Method for molding and processing variable capacitor

Abstract

A method for molding and processing a variable capacitor, the method comprising the following steps: feeding a molten material into a molding apparatus, molding a housing of a capacitor by means of the molding apparatus, and removing the molded housing from the molding apparatus; mounting a semiconductor substrate inside the molded housing, forming a first well of a first conductivity type in a first region of the semiconductor substrate, and then forming a second well of a second conductivity type in a second region adjacent to the first region of the semiconductor substrate; and forming a first insulating film above the first region and the second region of the semiconductor substrate, and forming a gate electrode above the first insulating film of the first region, wherein the molding apparatus comprises a fixing base. By using the method for molding and processing a variable capacitor, a workpiece can be conveniently molded in one step, the processing operation is simple, continuous processing can be achieved, and the processing efficiency is high.

Description

A forming method for a variable capacitor Technical Field

[0001] The present invention relates to the technical field of variable capacitors, and in particular to a forming and processing method of a variable capacitor. Background Art

[0002] A variable capacitor is a capacitor whose capacitance can be adjusted within a certain range. By changing the relative effective area between the pole pieces or the distance between the pole pieces, its capacitance changes accordingly. It is usually used as a tuning capacitor in radio receiving circuits. It is generally composed of two sets of mutually insulated pole pieces: a fixed set of pole pieces is called a stator, and a movable set of pole pieces is called a rotor. The rotors of several variable capacitors can be assembled on the same shaft to form a coaxial variable capacitor (commonly known as a double, triple, etc.). Variable capacitors have a long handle that can be equipped with a pull wire or dial for adjustment. The appearance is shown in the figure: A variable capacitor is a capacitor whose capacitance can be adjusted within a certain range. It is usually used as a tuning capacitor in radio receiving circuits. The variable capacitor shells currently used are usually made by machine tool processing, which requires multiple milling processes. The processing method is relatively cumbersome and has low processing efficiency. Technical issues

[0003] In response to the shortcomings of the existing technology, the present invention provides a forming and processing method for a variable capacitor, which solves the problem that the variable capacitor housing currently used is usually made by machine tool processing, which requires multiple milling processes, is relatively cumbersome, and has low processing efficiency. Technical Solutions

[0004] To achieve the above objectives, the present invention is implemented through the following technical solutions: A forming method for a variable capacitor comprises the following steps:

[0005] S1. feeding the molten material into a molding device, molding the capacitor housing through the molding device, and removing the molded housing from the molding device;

[0006] S2, installing the semiconductor substrate inside the molded housing, forming a first well of a first conductivity type in a first region of the semiconductor substrate, and then forming a second well of a second conductivity type in a second region adjacent to the first region of the semiconductor substrate;

[0007] S3. Form a first insulating film over the first region and the second region of the semiconductor substrate, and form a gate over the first insulating film in the first region.

[0008] Preferably, the molding device includes a fixed base, the top of the fixed base is rotatably connected to a rotating disk via a rotating table, the top of the rotating disk is provided with a mounting groove, the bottom of the inner wall of the mounting groove is provided with a communicating hole, a molding die is provided inside the mounting groove, and the side surfaces of the fixed base are respectively provided with a material changing device, a spraying device, a material injection device and a cooling device;

[0009] The forming mold includes a die, a slide groove is provided on one side of the die, an injection hole is provided at the center position of the bottom inner wall of the die, one end of the slide groove is connected to the top of the side of the injection hole, a cut-off block is slidably connected to the inner wall of the slide groove, an expansion cavity is provided inside the cut-off block, a slide hole is provided at the bottom of one end of the expansion cavity, a push rod is slidably connected to the inner wall of the bottom of the slide hole, both ends of the push rod are fixedly connected to plugs, and the inner wall of the die is slidably connected to the punch.

[0010] During use, the die is placed inside the mounting groove through the material changing device, and then the rotating disk is driven to rotate by the fixed base, and the rotating disk drives the die to move to the bottom of the spraying device, and the release agent is sprayed inside the die through the spraying device box. Then the rotating disk drives the die to move to the position of the injection device, and the injection device injects material into the die, and extends the punch into the die to squeeze the material inside the die and shape the material inside the die. Then the rotating disk drives the die to move to the position of the cooling device, and the molded part inside the die is cooled by the cooling device. After cooling, the rotating disk drives the die to move to the position of the material changing device, and the die inside the mounting groove is taken out by the material changing device, and then a new die is placed, which makes it convenient for the workpiece to be formed in one time, the processing operation is simple, and it can be realized The present invention is a continuous processing with high processing efficiency. A forming die is provided, and a slide groove and a cut-off block are provided inside the forming die. When the injection device injects the molten material into the die, the temperature of the die and the cut-off block rises, and the thermal expansion medium inside the expansion cavity expands due to the heat, pushing the piston to move outside the expansion cavity. While pushing the piston to move outward, the cut-off block is pushed back through the baffle so that the cut-off block is inserted into the injection hole. At this time, the cut-off block blocks the injection hole, and the thermal expansion medium inside the expansion cavity continues to expand, pushing the plug into the injection hole and the communicating hole, so that the material inside the injection hole and the communicating hole can be pushed out, which is convenient for cutting off the material between the injection device and the die, making it more convenient for the rotating disk to drive the die to move, and avoiding the adhesion of the material to the bottom of the rotating disk.

[0011] Preferably, the die is arranged inside the mounting groove and is slidably connected to the inner wall of the mounting groove, the top of the punch is fixed on the injection device, and the end of the inner wall of the expansion cavity away from the sliding hole is slidably connected to a push piston, and the push piston, one end of the push piston passes through the expansion cavity and is slidably connected to the cut-off block, and one side of the die is fixedly connected to a top plate adapted to the push piston.

[0012] Preferably, the expansion cavity is filled with a thermal expansion medium, a receiving groove adapted to the plug is provided at the bottom of the cut-off block, the plug at the bottom of the push rod is adapted to the shape of the inner wall of the injection hole, and the shape of the inner wall of the injection hole is adapted to the shape of the connecting hole.

[0013] Preferably, the injection device includes an injection base, one side of the injection base is fixedly connected to a bracket, the top of the bracket is fixedly connected to a telescopic rod, the bottom of the telescopic rod is fixedly connected to a positioning seat, a melting chamber is provided inside the injection base, the top of the melting chamber is connected to a telescopic tube, the bottom of the inner wall of the melting chamber is provided with an extrusion plug, the bottom of the extrusion plug is fixedly connected to a push rod, and an injection device is provided. When the rotating disk drives the die to move to the position of the injection device, the telescopic tube extends and is inserted into the communicating hole, and the push rod drives the extrusion plug to rise and squeezes the material inside the melting chamber into the die. When the injection is completed, the telescopic rod drives the positioning seat and the punch at the bottom of the positioning seat to move downward. The punch is inserted into the die to form a shape and then is pulled out from the inside of the molding material, which is convenient for integrating injection and molding, and improving work efficiency through one-time molding.

[0014] Preferably, one side of the injection base is fixedly connected to the side of the fixed base, and the bottom of the positioning seat is fixedly connected to the top of the punch.

[0015] Preferably, a heating device is provided inside the melting chamber, and the portion of the melting chamber above the extrusion plug is filled with molten material.

[0016] Preferably, the cooling device includes a circulating water tank, the top of one side of the circulating water tank is connected to the water inlet of the circulating water pump, the top of the circulating water tank is connected to a cooling water pipe, a cooling water pump is provided on the cooling water pipe, the top of the cooling water pipe is connected to a cooling nozzle, the outer sleeve of the cooling nozzle is provided with a telescopic sleeve, the top of the telescopic sleeve is fixedly connected to a sealing ring, and a cooling device is provided. When the rotating disk drives the die through the injection device to move to the position of the cooling device, the telescopic sleeve extends and drives the sealing ring to stick tightly to the bottom of the rotating disk, and the cooling water pump draws out the cooling water inside the circulating water tank and sprays it on the rotating disk through the cooling nozzle, so as to cool the rotating disk and the die on the rotating disk, thereby facilitating rapid cooling and shaping of the molded parts inside the die.

[0017] Preferably, one side of the circulating water tank is fixedly connected to the side of the fixed base, the water outlet of the circulating water pump is connected to the external water tank, the bottom of one side of the circulating water tank is connected to the external water tank through a connecting pipe, and the bottom of the cooling water pipe extends to the bottom of the inner wall of the circulating water tank. Beneficial effects

[0018] The present invention provides a forming method for a variable capacitor, which has the following beneficial effects:

[0019] (1) A forming processing method for a variable capacitor, wherein a die is placed inside a mounting groove through a material changing device, and then a rotating disk is driven to rotate by a fixed base, and the rotating disk drives the die to move to the bottom of a spraying device, and a release agent is sprayed inside the die through a spraying device box, and then the rotating disk drives the die to move to the position of a material injection device, and the injection device injects material into the die, and extends a punch into the die, squeezes the material inside the die and shapes the material inside the die, and then the rotating disk drives the die to move to the position of a cooling device, and the cooling device cools the molded part inside the die. After cooling, the rotating disk drives the die to move to the position of a material changing device, and the die inside the mounting groove is taken out by the material changing device, and then a new die is placed, so that the workpiece can be formed in one time, the processing operation is simple, and continuous processing can be achieved, and the processing efficiency is high.

[0020] (2) A forming processing method for a variable capacitor is provided with a forming mold, and a slide groove and a cut-off block are provided inside the forming mold. When the injection device injects the molten material into the die, the temperature of the die and the cut-off block increases, and the thermal expansion medium inside the expansion cavity expands due to the heat, pushing the piston to move outside the expansion cavity. While pushing the piston to move outward, the cut-off block is pushed back through the baffle, so that the cut-off block is inserted into the injection hole. At this time, the cut-off block blocks the injection hole, and the thermal expansion medium inside the expansion cavity continues to expand, pushing the plug into the injection hole and the connecting hole, so that the material inside the injection hole and the connecting hole can be pushed out, which is convenient for cutting off the material between the injection device and the die, making it more convenient for the rotating disk to drive the die to move, and avoiding the material from sticking to the bottom of the rotating disk.

[0021] (3) A molding processing method for a variable capacitor is provided with an injection device. When the rotating disk drives the die to move to the position of the injection device, the telescopic tube extends and is inserted into the connecting hole. The push rod drives the extrusion plug to rise and squeezes the material inside the molten cavity into the die. When the injection is completed, the telescopic rod drives the positioning seat and the punch at the bottom of the positioning seat to move downward. The punch is inserted into the die to form the material and then withdrawn from the molding material. This facilitates the integration of injection and molding, and improves work efficiency by forming the material in one step.

[0022] (IV) A molding processing method for a variable capacitor is provided with a cooling device. When the rotating disk drives the die to move through the injection device to the position of the cooling device, the telescopic sleeve extends and drives the sealing ring to be pressed against the bottom of the rotating disk. The cooling water pump draws out the cooling water inside the circulating water tank and sprays it onto the rotating disk through the cooling nozzle, thereby cooling the rotating disk and the die on the rotating disk, and facilitating the rapid cooling and shaping of the molded part inside the die. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG1 is a flow chart of the present invention;

[0024] FIG2 is a schematic structural diagram of the present invention;

[0025] FIG3 is a schematic structural diagram of a forming die according to the present invention;

[0026] FIG4 is a schematic structural diagram of the injection device of the present invention;

[0027] FIG5 is a schematic diagram of the internal structure of the injection device of the present invention;

[0028] FIG6 is a schematic structural diagram of the cooling device of the present invention.

[0029] In the figure: 1. Fixed base; 2. Rotating disk; 3. Mounting groove; 4. Connecting hole; 5. Forming die; 51. Concave die; 52. Slide groove; 53. Injection hole; 54. Cut-off block; 55. Expansion cavity; 56. Slide hole; 57. Ejector rod; 58. Plug; 59. Punch; 50. Push piston; 6. Material changing device; 7. Spraying device; 8. Injection device; 81. Injection base; 82. Bracket; 83. Telescopic rod; 84. Positioning seat; 85. Melting cavity; 86. Telescopic tube; 87. Extrusion plug; 88. Push rod; 9. Cooling device; 91. Circulating water tank; 92. Circulating water pump; 93. Cooling water pipe; 94. Cooling water pump; 95. Cooling nozzle; 96. Telescopic sleeve; 97. Sealing ring. Modes for Carrying Out the Invention

[0030] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention. Example 1:

[0031] Referring to FIG. 1 , the present invention provides a method for forming a variable capacitor, comprising the following steps:

[0032] S1. feeding the molten material into a molding device, molding the capacitor housing through the molding device, and removing the molded housing from the molding device;

[0033] S2, installing the semiconductor substrate inside the molded housing, forming a first well of a first conductivity type in a first region of the semiconductor substrate, and then forming a second well of a second conductivity type in a second region adjacent to the first region of the semiconductor substrate;

[0034] S3. Form a first insulating film over the first region and the second region of the semiconductor substrate, and form a gate over the first insulating film in the first region. Example 2:

[0035] Referring to Figures 1-4 , based on the first embodiment, the present invention provides a technical solution: a method for forming a variable capacitor, wherein the forming device includes a fixed base 1, the top of which is rotatably connected to a rotating disk 2 via a rotating table, the top of which is provided with a mounting groove 3, the bottom of the inner wall of the mounting groove 3 is provided with a communicating hole 4, and a forming mold 5 is provided within the mounting groove 3. A material changing device 6, a spraying device 7, an injection device 8, and a cooling device 9 are respectively provided on the side of the fixed base 1;

[0036] The forming mold 5 includes a die 51, a slide groove 52 is provided on one side of the die 51, an injection hole 53 is provided at the center of the bottom of the inner wall of the die 51, one end of the slide groove 52 is connected to the top of the side of the injection hole 53, a cut-off block 54 is slidably connected to the inner wall of the slide groove 52, an expansion cavity 55 is provided inside the cut-off block 54, a slide hole 56 is provided at the bottom of one end of the expansion cavity 55, a push rod 57 is slidably connected to the inner wall of the bottom of the slide hole 56, and plugs 58 are fixedly connected at both ends of the push rod 57, and a punch 59 is slidably connected to the inner wall of the die 51.

[0037] The die 51 is arranged inside the mounting groove 3 and is slidably connected to the inner wall of the mounting groove 3. The top of the punch 59 is fixed on the injection device 8. The end of the inner wall of the expansion cavity 55 away from the sliding hole 56 is slidably connected with the pushing piston 50. The pushing piston 50 has one end that passes through the expansion cavity 55 and is slidably connected to the cut-off block 54. One side of the die 51 is fixedly connected to a top plate that is adapted to the pushing piston 50.

[0038] The expansion cavity 55 is filled with a thermal expansion medium, and a receiving groove adapted to the plug 58 is provided at the bottom of the cut-off block 54. The plug 58 at the bottom of the push rod 57 is adapted to the shape of the inner wall of the injection hole 53, and the shape of the inner wall of the injection hole 53 is adapted to the shape of the connecting hole 4.

[0039] When in use, the die 51 is placed inside the mounting groove 3 through the material changing device 6, and then the rotating disk 2 is driven to rotate by the fixed base 1, and the rotating disk 2 drives the die 51 to move to the bottom of the spraying device 7, and the release agent is sprayed inside the die 51 through the spraying device 7, and then the rotating disk 2 drives the die 51 to move to the position of the injection device 8, and the injection device 8 injects material into the die 51, and extends the punch 59 into the die 51, squeezes the material inside the die 51 and shapes the material inside the die 51, and then the rotating disk 2 drives the die 51 to move to the position of the cooling device 9, and the molded part inside the die 51 is cooled by the cooling device 9. After cooling, the rotating disk 2 drives the die 51 to move to the position of the material changing device 6, and the die 51 inside the mounting groove 3 is taken out by the material changing device 6, and then a new die 51 is placed, which makes it convenient for the workpiece to be formed at one time, the processing operation is simple, and continuous molding can be achieved. Continuous processing has high processing efficiency. A forming mold 5 is provided, and a slide groove 52 and a cut-off block 54 are provided inside the forming mold 5. When the injection device 8 injects the molten material into the die 51, the temperature of the die 51 and the cut-off block 54 rises, and the thermal expansion medium inside the expansion cavity 55 expands due to the heat, pushing the piston 50 to move outside the expansion cavity 55. While pushing the piston 50 to move outward, the cut-off block 54 is pushed back through the baffle so that the cut-off block 54 is inserted into the injection hole 53. At this time, the cut-off block 54 blocks the injection hole 53, and the thermal expansion medium inside the expansion cavity 55 continues to expand, pushing the plug 58 into the injection hole 53 and the connecting hole 4, so that the material inside the injection hole 53 and the connecting hole 4 can be pushed out, making it convenient to cut off the material between the injection device 8 and the die 51, making it more convenient for the rotating disk 2 to drive the die 51 to move, and avoiding the adhesion of the material to the bottom of the rotating disk 2. Example 3:

[0040] Please refer to Figures 1-5. On the basis of the first and second embodiments, the present invention provides a technical solution: the injection device 8 includes an injection base 81, one side of the injection base 81 is fixedly connected to a bracket 82, the top of the bracket 82 is fixedly connected to a telescopic rod 83, the bottom of the telescopic rod 83 is fixedly connected to a positioning seat 84, a melting cavity 85 is provided inside the injection base 81, the top of the melting cavity 85 is connected to a telescopic tube 86, an extrusion plug 87 is provided at the bottom of the inner wall of the melting cavity 85, and a push rod 88 is fixedly connected to the bottom of the extrusion plug 87, one side of the injection base 81 is fixedly connected to the side of the fixed base 1, the bottom of the positioning seat 84 is fixedly connected to the top of the punch 59, and the melting cavity 85 is provided with a melting cavity 85. 5 is provided with a heating device inside. The portion of the melting cavity 85 above the extrusion plug 87 is filled with molten material and provided with an injection device 8. When the rotating disk 2 drives the die 51 to move to the position of the injection device 8, the telescopic tube 86 extends and inserts into the communicating hole 4. The push rod 88 drives the extrusion plug 87 upward to squeeze the material inside the melting cavity 85 into the die 51. When the injection is completed, the telescopic rod 83 drives the positioning seat 84 and the punch 59 at the bottom of the positioning seat 84 to move downward. The punch 59 is inserted into the die 51 to form the material and then withdrawn from the molding material. This facilitates the integration of injection and molding, and improves work efficiency by molding in one step. Example 4:

[0041] Please refer to Figures 1-6. Based on the first, second and third embodiments, the present invention provides a technical solution: the cooling device 9 includes a circulating water tank 91, the top of one side of the circulating water tank 91 is connected to the water inlet of the circulating water pump 92, the top of the circulating water tank 91 is connected to a cooling water pipe 93, a cooling water pump 94 is provided on the cooling water pipe 93, the top of the cooling water pipe 93 is connected to a cooling nozzle 95, the outer surface of the cooling nozzle 95 is provided with a telescopic sleeve 96, the top of the telescopic sleeve 96 is fixedly connected to a sealing ring 97, one side of the circulating water tank 91 is fixedly connected to the side of the fixed base 1, and the water outlet of the circulating water pump 92 is connected to the cooling water pipe 93. It is connected to the external water tank, and the bottom of one side of the circulating water tank 91 is connected to the external water tank through a connecting pipe. The bottom of the cooling water pipe 93 extends to the bottom of the inner wall of the circulating water tank 91. A cooling device 9 is provided. When the rotating disk 2 drives the die 51 through the injection device 8 to move to the position of the cooling device 9, the telescopic sleeve 96 extends and drives the sealing ring 97 to stick tightly to the bottom of the rotating disk 2. The cooling water pump 92 draws out the cooling water inside the circulating water tank 91 and sprays it on the rotating disk 2 through the cooling nozzle 95. The rotating disk 2 and the die 51 on the rotating disk 2 can be cooled, which facilitates the rapid cooling and shaping of the molded parts inside the die 51.

[0042] Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field and related fields without making creative efforts should fall within the scope of protection of the present invention. Structures, devices, and operating methods not specifically described and explained in the present invention shall be implemented in accordance with conventional means in the field unless otherwise specified or limited.

Claims

1. A forming and processing method for a variable capacitor, characterized in that: It includes the following steps: S1. Feed the molten material into the forming device, form the outer shell of the capacitor through the forming device, and remove the formed outer shell from the forming device; The forming device includes a fixed base (1), a rotating disk (2) is rotatably connected to the top of the fixed base (1) through a rotating table, an installation groove (3) is arranged on the top of the rotating disk (2), a communication hole (4) is opened at the bottom of the inner wall of the installation groove (3), a forming die (5) is arranged inside the installation groove (3), and a material changing device (6), a spraying device (7), a material injection device (8) and a cooling device (9) are respectively arranged on the side of the fixed base (1); The forming die (5) includes a female die (51), a sliding groove (52) is opened on one side of the female die (51), a material injection hole (53) is opened at the center position of the bottom of the inner wall of the female die (51), one end of the sliding groove (52) communicates with the top of the side of the material injection hole (53), a truncation block (54) is slidably connected to the inner wall of the sliding groove (52), an expansion cavity (55) is opened inside the truncation block (54), a sliding hole (56) is opened at the bottom of one end of the expansion cavity (55), a push rod (57) is slidably connected to the inner wall of the bottom of the sliding hole (56), plugging plugs (58) are fixedly connected to both ends of the push rod (57), and a male die (59) is slidably connected to the inner wall of the female die (51); The material injection device (8) includes a material injection base (81), a bracket (82) is fixedly connected to one side of the material injection base (81), a telescopic rod (83) is fixedly connected to the top of the bracket (82), a positioning seat (84) is fixedly connected to the bottom of the telescopic rod (83), a molten cavity (85) is arranged inside the material injection base (81), a telescopic tube (86) is communicated with the top of the molten cavity (85), an extrusion plug (87) is arranged at the bottom of the inner wall of the molten cavity (85), and a push rod (88) is fixedly connected to the bottom of the extrusion plug (87); S2. Install the semiconductor substrate inside the formed outer shell, form a first well of a first conduction type in the first region of the semiconductor substrate, and then form a second well of a second conduction type in a second region adjacent to the first region of the semiconductor substrate; S3. Form a first insulating film above the first region and the second region of the semiconductor substrate, and form a gate above the first insulating film in the first region.

2. A forming and processing method for a variable capacitor according to claim 1, characterized in that: The female die (51) is arranged inside the installation groove (3) and is slidably connected to the inner wall of the installation groove (3), the top of the male die (59) is fixed on the material injection device (8), a pushing piston (50) is slidably connected to one end of the inner wall of the expansion cavity (55) away from the sliding hole (56), the pushing piston (50), the pushing piston (50) penetrates through the expansion cavity (55) at one end and is slidably connected to the truncation block (54), and a top plate adapted to the pushing piston (50) is fixedly connected to one side of the female die (51).

3. A forming and processing method of a variable capacitor according to claim 1, characterized in that: The expansion cavity (55) is filled with a thermal expansion medium. The bottom of the truncation block (54) is provided with a storage groove adapted to the plug (58). The plug (58) at the bottom of the ejector rod (57) is adapted to the shape of the inner wall of the injection hole (53), and the shape of the inner wall of the injection hole (53) is adapted to the shape of the communication hole (4).

4. A forming and processing method of a variable capacitor according to claim 1, characterized in that: One side of the injection base (81) is fixedly connected to the side surface of the fixed base (1), and the bottom of the positioning seat (84) is fixedly connected to the top of the punch (59).

5. A forming and processing method of a variable capacitor according to claim 1, characterized in that: A heating device is provided inside the melting cavity (85), and the part of the melting cavity (85) above the extrusion plug (87) is filled with molten material.

6. A forming and processing method of a variable capacitor according to claim 1, characterized in that: The cooling device (9) includes a circulating water tank (91). The top of one side of the circulating water tank (91) is communicated with the water inlet of a circulating water pump (92). The top of the circulating water tank (91) is communicated with a cooling water pipe (93). A cooling water pump (94) is provided on the cooling water pipe (93). The top of the cooling water pipe (93) is communicated with a cooling spray head (95). A telescopic sleeve (96) is sleeved outside the cooling spray head (95), and a sealing ring (97) is fixedly connected to the top of the telescopic sleeve (96).

7. A forming and processing method of a variable capacitor according to claim 6, characterized in that: One side of the circulating water tank (91) is fixedly connected to the side surface of the fixed base (1). The water outlet of the circulating water pump (92) is communicated with an external water tank. One side of the bottom of the circulating water tank (91) is communicated with the external water tank through a connecting pipe. The bottom of the cooling water pipe (93) extends to the bottom of the inner wall of the circulating water tank (91).

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