JPH0377010B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for controlling residual moment of a spiral steel pipe, which can impart a desired residual moment to a steel pipe manufactured by spirally winding a strip. .

[Prior Art] Spiral steel pipes have a wide variety of uses, such as being used as piles in bank protection construction or as oil pipes (line pipes), and an outline of the manufacturing equipment is shown in FIG. 15. Three bending rolls 18, 19 and 2 arranged in a pyramid shape
The strip 24 unwound from the coil is fed in the longitudinal direction into a bending device equipped with a 0.0mm bending device, and the strip 24 is bent into a spiral shape, and the side edges of the bent strip are aligned with the part that has already become a tube. The inner surface of the tube is welded with an inner welding torch 25, and then the outer surface is welded with an outer welding torch 26 to form a spiral steel pipe.

Although FIG. 15 does not show the pressure rolls on the outer or inner surface of the tube, there are actually three methods depending on how the pressure rolls are arranged. That is, as shown in FIG. 3, for example, a large number of presser rolls 37 are provided on the outside of the strip formed into a spiral shape by a bending device to restrain the outer peripheral surface of the strip (restrict the spring back of the strip). There are three methods: a presser method, an internal presser method in which a number of presser rolls 52 are provided inside the strip to restrain the inner peripheral surface of the strip as shown in FIG. 6, and a method without presser rolls.

When manufacturing a spiral steel pipe using the external pressing method, the spring back in the diametrical direction of the strip (tubular body) is restrained by the external pressing roll and the strip is welded at the seam to form a spiral steel pipe. If a slit extending in the axial direction is made at one location in the circumferential direction, a spiral steel pipe with a positive residual moment (also referred to as positive ring opening degree; the ring opening degree will be described later) that opens in the circumferential direction can be obtained. It will be done.

On the other hand, when manufacturing spiral steel pipes using the internal pressing method, the joints are welded while the spring back in the diametrical direction of the strip (tubular body) is restrained by internal pressing rolls to form spiral steel pipes. If a slit extending in the axial direction is inserted at one location in the circumferential direction, a spiral steel pipe having a negative residual moment (negative ring opening degree) that closes in the circumferential direction can be obtained.

Furthermore, in the method without presser rolls, the formed strip (tubular body) is bent to a diameter that matches the product pipe diameter after springback, so this method has zero residual moment. A spiral steel tube of 100% is obtained.

Therefore, it is desired that the spiral steel pipe has a different residual moment depending on its use. For example, when a spiral steel pipe is used as a line pipe for transporting crude oil containing sour gas, it is desired that the pipe has an appropriate negative residual moment. This is because if the tube has a positive residual moment, tension will act in the circumferential direction of the tube, promoting stress corrosion cracking. Further, when a spiral steel pipe is used as a line pipe, if it has a positive residual moment, there is a problem that the pipe expands due to the hydraulic pressure inside the pipe and reduces the strength of the pipe.

On the other hand, when using spiral steel pipes as piles,
A member called a sheet pile claw is welded to the outer circumferential surface of the tube.
In this case, in a spiral steel pipe having a negative or zero residual moment, the roundness of the pipe cross section is broken, and the cross-sectional shape becomes distorted. Therefore, when a spiral steel pipe is used as a pile, a pipe having an appropriate positive residual moment is desired.

In this way, spiral steel pipes can be freely manufactured with appropriate values ranging from positive to negative values depending on their use, and at the same time,
A single manufacturing facility (external press roll system or internal press roll system) can produce tubes with negative residual moment using the external press method, or tubes with positive residual moment using the internal press system. It has been strongly desired to realize a technology that can arbitrarily apply residual moments in both regions.

As residual moment control means for spiral steel pipes that have been proposed in the past, for example,
Publication No. 12757, Japanese Patent Application Publication No. 142361/1983, Japanese Patent Application Publication No. 1987-142361
55-130333, etc. Japanese Unexamined Patent Publication 1973-
What is shown in Publication No. 12757 is to control the residual moment to near zero and prevent the expansion of the pipe diameter due to the water pressure test after forming. The content of JP-A-53-142361 is to make the radius approximately equal to the product radius after spring-back, and JP-A-53-142361 deals with the reverse bending phenomenon that is a problem when implementing the content of JP-A-53-12757. Discloses a method to solve the problem. Therefore, these are simply means to control the residual moment to near zero,
Even with the external pressing roll method, there is no disclosure that positive or negative residual moments can be applied arbitrarily.

Furthermore, the content disclosed in JP-A No. 55-130333 is that a tube having a residual moment having a desired positive value is manufactured using a spiral steel tube manufacturing line using an external surface pressing method. Although it is possible to produce a spiral steel pipe with a residual moment having a desired positive value, it is not possible to produce a pipe with a negative residual moment, and the mechanism for controlling the residual moment is complicated. .

Therefore, the present applicant has proposed a method and apparatus for manufacturing spiral steel pipes that solves the problems of these conventional techniques and can impart a residual moment in either the positive or negative range and any value regardless of the manufacturing method ( (Japanese Patent Application Laid-open No. 56-59532). The feature of this technology is that a bending moment imparting roll that can be freely adjusted in the tube diameter direction is provided near the downstream side of the exit side bending roll of the three bending rolls, and the curvature of the strip after bending is controlled by the roll. The point is to correct the product curvature and give residual moments in both positive and negative regions.

[Problems to be Solved by the Invention] The spiral steel pipe manufacturing technology described in JP-A-56-59532 has excellent effects that cannot be obtained with conventional spiral steel pipe manufacturing methods for controlling residual moment. It has become clear that it exhibits However, as a result of various studies carried out by the present inventors in implementing this technology,
The present invention was completed based on the discovery that the positioning of three pyramid-shaped bending rolls, which are the basic forming means for spiral steel pipes, is an extremely important element for residual moment control in actual operations. It came to this. Regarding this point, Japanese Patent Application Laid-Open No. 56-59532
No countermeasures have been taken in any of the above-mentioned conventional examples as well as in the Publication No. 1.

That is, based on the spiral steel pipe manufacturing technology described in the above-mentioned Japanese Patent Laid-Open No. 56-59532 of the present invention, a spiral steel pipe having an arbitrary value of residual moment in the positive and negative regions can be manufactured without being particular about the manufacturing method. The purpose of this invention is to provide a method that can be manufactured with high precision even if the thickness and mechanical properties of the input material (strip) vary.

[Means for Solving the Problems] The gist of the present invention is to bend a strip into a spiral shape while feeding the strip in its longitudinal direction into a bending device equipped with three forming rolls arranged in a pyramid shape. The outer or inner circumferential surface of the strip is restrained by a presser roll provided on the outside or inside of the spirally formed strip, and the seam between the part that has already become a tube and the side edge of the bent strip is In the method of manufacturing spiral steel pipes by continuous welding, first, the position of the inner bending roll of the three forming rolls is fixed as a reference roll, and the position (rolling amount) δ of the exit side outer bending roll is fixed. ₂ is set using the following formula, and the residual moment and average pressure increase δ _n (=(δ ₁ +
δ ₂ )/2) is determined in advance, and the position (roll-up amount) δ ₁ of the entry side outer surface bending roll is determined based on the average roll-up amount δ _n corresponding to the required residual moment.
In order to make the diameter of the tubular body formed by the bending device equal to the product tube diameter, the bending moment imparting roll adjacent to the rear stage in the strip traveling direction of the exit outer surface bending roll is set in the tube radial direction. Residual moment control method for spiral steel pipe characterized by adjusting position δ ₂ = ρ _p + r _e −√ ( _p + _e ) ² − ₂ where P _p : Product pipe radius r _e : Bending roll radius L: inner surface It is the distance between the axis of the outer bending roll and the axis of the exit outer bending roll.

[Function] As described above, in the present invention, the positions of the inner surface forming roll and the exit side outer surface forming roll are preset, and the positions of the inner surface forming roll and the exit side outer surface forming roll are not changed during the operation. do not have. The position of the entry side external bending roll is determined in advance by determining the relationship between the residual moment and the average roll-up amount, and is determined based on the average roll-up amount corresponding to the required residual moment, so it should be applied to the product pipe. When the direction (positive or negative) of the residual moment changes, only the position of the entry side outer surface forming roll changes (change in the amount of rolling up).

Therefore, since only the position of the entry side external forming roll is affected by the residual moment of the product pipe, compared to the case where the lifting amounts of both the input and exit side forming rolls are adjusted together, Residual moment control becomes easy and accurate.

In addition, in the present invention, the strip (tubular body) that has been bent into a spiral shape by the bending device including these three forming rolls is placed adjacent to the exit bending roll at the latter stage in the strip traveling direction. By adjusting the position of the bending moment imparting roll in the pipe radial direction, its diameter can be precisely matched to the diameter of the product pipe.

Below, we will examine the forming process of spiral steel pipes based on simple bending theory, and discuss the control of the product pipe diameter and residual moment based on that theory.
The present invention will be explained in detail.

First, the ring opening degree, which has a one-to-one correspondence with the residual moment in a spiral steel pipe, will be explained.

As shown in Fig. 1b, from the geometrical relationship caused by the ring opening, ρ _p is the radius of the product pipe, and ρ _p is the radius of the product pipe. The radius of curvature of the tube after it has completely _opened ( _springbacked ) in the circumferential _direction when From these two equations, the ring opening degree γ can be calculated as γ
Defining ≡α/D _p , γ is given by the following equation.
Here, D _p is the tube diameter at the center of the strip thickness.

γ＝ρ _p /ρ _p sinρ _p /ρ _p π＝sinωπ／ω……(1
) Here, ω≡ρ _p /ρ _p .

Next, how the curvature changes due to the ring opening will be explained from the relationship between the bending moment and the curvature. As shown in Figure 2, for example, a material bent to point A with a maximum curvature of 1/ρ _i is
The product pipe curvature at the point is 1/ρ _p , and the side edge end abutting parts are welded to form a spiral steel pipe. This spiral steel tube has a positive residual moment _M1 . When a slit extending in the axial direction is inserted at one point in the circumferential direction of this spiral steel pipe and the ring is opened, the residual moment is released, and the curvature of the pipe after the ring is opened is curvature 1 shown at point C in Fig. 2. /ρ _p .

It is exactly the same when the maximum curvature is further increased and the product is bent to point A′ to give a negative residual moment M ₂ to the product pipe, but in this case, the curvature
In order to change the curvature from C' to B' (the curvature of the product tube), the bent and formed strip (formed tube) must be expanded from the inside. When a spiral steel pipe is formed by welding the side edge end abutting portions with a product pipe curvature of 1/ρ _p at point B′, a ring is opened by inserting a slit extending in the axial direction at one point in the circumferential direction. , as is clear from Fig. 2, the radius of curvature is smaller than that of the product pipe, and α shown in Fig. 1 is
Negative, that is, γ is negative.

Since ω is usually a value around 1, an approximate calculation is expressed as γ=sinωπ/ω≒π(1−ω)/ω (2).

On the other hand, if the stress-strain relationship of the material is, for example, an elastic perfectly plastic body, then according to simple bending theory, 1/ρ _p = 1/ρ _i [1-3/2(σ _Y ρ _i /Et) + 1/2( σ _Y ρ _i /Et)] ...(3). Here, E, σ _Y , and 2t are the Young's modulus, yield stress, and strip thickness of the material, respectively.

According to the experimental results by the inventors, it was confirmed that σ ^* =1.15σ _i should be used instead of σ _Y . σ _i is the deformation resistance corresponding to the maximum strain t/ρ _i due to bending. Therefore, hereinafter in this specification, σ _Y shall mean σ ^* .

However, in normal bending, the third term in ``'' in equation (3) can be ignored, so ω≡ρ _p /ρ _p ≒ρ _p /ρ _i (1-3/2・σ _Y・ρ _i /
Et)...(4).

From equations (2) and (4), Young's modulus E and yield stress σ _Y of the material
Once the pipe cross-sectional dimensions (thickness: 2t, curvature: ρ _p ) and the maximum bending curvature 1/ρ _i are determined, the link opening degree γ is determined. Incidentally, in a spiral steel pipe with a positive or zero residual moment, γ≧o, (ω≦1) and ρ _p ≧ρ _p ≧ρ _i In a spiral steel pipe with a negative residual moment, γ<o, (ω >1), then ρ _p > ρ _p > ρ _i .

In addition, the residual stress on the outermost surface of the product pipe is σ _R
Then, by calculation using simple bending theory, the ring opening degree can also be given by the following formula. That is, γ=πε/1−ε, ε≡σ _Y・σ _p /E・t(1/2+
σ _R /σ _Y )……(5) Furthermore, the bending moment M per unit length of the pipe and the residual moment M _p per unit length of the pipe at the maximum curvature 1/ρ _i are respectively M=σ _Y t ² [1-1/3(σ _Y ρ _i /Et) ² ] ...(6) It is expressed as

As is clear from the above bending logic, the strip is first bent by the strip bending means to a radius of curvature ρ _i which is less than the product tube radius ρ _p . The direction of the residual moment in the _{product tube} (positive, The value is determined as negative).

[Example] Next, a case will be described in which the present invention is implemented using an external pressing type pipe manufacturing apparatus shown in FIG. 3 and an internal pressing type pipe manufacturing apparatus shown in FIG. 6. The devices shown in FIGS. 3 and 6 are devices disclosed by the present inventors in Japanese Patent Application Laid-open No. 56-59532.

As shown in FIG.
and an exit outer surface molding stand 13 are provided. In addition, a frame (not shown) on the base 11
An inner surface molding stand 14 is suspended from. Inlet side, outlet side and inner surface molding stand 12,1
3 and 14 have bending rolls 18,
19 and 20 are rotatably attached. These forming rolls 18, 19 and 20 are
When viewed from the front, they are arranged in a pyramid shape.
In this specification, the term "roll" refers to a set of split rolls.

As shown in FIG. 3, a forming case 36 having a C-shaped cross section and extending in the tube axis direction is supported on the base 11 by pillars 35. As shown in FIG. The forming case 36 includes a large number of outer pressing rolls 37 arranged along the outer peripheral surface of the formed tube 2.
is rotatably attached via a support member 38 including a screw mechanism. External pressing roll 37
is moved back and forth in the radial direction of the tube 2 by the screw mechanism of the support member 38 to adjust the holding position. Further, the outer pressing roll 37 contacts the outer circumferential surface of the tube 2 and rotates according to the spiral movement of the tube 2.

Attached to the inner surface forming stand 14 is one bending moment imparting roll 41 that is divided into a plurality of pieces along the tube axis direction when viewed in a cross section perpendicular to the tube axis of the spiral steel tube. As shown in FIG. 3, the position of the bending moment imparting roll 41 in the tube circumferential direction is between the exit side outer surface forming roll 19 and the outer surface presser roll 37 that comes into contact with it first, that is, on the exit side, and is determined by the arrangement conditions of the device. It is desirable to be as close to the outer surface forming roll 19 as possible. The bending moment imparting roll 41 is attached so that its position can be adjusted in the radial direction of the tube by an appropriate means.

A method of manufacturing a spiral steel pipe according to the present invention using the pipe manufacturing apparatus configured as described above will be described below.

First, the forming rolls 18, 19 and 20 press the inner surface of the strip tube 2, with the inner surface forming roll 20 pressing the area that is to become the inner surface of the strip tube 2, and the inlet and outlet outer surface forming rolls 18, 19 forming the outer surface of the strip tube 2. Support the right parts. The maximum curvature is 1/ρ _i at the position of the inner surface forming roll 20, and the curvature of the product pipe is approximately 1/ρ i at the position of the exit side outer surface forming roll 19.
The position of each forming roll is set so that ρ _p . The outer pressing roll 37 and the bending moment applying roll 41 are the forming rolls 18 and 19.
and 20 are set at that position (tube radial position) to guide and restrain the strip so that the curvature of the bent strip (formed tube) matches the curvature of the product tube. Note that the details of the position setting of each roll will be described later.

Steel strips are continuously fed into the pipe-making apparatus with each roll positioned in this manner, as shown in FIG. The strip 1 is bent between the inlet outer forming roll 18 and the inner forming roll 20 to increase its curvature, and reaches a maximum curvature 1/ρ _i at the inner forming roll 20. Between the inner surface forming roll 20 and the exit side outer surface forming roll 19, the curvature of the strip 1 gradually decreases due to spring back, and at the position of the exit side outer surface forming roll 19, the strip 1 has approximately the final curvature 1/ρ _p
becomes. Therefore, the bending moment imparting roll 41
The part that has already been welded to the side edge of the strip formed into a spiral tubular shape with the final curvature 1/ρ _p maintained by pushing it out or being guided and constrained by the outer pressing rolls 37 to form a spiral steel pipe. The abutments at the side edges of the strip are continuously internally welded with a welding torch.

To manufacture a spiral steel pipe with a negative residual moment using the pipe manufacturing apparatus shown in Fig. 3 above,
As shown in FIG. 4, in order to obtain the maximum bending curvature 1/ρ _i at which a predetermined value of negative residual moment occurs, the amount of roll-up of the bending rolls 18 and 19 (position in the pipe radial direction, residual moment and pressure) is determined. The relationship with the upper weight has been determined in advance), bending is performed, and the formed strip (formed tube: shown by the two-dot chain line in FIG. 4) is rolled by a residual moment imparting roll 41 as shown in FIG. Expand the pipe until it reaches the diameter shown by the solid line.

That is, the strip is bent to a curvature of 1/ρ _{' i} at point A' in FIG. curvature from C′
to B′). In this state, the side edges of the formed strip and the abutting portions of the side edges of the strip that have already been welded to form the spiral steel pipe are continuously welded. The spiral steel pipe thus obtained is
It has a negative residual moment M ₂ in Figure 2.

On the other hand, in order to manufacture a spiral steel pipe with a positive residual moment using the apparatus shown in FIG.
As shown in the figure, the formed strip (formed tube: shown by the two-dot chain line in Fig. 5) is pressed against its outer surface by bending it to the maximum bending curvature 1/ρ _i that produces a positive residual moment of a predetermined value. The product tube is guided and restrained by the rolls 37 so as to match the curvature 1/ρ _p (indicated by the solid line in FIG. 5) of the product tube. In this state, the side edges of the formed strip and the abutting portions of the side edges of the strip that have already been welded to form the spiral steel pipe are continuously welded. The spiral steel pipe thus obtained has a positive residual moment. This is a normal operation.

That is, the strip is bent to have a curvature of 1/ρ _i at point A in FIG. 2, and the curvature of the product pipe is 1/ρ _p (B
While the strip is spring-backed until it reaches a point) and restrained by an external press roll, the part that has already been welded to form a spiral steel pipe is continuously welded at the part where it meets the side edge end of the strip. The spiral steel pipe thus obtained has a positive residual moment of _M1 .

In this way, if the maximum curvature in the bending of the strip is set to a predetermined value between A and A' in FIG. A spiral steel pipe with residual moment can be obtained.

Next, in FIG. 6, the same members as those shown in FIG. 3 are given the same reference numerals, and their explanations will be omitted. The strip is bent into a spiral steel pipe 2 by a strip bending means constituted by outer bending rolls 18, 19 and inner bending rolls 20. When the strip is bent into a spiral shape, a large number of inner pressing rolls 52 are supported by a frame 51 so as to be able to move forward and backward in the radial direction of the tube 2, and a tube shaft of the spiral steel tube supported by a stand 54 is used. The pipe diameter D _p is set by the bending moment imparting roll 55, which is divided into a plurality of parts along the pipe axis direction when viewed in a vertical cross section.
is maintained. The bending moment imparting roll 55 is provided after the exit outer surface bending roll 19.
It is installed so that it is located outside the forming tube. The inner surface forming stand 14 and the pedestal 51 are supported by an inner surface pressing roll support 57 disposed inside the tube 2 .

In order to manufacture a spiral steel pipe with a positive residual moment using the internal pressing type pipe manufacturing apparatus shown in FIG. 2
Applying the bending at point A in the figure to the strip, the seventh
A formed tube is formed as indicated by the two-dot chain line in the figure, and is compressed by the bending moment imparting rolls 55 so that it has a product tube diameter as indicated by the solid line in FIG. Under this condition, the portions that have already been welded to form the spiral steel tube are continuously welded at the abutting portions of the side edges of the strip. The spiral steel pipe thus obtained is
It has a positive residual moment. In other words, the curvature of point C shown in FIG.
The strip (formed tube) that has been bent and formed to have the curvature of a point is compressed to obtain the planned product tube diameter,
Continuously weld the abutment areas. The spiral steel pipe thus obtained has a positive residual moment of _M1 .

On the other hand, in order to manufacture a spiral steel pipe having a negative residual moment using the pipe manufacturing apparatus shown in FIG.
The strip is guided and restrained by the group of inner pressing rolls 52 so as to be forced and expanded to achieve the curvature of the product tube shown by the solid line. Under this condition, the abutting portions of the previously welded spiral steel pipes with the side edges of the strips are continuously welded. The spiral steel pipe thus obtained has a negative residual moment. That is, in Figure 2
The strip is bent to the curvature of point A′,
The curvature at point B' (the curvature of the product tube) is expanded by the inner pressing roll 52, and under this condition, the abutting portions are continuously welded. The spiral steel pipe thus obtained has a negative residual moment of _M2 .

In this way, even when using the pipe manufacturing apparatus shown in FIG. 6, the maximum curvature in bending the strip is
By setting the residual moment to a predetermined value between A and A' in FIG. 2, it is possible to obtain a spiral steel pipe having a desired value of residual moment in the desired positive and negative ranges between B and B'.

As described above, according to the present invention, not only can spiral steel pipes having a positive residual moment and spiral steel pipes having a negative residual moment be made separately using the same pipe manufacturing apparatus, but also spiral steel pipes having a positive residual moment and a spiral steel pipe having a negative residual moment can be manufactured separately. 1, which changes continuously from the residual moment in the positive region to the residual moment in the negative region.
We can also produce regular spiral steel pipes.

Next, the basic concept of the residual moment control method of the present invention will be explained.

(1) Initial setting of residual moment or ring opening by the entrance bending roll Young's modulus of material, yield point (E, σ _Y ), pipe size (2t, ρ _p ), and desired residual moment, i.e., ring opening Given the degree γ, the maximum curvature 1/ρ _i of bending by the bending device is (2)
From equation (4), it is given by the following equation.

1/ρ _i =1/ρ _p (π/π+γ+3/2・σ _Y・σ _p /
E・t)...(8) Normally, it is difficult to directly measure ρ _i , so for example, the relationship between the curvature of the strip directly under the inner bending roll of the bending device and the roll position of the forming device is determined. By setting the roll position corresponding to ρ _i in equation (8), setting of the initial value of γ is achieved. This point will be explained below.

The inventors conducted a logical analysis of the bending of a strip using three forming rolls arranged in a pyramid shape, and found that the ring opening degree γ (i.e., residual moment) was adjusted by the positional relationship of these forming rolls. I found out what I can do. This shows the positional relationship of the forming rolls.
This will be explained in detail with reference to the drawings.

As shown in FIG. 9, the forming rolls are comprised of an input outer forming roll 18, an inner forming roll 20, and an exit outer forming roll 19. These forming rolls all have the same diameter r, and r _e shown in the figure is the equivalent radius of the forming roll, and r _e =r+t (here, the plate thickness is 2t). Therefore, the figures are drawn so that each forming roll is tangent to the thickness centerline N of the strip being bent. The horizontal distances of the input and output outer surface forming rolls 18 and 19 with respect to the inner surface forming roll 20 are equal L.
It is. In addition, the input/output outer surface forming roll 18,
The height position (roll-up amount) of 19 is the inner forming roll 2.
The distances δ 1 and δ 2 from the horizontal line H touching the lower end of 0 to the upper end of each roll are expressed as δ ₁ and δ ₂ . Here, assuming that the average roll-up amount of the forming rolls is δ _n = (δ ₁ + δ ₂ )/2, the value δ _n /L ² is the longitudinal elastic modulus E of the material, the yield stress σ _Y , the radius ρ _p of the product tube, and It is determined by the wall thickness 2t and the ring opening degree γ.

By the way, in a bending forming apparatus, generally the forming roll radius r and the inter-roll distance L are fixed, so the amount that can be adjusted during the forming operation in terms of the roll position relationship is the above-mentioned average roll-up amount δ _n . According to the research results of the present inventors, L/√
It is desirable to select the value of L so that D.2t=1.2 to 1.4. Here, D is the outer diameter of the finished tube. This value of L was obtained through empirical and partly experimental studies regarding welding stability and ease of controlling the lift amount. Coefficient 1.2 ~
1.4 depends on the material strength, the greater the strength, the
It is preferable to take a large coefficient. δ _n is adjusted by the roll-up amount δ ₁ of the input side outer surface forming roll 18 and the roll-up amount δ ₂ of the exit side outer surface forming roll 19, but the inventors further set δ ₂ to an appropriate value. We found that the residual moment can be adjusted accurately by fixing it and adjusting only δ ₁ . Next, this will be explained.

Ideally, as shown in FIG. 9, the contact surface of the exit side forming roll 19 should be on the outer periphery of the strip bent at the final radius of curvature ρ _p . (In the figure, the exit external forming roll, drawn with an equivalent radius r _e , is shown touching the strip centerline N at point P.) If such contact does not occur, e.g. If the position of 19 is too high (δ ₂ is too large), the strip in the vicinity of contacting this outer forming roll 19 will curve in the opposite direction so that the outer surface of the tube is concave. For this reason, energy is wasted in forming, and it becomes impossible to adjust the residual moment. On the other hand, if the position of the exit outer forming roll 19 is too low (δ ₂ is too small), the outer forming roll 19 will move away from the strip, making it impossible to bend and form the strip to the desired curvature.

The appropriate position, ie, the optimum roll-up amount δ ₂ of the exit side forming roll 19 is determined as follows with reference to FIG. If the effective bending length at the center of the thickness of the strip is l and the bending angle is θ, then from the geometrical relationship l=ρ _p sinθ ...(9) L=l+ _re sinθ ...(10) Equation (9) ), from (10), L = (ρ _p + r _e ) sin θ ... (11) Also, the effective pressure increase amount (height at the position of contact P) δ ^*
is expressed as δ ^* = δ _{2 −re} (1−cosθ) = ρ _p (1−cosθ) ... (12), and from this, δ ₂ = (ρ _p + _re ) (1−cosθ) ... (13) From equations (11) and (13), L ² / (ρ _p + r _e ) ² + (ρ _p + r _e −δ ₂ ) ² / (ρ _p + r _e )
² = 1... (14) From formula (14), δ ₂ = ρ _p + r _e -√ (ρ _p + r _e ) ² - L ² ... (15) Therefore, the rolling up of the exit side outer surface forming roll 19 The quantity δ ₂ may be set in advance to the value given by equation (15).

FIG. 10 is a graph showing the relationship between γ and δ _n /L ² , which confirms the above results through experiments. In this experiment, the pipe radius ρ _p = 400 mm and the plate thickness is 2t.
= 9 mm, forming roll radius r = 40 mm, and strip yield stress σ _Y = 30 Kg/ ^mm2 , L
are 90mm, 100mm, and 110mm, respectively, δ ₂
The changes in γ were investigated when δ ₁ was determined and δ ₁ was used as a variable, and when δ 1 was determined and δ ₂ was used as a variable.

As is clear from this graph, when the rolling-up amount δ ₁ of the entrance side external forming roll is increased as a variable, that is, when δ _n /L ² is increased, the residual mormont changes from positive to negative. I understand (see deformation curve E). However, when the rolling-up amount δ ₂ of the exit side forming roll is changed, if the value becomes too large, the deformation curve F including the reverse bending portion G occurs, and the ring opening degree γ is originally negative. Sometimes something that should be has a positive value.

In this way, there is a certain relationship between δ _n /L ² and ring opening degree γ (residual moment), so
Average roll-up amount of forming rolls δ _n (=(δ ₁ + δ ₂ )/2)
The residual moment can be adjusted by
Furthermore, according to formula (15), the exit side outer surface forming roll 19
If the rolling-up amount δ ₂ is set, the residual moment can be adjusted only by the rolling-up amount δ ₁ of the entry side outer surface forming roll 18. In other words, in the present invention, if the relationship between the residual moment (ring opening degree γ) and the average roll-up amount δ _n is determined in advance, the relationship shown in FIG. 10 can be determined in advance for each material used, and the product By determining δ _n /L ² from the required positive or negative residual moment (i.e. ring opening degree γ) to be applied to the pipe, the rolling-up amount δ ₁ of the entrance side external forming roll 18 can be set. It becomes possible.

The inventors have determined that the roll-up amount δ ₁ of the entrance outer surface forming roll
We confirmed through another experiment that it is effective to adjust the residual moment by using only the residual moment. The results are shown in FIGS. 11 and 12. The tube diameter and other experimental conditions were the same as those of the experiment conducted with respect to FIG.

In these drawings, L = 100 mm and the distance from the inner forming roll is plotted on the horizontal axis (0 position is the inner forming roll, -100 position is the entry side bending roll,
100 positions indicate the respective positions of the exit bending rolls), and the change in curvature is plotted on the vertical axis. FIG. 11 shows the case where the rolling up amount δ ₁ of the input side outer surface forming roll is changed, and FIG. 12 shows the case where the rolling up amount δ ₂ of the exit side outer surface forming roll is changed. In either case, the curvature increases rapidly on the inlet side of the forming section, reaches its maximum almost directly below the inner forming roll (0 position), and then decreases significantly on the exit side of the inner forming roll. Finally, it becomes equal to the product curvature on the exit side of the molding section. However, when δ ₁ is changed, no abnormality occurs, but the rolling up amount δ ₂ of the exit external surface forming roll
In the case of Fig. ₁₂ in which the
If it is too large, the curvature 1/ρ will decrease significantly near the exit-side outer surface forming roll (see broken line). This phenomenon is due to the combined effect of the Bauschinger effect and reverse bending represented by curves C'' to B'' shown in FIG. As a result, as shown in Figure 2, the product pipe diameter (2ρ _p )
Spiral steel pipes finished with a positive residual moment M ₃ instead of the required negative residual moment
will be granted.

In this way, when only the rolling-up amount δ _{2 of the} exit side forming roll is changed, as is clear from FIG. occurs. As a result, not only is it difficult to control the residual moment, but
Wasted energy is consumed and roll marks are more likely to occur.

Conversely, when the average pressure increase amount δ _n is small and the pressure increase amount δ ₂ to be changed is also small, the 13th
Forming load of the exit side external forming roll 19 shown in the figure
Q ₁ is almost zero. The strip 1 is therefore formed by forming rolls 18,1 in a pyramidal arrangement.
Instead of the sets 9 and 20, forming rolls 18, 2
0 and presser roll 37 (the set shown with diagonal lines), the important exit forming roll is hardly involved, resulting in an extremely unstable forming process.

(2) Response to disturbances (changes in σ _Y and 2t) During forming, the yield stress σ _Y and plate thickness of the strip
The adjustment of the residual moment M _p when a disturbance occurs due to a change in 2t will be explained.

Since there is elastic deformation of the rolling up device, housing, etc. of the forming apparatus, the apparent rolling up amount S _n of the forming roll does not match the true rolling up amount δ _n , and the relationship between the two is given by the following equation.

Q=K(S _n −δ _n ) (16) Here, Q is the bending forming load and K is the spring constant of the forming suntad.

On the other hand, the inventors experimentally determined that the forming force Q of the material
I learned that can be considered to be approximately a function of σ _Y , 2t, and δ _n . That is, Q=(σ _Y , 2t, δ _n ) ...(17) Q=(σ _Y , 2t, δ _n ) is shown in Figure 14, which will be explained next.
is shown qualitatively using a graph.

Also, since approximately δ∝1/ρ, δ _n is ρ _i
is a function of That is, δ _n ≒ Ψ (ρ _i ) ... (18) From equations (16) to (18), S _n = 1/K・(σ _Y , 2t, δ _n ) + Ψ (ρ _i ) ... (19) Now The concept of residual moment adjustment will be explained using an example where σ _Y changes to σ′ _Y during molding. Product diameter (2ρ _p ) and residual moment (γ)
In order to keep constant, according to the relationship in equation (8),
It is necessary to change ρ _i →ρ′ _i according to σ _Y →σ′ _Y. In other words, by equation (19), from S _n to S′ _n =1/K・(σ _Y , 2t, δ _n )+Ψ( The setting of the lifting amount of the forming roll (only the exit side forming roll as described above) may be changed to ρ _i .

FIG. 14 is a graph explaining the above calculation. Elastic property straight line group S _n of the forming device,
S′ _n and S″ _n represent equation (16) with S _n as a parameter. Forming load curve group Q, Q′,
Q″ is expressed by equation (17) with yield stress σ _Y as a parameter. Equation (17) also uses plate thickness 2t as a variable, but here the plate thickness is assumed to be constant. Straight line
M _p represents the required residual moment.
That is, if the required residual moment M _p is given, M _p ≒ Ql and approximately δ∝1/ρ, for example, the straight line in Fig. 2 can be approximately represented by the straight line M _p on Fig. 14. can.

In FIG. 14, point a indicates that a tube with a residual moment M _p can be obtained by forming a strip with a yield stress σ _Y by a roll-up amount δ _n . Now, if the yield stress changes to σ′ _Y , then
The forming load changes according to equation (17), and the load curve is
It becomes Q′. In order to obtain the required residual moment, it is necessary to form with the forming load at the intersection b of the straight line M _p and the curve Q'. The apparent uplift amount at this time is the amount indicated by the straight line S′ _n passing through this intersection b.
S′ _n . Even when the plate thickness 2t changes, the required residual moment can be applied to the pipe in the same manner as above.

[Effects of the Invention] According to the method of the present invention described above, it is possible to separately produce spiral steel pipes having a positive residual moment and spiral steel pipes having a negative residual moment at desired values using the same pipe-making apparatus. Not only is it possible, but it is also possible, if desired, to produce a single spiral steel tube in which the residual moment changes continuously from one end to the other from a residual moment in the positive region to a residual moment in the negative region.

Furthermore, according to the present invention, the positions of the three bending rolls in a pyramid arrangement, which are the basis for imparting the required curvature to the strip, can be set extremely rationally. ) The residual moment can be controlled with high precision even if the thickness and mechanical properties of the steel pipe vary, greatly contributing to the improvement of spiral steel pipe manufacturing technology.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the ring opening degree, where a shows the state before the ring is opened and b shows the state after the ring is opened. FIG. 2 is a diagram showing the relationship between the curvature and bending moment of the pipe during forming and after completion. FIG. 3 is a front view of an external pressing type pipe manufacturing apparatus in which bending moment imparting rolls are installed, which is an example of the apparatus to which the method of the present invention is applied. FIGS. 4 and 5 are explanatory diagrams of the bending industry using the external pressing method. FIG. 6 is a front view of an internal pressing type pipe manufacturing apparatus in which bending moment imparting rolls are installed, which is an example of the apparatus to which the method of the present invention is applied. FIGS. 7 and 8 are explanatory diagrams of the bending industry using the internal pressing method.
FIG. 9 is a diagram illustrating the mutual positional relationship of forming rolls in the present invention. Figure 10 shows the position of the forming roll (δ _n /L ² ) and the residual moment (γ).
3 is a graph showing an example of the relationship between FIG. 11 and FIG. 12 are diagrams showing an example of a change in curvature when the amount of rolling up of the inlet forming roll and the outlet forming roll is adjusted, respectively. FIG. 13 is a diagram illustrating the actions of the forming roll and presser roll when the lifting amount is small. FIG. 14 is a diagram illustrating a method of controlling the residual moment according to the present invention by controlling the position of the entrance outer surface bending roll. FIG. 15 is a diagram schematically showing a spiral steel pipe making machine. 1... Strip, 18... Inlet outer bending roll, 19 Outer outer bending roll, 20...
...Inner surface bending roll, 37...Outer surface press roll, 52...Inner surface press roll, 41, 55...Residual moment imparting roll.

Claims (1)

[Scope of Claims] 1. The strip 1 is bent into a spiral shape while feeding it in the longitudinal direction into a bending device equipped with three forming rolls 18, 19, 20 arranged in a pyramid shape. Presser roll 3 provided on the outside or inside of the strip
7 or 52 to restrain the outer or inner circumferential surface of the strip, and continuously weld the joint between the part that has already become a pipe and the side edge of the bent strip to produce a spiral steel pipe. , First, the position of the inner bending roll 20 of the three forming rolls is fixed as a reference roll, the position (rolling up amount) δ ₂ of the exit outer surface bending roll 19 is set by the following formula, and the residual moment is and the average pressure increase δ _n (=(δ ₁ +
δ ₂ )/2) is determined in advance, and the position (roll-up amount) δ ₁ of the entry side external bending roll 18 is set based on the average roll-up amount δ _n corresponding to the required residual moment. At the same time, in order to make the diameter of the tubular body formed by the bending device equal to the product tube diameter, the bending moment imparting roll 41 or 55 adjacent to the exit side outer surface bending roll 19 in the strip traveling direction is used. A method for controlling the residual moment of a spiral steel pipe, which is characterized by adjusting the radial position. δ ₂ = ρ _p + r _e −√ ( _p + _e ) ² − ₂ where P _p : Product pipe radius r _e : Bending roll radius L: Between the center of the inner and outer bending rolls and the center of the outlet outer bending roll distance of