Three-stage aging furnace for aluminum alloy plates and heat preservation time calculation method

Abstract

The invention discloses an aluminum alloy plate three-stage aging furnace and a heat preservation time calculation method, and relates to the technical field of aluminum alloy plate production. The aluminum alloy plate three-stage aging furnace comprises a furnace body and a hearth which is arranged in the furnace body and is used for carrying out aging treatment on plates; a suspended ceiling is mounted in the hearth in an up-down sliding manner, the suspended ceiling is in sealing contact with the side wall of the hearth, the hearth is divided into an upper hearth and a lower hearth by the suspended ceiling, and a plate needing aging treatment is positioned in the lower hearth; an air inlet and an air outlet are formed in the side wall of the lower hearth; an air supply system is connected between the air inlet and the air outlet; a lifting driving device for driving the suspended ceiling to slide up and down and a control system in signal connection with the lifting driving device are arranged on the outer side of the furnace body; the control system is in signal connection with the air supply system. The calculation mode of the three-stage aging furnace and the heat preservation time is optimized, so that the stress corrosion resistance of the treated aluminum alloy plate is improved, and meanwhile, the strength loss is small.

Description

Technical Field

[0001] The invention relates to the technical field of aluminum alloy plate production, and in particular to a three-stage aging furnace for aluminum alloy plates and a method for calculating the insulation time. Background Art

[0002] After three-stage aging, aluminum alloy sheets can reach T77 state, which has both the high strength of T6 state and the corrosion resistance of T73 state. The three-stage aging of aluminum alloy sheets at present is pre-aging, regression aging treatment and re-aging heat treatment. After three-stage aging treatment, aluminum alloy sheets have higher electrical conductivity and less strength loss, meeting the requirements of aerospace for aluminum alloy sheets.

[0003] The treatment processes for pre-aging and re-aging are the same, but in the regression aging treatment, the different holding temperatures and holding times have different effects on the regression state of the plate. For example, the commonly used holding temperature in the existing process is 180°C (the holding temperature of 180°C can slow down the regression treatment speed and can more conveniently control the regression process, so T77 aging can be performed on thicker plates), and the holding time is 2.5 hours (the longer the holding time, the higher the conductivity of the plate, the faster the conductivity increases, the corrosion resistance increases, but the strength of the plate decreases). In order to reduce the impact of the heating and cooling processes on the regression state during the regression aging treatment, the regression aging treatment requires rapid heating, insulation, and rapid cooling.

[0004] The existing three-stage aging furnace has the following problems during the regression aging treatment:

[0005] 1. The furnace volume of the three-stage aging furnace is large, and the heating and cooling time is long. Although it does not reach the required insulation temperature, it will still affect the performance of the aluminum alloy plate, and it increases the insulation time to a certain extent;

[0006] 2. The current method of calculating the insulation time is that the equipment starts timing automatically after all load thermocouples (thermocouples inserted inside the plate) reach the lower limit of the insulation temperature. After the required insulation time is reached, the cooling fan automatically starts to cool down. This results in the existing method of calculating the insulation time being unable to accumulate the impact of part of the time during the heating process on the performance of the plate into the insulation time, and thus the insulation time cannot be accurately calculated, resulting in an unstable return state of the plate. Summary of the invention

[0007] The purpose of the present invention is to provide a three-stage aging furnace for aluminum alloy plates and a method for calculating the holding time, which optimizes the calculation method of the three-stage aging furnace and the holding time, so that the stress corrosion resistance of the treated aluminum alloy plates is improved while the strength loss is small.

[0008] In order to achieve the above object, the technical solution of the present invention is:

[0009] A three-stage aging furnace for aluminum alloy plates comprises a furnace body and a furnace chamber arranged in the furnace body and performing aging treatment on the plates; a suspended ceiling is installed in the furnace chamber so as to slide up and down, the suspended ceiling is in sealing contact with the side wall of the furnace chamber, the suspended ceiling divides the furnace chamber into an upper furnace chamber and a lower furnace chamber, and the plates to be aging treated are located in the lower furnace chamber; an air inlet for supplying heating / cold air to the lower furnace chamber and an air outlet for air circulation are arranged on the side wall of the lower furnace chamber; an air supply system is connected between the air inlet and the air outlet; a lifting drive device for driving the suspended ceiling to slide up and down and a control system connected to the lifting drive device by signal are arranged on the outer side of the furnace body; the control system signal is connected to the air supply system.

[0010] After adopting the above structure, the suspended ceiling divides the furnace into an upper furnace and a lower furnace. The lower furnace is used as a space for aging treatment of the plate. The height of the lower furnace is controlled by raising and lowering the suspended ceiling. The volume of the lower furnace can be adjusted according to the thickness of the plate to minimize its volume, thereby improving the thermal efficiency or cooling efficiency and achieving the purpose of rapid heating and cooling of the plate. During the aging treatment, the temperature rise and fall speeds are slow due to the excessive volume of the furnace, which is equivalent to increasing a certain amount of insulation time and affecting the effect of the aging treatment of the plate.

[0011] In order to realize the integrated design of the aging furnace and to arrange it reasonably, a wind cavity is formed between the furnace body and the furnace, and the air inlet and the air outlet are respectively connected to the left and right sides of the ventilation cavity; the air supply system is installed in the wind cavity and includes a hot air system and a cold air system.

[0012] In order to further optimize the layout of the hot air system and the cold air system, the hot air system includes a heat exchanger fixedly installed in the air cavity and a circulating fan that sucks air from the air outlet and discharges air toward the air inlet, and the driving system of the circulating fan is located outside the furnace body; the cold air system includes a cold air inlet arranged in the air cavity, which extends to the outside of the furnace body and is connected to the cooling fan through a valve.

[0013] In order to enable the entire lower furnace to achieve rapid heating and cooling, it is divided into multiple partitions from front to back. An air inlet and an air outlet are arranged on the lower furnace corresponding to each partition. A circulating fan is installed on each air inlet, and each air outlet is connected to the ventilation cavity through an independent pipe; a group of heat exchangers and cold air inlets are arranged in the air cavity corresponding to each partition.

[0014] In order to increase the ceiling lifting temperature, the lifting drive device includes a plurality of worm gear lifts evenly fixed on the top of the furnace body and a motor driving the worm gear lifts; the lead screw of the worm gear lifts extends downward into the furnace body, passes through the furnace chamber and is fixed on the ceiling.

[0015] A method for calculating the holding time of heat treatment using any of the above-mentioned three-stage aging furnaces for aluminum alloy plates, comprising the following steps: S1: placing the plate to be treated on a discharge table, and inserting a thermocouple into the plate; S2: controlling the three-stage aging furnace for aluminum alloy plates through a control system to sequentially perform pre-aging, regression aging and re-aging heat treatment on the plate; wherein the holding time for regression aging treatment adopts a cumulative temperature recording method, and the cumulative temperature recording method comprises the following steps: 1) setting an initial temperature lower than a target holding temperature, and starting cumulative temperature recording when the load temperature collected by the thermocouple reaches the initial temperature; 2) converting the load temperature collected in each time interval into an effective holding time by a formula, and then accumulating all the effective holding times; 3) after the total time obtained by accumulating all the effective holding times reaches the target effective holding time, the lower furnace is rapidly cooled.

[0016] After adopting the above method, the part of time higher than the initial temperature in the heating process is converted into the effective holding time through a formula, thereby improving the accuracy of the holding time and ensuring that the performance of the plate after aging treatment is guaranteed to the maximum extent; in addition, through the calculation method of this formula, a connection relationship can be established between the holding time and the holding temperature, so that the two can be converted into each other to achieve the ultimate aging effect.

[0017] In order to achieve rapid heating and cooling, the above S1 also includes adjusting the height of the lower furnace according to the thickness of the plate.

[0018] In order to achieve the maximum performance conversion, the conversion formula between load temperature and effective insulation time in step 2) above is: t1 = t2*exp(Q / (T1+460)-Q / (T2+460)); where t1 is the effective insulation time, in hours; t2 is the heating time (the interval time of temperature collection); T1: target temperature, in hours. 0 F; T2: actual temperature, in 0 F; Q: Thermal activation energy of the alloy, which varies for different alloys.

[0019] In order to realize automatic control, t2, T1, Q, target effective insulation time and initial temperature are input into the control system in advance. The control system automatically calculates the comparison between the effective insulation time and the target effective insulation time, and then controls the cold air system to cool down quickly.

[0020] In order to maximize the conversion of the load temperature in the heating process into the effective holding time; and the rapid cooling is to reduce the temperature to below the initial temperature in the shortest time, ignoring its conversion into the effective holding time to avoid calculation errors, the heating rate is 150℃ / h and the cooling rate is 300℃ / h.

[0021] After adopting the above technical solution, the beneficial effects of the present invention are:

[0022] The present invention solves the technical problem in the prior art that the effective holding time cannot be well controlled due to the slow heating and cooling speeds of the aging furnace, resulting in poor effect of the three-stage aging of the aluminum alloy plate. The present invention optimizes the structure of the three-stage aging furnace and the calculation method of the holding time, so that the stress corrosion resistance of the treated aluminum alloy plate is improved, while the strength loss is small. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a structural schematic diagram of a three-stage aging furnace for aluminum alloy plates of the present invention;

[0024] Figure 2 It is a schematic diagram of the internal circulation direction of hot air during the heating process;

[0025] Figure 3 It is a schematic diagram of the direction of cold air during the cooling process;

[0026] Figure 4 It is after the aging treatment of the present invention.

[0027] In the figure, 1. furnace body, 2. furnace, 21. ceiling, 22. air inlet, 23. air outlet, 24. unloading table, 25. worm gear elevator, 251. screw, 3. air supply system, 31. heat exchanger, 32. circulating fan, 33. cold air inlet, 34. cooling fan. DETAILED DESCRIPTION

[0028] The present invention will be further described below in conjunction with the accompanying drawings.

[0029] The orientations mentioned in this specification are based on the orientations of the three-stage aging furnace and the insulation time calculation method for aluminum alloy plates of the present invention when they are working normally, and do not limit the orientations during storage and transportation. They only represent relative positional relationships, not absolute positional relationships.

[0030] like Figure 1 As shown, a three-stage aging furnace for aluminum alloy plates comprises a furnace body 1 and a furnace chamber 2 disposed in the furnace body 1 for aging the plates. The furnace body 1 extends forward and backward and is provided with an inlet and outlet connecting the outside with the inside of the furnace chamber 2 on one side of its front end; a switch door (not shown in the figure) is installed on the inlet and outlet. By opening the switch door, the plates are transported to the furnace chamber 2 for aging treatment.

[0031] The furnace body 1 is welded by steel plates and reinforced rolled steel, and an insulation layer is arranged on the inside thereof, which prevents the outer surface temperature of the furnace body 1 from exceeding 10°C above the room temperature. An internal coating is also arranged inside the insulation layer to prevent corrosion of the insulation layer. The furnace 2 is suspended in the furnace body 1 by hanging steel, and its bottom is supported on the bottom of the furnace body 1 and fixedly connected to the furnace body 1. A discharge table 24 is arranged at the bottom of the furnace 2. A ceiling 21 is installed in the furnace 2 above the discharge table 24 so as to slide up and down. The ceiling 21 is in sealing contact with the side wall of the furnace 2. The ceiling 21 divides the furnace 2 into an upper furnace and a lower furnace. An air inlet 22 for supplying heating / cooling air to the lower furnace and an air outlet 23 for air circulation are arranged on the side wall of the lower furnace. An air supply system 3 is connected between the air inlet 22 and the air outlet 23; the air supply system 3 supplies hot / cold air to the air inlet 22, and heats or cools the air discharged from the air outlet 23, thereby realizing air circulation. The hot air or cold air heats / cools the lower furnace, thereby realizing aging treatment of the plates in the furnace 2.

[0032] The outer side of the furnace body 1 is provided with a lifting driving device for driving the suspended ceiling 21 to slide up and down and a control system connected with the lifting driving device by signal.

[0033] The lifting drive device drives the ceiling 21 to slide up and down to adjust the height of the lower furnace; in this embodiment, the lifting drive device includes a plurality of worm gear lifts 25 uniformly fixed on the top of the furnace body 1 and a motor driving the worm gear lifts 25 to operate; the lead screw 251 of the worm gear lift 25 extends downward into the furnace body 1, and penetrates the furnace 2 and is fixed on the ceiling 21. The rotation of the worm gear lift 25 drives the lead screw 251 to move up and down, thereby driving the ceiling 21 to slide up and down, and realizing the height adjustment of the lower furnace. The lifting drive device can be a variety of structures, such as an electric cylinder or an electric push rod, and can also use a lead screw and a slider to achieve the up and down lifting of the ceiling 21. It can be reasonably set according to actual conditions, and this embodiment does not limit this. In order to reduce the investment in the motor, all the worm gear lifts 25 are connected to the same motor, and the operation of one motor drives the ceiling 21 to slide up and down, thereby reducing the investment in the drive device and reducing the production cost.

[0034] An automatic material height detection system can be installed in the lower furnace as needed. The signal of the automatic material height detection system is connected to the control system. The material height that needs aging treatment is detected by the automatic material height detection system and then transmitted to the control system. The control system controls the motor to rotate, so that the ceiling 21 slides downward, compressing the height of the lower furnace, thereby reducing the volume of the lower furnace, improving the thermal efficiency or cooling efficiency, and achieving the purpose of rapid heating and cooling of the plate; avoiding the slow heating and cooling speed during aging treatment, which affects the insulation time and affects the effect of the aging treatment of the plate.

[0035] The control system signal is connected to the air supply system 3. For the integrated design of the aging furnace, a wind cavity is formed between the furnace body 1 and the furnace 2, and the air inlet 22 and the air outlet 23 are respectively connected to the left and right sides of the ventilation cavity; the air supply system 3 is installed in the wind cavity and includes a hot air system and a cold air system.

[0036] The hot air system is used to heat the circulating air, and includes a heat exchanger 31 fixedly installed in the air cavity and a circulating fan 32 that sucks air from the air outlet 23 and discharges air toward the air inlet 22. The circulating fan 32 is fixed on the air inlet 22, and the driving system of the circulating fan 32 is located outside the furnace body 1, so as to avoid damage to the driving system caused by high-temperature air. In this embodiment, the heat exchanger 31 is an electric heating tube, and the air passing through is heated by the heat exchanger 31.

[0037] The cold air system includes a cold air inlet 33 arranged in the air cavity, which extends to the outside of the furnace body 1 and is connected to the cooling fan 34 through a valve. In order to improve the cooling efficiency, a refrigeration device can also be installed at the air inlet position of the cooling fan 34 to cool the inhaled air. An exhaust port is arranged at the top of the air cavity, which is connected to the outside of the furnace body 1, and a pressure valve is arranged at one end of the outside. When the gas pressure in the air cavity is too high, the pressure valve can be pushed open to achieve automatic exhaust.

[0038] like Figure 2 As shown, the heating process: this process is the internal circulation process of the furnace body 1. The circulating fan 32 draws the high-temperature air heated by the electric heating tube into the lower furnace to heat the lower furnace. The air returns to the wind cavity from the air outlet 23, is heated again by the electric heating tube, and then returns to the lower furnace, thereby realizing the rapid internal circulation of hot air. The direction of the solid arrow in the figure is the internal circulation direction of the hot air.

[0039] like Figure 3 As shown, the cooling process: in this process, external cold air is introduced into the furnace body 1, and the air in the furnace body 1 is discharged; when cooling is required, the electric heating tube stops working, the cold air inlet 33 is opened, and the cooling fan 34 attracts external cold air into the wind cavity, and then under the action of the circulating fan 32, it enters the lower furnace and cools the lower furnace. With the entry of cold air, the air pressure in the furnace body 1 increases, and the hot air rises to push the pressure valve open, and is discharged from the furnace body 1 through the exhaust port, thereby achieving rapid cooling. The direction of the hollow arrow in the figure is the internal circulation direction of the cold air.

[0040] In order to make the air more directional when circulating in the furnace body 1 and avoid turbulence that affects the air flow speed, the air outlet 23 is connected to the air cavity through an arc tube to guide the airflow.

[0041] Because the furnace 2 is relatively long from front to back, in order to improve the air flow efficiency, the furnace 2 is divided into multiple partitions from front to back, and each partition is provided with an air inlet 22, so there are multiple air inlets 22, and each air inlet 22 is installed with a set of fans 26. By setting multiple sets of fans 26, the speed of air return is increased, and the heating efficiency or cooling efficiency is improved. An air inlet 22 and an air outlet 23 are set on the lower furnace corresponding to each partition, and a circulation fan 32 is installed on each air inlet 22, and each air outlet 23 is connected to the air cavity through an independent pipeline; a set of heat exchangers 31 and cold air inlets 33 are set in the air cavity corresponding to each partition.

[0042] A method for calculating the holding time of heat treatment in the above-mentioned three-stage aging furnace for aluminum alloy plates comprises the following steps:

[0043] S1: Place the plate to be processed on the unloading table 24 and insert the thermocouple into the plate; in order to improve the efficiency of heating and cooling and minimize the impact of this process on the insulation time, the height of the lower furnace is adjusted according to the thickness of the plate.

[0044] The insertion depth and arrangement position of the thermocouple will affect the measurement accuracy of the load temperature. In order to improve the accuracy of the thermocouple measurement data, the puppet position is drawn in advance on the unloading table 24 to prevent the accuracy of the load temperature collection caused by the different positions of each zone; then the plate is punched with a special tool, and the thermocouple is inserted into the inside of the plate to fix the thermocouple and prevent uneven depth and uneven tightness of the thermocouple; because of the difference in depth and tightness, the collected temperature will be different and the time to reach the temperature will be different, which will affect the accuracy of temperature collection.

[0045] S2: The control system controls the aluminum alloy plate three-stage aging furnace to perform pre-aging, regression aging treatment and re-aging heat treatment on the plate in sequence; the pre-aging, regression aging treatment and re-aging heat treatment can refer to the existing technology and will not be described in detail here.

[0046] The difference from the prior art is that the second-stage regression aging treatment is different. The regression aging treatment includes a heating process, a heat preservation process and a cooling process. The heat preservation time of the regression aging treatment in this application adopts a cumulative temperature recording method, which includes the following steps:

[0047] 1) Set an initial temperature lower than the target insulation temperature. When the load temperature collected by the thermocouple reaches the initial temperature, start accumulating the temperature.

[0048] 2) Convert the load temperature collected in each time interval into the effective insulation time through the formula, and then accumulate all the effective insulation time;

[0049] The conversion formula between load temperature and effective holding time is:

[0050] t1=t2*exp(Q / (T1+460)-Q / (T2+460));

[0051] Among them, t1 is the effective insulation time, in hours;

[0052] t2 is the heating time (interval time of temperature collection);

[0053] T1: target temperature, in 0 F;

[0054] T2: actual temperature, in 0 F;

[0055] Q: Thermal activation energy of alloy. The activation energy of different alloys is different.

[0056] 3) After the total time accumulated from all effective insulation times reaches the target effective insulation time, the lower furnace is cooled down rapidly.

[0057] It is recommended to set the heating rate to 150℃ / h and the cooling rate to 300℃ / h. The specific values ​​can be set according to the equipment capacity, and this embodiment does not limit this. Through this setting, the load temperature of the heating process can be converted into effective heat preservation time to the maximum extent, and the temperature can be quickly cooled to below the initial temperature in the shortest time, thereby ignoring its conversion into effective heat preservation time, avoiding the total time greatly exceeding the target effective heat preservation time, and affecting the heat preservation treatment effect.

[0058] By using the cumulative temperature recording method, it is only necessary to input t2, T1, Q, target effective insulation time and initial temperature into the control system in advance, and the control system automatically calculates the comparison between the effective insulation time and the target effective insulation time, and controls the three-level aging furnace of aluminum alloy plates to perform corresponding operations. Through this formula calculation method, a connection relationship can be established between the insulation time and the insulation temperature, so that the two can be converted to each other in order to achieve the final aging effect; for example: by lowering a certain insulation temperature, the insulation time can be increased accordingly, and the low temperature can make the regression state relatively slow, so that the regression degree can be better controlled, and the final effect is the same.

[0059] The above cumulative temperature recording method will have higher requirements on the insulation uniformity of the aging furnace, the accuracy of the temperature collected by the thermocouple, and the accuracy of the equipment correction compensation. Relevant requirements need to be formulated and strictly implemented as required.

[0060] Improvement of equipment setting parameters. In order to match this temperature recording method, some equipment parameters are improved:

[0061] a.PID value

[0062] That is: Proportional, Integral, Differential. The PID control algorithm is a control algorithm that combines the three links of proportional, integral and differential. When the PID parameters are optimized for steady-state control at or near the set value, the high and low reduction parameters are used to reduce overshoot and undershoot of large step changes in temperature. They set the degree above and below the set value at which the controller starts to increase or decrease the output power.

[0063] It is recommended to use P: +3, I: 150, D: 0. Reasonable PID value can make the furnace gas temperature close to the insulation temperature to achieve rapid stability.

[0064] b. Cooling fan speed

[0065] Recommendation: 50Hz (select according to the capacity of your own equipment. The higher the frequency, the better the cooling rate. However, too high a frequency may cause the cooling fan to fail prematurely).

[0066] Sample preparation: Two groups of tensile samples were taken longitudinally and transversely from the sample, and were subjected to three-level regression aging test respectively; the second-level insulation time in the three-level regression aging treatment of group 01 adopted the cumulative temperature recording method in this application, and the insulation time was 2.5h; the second-level insulation time in the three-level regression aging treatment of group 02 adopted the original temperature recording method, and the insulation time was 2.5h. The two groups of samples were tested for mechanical properties tensile, fracture toughness, and electrical conductivity. Comparison of the test results:

[0067]

[0068] By comparing the above table, it can be seen that although the alloy No. 01 and the alloy No. 02 were treated for 2.5h at the same time, the actual insulation time of the alloy No. 02 was higher than 2.5h, so its conductivity was higher and the performance loss in strength was greater. However, the 2.5h obtained by the reasonable calculation of the formula in this application can better and more stably control the balance between corrosion resistance and strength, ensuring that the produced plate has both sufficient corrosion resistance and high strength.

[0069] And from Figure 4It can be seen that its grain boundary structure shows characteristics similar to the T6 state, and the grain boundary precipitation phase is coarse and discontinuously distributed. The plate material is greatly improved, and its corrosion resistance is also improved accordingly. The T77 state has both the high strength of the T6 state and the corrosion resistance of the T73 state. This is because the 7150 alloy is an Al-Zn-Mg-Cu alloy, and the precipitation process is carried out in the order of supersaturated solid bath-GP zone-η' phase-η phase. After the first stage pre-aging at 121℃ to the peak state, the gold-containing matrix is ​​the GP zone and fine dispersed η phase, and the grain boundary is a continuous chain precipitate η' phase-η phase. The second stage of aging is a regression treatment. Since the grain boundary is an easy diffusion channel for solute atoms, the solute segregation degree at the grain boundary is high during pre-aging, the nucleation speed is fast, and the precipitate phase grows rapidly after nucleation. Therefore, the relatively stable η′ phase-η phase formed after the first stage of aging does not dissolve back under high temperature regression, but evolves in a more stable direction. The size of the precipitates at the grain boundary gradually increases and begins to aggregate and isolate, forming a discontinuous structure. During the third stage of re-aging, the strengthening phase re-precipitates in the supersaturated alloy matrix after regression, so that the strength of the alloy is restored to a strength close to the peak state, so that the alloy after T77 treatment not only maintains the strength of the T6 peak aging state, but also makes the morphology and characteristics of the precipitate phase at the grain boundary similar to the T73 state.

[0070] Therefore, by improving the aging furnace and optimizing the calculation method of the holding time, the plate after aging treatment can have both the high strength of the T6 state and the corrosion resistance of the T73 state in the T77 state.

[0071] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A three-stage aging furnace for aluminum alloy plates, comprising a furnace body and a furnace chamber arranged in the furnace body and performing aging treatment on the plates; characterized in that: A suspended ceiling is installed in the furnace for sliding up and down, the suspended ceiling is in sealing contact with the side wall of the furnace, and the suspended ceiling divides the furnace into an upper furnace and a lower furnace, and the plate to be aged is located in the lower furnace; An air inlet for supplying heating / cooling air to the lower furnace and an air outlet for air circulation are provided on the side wall of the lower furnace; an air supply system is connected between the air inlet and the air outlet; The outer side of the furnace body is provided with a lifting drive device for driving the suspended ceiling to slide up and down and a control system connected with the lifting drive device by signal; the control system signal is connected with the air supply system.

2. The three-stage aging furnace for aluminum alloy sheets according to claim 1, characterized in that: An air cavity is formed between the furnace body and the furnace, and the air inlet and the air outlet are connected to the left and right sides of the air cavity respectively; the air supply system is installed in the air cavity and includes a hot air system and a cold air system.

3. The three-stage aging furnace for aluminum alloy sheets according to claim 2, characterized in that: The hot air system includes a heat exchanger fixedly installed in the air cavity and a circulation fan that sucks air from the air outlet and discharges air toward the air inlet, and the driving system of the circulation fan is located outside the furnace body; The cold air system comprises a cold air inlet arranged in the air cavity, the cold air inlet extends to the outside of the furnace body and is connected to a cooling fan through a valve.

4. The three-stage aging furnace for aluminum alloy sheet according to claim 3, characterized in that: It is divided into multiple partitions from front to back. An air inlet and an air outlet are arranged on the lower furnace corresponding to each partition, a circulating fan is installed on each air inlet, and each air outlet is connected to the ventilation cavity through an independent pipeline; A set of heat exchangers and cold air inlets are arranged in the air cavity corresponding to each partition.

5. The three-stage aging furnace for aluminum alloy plates according to claim 1, characterized in that: The lifting drive device includes a plurality of worm gear lifters uniformly fixed on the top of the furnace body and a motor driving the worm gear lifters to operate; The lead screw of the worm gear elevator extends downward into the interior of the furnace body, passes through the furnace chamber and is fixed on the ceiling.

6. A method for calculating the holding time of heat treatment in the three-stage aging furnace for aluminum alloy plates according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1: Place the plate to be processed on the unloading table and insert the thermocouple into the plate; S2: Control the aluminum alloy plate three-stage aging furnace through the control system to perform pre-aging, regression aging and re-aging heat treatment on the plate in sequence; Among them, the insulation time of the regression aging treatment adopts the cumulative temperature recording method, and the cumulative temperature recording method includes the following steps: 1) Set an initial temperature lower than the target insulation temperature. When the load temperature collected by the thermocouple reaches the initial temperature, start accumulating the temperature. 2) Convert the load temperature collected in each time interval into the effective insulation time through the formula, and then accumulate all the effective insulation time; 3) After the total time accumulated from all effective insulation times reaches the target effective insulation time, the lower furnace is cooled down rapidly.

7. A method for calculating the holding time according to claim 6, characterized in that: The above S1 also includes adjusting the height of the lower furnace according to the thickness of the plate.

8. A method for calculating the holding time according to claim 6, characterized in that: The formula for converting the load temperature and the effective holding time in step 2) above is: t1=t2*exp(Q / (T1+460)-Q / (T2+460)); Among them, t1 is the effective insulation time, in hours; t2 is the heating time (interval time of temperature collection); T1: target temperature, in 0 F; T2: actual temperature, in 0 F; Q: Thermal activation energy of alloy. The activation energy of different alloys is different.

9. A method for calculating the holding time according to claim 8, characterized in that: Input t2, T1, Q, target effective insulation time and initial temperature into the control system in advance. The control system automatically calculates the comparison between the effective insulation time and the target effective insulation time, and then controls the cold air system to cool down quickly.

10. A method for calculating the holding time according to claim 9, characterized in that: The heating rate is 150℃ / h and the cooling rate is 300℃ / h.

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