Indium phosphide crystal preparation annealing equipment

Abstract

The invention relates to the technical field of indium phosphide crystal production, and particularly discloses indium phosphide crystal preparation annealing equipment which comprises a horizontally-arranged supporting base, an annealing furnace is fixedly mounted on the upper surface of the left end of the supporting base, an access door is mounted on the left side of the annealing furnace, and a longitudinally-arranged mounting plate is mounted above the right end of the supporting base. A mounting plate is arranged on the left side of the mounting plate, a clamping plate is mounted outside the mounting plate through bolts, and an indium phosphide rod needing to be annealed is clamped and fixed through the clamping plate; the inner space of the annealing furnace on the left side of the partition plate is a heat preservation bin. According to the annealing equipment for preparing the indium phosphide crystals, before the next group of indium phosphide rods start to be annealed, high-temperature helium in the heat preservation bin is conveyed into the preheating spray head by the conveying air pump through the connecting hose and is sprayed out, and the high-temperature helium is sprayed to the surfaces of the indium phosphide rods to preheat the indium phosphide rods; therefore, the annealing effect is prevented from being affected by too fast temperature rise of the indium phosphide rod during subsequent heating.

Description

Technical Field

[0001] The invention relates to the technical field of indium phosphide crystal production, in particular to an indium phosphide crystal preparation annealing device. Background Art

[0002] Indium phosphide crystal is an important III-V compound semiconductor material composed of indium and phosphorus elements. It has unique physical and chemical properties and is widely used in optoelectronic devices, high-frequency electronic devices, quantum technology and other fields. After its growth, it is slowly heated and cooled through annealing to release the accumulated thermal stress in the crystal, thereby improving its mechanical strength and reducing the fragmentation rate.

[0003] In the prior art, Chinese patent application number CN202411115421.9 discloses an annealing device for preparing indium phosphide crystals, comprising an annealing furnace body, three placement plates are arranged inside the annealing furnace body, and multiple space height adjustment mechanisms are fixedly connected between the three placement plates, wherein the external bottom ends of two of the space height adjustment mechanisms are fixedly connected to exhaust mechanisms, the internal bottom end of the annealing furnace body is slidably connected to two pop-up mechanisms, the front side of the annealing furnace body is rotatably connected to a furnace door, and the space height adjustment mechanism includes a bottom cylinder.

[0004] For example, in the prior art, the Chinese patent application number CN202110787961.1 discloses an annealing mechanism for an indium phosphide crystal preparation device, comprising a platform, a preparation assembly, and an annealing assembly arranged on the top of the platform; the preparation assembly comprises an upper box body and a lower box body, the upper box body and the lower box body are connected by a hinge, a preparation cylinder is provided in the enclosed space inside the upper box body and the lower box body, a preparation cavity is provided inside the preparation cylinder, a number of heating tubes are provided circumferentially on the inner side of the preparation cavity, and an annealing port is provided on one side of the preparation assembly; a first slide and a second slide are provided on the top of the platform, the first slide and the second slide are arranged in parallel, and the first slide and the second slide are both connected with a card block.

[0005] Another example of the prior art is a Chinese patent application numbered CN202311071433.1, which discloses a method and apparatus for semiconductor crystal growth and in-situ annealing, relating to the field of semiconductor crystal preparation technology. The method for semiconductor crystal growth and in-situ annealing comprises the following steps: S1. First, the crucible lid is welded or sintered to the crucible, followed by placing solid boron oxide and solid indium phosphide inside the crucible, and then placing the crucible on the upper end of the crucible support; S2. The main furnace body and upper furnace cover are closed, and the system is evacuated to 10-2Pa-10Pa through the gas charging and discharging pipes, and then an inert gas is introduced to 3-5MPa.

[0006] Based on the above materials, it can be seen that the annealing device in the prior art generally achieves the purpose of annealing by placing the indium phosphide crystal in an annealing furnace, heating it, and then cooling it. However, in actual use, the crystal placed in the annealing furnace is directly heated without any preheating measures, causing the crystal problem to rise too quickly, which may cause uneven heating and affect the annealing effect. Summary of the Invention

[0007] The object of the present invention is to provide an annealing device for preparing indium phosphide crystals to solve the problem in the above background technology that the lack of preheating leads to uneven heating and affects the annealing effect.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solutions: an indium phosphide crystal preparation annealing device, comprising a horizontally placed support base, an annealing furnace fixedly mounted on the upper surface of the left end of the support base, and an inspection door mounted on the left side of the annealing furnace, a longitudinally arranged mounting plate mounted above the right end of the support base, and a mounting disk mounted on the left side of the mounting plate, and a clamping plate mounted on the outside of the mounting disk by bolts, and the clamping plate is used to clamp and fix the indium phosphide rod to be annealed; a longitudinally arranged partition plate is fixedly mounted inside the annealing furnace, the internal space of the annealing furnace on the left side of the partition plate is an insulation chamber, and the internal space of the annealing furnace on the right side of the partition plate is a heating chamber, and electric heaters uniformly arranged at equal intervals are fixedly mounted inside the heating chamber; a preheating nozzle is mounted inside the heating chamber, the preheating nozzle utilizes the residual heat of annealing to uniformly preheat the indium phosphide rod, and a reciprocating mechanism is provided inside the heating chamber to drive the preheating nozzle to move periodically.

[0009] Preferably, a delivery air pump is fixedly installed inside the insulation chamber, and the delivery air pump is connected to the preheating nozzle through a connecting hose fixedly installed therewith, and the connecting hose is a high-temperature resistant metal hose. The delivery air pump is used in conjunction with the connecting hose and the preheating nozzle to circulate helium in the heating chamber and the insulation chamber.

[0010] Preferably, the reciprocating mechanism includes a reciprocating screw installed inside the preheating nozzle with a through thread, the position of the preheating nozzle corresponds to the position of the indium phosphide rod up and down, and the reciprocating screw is rotatably installed in the mounting frame, and the two mounting frames are respectively fixedly installed at the upper and lower ends of the heating chamber, and the rotation of the reciprocating screw drives the preheating nozzle installed with a through thread on the outside to move back and forth left and right.

[0011] Preferably, a driven roller is fixedly installed at the top end of the reciprocating screw rod to drive it to rotate, and the driven roller rubs against the surface of the contact plate. The contact plate and the driven roller are both made of high-temperature resistant stainless steel, and the surface of the contact plate is polished into a rough structure using a sander.

[0012] Preferably, the contact plate contacts and squeezes the indium phosphide rod extending into the heating chamber, and the contact plate is connected to a second motor fixedly installed inside the heating chamber. The second motor is used to push the contact plate to contact and squeeze the indium phosphide rod, and the contact plate is used to slightly squeeze the indium phosphide rod to prevent the front end of the indium phosphide rod from bending due to gravity.

[0013] Preferably, a stirring plate for stirring the gas inside the heating chamber is fixedly installed between the upper and lower preheating nozzles, and the stirring plate is provided with through holes distributed in a matrix pattern, and the stirring plate and the indium phosphide rod avoid each other, and the stirring plate is set to be made of lightweight stainless steel.

[0014] Preferably, a first motor for driving the mounting plate to rotate is fixedly mounted on the outside of the mounting plate, and the mounting plate is fixedly mounted between a fixed tripod on the outside of the mounting plate and the movable slider.

[0015] Preferably, a sealing ring is fixedly installed on the outer surface of the mounting plate, which fits and seals with the outer wall of the annealing furnace, and a left-right sliding structure is formed between the movable slider and the electric slide rail, and the electric slide rail is fixedly installed on the upper surface of the support base, and automatic loading and unloading operations are realized by sliding the movable slider on the electric slide rail.

[0016] Preferably, an insulation board is fixedly installed on the inner wall of the insulation chamber, and the insulation board is set to asbestos material, and the insulation chamber is filled with helium to protect the indium phosphide rods during annealing. The insulation board is used to achieve a better insulation effect for the helium, thereby better utilizing the waste heat.

[0017] Preferably, an air inlet pipe for providing helium is fixedly installed through the top of the heat preservation chamber, and an exhaust pipe for exhausting air is fixedly installed through the front side of the heating chamber, and both the air inlet pipe and the exhaust pipe are provided with electrically controlled valves.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: the indium phosphide crystal preparation annealing equipment adopts a new structural design, the specific contents of which are as follows: 1. During the annealing process of the indium phosphide rod (the grown indium phosphide crystal), helium is filled into the heating chamber to expel the air in the heating chamber to prevent the indium phosphide rod from oxidizing with oxygen during the annealing process. After the annealing is completed, the helium in the heating chamber is transported to the insulation chamber through the air delivery pump. The insulation board in the insulation chamber is used to keep the helium warm, thereby reducing the heat loss and waste of the helium. Furthermore, before the next group of indium phosphide rods begins annealing, a delivery air pump is used to deliver high-temperature helium in the heat preservation chamber through a connecting hose to the preheating nozzle and spray it out. The high-temperature helium is sprayed onto the surface of the indium phosphide rods to preheat them, thereby preventing the indium phosphide rods from rising too quickly in temperature during subsequent heating and affecting the annealing effect.

[0019] 2. During the annealing process, the second motor drives the contact disk to rotate. Under the transmission action of the contact disk, the driven roller drives the reciprocating screw to rotate. The rotation of the reciprocating screw drives the preheating nozzle installed with a threaded hole on its outside to move back and forth, thereby improving the uniformity of the preheating of the indium phosphide rod (the contact disk can slightly squeeze the indium phosphide rod within a controllable range to prevent the front end of the indium phosphide rod from bending due to gravity); Furthermore, a stirring plate is fixedly installed on the outside of the preheating nozzle. When the indium phosphide rod in the heating chamber is heated by the electric heater, the preheating nozzle drives the stirring plate to move synchronously. At this time, the movement of the stirring plate is coordinated with the through-flow stirring air opened inside it, thereby improving the heating uniformity of the indium phosphide rod.

[0020] 3. A sealing ring is fixed on the outer surface of the mounting plate. After the indium phosphide rod is sent into the heating chamber using the mounting plate, the sealing ring is used to improve the sealing between the mounting plate and the outer wall of the annealing furnace to reduce the leakage of helium and heat. The mounting plate slides between the moving slider and the electric slide rail to realize automatic loading and unloading operations. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the overall structure of the present invention; Figure 2 This is a schematic diagram of the mounting plate structure of the present invention; Figure 3 For the present invention Figure 2 A in the middle is an enlarged structural diagram; Figure 4 This is a structural diagram of the connection relationship between the mounting plate and the movable slider of the present invention; Figure 5 Schematic diagram of the internal structure of the annealing furnace of the present invention; Figure 6 This is a schematic diagram of the internal structure of the heat preservation bin of the present invention; Figure 7 This is a schematic structural diagram of the positional relationship between the indium phosphide rod and the heating chamber of the present invention; Figure 8 For the present invention Figure 7 The enlarged structural diagram at B in the middle; Figure 9 This is a schematic diagram of the installation position structure of the stirring plate of the present invention; Figure 10 This is a schematic diagram of the preheating nozzle structure of the present invention.

[0022] In the figure: 1. Support base; 2. Annealing furnace; 3. Inspection door; 4. Mounting plate; 5. Moving slider; 6. Fixed tripod; 7. Mounting plate; 8. Clamping plate; 9. Indium phosphide rod; 10. First motor; 11. Sealing ring; 12. Electric slide rail; 13. Partition plate; 14. Insulation chamber; 1401, Insulation plate; 15. Heating chamber; 1501, Electric heater; 16. Inlet pipe; 17. Exhaust pipe; 18. Second motor; 19. Contact plate; 20. Delivery air pump; 21. Preheating nozzle; 22. Connecting hose; 23. Reciprocating screw; 24. Mounting frame; 25. Driven roller; 26. Stirring plate; 27. Through hole. DETAILED DESCRIPTION

[0023] 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.

[0024] Example 1: Please refer to Figure 1-Figure 5 In order to achieve the purpose of annealing indium phosphide crystals, this embodiment provides the following technical solutions, which specifically disclose: a horizontally placed support base 1, an annealing furnace 2 is fixedly installed on the upper surface of the left end of the support base 1, and an inspection door 3 is installed on the left side of the annealing furnace 2, a longitudinally arranged mounting plate 4 is installed above the right end of the support base 1, and a mounting disk 7 is arranged on the left side of the mounting plate 4, and a clamping plate 8 is installed on the outside of the mounting disk 7 by bolts, and the clamping plate 8 is used to clamp and fix the indium phosphide rod 9 to be annealed, a longitudinally arranged partition plate 13 is fixedly installed inside the annealing furnace 2, the internal space of the annealing furnace 2 on the left side of the partition plate 13 is a heat preservation chamber 14, and the internal space of the annealing furnace 2 on the right side of the partition plate 13 is a heating chamber 15, and the interior of the heating chamber 15 is fixedly installed with electric heaters 1501 evenly arranged at equal intervals; the mounting plate 4 is fixedly installed outside It is equipped with a first motor 10 for driving the mounting plate 7 to rotate, and the mounting plate 4 is fixedly installed between the fixed tripod 6 and the movable slider 5 on its outside. A sealing ring 11 is fixedly installed on the outer surface of the mounting plate 4 to seal with the outer wall of the annealing furnace 2, and a left-right sliding structure is formed between the movable slider 5 and the electric slide rail 12, and the electric slide rail 12 is fixedly installed on the upper surface of the support base 1. An insulation board 1401 is fixedly installed on the inner wall of the insulation chamber 14, and the insulation board 1401 is set to asbestos material, and the insulation chamber 14 is filled with helium to protect the indium phosphide rod 9 during annealing. An air inlet pipe 16 for providing helium is fixedly installed above the insulation chamber 14, and an exhaust pipe 17 for exhausting air is fixedly installed on the front side of the heating chamber 15, and both the air inlet pipe 16 and the exhaust pipe 17 are provided with electrically controlled valves.

[0025] When using the device, first place the indium phosphide rod 9 to be annealed (i.e., the rod-shaped indium phosphide crystal formed after growth) on the left side of the mounting plate 7, then use bolts to cooperate with the clamping plate 8 to clamp the indium phosphide rod 9, then turn on the electric slide 12, so that the electric slide 12 drives the movable slider 5 above it to slide to the left, so that the indium phosphide rod 9 is sent into the heating chamber 15 inside the annealing furnace 2 by using the mounting plate 4 (the mounting plate 4 is fixedly mounted with the movable slider 5 using the fixed tripod 6). At this time, the sealing ring 11 is used to improve the sealing effect between the mounting plate 4 and the outer wall of the annealing furnace 2 (the heating chamber 15 is filled with helium, and the air is discharged from the exhaust pipe 17 under the squeezing effect of the helium). Then, the electric heater 1501 inside the heating chamber 15 is turned on, and the indium phosphide rod 9 is heated by the electric heater 1501. At the same time, the first motor 10 outside the mounting plate 4 is turned on, and the first motor 10 drives the mounting plate 7 to rotate, so that the mounting plate 7 drives the indium phosphide rod 9 to rotate, thereby improving its heating uniformity.

[0026] Example 2: Please refer to Figures 5-10 In order to achieve the purpose of preheating the indium phosphide crystal by utilizing the waste heat, this embodiment provides the following technical solutions, which specifically disclose: a preheating nozzle 21 is installed inside the heating chamber 15, and the preheating nozzle 21 utilizes the waste heat of annealing to uniformly preheat the indium phosphide rod 9, and a reciprocating mechanism is provided inside the heating chamber 15 to drive the preheating nozzle 21 to move periodically, a delivery air pump 20 is fixedly installed inside the heat preservation chamber 14, and the delivery air pump 20 is connected to the preheating nozzle 21 through a connecting hose 22 fixedly installed therewith, and the connecting hose 22 is a high-temperature resistant metal hose, and the reciprocating mechanism includes a reciprocating screw 23 threadedly installed inside the preheating nozzle 21, and the position of the preheating nozzle 21 corresponds to the position of the indium phosphide rod 9 in the upper and lower directions. , and the reciprocating screw 23 is rotatably mounted in the mounting frame 24, and the two mounting frames 24 are respectively fixedly mounted at the upper and lower ends inside the heating chamber 15. A driven roller 25 is fixedly mounted on the top of the reciprocating screw 23 for driving it to rotate, and the driven roller 25 is in contact with and rubbed against the surface of the contact disk 19. The contact disk 19 contacts and squeezes the indium phosphide rod 9 extending into the heating chamber 15, and the contact disk 19 is rotatably connected to the second motor 18 fixedly mounted inside the heating chamber 15. A stirring plate 26 for stirring the gas inside the heating chamber 15 is fixedly mounted between the upper and lower preheating nozzles 21, and a through-hole 27 distributed in a matrix is ​​opened inside the stirring plate 26, and the stirring plate 26 and the indium phosphide rod 9 avoid each other.

[0027] After the indium phosphide rods 9 are heated, the delivery air pump 20 is first turned on to draw the helium inside the heating chamber 15 into the insulation chamber 14 through the preheating nozzle 21 and the connecting hose 22. At this time, the heat insulation board 1401 on the inner wall of the insulation chamber 14 is used to isolate the heat transfer to achieve the purpose of heat preservation of the helium. Then, the heated indium phosphide rods 9 are removed from the heating chamber 15 through the mounting plate 4 and naturally cooled to finally achieve the purpose of annealing. After the next group is sent into the heating chamber 15, the delivery air pump 20 is first turned on. The delivery air pump 20 ejects the helium in the heat preservation chamber 14 from the preheating nozzle 21 through the connecting hose 22, and uses the high-temperature helium to preheat the surface of the indium phosphide rod 9. At the same time, the first motor 10 drives the indium phosphide rod 9 to rotate, and the second motor 18 drives the contact plate 19 to rotate. The contact plate 19 slightly squeezes the indium phosphide rod 9 to prevent the front end of the indium phosphide rod 9 from bending due to gravity. The first motor 10 and the second motor 18 keep rotating at the same speed to prevent the indium phosphide rod 9 from being subjected to large torque during rotation. Thus, the driven roller 25 is driven to rotate synchronously under the action of the contact disc 19 (a tooth block structure is provided between the contact surface of the contact disc 19 and the driven roller 25, and the engagement between the tooth blocks enables the contact disc 19 to drive the driven roller 25 to rotate). During the rotation process, the driven roller 25 drives the reciprocating screw 23 fixed thereto to rotate, and the reciprocating screw 23 drives the preheating nozzle 21 installed with a thread passing through its outer surface to move back and forth, thereby improving the uniformity of the preheating nozzle 21 on the indium phosphide rod 9. At the same time, helium can be transported to the heating chamber 15 (if helium is lost, helium is replenished by the air inlet pipe 16). After preheating is completed, the electric heater 1501 is turned on for heating. At this time, the preheating nozzle 21 is still moving left and right (no gas is sprayed outward). During the movement of the preheating nozzle 21, the stirring plate 26 fixed on its side is driven to move, so that the stirring plate 26 is used to cooperate with the through hole 27 opened inside the stirring plate to stir the gas inside the heating chamber 15, thereby improving the heating uniformity of the indium phosphide rod 9.

[0028] In the description of the present invention, all components in the heating chamber 15 are made of high-temperature resistant metal materials, such as the bearings of the rotating parts (CERASP series all-ceramic bearings), the reciprocating screw 23, the preheating nozzle 21 (high-temperature alloy or ceramic material), and the second motor 18 (nickel-based high-temperature alloy shell, which can withstand high temperatures above 900 degrees).

[0029] In the description of the present invention, unless otherwise specified, "plurality" means two or more; terms such as "upper," "lower," "left," "right," "inner," "outer," "front end," "rear end," "head," and "tail" indicate positions or relationships based on those shown in the accompanying drawings. These terms are intended solely to facilitate the description of the present invention and simplify the description. They do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limiting the present invention. Furthermore, terms such as "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0030] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. An indium phosphide crystal preparation annealing device, comprising a horizontally placed support base (1), an annealing furnace (2) fixedly mounted on the upper surface of the left end of the support base (1), and an inspection door (3) mounted on the left side of the annealing furnace (2), characterized in that: Also includes: A longitudinally arranged mounting plate (4) is installed above the right end of the support base (1), and a mounting plate (7) is provided on the left side of the mounting plate (4), and a clamping plate (8) is mounted on the outside of the mounting plate (7) by means of bolts, and the clamping plate (8) is used to clamp and fix the indium phosphide rod (9) to be annealed; A longitudinally arranged partition plate (13) is fixedly installed inside the annealing furnace (2); the internal space of the annealing furnace (2) on the left side of the partition plate (13) is a heat preservation chamber (14); the internal space of the annealing furnace (2) on the right side of the partition plate (13) is a heating chamber (15); and electric heaters (1501) are fixedly installed inside the heating chamber (15) at evenly spaced intervals. A preheating nozzle (21) is installed inside the heating chamber (15), and the preheating nozzle (21) uses the residual heat of annealing to uniformly preheat the indium phosphide rod (9). A reciprocating mechanism is provided inside the heating chamber (15) to drive the preheating nozzle (21) to move periodically.

2. The indium phosphide crystal preparation annealing equipment according to claim 1, characterized in that: A delivery air pump (20) is fixedly installed inside the heat preservation chamber (14), and the delivery air pump (20) is connected to the preheating nozzle (21) through a connecting hose (22) fixedly installed therewith, and the connecting hose (22) is a high-temperature resistant metal hose.

3. The indium phosphide crystal preparation annealing equipment according to claim 1, characterized in that: The reciprocating mechanism includes a reciprocating screw (23) threadedly mounted inside the preheating nozzle (21), the position of the preheating nozzle (21) and the position of the indium phosphide rod (9) corresponding to each other in the upper and lower directions, and the reciprocating screw (23) is rotatably mounted in a mounting frame (24), and the two mounting frames (24) are fixedly mounted at the upper and lower ends of the heating chamber (15) respectively.

4. The indium phosphide crystal preparation annealing equipment according to claim 3, characterized in that: A driven roller (25) is fixedly mounted on the top end of the reciprocating screw (23) for driving the reciprocating screw (23) to rotate, and the driven roller (25) is in contact with and rubs against the surface of the contact disk (19).

5. The indium phosphide crystal preparation annealing equipment according to claim 4, characterized in that: The abutment disk (19) contacts and squeezes the indium phosphide rod (9) extending into the interior of the heating chamber (15), and the abutment disk (19) is connected to a second motor (18) fixedly mounted inside the heating chamber (15).

6. The indium phosphide crystal preparation annealing equipment according to claim 5, characterized in that: A stirring plate (26) for stirring the gas inside the heating chamber (15) is fixedly installed between the upper and lower preheating nozzles (21), and the stirring plate (26) is provided with through holes (27) distributed in a matrix, and the stirring plate (26) and the indium phosphide rod (9) avoid each other.

7. The indium phosphide crystal preparation annealing equipment according to claim 1, characterized in that: A first motor (10) for driving the mounting plate (7) to rotate is fixedly mounted on the outside of the mounting plate (4), and the mounting plate (4) is fixedly mounted between a fixed tripod (6) on the outside of the mounting plate and the movable slider (5).

8. The indium phosphide crystal preparation annealing equipment according to claim 7, characterized in that: A sealing ring (11) is fixedly mounted on the outer surface of the mounting plate (4) and is sealed against the outer wall of the annealing furnace (2). A left-right sliding structure is formed between the movable slider (5) and the electric slide rail (12), and the electric slide rail (12) is fixedly mounted on the upper surface of the support base (1).

9. The indium phosphide crystal preparation annealing equipment according to claim 1, characterized in that: An insulation board (1401) is fixedly mounted on the inner wall of the insulation chamber (14), and the insulation board (1401) is made of asbestos. The interior of the insulation chamber (14) is filled with helium gas for protecting the indium phosphide rod (9) during annealing.

10. The indium phosphide crystal preparation annealing equipment according to claim 9, characterized in that: An air inlet pipe (16) for supplying helium is fixedly installed through the top of the heat preservation chamber (14), and an exhaust pipe (17) for exhausting air is fixedly installed through the front side of the heating chamber (15), and both the air inlet pipe (16) and the exhaust pipe (17) are provided with an electrically controlled valve.

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