A full hydrogen bell-type furnace load space air tightness automatic detection device and use method

Abstract

The present invention relates to an automatic detection device for the air tightness of the load space of a full hydrogen hood-type furnace and a method for using the same. An automatic detection device for the air tightness of the load space of a full hydrogen hood-type furnace comprises an inner cover, a pressure sensor, a temperature sensor, a small flow nitrogen valve, an exhaust valve, and a programmable logic controller. A method for using an automatic detection device for the air tightness of the load space of a full hydrogen hood-type furnace comprises the following steps: Step 1: Establishing and standing the pressure; Step 2: After the standing is completed, entering the tightness inspection process; Step 3: The normal pressure range for the tightness inspection is given by the programmable logic controller. The present invention effectively solves the problem of automatic detection of the seal of the full hydrogen hood-type furnace in each production cycle, and ensures the safety and efficiency of the production of the full hydrogen hood-type furnace. It has been verified in practice that the effect is fully achieved.

Description

Technical Field

[0001] The invention relates to an automatic detection device for air tightness of a load space of a full hydrogen bell-type furnace and a use method thereof. Background Art

[0002] The full hydrogen bell-type furnace is an annealing furnace that uses hydrogen. During the annealing process, the inner cover, that is, the load space, is filled with pure hydrogen. There is no doubt that the seal must be absolutely guaranteed, so the airtightness test must be carried out. The general conventional airtightness test is to establish a specified pressure in the container or space at a static room temperature, and then observe the pressure drop per unit time. If the pressure drop is within the specified range, it is qualified. The airtightness test of the full hydrogen bell-type furnace has its particularity: 1. The test is carried out in each production cycle, and it must be carried out automatically. After the bell-type furnace completes a production cycle, that is, completes the annealing of a furnace of materials, it is necessary to open the inner cover, reload new materials, and then buckle the inner cover to re-form a closed space to prepare for the next furnace annealing. At this time, the airtightness test begins. The bell-type furnace exists in the form of a furnace group, and large-scale continuous production must be able to automatically cope with this situation. 2. The test is carried out with materials, and the physical conditions of the materials loaded in each furnace are different, that is, their temperature, weight, volume, etc. are all different. Especially the temperature has a direct impact on the pressure of the closed space. 3. Not only will the pressure drop exceed the regulations and be unqualified, but the pressure rise will also fail the close inspection: the hood-type furnace is connected to a number of media, discharge pipes and valves. After the inner cover is fastened and compressed, these valves become the gateway for the load space to interact with the outside world. The pressure of some media is greater than the normal furnace pressure, so if these valves leak, the furnace pressure will rise instead of falling. Therefore, the airtightness test not only limits the pressure drop, but also the abnormal pressure rise. 4. The airtightness test of the full hydrogen hood-type furnace is not an idle static inspection, but a relatively dynamic test that is automatically carried out during the production process and takes into account various factors affecting the pressure. Therefore, the pressure standard is not a static range, but a relative static range that takes into account the normal pressure fluctuations caused by temperature changes and is maintained in a retention range. This patent is a method that can meet the above conditions. Summary of the invention

[0003] The purpose of the present invention is to solve the above problems and provide a device and method for automatically detecting the air tightness of the load space of a full hydrogen bell-type furnace.

[0004] The object of the present invention is achieved as follows: an automatic detection device for the air tightness of the load space of a full hydrogen bell-type furnace comprises an inner cover, a pressure sensor, a temperature sensor, a small flow nitrogen valve, a discharge valve, and a programmable logic controller. An air intake pipe and a discharge pipe are arranged below the inner cover. The pressure sensor is installed on the discharge pipe, and the pressure sensor signal is sent to the programmable logic controller. The temperature sensor is installed in the inner cover of the load space, and the temperature sensor signal is sent to the programmable logic controller. The small flow nitrogen valve is installed on the air intake pipe, and the discharge valve is installed on the discharge pipe. Both valves are controlled by the programmable logic controller.

[0005] A method for using an automatic air tightness detection device for a full hydrogen bell-type furnace load space comprises the following steps: Step 1: pressure establishment and standing: When a furnace annealing process reaches the air tightness detection stage, firstly, pressure is established in the load space, i.e., the inner hood, and the pressure is equal to the load space pressure balance point under normal production state, which is 47.5% of the load space pressure upper limit alarm value. If the load space pressure is lower than this value, a small flow nitrogen valve is opened, and nitrogen is added to increase the pressure. When the upper limit alarm value is reached, the valve is closed. If the load space pressure is greater than this value, a discharge valve is opened to reduce the pressure. When the upper limit alarm value is reached, the valve is closed. After the pressure is reached, all valves are closed and the pressure is kept standing for 1-5 minutes. If the load space pressure is kept within plus or minus 2.5% of this value, i.e., 45-50% of the upper limit alarm value, the air tightness detection process is started. If the load space pressure does not reach the upper limit alarm value, the valve is closed. This value is 47.5% of the upper alarm value of the load space pressure, or if it reaches and cannot be maintained within the specified range, plus or minus 2.5% of this value, that is, 45-50% of the upper alarm value, an alarm will be sounded after 30-60 minutes, and the tightness inspection has failed. It can be repeated after troubleshooting; Step 2: After the static state is completed, the tightness inspection process begins. At this time, all valves remain closed. The only factor affecting the load space pressure in the sealed state is the temperature. The programmable logic controller immediately gives the upper and lower limits of the pressure that should be maintained at the current temperature, that is, the tightness inspection pressure range. This process is maintained for 10-20 minutes, that is, within 10-20 minutes, if the load space pressure does not exceed the limit, the tightness inspection passes and enters the next step. Otherwise, the load space leaks and an alarm will be sounded. This process can be repeated after troubleshooting; if this process is not completed within 30-60 minutes, the same alarm will be sounded, and the load space leaks. After troubleshooting, the tightness inspection process can be started again from step 1, that is, pressure establishment. Step 3: The normal pressure range of the close inspection is given by the programmable logic controller: Based on the Clapeyron equation: PV=(m / M)RT, where R is the universal gas constant, m / M is the molar number, and V is the volume; the close inspection is in a closed state, the inlet and outlet valves are fully closed, the molar number m / M and the volume V remain unchanged here, and it is concluded that for the bell-type furnace load space during the close inspection, T / P remains unchanged, that is, the ratio of temperature to pressure at a certain moment is equal to the ratio of temperature to pressure at another moment: T1 / P1=T2 / P2, the temperature unit here is Kelvin, and the pressure refers to the absolute pressure, and the temperature is expressed in degrees. The units of the measured values ​​of the load and pressure sensors are: (dT+273) / 273=(dP+1013) / 1013, where dT is the difference between the instantaneous temperature of the load space and the starting temperature, in degrees Celsius; dP is the difference between the instantaneous pressure of the load space and the starting pressure, in mbar, 273 is the Kelvin temperature scale, and 1013 is the standard atmospheric pressure under absolute zero, in mbar. This is the basic theoretical formula for calculating pressure and temperature, that is, the pressure range of the precision inspection. When calculating the instantaneous reference pressure during the precision inspection, the empirical approximation formula is used:

[0006] (Ta - Ts + 273)*(Ps + 250) / 273-250, where Ta and Ts are the instantaneous temperature and starting temperature of the load space respectively, in degrees Celsius; Ps is the starting pressure of the load space, in mbar. The above formula calculates the reference pressure at each moment during the dense inspection process. When performing dense inspection, add or subtract 7 to 10 mbar from the reference pressure to form the pressure range of the dense inspection process.

[0007] Furthermore, a detection cycle is 30-60 minutes, that is, if any one of step 1, step 2 and step 3 is not completed and the secret check fails within 30-60 minutes, an alarm will be issued after 30-60 minutes indicating that the secret check has failed, and the process needs to be repeated after troubleshooting.

[0008] Further speaking, the pressure sensor is a pressure transmitter.

[0009] Furthermore, the temperature sensor is a thermocouple.

[0010] Furthermore, the small flow nitrogen valve is a pneumatic two-position valve with a solenoid valve, and the solenoid valve is controlled by a programmable logic controller to control the opening and closing of the small flow nitrogen valve.

[0011] Further, the discharge valve is a pneumatic two-position valve with a solenoid valve, and the solenoid valve is controlled by a programmable logic controller to control the opening and closing of the discharge valve.

[0012] The beneficial effect of the present invention is that the present invention effectively solves the problem of automatic seal detection in each production cycle of the full hydrogen bell-type furnace, and ensures the production safety and efficiency of the full hydrogen bell-type furnace. It has been verified in practice that the effect is fully achieved. DETAILED DESCRIPTION

[0013] In the production process of the full hydrogen bell-type furnace, the air tightness of the load space (inside the inner cover) is reliably detected to ensure safety. The hardware of this method consists of a pressure sensor, a temperature sensor, a small flow nitrogen valve, a discharge valve, a Siemens S7-300PLC, pipes and connections. The pressure sensor uses a pressure transmitter and is installed on the discharge pipe connected to the load space. In this way, the pressure of the load space is measured, and the signal is sent to the analog input module of the S7-300PLC. The temperature sensor uses a thermocouple, which is installed (inserted) in the inner cover to measure the temperature in the load space, and the signal is sent to the analog input module of the S7-300PLC. The small flow nitrogen valve is a pneumatic two-position valve with a solenoid valve, which is used to replenish a small amount of air in the load space when necessary to make it reach the starting pressure of the test. The solenoid valve is controlled by the relevant digital output signal of the S7-300PLC to control the opening and closing of the valve. The discharge valve is also a pneumatic two-position valve with a solenoid valve, which is used to release the pressure of the load space. Similarly, the solenoid valve is controlled by the relevant digital output signal of S7-300PLC, thereby controlling the opening and closing of the valve. The entire inspection process is automatic and the whole process is controlled by Siemens S7-300PLC.

[0014] 1. Pressure establishment and static: When a furnace annealing process reaches the airtightness detection stage, the pressure is first established in the inner cover (load space). The pressure is the load space pressure balance point under normal production conditions, which is about half of the load space pressure upper limit alarm value. In this example, the load space pressure upper limit alarm value is 95 mbar, and the pressure to be established is set at 45 mbar. If the load space pressure is lower than this value, the nitrogen small flow valve is opened, and nitrogen is added to increase the pressure, and it is closed when it reaches 45mbar; if the load space pressure is greater than this value, the outlet discharge valve is opened to reduce the pressure, and it is closed when it reaches 45mbar.

[0015] After the pressure is reached, all inlet and outlet valves are closed and the system enters a static holding state. This process takes 2 minutes. If the load space pressure does not exceed 48 mbar and does not fall below 44 mbar within two minutes, the tightness inspection process begins.

[0016] If the load space pressure never reaches 45mbar or reaches it but cannot be maintained for 2 minutes, an alarm will sound after 45 minutes and the inspection will fail. You can try again after troubleshooting.

[0017] 2. After the static state is completed, the close inspection process begins. At this time, all inlet and outlet valves remain closed, and the only factor affecting the load space pressure should be temperature. Siemens S7-300PLC immediately gives the upper and lower limits of the pressure that should be maintained at the current temperature. This process takes 15 minutes. That is, within 15 minutes, if the load space pressure does not exceed the limit, the close inspection passes and enters the next step; otherwise, the load space leaks and alarms. It can be restarted after troubleshooting. Of course, if the close inspection process is not completed within 45 minutes, the same alarm will be sounded: load space leaks. After troubleshooting, the whole process can be restarted, starting from the pressure buildup.

[0018] The pressure range is calculated by Siemens S7-300PLC. Based on the Clapeyron equation: PV=(m / M)RT. Where R is the universal gas constant, m / M is the molar number, and V is the volume. Obviously, the closed state during the close inspection, the inlet and outlet valves are fully closed, and the molar number m / M and volume V remain unchanged here. Therefore, it can be concluded that for the bell-type furnace load space during the close inspection, T / P remains unchanged. That is, the ratio of temperature to pressure at a certain moment is equal to the ratio of temperature to pressure at another moment: T1 / P1=T2 / P2. However, the temperature unit here is Kelvin, and the pressure refers to absolute pressure. Therefore, it is expressed in the units of temperature and pressure sensor measurement values: (dT+273) / 273=(dP+1013) / 1013, where dT is the difference between the instantaneous temperature and the starting temperature of the load space, in degrees Celsius; dP is the difference between the instantaneous pressure and the starting pressure of the load space, in mbar. 273 is the Kelvin temperature scale, 1013 is the standard atmospheric pressure below absolute zero, unit is mbar (the difference between the gauge pressure and the absolute pressure is one standard atmospheric pressure). This is the basic theoretical formula for calculating pressure and temperature, that is, the pressure range of the close inspection. When actually calculating the instant reference pressure during the close inspection process, the empirical approximation formula is used: (Ta - Ts + 273)*(Ps + 250) / 273-250, where Ta and Ts are the instant temperature and starting temperature of the load space, respectively, in degrees Celsius; Ps is the starting pressure of the load space, unit is mbar.

[0019] The above formula calculates the reference pressure at each moment during the close inspection process. During the close inspection, 7 to 10 mbar is added or subtracted from the reference pressure to form the pressure range of the close inspection process, namely the "close inspection process curve". However, when the reference pressure is greater than 48 mbar, the upper limit of the pressure is always set to 70 mbar. Example

[0020] The production and operation of each bell-type furnace is completed by a fixed furnace table and a matching inner cover, heating cover, and cooling cover. The bell-type structure is used because it better solves the sealing problem of hydrogen, so bell-type furnaces are more used for annealing in full hydrogen atmosphere, so they are often called "full hydrogen bell-type annealing furnaces". Before the start of each annealing production cycle, the annealing material (such as steel coils) is placed on the furnace table, and then the inner cover is buckled. It is hydraulically compressed. The inner cover is a cylindrical cover with an open bottom, which covers the annealing material on the furnace table and achieves sealing. The space inside the inner cover for the annealing material is professionally called the "load space". During the annealing process, this space must be filled with pure hydrogen.

[0021] The furnace table is a fixed structure with a furnace table motor and an impeller. The annealing material (steel coil) is placed on it, and the inner cover is buckled on it to form a load space. Small flow nitrogen enters the load space from the bottom of the furnace table along the axial pipe of the furnace table fan; and the exhaust pipe is formed by connecting the pipe at a hole on the furnace table. These two channels are or pass through the furnace table, that is, under the inner cover. So to be precise, the furnace table under the load space in the inner cover is connected with the intake pipe and the discharge pipe. The small flow nitrogen pipeline (intake pipeline) and the discharge pipeline of each furnace table are drawn out from the bottom of the furnace table, and are respectively connected to the nitrogen source pipeline (nitrogen main pipeline) and the main discharge pipeline to the outside of the workshop. The small flow nitrogen valve is installed on the connecting pipeline between the nitrogen source pipeline and the furnace table; similarly, the discharge valve is also installed on the connecting pipeline between the main discharge pipeline and the furnace table, and the pressure transmitter is installed in front of the discharge valve, that is, close to the furnace table. Since the discharge pipeline and the load space are connected, the pressure measured here is the pressure of the load space. It can be seen that although these two pipelines (small flow nitrogen and exhaust) pass through the bottom of the furnace, the load space can still remain sealed.

[0022] The temperature sensor (thermocouple) has an eye on the furnace table. The thermocouple is inserted into the load space to transmit the temperature signal to the programmable logic controller. The outlet of this eye is also sealed.

[0023] The small flow nitrogen valve is installed on the small flow nitrogen pipeline entering the furnace; the discharge valve is installed on the exhaust pipeline of each furnace; the pressure sensor is also installed on the exhaust pipeline of each furnace, between the discharge valve and the furnace.

[0024] After the sealing test and gas replacement are completed, a heating hood should be buckled on the outside of the inner cover. This heating hood is also a cylindrical shape with an open bottom, but it is equipped with components and pipes required for combustion, which is equivalent to a small movable heating furnace. It also forms a space between it and the inner cover, namely the combustion chamber. The heating hood heats the annealing material in the inner cover. After completion, the heating hood is removed, and then a cooling hood is buckled on the outside of the inner cover. The cooling hood has a fan to form air convection between the cooling hood and the inner cover for cooling. After cooling, the hydrogen in the inner cover is replaced, and the inner cover can be removed, and an annealing cycle of this furnace is completed. Then unload, reload, buckle the inner cover, and perform sealing test..., and repeat over and over again.

[0025] Bell-type furnaces usually exist in the form of furnace groups, that is, several furnaces share a set of media and pipelines, so there are concepts of nitrogen source pipelines (nitrogen main pipelines) and main emission pipelines. For example, the application site in this case currently has more than 100 full hydrogen bell-type furnaces, divided into 6 furnace groups, which is the world's largest full hydrogen bell-type furnace stainless steel annealing base.

[0026] This method of automatic detection of air tightness of the load space of the full hydrogen bell-type furnace has been put into use in the bell-type furnace of the hot rolling mill of Taigang. The Siemens S7-300PLC-CPU model used is: 315-2DP; the analog input module model is: 6ES7 331-7KF02-0AB0 (receiving temperature and pressure signals); the digital output module model is: 6ES7 322-1HF10-0AA0 (valve action command output); the valve is a pneumatic two-position valve with a solenoid valve.

[0027] Entering the close inspection stage, the pressure transmitter transmits the load space pressure analog signal to the PLC in real time. In the PLC, the base pressure is set to 45 mbar. If the load space pressure is lower than this value, the nitrogen small flow valve is opened, and nitrogen is added to increase the pressure, and it is closed when it reaches 45 mbar; if the load space pressure is greater than this value, the outlet discharge valve is opened to reduce the pressure, and it is closed when it reaches 45 mbar.

[0028] After the pressure is reached, all inlet and outlet valves are closed and the system enters a static holding state. This process takes 2 minutes. If the load space pressure does not exceed 48 mbar and does not fall below 44 mbar within two minutes, the tightness inspection process begins, that is, the upper and lower limits of the tightness inspection pressure are calculated and compared with the actual value of the load space pressure.

[0029] At this time, all inlet and outlet valves remain closed, and the only factor affecting the load space pressure should be temperature. The upper and lower limits of the pressure that should be maintained at the current temperature are given immediately. This process takes 15 minutes. That is, within 15 minutes, if the load space pressure does not exceed the limit, the close inspection passes and enters the next process; otherwise, an alarm is issued: the load space is leaking.

[0030] The whole inspection period is 45 minutes. That is, if the load space pressure does not reach 45mbar or reaches but cannot be maintained for 2 minutes, or if the load space pressure exceeds the upper or lower limit during the 15-minute inspection and the inspection cannot be completed, the inspection will be terminated and an alarm will be issued after 45 minutes. After investigation and treatment by relevant professionals, the whole inspection process can be carried out again.

[0031] If everything meets the requirements, the PLC will give a signal that the inspection is complete and production will proceed to the next process.

[0032] The pressure range is given by PLC calculation. Based on the Clapeyron equation: PV=(m / M)RT. Where R is the universal gas constant, m / M is the molar number, and V is the volume. Obviously, the closed state during the close inspection, the inlet and outlet valves are fully closed, and the molar number m / M and volume V remain unchanged here. Therefore, it can be concluded that for the bell-type furnace load space during the close inspection, T / P remains unchanged. That is, the ratio of temperature to pressure at a certain moment is equal to the ratio of temperature to pressure at another moment: T1 / P1=T2 / P2. However, the temperature unit here is Kelvin, and the pressure refers to absolute pressure. Therefore, it is expressed in the units of temperature and pressure sensor measurement values: (dT+273) / 273=(dP+1013) / 1013, where dT is the difference between the instantaneous temperature of the load space and the starting temperature, in degrees Celsius; dP is the difference between the instantaneous pressure of the load space and the starting pressure, in mbar. 273 is the Kelvin temperature scale, and 1013 is the standard atmospheric pressure below absolute zero, in mbar (the difference between the gauge pressure and the absolute pressure is one standard atmospheric pressure). This is the basic theoretical formula for calculating pressure and temperature, that is, the pressure range of the close inspection. When actually calculating the instant reference pressure during the close inspection process, the empirical approximation formula is used: (Ta -Ts + 273)*(Ps + 250) / 273-250, where Ta and Ts are the instant temperature and starting temperature of the load space, in degrees Celsius; Ps is the starting pressure of the load space, in mbar.

[0033] The above formula calculates the reference pressure at each moment during the close inspection process. During the close inspection, 7 to 10 mbar is added or subtracted from the reference pressure to form the pressure range of the close inspection process, namely the "close inspection process curve". One thing is that when the reference pressure is greater than 48 mbar, the upper pressure limit is always set to 70 mbar.

[0034] The bell-type furnace solves the hydrogen sealing problem relatively economically, and is therefore widely used in all-hydrogen mid-to-high-end annealing. Load space airtightness detection is a necessary step to achieve this. The large-scale all-hydrogen bell-type furnace annealing production airtightness detection has its own characteristics. This method describes: PLC automatic control, establishment of reference pressure, setting of static holding time, formulation of upper and lower pressure limits and monitoring, and formulation of the entire detection cycle time. This method of automatic detection of airtightness of the load space of the all-hydrogen bell-type furnace has effectively solved the effect of temperature on pressure. In the production process of the all-hydrogen bell-type furnace, the load space (inside the inner hood) is automatically and reliably detected to ensure safe production. At the same time, the linkage relationship between equal volume gas pressure and temperature also has a certain reference value for airtightness detection and control of other equipment under similar circumstances.

[0035] The above description is only a specific embodiment of the present invention, but the structural features of the protection scope of the present invention are not limited thereto. Any changes or modifications made by any technician in the field of the present invention are all covered by the patent scope of the present invention.

Claims

1. An automatic detection device for the air tightness of the load space of a full hydrogen bell-type furnace, characterized in that: It includes an inner cover, a pressure sensor, a temperature sensor, a small flow nitrogen valve, a discharge valve, and a programmable logic controller. An air intake pipe and a discharge pipe are arranged below the inner cover. The pressure sensor is installed on the discharge pipe, and the pressure sensor signal is sent to the programmable logic controller. The temperature sensor is installed in the inner cover of the load space, and the temperature sensor signal is sent to the programmable logic controller. The small flow nitrogen valve is installed on the air intake pipe, and the discharge valve is installed on the discharge pipe. Both valves are controlled by the programmable logic controller. The method for using the above-mentioned full hydrogen bell-type furnace load space air tightness automatic detection device comprises the following steps: Step 1: Pressure establishment and standing: When a furnace annealing process reaches the air tightness detection stage, firstly, the pressure is established in the load space, i.e., the inner cover. The pressure is the load space pressure balance point under normal production state, which is 47.5% of the upper limit alarm value of the load space pressure. If the load space pressure is lower than this value, the small flow nitrogen valve is opened, and nitrogen is added to increase the pressure. When the upper limit alarm value is reached, the valve is closed. If the load space pressure is greater than this value, the discharge valve is opened to reduce the pressure. When the upper limit alarm value is reached, the valve is closed. After the pressure is reached, all valves are closed and the pressure is kept standing for 1-5 minutes. If the load space pressure is maintained at plus or minus 2.5% of this value, i.e., 45-50% of the upper limit alarm value, the tightness inspection process is started. If the load space pressure does not reach the upper limit alarm value, i.e., 47.5% of the upper limit alarm value of the load space pressure, or reaches but cannot be maintained within the specified range, i.e., plus or minus 2.5% of this value, i.e., 45-50% of the upper limit alarm value, the tightness inspection process is started after 30-60 minutes. The tightness inspection fails and is repeated after investigation. Step 2: After the static state is completed, the process of close inspection begins. At this time, all valves remain closed. The only factor that affects the pressure of the load space in the sealed state is the temperature. The programmable logic controller immediately gives the upper and lower limits of the pressure that should be maintained at the current temperature, that is, the close inspection pressure range. This process is maintained for 10-20 minutes. If the load space pressure does not exceed the limit within 10-20 minutes, the close inspection passes and enters the next step. Otherwise, the load space leaks and an alarm is triggered. This process can be repeated after troubleshooting. If this process is not completed within 30-60 minutes, an alarm will be triggered, indicating that the load space is leaking. After troubleshooting, the close inspection process can be restarted from step 1, that is, pressure establishment. Step 3: The normal pressure range of the close inspection is given by the programmable logic controller: Based on the Clapeyron equation: PV=(m / M)RT, where R is the universal gas constant, m / M is the molar number, and V is the volume; the close inspection is in a closed state, the inlet and outlet valves are fully closed, the molar number m / M and the volume V remain unchanged here, and it is concluded that for the bell-type furnace load space during the close inspection, T / P remains unchanged, that is, the ratio of temperature to pressure at a certain moment is equal to the ratio of temperature to pressure at another moment: T1 / P1=T2 / P2, the temperature unit here is Kelvin, and the pressure refers to the absolute pressure, and the temperature is expressed in degrees. The units of the measured values ​​of the load and pressure sensors are: (dT+273) / 273=(dP+1013) / 1013, where dT is the difference between the instantaneous temperature of the load space and the starting temperature, in degrees Celsius; dP is the difference between the instantaneous pressure of the load space and the starting pressure, in mbar, 273 is the Kelvin temperature scale, and 1013 is the standard atmospheric pressure under absolute zero, in mbar. This is the basic theoretical formula for calculating pressure and temperature, that is, the pressure range of the precision inspection. When calculating the instantaneous reference pressure during the precision inspection, the empirical approximation formula is used: (Ta - Ts + 273)*(Ps + 250) / 273-250, where Ta and Ts are the instantaneous temperature and starting temperature of the load space, respectively, in degrees Celsius; Ps is the starting pressure of the load space, in mbar. The above formula calculates the reference pressure at each moment during the dense inspection process. When performing a dense inspection, add or subtract 7 to 10 mbar from the reference pressure to form the pressure range of the dense inspection process. One detection cycle is 30-60 minutes, that is, if any of step 1, step 2 and step 3 is not completed and the secret check fails within 30-60 minutes, an alarm will be given after 30-60 minutes that the secret check fails and the process needs to be repeated after troubleshooting.

2. The automatic detection device for air tightness of the load space of a full hydrogen bell-type furnace according to claim 1 is characterized in that: The pressure sensor is a pressure transmitter.

3. The automatic detection device for air tightness of the load space of a full hydrogen bell-type furnace according to claim 1 is characterized in that: The temperature sensor is a thermocouple.

4. The automatic detection device for air tightness of the load space of a full hydrogen bell-type furnace according to claim 1 is characterized in that: The small flow nitrogen valve is a pneumatic two-position valve with a solenoid valve. The solenoid valve is controlled by a programmable logic controller to control the opening and closing of the small flow nitrogen valve.

5. The automatic detection device for air tightness of the load space of a full hydrogen bell-type furnace according to claim 1 is characterized in that: The discharge valve is a pneumatic two-position valve with a solenoid valve, which is controlled by a programmable logic controller to control the opening and closing of the discharge valve.