Energy-saving efficient steam rotary kiln

Abstract

The invention discloses an energy-saving efficient steam rotary kiln and relates to the field of medium-low-temperature dry organic and inorganic chemical equipment, the energy-saving efficient steam rotary kiln comprises a kiln body, an air inlet box and a discharging box, the feeding end of the kiln body is rotatably and hermetically connected with the air inlet box, the discharging end of the kiln body is rotatably and hermetically connected with the discharging box, an air inlet is formed in the top of the air inlet box, and an air outlet is formed in the bottom of the discharging box; a discharging opening is formed in the bottom of the discharging box, and an air outlet is formed in the top of the discharging box; the kiln body is provided with a heating system, the heating system comprises an air inlet main pipe, a water drainage main pipe, a steam distributor, a water collector and a plurality of heating pipes, the steam distributor is close to the feeding end of the kiln body, and the water collector is located at the discharging end of the kiln body; the heating pipes are distributed along the center line of the kiln body in a circumferential array mode, one ends of the heating pipes are connected with the steam distributor, the other ends of the heating pipes are connected with the water collector, the air inlet main pipe is connected with the steam distributor and extends out of the air inlet box, and the drainage main pipe is connected with the water collector and extends out of the discharging box. The feeding end of the kiln body is higher than the discharging end of the kiln body. The heat transfer efficiency of steam can be improved.

Description

Technical Field

[0001] This application relates to the field of organic and inorganic chemical equipment for medium and low temperature drying, and in particular to an energy-saving, high-efficiency steam rotary kiln. Background Technology

[0002] Using a steam rotary kiln dryer for indirect drying of wet materials is one of the effective methods of utilizing the heat in steam. Because the steam comes into indirect contact with the material and there is no need for high-temperature drying gases produced by combustion, the drying temperature is lower than that of a direct-heating dryer, and the air temperature is easier to control. Indirect steam drying is particularly suitable for materials that are sensitive to high temperatures, such as rare earth drying, soda ash treatment, and the processing of organic chemicals such as PTA / CTA.

[0003] The structure of a steam rotary kiln dryer mainly consists of a kiln body, a transmission device, and a hot air duct, and it adopts roller support and variable frequency speed control technology. The steam rotary kiln dryer heats and dries the material by rotating the material within the kiln body, bringing the material into contact with the heating pipes inside the kiln.

[0004] In the prior art, heating systems are usually arranged in a circuitous manner inside a rotary kiln. For example, the invention patent application document with publication number CN104110947A discloses a rotary steam dryer. During its use, steam is introduced into the pipeline inside the cylinder from the inlet, travels in a circuitous manner inside the cylinder, and is discharged from the outlet. The inlet and outlet of the steam are located on the same side of the cylinder. Because the steam travels along a circuitous path, it is difficult for non-condensable gases in the steam (mainly air components mixed in the steam) to be discharged in time, which affects the heat transfer efficiency of the steam and thus affects the drying effect of the material. Summary of the Invention

[0005] In order to reduce the retention of non-condensable steam in the heating system of the steam rotary kiln dryer, which affects the steam heat transfer efficiency, this application provides an energy-saving and high-efficiency steam rotary kiln.

[0006] The energy-saving and high-efficiency steam rotary kiln provided in this application adopts the following technical solution: An energy-saving, high-efficiency steam rotary kiln includes a kiln body, an inlet box, and a discharge box. The feed end of the kiln body is rotary-sealed to the inlet box, and the discharge end of the kiln body is rotary-sealed to the discharge box. The top of the inlet box has an air inlet, the bottom of the discharge box has a discharge outlet, and the top of the discharge box has an air outlet. The kiln body is equipped with a heating system, which includes an inlet main pipe, a drain main pipe, a steam distributor, a water collector, and several heating tubes. The steam distributor is located near the feed end of the kiln body, and the water collector is located at the discharge end of the kiln body. The heating tubes are arranged in a circumferential array along the centerline of the kiln body. One end of each heating tube is connected to the steam distributor, and the other end is connected to the water collector. The inlet main pipe is connected to the steam distributor and extends out of the inlet box, and the drain main pipe is connected to the water collector and extends out of the discharge box. The kiln body is inclined, with the feed end of the kiln body higher than the discharge end.

[0007] By adopting the above technical solution, the feed end of the kiln is higher than the discharge end. During the rotation of the kiln, the material moves backward in a spiral motion due to gravity until it is discharged from the discharge port of the discharge box. Steam enters the steam distributor through the main inlet pipe and then enters the heating pipe. The condensate formed by the steam during the drying process enters the water collector and is discharged from the main drain pipe as the kiln rotates. The steam inlet and outlet are located on opposite sides of the kiln. The steam flows along a straight path in the heating pipe without detours, making it less likely for non-condensable steam to remain in the heating pipe, which is beneficial to promoting the heat transfer efficiency of the steam and thus improving the drying efficiency of the material, thereby increasing the throughput. The material temperature is low and the moisture content is high in the area near the kiln inlet. The steam moves in the same direction as the material, and the high-heat steam quickly releases a large amount of heat to the low-temperature material, which is conducive to achieving a miniaturized design of the equipment while maintaining the same production capacity.

[0008] Optionally, the centerline of the heating pipe forms an angle with the centerline of the kiln body, the angle between the heating pipe and the centerline of the kiln body is directed toward the discharge end of the kiln body, and the angle between the heating pipe and the centerline of the kiln body is less than or equal to the inclination angle of the kiln body.

[0009] By adopting the above technical solution, the condensate formed by cooling inside the heating tube flows into the water collector along the heating tube; by making the center line of the heating tube form an angle with the center line of the kiln body towards the discharge end of the kiln body, the flow rate of the condensate increases when the heating tube is rotated to the downward position, so that the condensate flows to the water collector as soon as possible, thereby reducing the impact of condensate adhering to the inner wall of the heating tube on the heat exchange efficiency between steam and material.

[0010] Optionally, the air inlet and air outlet of the heating tube are staggered along the circumference of the kiln body, and when the heating tube rotates with the kiln body, the position of the air outlet in the rotation direction of the heating tube lags behind the air inlet.

[0011] By adopting the above technical solution, the air inlet and outlet of the heating tube are staggered, and the air outlet lags behind the air inlet in the rotation direction of the heating tube, which enables the steam to flow in the heating tube in a path that is closer to a straight line.

[0012] Optionally, the inner side of the heating tube is provided with a spiral metal wire, and the spiral metal wire is in clearance fit with the heating tube.

[0013] By adopting the above technical solution, the spiral metal wire is fitted with the heating tube with a gap. When the heating tube rotates with the kiln body, the spiral metal wire will rotate relative to the heating tube due to inertia. This causes the spiral metal wire to rotate and scrape the inner wall of the heating tube, making it difficult for scale and other impurities to adhere inside the heating tube.

[0014] Optionally, the spiral metal wire includes multiple metal wire segments, the ends of which are bent to form straight segments, and adjacent straight segments of two adjacent metal wire segments are connected by a sleeve structure, the sleeve structure being interference-fitted with the straight segments.

[0015] By adopting the above technical solution, the spiral metal wire is composed of multiple metal wire segments connected in series. Adjacent straight segments of adjacent metal wire segments are joined together using a socket structure to form an overall structure with a larger length. By segmenting the spiral metal wire, the manufacturing and installation difficulties can be reduced while meeting dimensional requirements.

[0016] Optionally, the sleeve structure is a helical spring, with hooks at both ends of the helical spring, and the hooks of the helical spring are respectively hooked to two adjacent helical coils of the metal wire segments.

[0017] By adopting the above technical solution, the helical spring can undergo radial elastic deformation, making it easier to connect with a straight segment. After the helical spring connects two adjacent metal wire segments, the two hooks of the helical spring are hooked onto the helical coils of the two metal wire segments respectively, making the helical spring less likely to fall off.

[0018] Optionally, the surface of the spiral metal wire is provided with a titanium oxide coating.

[0019] By adopting the above technical solution, and by setting a titanium oxide coating on the surface of the spiral metal wire, condensate is less likely to adhere to the surface of the spiral metal wire, which helps to drain the condensate inside the heating tube.

[0020] Optionally, the spiral metal wire can rotate inside the heating tube, and the spiral direction of the spiral metal wire is consistent with the direction of the material being conveyed by the screw conveyor of the kiln body.

[0021] By adopting the above technical solution, since the spiral metal wire has a spiral structure, when the spiral metal wire rotates on the inner wall of the heating tube, it will exert a pushing force on the material on the inner wall of the heating tube. By utilizing the pushing force of the spiral metal wire, impurities and condensate on the inner wall of the heating tube can be pushed out of the heating tube.

[0022] Optionally, the side wall of the water collector is provided with several guide discs, each guide disc corresponding to a heating tube, the spiral metal wire abutting against the guide disc, and the thickness of the guide disc is gradually varied.

[0023] By adopting the above technical solution, when the spiral metal wire rotates inside the heating tube, the contact point of the spiral metal wire on the guide plate will change. Due to the gradual thickness setting of the guide plate, the spiral metal wire will be displaced along the axial direction, thereby increasing the friction of the spiral metal wire against the inner wall of the heating tube.

[0024] Optionally, the heating system is insulated from the kiln body, the spiral metal wire is used as the electric heating wire, the side wall of the steam distributor away from the water collector is set as the first conductive plate, the side wall of the water collector away from the steam distributor is set as the second conductive plate, the side wall of the air inlet box is fixed with a first conductive rod passing through it and abutting against the first conductive plate, the side wall of the discharge box is set with a second conductive rod passing through it and abutting against the second conductive plate, and the two ends of the spiral metal wire abut against the first conductive plate and the second conductive plate respectively.

[0025] By adopting the above technical solution, the first conductive rod and the second conductive rod can be used to connect the two ends of the power supply, so that the external power supply can form a current loop through the first conductive rod, the first conductive plate, the spiral metal wire, the second conductive plate and the second connecting rod, and the spiral metal wire can be used as a resistance wire for auxiliary heating.

[0026] In summary, this application includes at least one of the following beneficial technical effects: 1. The steam inlet and outlet are located on both sides of the kiln body. The steam flows along a straight path in the heating tubes without having to detour, which makes it less likely for non-condensable steam to remain in the heating tubes. This promotes the heat transfer efficiency of the steam, thereby improving the drying efficiency of the material and increasing the throughput.

[0027] 2. The spiral metal wire is fitted with the heating tube with a gap. As the heating tube rotates with the kiln body, the spiral metal wire will rotate relative to the heating tube due to inertia. This causes the spiral metal wire to rotate and scrape the inner wall of the heating tube, making it difficult for scale and other impurities to adhere inside the heating tube.

[0028] 3. The first conductive rod and the second conductive rod can be used to connect the two ends of the power supply, so that the external power supply can form a current loop through the first conductive rod, the first conductive plate, the spiral metal wire, the second conductive plate and the second connecting rod, so that the spiral metal wire can be used as a resistance wire for auxiliary heating. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the steam rotary kiln in Example 1.

[0030] Figure 2 This is a schematic diagram of the steam rotary kiln in Example 2.

[0031] Figure 3 This is a schematic diagram of the socket structure in Embodiment 2.

[0032] Figure 4 This is a schematic diagram of the steam rotary kiln in Example 3.

[0033] Figure 5 This is a schematic diagram of the steam rotary kiln in Example 4.

[0034] Figure 6 This is a schematic diagram of the installation status of the heating tubes in the same layer of Example 5.

[0035] Explanation of reference numerals in the attached figures: 1. Kiln body; 2. Air inlet box; 21. Air inlet; 3. Discharge box; 31. Air outlet; 32. Discharge outlet; 4. Feeder; 41. Feeding pipe; 5. Heating system; 51. Main air inlet pipe; 511. Branch air inlet pipe; 52. Main drainage pipe; 521. Branch drainage pipe; 53. Steam separator; 54. Water collector; 541. Guide plate; 55. Heating tube; 6. Spiral metal wire; 61. Metal wire segmentation; 62. Sleeve structure; 620. Helical spring; 621. Hook; 63. First conductive plate; 64. First conductive rod; 65. Second conductive plate; 66. Second conductive rod. Detailed Implementation

[0036] The following is in conjunction with the appendix Figure 1-6 This application will be described in further detail.

[0037] Example 1 This application discloses an energy-saving, high-efficiency steam rotary kiln. (Refer to...) Figure 1The energy-saving high-efficiency steam rotary kiln includes a kiln body 1, an air inlet box 2, and a discharge box 3. The feed end of the kiln body 1 is rotary sealed to the air inlet box 2, and the discharge end of the kiln body 1 is rotary sealed to the discharge box 3. The sealing method between the kiln body 1 and the air inlet box 2, and between the kiln body 1 and the discharge box 3, is a radial labyrinth laminated seal. The top of the air inlet box 2 is provided with an air inlet 21, the bottom of the discharge box 3 is provided with a discharge outlet 32, and the top of the discharge box 3 is provided with an air outlet 31. A feeding pipe 41 is connected to the side wall of the air inlet box 2. The feeding pipe 41 extends into the feed end of the kiln body 1 and has a rotary sealed connection node. The feeding pipe 41 serves as the output pipe of the feeder 4.

[0038] The kiln body 1 is equipped with a heating system 5, which includes an air inlet pipe 51, a drainage pipe 52, a steam distributor 53, a water collector 54, and several heating pipes 55. The steam distributor 53 and the water collector 54 are both annular structures. The steam distributor 53 is close to the feed end of the kiln body 1, and the water collector 54 is located at the discharge end of the kiln body 1. The heating pipes 55 are arranged in a circular array along the center line of the kiln body 1. The heating pipes 55 are set in multiple layers as needed, and the heating pipes 55 in different layers are arranged in concentric circles.

[0039] One end of the heating tube 55 is connected to the steam distributor 53, and the other end is connected to the water collector 54. One end of the heating tube 55 is flush with the inner wall of the steam distributor 53 near the water collector 54, and the other end of the heating tube 55 extends into the water collector 54, with a gap between it and the inner wall of the water collector 54.

[0040] One end of the main air inlet pipe 51 is closed and connected to several branch air inlet pipes 511. The branch air inlet pipes 511 are connected to the steam distributor 53. The portion of the branch air inlet pipes 511 near the center of the kiln body 1 bends towards the discharge end of the kiln body 1 to avoid the feed pipe 41. The other end of the main air inlet pipe 51 extends out of the air inlet box 2. One end of the main drainage pipe 52 is closed and connected to several branch drainage pipes 521. The branch drainage pipes 521 are connected to the water collector 54. The other end of the main drainage pipe 52 extends out of the discharge box 3. Both the main air inlet pipe 51 and the main drainage pipe 52 have rotary sealing connection nodes. The kiln body 1 is inclined, with the feed end of the kiln body 1 higher than the discharge end. The inclination angle of the kiln body 1 is specifically set to 1.5°.

[0041] The implementation principle of an energy-saving, high-efficiency steam rotary kiln according to an embodiment of this application is as follows: the feed end of the kiln body 1 is higher than the discharge end. During the rotation of the kiln body 1, the material moves backward by gravity within the kiln body 1 until it is discharged from the discharge port 32 of the discharge box 3. The inner space of the kiln body 1 serves as a humidified air channel. Air enters the humidified air channel from the air inlet 21 at a speed not exceeding 2 meters per second, carrying away the moisture generated during material drying from the air outlet 31. Steam enters the steam distributor 53 through the main air inlet 51, and then enters the heating tube 55. The condensate formed by the steam during the material drying process enters the water collector 54 and is discharged from the drainage main pipe 52 as the kiln body 1 rotates. The steam inlet and outlet are located on both sides of the kiln body 1, and the steam flows along a straight path within the heating tube 55 without detours. This prevents non-condensable steam from accumulating within the heating tube 55, which is beneficial for promoting the heat transfer efficiency of the steam and thus improving the drying efficiency of the material, thereby increasing the throughput. The material temperature is low and the moisture content is high in the area near the inlet of kiln body 1. Steam and material move in the same direction. Steam with high heat content quickly releases a large amount of heat to the low temperature material, which is conducive to the miniaturization design of equipment under the same production capacity.

[0042] Example 2 Reference Figure 2 and Figure 3 The difference between this embodiment and Embodiment 1 is that a spiral metal wire 6 is provided on the inner side of the heating tube 55, and the surface of the spiral metal wire 6 is coated with titanium oxide. The spiral metal wire 6 is in clearance fit with the heating tube 55. The spiral metal wire 6 includes multiple metal wire segments 61, and the ends of the metal wire segments 61 are bent to form straight segments. Adjacent straight segments of two adjacent metal wire segments 61 are connected by a sleeve structure 62, and the sleeve structure 62 is in interference fit with the straight segments.

[0043] The sleeve structure 62 is a metal sleeve or a helical spring 620. In this embodiment, it is specifically a helical spring 620. The two ends of the helical spring 620 are respectively provided with hooks 621. The hooks 621 of the helical spring 620 are respectively hooked to the helical coils of two adjacent metal wire segments 61.

[0044] As the heating tube 55 rotates with the kiln body 1, the spiral metal wire 6 can rotate inside the heating tube 55, allowing the spiral metal wire 6 to rub against the inner wall of the heating tube 55, reducing the accumulation of scale and other impurities on the inner wall of the heating tube 55. Furthermore, the spiral direction of the spiral metal wire 6 is consistent with the spiral movement direction of the material inside the kiln body 1, so that when the spiral metal wire 6 rotates, it can push the impurities and condensate on the inner wall of the heating tube 55 towards the outlet end of the heating tube 55.

[0045] The side wall of the water collector 54 is provided with several guide discs 541, each corresponding to a heating tube 55. A spiral metal wire 6 abuts against the guide disc 541, and the thickness of the guide disc 541 is gradually varying. When the spiral metal wire 6 rotates inside the heating tube 55, the contact point of the spiral metal wire 6 on the guide disc 541 changes. Due to the gradually varying thickness of the guide disc 541, the spiral metal wire 6 undergoes axial displacement, thereby increasing the friction between the spiral metal wire 6 and the inner wall of the heating tube 55.

[0046] Example 3 Reference Figure 4 The difference between this embodiment and embodiment 2 is that the spiral metal wire 6 is used as an electric heating wire, the material of the spiral metal wire 6 is nickel-chromium alloy or iron-chromium-aluminum alloy, etc., and the sleeve structure 62 in this embodiment is a metal sleeve.

[0047] In this embodiment, the side wall of the steam separator 53 away from the water collector 54 is designated as a first conductive plate 63, and the side wall of the water collector 54 away from the steam separator 53 serves as a second conductive plate 65. A first conductive rod 64 is fixedly inserted through the side wall of the air inlet box 2, abutting against the first conductive plate 63. A second conductive rod 66 is inserted through the side wall of the discharge box 3, abutting against the second conductive plate 65. The two ends of the spiral metal wire 6 abut against the first conductive plate 63 and the second conductive plate 65, respectively. The first conductive rod 64 is sealed to the air inlet box 2 with insulating glue, and the second conductive rod 66 is sealed to the discharge box 3 with insulating glue. The connection between the heating system 5 and the kiln body 1 is separated by insulating materials such as plastic or asbestos.

[0048] The first conductive rod 64 and the second conductive rod 66 can be used to connect the two ends of the power supply, so that the external power supply can form a current loop through the first conductive rod 64, the first conductive plate 63, the spiral metal wire 6, the second conductive plate 65 and the second connecting rod, so that the spiral metal wire 6 can be used as a resistance wire for auxiliary heating.

[0049] Example 4 Reference Figure 5 The difference between this embodiment and Embodiment 1 is that in this embodiment, the centerline of the heating tube 55 forms an angle with the centerline of the kiln body 1, and the angle between the heating tube 55 and the centerline of the kiln body 1 faces towards the discharge end of the kiln body 1. The angle between the heating tube 55 and the centerline of the kiln body 1 is less than or equal to the tilt angle of the kiln body 1. When the heating tube 55 rotates with the kiln body 1 to a downward position, the downward tilt angle of the heating tube 55 increases, causing the condensate in the heating tube 55 to flow faster towards the steam outlet end of the heating tube 55, reducing the amount of condensate adhering to the inner wall of the heating tube 55 and affecting the heat exchange efficiency between steam and material.

[0050] Example 5 Reference Figure 6The difference between this embodiment and embodiment 1 is that in this embodiment, the air inlet end and the air outlet end of the heating tube 55 are staggered along the circumference of the kiln body 1. When the heating tube 55 rotates with the kiln body 1, the position of the air outlet end in the rotation direction of the heating tube 55 lags behind the air inlet end. When the steam flows along the heating tube 55, the steam can flow in the heating tube 55 in a path that is closer to a straight line.

[0051] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. An energy-saving, high-efficiency steam rotary kiln, characterized in that: The kiln includes a kiln body (1), an air inlet box (2), and a discharge box (3). The feed end of the kiln body (1) is rotatably and sealed to the air inlet box (2), and the discharge end of the kiln body (1) is rotatably and sealed to the discharge box (3). The air inlet box (2) has an air inlet (21) at the top, and the discharge box (3) has a discharge outlet (32) at the bottom and an air outlet (31) at the top. The kiln body (1) is equipped with a heating system (5), which includes an air inlet main pipe (51), a drainage main pipe (52), a steam separator (53), a water collector (54), and several heating pipes (55). The steam separator (53) is located near the feed end of the kiln body (1), and the water collector (54) is located at the discharge end of the kiln body (1). The heating pipes (55) are arranged in a circular array along the center line of the kiln body (1). One end of the heating pipe (55) is connected to the steam separator (53), and the other end is connected to the water collector (54). The main air intake pipe (51) is connected to the steam separator (53) and extends out of the air intake box (2). The main drainage pipe (52) is connected to the water collector (54) and extends out of the discharge box (3). The kiln body (1) is inclined, and the feed end of the kiln body (1) is higher than the discharge end.

2. The energy-saving, high-efficiency steam rotary kiln according to claim 1, characterized in that: The centerline of the heating tube (55) forms an angle with the centerline of the kiln body (1), and the angle between the heating tube (55) and the centerline of the kiln body (1) is directed toward the discharge end of the kiln body (1). The angle between the heating tube (55) and the centerline of the kiln body (1) is less than or equal to the tilt angle of the kiln body (1).

3. The energy-saving, high-efficiency steam rotary kiln according to claim 1, characterized in that: The air inlet and air outlet of the heating tube (55) are offset along the circumference of the kiln body (1). When the heating tube (55) rotates with the kiln body (1), the position of the air outlet in the rotation direction of the heating tube (55) lags behind the air inlet.

4. The energy-saving, high-efficiency steam rotary kiln according to claim 1, characterized in that: The heating tube (55) has a spiral metal wire (6) on its inner side, and the spiral metal wire (6) is in clearance fit with the heating tube (55).

5. The energy-saving, high-efficiency steam rotary kiln according to claim 4, characterized in that: The spiral metal wire (6) includes multiple metal wire segments (61), the ends of which are bent to form straight segments. Adjacent straight segments of two adjacent metal wire segments (61) are connected by a sleeve structure (62), and the sleeve structure (62) is interference-fitted with the straight segments.

6. The energy-saving, high-efficiency steam rotary kiln according to claim 5, characterized in that: The sleeve structure (62) is a helical spring (620). The two ends of the helical spring (620) are respectively provided with hooks (621). The hooks (621) of the helical spring (620) are respectively hooked to the helical coils of two adjacent metal wire segments (61).

7. The energy-saving, high-efficiency steam rotary kiln according to claim 4, characterized in that: The surface of the spiral metal wire (6) is coated with titanium oxide.

8. The energy-saving, high-efficiency steam rotary kiln according to claim 4, characterized in that: The spiral metal wire (6) can rotate inside the heating tube (55), and the spiral direction of the spiral metal wire (6) is consistent with the direction of the material conveying spiral in the kiln body (1).

9. The energy-saving, high-efficiency steam rotary kiln according to claim 4, characterized in that: The side wall of the water collector (54) is provided with several guide discs (541), and the guide discs (541) are arranged in a one-to-one correspondence with the heating tubes (55). The spiral metal wire (6) abuts against the guide discs (541), and the thickness of the guide discs (541) is gradually changed.

10. The energy-saving, high-efficiency steam rotary kiln according to claim 4, characterized in that: The heating system (5) is insulated from the kiln body (1). The spiral metal wire (6) serves as an electric heating wire. The side wall of the steam separator (53) away from the water collector (54) is set as a first conductive plate (63). The side wall of the water collector (54) away from the steam separator (53) serves as a second conductive plate (65). A first conductive rod (64) is fixedly installed through the side wall of the air inlet box (2). The first conductive rod (64) abuts against the first conductive plate (63). A second conductive rod (66) is installed through the side wall of the discharge box (3). The second conductive rod (66) abuts against the second conductive plate (65). The two ends of the spiral metal wire (6) abut against the first conductive plate (63) and the second conductive plate (65) respectively.

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