Patent Application
20210229153
The present invention relates to a method for bend straightening.
Steel materials such as pipes and bar materials come to have bends in their producing process. Patent Document 1 and Patent Document 2 disclose straightening methods for straightening bends of a pipe or a bar material.
The straightening methods described in Patent Documents 1 and 2 present a method in which a load and a deflection in press straightening are measured continuously over time, and the load is removed when a limit within which the load increases in proportion to the deflection is exceeded and a value of (deflection−straightening load×proportionality coefficient) reaches a preset amount of straightening. In other words, in the straightening method, a bend of a pipe is straightened by measuring an amount of bend in advance before applying the straightening load, determining a deflection δ1 of a material in pressing for giving unbending deformation necessary to straighten the bend by a predetermined method, performing press bending until the deflection δ1 is reached, and then removing the load.
A concept of determining the deflection δ1 will be described below. First, an initial bend δ0 of a material placed on two supports separated by a span L is measured before straightening. As one of methods for the measurement, while the material placed on the two supports is rotated about its axis, an amplitude of a mid-span portion of the material is measured with a measuring instrument such as a dial gauge installed below the material. Half of the amplitude of the mid-span portion is considered to be a target value δ0 for an amount of the bending by which the bend straightening is to be performed.
To perform the bend straightening, the material is placed on the supports such that a direction of the bend of the material becomes a vertically upward direction, and a center portion of the material is bent downward with a press head attached to an end of a hydraulic cylinder. Regarding a relation between a load P applied at that time and a bending displacement δ of the material, deformation of the material is in an elasticity region in an initial stage being a beginning of pressing, where a P-δ curve has an inclination of X1. As the press bending proceeds with the load P gradually increasing, the deformation of the material, which is in the deform plastically region with the inclination λ1 in the beginning, reaches a plastic deformation region, the increase in the load P slows down, and a plastic bending of the material progresses. Then, when the bending displacement δ reaches the deflection δ1 of the press bending determined beforehand, pressing operation is stopped, and the load is removed. When the load is removed, the elastic deformation given to the material by the working load before the unloading is released, and after the load is completely removed, the plastic bending δ0 as permanent deformation remains. This enables unbending by the same amount as the initial amount of bend, and the bend straightening can be achieved.
Patent Documents 1 and 2 are characterized in that a bending amount δ1 up to a pressing bottom dead center position described above is determined with consideration given to a difference between the inclination λ1 in the elasticity region when a bending load is applied initially and an inclination λ2 when the load is removed after the pressing bottom dead center position is reached and the elastic deformation is released, that is at so-called spring back, on a load-displacement curve. In other words, an amount of pressing operation is determined, focusing on the fact that the inclination in loading and the inclination in unloading are λ1 and λ2, respectively, both of which do not match in general. The present inventors consider that a reason for this is due to Bauschinger effect and residual stress associated with a history of a straightened material.
Patent Document 1: JP63-199025A
Patent Document 2: JP10-5872A
According to these Patent Documents 1 and 2, the press bending amount δ1 is determined with reference to behavior of the relationship between the load and the displacement illustrated in
In other words, even when a bend is straightened by the methods described in Patent Documents 1 and 2, it was difficult to perform straightening with high accuracy by performing pressing operation only once. For example, a straightening level of 0.5 mm to 1 mm per 1 m is often required as a product specification; however, it is difficult to achieve such a straightening level by performing the pressing operation according to the method described in Patent Documents 1 and 2 once, due to the Bauschinger effect described above and subtle fluctuations in properties of a material and a machine and additionally various unevenness factors including backlash of a device and stiffness of the device. This makes it difficult to apply techniques of prior art to press straightening performed in an actual operation site, which brings about a situation where the press straightening still has to depend on a pressing operation by a skilled worker.
The present inventors conducted detailed studies about a flaw of prior art and found that the straightening with high accuracy to perform needs slight adjustment in amount of bend in its final stage, that is, finish straightening; however, this case requires straightening working in a light load region where no clear transition to the plasticity region can be read even when a load-displacement curve is observed by on-line measurement. In other words, as illustrated in
Is was further found that, in such a light-load deformation region, the inclination λ2 at the unloading is not constant and subtly changes depending on a level of a value of a pressing-bottom-dead-center load value at start of the unloading, as described in Patent Documents 1 and 2. In
Therefore, a concept of prior art, in which an operation amount of the press working is determined by estimating the inclination λ2 at the unloading with reference to a shape of the load-displacement curve in the pressing operation, cannot possibly realize the finish straightening. Hence, in a pressing operating region that is seemingly considered as the elasticity region, the present inventors conducted detailed studies about a relation between bottom dead center load P in the pressing operation and change AS in amount of bend of a pipe after unloading and determined, based on a database of the studies, to perform the unloading after performing the pressing operation until a pressing load P at which AS provides a target straightening amount So described above.
In addition, the present inventors found that determining an operation amount of pressing control to be a target load value to be applied to a steel material in a region that is not used in conventional practice makes the pressing control easy, which can increase an accuracy of the bend straightening as compared with the case of Patent Documents 1 and 2 where a displacement of the steel material in pressing is determined as the operation amount of the pressing control.
An objective of the present invention is to provide a method for bend straightening that includes determining a target load value, and performing pressing control using the target load value to increase the accuracy of the bend straightening.
The present invention is a method for bend straightening in which a pipe body having a bend is placed in a state where the pipe body is convex upward, the pipe body is pressed from above by a press unit at a target load value, whereby the pipe body is straightened, the method including: (a) a step of measuring a bottom-dead-center load value when the press unit is at a bottom dead center in the pressing; (b) a step of measuring an amount of change in amount of bend between an amount of bend of the pipe body before the pressing in the step (a) and an amount of bend of the pipe body after the pressing in the step (a); (c) a step of repeating the step (a) and the step (b) a plurality of times to create a relation between the bottom-dead-center load value and the amount of change in the amount of bend; and (d) a step of determining a target load value for next pressing from the relation.
According to the present invention, the bottom-dead-center load value and the amount of change in amount of bend are collected to create a relation between the bottom-dead-center load value and the amount of change in amount of bend, and from the relation, the target load value used for pressing the pipe body is determined. In addition, by using the target load value as an operation amount of pressing control, the pressing control can be made easy to perform, and an accuracy of bend straightening can be increased.
A method for bend straightening to be described below is a method for straightening a steel pipe being a pipe body by pressing a bend portion that occurs in the steel pipe using a press straightener.
The steel pipe 100 that is to be subject to the press straightening by the press straightener 1 has, for example, a curve-like bend. The bend of the steel pipe 100 occurs in, for example, hot or cold working in a producing process of the steel pipe 100.
The press straightener 1 includes a two-point support 2. The two-point support 2 supports the steel pipe 100 at two points, with its axis direction set to be a horizontal direction. The steel pipe 100 is placed on the two-point support 2 to be convex upward.
The press straightener 1 includes a press unit 3. The press unit 3 includes a press cylinder 31 and a press plate 32. The press unit 3 presses the steel pipe 100 placed on the two-point support 2 to apply a load to the steel pipe 100.
The press cylinder 31 includes a rod not illustrated, which has a rod end provided with the press plate 32. The press cylinder 31 is coupled to a hydraulic unit 33 and expands and contracts the rod via working of the hydraulic unit 33 to perform ascending and descending operation of the press plate 32 and the pressing control on the steel pipe 100.
The press plate 32 ascends and descends via the expansion and contraction of the press cylinder 31. By the rod of the press cylinder 31 expanding, the press plate 32 presses the steel pipe 100 placed on the two-point support 2 from above, applying the load to the steel pipe 100.
The press cylinder 31 is provided with a load cell 34. The load cell 34 measures a load value P with which the press plate 32 presses the steel pipe 100. During the pressing by the press plate 32, the load cell 34 measures the load value P as appropriate and outputs a value of the measurement to a controller 10 described below.
The press straightener 1 is provided with a displacement gauge 4. The displacement gauge 4 measures an amount of bend δ of the steel pipe 100 being pressed by the press unit 3.
The displacement gauge 4 measures an amount of bend δ of the steel pipe 100 by the press unit 3 with respect to the axis direction of the steel pipe 100. The displacement gauge 4 outputs a value of the measurement to the controller 10 described below. The displacement gauge 4 may be of a contact type that comes in contact with the steel pipe 100 to measure the amount of bend δ or may be of a noncontact type that measures the amount of bend δ without contact with the steel pipe 100.
The press straightener 1 includes a pair of rotating rollers 51 and the displacement gauge 4. The pair of rotating rollers 51 rotates while sandwiching one end of the steel pipe 100 to hold the steel pipe 100. The press straightener 1 causes the press unit 3 to press the steel pipe 100, lifts up the steel pipe 100 from the two-point support 2 after unloading, and causes the pair rotating rollers 51 to rotate the steel pipe 100.
The displacement gauge 4 measures a rotation amplitude value S of the steel pipe 100 rotated by the pair rotating rollers 51. The rotation amplitude value S is measured by the displacement gauge 4, and half of the rotation amplitude value can be measured as a residual amount of bend δa of the steel pipe 100 after the pressing. The displacement gauge 4 is, for example, a dial gauge.
When the pressing by the press unit 3 starts, the steel pipe 100 deforms elastically, and as the pressing further continues, the steel pipe 100 deforms plastically. When the steel pipe 100 is unloaded being bent in the plastic deformation region, the steel pipe 100 maintains its bent state. In the state where the steel pipe 100 is deformed plastically after the unloading, the amount of bend δ from the reference level described above is the residual amount of bend δa.
The displacement gauge 4 measures the rotation amplitude value S of the steel pipe 100 rotated by the pair rotating rollers 51 when the steel pipe 100 is bent downward. In other words, the residual amount of bend δa of the steel pipe 100 after the pressing is obtained by halving the rotation amplitude value S measured by the displacement gauge 4.
Return to
The controller 10 acquires results of the measurement from the load cell 34 and the displacement gauge 4.
The controller 10 uses the value of the measurement by the load cell 34 to perform feedback control on the hydraulic unit 33 and perform the pressing control on the press unit 3. In the pressing, the controller 10 measures a bottom-dead-center load value Pk when the press unit 3 is at its bottom dead center. When the press unit 3 is at its bottom dead center refers to when the rod (not illustrated) of the press cylinder 31 is at its bottom dead center.
From the value of the measurement by the displacement gauge 4, the controller 10 measures an amount of change M between the amount of bend δ of the steel pipe 100 before the pressing and the amount of bend δ of the steel pipe 100 after the pressing. Here, after the pressing means a state where the load of the pressing is removed, and no load is applied to the steel pipe 100 by the press unit 3.
In addition, the controller 10 measures the residual amount of bend δa of the steel pipe 100 from the rotation amplitude value S measured by the displacement gauge 4, as described with reference to
The controller 10 collects pluralities of bottom-dead-center load values Pk and amounts of change M to create Pk=f(Δδ), a relational expression of Pk-M.
In
In contrast, for example, in a case where the steel pipe 100 is pressed with a bottom-dead-center load value Pk of 2.7 [kN], the amount of change M in the amount of bend δ of the steel pipe 100 before and after the pressing is about 0 [mm]. In this case, the steel pipe 100 is deformed elastically.
After collecting the pluralities of bottom-dead-center load values Pk and amounts of change M measured, the controller 10 creates Pk=f(Δδ), the relational expression of Pk-Δδ. The relational expression Pk=f(Δδ) is a regression formula that is acquired from a plurality of data items, as illustrated as a solid line in
Pk=a·Δδ4+b·Δδ3+c·Δδ2+d·Δδ+e (1)
where a=−0.0269, b=0.174, c=−0.416, d=0.467, e=2.77. Note that Formula (1) is updated whenever a bottom-dead-center load value Pk and an amount of change M are measured.
From the relational expression Pk=f(Δδ) shown by Formula (1) and the residual amount of bend δa of the steel pipe 100, the controller 10 determines a load value for the next pressing (hereinafter, referred to as target load value Pa). Using the relational expression Pk=f(Δδ) makes it possible to determine a load value necessary to perform the bend straightening by deforming the steel pipe 100 plastically by the residual amount of bend δa. For example, in a case where the residual amount of bend δa of the steel pipe 100 is about 1.8 mm, a load value necessary to deform the steel pipe 100 plastically by about 1.8 mm is about 3.0 kN (see
When performing the pressing at the target load value Pa, the controller 10 performs feedback control on the hydraulic unit 33 to press the steel pipe 100 with reference to the result of the measurement by the load cell 34. The controller 10 then repeats the pressing of the steel pipe 100 until the residual amount of bend δa becomes not more than a threshold value, so as to straighten the steel pipe 100. The threshold value is preferably 1 mm, more preferably 0.5 mm.
A method for bend straightening performed by the press straightener 1 will be described below in detail.
First, the controller 10 causes the press unit 3 to press the steel pipe 100 (S1). Specifically, the controller 10 operates the hydraulic unit 33 to expand the rod of the press cylinder 31. The controller 10 then uses the press plate 32 to press the steel pipe 100 placed on the two-point support 2. At this time, the controller 10 controls the hydraulic unit 33 such that the load value P becomes the target load value Pa while acquiring the result of the measurement by the load cell 34.
In a case where step δ1 is performed first in the production or the relational expression Pk=f(Δδ) described above is not created with high accuracy because the database is built insufficiently, that is, in a case where the target load value Pa is not determined strictly from the relational expression Pk=f(Δδ), the controller 10 may start the operation based on a material strength level of the material and a simple elastic bending deformation prediction formula. Alternatively, the pressing may be performed according to an empirical rule of a worker or a load value determined by another method.
Next, the controller 10 measures the bottom-dead-center load value Pk (S2). Thereafter, the controller 10 performs unloading (S3) and measures the amount of change M (S4). The amount of change M is measured as the difference between the amount of bend δ of the steel pipe 100 before the pressing and the amount of bend δ of the steel pipe 100 after the pressing, as described above.
In step S5, from the bottom-dead-center load value Pk and the amount of change Δδ, the controller 10 creates the relational expression Pk=f(Δδ). At this time, in a case where the relational expression Pk=f(Δδ) has not been created, the controller 10 repeats step δ1 to step S4 a plurality of times to collect pluralities of bottom-dead-center load values Pk and amounts of change M, and then create the relational expression Pk=f(Δδ). In contrast, in a case where the relational expression Pk=f(Δδ) has already been created, the controller 10 uses the bottom-dead-center load value Pk measured in step S2 and the amount of change M measured in step S4 to update the relational expression Pk=f(Δδ).
Subsequently, the controller 10 controls the rotation of the pair of rotating rollers 51 to rotate the steel pipe 100 (S6). The controller 10 causes the displacement gauge 4 to measure the rotation amplitude value S (S7). The controller 10 determines the residual amount of bend δa of the steel pipe 100 from the measured rotation amplitude value S (S8).
The controller 10 determines whether the residual amount of bend δa of the steel pipe 100 after the straightening is not more than the threshold value (e.g., 1 mm or 0.5 mm) (S9). When the residual amount of bend δa is not more than the threshold value (S9: YES), the controller 10 determines that the steel pipe 100 is straight. The method for bend straightening is thus finished.
When the residual amount of bend δa is more than the threshold value (S9: NO), the controller 10 determines that the steel pipe 100 is not straight. The controller 10 then determines the target load value Pa from the relational expression Pk=f(Δδ) and the residual amount of bend δa (S10). Specifically, the controller 10 substitutes the residual amount of bend δa for Δδ in Formula (1) to calculate the load value Pk. The controller 10 determines the calculated load value Pk as the target load value Pa.
The controller 10 returns to step δ1 to press the steel pipe 100 with the determined target load value Pa. In a case where the steel pipe 100 is convex downward before being pressed in step S1, the steel pipe 100 is rotated to be convex upward.
By repeating the process described above, the bend of the steel pipe 100 is straightened, and the steel pipe 100 becomes straight. Since the relational expression Pk=f(Δδ) is updated whenever necessary, a reliability of the target load value Pa determined from the relational expression Pk=f(Δδ) increases as the pressing for the bend straightening is repeated. As a result, an accuracy of the bend straightening increases.
In the method for bend straightening of the present embodiment, the pressing control is performed using only the target load value Pa without measuring the amount of bend of the steel pipe 100 being pressed. Furthermore, as shown in
As described above, in conventional practice, the bend straightening is performed while observing a displacement of a steel pipe being pressed in the plastic deformation region using the inclination λ2 of an unload curve created in the plastic deformation region, as illustrated in
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-150091 | Aug 2018 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2019/030998 | 8/6/2019 | WO | 00 |
