JP2016055334A - Method of manufacturing bent metallic bar material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a member surface layer part from cracking in bending processing on a bar material made of Ni-based alloy.SOLUTION: A method of manufacturing a bent metallic bar material in which a bar material made of Ni-base alloy is plastically deformed by heating and clamping the bar material with a clamp arm, and swiveling the bar material by propelling to guide the bar material so that the bar material is curved drawing an arc includes: a step of preparing a processing temperature range map obtained by conducting a tensile strain imparting test using a test-piece manufactured under the same conditions with the bar material and showing a temperature range in which processing can be performed without causing any cracking; a step of determining processing conditions from the map; and a step of performing bending processing so that the processing conditions are met, the processing is carried out at a temperature higher than the allowable processing temperature calculated from the map when the bar material has a first attribute such that it is harder for the bar material to crack at a higher temperature and at a temperature lower than the allowable processing temperature calculated from the map when the bar material has a second attribute such that it is harder for the bar material to break at a lower temperature.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for manufacturing a bent metal strip and a bending apparatus, and more particularly to a technique for preventing cracks that may occur in a member surface layer portion when hot bending a metal strip made of a nickel-based alloy.

  Metal tubes made of nickel (Ni) -based alloys are used today in industrial facilities such as power plants, various plants, and factories as thick high-temperature, high-pressure, high-pressure members such as steam tubes for power generation boilers.

  These metal pipes (the target member of the present invention is not limited to a pipe, but will be described below as an example of a pipe as a typical embodiment) are standardized and shaped pipes such as elbows and bends that have been previously formed in a predetermined shape. On the other hand, pipes made by bending straight pipes according to the construction object (referred to as “bend pipes”) are widely used because they can flexibly meet the demands for various curvatures and pipe shapes. Has been.

  In order to manufacture such a bent tube, in general, a part of a straight metal tube to be processed is heated in an annular shape by an induction heating coil or the like, and at the front end side of the metal tube induction heating coil (tube tip) by a clamp arm. Side) and push the metal tube toward the induction heating coil. The clamp arm pivots around a support shaft and regulates the path of the metal tube in an arc shape. By pushing the metal tube while gripping the metal tube with such a clamp arm, the clamp arm is bent to the part heated by the induction heating coil. A moment is applied, and the metal tube can be continuously plastically deformed to draw an arc.

  Moreover, there is the following patent document as a technique for disclosing a technique related to the bending process of such a metal strip.

JP 2014-34725 A JP 2002-178042 A JP2013-158830A

  By the way, the metal strip made of such a Ni-based alloy tends to cause fine cracks (cracks) in the surface layer of the member at the time of hot bending, and proposals such as the above-mentioned patent document have been conventionally made to prevent this. Yes.

  For example, in the invention described in Patent Document 1, an austenitic alloy member containing components such as Ni, Cr and W has a maximum hardness HV0.1 (max) in a region from the outer surface to a depth of 5 mm, and an average crystal of the member If the particle size d (μm) is controlled so as to satisfy the formula [HV0.1 ≦ (−1/6) × d + 300], it is assumed that cracks can be prevented from occurring during hot bending.

  However, the members satisfying the above conditions, that is, the average crystal grain size d = 500 μm, the hardness is 180 HV, and [180 ≦ (−1/6) × 500 + 300 = 216.7] When a member was prepared and subjected to a bending test, it was confirmed that cracks were observed in the surface layer of the member, and the invention described in Patent Document 1 did not necessarily prevent the occurrence of cracks.

  The invention described in Patent Document 3 is a bending process after heating a superalloy member made of a Ni-based alloy or a Fe-Ni-based alloy in a heating furnace at a temperature of 1175 ° C. or higher and lower than 1250 ° C. (work hardening layer disappearing step). By carrying out, the grain boundary cracking of the member surface layer is prevented. However, when the present inventors performed hot bending after performing the same heat treatment (heating to 1200 ° C.), it was not possible to prevent cracking of the member surface layer portion.

  Further, in the invention described in this document (the same is true of the invention described in Patent Document 2), there is an inconvenience that it is necessary to perform heat treatment on all the objects to be processed one by one at a predetermined accurate temperature before the bending process. There is an increasing difficulty. Thus, it cannot be said that the conventional crack prevention technology for the metal strips made of Ni-base alloy is sufficient.

  Accordingly, an object of the present invention is to make it possible to more easily and sufficiently prevent the occurrence of cracks in the member surface layer portion during hot bending of a metal strip made of a Ni-based alloy.

  In order to solve the above-described problems and achieve the object, a method for manufacturing a bent metal strip according to the present invention heats a metal strip made of a nickel (Ni) -based alloy in a ring shape and heats the metal strip. The metal strip is gripped by a clamp arm that can grip the vicinity of the section and can be turned around a support shaft that is separated from the gripping section by a certain distance, and is held by the clamp arm by propelling the metal strip in the direction of the axis. By turning the part and guiding it so that at least a part of the metal strip is curved in an arc, a bending moment is applied to the heated portion of the metal strip, so that at least a part of the metal strip is continuously bent. The metal strip is bent by plastic deformation, but the step of preparing a processing temperature range map, the step of determining processing conditions from the processing temperature range map, and the processing conditions are satisfied. And a step of performing bending.

  Here, the processing temperature range map indicates an allowable processing temperature range in which bending can be performed without causing cracks, and for a test piece manufactured under the same conditions as the metal strip to be processed. It can be obtained by conducting a plurality of tensile strain application tests with different tensile strains and heating temperatures and determining whether or not cracks have occurred in the test pieces in these tests.

  Further, the above processing conditions determined from this processing temperature range map are higher than the allowable processing temperature calculated from the processing temperature range map when the metal strip has a first attribute that becomes harder to break as the temperature increases. On the other hand, when the metal strip has the second attribute that is harder to crack as the temperature is lower, plastic deformation is performed at a temperature lower than the allowable processing temperature calculated from the processing temperature range map.

  The inventor has been bending a large number of strips for many years. However, when bending is performed, cracks are less likely to occur as the processing temperature is increased by the strips. On the other hand, it is found that there are some which are less likely to crack as the processing temperature is lowered (this property is referred to as “second attribute”). It has been found that the correlation with the ease of cracking (this is called “cracking sensitivity”) cannot be defined uniformly.

  On the other hand, which of the above processing temperatures and cracking susceptibility shows the opposite behavior even if the composition is the same, the trace element contained in the strip material and the strip material used as the material for bending It is considered that the attribute related to cracking sensitivity is determined by various factors such as differences in manufacturing methods and combinations thereof, and it is difficult to specify the cause.

  Therefore, in the present invention, when bending is performed, a test for actually applying tensile strain is performed using a test piece manufactured under the same conditions as the object to be processed, and the object to be processed is the first or second in terms of crack sensitivity. Determine which attribute it has. The “same conditions” means that the components and the manufacturing method (the manufacturing method of a straight strip (for example, straight pipe) to be processed in the manufacturing method of the present invention) are the same. Further, in this tensile strain application test, for example, tensile strain is applied to the test piece while being heated by high frequency induction heating, and the hot bending state during processing is reproduced. A specific method for applying the tensile strain may be a tensile test in which the test piece is simply pulled in the axial direction, or a bending test in which the test piece is bent in the same manner as the workpiece.

  The tensile strain application test is performed a plurality of times (for various combinations of tensile strain and heating temperature) with different tensile strain and heating temperature (material temperature of the test piece). In these tests, it is determined whether or not a crack has occurred in the test piece. Tensile strain (the value of the maximum tensile strain generated in the test piece) is applied to one shaft, and the heating temperature is applied to the other shaft. A processing temperature range map is obtained by plotting the determination result of whether or not a crack has occurred in the taken two-dimensional (biaxial) graph.

  This processing temperature range map shows the allowable processing temperature range in which bending can be performed without causing cracks (more specific details will be described with reference to the drawings in a later embodiment). By referring to the map, the metal strip is a strip having a first attribute that is hard to break as the temperature is high, or a strip having a second attribute that is hard to break as the temperature is low. It is possible to determine whether or not there is a limit value at which bending can be performed without causing cracks. This limit value (this is the “allowable processing temperature”) is a lower limit value that may cause cracking at a temperature lower than this when the strip has the first attribute, When the said strip has the 2nd attribute, it becomes an upper limit which a crack may generate | occur | produce at temperature higher than this.

  Then, an allowable processing temperature corresponding to a tensile strain (maximum value of tensile strain) that is expected to occur in the processing target (metal strip) is calculated from the processing temperature range map, and the processing target is: When it has the first attribute, plastic deformation is performed at a temperature higher than the permissible processing temperature (lower limit), and when the processing target has the second attribute, at a temperature lower than the permissible processing temperature (upper limit). Perform plastic deformation. Note that, regardless of whether the processing target has the first or second attribute, it is a matter of course that the processing target is heated to a temperature at which the processing target is bent (plastically deformed) or higher. The above tensile strain is the maximum value of the tensile strain on the outer periphery of the bending where the maximum tensile strain occurs during processing. This value is the size of the bending radius and whether or not to perform compression bending. However, it can be calculated (predicted) if these conditions are determined, although it depends on the magnitude of the compressive force applied during processing.

  In order to obtain the processing temperature range map, it is necessary to carry out the tensile strain application test as described above. Once the test is carried out and the map is obtained, the metal produced with the same components and production method is used. Since it is not necessary to perform pre-treatment such as heat treatment for each strip for each strip, it is possible to increase the mass productivity of the bent metal strip.

  In one aspect of the present invention, the metal strip is heated by a coil, and the coil includes a first coil portion and a second coil portion that are arranged in order in the propelling direction of the metal strip. During the bending process, the first coil part is driven with a larger output than the second coil part so that the metal strip is heated to the processing temperature by the first coil part.

  In the conventional bending process, the portion of the metal tube immediately before the clamp arm is simply heated by a coil consisting of a one-turn winding (a coil configuration having only a second-stage coil portion 12b in FIG. 4 described later) ) Or when a coil having a plurality of coil portions is used (for example, a coil configuration comprising two-stage coil portions 12a and 12b as shown in FIG. 4 described later), It has been usual to drive with the same output without changing the input power (equivalent power supply to each coil unit).

  However, when considering conventional processing equipment (especially coils) from the new point of view of preventing cracks, when propelling metal strips, even at the initial stage (preheating stage) when entering the coil placement region. It has been found that a relatively large tensile force is applied to the bending outer periphery of the strip, and this tensile force may cause cracking. In the case of the conventional apparatus as described above, as described later with reference to the drawings, the metal strip reaches a temperature peak immediately after passing through the coil, and the temperature continues to rise while passing through the coil toward this peak. Such a temperature change is shown (see the broken line in FIG. 7).

  Therefore, in the manufacturing method according to one aspect of the present invention, in addition to processing based on the above-described processing conditions (temperature conditions determined by a processing temperature range map), the arrangement configuration of the coil is changed, and the coil is made of metal. The first coil part and the second coil part arranged so as to be arranged in order in the propelling direction of the strip are included, and during the bending process, the metal strip is heated to the processing temperature by the first coil part. Thus, the first coil part is driven with a larger output than the second coil part. In other words, the coil according to the aspect is arranged in the first coil portion arranged on the rear side (the side far from the clamp arm) and in the front side (side near the clamp arm) in the propelling direction of the metal strip. The first coil portion is a main heating coil that raises the temperature of the metal strip to the processing temperature, and the second coil portion is enhanced by the first coil portion. It was set as the heat retention coil which hold | maintains the temperature of a metal strip at processing temperature.

  According to such an aspect, the metal strip that has progressed to the coil placement region is quickly heated so as to reach the processing temperature from the beginning, and this temperature is maintained, so that the tensile force is applied in the preheating stage where the temperature is still low. It is possible to avoid a situation in which cracking occurs. In particular, when processing a strip with a large thickness (for example, a thick metal tube), the temperature of the inner surface of the strip (the inner surface of the tube) is less likely to increase as the thickness increases. In the configuration, the strip material is subjected to a large tensile force before the temperature is sufficiently increased, and cracks are likely to occur on the inner surface of the strip material. On the other hand, according to the coil according to the above aspect, since the temperature can be increased to the inner surface side of the strip material at an early stage, it is possible to effectively prevent the occurrence of such cracks that are likely to occur in the thick strip material. I can do it.

  The metal strip referred to in the present invention is typically a tubular member (metal tube / hollow member), but is not limited thereto, and rod-shaped members (solid members) having various cross-sectional shapes are also included in the present invention. Included in the metal strip. An example (weight ratio) of the composition of the Ni-based alloy according to the present invention includes 50% or more of Ni, 22% of Cr, 12% of Co, 9% of Mo, and further contains Al.

  ADVANTAGE OF THE INVENTION According to this invention, it can prevent more easily and fully that a crack generate | occur | produces in a member surface layer part in the hot bending process of the metal strip which consists of Ni base alloys.

  Other objects, features, and advantages of the present invention will become apparent from the following description of embodiments of the present invention described with reference to the drawings. Note that the present invention is not limited to these embodiments, and it will be apparent to those skilled in the art that various modifications can be made within the scope of the claims. Moreover, in each figure, the same code | symbol shows the same or an equivalent part.

FIG. 1 is a flowchart showing the steps of a method for manufacturing a bent metal strip (bending pipe) according to an embodiment of the present invention. FIG. 2 is a diagram (an example of a processing temperature range map) illustrating a result (first attribute) of performing a tensile strain application test using a test piece. FIG. 3 is a diagram (another example of a processing temperature range map) illustrating the result (second attribute) of a tensile strain application test using another test piece. FIG. 4 is a plan view schematically showing a bending apparatus (initial state) according to an embodiment of the present invention. FIG. 5 is a plan view schematically showing the bending apparatus (the state during processing) according to the embodiment. FIG. 6 is a cross-sectional view (A-A cross section in FIG. 4) of the coil placement portion (metal tube) of the bending apparatus according to the embodiment. FIG. 7 is a diagram showing a temperature change of the outer surface of the metal tube when the bending is performed by the bending apparatus according to the embodiment as compared with the case where the processing is performed by the conventional processing apparatus. FIG. 8 shows the change in tensile strain when the metal pipe having the first attribute shown in FIG. 3 is bent using the bending apparatus according to the embodiment, and the case where the conventional processing apparatus is used. It is a diagram shown in comparison. FIG. 9 is a diagram showing the temperature change of the outer surface of the metal tube and the temperature change of the inner surface when processing is performed by the bending apparatus according to the embodiment. FIG. 10 is a diagram showing a change in temperature of the outer surface of the metal tube and a change in temperature of the inner surface when processing is performed with a conventional bending apparatus.

  The method for manufacturing a bent metal strip according to an embodiment of the present invention is a method of manufacturing a bent pipe by bending a straight metal pipe (straight pipe). First, referring to FIG. The whole will be briefly described, and then each process will be described in detail.

  As shown in FIG. 1, in this method, first, a processing temperature range map is obtained by performing a tensile strain application test (step S1), and the attribute of the metal tube to be processed is determined (step S2). If the object to be processed has the first attribute, the allowable processing temperature is calculated from the tensile strain expected to occur in the object to be processed during bending (the maximum value of the tensile strain generated on the outer periphery of the bending). A temperature range map is used (step S3), and bending is performed using this as a processing condition (step S4). On the other hand, when the processing target has the second attribute, similarly, an allowable processing temperature is obtained from the tensile strain expected to be generated in the processing target using the processing temperature range map (step S5), and this is processed. Bending is performed as a condition (step S6). Each will be described in detail below.

[Determination of processing conditions (S1 to S3, S5)]
FIG. 2 to FIG. 3 show examples of processing temperature range maps, and plot the determination results as to whether cracks have occurred for various combinations of tensile strain and material temperature. In order to obtain a processing temperature range map, a tensile strain application test is performed. In this test, a plurality of test pieces having the same components and the same manufacturing method as the metal pipe to be processed are produced, and these test pieces are heated to various temperatures (for example, 850 ° C. to 1150 ° C.). Thus, tensile tests are performed to generate tensile strains of various sizes (for example, 5% to 20%) under the respective temperatures.

  Then, it is determined whether or not each test piece is cracked, and the result is plotted on a graph. The circles in the figure indicate that no cracks occurred, and the x marks indicate that cracks occurred. The curves in each figure show the boundary between when cracks occurred and when no cracks occurred. Show. As can be seen from these figures, depending on the object to be processed (test piece), it becomes harder to break as the temperature increases (FIG. 2 / first attribute), and it becomes easier to crack when the temperature becomes higher (FIG. 3 / second). Attribute).

  By performing the tensile strain application test using the test piece, it is possible to determine whether the metal pipe to be processed has the first attribute or the second attribute. If the metal tube has the first attribute as shown in FIG. 2, the temperature corresponding to the maximum tensile strain expected to occur in the workpiece is obtained from the curve in FIG. 2, and this is allowed. The processing temperature. This allowable processing temperature is a lower limit value at which bending can be performed without causing cracks, and the processing condition is to perform bending (plastic deformation) at a temperature higher than the allowable processing temperature. For example, when the tensile strain is 7.5%, the allowable processing temperature is 1080 ° C., and bending is performed at a higher temperature.

  On the other hand, when the said metal pipe has a 2nd attribute as shown in FIG. 3, the temperature corresponding to the said tensile strain is calculated | required from the curve of FIG. 3, and this is made into allowable process temperature. This allowable processing temperature is an upper limit value at which bending can be performed without causing cracks, and the processing condition is that bending processing (plastic deformation) is performed at a temperature lower than the allowable processing temperature. For example, when the tensile strain is 7.5%, the allowable processing temperature is 1020 ° C., and bending is performed at a lower temperature. Of course, as described above, the metal tube is heated to a temperature at which the metal tube can be bent (plastically deformed) or more at the time of processing even when the first or second attribute is provided.

[Perform bending (S4 or S6)]
4-6 is a top view which shows the bending apparatus which concerns on one Embodiment of this invention, and performs a bending process using the said apparatus, for example.

  As shown in FIGS. 4 to 6, this bending apparatus includes an induction heating coil 12 that annularly heats a part of the metal tube 11 to be processed, and a propulsion mechanism 14 that propels the metal tube 11 toward the coil 12. A clamp arm 31 that has a front clamp 33 for holding the front portion of the metal tube 11 and that imparts a bending moment to the metal tube 11 by rotating around the support shaft 32 as the metal tube 11 is propelled; 11 is provided with a compression mechanism 21 that generates a pulling force that is a force in the direction opposite to the propulsion 11 and applies a compressive force to the metal tube 11.

  Note that FIGS. 4 to 6 show front, rear, left, right, and up and down directions, and the present embodiment will be described based on these directions. Further, in the figure, symbol C is the center line of the metal tube 11, symbol R is the bending radius of the metal tube 11, symbol 11a is the inner surface of the metal tube 11, symbol 11b is the outer surface of the metal tube 11, and symbol t is the metal. Reference numeral 13 denotes a guide roller for guiding the metal tube 11.

  The propulsion mechanism 14 that propels the metal tube 11 includes a rear clamp 15 that holds the rear portion of the metal tube 11 and a propulsion drive unit 16 that applies a forward propulsive force to the metal tube 11 through the rear clamp 15. The propulsion drive unit 16 is constituted by, for example, a hydraulic cylinder.

  On the other hand, the compression mechanism 21 that applies a compression force to the metal tube 11 is fixed to the lower end portion of the clamp arm 31 and rotates together with the clamp arm 31 around the support shaft 32 of the clamp arm 31 (see arrow P4). The chain 23 meshes with the sprocket 24, and the compression drive unit 22 that generates a pulling back force P5 that pulls the chain 23 in the direction opposite to the propulsion direction of the metal tube 11 (rearward). The compression drive unit 22 may be constituted by, for example, a hydraulic cylinder.

  Note that the propulsion mechanism 14 and the compression mechanism 21 are not limited to specific structures, and the propulsion mechanism 14 in the present invention is capable of propelling the metal tube 11, and the compression mechanism 21 is a metal tube. Any structure can be used as long as it can apply a compressive force to 11 and is not limited to the illustrated structure.

  The coil 12 that heats the metal tube 11 is disposed behind the clamp arm 31. The coil 12 is composed of an induction heating coil, and a main heating coil portion 12a for raising the metal tube 11 to a processing temperature (a temperature for plastic deformation and a maximum temperature during processing), and also an induction heating coil and a main heating. And a heat retaining coil portion 12b that keeps the temperature of the metal tube 11 raised by the coil portion 12a at the processing temperature.

  Both of these coil parts 12a and 12b are driven by a drive part (not shown) including a power source for supplying high-frequency power, but the heating coil part 12a is supplied with high-frequency power compared to the heat retaining coil part 12b. The amount is increased (current is supplied to each coil portion so that the current density of the main heating coil portion 12a is larger than the current density of the heat retaining coil portion 12b). This is to prevent the crack due to the initial strain described later by quickly raising the temperature of the metal tube 11 to the processing temperature by the main heating coil portion 12a. Further, since the heat retaining coil portion 12b only needs to maintain the temperature raised by the main heating coil portion 12a, the power input amount may be smaller than that of the main heating coil portion 12a. To describe a specific example, for example, 70% of electric power is supplied to the main heating coil portion 12a and 30% of electric power is supplied to the heat retaining coil portion 12b, for example. In addition, although this heating coil part 12a and the heat insulation coil part 12b shall be provided with one coil part (one turn winding) in this embodiment, respectively, these each coil parts 12a and 12b are either One or both may be composed of a plurality of coil portions (windings of two or more turns).

  Further, a cooling mechanism capable of injecting cooling water so that the metal pipe 11 can be cooled immediately after bending (the cooling mechanism itself is not shown, but the cooling water injected from the cooling mechanism is indicated by reference numeral 10 in FIG. 5). Is integrally formed with the coil 12 (the heat retaining coil portion 12b), and during processing, the cooling water 10 is sprayed toward the outer surface 11b of the metal tube 11 immediately in front of the coil 12 (the heat retaining coil portion 12b), and heated and bent. The obtained metal tube 11 is cooled.

  In processing, the rear portion of the metal tube 11 is held by the rear clamp 15 and the front portion of the metal tube 11 is held by the front clamp 33, and the metal tube 11 is pushed forward by the hydraulic cylinder 16 via the rear clamp 15 (arrow). P1).

  When the metal tube 11 is propelled forward (see arrow P2), the clamp arm 31 receives the propulsive force P2 and rotates horizontally around the support shaft 32 (see arrow P3) to grip the metal tube 11. The front clamp 33 is pivoted to draw an arc around the support shaft 32. Along with this, a bending moment is applied to the metal tube 11 held by the front clamp 33, the portions heated by the coil 12 are bent one after another, and the metal tube 11 is continuously plastically deformed in an arc shape (FIG. 5). reference).

  On the other hand, in order to reduce the tensile strain of the metal tube 11 (bending outer peripheral side), the following compression bending can be performed.

  The sprocket 24 rotates and the chain 23 is taken up by the rotation of the clamp arm 31 accompanying the propulsion of the metal tube 11, and a force (retracting force backward) P <b> 5 is resisted by the compression drive unit 22. 23 and the sprocket 24, it is applied to the clamp arm 31. Thereby, the compressive force of a material axial direction is provided with respect to the metal pipe 11, and the tensile strain which generate | occur | produces in the metal pipe 11 during a bending process can be reduced. In addition, according to such a compression bending, in addition to being able to prevent a crack by reducing a tensile strain, it suppresses the thinning (thinning thickness becomes thin) of the bending outer periphery side of the metal pipe 11. Is also possible.

  FIG. 7 shows the temperature change of the outer surface 11b of the metal tube when the bending is performed by the bending apparatus according to the present embodiment in comparison with the case where the processing is performed by the conventional apparatus. As the metal tube 11 is propelled (time elapses), the point (part) approaches the coil 12, enters the coil 12, is heated, and then escapes from the coil 12 and is cooled by the cooling water 10. The temperature change until it is cooled is shown. In addition, the period shown with the code | symbol H1 in the same figure shows the period which has passed the 1st coil part, and the period shown with the code | symbol H2 has shown the period which has passed the 2nd coil part. . In the conventional apparatus, the same amount of power is supplied to the first-stage coil unit and the second-stage coil unit.

  As shown in FIG. 7, in the conventional apparatus (broken line), initial strain occurs in the period H1 where the temperature has not been sufficiently increased, whereas in the apparatus (solid line) of the present embodiment, the initial distortion occurs. When strain occurs, the temperature of the relevant part of the metal tube has risen sufficiently, preventing cracking due to tensile force when the temperature is low, and increasing the thrust even for thick-walled tubes. It can be plastically deformed without it. Even when the coil is composed of a single stage coil portion (one turn winding), the temperature changes as shown by the broken line in FIG. 7, that is, the temperature continues to rise while passing through the coil, and the temperature peak passes through the coil. It shows a temperature change just after

  Further, FIG. 8 compares the change in tensile strain when the metal pipe having the first attribute shown in FIG. 2 is processed using the bending apparatus according to the present embodiment, compared with the case where the conventional apparatus is used. It is shown.

  As shown in the figure, in the conventional apparatus (two-dot chain line), when the heating coil is heated to the processing temperature (in this case, 1150 ° C.), it exceeds the allowable processing temperature indicating the possibility of cracking. In the initial stage (preheating stage) where tensile strain begins to occur, the allowable processing temperature is below, and cracking may occur. On the other hand, according to the processing apparatus (one-dot chain line) of this embodiment, the allowable processing temperature is exceeded even in the initial stage where tensile strain starts to occur, and therefore cracking can be prevented.

  Furthermore, FIG. 9 shows the temperature change of the inner and outer surfaces 11a and 11b of the metal tube when the metal tube having a large thickness is processed by the bending apparatus according to the present embodiment. FIG. Similarly, the temperature change of the inner and outer surfaces 11a and 11b of the metal tube when the tube is processed by a conventional apparatus is shown.

  As can be seen from FIGS. 9 and 10, according to the apparatus of the present embodiment (FIG. 9), the temperature difference between the pipe outer surface 11b and the pipe inner surface 11a can be reduced as compared with the conventional apparatus (FIG. 10). A tube having a large wall thickness t has a particularly high temperature on the inner surface 11a compared to the outer surface 11b, and cracks are likely to occur compared to a tube having a smaller wall thickness t. According to the apparatus of this embodiment, however, Such a thick tube can also be better prevented from cracking than conventional devices.

  In particular, the material having the second attribute described above is desirably processed at a low temperature because cracking occurs when the processing temperature is high. However, if the temperature is too low, bending cannot be performed in the first place. When processing a thick-walled tube, for example, a tube having a wall thickness exceeding 40 mm, the temperature difference between the tube outer surface 11b and the tube inner surface 11a tends to increase, and therefore, the second attribute that limits the upper limit of the outer surface temperature. In such a pipe, the inner surface temperature is too low to bend (for example, the thrust for pushing the pipe becomes too large or the shape of the pipe cannot be secured during machining).

  On the other hand, if the processing apparatus (coil) of the embodiment is used, that is, if the processing method of the present invention using the processing conditions determined based on the processing temperature range map and the coil 12 are used in combination. Such a thick tube can be processed well without causing cracks.

C Center line of metal tube R Bending radius 11a Inner surface of metal tube 11b Outer surface of metal tube t Thickness of metal tube H1 Passing period of first-stage coil (part) H2 Passing period of second-stage coil (part) 11 Metal Strip material (metal pipe)
DESCRIPTION OF SYMBOLS 12 Induction heating coil 12a Main heating coil part 12b Thermal insulation coil part 13 Guide roller 14 Propulsion mechanism 15 Back clamp 16 Propulsion drive part 21 Compression mechanism 22 Compression drive part 23 Chain 24 Sprocket 31 Clamp arm 32 Support axis 33 Front clamp

Claims (2)

While heating a part of the metal strip made of nickel-based alloy in an annular shape,
The metal strip can be gripped by a clamp arm that can grip a position in the vicinity of the heating portion of the metal strip and can pivot around a support shaft that is spaced from the gripping portion by a certain distance,
The metal strip is heated by propelling the metal strip in the direction of the axis of the shaft to turn the gripping part by the clamp arm and guiding the metal strip to be curved in an arc. A bending metal strip is produced by bending a metal strip by plastically deforming at least a part of the strip continuously into a curved state by applying a bending moment to
The test pieces manufactured under the same conditions as the metal strip are subjected to multiple tensile strain tests with different tensile strain and heating temperature to determine whether or not cracks have occurred in the test pieces in these tests. A step of preparing a processing temperature range map indicating an allowable processing temperature range obtained by performing bending without causing cracks; and
Determining a processing condition from the processing temperature range map;
Performing the bending process so as to satisfy the processing conditions,
When the metal strip has the first attribute that is harder to break as the temperature is higher, the processing condition is that the plastic deformation is performed at a temperature higher than the allowable processing temperature calculated from the processing temperature range map. The bent metal strip is characterized in that when the metal strip has a second attribute that is harder to break as it is lower, the plastic deformation is performed at a temperature lower than an allowable processing temperature calculated from the processing temperature range map. A method of manufacturing the material. The heating of the metal strip is performed by a coil capable of heating the metal strip in an annular shape,
The coil includes a first coil portion and a second coil portion arranged in order in the propulsion direction of the metal strip,
The first coil unit is driven with a larger output than the second coil unit so that the metal strip is heated to a processing temperature by the first coil unit during the bending process. A method for producing a bent metal strip as described in 1.

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