Spinning necking forming device

Abstract

A power assembly of the spinning necking forming device is used for fixing a pipe blank and can drive the pipe blank to rotate around the axis of the pipe blank; the first telescopic cylinder is located on the periphery of the pipe blank on the power assembly, one end of the first telescopic cylinder is an installation end, the other end of the first telescopic cylinder is a movable end, the movable end is close to or away from the installation end through stretching, and the installation end is arranged in a pivoted mode so that the movable end can swing close to or away from the pipe blank in the radial direction of the pipe blank; the sliding table is fixed to the movable end and moves along with the movable end, the sliding table is rotationally provided with a spinning wheel, and the spinning wheel is used for abutting against the side wall of the pipe blank so as to roll the side wall of the pipe blank when the pipe blank rotates; the movable guide rail is matched with the sliding table, and the movable guide rail and the sliding table relatively slide only in the telescopic direction of the first telescopic cylinder; one end of the second telescopic cylinder is hinged to the movable guide rail for driving the movable guide rail to get close to or away from the pipe blank. The invention provides a spinning necking forming device which is easier to use.

Description

Technical Field

[0001] The present invention relates to the technical field of plastic processing of metal materials, and relates to a rotary necking forming device. Background Art

[0002] At present, the mainstream necking processes have significant limitations. For example: Although traditional rotary necking can form large-diameter thin-walled parts, there are problems such as large wall thickness differences and uneven grain refinement caused by multi-pass processing, and defects such as cracking and bulging are likely to occur; Although the differential rolling process can form large-diameter conical parts, it relies on welded seams, resulting in a reduction in the overall performance of the component, and there are also problems of dimensional errors caused by uneven inter-roll friction; Although die necking is efficient, it is limited by the ultimate necking coefficient, and forming defects such as instability in the force transmission area and wrinkling at the mouth are likely to occur.

[0003] In summary, there is a need for a more user-friendly rotary necking forming device at present. Summary of the Invention

[0004] The purpose of the present invention is to provide a rotary necking forming device, and the technical problem to be solved is how to provide a more user-friendly rotary necking forming device.

[0005] To achieve the above object, the solution of the present invention is: A rotary necking forming device for necking and forming a tube blank, comprising a power assembly and a rotary wheel assembly;

[0006] The power assembly is used to fix the tube blank and can drive the tube blank to rotate around its own axis;

[0007] The rotary wheel assembly includes a first telescopic cylinder, a slide table, a movable guide rail and a second telescopic cylinder;

[0008] The first telescopic cylinder is located outside the tube blank on the power assembly, one end is the installation end, the other end is the movable end, and the movable end is moved closer to or away from the installation end by telescoping. The installation end is pivotally arranged so that the movable end can swing closer to or away from the tube blank in the radial direction of the tube blank;

[0009] The slide table is fixed on the movable end and moves with the movable end. A rotary pressure wheel is rotatably installed on the slide table. The rotary pressure wheel is used to abut against the side wall of the tube blank to roll on the side wall of the tube blank when the tube blank rotates;

[0010] The movable guide rail cooperates with the slide table, and the two only slide relative to each other in the telescopic direction of the first telescopic cylinder;

[0011] The second telescopic cylinder is hinged to one end of the movable guide rail and is used to drive the movable guide rail to approach or move away from the tube blank.

[0012] Further, the position of the rotation axis of the installation end is fixed, and the extending direction is perpendicular to the axis of the tube blank.

[0013] Further, the other end of the second telescopic cylinder is fixedly arranged, and the second telescopic cylinder is perpendicular to the tube blank.

[0014] Further, it further includes a flame spray gun which is located on the periphery of the tube blank on the power assembly and is used for spraying fire towards the tube blank.

[0015] Further, it further includes an infrared temperature detector which is used for collecting the temperature of the tube blank.

[0016] Further, it further includes a support assembly which has a plurality of support wheels. Each support wheel is used for being arranged around the periphery of the tube blank on the power assembly, abuts and supports on the outer side wall of the tube blank, and rolls as the tube blank rotates.

[0017] Further, the support assembly further includes an upper frame, a lower frame and an opening and closing driving mechanism. The upper frame and the lower frame are respectively arranged on the radial two sides of the tube blank fixed on the power assembly. Some support wheels are installed on one side of the upper frame close to the tube blank, and the rest of the support wheels are installed on one side of the lower frame close to the tube blank. The upper frame and the lower frame approach or move away under the drive of the opening and closing driving mechanism. After approaching, each support wheel can abut on the outer side wall of the tube blank. After moving away, the support wheels on the upper frame and / or the lower frame leave the tube blank.

[0018] Further, the power assembly has a turntable which can rotate around its own axis. A clamping mechanism is arranged on the turntable and is used for fixing the tube blank from one end of the tube blank and making the tube blank coaxial with the turntable after fixing, so that the tube blank rotates driven by the turntable.

[0019] Further, the clamping mechanism includes a plurality of clamping assemblies. The plurality of clamping assemblies are arranged in a circumferential array along the axis of the turntable. Each clamping assembly includes an outer clamp, an inner clamp and an adjustment screw. The outer clamp is fixedly arranged on the turntable. The inner clamp is located on one side of the outer clamp close to the center of the turntable and is linearly slidably arranged on the turntable to approach or move away from the outer clamp along the radial direction of the turntable. The adjustment screw is rotatably installed on the turntable, and the extending direction is parallel to the sliding direction of the inner clamp and is screwed with the inner clamp to drive the inner clamp to slide through the rotation of the adjustment screw.

[0020] Further, the first telescopic cylinder and the second telescopic cylinder are connected with a controller to perform telescoping under the control of the controller.

[0021] After adopting the above scheme, the beneficial effects of the present invention are as follows: The power assembly drives the tube blank to rotate around its own axis. The first telescopic cylinder makes the movable end approach or move away from the mounting end through telescoping. The mounting end is pivotally arranged so that the movable end can swing closer to or away from the tube blank in the radial direction of the tube blank. The sliding table is fixed on the movable end and moves with the movable end. The sliding table is rotatably installed with a spinning wheel, and the spinning wheel is used to abut against the side wall of the tube blank to roll on the side wall of the tube blank when the tube blank rotates. The movable guide rail cooperates with the sliding table, and the two slide relative to each other in the telescoping direction of the first telescopic cylinder. One end of the second telescopic cylinder is hinged to the movable guide rail and is used to drive the movable guide rail to approach or move away from the tube blank. Furthermore, through the telescopic cooperation of the first telescopic cylinder and the second telescopic cylinder, the spinning wheel can be respectively driven to displace in the axial and radial directions of the tube blank. Then, combined with the power assembly driving the tube blank to rotate, rolling of the tube blank can be realized. The spinning process is more controllable and is easy to adjust according to different spinning requirements, providing a more user-friendly spinning necking forming device. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic structural diagram of the spinning necking forming device;

[0023] Figure 2 is a schematic diagram of the process of necking the tube blank through the spinning wheel;

[0024] Figure 3 is a schematic diagram of the process of supporting the tube blank through the support assembly;

[0025] Figure 4 is an exploded schematic diagram of the turntable;

[0026] Figure 5 is a schematic diagram of the process of fixing the tube blank through the turntable;

[0027] Figure 6 is a cross-sectional view of the cooperation between the sliding table and the movable guide rail.

[0028] Reference numeral description: 1 - tube blank, 2 - power assembly, 3 - spinning wheel assembly, 4 - first telescopic cylinder, 5 - sliding table, 6 - movable guide rail, 7 - second telescopic cylinder, 8 - mounting end, 9 - movable end, 10 - spinning wheel, 11 - flame spray gun, 12 - infrared temperature detector, 13 - support assembly, 14 - support wheel, 15 - upper frame, 16 - lower frame, 17 - opening and closing drive mechanism, 18 - turntable, 19 - clamping assembly, 20 - outer clamp, 21 - inner clamp, 22 - adjustment screw, 23 - controller, 24 - T-shaped cross-section part, 25 - mandrel, 26 - T-shaped groove, 27 - T-shaped block, 28 - screw perforation, 29 - central hole. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] In the claims, specification and the above-mentioned drawings of the present invention, unless otherwise explicitly defined, directional words, such as the use of terms such as "center", "lateral", "longitudinal", "horizontal", "vertical", "top", "bottom", "inside", "outside", "up", "down", "front", "back", "left", "right", "clockwise", "counterclockwise" and the like to indicate directions or positional relationships are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation or be constructed and operated in a specific orientation, so it cannot be understood as limiting the specific protection scope of the present invention.

[0031] A rotary compression mouth forming device, such as Figure 1-6 As shown, it is used to perform necking forming on a tube blank 1, wherein the tube blank 1 refers to a thin-walled rotating body blank to be necked, and the device includes a frame (the frame is not shown in the drawings), and a power assembly 2 and a rotary wheel assembly 3 arranged on the frame; in a preferred embodiment, a support assembly 13, a flame spray gun 11 and an infrared temperature detector 12 are also provided, which are described in detail below;

[0032] The power assembly 2 is used to fix the tube blank 1 and can drive the tube blank 1 to rotate around its own axis; specifically in this embodiment, the power assembly 2 has a turntable 18, which is connected to a drive motor through a clutch transmission. The transmission connection method is a conventional technical means in the mechanical field, and no further elaboration is given here. As long as the turntable 18 can rotate around its own axis under the drive of the drive motor, a clamping mechanism is provided on one side of the turntable 18. The clamping mechanism is used to fix the tube blank 1 from one end of the tube blank 1, and after fixation, the tube blank 1 can be coaxial with the turntable 18 to realize the rotation of the tube blank 1 around its own axis. A preferred specific structure of the clamping mechanism is given later, and of course it is not limited to the above-mentioned specific structure;

[0033] The rotary wheel assembly 3 includes a first telescopic cylinder 4, a slide 5, a movable guide rail 6 and a second telescopic cylinder 7;

[0034] The first telescopic cylinder 4 is a hydraulic telescopic cylinder in this embodiment to ensure sufficient power. It is located on the periphery of the tube blank 1 on the power assembly 2, with one end being a mounting end 8 and the other end being a movable end 9. The movable end 9 is moved closer to or away from the mounting end 8 by telescoping (the telescopic cylinder's own characteristics). The mounting end 8 is pivotally arranged, and the pivot axis is fixed in position. The extending direction of the pivot axis is perpendicular to the axis of the tube blank 1. More specifically, in this embodiment, it is pivotally connected to the frame, so that the movable end 9 can be swung closer to or away from the outer wall of the tube blank 1 in the radial direction of the tube blank 1 under the action of external force;

[0035] The sliding table 5 is fixed on the movable end 9 and moves with the displacement of the movable end. The sliding table 5 is rotatably installed with a spinning wheel 10. After the movable end 9 swings close to the outer wall of the tube blank 1, the spinning wheel 10 is used to abut against the side wall of the tube blank 1, so that when the tube blank 1 rotates, it rolls on the side wall of the tube blank 1, and the mouth of the tube blank 1 is pressed to shrink and deform through rolling pressure.

[0036] The movable guide rail 6 cooperates with the sliding table 5. As long as a structure is adopted that enables the two to only generate relative sliding in the telescopic direction of the first telescopic cylinder 4 (the telescopic direction here changes with the swing of the movable end), specifically in this embodiment, the sliding table 5 has a T-shaped cross-section part 24, and the extending direction of the T-shaped cross-section part 24 is consistent with the extending direction of the first telescopic cylinder 4. A guide groove matching the cross-sectional shape of the T-shaped cross-section part 24 extends on the guide rail 6, and the T-shaped cross-section part 24 is slidably fitted in the guide groove to realize that the guide rail 6 and the sliding table 5 can only slide relative to each other in the extending direction of the first telescopic cylinder.

[0037] The second telescopic cylinder 7. To ensure sufficient power, a hydraulic telescopic cylinder is specifically selected in this embodiment. One end of the second telescopic cylinder 7 is hinged to the movable guide rail 6 and is used to drive the movable guide rail 6 to approach or move away from the tube blank 1, thereby driving the swing of the movable end 9 of the first telescopic cylinder 4, and further adjusting the position of the spinning wheel 10 in the radial direction of the tube blank 1 and controlling the pressure of the spinning wheel 10 pressing on the barrel wall of the tube blank 1. Specifically in this embodiment, the other end of the second telescopic cylinder 7 is fixedly arranged, and the second telescopic cylinder 7 is perpendicular to the tube blank 1 to more easily control the spinning pressure.

[0038] Specifically in this embodiment, the first telescopic cylinder 4 and the second telescopic cylinder 7 are connected to a controller 23 to perform telescoping under the control of the controller 23. The controller is any existing programmable controller. The controller coordinates the telescoping actions of the first telescopic cylinder 4 and the second telescopic cylinder 7 to control the spinning process. For spinning workpieces of different shapes, different control programs can be set. As for how to write the program, those skilled in the art can complete it according to conventional technical means, and it will not be elaborated in this embodiment.

[0039] In a preferred embodiment provided with a flame spray gun 11, the flame spray gun 11 is located around the tube blank 1 on the power assembly 2 and is used to spray fire towards the tube blank 1 to heat the tube blank 1 and make the tube blank 1 easier to deform.

[0040] In a preferred embodiment provided with a flame spray gun 11, more preferably, an infrared temperature detector 12 is also provided. The infrared temperature detector 12 is used to collect the temperature of the tube blank 1 to prevent the flame spray gun 11 from heating the tube blank 1 to too high a temperature and affecting the metal properties of the tube blank 1.

[0041] The support assembly 13 has a plurality of support wheels 14. Each support wheel 14 is used to be arranged around the outer periphery of the tube blank 1 on the power assembly 2, abuts and supports on the outer side wall of the tube blank 1, and rolls as the tube blank 1 rotates, so as to support the tube blank 1 and improve the processing stability. For the convenience of loading and unloading the tube blank 1, in a preferred embodiment, the support assembly 13 further includes an upper frame 15, a lower frame 16 and an opening and closing drive mechanism 17. The upper frame 15 and the lower frame 16 are respectively arranged on the radial two sides of the tube blank 1 fixed on the power assembly 2. Some support wheels 14 are installed on one side of the upper frame 15 close to the tube blank 1, and the rest of the support wheels 14 are installed on one side of the lower frame 16 close to the tube blank 1. The upper frame 15 and the lower frame 16 approach or move away under the drive of the opening and closing drive mechanism 17. After approaching, each support wheel 14 can abut on the outer side wall of the tube blank 1. After moving away, the support wheels 14 on the upper frame 15 and / or the lower frame 16 leave the tube blank 1. More specifically, in this embodiment, the lower frame 16 is fixed, the upper frame 15 is located directly above the lower frame 16 and is longitudinally slidably arranged. The opening and closing drive mechanism 17 is a hydraulic cylinder, which is connected to the upper frame 15 and drives the upper frame 15 to rise away from the lower frame 16 and descend close to the lower frame 16.

[0042] In order to ensure the coaxiality of the tube blank 1 and the turntable 18 after the tube blank 1 is installed on the turntable 18, in a preferred embodiment, the clamping mechanism includes a plurality of clamping assemblies 19. In this embodiment, four clamping assemblies 19 are provided, and each clamping assembly 19 is evenly arranged in a circumferential array along the axis of the turntable 18. Each clamping assembly 19 includes an outer clamp 20, an inner clamp 21 and an adjustment screw 22. The outer clamp 20 is fixedly arranged on the turntable 18. The inner clamp 21 is located on the side of the outer clamp 20 close to the center of the turntable 18 and is linearly slidably arranged on the turntable 18, specifically sliding linearly along the radial direction of the turntable 18. A T-shaped groove 26 is respectively provided on the turntable 18 corresponding to each inner clamp 21, and a T-shaped block 27 is provided on each inner clamp 21. Through the cooperation of the T-shaped groove 26 and the T-shaped block 27, the inner clamp 21 slides along the radial direction of the turntable to slide radially outward on the turntable 18 to approach the outer clamp 20 and slide inward away from the outer clamp 20. The adjustment screw 22 is rotatably installed on the turntable 18, and the extending direction is parallel to the sliding direction of the inner clamp 21 and is screwed with the inner clamp 21 to drive the inner clamp 21 to slide through the rotation of the adjustment screw 22, and a thread self-locking is also formed to prevent the displacement and loosening of the inner clamp 21. More specifically, in this embodiment, a mandrel fixing hole is provided at the center of the turntable 28, and a mandrel 25 is fixed to the screw fixing hole by screws. A central hole 29 is respectively provided on the outer circle of the mandrel 25 corresponding to the adjustment screw 22 of each clamping assembly 19, and a screw perforation 28 is provided on the outer circle of the turntable 18 corresponding to each T-shaped groove 26. One end of the adjustment screw 22 penetrates through the screw perforation 28, the other end is inserted into the central hole 29, and the middle section extends in the T-shaped groove 26 and is screwed with the T-shaped block 27 on the inner clamp 21. And the end of the adjustment screw 22 extends out of the screw perforation 28 to the outer circle of the turntable 18, and the end forms a hexagonal prism shape for a wrench to twist. By twisting each adjustment screw 22, the position of the tube blank 1 installed on the turntable 18 can be adjusted, and thus the coaxiality of the tube blank 1 and the turntable 18 can be ensured.

[0043] In a preferred embodiment, to accommodate the shrinkage of the tube blank 1 after heating, the outer diameter of the inner clamp 21 is the same as the inner diameter of the tube blank 1, but the inner diameter of the outer clamp 20 is larger than the outer diameter of the tube blank 1.

[0044] In order to ensure that the tube blank 1 can be clamped, friction lines are preferably formed on the surfaces of both the inner clamp 21 and the outer clamp 20 to increase the friction at the contact position with the tube blank 1.

[0045] A rotary necking forming method, in combination with Figure 1-6 as shown, using the aforementioned rotary necking forming device, includes the following steps:

[0046] Step 1: Fix the tube blank 1 to be processed onto the power assembly 2. Specifically, first place the end of the tube blank 1 against the turntable 18, and position the tube blank 1 in the middle of each outer clamp 20. Then, move each inner clamp 21 by rotating the adjustment screw 22 to press against the inner wall of the tube blank 1 respectively, so that the side wall of the tube blank 1 is clamped between the inner clamp 21 and the outer clamp 20 to fix the tube blank 1. Rotate the tube blank 1 through the power assembly 2 and observe whether the tube blank 1 rotates smoothly. If there is radial runout during rotation, turn the corresponding adjustment screw 22 to adjust the position of the tube blank 1 on the turntable 18, so as to ensure that the tube blank 1 is coaxial with the turntable 18 by rotating each adjustment screw 22.

[0047] Step 2: Drive the tube blank 2 to rotate through the power assembly 2. Specifically, rotate the turntable 18 around its own axis, and the axis of rotation during rotation is coaxial with the axis of the tube blank 2.

[0048] Step 3: Control the first telescopic cylinder 4 and the second telescopic cylinder 7 to extend and retract, so that the spinning wheel 1 presses against the side wall of the tube blank 2 and travels from one end of the area to be necked down to the other end. During the traveling process, according to the contour shape of the area to be necked down of the tube blank 1, when the spinning wheel 1 travels to different axial positions of the tube blank 1, the second telescopic cylinder 7 extends different lengths. If the necking down of the tube blank 1 cannot be completed by performing Step 3 once, repeat Step 3 until the necking down process is completed. And when repeating, the traveling path of the spinning wheel in the next time can be opposite to that in the previous time, so that it is not necessary to move the spinning wheel away from the tube blank to readjust the position.

[0049] Preferably, if you want to make the necking down process more efficient or for materials that are difficult to deform, you can turn on the flame spray gun 11 during Step 3 to spray and heat the area to be processed of the tube blank 1, thereby softening the tube blank 1. To avoid overheating the tube blank 1 and affecting its metal properties, during the heating process, the temperature of the tube blank 1 can be monitored by the infrared temperature detector 12 to control the heating temperature of the tube blank 1 by the flame spray gun 11.

[0050] The above is only the preferred embodiment of the present invention and does not limit the design of this case. All equivalent changes made according to the key design of this case fall within the protection scope of this case.

Claims

1. A rotary shrinking neck forming device for shrinking a tube blank (1), characterized in that: It comprises a power assembly (2) and a rotating wheel assembly (3); The power assembly (2) is used to fix the tube blank (1) and can drive the tube blank (1) to rotate around its own axis; The rotary wheel assembly (3) comprises a first telescopic cylinder (4), a slide table (5), a movable guide rail (6) and a second telescopic cylinder (7); A first telescopic cylinder (4) is located on the periphery of the tube blank (1) on the power assembly (2), one end of which is a mounting end (8) and the other end of which is a movable end (9). The movable end (9) is moved closer to or farther from the mounting end (8) by telescoping. The mounting end (8) is pivotally arranged so that the movable end (9) can be swung closer to or farther from the tube blank (1) in the radial direction of the tube blank (1); The slide (5) is fixed on the movable end (9). As the movable end moves, the slide (5) is rotated and equipped with a spinning wheel (10). The spinning wheel (10) is used to abut against the side wall of the tube blank (1) so as to roll against the side wall of the tube blank (1) when the tube blank (1) rotates. The movable guide rail (6) cooperates with the slide table (5), and the two slide relatively only in the telescopic direction of the first telescopic cylinder (4); The second telescopic cylinder (7) has one end hinged to the movable guide rail (6) and is used to drive the movable guide rail (6) to move closer to or away from the tube blank (1).

2. A rotary compression port forming device as claimed in claim 1, characterized in that: The pivot axis of the mounting end (8) is fixed in position, and its extension direction is perpendicular to the axis of the tube blank (1).

3. A rotary compression port forming device as claimed in claim 1, characterized in that: The other end of the second telescopic cylinder (7) is fixedly arranged, and the second telescopic cylinder (7) is perpendicular to the tube blank (1).

4. A rotary compression port forming device as claimed in claim 1, characterized in that: It also includes a flame spray gun (11), which is located on the periphery of the tube blank (1) on the power component (2) and is used to spray flame towards the tube blank (1).

5. A rotary compression port forming device as claimed in claim 1, characterized in that: It also includes an infrared temperature detector (12), which is used to collect the temperature of the tube blank (1).

6. A rotary compression port forming device as claimed in claim 1, characterized in that: It also includes a support assembly (13), the support assembly (13) having a plurality of support wheels (14), each support wheel (14) being arranged around the periphery of the tube blank (1) on the power assembly (2), being supported against the outer wall of the tube blank (1), and rolling as the tube blank (1) rotates.

7. A rotary compression port forming device as claimed in claim 7, characterized in that: The support assembly (13) further comprises an upper frame (15), a lower frame (16) and an opening and closing driving mechanism (17). The upper frame (15) and the lower frame (16) are arranged on both radial sides of a tube blank (1) fixed on the power assembly (2). Some support wheels (14) are installed on a side of the upper frame (15) close to the tube blank (1), and the remaining support wheels (14) are installed on a side of the lower frame (16) close to the tube blank (1). The upper frame (15) and the lower frame (16) are driven by the opening and closing driving mechanism (17) to approach or move away from each other, so that when approaching, each support wheel (14) can abut against the outer wall of the tube blank (1), and when moving away, the support wheels (14) on the upper frame (15) and / or the lower frame (16) can leave the tube blank (1).

8. A rotary compression port forming device as claimed in claim 1, characterized in that: The power assembly (2) has a turntable (18) which can rotate around its own axis. A clamping mechanism is arranged on the turntable (18). The clamping mechanism is used to fix the tube blank (1) from one end of the tube blank (1) and make the tube blank (1) coaxial with the turntable (18) after fixation, so that the tube blank (1) rotates under the drive of the turntable (18).

9. A rotary compression port forming device as claimed in claim 8, characterized in that: The clamping mechanism comprises a plurality of clamping assemblies (19), which are arranged in an array around the axis of the turntable (18), each clamping assembly (19) comprises an outer clamp (20), an inner clamp (21) and an adjusting screw (22), the outer clamp (20) being fixedly arranged on the turntable (18), the inner clamp (21) being located on a side of the outer clamp (20) close to the center of the turntable (18), and being linearly slidably arranged on the turntable (18) so as to approach or move away from the outer clamp (20) radially along the turntable (18), and the adjusting screw (22) being rotatably installed on the turntable (18), with an extension direction being parallel to a sliding direction of the inner clamp (21), and being threadedly connected to the inner clamp (21) so as to drive the inner clamp (21) to slide by the rotation of the adjusting screw (22).

10. A rotary compression port forming device as claimed in claim 1, characterized in that: The first telescopic cylinder (4) and the second telescopic cylinder (7) are connected to a controller (23) so as to be telescopic under the control of the controller (23).

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