Hydraulic system for hot-pressing sintering of aluminum nitride heater stable pressure

Abstract

The application discloses a hydraulic system for stabilizing pressure of a hot-pressing sintering aluminum nitride heater, which comprises a main oil tank and a stamping oil cylinder; the main oil tank is connected with a first main oil path, the first main oil path is connected with an upper cylinder total oil path and a lower cylinder oil path through a first two-position cartridge valve, the upper cylinder total oil path is connected with an inner cylinder oil path and the main oil tank through a second two-position cartridge valve, and an outer cylinder oil path is connected with the inner cylinder oil path through a cartridge valve; the first main oil path, a second main oil path and a third main oil path are connected with a pressure compensation main oil path; a first hydraulic control check valve is arranged on the inner cylinder oil path and the outer cylinder oil path, the first hydraulic control check valve is connected with a first pressure relief oil path connected with the second main oil path, and the inner cylinder oil path and the outer cylinder oil path are connected with a second pressure relief oil path between the first hydraulic control check valve and the stamping oil cylinder. The design of the inner cylinder and the outer cylinder can realize controllable pressure relief range of the stamping oil cylinder, the pressure relief oil path makes the stability of the pressurizing rate good, and the pressure fluctuation is small during the pressure relief process.

Description

Technical Field

[0001] This invention relates to the field of hydraulic systems, and in particular to a hydraulic system for stabilizing and maintaining pressure in a hot-pressed sintered aluminum nitride heater. Background Technology

[0002] The function of a hydraulic system is to increase the force by changing the pressure. A complete hydraulic system consists of five parts: power element, actuator, control element, auxiliary element, and hydraulic oil. Hydraulic systems can be divided into two categories: hydraulic transmission system and hydraulic control system. The hydraulic transmission system is mainly used to transmit power and motion, while the hydraulic control system is used to ensure that the output of the hydraulic system meets specific performance requirements.

[0003] In the prior art, a hydraulic system for an aluminum nitride heater is disclosed, which includes a main oil tank, a filter, a hydraulic pump, a relief valve, a cartridge valve, a proportional valve, a first hydraulically controlled check valve, and a pressurizing cylinder. The cartridge valve is used to control the oil supply direction, and the proportional valve is used to regulate the oil flow. However, with this structure, the pressure is easily exceeded during pressurization, and the pressure drops too quickly and cannot be controlled during depressurization, resulting in a large impact on the valve body and large pressure fluctuations. This directly impacts components such as pipelines, joints, and seals, leading to metal fatigue, cracks, or even pipe rupture, shortening the service life of components. At the same time, it interferes with the response of precision components such as proportional valves and servo valves, causing unstable movement of the pressurizing cylinder. Therefore, how to optimize the hydraulic system of the aluminum nitride heater to improve the stability of the pressurization rate and reduce pressure fluctuations during depressurization is a key research direction in the industry.

[0004] Therefore, it is necessary to design a new technical solution to solve the above problems. Summary of the Invention

[0005] In view of this, the present invention addresses the deficiencies of the existing technology, and its main objective is to provide a hydraulic system for stabilizing and maintaining pressure in a hot-pressed sintered aluminum nitride heater. The outer cylinder oil circuit is connected to the inner cylinder oil circuit via a cartridge valve, allowing oil to be supplied to the inner cylinder first during pressurization, and then to the outer cylinder via the cartridge valve after reaching the preset pressure. The inner and outer cylinder design enables controllability of the pressure relief range of the pressurized cylinder. A first pressure relief oil circuit is provided; when pressure adjustment is needed, only the corresponding filling valve of the inner cylinder needs to be opened to achieve small-range pressure regulation. Its pressure fluctuation is less than when the corresponding filling valve of the outer cylinder is opened. Furthermore, when the filling valve is open, the servo proportional valve acts as a pressure reducing valve, controlling the pressure reduction rate. The second pressure relief oil circuit has throttling buffer and pressure gradual change control functions, preventing pressure oscillations caused by sudden load changes, and enabling autonomous pressure reduction and automatic pressure stabilization. The PT throttling valve and the reversing switch valve act as pressure reducing valves with buffering functions, resulting in good stability of the pressurization rate and small pressure fluctuations during pressure relief.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A hydraulic system for stabilizing and maintaining pressure in a hot-pressed sintered aluminum nitride heater includes a main oil tank and a stamping cylinder. The stamping cylinder includes an upper cylinder and a lower cylinder. The upper cylinder includes an inner cylinder and an outer cylinder located on the outer periphery of the inner cylinder. The inner cylinder and the outer cylinder are respectively connected to an inner cylinder oil circuit and an outer cylinder oil circuit.

[0008] The main oil tank is connected to a first main oil circuit. The first main oil circuit is connected to the upper cylinder main oil circuit and the lower cylinder oil circuit connected to the lower cylinder through a first two-position cartridge valve. The upper cylinder main oil circuit is connected to the inner cylinder oil circuit and the main oil tank through a second two-position cartridge valve. The outer cylinder oil circuit is connected to the inner cylinder oil circuit through a cartridge valve.

[0009] The upper cylinder main oil circuit is connected to a control oil circuit for adjusting the oil flow. The control oil circuit is sequentially equipped with a front solenoid valve and a first servo proportional valve. The outlet of the first servo proportional valve is connected to the main oil tank.

[0010] The main oil tank is also connected to a second main oil circuit and a third main oil circuit. A dual pump is installed on the first main oil circuit and the second main oil circuit together. A first hydraulic pump is installed on the third main oil circuit. The first main oil circuit, the second main oil circuit, and the third main oil circuit are connected to a pressure-replenishing main oil circuit. The pressure-replenishing main oil circuit is connected to the lower cylinder oil circuit and the inner cylinder oil circuit respectively through a second servo proportional valve. The pressure-replenishing main oil circuit can selectively replenish oil for the inner cylinder and the lower cylinder.

[0011] Both the inner cylinder oil circuit and the outer cylinder oil circuit are equipped with a first hydraulic control check valve. The first hydraulic control check valve is connected to a first pressure relief oil circuit connected to the second main oil circuit. The first pressure relief oil circuit is equipped with a filling valve for controlling the opening and closing of the oil port of the first hydraulic control check valve.

[0012] The inner cylinder oil circuit and the outer cylinder oil circuit are connected together between the first hydraulic control check valve and the stamping cylinder to a second pressure relief oil circuit connected to the main oil tank. The second pressure relief oil circuit is equipped with a PT throttle valve and a reversing switch valve. The reversing switch valve is located on the side of the PT throttle valve closer to the main oil tank.

[0013] As a preferred embodiment, the first main oil circuit, the second main oil circuit, and the third main oil circuit are each provided with a first one-way valve that unidirectionally flows toward the stamping cylinder. The pressure replenishing main oil circuit is provided with a second one-way valve that unidirectionally flows toward the stamping cylinder between the second main oil circuit and the third main oil circuit. The pressure replenishing main oil circuit is provided with a first solenoid valve between the second one-way valve and the second main oil circuit.

[0014] As a preferred embodiment, both the first check valve of the second main oil circuit and the third main oil circuit are provided with an overflow oil circuit connected to the main oil tank, and the overflow oil circuit is provided with an overflow structure.

[0015] As a preferred embodiment, the second servo proportional valve is connected to the lower cylinder oil circuit and the inner cylinder oil circuit through the first and second supplementary pressure oil circuits, respectively. Both the first and second supplementary pressure oil circuits are equipped with a two-stage check valve that unidirectionally flows toward the stamping cylinder. A two-position two-way directional valve is provided on the input side of the two-stage check valve in the first supplementary pressure oil circuit.

[0016] As a preferred embodiment, the filling valve is a two-position four-way directional valve. The second main oil circuit, the main oil tank, and the first hydraulically controlled check valve are all connected to the two-position four-way directional valve. The two-position four-way directional valve is also connected to a reverse check valve. When the filling valve is open, the dual pump drives the oil to open the first hydraulically controlled check valve, thereby releasing the pressure of the pressurized oil cylinder. When the filling valve is closed, the first hydraulically controlled check valve is connected to the main oil tank and operates normally.

[0017] As a preferred embodiment, the inner cylinder oil circuit and the outer cylinder oil circuit are respectively connected to the second pressure relief oil circuit through the first branch and the second branch. Both the first branch and the second branch are equipped with a third one-way valve that unidirectionally flows towards the main oil tank. When the stamping cylinder is pressurized, the PT throttle valve adjusts the speed according to the oil pressure. When the stamping cylinder is depressurized, the damping orifice of the PT throttle valve acts as a pressure buffer until the oil pressure drops to the required stabilizing pressure. Then, the second pressure relief oil circuit is closed by the reversing switch valve to maintain the pressure inside the stamping cylinder.

[0018] As a preferred embodiment, both the first main oil circuit and the lower cylinder oil circuit are equipped with pressure reducing structures.

[0019] As a preferred embodiment, pressure sensors are installed in the main oil circuit of the upper cylinder, the oil circuit of the inner cylinder, and the oil circuit of the outer cylinder.

[0020] As a preferred embodiment, the main oil tank is also connected to a cooling system, which includes a cooling oil circuit connected in a closed loop to the main oil tank and a condenser, a first filter, and a second hydraulic pump arranged sequentially on the cooling oil circuit. The cooling system also includes an oil temperature sensor for monitoring the oil temperature in the main oil tank.

[0021] As a preferred embodiment, the main oil tank is also connected to a fluid replenishment system, which includes a level gauge for monitoring the amount of oil in the main oil tank.

[0022] Compared with the prior art, the present invention has obvious advantages and beneficial effects. Specifically, as can be seen from the above technical solution:

[0023] Its main features include an outer cylinder oil circuit connected to an inner cylinder oil circuit via a cartridge valve, allowing oil to be supplied to the inner cylinder first during pressurization, and then to the outer cylinder after reaching the preset pressure. The inner and outer cylinder design enables controllability of the pressure relief range of the pressurized cylinder. Combined with a first pressure relief oil circuit, when pressure adjustment is needed, only the corresponding filling valve of the inner cylinder needs to be opened to achieve small-range pressure regulation. The pressure fluctuation is less than when the corresponding filling valve of the outer cylinder is opened. Furthermore, when the filling valve is open, the servo proportional valve acts as a pressure reducing valve, controlling the pressure reduction rate. Additionally, the second pressure relief oil circuit has throttling buffer and pressure gradual change control functions, preventing pressure oscillations caused by sudden load changes, enabling autonomous pressure reduction and automatic pressure stabilization. The PT throttling valve and the reversing switch valve act as pressure reducing valves with buffering functions, resulting in good stability of the pressurization rate and small pressure fluctuations during pressure relief.

[0024] To more clearly illustrate the structural features and effects of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of a hydraulic system according to a preferred embodiment of the present invention.

[0026] Explanation of reference numerals in the attached diagram:

[0027] 10. Main fuel tank; 101. First main fuel line;

[0028] 102. Main oil circuit for upper cylinder; 103. Control oil circuit;

[0029] 104. Second main oil circuit; 105. Third main oil circuit;

[0030] 106. Main oil pressure replenishment circuit; 107. Overflow oil circuit;

[0031] 108. Second pressure relief oil circuit; 20. Stamping cylinder;

[0032] 21. Upper cylinder; 211. Inner cylinder;

[0033] 212. Outer cylinder; 22. Lower cylinder;

[0034] 201. Inner cylinder oil passage; 202. Outer cylinder oil passage;

[0035] 203. Lower cylinder oil circuit; 204. First branch circuit;

[0036] 205. Second branch; 30. First and second position cartridge valves;

[0037] 40. Second position cartridge valve; 50. Cartridge valve;

[0038] 60. Pre-positioned solenoid valve; 70. First servo proportional valve;

[0039] 80. Dual pump; 90. First hydraulic pump;

[0040] 100. Second servo proportional valve; 1001. First pressure compensation oil circuit;

[0041] 1002, Second pressure-replenishing oil circuit; 110, First check valve;

[0042] 120. Second check valve; 130. First solenoid valve;

[0043] 140. Two-stage check valve; 150. Two-position two-way directional valve;

[0044] 160. Relief valve; 170. Second solenoid valve;

[0045] 180. Second oil filter; 190. First hydraulic check valve;

[0046] 1901, First pressure relief oil circuit; 200, Filling valve;

[0047] 210. Reverse check valve; 220. PT throttle valve;

[0048] 230. Reversing switch valve; 240. Third check valve;

[0049] 250. Second hydraulically controlled check valve; 260. Third solenoid valve;

[0050] 270. Pressure sensor; 280. Cooling system;

[0051] 2801. Cooling oil circuit; 2802. Condenser;

[0052] 2803, First filter; 2804, Second hydraulic pump;

[0053] 2805. Oil temperature sensor; 290. Fluid replenishment system;

[0054] 2901, Level gauge; 2902, Liquid replenishment pipeline. Detailed Implementation

[0055] First, it should be noted that in the description of this invention, the terms "upper," "lower," "left," "right," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0056] Please refer to Figure 1 As shown, it illustrates the specific structure of a preferred embodiment of the present invention, including a main oil tank 10 and a stamping cylinder 20.

[0057] The stamping cylinder 20 includes an upper cylinder 21 and a lower cylinder 22. The upper cylinder 21 includes an inner cylinder 211 and an outer cylinder 212 located on the outer periphery of the inner cylinder 211. The inner cylinder 211 and the outer cylinder 212 are respectively connected to an inner cylinder oil passage 201 and an outer cylinder oil passage 202. The main oil tank 10 is connected to a first main oil passage 101. The first main oil passage 101 is connected to the upper cylinder main oil passage 102 and the lower cylinder oil passage 203 connected to the lower cylinder 22 through a first two-position cartridge valve 30. The upper cylinder main oil passage 102 is connected to the inner cylinder oil passage 201 and the main oil tank 10 through a second two-position cartridge valve 40. The outer cylinder oil passage 202 is connected to the inner cylinder oil passage 201 through a cartridge valve 50.

[0058] Among them, the first and second position cartridge valves 30, the second and second position cartridge valves 40, and the cartridge valve 50 are all controlled by solenoid valves. During the pressurization process, oil is supplied to the upper cylinder 21 and oil is discharged from the lower cylinder 22 at the same time, so that a pressure difference is formed between the upper cylinder 21 and the lower cylinder 22. The stamping cylinder 20 moves down to pressurize the product. During the depressurization process, oil is supplied to the lower cylinder 22 and oil is discharged from the upper cylinder 21 at the same time, so that a pressure difference is formed between the upper cylinder 21 and the lower cylinder 22. The stamping cylinder 20 moves up to depressurize the product.

[0059] The upper cylinder main oil circuit 102 is connected to a control oil circuit 103 for adjusting the oil flow. The control oil circuit 103 is sequentially equipped with a pre-solenoid valve 60 and a first servo proportional valve 70. The outlet of the first servo proportional valve 70 is connected to the main oil tank 10. The pre-solenoid valve 60 can control the opening and closing of the oil circuit. The first servo proportional valve 70 can adjust the oil flow by changing the relative position of the valve core in the valve body, thereby controlling the speed of the pressurization and depressurization process.

[0060] The main oil tank 10 is also connected to a second main oil circuit 104 and a third main oil circuit 105. A dual pump 80 is installed on the first main oil circuit 101 and the second main oil circuit 104. A first hydraulic pump 90 is installed on the third main oil circuit 105. The first main oil circuit 101, the second main oil circuit 104, and the third main oil circuit 105 are connected to a pressure-replenishing main oil circuit 106. The pressure-replenishing main oil circuit 106 is connected to the lower cylinder oil circuit 203 and the inner cylinder oil circuit 201 respectively through a second servo proportional valve 100. The pressure-replenishing main oil circuit 106 can selectively replenish oil for the inner cylinder 211 and the lower cylinder 22.

[0061] Specifically, the first main oil passage 101, the second main oil passage 104, and the third main oil passage 105 are each equipped with a first one-way valve 110 that unidirectionally flows toward the stamping cylinder 20. The pressure-replenishing main oil passage 106 is equipped with a second one-way valve 120 that unidirectionally flows toward the stamping cylinder 20 between the second main oil passage 104 and the third main oil passage 105. The pressure-replenishing main oil passage 106 is equipped with a first solenoid valve 130 between the second one-way valve 120 and the second main oil passage 104. The second servo proportional valve 100 is connected to the lower cylinder oil passage 203 and the inner cylinder oil passage 201 respectively through the first pressure-replenishing oil passage 1001 and the second pressure-replenishing oil passage 1002. The first pressure-replenishing oil passage 100... Both the first and second pressure replenishing oil circuits 1001 and 1002 are equipped with a two-stage check valve 140 that unidirectionally flows toward the stamping cylinder 20. The first pressure replenishing oil circuit 1001 is equipped with a two-position two-way directional valve 150 on the input side of the two-stage check valve 140. The second servo proportional valve 100 can adjust the oil flow of the main pressure replenishing oil circuit 106 as needed. By controlling the position of its valve core, the main pressure replenishing oil circuit 106 can be opened and closed. When replenishing oil to the upper cylinder 21, the stamping cylinder 20 is pressurized. When replenishing oil to the lower cylinder 22, the stamping cylinder 20 is depressurized. The two-position two-way directional valve 150 can be used to close the emergency oil circuit. The two-stage check valve 140 can be used to prevent oil backflow.

[0062] Preferably, an overflow oil passage 107 connected to the main oil tank 10 is provided between the first check valve 110 of the second main oil passage 104 and the third main oil passage 105 and the main oil tank 10. The overflow oil passage 107 is provided with an overflow structure, which includes an overflow valve 160 and a second solenoid valve 170 for controlling the overflow valve 160. A second oil filter 180 is provided on the input side of the overflow structure of the second main oil passage 104 and the third main oil passage 105.

[0063] Both the inner cylinder oil passage 201 and the outer cylinder oil passage 202 are equipped with a first hydraulic control check valve 190. The first hydraulic control check valve 190 is connected to a first pressure relief oil passage 1901 connected to the second main oil passage 104. The first pressure relief oil passage 1901 is equipped with a filling valve 200 for controlling the opening and closing of the oil port of the first hydraulic control check valve 190.

[0064] Specifically, the filling valve 200 is a two-position four-way directional valve. The second main oil circuit 104, the main oil tank 10, and the first hydraulically controlled check valve 190 are all connected to the two-position four-way directional valve. The two-position four-way directional valve is also connected to a reverse check valve 210. When the filling valve 200 is open, the dual pump 80 drives the oil to open the first hydraulically controlled check valve 190, thereby releasing the pressure of the pressurized cylinder 20. When the filling valve 200 is closed, the first hydraulically controlled check valve 190 is connected to the main oil tank 10, and there is no external pressure at the first hydraulically controlled check valve 190. Normal operation, with forward flow and reverse cut-off, prevents backflow of oil in the pressurizing cylinder 20. When the filling valve 200 is open, the first servo proportional valve 70 acts as a pressure reducing valve. By adjusting the position of the valve core, the pressure reducing rate can be controlled. When the filling valve 200 is closed, its inlet is connected to the reverse check valve 210. The reverse check valve 210 prevents oil from flowing back to the oil tank, maintaining the pressure inside the oil circuit. This ensures that the first hydraulic control check valve 190 can be quickly opened when the filling valve 200 is opened next time, and also makes the oil circuit pressure stable, without generating huge pressure fluctuations that could damage the pump.

[0065] The inner cylinder oil passage 201 and the outer cylinder oil passage 202 are connected together between the first hydraulic check valve 190 and the stamping cylinder 20 to a second pressure relief oil passage 108 connected to the main oil tank 10. The second pressure relief oil passage 108 is equipped with a PT throttle valve 220 and a reversing switch valve 230. The reversing switch valve 230 is located on the side of the PT throttle valve 220 closer to the main oil tank 10.

[0066] Specifically, the inner cylinder oil passage 201 and the outer cylinder oil passage 202 are connected to the second pressure relief oil passage 108 through the first branch 204 and the second branch 205, respectively. The first branch 204 and the second branch 205 are each provided with a third one-way valve 240 that unidirectionally flows toward the main oil tank 10. When the stamping cylinder 20 is pressurized, the PT throttle valve 220 adjusts the speed according to the oil pressure. When the stamping cylinder 20 is depressurized, the damping orifice of the PT throttle valve 220 acts as a pressure buffer until the oil pressure drops to the required stabilizing pressure. Then, the second pressure relief oil passage 108 is closed by the reversing switch valve 230 to maintain the pressure inside the stamping cylinder 20.

[0067] Among them, the PT throttle valve 220 and the reversing switch valve 230 act as pressure reducing valves with buffer function. The second pressure relief oil circuit 108 has the functions of throttling buffer and pressure gradual change control, which can prevent pressure oscillation caused by sudden load changes, realize autonomous pressure reduction and automatic pressure stabilization, realize accurate control of pressurization rate and slow pressure reduction to accurately control the pressure holding pressure, avoid damage to pipeline components by hydraulic shock, realize slow pressure relief and rapid pressure stabilization, and also play a role in maintaining a stable pressurization rate during pressurization.

[0068] Pressure reducing structures are provided on the first main oil circuit 101 and the lower cylinder oil circuit 203. The pressure reducing structures include a second hydraulic control check valve 250 and a third solenoid valve 260 that controls the second hydraulic control check valve 250. The second hydraulic control check valve 250 will automatically open when the value exceeds the threshold during operation, thereby realizing pressure relief. Pressure sensors 270 are provided on the upper cylinder main oil circuit 102, the inner cylinder oil circuit 201, and the outer cylinder oil circuit 202.

[0069] The main oil tank 10 is also connected to a cooling system 280. The cooling system 280 includes a cooling oil circuit 2801 connected in a closed loop to the main oil tank 10, and a condenser 2802, a first filter 2803, and a second hydraulic pump 2804 sequentially arranged on the cooling oil circuit 2801. The cooling system 280 also includes an oil temperature sensor 2805 for monitoring the oil temperature in the main oil tank 10. The oil temperature sensor 2805 monitors the oil temperature in the main oil tank 10 in real time. When the temperature is too high, the second hydraulic pump 2804 starts, so that the oil passes through the condenser 2802 and the first filter 2803 in sequence and returns to the main oil tank 10 for circulation cooling. When the oil temperature drops to a set level, the second hydraulic pump 2804 stops.

[0070] The main oil tank 10 is also connected to a fluid replenishment system 290. The fluid replenishment system 290 includes a level gauge 2901 for monitoring the amount of oil in the main oil tank 10. The level gauge 2901 is connected to a fluid replenishment pipe 2902. By monitoring the amount of oil in the main oil tank 10 through the level gauge 2901, manual fluid replenishment is prompted or automatic fluid replenishment is controlled to maintain a sufficient amount of oil in the main oil tank 10 and maintain the normal operation of the hydraulic system.

[0071] The key design focus of this invention is:

[0072] Its main features include an outer cylinder oil circuit connected to an inner cylinder oil circuit via a cartridge valve, allowing oil to be supplied to the inner cylinder first during pressurization, and then to the outer cylinder after reaching the preset pressure. The inner and outer cylinder design enables controllability of the pressure relief range of the pressurized cylinder. Combined with a first pressure relief oil circuit, when pressure adjustment is needed, only the corresponding filling valve of the inner cylinder needs to be opened to achieve small-range pressure regulation. The pressure fluctuation is less than when the corresponding filling valve of the outer cylinder is opened. Furthermore, when the filling valve is open, the servo proportional valve acts as a pressure reducing valve, controlling the pressure reduction rate. Additionally, the second pressure relief oil circuit has throttling buffer and pressure gradual change control functions, preventing pressure oscillations caused by sudden load changes, enabling autonomous pressure reduction and automatic pressure stabilization. The PT throttling valve and the reversing switch valve act as pressure reducing valves with buffering functions, resulting in good stability of the pressurization rate and small pressure fluctuations during pressure relief.

[0073] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the technical scope of the present invention. Therefore, any minor modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A hydraulic system for stabilizing and maintaining pressure in a hot-pressed sintered aluminum nitride heater, comprising a main oil tank and a pressing cylinder, the pressing cylinder comprising an upper cylinder and a lower cylinder, the upper cylinder comprising an inner cylinder and an outer cylinder located on the outer periphery of the inner cylinder, the inner cylinder and the outer cylinder being respectively connected to an inner cylinder oil circuit and an outer cylinder oil circuit; characterized in that: The main oil tank is connected to a first main oil circuit. The first main oil circuit is connected to the upper cylinder main oil circuit and the lower cylinder oil circuit connected to the lower cylinder through a first two-position cartridge valve. The upper cylinder main oil circuit is connected to the inner cylinder oil circuit and the main oil tank through a second two-position cartridge valve. The outer cylinder oil circuit is connected to the inner cylinder oil circuit through a cartridge valve. The upper cylinder main oil circuit is connected to a control oil circuit for adjusting the oil flow. The control oil circuit is sequentially equipped with a front solenoid valve and a first servo proportional valve. The outlet of the first servo proportional valve is connected to the main oil tank. The main oil tank is also connected to a second main oil circuit and a third main oil circuit. A dual pump is installed on the first main oil circuit and the second main oil circuit together. A first hydraulic pump is installed on the third main oil circuit. The first main oil circuit, the second main oil circuit, and the third main oil circuit are connected to a pressure-replenishing main oil circuit. The pressure-replenishing main oil circuit is connected to the lower cylinder oil circuit and the inner cylinder oil circuit respectively through a second servo proportional valve. The pressure-replenishing main oil circuit can selectively replenish oil for the inner cylinder and the lower cylinder. Both the inner cylinder oil circuit and the outer cylinder oil circuit are equipped with a first hydraulically controlled check valve. The first hydraulically controlled check valve is connected to a first pressure relief oil circuit connected to the second main oil circuit. The first pressure relief oil circuit is equipped with a filling valve for controlling the opening and closing of the oil port of the first hydraulically controlled check valve. The filling valve is a two-position four-way directional valve. The second main oil circuit, the main oil tank, and the first hydraulically controlled check valve are all connected to the two-position four-way directional valve. The two-position four-way directional valve is also connected to a reverse check valve. When the filling valve is open, the dual pump drives the oil to push open the first hydraulically controlled check valve, thereby realizing the pressure relief of the pressurized oil cylinder. When the filling valve is closed, the first hydraulically controlled check valve is connected to the main oil tank and the first hydraulically controlled check valve works normally. The inner cylinder oil circuit and the outer cylinder oil circuit are connected together between the first hydraulic check valve and the stamping cylinder to a second pressure relief oil circuit connected to the main oil tank. The second pressure relief oil circuit is equipped with a PT throttle valve and a reversing switch valve. The reversing switch valve is located on the side of the PT throttle valve closer to the main oil tank. The inner cylinder oil circuit and the outer cylinder oil circuit are connected to the second pressure relief oil circuit through a first branch and a second branch, respectively. Both the first branch and the second branch are equipped with a third check valve that unidirectionally flows towards the main oil tank. When the stamping cylinder is pressurized, the PT throttle valve adjusts the speed according to the oil pressure. When the stamping cylinder is depressurized, the damping orifice of the PT throttle valve acts as a pressure buffer until the oil pressure drops to the required stabilizing pressure. Then, the reversing switch valve closes the second pressure relief oil circuit to maintain the pressure inside the stamping cylinder.

2. The hydraulic system for stabilizing and maintaining pressure in a hot-pressed sintered aluminum nitride heater according to claim 1, characterized in that: Each of the first main oil circuit, the second main oil circuit, and the third main oil circuit is equipped with a first one-way valve that unidirectionally flows toward the stamping cylinder. The pressure replenishing main oil circuit is equipped with a second one-way valve that unidirectionally flows toward the stamping cylinder between the second main oil circuit and the third main oil circuit. The pressure replenishing main oil circuit is equipped with a first solenoid valve between the second one-way valve and the second main oil circuit.

3. The hydraulic system for stabilizing and maintaining pressure in a hot-pressed sintered aluminum nitride heater according to claim 2, characterized in that: The first check valve of the second main oil circuit and the third main oil circuit are both provided with an overflow oil circuit connected to the main oil tank, and the overflow oil circuit is provided with an overflow structure.

4. The hydraulic system for stabilizing and maintaining pressure in a hot-pressed sintered aluminum nitride heater according to claim 1, characterized in that: The second servo proportional valve is connected to the lower cylinder oil circuit and the inner cylinder oil circuit through the first and second supplementary pressure oil circuits respectively. The first and second supplementary pressure oil circuits are each equipped with a two-stage check valve that unidirectionally flows toward the stamping cylinder. A two-position two-way directional valve is provided on the input side of the two-stage check valve in the first supplementary pressure oil circuit.

5. A hydraulic system for stabilizing and maintaining pressure in a hot-pressed sintered aluminum nitride heater according to claim 1, characterized in that: Both the first main oil circuit and the lower cylinder oil circuit are equipped with pressure reducing structures.

6. A hydraulic system for stabilizing and maintaining pressure in a hot-pressed sintered aluminum nitride heater according to claim 1, characterized in that: Pressure sensors are installed in the main oil circuit of the upper cylinder, the oil circuit of the inner cylinder, and the oil circuit of the outer cylinder.

7. A hydraulic system for stabilizing and maintaining pressure in a hot-pressed sintered aluminum nitride heater according to claim 1, characterized in that: The main oil tank is also connected to a cooling system, which includes a cooling oil circuit connected in a closed loop to the main oil tank and a condenser, a first filter, and a second hydraulic pump arranged sequentially on the cooling oil circuit. The cooling system also includes an oil temperature sensor for monitoring the oil temperature in the main oil tank.

8. A hydraulic system for stabilizing and maintaining pressure in a hot-pressed sintered aluminum nitride heater according to claim 1, characterized in that: The main oil tank is also connected to a fluid replenishment system, which includes a level gauge for monitoring the amount of oil in the main oil tank.

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