JPH0442095B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for straightening a pipe using an inclined opposing roll straightening machine, and more specifically, to straightening a bent pipe,
The present invention relates to a method for straightening a tube capable of improving roundness, particularly to improving roundness. [Prior Art] Various roll arrangement types are known as pipe straightening machines, for example, as shown in Fig. 4,
2. Description of the Related Art A straightening machine with a vertical roll arrangement of a so-called 6-roll type (2-2-2 type) with 3 pairs of slanted opposing rolls 1, 2, and 3 is known. In this straightening machine, among three pairs of opposing rolls, each of the upper rolls 1a, 2a, 3a on the entry side, intermediate side, and exit side and the lower roll 2b in the middle can be moved up and down by a screw type reduction device 4. Each lower roll 1b, 3b is fixed, and the roll interval of each roll 1, 2, 3 is made slightly smaller than the outside diameter of the pipe to apply pressure (crush) to the pipe P, and the intermediate upper and lower rolls 2a, 2b are The upper and lower rolls 1a, 1b on the input side and the upper and lower rolls 3a, 3 on the output side
deviate slightly above b (offset), enter side,
Upper rolls 1a, 3a on the exit side and lower roll 2 on the intermediate side
In step b, bending stress is applied to the tube to correct the bend. In this straightening, the tube outer diameter D and the roll interval A
Since the crushing amount δ, which is the difference between the Due to deformation, etc., the amount of crushing fluctuated together with the variation in the outside diameter D of the tube. FIG. 5 is a graph showing a mill rigidity curve X and a tube plasticity curve Y, with the roll gap and tube outer diameter plotted on the horizontal axis and the load plotted on the vertical axis. As mentioned above, there is a roll gap A' due to a setting error with respect to the set roll gap A, and there is also a tube outside diameter D' due to variations in the tube outside diameter D.
Therefore, with respect to the amount of crushing δ ₀ when the roll gap is A and the outside diameter of the tube is D, the roll gap varies, and when this is A' and the outside diameter of the tube is D, the amount of crushing is δ ₁ , and the variation in the outside diameter of the tube is When the roll gap is SA at D', the amount of crushing is δ ₂ , which varies from process to process. Therefore, when the amount of crushing fluctuates in this manner, sufficient correction may not be made, and the amount of crushing may become excessive, resulting in residual stress that may cause stress corrosion cracking in the product. In order to prevent this residual stress from occurring, it is desirable to keep the amount of crushing constant within a predetermined range in the straightening process so that residual stress does not occur. The applicant of the present application proposed a method disclosed in Japanese Patent Application Laid-open No. 128318/1983 in order to properly correct the problem and prevent the generation of excessive residual stress. In this method, as shown in FIG. 6, among the rolls of an inclined opposed roll straightening machine, a hydraulic pressure lowering device, for example, a hydraulic pump 8 A device is provided in which the pressure oil sent from the constant pressure valve 9 is set at a predetermined pressure by a constant pressure valve 9 and can be supplied to the cylinders 7 attached to the rolls 1b, 3b, and 2a, respectively. Set from the amount of crushing you want to give to the pipe and the plasticity curve of the pipe,
This is a method in which the set pressure is kept constant and the pipe is straightened by a predetermined amount of crushing. [Problem to be solved by the invention] When correcting with this method, the set pressure is kept constant and the pressure below is kept constant, so the seventh
The mill stiffness curve is shown in the figure. FIG. 7, like FIG. 5, is a graph showing the mill stiffness curve As can be understood, the mill stiffness curve has a constant value above the load corresponding to the set pressure of the constant pressure valve 9, and therefore, even after correction, the pipe outer diameter D', which varies with respect to the pipe outer diameter D, remains constant. The amount of crushing δ ₃ at this time is equal to the amount of crushing δ ₀ when the tube outer diameter is D. In other words, the amount of crushing is the same at each position regardless of whether the pipe has a large outer diameter or a small outer diameter. Therefore, this method has the problem that although no residual stress is generated, it is difficult to improve the roundness of the tube. [Means for Solving the Problems] The present invention has been made in view of the above problems, and involves reducing the rolls for imparting crushing to the pipe at a predetermined hydraulic pressure using a hydraulic pressure reduction device, and also reducing the pressure of the rolls. A pipe that can straighten the bend of the pipe, prevent the generation of excessive residual stress, and improve roundness by preventing backflow of liquid in the hydraulic pressure reduction device when the force received from the pipe exceeds a specified pressure. The purpose is to provide a method for correcting this. A method for straightening a pipe according to the present invention is a method for straightening a bend in a pipe by passing a pipe between a pair of rolls equipped with at least a hydraulic pressure reducing device and applying a crush to the pipe, in which a hydraulic pressure is applied to drive the rolls to reduce pressure. A pressure regulator for the hydraulic pressure in the hydraulic cylinder is provided between the cylinder and the hydraulic pressure source, and the hydraulic pressure in the hydraulic cylinder is lower than the regulated hydraulic pressure by the force applied to the hydraulic cylinder from the roll side. In order to prevent the liquid from flowing back toward the hydraulic pressure source when the pressure rises, and to improve the roundness of the tube, the tube is lowered with a regulated hydraulic pressure or a higher hydraulic pressure, It is characterized by adding a crush. [Example] The present invention will be specifically described below based on the drawings.
FIG. 1 shows the present invention using an inclined facing six roll type (2-2-
2) is a schematic diagram showing an implementation state when applied to a vertical roll arrangement straightening machine, and P in the figure indicates a pipe to be straightened. The pipe P is the entrance roll 1 of the straightening machine,
The pipe is skewed in the longitudinal direction of the pipe axis (in the direction of the white arrow) by intermediate rolls 2 and exit rolls 3, and the straightening machine applies a predetermined offset amount and required crush amount to the pipe P between rolls 1, 2, and 3. It is configured so that it can be granted. Conventional screw-type lowering devices 4, 4, 4 are provided on each of the upper rolls 1a, 3a on the entry side and the exit side, and the intermediate lower roll 2b, respectively, for adjusting the roll position.
The height of each of these rolls 1a, 2b, 3a is adjusted by means of rolling down devices 4, 4, 4, respectively, so as to apply a predetermined amount of offset to the pipe P. The pivot parts of the lower entry roll 1b and the lower exit roll 3b are supported by single acting cylinders 11, 11 which are part of the hydraulic lowering devices 10, 10.
The height of b, 3b and the pipe pressure reduction force are determined by the hydraulic pressure reduction device 10,
It is designed to be adjusted at 10. The single-acting cylinders 11, 11 have cylinder tubes attached to pivot supports of the rolls 1b, 3b with the cylinder rods facing downward, and the cylinder rods are fixed. In the rod advance oil chamber 11a of the single-acting cylinder 11, there is a throttle valve 1 with a check valve that allows the pressure oil sent out at a sufficiently high pressure from the hydraulic pump 16 to return freely.
5 to a proportional electromagnetic pressure reducing valve 13 with variable secondary pressure, and pressure oil reduced to its set pressure is supplied via a check valve 12. Further, a bypass passage 10b for returning pressure oil is connected from the cylinder side of the check valve 12 to the pump side of the pressure reducing valve 13, and a check valve 14 is attached to the bypass passage 10b. Therefore, the pressure inside the single acting cylinder 11 of the hydraulic pressure reduction device 10 becomes the pressure set in the pressure reducing valve 13, but
When the pressure in the oil chamber 11a becomes higher than the set pressure of the pressure reducing valve 13 due to the force received from the roll 1b of the single-acting cylinder 11, the pressure on the pump side of the check valve 14 is sufficiently high, so that Pressure oil does not return, and the pipe P is crushed with the same force as the force that the single acting cylinder 11 receives from the roll 1b. Note that when the pressure in the oil chamber 11a becomes higher than the set pressure of the pressure reducing valve 13 and higher than the pump side pressure, the pressure oil returns to the pump side via the check valve 14, and the pressure oil returns to the pump side via the check valve 14. A relief valve (not shown) provides for drainage to a tank. The pivot portion of the intermediate upper roll 2a is supported by a double-acting cylinder 21 that is a part of the hydraulic lowering device 20 and a fixed screw type lowering device 4, and the height of the roll 2a is determined by the hydraulic lowering device 20. and a screw-type rolling down device 4, and the pipe rolling force of the roll 2a is adjusted by a hydraulic rolling down device 20. The double-acting cylinder 21 has a cylinder tube attached to the pivot portion of the roll 2a with the cylinder rod facing upward, and the cylinder rod serves as a screw for the lowering device 4. The hydraulic lowering device 20 is configured to be able to press the roll 2a downward and lift it upward, and a sufficiently high pressure is applied from the hydraulic pump 25 to the (lower) oil chamber 21a for rod advancement of the double-acting cylinder 21. The pressure oil sent out is supplied to a proportional electromagnetic pressure reducing valve 23 with variable secondary pressure, and the pressure oil reduced to the set pressure is supplied via a check valve 22. Further, a bypass passage 20b for returning pressure oil is connected from the cylinder side of the check valve 22 to the pump side of the pressure reducing valve 23.
A check valve 24 is provided at b. In addition, a hydraulic pump 26 is provided in the (upper) oil chamber 21b for rod entry and exit.
The pressure oil sent out from the roll is supplied to the constant pressure valve 25 so as to be maintained at a constant pressure corresponding to the weight of the roll. Therefore, the oil chamber 2 for advancing the rod of the double-acting cylinder 21
The pressure inside 1a becomes the pressure set in the pressure reducing valve 23, but due to the force received from the roll 2a, the oil chamber 21a
When the pressure becomes higher than the set pressure of the oil chamber 21a, the pressure on the pump side of the check valve 24 is sufficiently high so that pressure oil does not return through the check valve 24, and the roll 2a of the oil chamber 21a
The pipe P is crushed with the same force as the force received from the pipe P. Since the pressure in the oil chamber 21b is set to a value corresponding to the weight of the roll, the hydraulic lowering device 20,
The double-acting cylinder 21 is not affected by the roll's own weight, and can adjust the pressure force applied to the pipe P by the roll 2a based on the pressure difference between the oil chambers 21a and 21b. Note that optical sensors (not shown) are installed on the entry and exit sides of each roll 1, 2, and 3, and while these detect the presence of a pipe between each roll, they do not output a detection signal. The input control device (not shown) includes a valve (not shown) provided between the hydraulic pump 16 and the throttle valve with check valve 15 and a valve provided between the hydraulic pump 26 and the pressure reducing valve 23 (not shown). (not shown) to supply pressure oil sent from the hydraulic pumps 16 and 26 to each oil chamber. The straightening method of the present invention, which aims to straighten the bending of a tube and improve its roundness using the straightening machine configured as described above, will be described below. First, transfer of the rolled pipe P is started. When the tip of the pipe P enters the entrance roll 1, an optical sensor (not shown) detects this, and this detection causes a control device (not shown) to adjust the mill stiffness curve X and the pipe plasticity curve Y shown in FIG. Based on this, a valve (not shown) is switched to supply oil to the pressure reducing valve 13, which is set at a pressure determined to provide a predetermined amount of crushing δ ₀ when the pipe outer diameter D is close to the nominal value. As a result, the tip of the tube begins to be compressed as soon as it enters the roll 1, and the pressure reduction position of the roll 1b is at the pressure reducing valve 13.
The position will be the roll gap where the oil pressure determined by is obtained. As shown in Fig. 2, if the roll gap at this time is A and the outer diameter of the tube tip is D, the amount of crushing will be δ ₀ , but due to the action of the pressure reducing valve 13, it will be D'' which is smaller than the tube outer diameter D. Also, even if A' is smaller than the roll gap A, the rolling load is uniform, so the crushing amount is constant at δ _0. However, for example, if D' is larger than D, the check valve Due to the action of 12, the oil pressure in the oil chamber 11 increases, the rolling load increases, and the amount of crushing becomes δ ₄ (>δ ₀ ).
becomes. Now, as the pipe P is transferred and the pipe outer diameter D becomes smaller as shown in FIG. Then, the roll gap becomes smaller [FIG. 3B] and a predetermined amount of crushing δ ₀ is applied to the pipe P [FIG. 3D]. When the outside diameter of the pipe starts to increase after reaching the minimum value _D1 , the presence of the check valve 12 prevents the pressure oil from flowing back, and the third
As shown in Figure C, the roll gap is fixed at A ₁ when D ₁ , so in the subsequent portion with a diameter larger than D ₁ , the crush amount larger than the crush amount δ ₀ will be the same as the outer diameter D ₁ . It continues to be applied to the tube P until it becomes the same [Fig. 3 D]. The outer diameter of the tube is further reduced to D ₂
(D ₂ <D ₁ ), the pressure reducing valve 13
The roll gap is reduced to _A2 by the action of
A crash amount δ ₀ is given. When the pipe diameter is larger than _D2 , the oil chamber 11a
The internal oil pressure increases again, and the amount of crushing becomes a value larger than δ ₀ . The mill stiffness curve X at roll gap A ₁ when the minimum value D ₁ is taken is shown by the two-dot chain line in Fig. 2, but in the changing region from D'' to D', the load exceeds the plateau. , the amount of crushing is larger than δ ₀ , for example δ _5. The above-mentioned crushing is similarly performed by rolls 2 and 3. As a result, δ ₀ is applied over the entire length of the pipe.
A large amount of crushing is applied to the circumferential portion of the tube where the outer diameter is larger than the diameter of the tip of the tube, resulting in high roundness. When the rear end of the tube exits each roll 1, 2, and 3, valves (not shown) between the throttle valve with a check valve and the hydraulic pump and between the pressure reducing valve and the hydraulic pump are switched to communicate these spaces with the tank. As a result, each cylinder 11,
21 internal pressure oil flows back to the tank from the check valves 14, 24. Note that the present invention can improve the roundness of a pipe even when the purpose is not to straighten the bend of the pipe and an offset is not applied to the pipe. The present invention also makes it possible to maintain a constant load when applying crushing to a pipe of a predetermined outer diameter even when the roll gap A' is set or changed from the target set value A due to variations in the roll gap. Therefore, a predetermined amount of crushing can be applied to the pipe in a range below a predetermined pipe outer diameter, and an increased amount of crushing can be applied at a circumferential position of the pipe larger than the predetermined pipe outer diameter. Therefore, the present invention can improve the roundness even when the roll gap changes or when the roll gap is set differently. Further, in the above embodiment, the cylinder tube is attached to the pivot portion of the roll, but it goes without saying that the present invention can also be practiced by attaching the cylinder rod to the pivot portion of the roll with the direction of the cylinder rod reversed. . Furthermore, in the above embodiment, each hydraulic pressure lowering device 1
Check valves 12 and 22 are installed at 0 and 20, but if the pipe is poorly round, the cylinder rod advances and retracts rapidly and the response of the pressure reducing valve is delayed, causing problems with the check valves 12 and 22. This can be omitted since it has the same effect. Furthermore, the present invention is directed to a 6-roll type (2-2-
Of course, it can be applied not only to the vertical roll arrangement straightening machine (type 2) but also to other inclined opposing roll type straightening machines, such as 5-roll type, 6-roll type straightening machines, horizontal roll arrangement straightening machines, etc. However, when the present invention is applied to a horizontal roll arrangement straightening machine, it can be implemented even if all single-acting cylinders are used since the weight of the rolls does not affect the tube pressure of the rolls. Further, in the above embodiment, pressure oil is used to operate the cylinder, but the present invention is not limited to this and can be implemented using other liquids. [Effects] Next, the effects of the present invention will be explained. The present invention corrects bends in pipes, prevents excessive residual stress,
In order to improve roundness, the rolling force range is 7.5 to 68 tons for single-acting cylinders, and 0 for double-acting cylinders.
Test tubes with different amounts of ellipse were straightened as ~60.5 tons. Table 1 is a table summarizing the dimensions of the sample tube, its ellipse amount, and the ellipse amount after the above-mentioned correction.For comparison, the same sample tube was straightened using the conventional method disclosed in JP-A No. 128318/1983. The results are also shown.

[Table] As can be understood from this table, in the comparative example, only about 20% of the ellipse before correction was corrected, but
In the present invention, the ellipse amount before correction has a small outer diameter from the beginning.
With the exception of the 114 mm x 5 mm thick tube, more than 90% of the ellipse before correction could be corrected for the other tubes, making it possible to manufacture tubes with high roundness. As detailed above, the present invention automatically adjusts the amount of correction according to the shape of the outer surface of the tube so that the amount of crushing is greater than the predetermined amount at circumferential positions where the outer diameter of the tube is large, and the amount of crushing is greater than the predetermined amount at circumferential positions where the outer diameter is small. Since the tube is straightened by changing the angle of the tube, it has excellent effects such as high roundness, suppressing residual stress, and making it possible to manufacture a tube without bending.

[Brief explanation of drawings]

Figure 1 is a schematic diagram showing the implementation state of the present invention, Figure 2 is a schematic diagram showing the implementation state of the present invention.
The figure is an explanatory diagram of the roll load of the present invention, Figure 3 is an explanatory diagram of the straightening method of the present invention, Figures 4 and 6 are schematic diagrams of a conventional straightening machine, and Figures 5 and 7 are the contents of the correction. It is an explanatory diagram. P...Pipe, 1,2,3...Roll, 10,20
...Hydraulic lowering device.

Claims (1)

[Claims] 1. In a method of straightening a bend in a pipe by passing a pipe between a pair of rolls equipped with at least a hydraulic pressure reducing device and applying a crush to the pipe, there is a method in which a pipe is passed between a pair of rolls equipped with at least a hydraulic pressure reducing device, and a pipe is passed between a hydraulic cylinder that drives the rolls to reduce pressure and a hydraulic pressure source. In addition to providing a pressure regulator for the hydraulic pressure in the hydraulic cylinder, if the hydraulic pressure in the hydraulic cylinder rises above the regulated hydraulic pressure due to the force applied to the hydraulic cylinder from the roll side, a pressure regulator is provided to the hydraulic pressure source side. In order to prevent backflow of the liquid, and to improve the roundness of the pipe, the pipe is compressed with a regulated hydraulic pressure or a higher hydraulic pressure to impart a crush. How to straighten the tube.