Drilling device for pneumatic ball valve machining

Abstract

The drilling device for pneumatic ball valve machining comprises a drilling rack, a drilling mechanism is installed at the top of the drilling rack, a clamping driving mechanism is installed at the bottom of the drilling mechanism, a machining table is installed on the drilling rack, a limiting seat is installed on the surface of the machining table in a threaded connection mode, and a limiting groove is formed in the surface of the limiting seat; four groups of mounting columns are uniformly mounted on the surface of the drilling rack, the tops of the mounting columns penetrate through the guide sheets and are fixedly connected with an extension plate, and the extension plate is fixedly arranged on the side wall of the top plate. According to the drilling device for pneumatic ball valve machining, a first clamping seat, a second clamping seat and a limiting groove are distributed in a triangular shape, a ball valve pipeline can be stably clamped and fixed, when the surface of the ball valve pipeline is stressed for drilling, the ball valve pipeline cannot be loosened, the drilling position cannot be displaced, drilling failure is avoided, and the drilling efficiency is improved. And even the product is scrapped.

Description

Technical Field

[0001] The invention relates to the field of drilling devices, in particular to a drilling device for processing a pneumatic ball valve. Background Art

[0002] Drilling device refers to the general term for equipment used to make holes in solid materials. Common drilling devices include electric drills and drilling machines. With the further development of processing technology, the efficiency of drilling devices has also been greatly improved. They are widely used in the reinforcement of building beams, plates, columns, walls, etc., decoration, wall installation, brackets, railings, billboards, air conditioner outdoor units, guide rails, satellite receivers, elevators, steel structure workshops, etc.

[0003] The existing drilling device for processing pneumatic ball valves is not firmly fixed on the outer wall of the pipe of the pneumatic ball valve, which affects the use of the device. In addition, it is labor-intensive to use the drilling device for processing, which reduces the work efficiency of workers.

[0004] To solve the above problem, after searching, the publication number CN211539587U discloses a drilling device for processing a pneumatic ball valve, which includes: screwing the clamps on both sides of the sleeve into the side of the sleeve until the rubber pad located on the inner side of the clamp is tightly fitted with the outer wall of the pipe, and then stopping the rotation of the clamp, so that the sleeve and the outer wall of the pipe of the pneumatic ball valve are fixed;

[0005] Although the above-mentioned device can use the staples to limit and fix the ball valve pipe that needs to be drilled before drilling, in actual use, when it is necessary to drill a hole in the top side wall of the pipe, two sets of staples clamp and fix the two side walls of the ball valve pipe through a single-point clamping method. Since the contact area between the ball valve pipe and the staples is small, the ball valve pipe is prone to loosening when the pipe is subjected to force drilling, resulting in drilling failure or even product scrapping. Summary of the invention

[0006] The object of the present invention is to provide a drilling device for machining a pneumatic ball valve to solve the defects mentioned in the above background technology.

[0007] To achieve the above-mentioned purpose, a drilling device for processing pneumatic ball valves is provided, comprising a drilling frame, a drilling mechanism is installed on the top of the drilling frame, a clamping drive mechanism is installed on the bottom of the drilling mechanism, a processing table is installed on the drilling frame, a limit seat is screwed on the surface of the processing table, a limit groove is provided on the surface of the limit seat, four groups of mounting columns are evenly installed on the surface of the drilling frame, the top of the mounting column passes through the guide plate and is fixedly connected to the extension plate, the extension plate is fixedly set on the side wall of the top plate, and the guide plate is fixedly set on the side wall of the lifting platform.

[0008] As an improvement of the above scheme, the drilling mechanism includes a top plate, an extension plate, a drilling motor, a lifting platform, a drill rod and a guide plate. A cylinder is screwed on the surface of the top plate, a drilling motor is screwed on the surface of the lifting platform, and the output shaft of the cylinder is fixedly connected to the drilling motor.

[0009] As an improvement of the above scheme, two groups of extension plates are installed on both sides of the top plate, guide plates are installed on both sides of the lifting platform, the top plate and the lifting platform are arranged in parallel, a drill rod is movably installed at the bottom of the lifting platform, and the output shaft of the drilling motor is fixedly connected to the drill rod.

[0010] As an improvement of the above scheme, the cross-section of the limit seat is set in a "T" shape, and a ball valve pipe is positioned and placed in the limit groove opened on the surface of the limit seat. The ball valve pipe is clamped and fixed on the limit seat by the first clamping seat and the second clamping seat on the clamping drive mechanism, and the limit groove is set in an arc shape.

[0011] As an improvement of the above-mentioned scheme, the clamping drive mechanism includes a first clamping seat, a second clamping seat, a positioning seat, a connecting block, a movable plate, a guide rod, a fixing frame and a gear. Positioning seats are installed on the back of the first clamping seat and the second clamping seat, connecting blocks are screwed on the outer sides of the two groups of positioning seats, and movable plates are fixedly arranged on the outer sides of the two groups of connecting blocks.

[0012] As an improvement of the above scheme, driving plates are fixedly provided at the bottom of the two groups of movable plates, and racks are screwed on the two groups of driving plates. Gears are movably installed between the two groups of racks. The upper and lower sides of the gears are respectively meshed with the two groups of racks. The first clamping seat and the second clamping seat are driven to move synchronously toward each other by two groups of racks, gears and stepper motors.

[0013] As an improvement on the above scheme, sliders are fixedly provided on the two sets of driving plates, slide rails are provided at the bottom of the processing table, and slide rails are provided on the surface of the drilling machine frame. At the same time, the two sets of driving plates are respectively slidably provided inside the two sets of slide rails, and the cross-sections of the slide rails and the sliders are both dovetail-shaped; fixed frames are fixedly provided on both sides of the processing table, and two sets of guide rods are respectively installed on the fixed frames, and the guide rods are inserted into the guide holes provided on the movable plate and the driving plate.

[0014] As an improvement of the above scheme, the rotating shaft of the gear is fixedly connected to the output shaft of the stepper motor, and the stepper motor is screwed to the surface of the connecting frame, the bottom of the connecting frame is screwed and fixed to the surface of the drilling frame, and the drilling frame and the connecting frame are reinforced by a trapezoidal reinforcement plate.

[0015] As an improvement of the above solution, the ends of the first clamping seat and the second clamping seat are both provided with arc-shaped slots, and the first clamping seat and the second clamping seat are respectively clamped and fixed on both sides of the ball valve pipeline through the arc-shaped slots thereon.

[0016] As an improvement on the above scheme, the back sides of the first clamping seat and the second clamping seat are both provided with fixing grooves, the interior of the fixing grooves is plugged and fixed with a T-shaped seat, and the T-shaped seat is fixed to the surface of the positioning seat; the ball valve pipeline is clamped and fixed at three places on the limit seat through the limit groove, the first clamping seat and the second clamping seat.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. The present invention can stably clamp and fix the ball valve pipeline by the first clamping seat, the second clamping seat and the limiting groove being distributed in a triangular shape. When the surface of the ball valve pipeline is subjected to force drilling, the ball valve pipeline will not loosen and the position of the drilling hole will not be displaced, thereby avoiding drilling failure or even product scrapping.

[0019] 2. The present invention has a first clamping seat and a second clamping seat that are soft in texture, and a limit seat that is detachable on a processing table. According to the different curvatures of the ball valve pipeline, different limit grooves with matching curvatures can be selected to clamp and fix ball valve pipelines of different types, thereby improving the adaptability of the device and being capable of drilling holes in a large number of ball valve pipelines of different diameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 It is a front view schematic diagram of the structure of the present invention;

[0022] Figure 2 for Figure 1 Bottom view of

[0023] Figure 3 for Figure 1 A top view of

[0024] Figure 4 for Figure 1 Rear view of

[0025] Figure 5 It is a schematic diagram of the structure of the clamping drive mechanism;

[0026] Figure 6 for Figure 5 Front view of

[0027] Figure 7 for Figure 5 Rear view of

[0028] Figure 8 for Figure 5 A cross-sectional view of

[0029] Fig. 9 for Figure 7 sectional view of .

[0030] The following are the descriptions of the reference numerals:

[0031] 1. Drilling frame; 2. Clamping drive mechanism; 20. First clamping seat; 21. Second clamping seat; 22. Positioning seat; 23. Connecting block; 24. Moving plate; 241. Driving plate; 242. Rack; 243. Sliding block; 244. Slide rail; 25. Guide rod; 26. Fixed frame; 27. Gear; 271. Stepping motor; 272. Connecting frame; 3. Processing table; 31. Limit seat; 32. Limit groove; 4. Ball valve pipeline; 5. Mounting column; 6. Drilling mechanism; 60. Cylinder; 61. Top plate; 62. Extension plate; 63. Drilling motor; 64. Lifting platform; 65. Drill rod; 66. Guide sheet. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0034] In the present invention, unless otherwise clearly specified and limited, the terms "connection", "fixation", etc. should be understood in a broad sense. For example, "fixation" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0035] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the meaning of "and / or" appearing in the full text includes three parallel schemes. Taking "A and / or B" as an example, it includes scheme A, or scheme B, or a scheme that satisfies both A and B. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in the field to implement. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0036] Specific implementation method 1: Please refer to Figure 1-4 The present invention provides a drilling device for processing a pneumatic ball valve, comprising a drilling frame 1, a drilling mechanism 6 is installed on the top of the drilling frame 1, a clamping drive mechanism 2 is installed on the bottom of the drilling mechanism 6, a processing table 3 is installed on the drilling frame 1, a limit seat 31 is screwed on the surface of the processing table 3, a limit groove 32 is provided on the surface of the limit seat 31, four groups of mounting columns 5 are evenly installed on the surface of the drilling frame 1, the top of the mounting column 5 passes through a guide piece 66 and is fixedly connected to an extension plate 62, the extension plate 62 is fixedly arranged on the side wall of the top plate 61, and the guide piece 66 is fixedly arranged on the side wall of the lifting platform 64.

[0037] like Figure 1 , Figure 2 and Figure 4 As shown, specific embodiment 2: This embodiment is a further limitation of specific embodiment 1, the drilling mechanism 6 includes a top plate 61, an extension plate 62, a drilling motor 63, a lifting platform 64, a drill rod 65 and a guide plate 66, the surface of the top plate 61 is screwed with a cylinder 60, the surface of the lifting platform 64 is screwed with a drilling motor 63, and the output shaft of the cylinder 60 is fixedly connected to the drilling motor 63.

[0038] like Figure 1 and Figure 3 As shown, specific implementation method three: This implementation method is a further limitation of specific implementation method two, two groups of extension plates 62 are respectively installed on both sides of the top plate 61, guide plates 66 are respectively installed on both sides of the lifting platform 64, the top plate 61 and the lifting platform 64 are arranged in parallel, a drill rod 65 is movably installed at the bottom of the lifting platform 64, and the output shaft of the drilling motor 63 is fixedly connected to the drill rod 65.

[0039] like Figure 5 , Figure 6 , Figure 7 and Figure 8As shown, specific implementation mode four: This implementation mode is a further limitation of specific implementation mode one, the cross-section of the limit seat 31 is set in a "T" shape, and the ball valve pipe 4 is positioned and placed in the limit groove 32 opened on the surface of the limit seat 31. The ball valve pipe 4 is clamped and fixed on the limit seat 31 by the first clamping seat 20 and the second clamping seat 21 on the clamping drive mechanism 2, and the limit groove 32 is set in an arc shape.

[0040] like Figure 1 , Figure 3 and Figure 7 As shown, specific implementation mode five: This implementation mode is a further limitation of specific implementation mode four, and the clamping drive mechanism 2 includes a first clamping seat 20, a second clamping seat 21, a positioning seat 22, a connecting block 23, a movable plate 24, a guide rod 25, a fixing frame 26 and a gear 27. The back sides of the first clamping seat 20 and the second clamping seat 21 are both equipped with positioning seats 22, and the outer sides of the two groups of positioning seats 22 are both screwed with connecting blocks 23, and the outer sides of the two groups of connecting blocks 23 are both fixedly provided with movable plates 24.

[0041] Working principle: When performing actual operation, first place the ball valve pipe 4 on the pneumatic ball valve inside the limiting groove 32 on the limiting seat 31, and align the position where the hole needs to be opened on the ball valve pipe 4 with the drill rod 65. At this time, start the external switch of the stepper motor 271, and the stepper motor 271 drives the racks 242 meshing on its upper and lower sides through the gear 27. The two groups of racks 242 move inward synchronously, and drive the first clamping seat 20 and the second clamping seat 21 to move closer to the ball valve pipe 4 through the two groups of moving plates 24, so as to complete the clamping and fixing work on both sides of the ball valve pipe 4. The first clamping seat 20 and the second clamping seat 21 are respectively clamped and fixed on both sides of the ball valve pipe 4 through the arc-shaped card grooves thereon, and the bottom of the ball valve pipe 4 is supported and fixed by the arc-shaped limiting groove 32. The first clamping seat 20, the second clamping seat 21 and the limiting groove 32 are triangular. The ball valve pipe 4 is stably clamped and fixed. When the surface of the ball valve pipe 4 is subjected to force drilling, the ball valve pipe 4 will not loosen and the drilling position will not be displaced, thereby avoiding drilling failure or even product scrapping. When the ball valve pipe 4 is clamped, the cylinder 60 and the drilling motor 63 work synchronously. The drilling motor 63 drives the drill rod 65 to rotate at high speed. The drill rod 65 can move downward under the drive of the cylinder 60, so that the drill rod 65 can drill the top wall of the ball valve pipe 4. In the process of drilling the ball valve pipe 4, it is necessary to spray water to cool the position where the ball valve pipe 4 is drilled. When the drill rod 65 is lifted, the two sets of guide plates 66 on both sides of the lifting platform 64 are interspersed with mounting columns 5, which can limit and guide the lifting platform 64 during lifting, thereby avoiding tilting of the drill rod 65 when it moves downward.

[0042] like Figure 5 As shown, specific embodiment six: This embodiment is a further limitation of specific embodiment five, a driving plate 241 is fixedly provided at the bottom of the two groups of movable plates 24, and racks 242 are screwed on the two groups of driving plates 241, a gear 27 is movably installed between the two groups of racks 242, and the upper and lower sides of the gear 27 are respectively meshed with the two groups of racks 242, and the first clamping seat 20 and the second clamping seat 21 are driven to move synchronously toward each other by the two groups of racks 242, the gear 27 and the stepping motor 271.

[0043] like Figure 7 , Figure 8 and Fig. 9 As shown, specific implementation mode seven: This implementation mode is a further limitation of specific implementation mode six, and sliders 243 are fixedly provided on the two groups of driving plates 241, a slide rail 244 is provided at the bottom of the processing table 3, and a slide rail 244 is provided on the surface of the drilling machine frame 1. At the same time, the two groups of driving plates 241 are respectively slidably provided inside the two groups of slide rails 244, and the cross-sections of the slide rails 244 and the sliders 243 are both dovetail-shaped; fixed frames 26 are fixedly provided on both sides of the processing table 3, and two groups of guide rods 25 are respectively installed on the fixed frames 26, and the guide rods 25 are inserted into the guide holes provided on the movable plate 24 and the driving plate 241.

[0044] like Figure 7 , Figure 8 and Fig. 9 As shown, specific embodiment eight: This embodiment is a further limitation of specific embodiment six, the rotating shaft of the gear 27 is fixedly connected to the output shaft of the stepper motor 271, and the stepper motor 271 is screwed to the surface of the connecting frame 272, the bottom of the connecting frame 272 is screwed and fixed to the surface of the drilling frame 1, and the drilling frame 1 and the connecting frame 272 are reinforced by a trapezoidal reinforcing plate.

[0045] like Figure 1 , Figure 3 and Figure 7 As shown, specific embodiment nine: This embodiment is a further limitation of specific embodiment four, and arc-shaped grooves are provided at the ends of the first clamping seat 20 and the second clamping seat 21, and the first clamping seat 20 and the second clamping seat 21 are respectively clamped and fixed on both sides of the ball valve pipe 4 through the arc-shaped grooves thereon.

[0046] like Figure 5 As shown, specific embodiment ten: This embodiment is a further limitation of specific embodiment nine, and fixing grooves are provided on the backs of the first clamping seat 20 and the second clamping seat 21, and a T-shaped seat is inserted and fixed inside the fixing groove, and the T-shaped seat is fixed to the surface of the positioning seat 22; the ball valve pipeline 4 is clamped and fixed at three places on the limiting seat 31 through the limiting groove 32, the first clamping seat 20 and the second clamping seat 21.

[0047] The two groups of racks 242 move inward synchronously, and drive the first clamping seat 20 and the second clamping seat 21 to move closer to the ball valve pipe 4 through the two groups of movable plates 24; when the two groups of movable plates 24 are moving laterally, in order to avoid the two groups of movable plates 24 from tilting, two groups of guide rods 25 for limiting and guiding are inserted on the two groups of movable plates 24, which can limit and guide the two groups of movable plates 24 that move laterally to avoid the two groups of movable plates 24 from tilting during movement. At the same time, when the output shaft of the stepper motor 271 is reversed, the two groups of movable plates 24 respectively drive the first clamping seat 20 and the second clamping seat 21 to move away from the ball valve pipe 4, so that the ball valve pipe 4 that has completed the drilling operation can be removed; the first clamping seat 20 and the second clamping seat 21 are provided with arc grooves on their surfaces, and the arc grooves are attached to the circumferential side walls of the ball valve pipe 4 to increase the contact area with the ball valve pipe 4 and improve the stability when clamping the ball valve pipe 4.

[0048] The above description is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the inventive concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A drilling device for processing a pneumatic ball valve, comprising a drilling frame (1), characterized in that: A drilling mechanism (6) is installed on the top of the drilling frame (1), a clamping drive mechanism (2) is installed on the bottom of the drilling mechanism (6), a processing table (3) is installed on the drilling frame (1), a limit seat (31) is screwed on the surface of the processing table (3), a limit groove (32) is provided on the surface of the limit seat (31), four groups of mounting columns (5) are evenly installed on the surface of the drilling frame (1), the top of the mounting column (5) passes through the guide plate (66) and is fixedly connected to the extension plate (62), the extension plate (62) is fixedly arranged on the side wall of the top plate (61), and the guide plate (66) is fixedly arranged on the side wall of the lifting platform (64).

2. A drilling device for machining a pneumatic ball valve as claimed in claim 1, characterized in that: The drilling mechanism (6) comprises a top plate (61), an extension plate (62), a drilling motor (63), a lifting platform (64), a drilling rod (65) and a guide plate (66); a cylinder (60) is screwed on the surface of the top plate (61); a drilling motor (63) is screwed on the surface of the lifting platform (64); and an output shaft of the cylinder (60) is fixedly connected to the drilling motor (63).

3. A drilling device for machining a pneumatic ball valve as claimed in claim 2, characterized in that: Two groups of extension plates (62) are respectively installed on both sides of the top plate (61), and guide plates (66) are respectively installed on both sides of the lifting platform (64). The top plate (61) and the lifting platform (64) are arranged in parallel. A drill rod (65) is movably installed at the bottom of the lifting platform (64), and the output shaft of the drilling motor (63) is fixedly connected to the drill rod (65).

4. A drilling device for machining a pneumatic ball valve as claimed in claim 1, characterized in that: The cross section of the limit seat (31) is set in a "T" shape. A ball valve pipeline (4) is positioned and placed in a limit groove (32) provided on the surface of the limit seat (31). The ball valve pipeline (4) is clamped and fixed on the limit seat (31) by a first clamping seat (20) and a second clamping seat (21) on the clamping drive mechanism (2). The limit groove (32) is set in an arc shape.

5. A drilling device for machining a pneumatic ball valve as claimed in claim 4, characterized in that: The clamping drive mechanism (2) comprises a first clamping seat (20), a second clamping seat (21), a positioning seat (22), a connecting block (23), a movable plate (24), a guide rod (25), a fixing frame (26) and a gear (27); the first clamping seat (20) and the second clamping seat (21) are both provided with positioning seats (22) on their backs; the connecting blocks (23) are both screwed on the outer sides of the two groups of positioning seats (22); and the movable plates (24) are both fixedly provided on the outer sides of the two groups of connecting blocks (23).

6. A drilling device for machining a pneumatic ball valve as claimed in claim 5, characterized in that: A driving plate (241) is fixedly arranged at the bottom of the two groups of movable plates (24), and racks (242) are screwed on the two groups of driving plates (241). A gear (27) is movably installed between the two groups of racks (242). The upper and lower sides of the gear (27) are respectively meshed with the two groups of racks (242). The first clamping seat (20) and the second clamping seat (21) are driven to move synchronously toward each other through the two groups of racks (242), the gear (27) and the stepping motor (271).

7. A drilling device for machining a pneumatic ball valve as claimed in claim 6, characterized in that: Slide blocks (243) are fixedly arranged on the two groups of driving plates (241), a slide rail (244) is provided at the bottom of the processing table (3), and a slide rail (244) is provided on the surface of the drilling machine frame (1). At the same time, the two groups of driving plates (241) are respectively slidably arranged inside the two groups of slide rails (244), and the cross-sections of the slide rails (244) and the slide blocks (243) are both dovetail-shaped; fixed frames (26) are fixedly arranged on both sides of the processing table (3), and two groups of guide rods (25) are respectively installed on the fixed frames (26), and the guide rods (25) are inserted into the guide holes provided on the movable plate (24) and the driving plate (241).

8. A drilling device for machining a pneumatic ball valve as claimed in claim 6, characterized in that: The rotating shaft of the gear (27) is fixedly connected to the output shaft of the stepper motor (271), and the stepper motor (271) is screwed to the surface of the connecting frame (272), the bottom of the connecting frame (272) is screwed and fixed to the surface of the drilling frame (1), and the drilling frame (1) and the connecting frame (272) are reinforced by a trapezoidal reinforcing plate.

9. A drilling device for machining a pneumatic ball valve as claimed in claim 4, characterized in that: The ends of the first clamping seat (20) and the second clamping seat (21) are both provided with arc-shaped clamping grooves, and the first clamping seat (20) and the second clamping seat (21) are respectively clamped and fixed on both sides of the ball valve pipeline (4) through the arc-shaped clamping grooves thereon.

10. A drilling device for machining a pneumatic ball valve as claimed in claim 9, characterized in that: The backs of the first clamping seat (20) and the second clamping seat (21) are both provided with fixing grooves, the interior of the fixing grooves is plugged with a fixed T-shaped seat, and the T-shaped seat is fixed to the surface of the positioning seat (22); the ball valve pipeline (4) is clamped and fixed at three locations on the limiting seat (31) through the limiting groove (32), the first clamping seat (20) and the second clamping seat (21).

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