Method for backfilling of irregular structures with spherical bentonite pellets

Abstract

The application discloses a backfilling method of spherical bentonite group particles in irregular structures, which comprises the preparation of the spherical bentonite group particles, the backfilling of the spherical bentonite group particles and the compaction of the spherical bentonite group particles. The application proposes the idea of backfilling by using bentonite group particles aiming at the high-quality backfilling problem of irregular structures in narrow spaces in radioactive waste disposal, determines the preparation conditions of the spherical bentonite group particles, designs a bentonite group particle spraying device, and proposes the backfilling ratio of the bentonite group particles + dry powder and the compaction mode by using a vibrating pipe, so that the backfilling quality and efficiency of irregular structures in radioactive waste disposal can be significantly improved. Meanwhile, the technology can be popularized to the backfilling engineering of the entire radioactive waste disposal structure and other waste disposal fields. The application solves the problem of low backfilling efficiency and quality of irregular parts or narrow spaces in radioactive waste disposal, and guarantees the quality and reliability of the backfilling structure.

Description

Technical Field

[0001] This invention relates to the field of radioactive waste treatment and disposal research technology, specifically a method for backfilling spherical bentonite pellets in irregular structures. Background Technology

[0002] To ensure the long-term safe disposal of long-lived radionuclides such as plutonium and uranium, as well as highly radioactive waste, the International Atomic Energy Agency (IAEA) has proposed using multiple barriers—natural barriers like granite and artificial barriers such as concrete and bentonite—to encase waste containers or containers. This effectively isolates groundwater from radioactive waste, ensuring its long-term safety. Sodium-based bentonite, such as Kolbenz, is particularly suitable due to its extremely low permeability after compaction (permeability coefficient less than 10). -9 Due to its high adsorption capacity for radionuclides (m / s) and strong adsorption capacity for radioactive nuclides, bentonite is often chosen as the primary buffer / backfill material in radioactive waste disposal. During on-site operations, bentonite is typically required to be compacted to a certain density (1.5 g / cm³). 3 The bentonite layer is backfilled with a certain thickness (greater than 50cm) to ensure that the bentonite layer can limit the infiltration of water and block the migration of radionuclides.

[0003] The method of bentonite backfilling determines the efficiency and quality of the backfilling project. Currently, in the field of radioactive waste disposal, the main methods of bentonite backfilling are in-situ compaction of bulk materials and on-site construction of compacted blocks. In-situ compaction of bulk materials involves transporting bentonite, prepared to its optimal moisture content, to the waste disposal site, and then using dynamic or static methods to directly compact the bulk bentonite to a set dry density using mechanical equipment. On the other hand, on-site construction of compacted blocks involves using specialized machinery in a dedicated processing workshop outside the disposal site to compact bentonite, prepared to a specific moisture content, into blocks of a specific density and shape. These blocks are then transported and hoisted to the disposal site and finally constructed into the required backfill structure.

[0004] However, in actual operations, many irregular structures often arise due to site conditions, space limitations, and the design requirements of waste disposal methods. These include gaps between rough rock walls and artificial barrier layers, channels between waste bins, and irregular spaces between waste bins and artificial barrier layers. Backfilling these irregular structures is often difficult because the limited space and irregular structure make mechanical in-situ compaction or bentonite block construction difficult. Even manual backfilling is challenging due to the small space, often requiring simple filling with loose bentonite material. This results in loose backfill in these structural areas, low backfilling efficiency, and difficulty in ensuring backfill quality (compacted dry density not reaching 1.5 g / cm³). 3 (This is due to the design requirements), making it a relatively weak link in the entire radioactive waste disposal operation.

[0005] To address the aforementioned challenges, this invention proposes a backfilling approach using bentonite aggregates. Bentonite aggregates refer to bentonite with a specific moisture content compressed into agglomerated particles of a specific size and density using compaction molds or machinery. Because they are pre-compacted to a certain density, the backfilling efficiency is higher compared to in-situ compaction. Furthermore, spherical bentonite aggregates are easily incorporated into irregular pores through air-filling, and after further vibration, high backfill quality can be achieved. In actual backfilling operations, this method offers advantages such as flexible operation, easy construction, and strong uniformity. Through practical backfilling operations using bentonite aggregates, this invention establishes a process for preparing spherical bentonite aggregates, designs a bentonite aggregate spraying device, and proposes a backfilling compaction method using a steel bar vibrator and a combination of bentonite aggregates and dry powder backfilling. Summary of the Invention

[0006] The purpose of this invention is to provide a method for backfilling spherical bentonite pellets in irregular structures, so as to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for backfilling spherical bentonite pellets in irregular structures includes the preparation, backfilling, and compaction of spherical bentonite pellets. The backfilling process includes a portable spherical bentonite pellet spraying device. This device comprises a pellet loading port, a pellet loading box, a compressed gas storage tank, a feeding pipe, a gas supply pipe, a pellet spraying control unit, a control switch, a shoulder strap, a battery power supply unit, a gas control unit, a pellet feeding hopper funnel, and a pellet spraying vibrating pipe. The pellet loading box has a pellet loading port at its top and a compressed gas storage tank at its bottom. A battery power supply unit is installed on one side of the compressed gas storage tank. Two shoulder straps are installed on the common side of the pellet loading box on the battery power supply unit. A feeding pipe is connected to the bottom of one side of the pellet loading box. The other end of the feeding pipe is connected to the pellet feeding hopper funnel. A pellet injection control unit is installed at the bottom of the pellet injection control unit. A control switch is installed at the bottom of the pellet injection control unit. A pellet injection vibrating pipe is installed on the pellet feeding hopper funnel. A gas supply pipe is installed between the pellet injection control unit and the compressed gas storage tank. The gas control unit is electrically connected to the control switch. The control switch is electrically connected to the battery power supply unit.

[0009] As a further aspect of the present invention, the method for preparing the spherical bentonite pellets is as follows;

[0010] Step 1: First, mix 200-mesh bentonite powder with water in a mixer to humidify it, adjust the moisture content to 20%, seal and let it stand for 24 hours for later use.

[0011] Step 2: Then, the bentonite bulk material with a moisture content of 20% is fed into the feed port of a double-roller extrusion granulator with a hemispherical groove (1 cm in diameter) on the surface of the extrusion die; the rotor speed of the granulator die is set to 6-8 rpm, and the distance between the two dies is adjusted so that the die contact pressure is 10.3 MPa, and primary bentonite pellets are prepared.

[0012] Step 3: Finally, the primary bentonite granules are fed into the polishing machine. Under the action of centrifugal force, the granules roll rapidly along the outer wall of the polishing machine turntable and are constantly collided and shaped. After polishing for 5 minutes, spherical granules with a relatively smooth surface are obtained.

[0013] As a further aspect of the present invention, the backfilling method for the spherical bentonite pellets is as follows;

[0014] Step 1: First, load 20 kg of spherical bentonite pellets into the pellet loading box of the portable spherical bentonite pellet spraying device;

[0015] Step 2: Then turn on the control switch of the portable spherical bentonite pellet spraying device to spray pellets along the pellet spraying pipe at a speed of 20 pellets per second into the irregular structure of the site (such as narrow gaps). It can fill a space of about 15L within 10 minutes.

[0016] As a further aspect of the present invention, the compaction method of the spherical bentonite pellets is as follows;

[0017] Step 1: Spread bentonite dry powder on the surface of the spherical bentonite aggregate layer according to the mass ratio of aggregate to dry powder of 1:4.

[0018] Step 2: Then, compact the material using a vibrator and measure its compacted dry density.

[0019] As a further embodiment of the present invention: the bottom of the pellet loading box is sloped towards the feeding pipe.

[0020] As a further embodiment of the present invention: the pellet injection control unit includes a pellet conveying track, a pellet centrifugal turntable, a pellet injection port, a compressed gas injection port, a conveyor belt, and a stepper motor. The pellet conveying track is installed at the bottom of the pellet feeding hopper funnel. The pellet centrifugal turntable is installed at the bottom of the pellet conveying track. Spherical pellets are disposed inside the pellet conveying track. A stepper motor is installed at the bottom of the pellet conveying track on one side of the pellet centrifugal turntable. The output shaft of the stepper motor and the pellet centrifugal turntable are connected by a conveyor belt. A pellet injection port and a compressed gas injection port are respectively provided on the left and right sides of the outlet position of the pellet conveying track. The stepper motor is electrically connected to a control switch.

[0021] As a further aspect of the present invention, the pellet spraying vibrating pipe has a slender structure.

[0022] As a further embodiment of the present invention: the pellet spraying vibrating pipe mainly includes a pellet spraying pipe, a vibrator groove and a vibration motor. The bottom of the pellet spraying pipe is provided with a vibrator groove, and a vibration motor is installed in the vibrator groove. The vibration motor is electrically connected to a control switch through a wire.

[0023] As a further aspect of the present invention, the control switch has two buttons.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] This invention addresses the challenge of high-quality backfilling of irregular structures within confined spaces in radioactive waste disposal. It proposes a method using bentonite pellets for backfilling, defines the preparation conditions for spherical bentonite pellets, designs a bentonite pellet injection device, and proposes a backfilling ratio of bentonite pellets + dry powder, along with a vibratory compaction method using vibratory pipes. This significantly improves the quality and efficiency of backfilling irregular structures in radioactive waste disposal. Furthermore, this technology can be extended to the entire radioactive waste disposal structure backfilling project and other waste disposal fields. This invention solves the problem of low efficiency and quality in backfilling irregular areas or confined spaces in radioactive waste disposal, ensuring the quality and reliability of the backfill structure. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the overall structure of the present invention.

[0027] Figure 2 For the present invention Figure 1 A schematic diagram of the internal structure of the medium-sized pellet filling box.

[0028] Figure 3 For the present invention Figure 1 A schematic diagram of the structure of the medium-sized pellet injection control unit.

[0029] Figure 4 For the present invention Figure 1 Schematic diagram of the structure of the medium-sized pellet spray vibratory pipe.

[0030] 1. Pellet loading port; 2. Pellet loading box; 3. Compressed gas storage tank; 4. Feeding pipe; 5. Gas supply pipe; 6. Pellet injection control unit; 7. Control switch; 8. Shoulder belt; 9. Battery power supply unit; 10. Gas control unit; 11. Pellet feeding hopper funnel; 12. Pellet injection vibrating pipe; 13. Pellet conveying track; 14. Pellet centrifugal turntable; 15. Pellet injection nozzle; 16. Spherical pellets; 17. Compressed gas injection nozzle; 18. Conveyor belt; 19. Stepper motor; 20. Injection pipe; 21. Vibrator groove; 22. Vibration motor. Detailed Implementation

[0031] 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.

[0032] Please see Figures 1-4 In this embodiment of the invention, the backfilling method of spherical bentonite pellets in an irregular structure includes the preparation of spherical bentonite pellets, the backfilling of spherical bentonite pellets, and the compaction of spherical bentonite pellets.

[0033] 1. Preparation method of spherical bentonite pellets

[0034] Considering that spherical particles have strong flowability and filling capacity, the shape of bentonite pellets is selected as spherical; in order to prepare high-density bentonite pellets, a double-roller extrusion granulator is selected, with double extrusion dies, and the rotor speed of the dies is 6-8 rpm, the die contact pressure is ~10.3 MPa; the surface of the extrusion die is a hemispherical groove (1 cm in diameter).

[0035] The moisture content of bentonite is the most critical factor determining the quality of bentonite pellet preparation. To determine the optimal moisture content conditions, different masses of water were added to equal amounts of dry bentonite powder, so that the moisture content of each bentonite sample was 10%, 15%, 20% and 25%, respectively. The samples were then sealed and stored for 24 hours to ensure that the bentonite was uniformly moistened.

[0036] Experiments were conducted on the preparation of bentonite pellets using a double-roller extrusion granulator. The results showed that bentonite pellets with a moisture content of 10% had the lowest forming rate (less than 15%), while bentonite pellets with a moisture content of 25% were difficult to demold and adhered extensively to the mold surface. In contrast, bentonite pellets with a moisture content of 20% had the highest forming rate (greater than 90%). Therefore, the moisture content should be set to 20% when preparing bentonite pellets.

[0037] The primary bentonite granules produced from the granulator are ellipsoidal with relatively rough edges in the center, indicating the presence of loose bentonite soil. Therefore, to further improve their compaction quality, the shaped granules are fed into a polishing machine. Under centrifugal force, the primary bentonite granules roll rapidly along the outer wall of the polishing machine's rotating disc, continuously colliding and reshaping. After polishing for 5 minutes, they become relatively smooth spheres. The compacted dry density of a single spherical bentonite granule is measured to be 2.3 g / cm³. 3 The weight is approximately 1.1g.

[0038] 2. Backfilling method for spherical bentonite pellets

[0039] Backfilling of spherical bentonite pellets includes using a portable spherical bentonite pellet spraying device. This device is designed to meet the needs of pellet backfilling operations in confined spaces and irregular structures. Figure 1 As shown, the portable spherical bentonite pelletizing device includes a pellet loading port 1, a pellet loading box 2, a compressed gas storage tank 3, a feeding pipe 4, an air supply pipe 5, a pelletizing control unit 6, a control switch 7, a shoulder strap 8, a battery power supply unit 9, a gas control unit 10, a pellet feeding hopper funnel 11, and a pelletizing spray vibrating pipe 12. The pellet loading box 2 has a pellet loading port 1 at its upper part, and a compressed gas storage tank 3 is installed at the bottom of the pellet loading box 2. A battery power supply unit 9 is installed on one side of the compressed gas storage tank 3. The battery power supply unit 9 is connected to the pellet loading box 2. Two shoulder straps 8 are installed on one side. A feeding pipe 4 is connected to the bottom of one side of the pellet feeding box 2. The other end of the feeding pipe 4 is connected to the pellet feeding hopper funnel 11. A pellet spray control unit 6 is installed at the bottom of the pellet spray control unit 6. A control switch 7 is installed at the bottom of the pellet spray control unit 6. A pellet spray vibrating pipe 12 is installed on the pellet feeding hopper funnel 11. A gas supply pipe 5 is installed between the pellet spray control unit 6 and the compressed gas storage tank 3. The gas control unit 10 is electrically connected to the control switch 7. The control switch 7 is electrically connected to the battery power supply unit 9.

[0040] The internal structure of the pellet filling box 2 is as follows Figure 2 As shown, the bottom of the pellet loading box 2 is sloped towards the feeding pipe 4 to facilitate the automatic and continuous falling of pellets into the feeding pipe 4.

[0041] The structure of the agglomerate injection control unit 6 is as follows: Figure 3 As shown, the pellet injection control unit 6 includes a pellet conveying track 13, a pellet centrifugal turntable 14, a pellet injection port 15, a compressed gas injection port 17, a conveyor belt 18, and a stepper motor 19. The pellet conveying track 13 is installed at the bottom of the pellet feeding hopper 11. The pellet centrifugal turntable 14 is installed at the bottom of the pellet conveying track 13. Spherical pellets 16 are arranged inside the pellet conveying track 13. The stepper motor 19 is installed at the bottom of the pellet conveying track 13 on one side of the pellet centrifugal turntable 14. The output shaft of the stepper motor 19 and the pellet centrifugal turntable 14 are connected by the conveyor belt 18. The pellet injection port 15 and the compressed gas injection port 17 are respectively arranged on the left and right sides of the outlet position of the pellet conveying track 13. The stepper motor 19 is electrically connected to the control switch 7.

[0042] like Figure 4As shown, the pellet spraying vibratory pipe 12 has a slender structure, which is intended to facilitate the injection and compaction of pellets into irregular structures such as narrow gaps. The pellet spraying vibratory pipe 12 mainly includes a pellet spraying pipe 20, a vibrator groove 21, and a vibratory motor 22. The bottom of the pellet spraying pipe 20 is provided with a vibrator groove 21, and a vibratory motor 22 is installed in the vibrator groove 21. The vibratory motor 22 is electrically connected to the control switch 7 through a wire. The control switch 7 has two buttons, which control the spherical pellets 16 to be sprayed out of the pellet spraying vibratory pipe 12 and start the vibratory motor 22 to compact the pellet layer.

[0043] The operating principle of the portable spherical bentonite pellet injection device is as follows:

[0044] Spherical bentonite granules are loaded into the pellet loading box 2 through the pellet loading port 1. The spherical granules 16 in the pellet loading box 2 then enter the pellet feeding hopper 11 through the feeding pipe 4, and then enter the pellet centrifugal turntable 14. Driven by the stepper motor 19, the pellet centrifugal turntable 14 rotates rapidly. Due to centrifugal force, the spherical granules 16 on the pellet centrifugal turntable 14 enter the pellet conveying track 13 and are sent to the pellet injection port 15. The control switch 7 of the portable spherical bentonite pellet injection device is activated to release the pellets. When the injection button is pressed, the compressed gas in the compressed gas storage tank 3 is regulated by the gas control unit 10 and enters the compressed gas injection port 17. The compressed gas then acts on the spherical agglomerates 16 in the agglomerate injection port 15, and the spherical agglomerates 16 are sprayed out at high frequency along the agglomerate injection pipe 20 into the irregular structure (slit, etc.) of the site. When the vibration button in the control switch 7 of the portable spherical bentonite agglomerate injection device is activated, the vibration motor 22 in the agglomerate injection vibration pipe 12 is triggered to compact the agglomerate layer.

[0045] 3. Compaction method for spherical bentonite pellets

[0046] After bentonite granules are blown into the irregular structure using a granulation spraying machine, further compaction is required. To reduce the gaps between the granules, bentonite dry powder is first laid on the surface of the granule layer, and then it is vibrated and compacted using a portable spherical bentonite granulation spraying device with a granulation spraying vibrating pipe 12. The mass ratio of granules to dry powder is the key to determining the quality of further compaction of the granules.

[0047] Assuming the bulk density of bentonite aggregates is 1.5 g / cm³ 3 Then, according to the porosity calculation formula:

[0048]

[0049] in Porosity; This refers to the bulk density of the aggregates. The dry density of bentonite powder is 2.3 g / cm³. 3The bulk density calculated from the above formula is 1.5 g / cm³. 3 The porosity of the bentonite aggregate layer was 25%, indicating that under ideal conditions, a bentonite powder to aggregate mass ratio of 1:3 can completely fill the pores between the aggregates. Based on the above analysis, compaction experiments were conducted on aggregate layers with bentonite powder to aggregate mass ratios of 1:3, 1:4, 1:5, and 1:6. The compaction was performed using the vibrating tube of a portable spherical bentonite aggregate injection device. The results showed that, under the same vibration frequency, the compacted dry densities of the bentonite powder to aggregate mass ratios of 1:3, 1:4, 1:5, and 1:6 were 1.54 g / cm³. 3 1.62g / cm 3 1.51g / cm 3 1.46 g / cm 3 Therefore, when backfilling with bentonite pellets, the mass ratio of bentonite dry powder to pellets should be 1:4.

[0050] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for backfilling spherical bentonite aggregates in irregular structures, comprising the preparation of spherical bentonite aggregates, backfilling of spherical bentonite aggregates, and compaction of spherical bentonite aggregates, characterized in that: The backfilling of the spherical bentonite pellets includes a portable spherical bentonite pellet spraying device. The portable spherical bentonite pellet spraying device includes a pellet loading port (1), a pellet loading box (2), a compressed gas storage tank (3), a feeding pipe (4), a gas supply pipe (5), a pellet spraying control unit (6), a control switch (7), a shoulder strap (8), a battery power supply unit (9), a gas control unit (10), a pellet feeding hopper funnel (11), and a pellet spraying vibrating pipe (12). The pellet loading box (2) has a pellet loading port (1) at the top, and a compressed gas storage tank (3) is installed at the bottom of the pellet loading box (2). A battery power supply unit (9) is installed on one side of the compressed gas storage tank (3). Two straps (8) are installed on a common side of the pellet loading box (2). A feeding pipe (4) is connected to the bottom of one side of the pellet loading box (2). The other end of the feeding pipe (4) is connected to the pellet feeding hopper funnel (11). A pellet spray control unit (6) is installed at the bottom of the pellet spray control unit (6). A control switch (7) is installed at the bottom of the pellet spray control unit (6). A pellet spray vibrating pipe (12) is installed on the pellet feeding hopper funnel (11). A gas supply pipe (5) is installed between the pellet spray control unit (6) and the compressed gas storage tank (3). The gas control unit (10) is electrically connected to the control switch (7). The control switch (7) is electrically connected to the battery power supply unit (9).

2. The backfilling method for spherical bentonite aggregates in irregular structures according to claim 1, characterized in that: The method for preparing the spherical bentonite pellets is as follows; Step 1: First, mix 200-mesh bentonite powder with water in a mixer to humidify it, adjust the moisture content to 20%, seal and let it stand for 24 hours for later use. Step 2: Then, the bentonite bulk material with a moisture content of 20% is transported into the feed inlet of a double-roller extrusion granulator with a hemispherical groove on the surface of the extrusion die. The diameter of the hemispherical groove is 1 cm. The rotor speed of the granulator die is set to 6-8 rpm. The distance between the two dies is adjusted so that the die contact pressure is 10.3 MPa, and primary bentonite pellets are prepared. Step 3: Finally, the primary bentonite granules are fed into the polishing machine. Under the action of centrifugal force, the granules roll rapidly along the outer wall of the polishing machine turntable and are constantly collided and shaped. After polishing for 5 minutes, spherical granules with a relatively smooth surface are obtained.

3. The method for backfilling spherical bentonite aggregates in irregular structures according to claim 1, characterized in that: The backfilling method for the spherical bentonite pellets is as follows; Step 1: First, load 20 kg of spherical bentonite pellets into the pellet loading box (2) of the portable spherical bentonite pellet spraying device; Step 2: Then turn on the control switch (7) of the portable spherical bentonite pellet spraying device, and spray the pellets along the pellet spraying pipe at a speed of 20 pellets per second into the irregular structure of the site. The space can be filled within 15L within 10 minutes.

4. The method for backfilling spherical bentonite aggregates in irregular structures according to claim 1, characterized in that: The compaction method for the spherical bentonite pellets is as follows; Step 1: Spread bentonite dry powder on the surface of the spherical bentonite aggregate layer according to the mass ratio of aggregate to dry powder of 1:

4. Step 2: Then, compact the material using a vibrator and measure its compacted dry density.

5. The method for backfilling spherical bentonite aggregates in irregular structures according to claim 1, characterized in that: The bottom of the pellet loading box (2) is sloped towards the feeding pipe (4).

6. The method for backfilling spherical bentonite aggregates in irregular structures according to claim 1, characterized in that: The pellet injection control unit (6) includes a pellet conveying track (13), a pellet centrifugal turntable (14), a pellet injection port (15), a compressed gas injection port (17), a conveyor belt (18), and a stepper motor (19). The pellet conveying track (13) is installed at the bottom of the pellet feeding hopper (11). The pellet centrifugal turntable (14) is installed at the bottom of the pellet conveying track (13). Spherical pellets (16) are arranged inside the pellet conveying track (13). A stepper motor (19) is installed at the bottom of the pellet conveying track (13) on one side of the pellet centrifugal turntable (14). The output shaft of the stepper motor (19) and the pellet centrifugal turntable (14) are connected by transmission via the conveyor belt (18). The pellet injection port (15) and the compressed gas injection port (17) are respectively arranged on the left and right sides of the outlet position of the pellet conveying track (13). The stepper motor (19) is electrically connected to the control switch (7).

7. The method for backfilling spherical bentonite aggregates in irregular structures according to claim 1, characterized in that: The pellet spraying vibrating pipe (12) has a slender structure.

8. The method for backfilling spherical bentonite aggregates in irregular structures according to claim 1, characterized in that: The pellet spraying vibratory pipe (12) mainly includes a pellet spraying pipe (20), a vibrator groove (21) and a vibratory motor (22). The bottom of the pellet spraying pipe (20) is provided with a vibrator groove (21), and a vibratory motor (22) is installed in the vibrator groove (21). The vibratory motor (22) is electrically connected to the control switch (7) through a wire.

9. The method for backfilling spherical bentonite aggregates in irregular structures according to claim 1, characterized in that: The control switch (7) has two buttons.

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