JP2021049557A - Press punch, manufacturing method of seamless tube, and thickness deviation detection method of seamless tube - Google Patents

Abstract

To provide a press punch, a manufacturing method of a seamless tube, and a thickness deviation detection method of the seamless tube, capable of suppressing degradation of a product such as the seamless tube.SOLUTION: A press punch 1 molds a billet 51 into a hollow billet 52 by pushing plug 5 attached to the tip of a core grid 4 into the billet 51 for seamless tube molding. The press punch 1 has a deviation detection part 10 for detecting a deviation Δσ of a circumferential position of compression stress σ in the axial direction of the core grid 4.SELECTED DRAWING: Figure 3

Description

The present invention relates to a press punch, a method for manufacturing a seamless tube, and a method for detecting uneven thickness of a seamless tube.

Conventionally, a Eugene-Sejurne pipe manufacturing method is known as a method for manufacturing a seamless pipe (see, for example, Patent Document 1). In the Eugene Sejurne pipe making method, a spreading drilling step and an extrusion molding step are generally carried out.

Specifically, in the spreading and drilling process, after heating a cylindrical or columnar billet, the billet is charged into a container, and the plug with a plug attached to the tip of a shaft-shaped core metal is used as a billet. Insert to obtain a cylindrical hollow billet having a predetermined inner diameter in a cylindrical or cylindrical billet. In the extrusion molding process, after heating the hollow billet obtained in the expansion and drilling process, the hollow billet is charged into a container, the hollow billet is pushed by the stem, and the hollow billet is extruded from the gap between the die and the mandrel. , Obtain a seamless tube (extruded tube) of the desired shape.

Japanese Unexamined Patent Publication No. 6-269844

When a hollow billet is formed from a billet by perforating the billet by pushing a plug from above, a primary uneven thickness may occur in the obtained hollow billet 100 as shown in FIG. .. The state in which the primary uneven thickness occurs in the hollow billet 100 means a state in which the maximum portion 100a and the minimum portion 100b each exist in one place in the thickness distribution in the circumferential direction of the hollow billet 100. When a primary uneven thickness occurs in a hollow billet, there is a possibility that a primary uneven thickness may occur in a seamless pipe (extruded pipe) obtained from the hollow billet. That is, the quality of the seamless pipe may deteriorate. However, the primary uneven thickness is not detected when the billet is perforated.

Therefore, one of the objects of the present invention is to provide a press punch, a method for manufacturing a seamless tube, and a method for detecting uneven thickness of a seamless tube, which can suppress deterioration of the quality of products such as a seamless tube. To do.

The gist of the present invention is as follows.

(1) A press drilling machine that pushes a plug attached to the tip of a core metal into a metal material for forming a hollow member to form the material into a hollow billet.
A press drilling machine including a deviation detection unit that detects a deviation of the compressive stress in the circumferential position of the core metal in the axial direction.

(2) The deviation detecting unit includes an element for detecting the compressive stress.
The press punching machine according to (1), wherein a plurality of the elements are arranged apart from each other in the circumferential direction of the core metal at the root side portion of the core metal.

(3) The deviation detection unit further includes a determination unit for determining the deviation.
The determination unit stores the detected values of the compressive stress detected by each of the elements in chronological order, and uses the maximum value of the difference between the detected values of the elements at the same time as the deviation. The press punching machine according to 2).

(4) The deviation detection unit further includes a determination unit for determining the deviation.
The press punching machine according to any one of (1) to (3) above, wherein the determination unit determines an abnormality when the deviation exceeds a predetermined threshold value.

(5) A plurality of the threshold values are set, and the threshold values are set.
The press punching machine according to (4), wherein the determination unit makes an abnormality determination according to the deviations with respect to the plurality of threshold values.

(6) A predetermined first threshold value as the threshold value is defined.
The press punching machine according to (5), wherein the determination unit stops the drilling operation by the plug when the deviation exceeds the first threshold value.

(7) As the threshold value, a predetermined second threshold value smaller than the first threshold value is defined.
The press punching machine according to (6), wherein the determination unit notifies an abnormality in dimensional accuracy of the hollow billet when the deviation is larger than the second threshold value and equal to or less than the first threshold value. ..

(8) The determination unit continuously abnormally occurs when the deviation exceeds the predetermined threshold value in succession for a plurality of the materials during the pushing operation of the plug with respect to the material. The press punching machine according to any one of (4) to (7) above, which notifies that the above (4) to (7) has occurred.

(9) When the plug attached to the tip of the core metal is pushed into the metal material to form the material into a hollow billet, the deviation of the compressive stress in the axial direction of the core metal at the circumferential position is detected.
A method for manufacturing a seamless tube, in which a seamless tube is formed by extrusion molding the hollow billet.

(10) When the deviation is larger than the predetermined second threshold value and equal to or less than the predetermined first threshold value, the wall thickness of the hollow billet is measured at a plurality of positions in the circumferential direction. And
When the deviation of the wall thickness at a plurality of positions in the circumferential direction is within a predetermined specified range, the hollow billet is extruded.
The seamless tube manufacturing method according to (9), wherein when the deviation in wall thickness is out of the specified range, the hollow billet is cut and then extruded.

(11) When the plug attached to the tip of the core metal is pushed into the metal material for seamless pipe to form the material into a hollow billet, the deviation of the compressive stress in the axial direction of the core metal at the circumferential position is calculated. A method for detecting uneven thickness without a seam.

According to the present invention, it is possible to suppress quality deterioration of products such as seamless pipes.

FIG. 1 is a diagram showing a primary uneven thickness generated in a hollow billet. FIG. 2A is a schematic view of a core metal and a plug used for drilling a billet, and shows a state in which the core metal is bent. FIG. 2B shows the difference (deviation) between the maximum value and the minimum value of the axial compressive stress in each part of the core metal in the circumferential direction in the vicinity of the core metal root portion, and the uneven thickness ratio of the hollow billet. It is a schematic graph which shows the relationship. FIG. 3 is a schematic vertical cross-sectional view of a press punching machine used in the spreading drilling process, a billet in the middle of drilling, and a hollow billet. FIG. 4 is a conceptual graph showing the relationship between the billet on which the pilot hole is formed and the time and the compressive stress of each strain gauge when the billet is subjected to the expansion drilling step. FIG. 5 is a schematic view showing an extrusion molding process. FIG. 6A shows the time and the maximum compressive stress and the minimum compressive stress of each strain gauge when the deviation is larger than the predetermined second threshold value and equal to or less than the predetermined first threshold value. It is a conceptual graph showing the relationship. FIG. 6B is a conceptual graph showing the relationship between time and the maximum compressive stress and the minimum compressive stress of each strain gauge when the deviation exceeds a predetermined first threshold value. .. FIG. 7A is a schematic view showing a state of wall thickness measurement when the deviation is larger than the second threshold value and equal to or less than the first threshold value. FIG. 7B is a schematic view showing the inner surface cutting of the hollow billet when the deviation of the wall thickness is out of the permissible range.

Hereinafter, a press punch, a method for manufacturing a seamless tube, and a method for detecting uneven thickness of a seamless tube according to an embodiment of the present invention will be described.

<Background to the idea of the present invention>
In the Eugene-Sergene pipe making method, as described above, the spreading drilling step and the extrusion molding step are carried out. In this spreading and drilling step, a cylindrical or cylindrical heated billet is passed through a plug attached to the tip of a shaft-shaped core metal to form a cylindrical hollow billet. In the spreading and drilling process, the plug attached to the core metal is pushed into the billet with a high load. Therefore, if the orientation of the core metal and the plug is tilted with respect to the orientation of the billet, the primary uneven thickness of the hollow billet deteriorates, and the primary uneven thickness of the seamless pipe also deteriorates. The inventor of the present application has conducted diligent research focusing on the inclination of this plug. As a result, the following findings were obtained.

FIG. 2A is a schematic view of the core metal 4 and the plug 5 used for drilling the billet 51, and shows a state in which the core metal is bent. FIG. 2B shows the difference (deviation Δσ) between the maximum value σmax and the minimum value σmin of the axial compressive stress σ in each portion of the core metal 4 in the circumferential direction C in the vicinity of the core metal root portion 4b, and the hollow. It is a schematic graph which shows the relationship with the uneven thickness ratio of a billet 52. Here, the uneven wall ratio is {(maximum wall thickness value-minimum wall thickness value) / average wall thickness} × 100 (%) in the hollow billet 52. The average wall thickness of the denominator = (maximum wall thickness + minimum wall thickness) / 2. The amount of bending of the core metal tip portion 4a means the maximum amount of eccentricity in the billet radial direction of the center of the core metal tip portion 4a with respect to the center of the core metal root portion 4b as viewed from the axial direction of the core metal 4.

The graph of FIG. 2B is the result obtained by the drilling experiment. From the graph of FIG. 2B, it can be seen that the larger the deviation σmax−σmin (that is, the deviation Δσ) of the compressive stress σ, the larger the thickness deviation ratio. This is because the bending compressive stress acts on the part where the compressive stress σ is high, the bending tensile stress acts on the part where the compressive stress σ is low, and the core metal 4 bends, so that the plug 5 is drilled in a tilted state. Because. That is, when the core metal 4 is bent, there is a deviation between the compressive stress σ at the portion where the core metal root portion 4b is most contracted due to the bending and the compressive stress σ at the other portion of the core metal base portion 4b. Δσ is generated. From the above, it can be seen that the core metal 4 is bent when a deviation Δσ occurs in the axial compressive stress σ of each part in the circumferential direction of the core metal 4, and as a result, the uneven thickness of the hollow billet 52 is uneven. You can also see the deterioration of the rate. The inventor of the present application has conceived the present invention based on the above findings.

<Explanation of Embodiment>
The seamless pipe manufacturing method according to the embodiment includes a spreading drilling step and an extrusion molding step. FIG. 3 is a diagram for explaining a spreading and drilling process.

FIG. 3 is a schematic vertical cross-sectional view of the press punching machine 1 used in the spreading drilling step, the billet 51 in the middle of drilling, and the hollow billet 52. With reference to FIG. 3, the press punching machine 1 of the present embodiment is a vertical press punching machine, and a plug 5 attached to the tip portion 4a of the core metal 4 is passed through the billet 51 from above the billet 51. The billet 51 is expanded and perforated, whereby the billet 51 is formed into a hollow billet 52. The billet 51 is an example of a “metal material for molding a hollow member”. In the present embodiment, a mode in which the press punching machine 1 is a vertical press punching machine will be described as an example, but this may not be the case. The present invention may be applied to a horizontal press drilling machine in which a plug penetrates a billet in the horizontal direction.

The billet 51 cuts the outer surface of an iron ingot formed by block-rolling a metal bloom such as steel or high-speed forging, and in some cases, forming a through hole in the iron ingot by cutting. It is completed with. The billet 51 is formed into a hollow billet 52 in the press drilling machine 1 in a state of being preheated to about 1200 ° C.

The press drilling machine 1 includes a cylindrical container 2, a cylindrical die 3 provided at the lower end of the container 2, a core metal 4 inserted into the container 2, and a tip portion 4a (lower end portion) of the core metal 4. ), The drive unit 6 that moves the core metal 4 up and down, the load cell 7 that detects the load between the drive unit 6 and the core metal 4, and the strain gauge attached to the core metal 4. It has a deviation detecting unit 10 including 11.

As the container 2, die 3, core metal 4 and plug 5, the container, die, core metal and plug used in the conventional seamless pipe manufacturing method (Eugene Sejurne pipe manufacturing method) can be used. Since it can be done, only a brief explanation will be given, and a detailed explanation will be omitted.

The core metal 4 is a shaft-shaped member extending vertically. The plug 5 is formed in a conical shape, and the sharpened portion of the plug 5 faces the die 3 side. The core metal 4 and the plug 5 are made of metal. The drive unit 6 includes an actuator such as an electric motor or a hydraulic cylinder, and is attached to the root portion 4b of the core metal 4. The drive unit 6 moves the core metal 4 and the plug 5 in the axial direction (vertical direction) of the core metal 4.

The load cell 7 detects the load acting on the core metal 4 from the drive unit 6. The load value detected in the load cell 7 is output to the determination unit 12 described later in the deviation detection unit 10.

The deviation detection unit 10 is provided to detect the deviation Δσ at the circumferential position of the compressive stress σ in the axial direction of the core metal 4. The deviation detection unit 10 has a plurality of strain gauges 11, a determination unit 12 electrically connected to each strain gauge 11, and a notification unit 13.

The strain gauge 11 is provided as an element for detecting the compressive stress σ. The strain gauge 11 is arranged at the root side portion of the core metal 4. The "root side portion of the core metal 4" is a portion within 10% of the root portion 4b side of the total length of the core metal 4, preferably a portion within 5% of the root portion 4b side of the total length of the core metal 4. The root portion 4b is a boundary between the core metal 4 and the drive portion 6. In the present embodiment, the strain gauge 11 is provided at the root portion 4b of the core metal 4. A plurality of strain gauges 11 are arranged apart from each other in the circumferential direction C. In this embodiment, four strain gauges 11 are arranged at equal pitches of 90 ° in the circumferential direction C. It is sufficient that at least two strain gauges 11 are provided. Further, it is preferable that the strain gauges 11 have at least a pair of strain gauges 11 arranged at a pitch of 180 ° in the circumferential direction C. Each strain gauge 11 detects the axial strain of the core metal 4 at the portion attached to the core metal 4. Each strain gauge 11 outputs an electric signal according to the amount of strain in the axial direction of the core metal 4.

The determination unit 12 processes the electric signal output from the strain gauge 11 and outputs a signal according to the processing result. The determination unit 12 may be a computer including a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), or a PLC (Programmable Logic Controller). The determination unit 12 calculates the compressive stress σ of the core metal 4 at the position where each strain gauge 11 is attached by processing the output signal from each strain gauge 11. The determination unit 12 stores the detected values of the compressive stress σ detected by each strain gauge 11 in chronological order. Then, the determination unit 12 uses the maximum value of the difference between the detected values of the compressive stress σ in each strain gauge 11 at the same time, that is, σmax−σmin as the deviation Δσ.

Further, the determination unit 12 is electrically connected to each of the drive unit 6 and the notification unit 13. The determination unit 12 is configured to be able to output a stop signal for stopping the operation of the drive unit 6 to the drive unit 6. The notification unit 13 includes, for example, lamps of a plurality of colors. For example, the determination unit 12 can turn on the red lamp by the notification unit 13 at the same time as stopping the drive unit 6. Further, the determination unit 12 can turn on the yellow lamp on the notification unit 13 at the time of the dimensional accuracy abnormality notification described later. The notification unit 13 is not limited to the configuration including the lamp, and may be a display device such as a liquid crystal monitor.

The determination unit while transmitting the load from the drive unit 6 to the core metal 4 and the plug 5 to press the plug 5 against the billet 51 and penetrating the plug 5 through the billet 51, that is, while the spreading drilling process is being performed. 12 calculates the deviation Δσ of the compressive stress σ of the core metal 4 in the circumferential direction C by using the compressive stress σ detected by each strain gauge 11a to 11d.

Here, an example of the compressive stress σ of the place where each strain gauge 11 is installed (hereinafter referred to as a measurement place) in the time from the start to the completion of the spreading drilling process is shown in FIG. FIG. 4 shows the relationship between the billet 51 in which the prepared hole 51a is formed and the time t and the compressive stress σ of each strain gauge 11 (11a to 11d) when the billet 51 is subjected to the expansion drilling step. It is a conceptual graph showing. FIG. 4 shows a state in which the deviation Δσ of the compressive stress σ is low when the abnormality determination described later is not performed. It should be noted that even when the prepared hole 51a is not formed in the billet 51 in advance, the same tendency as in the case where the prepared hole 51a is formed in advance is shown. To establish.

Explaining with reference to FIG. 4, the billet 51 has a slight difference in temperature distribution in the circumferential direction C. Therefore, strain gauges 11a and 11b are attached to the billet 51 at 0 ° and 90 ° in the circumferential direction C, which is the high temperature side, respectively, and 180 ° and 270 in the circumferential direction C, which is the low temperature side. An example is shown in which strain gauges 11c and 11d are attached to the ° positions, respectively. That is, a pair of strain gauges 11a and 11c arranged to face each other at the 0 ° position and a 180 ° position, and a pair of strain gauges 11b and 11d arranged to face each other at the 90 ° position and the 270 ° position are provided. Has been done.

In the example shown in FIG. 4, the plug 5 starts contact with the billet 51 about 0.5 seconds after the start of the spreading and drilling process. Then, it can be seen that the plug 5 pushes the pilot hole 51a of the billet 51 open for about 0.75 seconds to 1.5 seconds. The following configuration can be exemplified as a method for detecting the deviation Δσ.

Specifically, the determination unit 12 detects the compressive stress σ of the core metal 4 at the measurement points where the strain gauges 11a to 11d are installed from the start to the completion of the expansion and drilling process at a predetermined sampling cycle. To do. Then, the difference between the maximum value and the minimum value of the compressive stress of each strain gauge at each sampling time is calculated as the deviation Δσ at each sampling time.

<Example of operation in the spreading and drilling process>
Next, an operation example of the operation of the molding process from the billet 51 to the hollow billet 52 in the spreading and drilling process will be described. With reference to FIG. 3, in the spreading and drilling step, the plug 5 attached to the core metal 4 penetrates the billet 51 in which the prepared hole 51a is formed in advance or the prepared hole 51a is not formed. .. As a result, the hollow billet 52 having the through hole 52a is completed. In this spreading drilling step, signals from the strain gauges 11a to 11d are output to the determination unit 12. Then, the determination unit 12 calculates the compressive stress σ at each strain gauge 11a to 11d (measurement point) by processing the signals detected by the strain gauges 11a to 11d. When the deviation Δσ between the maximum value and the minimum value of the compressive stress σ is less than the predetermined first threshold value Δσ1, that is, when the deviation Δσ shown in FIG. 4 is the deviation Δσ, the determination unit 12 forms the hollow billet 52. Does not warn against. At this time, the hollow billet 52 is taken out from the press drilling machine 1, induced and heated by an induction heating coil (not shown), and then extruded by the horizontal press punching machine 21 shown in FIG. It becomes 53.

FIG. 5 is a schematic view showing an extrusion molding process. As shown in FIG. 5, in the horizontal press punching machine 21, the hollow billet 52 is housed in the container 22, and the mandrel 23 is inserted into the through hole 52a of the hollow billet 52, and the mandrel 23 is inserted through the dummy block 24 through the stem 25. The hollow billet 52 is extruded to obtain a seamless tube 53 as a hollow member. At this time, the die stand 26 is installed in the container 22, and the tip portion of the mandrel 23 is inserted inside the die 27 supported by the die stand 26. An annular gap is formed between the die 27 and the mandrel 23, and the hollow billet 52 is pushed out in a tubular shape in the direction of pushing the stem 25 from the gap, so that the hollow billet 52 becomes a seamless tube 53.

On the other hand, the deviation Δσ may exceed the permissible value during the expansion drilling process shown in FIG. An example of the deviation Δσ in the time from the start to the completion of the expansion drilling process is shown in FIGS. 6 (A) and 6 (B). FIG. 6A shows the time t and the maximum compressive stress among the strain gauges 11a to 11d when the deviation Δσ is larger than the predetermined second threshold value Δσ2 and equal to or less than the predetermined first threshold value Δσ1. It is a conceptual graph which shows the relationship between σmax and the minimum compressive stress σmin. FIG. 6B shows the relationship between the time t, the maximum compressive stress σmax of each strain gauge 11a to 11d, and the minimum compressive stress σmin when the deviation Δσ exceeds a predetermined first threshold value Δσ1. It is a conceptual graph showing.

With reference to FIGS. 3 and 6 (A), in the spreading drilling process, when there is a relatively small temperature difference (small uneven heat) in each part of the billet 51 in the circumferential direction C, or when the core metal 4 and the core metal 4 and each portion have a relatively small temperature difference. The central axis of the plug 5 may be slightly inclined with respect to the central axis of the billet 51. In this case, the core metal 4 is slightly tilted by receiving a non-uniform load in the circumferential direction C from the plug 5 punching the billet 51 during the spreading drilling process. As a result, among the strain gauges 11a to 11d, the deviation Δσ as the difference between the maximum σmax and the minimum σmin of the compressive stress σ is larger than the predetermined second threshold value Δσ2 and equal to or less than the predetermined first threshold value Δσ1 ( Δσ2 <Δσ ≦ Δσ1). The second threshold value Δσ2 is a value when the dimensional accuracy (quality) of the seamless pipe 53 is poor and the deviation Δσ is large enough to make the seamless pipe 53 a defective product. The specific value of the second threshold value Δσ2 is appropriately set according to the material and dimensions of the seamless pipe 53. In this way, when the deviation Δσ exceeds the predetermined second threshold value Δσ2, the determination unit 12 makes an abnormality determination.

As described above, when the deviation Δσ is Δσ2 <Δσ ≦ Δσ1, the determination unit 12 determines the dimensional accuracy of the hollow billet 52 during or after the operation of molding the billet 51 into the hollow billet 52. Notify an abnormality. This notification is performed, for example, by the determination unit 12 turning on the yellow lamp of the notification unit 13.

In this case, the hollow billet 52 notified of the dimensional accuracy abnormality is naturally cooled or water-cooled to a predetermined temperature. Then, as shown in FIG. 7A, the cooled hollow billet 52 is measured for wall thickness at a plurality of points in the circumferential direction C by a measuring instrument 31 such as a caliper or a micrometer. Then, as a result of this measurement, when the deviation of the wall thickness is within a predetermined specified range, the hollow billet 52 is reheated by the above-mentioned induction heating, and then the hollow billet 52 is extruded by a horizontal press punch 21. As a result, the seamless tube 53 is formed. The above-mentioned specified range is appropriately set according to the material, wall thickness, outer diameter, etc. of the seamless pipe 53. On the other hand, when the deviation of the wall thickness is out of the specified range as a result of the above-mentioned dimensional measurement of the hollow billet 52, a cutting tool 32 is used on the inner peripheral surface of the hollow billet 52, for example, as shown in FIG. 7 (B). By cutting the hollow billet 52, the deviation of the wall thickness of the hollow billet 52 is kept within an allowable range. The machined hollow billet 52 is reheated by the above-mentioned induction heating and then extruded to form a seamless tube 53. With such a configuration, the hollow billet 52 can be used as a material that does not cause a defect of the seamless tube 53 even if the hollow billet 52 has a large deviation Δσ to some extent.

On the other hand, referring to FIGS. 3 and 6 (B), in the spreading and drilling process, when there is a relatively large temperature difference (large uneven heat) in each part of the billet 51 in the circumferential direction C, or when there is a core. The central axis of the gold 4 and the plug 5 may be inclined relatively large with respect to the central axis of the billet 51. In this case, the core metal 4 is greatly tilted by receiving a non-uniform load in the circumferential direction C from the plug 5 in which the billet 51 is drilled during the spreading and drilling process. As a result, the deviation Δσ exceeds a predetermined first threshold value Δσ1. The first threshold value Δσ1 is a value at a level at which the core metal 4 is broken (bent). The specific value of the first threshold value Δσ1 is appropriately set according to the material and dimensions of the seamless pipe 53.

When the deviation Δσ is larger than Δσ1, the determination unit 12 stops the drilling operation by the plug 5. Specifically, the determination unit 12 outputs a stop signal to the drive unit 6 to immediately stop the operation of the core metal 4 and the plug 5. At this time, the determination unit 12 lights the red lamp of the notification unit 13, and the determination unit 12 has a deviation Δσ of Δσ1 <Δσ and the load detected by the load cell 7 exceeds a predetermined threshold value. Occasionally, the drilling operation by the plug 5 may be stopped.

In the spreading and drilling step, the deviation Δσ exceeds the second threshold value Δσ2, that is, the determination unit 12 continuously determines the abnormality for a predetermined number (for example, several tens) of billets 51. In that case, the determination unit 12 notifies the abnormality to that effect. That is, when the deviation Δσ exceeds the second threshold value Δσ2 in each of the pushing operations of the plug 5 with respect to the billet 51, the determination unit 12 continuously occurs for the plurality of billets 51. Notify that an abnormality has occurred. In this case, the determination unit 12 notifies the abnormality by blinking, for example, the yellow lamp of the notification unit 13. When this abnormality is notified, the worker takes out the corresponding billet 51 from the press punching machine 1, investigates the billet 51, and maintains the press punching machine 1. As a result, it is possible to suppress deterioration of the yield of the seamless pipe 53 and dimensional defects, and it is possible to suppress breakage of the core metal 4.

As described above, according to the present embodiment, when the plug 5 attached to the tip of the core metal 4 is pushed into the billet 51 to form the billet 51 into a hollow billet, the compressive stress in the axial direction of the core metal 4 is formed. The deviation Δσ at the circumferential position of σ is detected. Since the deviation Δσ of the compressive stress σ of the core metal 4 correlates with the uneven thickness ratio of the hollow billet 52 which is the material of the seamless tube 53, the uneven thickness ratio of the hollow billet 52 is monitored by monitoring the deviation Δσ. it can. Thereby, when the deviation Δσ exceeds the second threshold value Δσ2, the case where the hollow billet 52 has a large uneven thickness and the seamless pipe 53 is likely to be a defective product can be detected more accurately. As a result, it is possible to prevent the hollow billet 52 having low dimensional accuracy from being formed into the seamless tube 53. Therefore, a seamless tube 53 with higher dimensional accuracy can be manufactured.

Further, according to the present embodiment, a plurality of strain gauges 11 are arranged apart from each other in the circumferential direction C at the root side portion of the core metal 4. According to this configuration, the deviation Δσ of the compressive stress σ in the circumferential direction C can be detected more accurately. In particular, by arranging a pair of strain gauges 11 at a pitch of 180 ° in the circumferential direction C, the deviation Δσ of the compressive stress in the circumferential direction C can be detected more accurately. Further, by installing the strain gauge 11 at at least one of the place where the temperature of the billet 51 is the highest and the place where the temperature of the billet 51 is the lowest in the circumferential direction C, the deviation Δσ of the compressive stress σ in the circumferential direction C can be detected more accurately.

Further, according to the present embodiment, the determination unit 12 stores the detected values of the compressive stress σ along the time series, and uses the maximum value of the difference between the detected values of the strain gauges 11 at the same time as the deviation Δσ. According to this configuration, the determination unit 12 can determine the degree of the deviation Δσ of the compressive stress σ in real time and can also determine it even after the expansion drilling step.

Further, according to the present embodiment, the determination unit 12 makes an abnormality determination when the deviation Δσ exceeds the second threshold value Δσ2. More specifically, the determination unit 12 makes an abnormality determination according to the height of the deviation Δσ with respect to the plurality of threshold values Δσ1 and Δσ2. According to this configuration, when the deviation Δσ exceeds the second threshold value Δσ2 and is equal to or less than the first threshold value, the hollow billet 52 has an uneven thickness that causes a defective product of the seamless pipe 53. Can be detected. Further, when the deviation Δσ exceeds the first threshold value Δσ1, it can be detected that the core metal 4 is bent and deformed so that the core metal 4 is broken.

Although an example of the present invention has been described above, this does not have to be the case. The present invention can be modified in various ways within the scope of the claims.

The present invention can be used in a press punch, a method for manufacturing a seamless tube, and a method for detecting uneven thickness of a seamless tube.

1 Press punch 4 Core metal 4a Tip 5 Plug 10 Deviation detection 11 Strain gauge (element)
12 Judgment unit 51 Billet (metal material)
52 Hollow billet 53 Seamless pipe (hollow member)
Circumferential direction of C core metal σ Compressive stress Δσ Deviation Δσ 1 First threshold value (threshold value)
Δσ2 Second threshold (threshold)

Claims (11)

A press drilling machine that pushes a plug attached to the tip of a core metal into a metal material for forming a hollow member to form the material into a hollow billet.
A press drilling machine including a deviation detection unit that detects a deviation of the compressive stress in the circumferential position of the core metal in the axial direction. The deviation detecting unit includes an element for detecting the compressive stress.
The press drilling machine according to claim 1, wherein a plurality of the elements are arranged apart from each other in the circumferential direction of the core metal at the root side portion of the core metal. The deviation detection unit further includes a determination unit for determining the deviation.
The determination unit stores the detected values of the compressive stress detected by each of the elements in a time series, and uses the maximum value of the difference between the detected values of the elements at the same time as the deviation. 2. The press punching machine according to 2. The deviation detection unit further includes a determination unit for determining the deviation.
The press punch according to any one of claims 1 to 3, wherein the determination unit determines an abnormality when the deviation exceeds a predetermined threshold value. A plurality of the threshold values are set, and the threshold values are set.
The press punch according to claim 4, wherein the determination unit determines an abnormality according to the deviation with respect to the plurality of threshold values. A predetermined first threshold value as the threshold value is defined, and
The press punching machine according to claim 5, wherein the determination unit stops the drilling operation by the plug when the deviation exceeds the first threshold value. As the threshold value, a predetermined second threshold value smaller than the first threshold value is defined.
The press punch according to claim 6, wherein the determination unit notifies an abnormality in dimensional accuracy of the hollow billet when the deviation is larger than the second threshold value and equal to or less than the first threshold value. In the determination unit, when the deviation exceeds the predetermined threshold value during the pushing operation of the plug with respect to the material, when the deviation occurs continuously with respect to the plurality of materials, a continuous abnormality occurs. The press drilling machine according to any one of claims 4 to 7, which notifies that the machine is present. When the plug attached to the tip of the core metal is pushed into the metal material to form the material into a hollow billet, the deviation of the compressive stress in the axial direction of the core metal at the circumferential position is detected.
A method for manufacturing a seamless tube, in which a seamless tube is formed by extrusion molding the hollow billet. When the deviation is larger than the predetermined second threshold value and equal to or less than the predetermined first threshold value, the wall thickness of the hollow billet is measured, and the wall thickness at a plurality of positions in the circumferential direction is measured.
When the deviation of the wall thickness at a plurality of positions in the circumferential direction is within a predetermined specified range, the hollow billet is extruded.
The seamless pipe manufacturing method according to claim 9, wherein when the deviation of the wall thickness is out of the specified range, the hollow billet is cut and then the extrusion molding is performed. When the plug attached to the tip of the core metal is pushed into the metal material for seamless pipe to form the material into a hollow billet, the deviation of the compressive stress in the axial direction of the core metal at the circumferential position is detected. A method for detecting uneven thickness without a seam.

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