Coal mine goaf grouting fire prevention and extinguishing device

Abstract

This invention relates to a shotcrete fire prevention and extinguishing device for coal mine goaf areas, comprising: a base frame for supporting the device; a shotcrete nozzle mounting frame disposed above the base frame for mounting the shotcrete nozzles; a left-right swinging mechanism disposed on the base frame and connected to the shotcrete nozzle mounting frame for driving the shotcrete nozzle mounting frame and the shotcrete nozzles to swing left and right; and a right-right swinging mechanism disposed on the base frame and connected to the hinged component of the shotcrete nozzle mounting frame for driving the shotcrete nozzles to swing up and down. This invention, by setting the left-right swinging mechanism and the right-right swinging mechanism to jointly drive the shotcrete nozzles, enables the shotcrete nozzles to achieve compound swinging in both horizontal and vertical directions, thereby achieving large-area, three-dimensional slurry coverage at a single workstation. This effectively solves the problems of existing technologies where the nozzles can only swing up and down, resulting in small coverage areas and the need for frequent device relocation, significantly improving the efficiency and safety of fire prevention and extinguishing operations.

Description

Technical Field

[0001] This invention relates to the field of coal mine safety equipment technology, and in particular to a spraying fire prevention and extinguishing device for coal mine goaf areas. Background Technology

[0002] Spontaneous combustion in coal mines is one of the most significant hazards threatening safe production. Currently, fire prevention and extinguishing technologies used in the coal mining industry mainly include grouting, colloidal methods, pressure equalization ventilation, inhibitors, inert gas injection, and foaming. Among these, grouting technology, by injecting materials such as gels and three-phase foams into spontaneous combustion hazard areas such as goafs, can effectively prevent the oxidation process of coal, inhibit fire development, and ultimately extinguish the fire. This technology is widely used in coal mines with severe spontaneous combustion, high production and efficiency, and high-gas, easily spontaneously combustible coal seams due to its significant effectiveness and strong adaptability.

[0003] In practical applications of grouting for fire prevention and extinguishing, the spray coverage of the grouting device directly affects the fire extinguishing efficiency. For example, Chinese invention patent CN108757002A discloses a grouting fire prevention and extinguishing device and method for coal mine goaf areas. This device can control the vertical swing amplitude of the nozzle by adjusting the connection position between the support rod and the U-shaped support plate on the grouting steel pipe, thereby adjusting the coverage area of ​​the grout in the vertical direction.

[0004] However, the nozzle can only oscillate vertically, resulting in insufficient horizontal coverage in a single operation. When treating large areas of goaf, repeated adjustments to the spraying position are necessary, leading to low efficiency and affecting the timeliness and continuity of fire suppression. Therefore, there is an urgent need to develop a shotcrete fire suppression device capable of achieving a wider horizontal coverage range. Summary of the Invention

[0005] To address the problem of insufficient coverage width and the need for frequent adjustments to the spraying position in existing shotcrete devices, this invention provides a shotcrete fire prevention and extinguishing device for coal mine goaf areas, which increases the coverage area of ​​single-point operations and thus effectively improves the overall construction efficiency of grouting for fire prevention and extinguishing.

[0006] The technical solution is as follows: A coal mine goaf spraying fire prevention and extinguishing device, comprising: a base frame for supporting the device; a spray nozzle mounting frame disposed above the base frame for mounting the spray nozzles; a left-right swinging mechanism disposed on the base frame and connected to the spray nozzle mounting frame for driving the spray nozzle mounting frame and the spray nozzles to swing left and right; a right-up swinging mechanism disposed on the base frame and connected to the hinge component of the spray nozzle mounting frame for driving the spray nozzles to swing up and down; and a drive mechanism disposed on the base frame and connected to the left-right swinging mechanism and the right-up swinging mechanism.

[0007] As a further improvement, the spray nozzle mounting bracket includes a sleeve, one end of which is adjustablely connected to the swing end of the left and right swing mechanism, and the other end of the sleeve is provided with an external gripper, which is hinged to an internal gripper for clamping the spray nozzle via a first pin.

[0008] As a further improvement, the left-right swinging mechanism includes: a ring, vertically arranged and rotatable around its central axis, with a connecting rib plate on the inner side of the ring, and a groove and mounting hole radially formed on the connecting rib plate; a vertical shaft, rotatably connected to the base frame at its lower end and connected to the straight rod at its upper end, with a horizontally extending transverse shaft in the middle; a U-shaped hinge, with its open end hinged to both ends of the transverse shaft, and a pin vertically arranged at its closed end; a slider, disposed in the groove, with a central hole in its middle, in which a sphere is embedded, and a channel penetrating both ends of the sphere's surface; the front end of the pin movably inserts into the channel; and an adjusting bolt, passing through the mounting hole and abutting the slider, used to lock or adjust the radial position of the slider in the groove; when the ring rotates, the vertical shaft and left-right swinging are driven by the cooperation of the pin and the sphere channel.

[0009] As a further improvement, the up-and-down swing mechanism includes: two connecting arms, one end of which is fixed to both ends of the first pin, and the other end of which is connected to a crossbar; at least one counterweight assembly, which includes a vertical connecting rod and a counterweight ball disposed at the lower end of the vertical connecting rod, the upper end of the vertical connecting rod being sleeved on the crossbar; at least one tension spring, one end of which is connected to the crossbar, and the other end of which is connected to a hook at the lower end of the outer jaw clamp; and a lifting assembly for driving the counterweight assembly to move up and down in the vertical direction to change the pitch angle of the spray nozzle.

[0010] As a further improvement, the lifting assembly includes: a reciprocating ball screw, horizontally mounted on the base frame; a screw nut, assembled on the reciprocating ball screw; a vertical connecting frame, the lower end of which is connected to the screw nut; and an arc-shaped lifting frame, the inner side of which is inclined, and the outer side is connected to the vertical connecting frame through an extension. The arc-shaped lifting frame is located below the counterweight assembly, and pushes the counterweight assembly upward through the inclined surface, thereby adjusting the pitch angle of the spray nozzle.

[0011] As a further improvement, the vertical connecting frame is provided with a vertically extending groove, and the outer extension is fixedly connected to the vertical connecting frame by connecting bolts passing through the vertical groove.

[0012] As a further improvement, the sleeve is provided with a threaded hole and equipped with an adjusting screw for locking the position of the sleeve on the crossbar.

[0013] As a further improvement, the outer tiger's mouth clamp is provided with limiting baffles at both ends to limit the rotation angle of the inner tiger's mouth clamp.

[0014] Compared with the prior art, the present invention has the following advantages: 1. This invention uses a combination of left-right swing mechanism and up-down swing mechanism to drive the spray nozzle, enabling the nozzle to swing in both horizontal and vertical directions. This allows for large-area, three-dimensional slurry coverage at a single workstation, effectively solving the problems of existing nozzles that can only swing up and down, resulting in small coverage area and the need for frequent device movement. This significantly improves the efficiency and safety of fire prevention and extinguishing operations.

[0015] 2. The left and right swing mechanism of the present invention adopts a structure in which a rotating ring and a pin-slider mechanism drive the vertical shaft to swing, which transforms the continuous rotational motion of the ring into a large-angle reciprocating swing of the spray nozzle mounting bracket. Its transmission is smooth and its structure is simple, and it can reliably achieve a large range of coverage of the spray nozzle in the horizontal direction.

[0016] 3. The up-and-down swing mechanism of the present invention forms a balance adjustment system through a connecting arm, crossbar, counterweight assembly, and tension spring. Combined with a dedicated lifting assembly to drive the counterweight ball up and down, it precisely controls the pitch angle of the spray nozzle. This structure utilizes the principle of gravity and elasticity balance, making angle adjustment labor-saving, stable, and easy to control precisely.

[0017] 4. The lifting assembly of the present invention uses a reciprocating ball screw to drive the horizontal movement of the arc-shaped lifting frame with an inclined surface, and the inclined surface pushes the counterweight assembly to rise smoothly.

[0018] 5. This invention achieves adjustable installation height of the arc-shaped lifting frame through the cooperation of the vertical groove on the vertical connecting frame and the connecting bolts. This allows the device to adapt to different specifications of counterweight components or different initial balance states, enhancing the device's versatility and ease of debugging.

[0019] 6. The present invention provides limiting baffles at both ends of the outer jaw clamp, which can effectively limit the swing angle range of the inner jaw clamp and the spray nozzle, prevent structural damage caused by overload or misoperation, and improve the safety and reliability of equipment operation. Attached Figure Description

[0020] Figure 1 This is a three-dimensional structural diagram of the present invention.

[0021] Figure 2 This is a schematic diagram of the structure of the left and right swinging mechanism installed on the base frame of the present invention.

[0022] Figure 3 This is a partial structural schematic diagram of the left-right swing mechanism of the present invention.

[0023] Figure 4 This is a schematic diagram of the structure of the spray nozzle mounting bracket of the present invention.

[0024] Figure 5 This is a three-dimensional structural diagram of the up-and-down swing mechanism of the present invention.

[0025] Figure 6 This is a partial structural schematic diagram of the up-and-down swing mechanism of the present invention.

[0026] The meanings of the reference numerals in the figure are as follows: 101: base frame; 200: shotcrete nozzle mounting bracket; 201: sleeve; 202: outer jaw clamp; 203: first pin; 204: inner jaw clamp; 300: shotcrete nozzle; 400: left and right swinging mechanism; 401: ring; 402: connecting rib plate; 4021: mounting hole; 403: vertical shaft; 404: horizontal shaft; 405: U-shaped hinge; 406: pin; 407: embedding groove; 408: slider; 409: center hole; 410: sphere; 411: channel. 500: Up-and-down swing mechanism; 501: Connecting arm; 502: Horizontal bar; 503: Counterweight assembly; 504: Vertical connecting rod; 505: Counterweight ball; 506: Sleeve; 507: Tension spring; 509: Reciprocating ball screw; 510: Screw nut; 511: Vertical connecting frame; 512: Arc-shaped lifting frame; 513: Inclined surface; 514: Outer extension; 515: Vertical groove; 516: Connecting bolt; 517: Adjusting screw; 518: Limiting baffle; 520: Screw frame; 6: Hook; 700: Drive mechanism. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] This embodiment provides a shotcrete fire prevention and extinguishing device for coal mine goaf areas, the structure of which is as follows: Figures 1 to 6As shown, the device includes a base frame 101 with height-adjustable support legs at its bottom to adapt to uneven ground. Above the base frame 101, a nozzle mounting bracket 200 is installed for fixing nozzles 300. The rear end of the nozzle 300 is connected to an external mortar pump via a pressure-resistant hose for delivering extinguishing mortar. To achieve wide coverage by the nozzles 300, the device integrates two swing drive systems: a left-right swing mechanism 400 mounted on the base frame 101 and connected to the nozzle mounting bracket 200, for driving the nozzles 300 to swing horizontally; and a right-down swing mechanism 500, also mounted on the base frame 101 and connected to the hinge of the nozzle mounting bracket 200, for driving the nozzles 300 to adjust their pitch angle. Both mechanisms are powered by a drive mechanism 700 mounted on the base frame 101. Through a combination of left-right and up-down swinging motions, the spray nozzle 300 can form a three-dimensional scanning spray trajectory at a fixed position, thereby covering a large area of ​​the goaf in one go. This fundamentally solves the problems of existing technologies where the nozzle can only swing up and down, the coverage width is insufficient, and frequent relocation of equipment is required, greatly improving the efficiency and safety of fire prevention and extinguishing operations.

[0029] In one specific embodiment, the structure of the spray nozzle mounting bracket 200 is as follows: Figure 4 As shown, it includes a sleeve 201. One end of the sleeve 201 is designed as an adjustable connection end, which is machined with external threads and fitted with a locking nut. The port is a contraction end, used for adjustable connection to the swing output end of the left-right swing mechanism 400. By tightening or loosening the locking nut, the insertion depth of the sleeve 201 can be fixed or adjusted, thereby achieving fine adjustment of the extension length of the spray nozzle 300. The other end of the sleeve 201 is welded or integrally formed with an external jaw clamp 202, which is hinged to an internal jaw clamp 204 via a first pin 203. The body of the spray nozzle 300 is securely clamped in the internal jaw clamp 204. This hinged structure not only provides stable support for the spray nozzle 300, but more importantly, its first pin 203 constitutes the rotational pivot of the spray nozzle 300 for up-and-down swinging, ensuring the accuracy and stability of the pitching motion. For safety, limit baffles 518 are also provided at both ends of the outer tiger mouth clamp 202 to limit the rotation angle range of the inner tiger mouth clamp 204 around the first pin shaft 203, and to prevent structural damage due to overload.

[0030] The detailed structure of the left and right swinging mechanism 400 is as follows: Figure 2 and Figure 3As shown, it includes a vertically arranged circular ring 401, which can rotate around its central axis via bearings and other components. At least one connecting rib plate 402 is fixedly arranged inside the circular ring 401. The connecting rib plate 402 has an elongated groove 407 and a mounting hole 4021 formed along the radial direction of the circular ring 401. A slider 408 is placed in the groove 407 and can slide radially along the groove. A central hole 409 is formed in the middle of the slider 408, and a sphere 410 (such as a bearing ball) that can move freely 360 degrees is embedded in the central hole 409. A channel 411 passing through the center of the sphere 410 and extending to both ends is machined on its surface. At least two adjusting bolts pass through the mounting holes 4021 and are fitted with nuts, with their ends abutting against the slider 408. Tightening the adjusting bolts locks the slider 408 in any radial position within the groove 407; loosening them allows adjustment of the slider's position. Furthermore, the power output section of the mechanism includes a vertical shaft 403, the lower end of which is rotatably connected to the base frame 101 via a bearing, and the upper end is fixedly connected to the sleeve 201 of the spray nozzle mounting bracket 200. A horizontal shaft 404 extending horizontally to both sides is fixedly installed in the middle of the vertical shaft 403. A U-shaped hinge 405, the open end of which is hinged to both ends of the horizontal shaft 404 via a bearing or bushing, allows the U-shaped hinge 405 to swing around the horizontal shaft 404. At the closed end of the U-shaped hinge 405, i.e., the back side opposite the open end, a pin 406 is fixed perpendicularly to this end face. The front end of the pin 406 is movably inserted into the channel 411 of the aforementioned sphere 410. When the drive mechanism 700 drives the ring 401 to rotate at a constant speed, the pin 406 is connected to the slider 408 through the ball 410, and the slider 408 moves in a circular motion with the ring 401. This forces the pin 406 to drive the U-shaped hinge 405 and the vertical shaft 403 to swing back and forth, thereby driving the spray nozzle mounting bracket 200 and the spray nozzle 300 to perform horizontal sweeping. By adjusting the radial position of the slider 408 in the mounting groove 407, the radius of rotation of the pin 406 can be changed, thereby achieving stepless adjustment of the left and right swing amplitude of the spray nozzle 300 to adapt to the coverage requirements of different width areas.

[0031] The structure of the up-and-down swing mechanism 500 is as follows: Figure 5 and Figure 6As shown. Its actuator acts directly on the hinge point of the spray nozzle mounting bracket 200. Specifically, it includes two connecting arms 501, one end of which is fixedly connected to both ends of the first pin 203 and rotates together with the first pin 203. The other ends of the two connecting arms 501 are connected to a crossbar 502. At least one counterweight component 503 is mounted on the crossbar 502. Each counterweight component 503 includes a vertical connecting rod 504 and a counterweight ball 505 fixed at its lower end. The upper end of the vertical connecting rod 504 is sleeved on the crossbar 502 through a sleeve 506. The sleeve 506 has a threaded hole and is fitted with an adjusting screw 517. Tightening the adjusting screw 517 can lock it in any position on the crossbar 502, and loosening it can move it to adjust the counterweight arm to balance the spray nozzle torque under different working conditions. To provide initial restoring force, at least one tension spring 507 is provided, one end of which is connected to the crossbar 502 or sleeve 506, and the other end is connected to the hook 6 provided at the bottom of the outer jaw clamp 202. In the natural state, the tension of the tension spring 507 and the gravity of the counterweight assembly 503 work together to keep the nozzle of the spray nozzle 300 at an initial elevation angle. The lifting assembly that drives the spray nozzle 300 to change the elevation angle includes a reciprocating ball screw 509 horizontally mounted on the base frame 101 via a screw bracket 520. A screw nut 510 is fitted on the screw and slides with the screw bracket 520 to prevent rotation. The screw nut 510 is usually covered with a protective shell. The lower end of a vertical connecting bracket 511 is fixed to the top of the protective shell, and a vertically extending elongated slot 515 is formed on it. An arc-shaped lifting frame 512 with an inner inclined surface 513 is connected to a vertical connecting frame 511 via an extension 514 on its outer side. In a preferred embodiment, the arc-shaped lifting frame 512 is preferably a 180-degree semi-circular arc, specifically fixed by connecting bolts 516 passing through the vertical slot 515 and the extension 514. This design allows for fine-tuning of the installation height of the arc-shaped lifting frame 512 according to the initial height of the counterweight balls 505. The arc-shaped lifting frame 512 is positioned directly below all the counterweight balls 505. When the drive mechanism 700 drives the reciprocating ball screw 509 to rotate, causing the screw nut 510 and the entire lifting assembly connected thereto to move horizontally, the inclined surface 513 of the arc-shaped lifting frame 512 gradually approaches and lifts the counterweight balls 505, causing them to rise. The upward movement of the counterweight ball 505 is transmitted as torque to the first pin 203 via the vertical connecting rod 504, sleeve 506, crossbar 502, and connecting arm 501. This torque overcomes the tension of the tension spring 507, forcing the inner jaw clamp 204 and the spray nozzle 300 to rotate downwards around the first pin 203, thus adjusting the pitch angle of the nozzle. When the lifting assembly moves away in the opposite direction, the spray nozzle 300 returns to its initial pitch angle under the combined action of the tension spring and the counterweight. This process achieves linear, smooth, and controllable driving of the spray nozzle's pitch angle.

[0032] In a preferred embodiment, the drive mechanism 700 is a geared motor. To simplify the structure, the output shaft of the geared motor is directly connected to one end of the reciprocating ball screw 509 via a coupling, while the other end of the reciprocating ball screw 509 is connected to the drive shaft of the ring 401 via another set of couplings. In this way, a single power source can simultaneously drive the left-right swing mechanism and the up-down swing mechanism to work in a coordinated manner.

[0033] The working principle or steps of this device are as follows: First, place the device in a suitable location near the goaf, adjust the base support legs to stabilize the device, and connect the pipeline between the shotcrete pump and the shotcrete nozzle 300. Based on the width and height of the area to be covered, pre-set the radial position of the slider 408 using adjusting bolts to determine the horizontal swing amplitude, and adjust the initial height of the arc-shaped lifting frame 512 using connecting bolts 516. Start the drive mechanism 700 (geared motor). The motor drives the reciprocating ball screw 509 to rotate, causing the screw nut 510 and its lifting assembly to move slowly in a reciprocating linear motion along the screw. This causes the arc-shaped lifting frame 512 to periodically lift and lower the counterweight ball 505, causing the shotcrete nozzle 300 to swing up and down in a vertical plane. On the other hand, the motor's power is simultaneously transmitted to the ring 401, causing it to rotate at a uniform speed. Through the transmission of the slider 408, ball 410, pin 406, and U-shaped hinge 405, the rotational motion is converted into large-angle left-right reciprocating oscillations of the vertical shaft 403 and the spray nozzle 300 in the horizontal plane. The combination of these two oscillations allows the slurry ejected from the spray nozzle 300 to form a dense, mesh-like coverage area on the goaf section. During this process, the spray pump can be activated, and the fire extinguishing slurry is evenly sprayed onto the target area along with the combined oscillation of the spray nozzle, achieving efficient and large-area fire prevention and extinguishing operations without the need for frequent movement of the main body of the device during operation.

[0034] The embodiments described above are merely preferred embodiments of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications, improvements, and substitutions without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A spraying fire prevention and extinguishing device for coal mine goaf areas, characterized in that, include: The base frame (101) is used to support this device; A shotcrete nozzle mounting bracket (200) is disposed above the base frame (101) for mounting shotcrete nozzles (300). A left-right swing mechanism (400) is provided on the base frame (101) and connected to the spray nozzle mounting bracket (200) for driving the spray nozzle mounting bracket (200) and the spray nozzle (300) to swing left and right; The up-and-down swing mechanism (500) is mounted on the base frame (101) and connected to the hinge component of the spray nozzle mounting bracket (200) for driving the spray nozzle (300) to swing up and down. The drive mechanism (700) is mounted on the base frame (101) and is connected to the left-right swing mechanism (400) and the up-down swing mechanism (500) in a transmission connection.

2. The coal mine goaf spraying fire prevention and extinguishing device according to claim 1, characterized in that, The spray nozzle mounting bracket (200) includes a sleeve (201), one end of which is adjustablely connected to the swing end of the left and right swing mechanism (400), and the other end of the sleeve (201) is provided with an outer jaw clamp (202), and the outer jaw clamp (202) is hinged to an inner jaw clamp (204) for clamping the spray nozzle (300) via a first pin (203).

3. The coal mine goaf spraying fire prevention and extinguishing device according to claim 2, characterized in that, The left and right swinging mechanism (400) includes: A circular ring (401) is arranged vertically and can rotate around its central axis. A connecting rib plate (402) is provided on the inner side of the circular ring (401). An embedding groove (407) and a mounting hole (4021) are provided on the connecting rib plate (402) along the radial direction of the circular ring. The vertical shaft (403) is rotatably connected at its lower end to the base frame (101) and at its upper end to the straight rod (201). A horizontally extending horizontal shaft (404) is provided in the middle. The U-shaped hinge (405) has its open end hinged to both ends of the horizontal shaft (404), and its closed end is vertically provided with a pin (406). A slider (408) is disposed in the mounting groove (407), and a central hole (409) is provided in the middle of the slider. A ball (410) is embedded in the central hole (409). A channel (411) is provided on the surface of the ball (410) that passes through both ends. The front end of the pin (406) is movably inserted into the channel (411). An adjusting bolt passes through the mounting hole and abuts against the slider (408) to lock or adjust the radial position of the slider in the recess. When the ring (401) rotates, the vertical shaft (403) is driven to swing left and right through the cooperation of the pin (406) and the ball channel.

4. The coal mine goaf spraying fire prevention and extinguishing device according to claim 3, characterized in that, The up-and-down swing mechanism (500) includes: Two connecting arms (501) have one end fixed to both ends of the first pin (203), and the other end is connected to a crossbar (502). At least one counterweight assembly (503) includes a vertical connecting rod (504) and a counterweight ball (505) disposed at the lower end of the vertical connecting rod (504), the upper end of the vertical connecting rod (504) being sleeved on the horizontal bar (502) by a sleeve (506); At least one tension spring (507) has one end connected to the crossbar (502) and the other end connected to the hook (6) at the lower end of the outer tiger mouth clamp (202); A lifting component is used to drive the counterweight component (503) to rise and fall in the vertical direction to change the pitch angle of the spray nozzle (300).

5. The coal mine goaf spraying fire prevention and extinguishing device according to claim 4, characterized in that, The lifting component includes: A reciprocating ball screw (509) is horizontally mounted on the base frame (101); A lead screw nut (510) is mounted on the reciprocating ball screw (509); A vertical connecting frame (511) is connected at its lower end to the lead screw nut (510); The arc-shaped lifting frame (512) has an inner inclined surface (513) and an outer extension (514) connected to the vertical connecting frame (511). The arc-shaped lifting frame (512) is located below the counterweight assembly (503). The counterweight assembly (503) is pushed up by the inclined surface (513), and the pitch angle of the spray nozzle (300) can be adjusted.

6. The coal mine goaf spraying fire prevention and extinguishing device according to claim 5, characterized in that, The vertical connecting frame (511) has a vertically extending groove (515), and the extension (514) is fixedly connected to the vertical connecting frame (511) by a connecting bolt (516) passing through the vertical groove (515).

7. The coal mine goaf spraying fire prevention and extinguishing device according to claim 5, characterized in that, The sleeve (506) is provided with a threaded hole and equipped with an adjusting screw (517) for locking the position of the sleeve (506) on the crossbar (502).

8. The coal mine goaf spraying fire prevention and extinguishing device according to claim 2, characterized in that, The outer tiger mouth clamp (202) is provided with limiting baffles (518) at both ends to limit the rotation angle of the inner tiger mouth clamp (204).

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