of the edge wave generation of the open pipe and the resulting flaws in the welded pipe. The situation was investigated. Regarding the stability of the molding, there is no occurrence of rolling; good: O, there is rolling, poor: X, and for scratches that start, flaws: X, no flaws: Δ, edge waves Indicates that there is an edge wave: ×, and no edge wave: Δ, Table 2
Table 2 shows the test conditions.

[0050]

[Table 2]

As shown in Table 2, Test No. B1 and N
o. In B4, rolling was not generated, and edge waves and biting flaws were not generated. On the other hand, test N
o. In B2, rolling and edge waves were not generated and good, but biting flaws were generated. This is presumably because (L1-L2) of the first stand became a negative value, and the pressing force in the width direction acting on the steel strip became excessive. Test No.
In B3, rolling and biting flaws were not generated and good, but edge waves were generated.

From the above test, it was found that the generation of edge waves was suppressed by setting the molding rate to 35% or less, and the generation of biting flaws was suppressed by setting L1 ≧ L2.

[0053]

According to the present invention, an open pipe can be formed stably from a metal strip without using a breakdown roll. Accordingly, it is possible to replace the rolling mill with the mandrel having the inner bead cutting blade inserted into the inside of the welded pipe, and it is possible to reduce the occurrence of defective products. Further, according to the present invention, generation of edge waves is suppressed,
In particular, a thin welded pipe can be stably manufactured.
Further, according to the present invention, since a biting flaw and an increase in the thickness of an edge portion are suppressed, a high quality welded pipe having few surface flaws and welding defects can be manufactured.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of a production line for a welded pipe according to an embodiment of the present invention.

FIG. 2 is a front view schematically illustrating an example of the shape of a flanged roll.

FIG. 3 is a schematic view showing a state in which a pair of flanged rolls are arranged in a stand and a cross section of a steel strip as a material to be formed.

FIG. 4 is a front view schematically showing an example of the shape of a brimless roll.

[Explanation of symbols]

10: steel strip, 11: heating furnace, 12: hot forming apparatus, 1
3: 1st stand, 13a: brim roll, 14: 2nd stand, 14a: brimless roll, 15: fin pass roll, 16: high frequency induction coil, 17: squeeze roll, 18: open pipe, 19: welded pipe , 21: pressing surface, 22: flange, 23: flange end.

Claims (4)

[Claims] 1. A heated metal strip is bent into an open pipe by a hot forming apparatus having a plurality of stands each having a pair of side rolls each having an arcuate pressing surface, and then bending the open metal pipe into an open pipe. A plurality of stands, wherein at least the most upstream stand of the plurality of stands is a side roll having a brim portion having a brim portion continuous to the pressing surface. Manufacturing method of welded pipe. 2. The method for producing a welded pipe according to claim 1, wherein a forming ratio α defined by the following equation of the most upstream stand is 35% or less. α = R0 / R1 × 100 (%) where R0 is the radius of curvature of the welded pipe, and R1 is the radius of curvature of the pressing surface of the side roll in the most upstream stand. 3. In the stand having the flanged roll, the parameters L1 and L2 defined by the following formula are L1 ≧ L3.
The method according to claim 1, wherein the relationship of L2 is satisfied. L1 = πRP (α + β) / 90 L2 = B · RP / (RP−t / 2) where β = Arcsin (G1 / RP) -Arcsin {(G1-G) / RP}, α: for the arc on the pressure surface Central angle, G1: distance between a straight line passing through the center of curvature of the pressing surface and parallel to the roll axis and the flange end of the pressing surface, G: 1/2 of the roll gap B: width of the metal band, RP: radius of curvature of the pressing surface , T: thickness of the metal strip. 4. The method for manufacturing a welded pipe according to claim 3, wherein the roll gap of the stand having the rimmed roll is adjusted so that the relationship is satisfied.