Hot stamping forming method and device for high-pressure and high-density plate-fin heat exchanger fins

Abstract

The present invention discloses a hot stamping forming method and device for the fins of a high-pressure and high-density plate-fin heat exchanger. As the pitch of the high-pressure and high-density fins decreases, the thickness of the stamping tool becomes thinner and thinner, which results in the forming force borne by the mold and the tool during the cold stamping forming process becoming larger and larger, and the mold and the tool are prone to deformation, wear, or even breakage. In view of the problem that the cold stamping technology cannot complete the stamping of high-density and high-pressure fins, the present invention proposes a hot stamping forming method for high-pressure and high-density fins. The forming lateral force borne by the stamping mold is greatly reduced compared with the traditional cold stamping, the requirements for the mechanical properties of the mold and tool materials are reduced, and the forming difficulty is reduced, thereby breaking through the fin process technology limit of high-pressure, high-density, and microchannel plate-fin heat exchangers with large thickness and small wing pitch. The process of the present invention is: after the coated aluminum alloy sheet is subjected to a solid solution insulation treatment, it is quickly transferred to the fin forming machine for hot stamping forming, and then quickly quenched and subjected to artificial aging treatment and cleaning.

Description

Technical Field

[0001] The invention belongs to the technical field of compact heat exchangers and precision machining thereof, and in particular relates to a hot stamping forming method and device for high-pressure and high-density fins. Background Art

[0002] Plate-fin heat exchanger is a compact heat exchange device with the advantages of high heat transfer efficiency, large heat exchange surface per unit volume, compact structure, and wide temperature range. It is widely used in large-scale petrochemical, coal chemical, air separation, natural gas liquefaction, and steel metallurgy industries.

[0003] Fins are the core components of plate-fin heat exchangers. They are usually formed by cold stamping aluminum sheets using a modular mold and then brazed to form a heat exchanger. The design and manufacture of fins is the key to the performance of plate-fin heat exchangers.

[0004] In heat transfer, it is usually defined as follows: microscale is 1μm~1mm, fine scale is 100μm~1mm, and larger than 1mm is macroscale.

[0005] Research shows that at the microscale, the surface area to volume ratio is as high as a million times, the temperature field and velocity field are more effective, the heat transfer enhancement effect is more obvious, the heat transfer surface per unit volume is large, the heat transfer efficiency is greatly improved, and the cost is reduced. When the flow channel size is as small as the microchannel scale of 0.5mm to 1mm, the convective heat transfer coefficient can be increased by 50% to 100%. In order to increase the pressure resistance of the heat exchanger, the thickness of the fins is constantly increasing.

[0006] At present, foreign countries have developed microchannel plate-fin heat exchangers with high-pressure and high-density fins, and put them into use on extra-large air separation and coal chemical equipment. Under the condition of the same heat exchange capacity, they have less consumables, smaller volume, lighter weight, lower cost, higher pressure bearing capacity and economy.

[0007] The fin thickness of high-pressure and high-density fins is getting larger and larger, while the pitch is getting smaller and smaller. During the cold stamping process, the tool thickness is getting thinner and thinner, and the forming force borne by the mold and tool is getting larger and larger. The material strength requirements are getting higher and higher. The mold and tool are easily deformed, worn, or even broken. At present, the traditional cold stamping technology used in China can only produce low- and medium-density fins with an aluminum alloy thickness of less than 0.5mm and a pitch of more than 1.00mm, and has reached the technical limit of the existing fin processing technology. Therefore, the development of high-pressure and high-density fins is a "bottleneck" problem in the manufacture of microchannel plate-fin heat exchangers.

[0008] Studies have shown that when the temperature of aluminum alloy increases, the yield strength σ s Decreases, while the elongation increases. Taking 3003H14 as an example, at 25℃, the yield strength σ s is 145MPa, the elongation is 16%; at 200℃, the yield strength σs is 62MPa, the elongation is 20%; at 300℃, the yield strength σ s The yield strength σ is 17MPa and the elongation is 70%. s The thickness of the blade increases during hot working of fins with the same spacing due to the thermal expansion and contraction of aluminum alloy.

[0009] In summary, the plate-fin heat exchanger adopts the hot forming fin processing technology of aluminum alloy plate. The aluminum alloy plate has good plasticity and small springback at high temperature. The forming force of the mold and the tool will be greatly reduced, the requirements for the mechanical properties of the mold and tool materials will be reduced, the forming difficulty will be reduced, and the forming accuracy will be high, thus providing a new process method for the high-pressure and high-density fin processing of aluminum plate-fin heat exchangers. Summary of the invention

[0010] In view of the problem that the above traditional cold stamping technology cannot complete the stamping of high-density and high-pressure fins, the present invention proposes a hot stamping forming method for high-pressure and high-density fins. This process method combines stamping forming with aluminum alloy heat treatment process, which is a typical workpiece forming and property integration technology, which not only improves the formability of aluminum alloy, but also ensures the mechanical properties of the material. Under this process method, the forming lateral force on the stamping die is greatly reduced compared with traditional cold stamping, the requirements for the mechanical properties of the die and tool materials are reduced, the plastic elongation of the aluminum alloy sheet is high, the rebound is small, and the forming difficulty is reduced, thereby breaking through the fin process technology limit of high-pressure, high-density, microchannel plate-fin heat exchangers with large thickness and small wing pitch.

[0011] In a first aspect, the present invention provides a hot stamping forming method for high-pressure and high-density plate-fin heat exchanger fins, and the specific steps are as follows:

[0012] Step 1: After adding a coating to the surface of the processed aluminum alloy plate, the plate is sent to a heating furnace for heating to perform a solid solution treatment on the coated aluminum plate.

[0013] Step 2: sending the coated aluminum plate that has undergone solid solution treatment to a stamping fin forming machine for stamping processing; the width of the stamping tool of the stamping fin forming machine is greater than the fin spacing of the heat exchanger fins.

[0014] Step 3: oil-quenching the heat exchanger fins obtained by stamping in step 2.

[0015] Step 4: Perform artificial aging treatment on the heat exchanger fins obtained after quenching at a preset temperature.

[0016] Step 5: Clean the heat exchanger fins obtained in step 4 to remove the coating and oil stains on the heat exchanger fins.

[0017] Preferably, in step 2, the width of the punching tool d2 = αm ·L1(T1-T2)+d1; where d1 is the original thickness of the tool; α m is the average linear expansion coefficient, and its expression is (where α m The value can be determined by querying the specific aluminum alloy plate model, t1 is the temperature of the aluminum alloy material after heating, t2 is the room temperature, l1 and l2 are the lengths of the aluminum alloy at t1 and t2 respectively); T1 is the heating temperature in step 1; T2 is the working environment temperature of the heat exchanger fin, and L1 is the wing pitch of the hot-formed fin. The width design of the tool can be determined by the average linear expansion coefficient α of the aluminum alloy during thermal expansion and cooling. m The formula is inspired by the fact that when α is known m The fin pitch L1 of the hot-processed uncooled formed fin, the temperature difference T1-T2 before and after fin cooling and the original thickness of the tool can be used to obtain the shrinkage distance of the fin, and then the tool thickness can be redesigned.

[0018] Preferably, the oil-cooled quenching tank used in step 3 is provided with a constant temperature device, which is composed of a refrigeration device and a heating device, the refrigeration device is used to reduce the heat radiation of the quenching oil temperature increase, and the heating device is used to compensate for the temperature difference in the supercooling state to ensure constant temperature oil-cooled quenching;

[0019] Preferably, in step 1, the main component of the coating material used for the coating is ceramic powder.

[0020] Preferably, the temperature control accuracy of the heating furnace is ±1.0°C, and the insulation accuracy is ±3.0°C.

[0021] Preferably, in step 1, the heating temperature of the coated aluminum plate is determined according to a comparison table of mechanical properties and temperature of the processed aluminum alloy plate, so that the yield strength of the processed aluminum alloy plate is reduced to less than 30 MPa.

[0022] Preferably, in step 1, the heating rate of the heating furnace is 180°C / h to 300°C / h. In step 3, the quenching temperature is 60°C to 80°C.

[0023] Preferably, in step 4, the artificial aging treatment is heating at 80°C to 180°C for 12h to 24h. The artificial aging device is used to improve the yield strength and hardness of the formed fins; and the cleaning tank is used to clean the oil stains from oil cooling quenching.

[0024] In a second aspect, the present invention provides a hot stamping forming device for high-pressure and high-density plate-fin heat exchanger fins, which includes a solid solution insulation module, a hot stamping module, a quenching module, an artificial aging module and a cleaning module. The solid solution insulation module includes a heating furnace, and a first conveying mechanism, a heating device and an internal circulation component installed in the heating furnace. The first conveying mechanism is connected to the furnace inlet and the furnace outlet of the heating furnace, and is used to convey the coated aluminum plate into and out of the heating furnace.

[0025] The hot stamping module is used to stamp the coated aluminum plate after solid solution treatment, and the width of the stamping tool used is greater than the fin pitch of the heat exchanger fin being processed. The artificial aging module is used to perform artificial aging treatment on the heat exchanger fin after quenching. The cleaning module is filled with an organic solvent to remove the coating and oil stains on the surface of the heat exchanger fin.

[0026] Preferably, the quenching module comprises a quenching tank, a cooler, a heater and a temperature sensor. The quenching tank is filled with oil. The output port of the quenching tank is connected to the input port of the quenching tank through the cooler and the heater connected in series to form an oil cooling circulation system. The temperature sensor is arranged in the heater or between the heater and the cooler.

[0027] The beneficial effects of the present invention are:

[0028] 1. The present invention prepares heat exchanger fins by hot stamping after solution treatment of aluminum alloy plates, so that the yield strength of aluminum alloy plates during stamping is greatly reduced, the elongation is improved, and it is easier to deform, so that aluminum alloy wings with a thickness of 0.5 mm or more can be processed by stamping, solving the problem that the mold is easily damaged due to excessive lateral force during the stamping of high-density and high-pressure microchannel fins. In addition, since aluminum alloy plates have good plasticity and small rebound at high temperatures, the forming force of the mold and the tool will be greatly reduced, which reduces the requirements for the mechanical properties of the mold and tool materials, reduces the difficulty of forming, and has high forming accuracy, thereby breaking through the fin process technology limit of high-pressure, high-density, microchannel plate-fin heat exchangers with large thickness and small wing pitch.

[0029] 2. The present invention performs coating on the aluminum alloy plate before solution treatment, thereby preventing oxidation of the aluminum alloy plate during heating without providing a closed inert gas atmosphere, thereby ensuring the quality of the heat exchanger fins obtained by hot stamping.

[0030] 3. According to the characteristic that the heat exchanger fins will shrink after hot stamping, the present invention sets a stamping tool larger than the fin spacing to ensure the accuracy of the obtained heat exchanger fins.

[0031] 4. The range of heating rate for solution treatment provided by the present invention can ensure that the recrystallized grain structure of the aluminum alloy plate is finer along the RD direction during solution treatment, with the largest number of equiaxed grains, and has little effect on the microstructure of the aluminum alloy, thus avoiding changes in the basic properties of the aluminum alloy. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A schematic diagram of the structure of a fin hot stamping forming device provided by the present invention;

[0033] Figure 2A process flow chart of the fin hot stamping forming method provided by the present invention. DETAILED DESCRIPTION

[0034] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] like Figure 1 As shown, a hot stamping forming device for high-pressure and high-density plate-fin heat exchanger fins comprises a solid solution insulation module 1, a hot stamping module 2, a quenching module 3, an artificial aging module 4 and a cleaning module 5 arranged in sequence. The solid solution insulation module 1 comprises a heating furnace 1-1, and a first conveying mechanism 1-2, a heating device 1-3 and an internal circulation component 1-4 installed in the heating furnace 1-1. The first conveying mechanism 1-2 is connected to the furnace inlet and the furnace outlet of the heating furnace 1-1, and is used to convey the coated aluminum plate 6 into and out of the heating furnace 1-1. The output end of the first conveying mechanism 1-2 is connected to the hot stamping module 2. The hot stamping module 2 adopts a stamping forming machine. The width of the stamping tool 2-1 in the hot stamping module 2 is greater than the fin spacing of the heat exchanger fin 8 to be processed, thereby compensating for the shrinkage of the heat exchanger fin 8 after cooling and improving the dimensional accuracy of the heat exchanger fin 8. The hot stamping module 2 performs continuous stamping processing on the coated aluminum plate 6 under the control of the computer 7 and the die control device to form the heat exchanger fin 8. The computer 7 and the die control device are used to improve the die stamping forming accuracy.

[0036] The quenching module 3 includes a quenching tank 3-1, a cooler 3-2, a heater 3-3 and a temperature sensor 3-4. The quenching tank 3-1 is filled with oil for quenching the heat exchanger fins 8. The output port of the quenching tank 3-1 is connected to the input port of the quenching tank 3-1 through the cooler 3-2 and the heater 3-3 connected in series to form an oil cooling circulation system. The temperature sensor 3-4 is arranged in the heater 3-3 or between the heater 3-3 and the cooler 3-2 to ensure that the temperature of the oil delivered to the quenching tank 3-1 is constant.

[0037] The artificial aging module 4 is used to heat the heat exchanger fins 8 after quenching to perform artificial aging treatment. The cleaning module 5 removes the coating and oil stains on the surface of the heat exchanger fins 8 by using an organic solvent 5-1.

[0038] like Figure 2 As shown, the specific steps of preparing the heat exchanger fins using the hot stamping forming device for the high-pressure and high-density plate-fin heat exchanger fins are as follows:

[0039] Step 1: Solid solution and heat preservation. Solid solution and heat preservation refers to heating the alloy to a high temperature single-phase region and maintaining it at a constant temperature so that the excess phase is fully dissolved into the alloy matrix to form a uniform high-temperature solid solution.

[0040] Since aluminum alloy thin plates are very easy to oxidize under high-temperature air, the use of inert gas filling or vacuum treatment requires the entire set of equipment to be in a closed state, the equipment cost is expensive, and the operation is difficult. Therefore, a coating is first added to the surface of the aluminum alloy thin plate (the coating can be treated with a coating with ceramic powder as the main component), and then the aluminum alloy thin plate is sent into a heating furnace 1-1 with a temperature control accuracy of ±1.0°C and a thermal insulation accuracy of ±3.0°C by using a crawler; according to the specific mechanical properties and temperature comparison table of the aluminum alloy thin plate model, the aluminum alloy thin plate is heated at a heating rate of 180°C / h to 300°C / h to a temperature at which the yield strength of the aluminum alloy thin plate drops to 30MPa (generally heated to 370°C to 470°C, depending on the specific aluminum alloy thin plate model), so that the aluminum alloy thin plate is fully solution treated. A lower solution temperature is selected within the solution temperature range of the aluminum alloy sheet model (for example, the yield strength of 5052H34 at 370°C has dropped to 21MPa, so 370°C can be selected as its solution temperature) to improve the thickness uniformity of the formed fins. After reaching the specified temperature, constant temperature heating is performed and the heating furnace 1-1 is kept warm for a specified time.

[0041] Solution heat preservation makes the dislocation of aluminum alloy sheet continuously reduced during stamping, the flow stress decreased, and the material grain changed, so that the yield strength was greatly reduced and the elongation was increased. The superior mechanical properties after heating make the sheet easier to deform when subjected to the stamping pressure of the fin forming machine; the high elongation makes it difficult for the sheet to be pulled and broken during the stamping process and the lateral force of the fin stamping is reduced. The heating furnace 1-1 uses a heating rate of 180℃ / h to 300℃ / h to ensure that the recrystallized grain structure of the aluminum alloy sheet is finer along the RD direction during solution treatment, and the equiaxed grains are the most, which has little effect on the microstructure of the aluminum alloy. Too low a heating rate (such as 50℃ / h) will cause a large amount of soluble precipitated phases of the aluminum alloy to not melt into the aluminum matrix, making the microstructure deformed grains and changing the basic properties of the aluminum alloy.

[0042] Step 2: Hot stamping. First, design and replace the appropriate tool. Due to the thermal expansion and contraction of aluminum alloy, the fin thickness, wing pitch, and wing height are affected to a certain extent. For example, for fins with the same spacing, the blade thickness increases during hot forming to compensate for the problem of reduced wing pitch after cooling.

[0043] The average linear expansion coefficient of this type of aluminum alloy during the cooling process is used (Wherein, T1 is the temperature of the aluminum alloy plate after heating, T2 is the room temperature, L1 and L2 are the lengths of the aluminum alloy at T1 and T2 respectively). The shrinkage distance of the fin pitch is calculated by the temperature, fin pitch and room temperature of the hot stamping fins. After redesign, the tool thickness is the original thickness plus the shrinkage distance of the fin pitch.

[0044] Then the aluminum alloy sheet that has reached the holding time is transferred from the heating furnace 1-1 to the fin forming machine to punch high-pressure and high-density fins. The punching speed is controlled to ensure good formability and punching accuracy of the aluminum alloy sheet.

[0045] Step 3: Pressure quenching. Transfer the stamped fins to the oil cooling tank, determine the oil cooling temperature (generally 60℃~80℃) according to the specific aluminum alloy plate model, perform oil cooling quenching, and use a circulating cooling device (consisting of a refrigeration device and a heating device, the refrigeration device is used to reduce the thermal radiation of the oil heating during the quenching process, and the heating device compensates for overcooling) to ensure the constant temperature of the oil. Due to the short hot stamping time, the temperature change of the fins is small, and it can be directly cooled without reheating. During the contact heat exchange process of quenching, control the contact pressure to ensure the critical cooling rate of quenching.

[0046] After solution treatment, the yield strength, hardness and other mechanical parameters of the plate are reduced, so that the hardness and yield strength of the high-density and high-pressure microchannel fins obtained by hot stamping do not meet the fin performance indicators, so quenching is required to improve the yield strength, hardness and other mechanical performance indicators of the formed fins. Due to the fast hot stamping time, the temperature change of the fins is small, and it can be directly cooled without reheating. The quenching methods include air cooling, water cooling, wind cooling, oil cooling, etc. Water cooling quenching requires a compressed air pipe in the quenching water tank to quickly break through the film boiling stage of aluminum alloy water cooling to ensure the cooling capacity and cooling uniformity of water cooling; air cooling has a slow cooling speed, which may cause the fixed supersaturated solid solution to be decomposed; air cooling quenching equipment has a high cost. In summary, oil cooling quenching is selected to improve the hardness, yield strength and other mechanical performance indicators of the fins.

[0047] Step 4: Artificial aging treatment. After quenching, the strength or hardness of aluminum alloy does not reach the peak immediately, and its plasticity does not decrease but increases. After being placed at room temperature for a considerable period of time (for example, 4 to 6 days and nights), the strength and hardness of the quenched alloy are significantly improved, while the plasticity decreases. The phenomenon that the strength and hardness of the quenched alloy change significantly over time is called aging. Artificial aging treatment refers to the process of heating the alloy after solid solution and quenching treatment to an appropriate temperature above room temperature and keeping it for a certain period of time to change the properties of the alloy.

[0048] The specific process is: the formed fin is transferred to the artificial aging module 4 for low-temperature heating, generally the heating temperature is 80℃~180℃, and the aging time is 12h~24h. (The appropriate aging temperature and aging time should be selected according to the specific aluminum alloy model parameters.) This operation can decompose the supersaturated solid solution produced by the solution treatment, and make the second phase particles precipitate from the supersaturated solid solution and distribute around the aluminum grains, thereby improving the mechanical properties parameters such as yield strength, tensile strength, and hardness of the fin, so that the pressure resistance of the formed fin is improved and it is not easy to deform.

[0049] Step 5: Fin cleaning. Take the formed fin out of the heating furnace 1-1, clean the oil stains on the fin with an organic solvent 5-1, and then use deionized water and ultrasonic cleaning to clean the ceramic powder coating.

[0050] The above contents are implementation methods given in combination with specific examples, which are further explanations of the present invention, and it cannot be determined that the specific implementation of the present invention is limited to these explanations. For those skilled in the art of the present invention, without departing from the inventive concept, they can also make a certain degree of simple deduction or replacement, which should be regarded as belonging to the protection scope of the present invention.

Claims

1. A hot stamping method for high-pressure and high-density plate-fin heat exchanger fins, characterized in that: Step 1, after adding a coating to the surface of the processed aluminum alloy plate, the plate is sent into a heating furnace and heated to 370°C~470°C to perform a solid solution treatment on the coated aluminum plate; the heating rate of the heating furnace is 180°C / h~300°C / h; the main component of the coating used in the coating is ceramic powder; the heating temperature of the coated aluminum plate is determined according to the mechanical properties and temperature comparison table of the processed aluminum alloy plate, so that the yield strength of the processed aluminum alloy plate is reduced to less than 30MPa; Step 2: Send the solution treated coated aluminum plate to a stamping fin forming machine for stamping processing; the width of the stamping tool of the stamping fin forming machine is greater than the fin spacing of the heat exchanger fins; the width of the stamping tool d 2= α m · L 1( T 1- T 2)+ d 1; among them, T 1 is the heating temperature of the coated aluminum plate in step 1; T 2 is room temperature; L 1 is the fin pitch of the heat exchanger fin; d 1 is the cold stamping wing distance L 1. The thickness of the tool used for the heat exchanger fin; α m For the processed aluminum alloy plate at temperature T 1 corresponds to the average linear expansion coefficient; Step 3, oil-cooling quenching the heat exchanger fins obtained by stamping in step 2; the quenching temperature is 60° C. to 80° C.; Step 4, subjecting the heat exchanger fins obtained after quenching to artificial aging treatment at a preset temperature; removing oil stains by washing with an organic solvent, and removing the coating by ultrasonic cleaning with deionized water; the artificial aging treatment is heating at a temperature of 80°C to 180°C for 12h to 24h; Step 5: Clean the heat exchanger fins obtained in step 4 to remove the coating and oil stains on the heat exchanger fins.

2. The hot stamping forming method of high-pressure and high-density plate-fin heat exchanger fins according to claim 1 is characterized in that: The oil-cooled quenching tank used in step 3 is provided with a constant temperature device, which consists of a refrigeration device and a heating device. The refrigeration device is used to reduce the thermal radiation caused by the increase in quenching oil temperature, and the heating device is used to compensate for the temperature difference in the supercooling state to ensure constant temperature oil-cooled quenching.

3. The hot stamping forming method of high-pressure and high-density plate-fin heat exchanger fins according to claim 1, characterized in that: The temperature control accuracy of the heating furnace is ±1.0°C, and the insulation accuracy is ±3.0°C.

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