A method for preparing continuously extruded microchannel aluminum flat tubes

Abstract

This invention discloses a method for preparing continuously extruded microchannel aluminum flat tubes, belonging to the field of microchannel aluminum flat tube preparation technology. The method includes: S1 Raw material preparation: providing an aluminum alloy round rod, wherein the chemical composition of the aluminum alloy, by mass percentage, is Mn 0.95%-1.20%, Si≤0.20%, Fe≤0.20%, Cu0.02%-0.05%, Ti0.06%-0.12%, with the balance being Al and unavoidable impurities; S2 Straightening: straightening the aluminum alloy round rod, controlling the curvature ≤2mm / m; S3 Surface cleaning: sequentially subjecting the straightened round rod to ultrasonic cleaning, hot water rinsing, and drying; S4 Continuous extrusion: feeding the cleaned round rod into a continuous extrusion press and extruding it using a die; S5 Zinc spraying treatment: spraying zinc onto the surface of the extruded microchannel aluminum flat tube. This invention, while achieving continuous extrusion processing of microchannel aluminum flat tubes, also improves the metal flow state and weld quality, and realizes quantitative control and intelligent collaboration of each key step.

Description

Technical Field

[0001] This invention relates to the field of microchannel aluminum flat tube preparation technology, and more specifically, to a method for preparing continuously extruded microchannel aluminum flat tubes. Background Technology

[0002] Microchannel aluminum flat tubes, also known as "parallel flow aluminum flat tubes," are thin-walled, porous, flat tubular materials made from refined aluminum rods through hot extrusion and surface zinc spraying for corrosion protection. They are mainly used in air conditioning systems for various refrigerants as pipe components that carry new environmentally friendly refrigerants. The use of new environmentally friendly materials is a key material for the next generation of parallel flow microchannel air conditioning heat exchangers.

[0003] Existing methods for producing hollow microchannel aluminum flat tubes using conventional continuous extrusion suffer from drawbacks. These include unsatisfactory pretreatment of the billet and difficulty in achieving a large extrusion ratio. Consequently, the weld quality and high-pressure resistance of the hollow products are significantly inferior to those produced by conventional positive extrusion-drawing methods. This limitation severely restricts the application of continuous extrusion in the field of high-precision hollow profiles. Such products not only have complex cross-sectional shapes and high dimensional accuracy requirements but also demand high pressure resistance, and the presence of inclusions, pores, pinholes, or other micro-defects is absolutely unacceptable. In practice, the leakage rate of 1000 series aluminum alloy microchannel flat tubes produced using traditional continuous extrusion processes reaches as high as 10%–30%, severely impacting product yield and reliability. Summary of the Invention

[0004] In view of the problems existing in the prior art, the purpose of this invention is to provide a method for preparing microchannel aluminum flat tubes that can be continuously extruded. This invention not only realizes the continuous extrusion processing of microchannel aluminum flat tubes, but also improves the metal flow state and weld quality, and achieves quantitative control and intelligent coordination of each key step.

[0005] To solve the above problems, the present invention adopts the following technical solution:

[0006] A method for preparing continuously extruded microchannel aluminum flat tubes, comprising:

[0007] S1. Raw material preparation: Provide aluminum alloy round rods, wherein the chemical composition of the aluminum alloy, by mass percentage, is Mn 0.95%-1.20%, Si≤0.20%, Fe≤0.20%, Cu 0.02%-0.05%, Ti 0.06%-0.12%, with the balance being Al and unavoidable impurities;

[0008] S2. Straightening: Straighten the aluminum alloy round rod, controlling the curvature to ≤2mm / m;

[0009] S3. Surface cleaning: The straightened round rod is then ultrasonically cleaned, rinsed with hot water, and dried in sequence.

[0010] S4. Continuous extrusion: The cleaned round rod is fed into a continuous extrusion press and extruded into shape using a die.

[0011] S5. Zinc spraying treatment: Zinc is sprayed onto the surface of the extruded microchannel aluminum flat tube;

[0012] S6. Cooling, Flaw Detection, Marking and Winding: After zinc spraying, the flat tube is cooled, and after eddy current flaw detection and inkjet marking, it is wound into a reel.

[0013] Compared with the prior art, the advantages of this invention are:

[0014] (1) This invention controls the extrusion ratio at 1.0-7.5, which is significantly different from the extrusion ratio of over 400 times in traditional continuous extrusion. The core advantages of the low extrusion ratio include: significantly reduced energy consumption, resulting in outstanding energy-saving effects when producing products of the same specifications; a significant increase in the service life of continuous extruders and dies, reducing production costs; and, more importantly, a significant reduction in flow resistance during metal deformation, which mechanically inhibits the formation probability of surface defects such as aluminum chips. At the same time, this solution further optimizes the die structure parameters—the width of the upper die diversion bridge is 10.0 mm, the length of the lower die working zone is 1.15-1.30 mm, the radius of the bottom arc of the extrusion wheel groove is 3.5-5.0 mm, and the depth of the feed block guide groove is 10 mm—these parameters work synergistically with the low extrusion ratio process to make the metal flow in the die cavity more uniform and smooth, significantly improving weld quality and greatly reducing defects such as porosity and inclusions. With precise control of extrusion temperature (370-420℃), extrusion roller speed (6.5-12r / min), extrusion pressure (45-55MPa), and the gap between extrusion roller and extrusion shoe (0.8-1.2mm), the scrap rate caused by aluminum chip defects is reduced, and the pass rate is improved.

[0015] (2) This invention establishes a theoretical formula for calculating the inverse bending radius based on yield strength, elastic modulus, and the radius of the round rod in the straightening stage, and comprehensively considers the inverse bending ratio of the neutral layer offset. Through precise calculation of the angle between the two-roller straightener and the roller system, accurate straightening of the round rod with a bending degree ≤2mm / m is achieved, providing a billet with uniform geometric dimensions for subsequent continuous extrusion. In the surface cleaning stage, a multi-parameter linkage model is constructed based on ultrasonic frequency, pulse duty cycle, power, temperature, and the diameter and oil stain level of the round rod, realizing intelligent matching and real-time adjustment of cleaning parameters. Hot water rinsing adopts PID closed-loop control to ensure that the temperature is stable at the set value of 65℃. In the drying step, compressed air is used to blow at a 45° angle and a pressure of 0.4-0.6MPa for 3-5s, establishing a three-stage process chain of cleaning, rinsing, and drying, which significantly improves the thoroughness and consistency of surface cleaning, eliminating weld defects and surface aluminum chips caused by foreign matter from the source. Attached Figure Description

[0016] Figure 1This is a flowchart illustrating the steps of a continuously extrudable microchannel aluminum flat tube preparation method according to the present invention.

[0017] Figure 2 This is a flowchart of step S2, straightening, in a method for preparing a continuously extrudable microchannel aluminum flat tube according to the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0019] Example:

[0020] Please see Figure 1-2 A method for preparing continuously extruded microchannel aluminum flat tubes, comprising:

[0021] S1. Raw material preparation: Provide aluminum alloy round rods. The chemical composition of the aluminum alloy, by mass percentage, is Mn 0.95%-1.20%, Si≤0.20%, Fe≤0.20%, Cu 0.02%-0.05%, Ti 0.06%-0.12%, with the balance being Al and unavoidable impurities.

[0022] S2. Straightening: Straighten the aluminum alloy round rod, controlling the curvature to ≤2mm / m;

[0023] S3. Surface cleaning: The straightened round rod is then ultrasonically cleaned, rinsed with hot water, and dried in sequence.

[0024] S4. Continuous extrusion: The cleaned round rod is fed into a continuous extrusion press and extruded into shape using a die.

[0025] S5. Zinc spraying treatment: Zinc is sprayed onto the surface of the extruded microchannel aluminum flat tube;

[0026] S6. Cooling, Flaw Detection, Marking and Winding: After zinc spraying, the flat tube is cooled, and after eddy current flaw detection and inkjet marking, it is wound into a reel.

[0027] In a specific embodiment of the present invention, a specific Mn content aluminum alloy formulation is used to achieve higher compressive strength and corrosion resistance while ensuring the continuous extrusion processability. This solves the problem of insufficient strength in traditional 1000 series aluminum alloy continuous extrusion products. Strictly limiting Si≤0.20% and Fe≤0.20% can reduce the formation of harmful phases and improve weld quality. The integrated design of the entire process improves the product qualification rate and reduces the scrap rate caused by aluminum chip defects. At the same time, the continuous extrusion process itself has the advantages of low equipment investment and high production efficiency. After optimization by this solution, the product quality stability is further improved.

[0028] Specifically, step S1 includes:

[0029] Based on the target chemical composition, according to Calculate the proportion coefficient of each alloying element relative to pure aluminum, where i represents the i-th alloying element. The mass percentage of the i-th alloying element in the target aluminum alloy is expressed in %. The sum of the target mass percentages of all alloying elements, expressed in %. Let be the mass ratio coefficient of the i-th alloying element to pure aluminum, dimensionless, based on the actual mass of the molten aluminum;

[0030] According to the formula Calculate the required mass of raw materials to be added for each alloying element. Where M is the mass of molten aluminum in the smelting furnace, in kg. The mass percentage of the i-th alloying element in the added raw materials is expressed in %. The mass of raw material required to be added for the i-th alloying element, in kg;

[0031] According to the calculation Mn source, Si source, Fe source, Cu source and Ti source are added to aluminum liquid respectively and stirred evenly to obtain an aluminum alloy melt with chemical composition satisfying Mn 0.95%-1.20%, Si≤0.20%, Fe≤0.20%, Cu0.02%-0.05%, Ti0.06%-0.12%, and the balance being Al and unavoidable impurities;

[0032] The obtained aluminum alloy melt is refined, degassed, and allowed to stand before being cast into round rods, which are then used as raw materials for continuous extrusion.

[0033] In a specific embodiment of the present invention, the target chemical composition is taken as the median value of each element's control range: Mn 1.075%, Si 0.10%, Fe 0.10%, Cu 0.035%, Ti 0.09%, substituted into... Calculate the proportioning coefficient;

[0034] The mass M of molten aluminum is measured in real time using a floor scale or flow meter, with an accuracy of ±1 kg. (Raw material mass) Weighed using an electronic scale, with an accuracy of ±0.1 kg;

[0035] When adding Mn source, Si source, Fe source, Cu source, or Ti source, control the temperature of the aluminum liquid at 725℃-750℃. Stir for 5-10 minutes after each addition and keep warm for 8-10 minutes.

[0036] Specifically, step S2 includes:

[0037] Determine the straightening inflection radius: based on the yield strength of the aluminum alloy round rod. , elastic modulus E and radius of the round rod According to the formula Calculate the theoretical inflection radius Where E is the elastic modulus of the aluminum alloy round rod, with the unit being MPa. The radius of the round rod is in mm. The yield strength of an aluminum alloy round rod is measured in MPa. To account for the inverse curvature ratio of the neutral layer offset, a dimensionless value is used, ranging from 1.0 to 1.5. The theoretical inflection radius is expressed in mm.

[0038] Setting the straightening roller parameters: A two-roll straightener is used, consisting of a concave roller and a convex roller. The waist radius of the concave roller is... and the waist radius of the convex roller All are 30-50 mm, with a difference in roll waist radius. The angle between the axis of the straightening roller and the axis of the round rod is 2-5mm. ,in The distance between the two points of contact between the round rod and the straightening roller, projected along the axis of the straightening roller, is expressed in mm. The radius of the straightening roller at the contact point is in mm. The angle between the cross-section of the straightening roller and the plane of the roller waist is expressed in degrees. The angle between the axis of the straightening roller and the axis of the round rod is in degrees. When calculating the angle of the concave roller, use a combination of +, - and + signs. When calculating the angle of the convex roller, use a combination of -, + and - signs.

[0039] Set the initial roll gap value: according to the formula Calculate the initial roll gap ,in This represents the maximum deflection applied to the concave roller, in mm. r is the contact state correction factor, with a value ranging from 1.0 to 1.3. The initial roll gap value is in mm;

[0040] Straightening operation: The aluminum alloy round rod is fed into the straightening machine and repeatedly bent and straightened under the determined parameters, and the curvature of the round rod after straightening is controlled to be ≤2 mm / m.

[0041] In a specific embodiment of the present invention, the yield strength of the aluminum alloy round rod The strength is 80-120 MPa, the elastic modulus E is 69-71 GPa, and the radius of the round rod is... It is 5-15 mm;

[0042] The contact state correction factor r is set to 1.15.

[0043] The straightening process involves 3-5 repeated bending cycles, with the straightening speed controlled at 0.5-1.5 m / s.

[0044] During the straightening process, an online laser rangefinder is used to monitor the curvature of the round rod in real time. When the curvature exceeds 2 mm / m, the included angle is adjusted through closed-loop feedback. or roller gap .

[0045] Specifically, in step S3, during the ultrasonic cleaning step, the ultrasonic frequency f, ultrasonic pulse duty cycle R, ultrasonic power P, cleaning fluid temperature T, and ultrasonic cleaning time are determined and adjusted in real time based on the diameter D of the round rod and the surface oil contamination level G. Cleaning parameters:

[0046] In step S3, the hot water rinsing step, the rinsing temperature is adjusted by a PID controller to set the temperature. Take 65℃, proportionality coefficient Pick Integral coefficient Pick Differential coefficients Pick The rinsing time is fixed at 2.5 seconds;

[0047] In the drying step, compressed air is used for purging. The purging pressure is 0.4-0.6 MPa, the purging angle is 45° with the axis of the round rod, and the purging time is 3-5 seconds.

[0048] In a specific embodiment of the present invention, the ultrasonic frequency f= Where W is the total mass of the round rods placed into the cleaning tank at one time, in kg, and f is the output frequency of the ultrasonic generator, in kHz;

[0049] Ultrasonic pulse duty cycle R= , where R is the duty cycle, dimensionless (%), representing the proportion of pulse working time to the total cycle, and G is the type of main contaminant on the surface of the round rod determined by visual inspection or rapid wiping method;

[0050] Ultrasonic power Where S is the total surface area of ​​the round rod, according to The unit of calculation is m², D is the diameter of the round rod in meters, L is the length of a single round rod in meters, and N is the number of round rods. For the target cavitation intensity, take Converted to P represents the output power of the ultrasonic generator, in W.

[0051] The closed-loop control of the cleaning fluid temperature T uses a PID control algorithm, according to the formula... Calculate heater output adjustment amount ,in The temperature deviation is expressed in °C. To set the temperature, use 65℃. To measure temperature in real time, Let be the proportionality coefficient, and take . , Let be the integral coefficient, and take . , Let be the differential coefficient, and take . , This refers to the heater power adjustment, expressed in watts (W).

[0052] Ultrasonic cleaning time ,in To preset the cavitation energy required per unit area, take , The actual cavitation intensity is measured in real time using the cavitation noise spectrum method, per unit. , The actual execution time of ultrasonic cleaning is expressed in seconds and is limited to [time range]. Within the range;

[0053] The temperature is collected in real time by a Pt100 platinum resistance temperature sensor inserted into the cleaning tank, with a sampling period of 0.5s and a measurement accuracy of ±0.1℃.

[0054] The cavitation noise spectrum method uses a piezoelectric sensor with a bandwidth of 20-100 kHz to collect cavitation noise signals, extracts the peak amplitude around 40 kHz through fast Fourier transform, and inverts the noise based on a pre-calibrated cavitation intensity-noise amplitude curve. .

[0055] Specifically, step S4 includes:

[0056] Extrusion ratio preset: based on the cross-sectional area of ​​the round rod raw material. The cross-sectional area of ​​the target microchannel aluminum flat tube According to the formula Calculate the actual extrusion ratio and set Within the range of 1.0-7.5;

[0057] Mold parameter settings: The width of the upper mold flow divider bridge is fixed at 10.0mm, and the length of the lower mold working belt is... The value is determined based on the wall thickness t of the flat tube, ranging from 1.15 to 1.30 mm, where t is the wall thickness of the microchannel aluminum flat tube in mm, k is the working zone length coefficient, ranging from 1.5 to 2.0, and L is the length of the lower die working zone in mm.

[0058] Setting the radius of the bottom arc of the extrusion wheel groove: radius of the bottom arc of the extrusion wheel groove The value is determined based on the diameter d of the round rod, and ranges from 3.5 to 5.0 mm.

[0059] Control of the gap between the extrusion roller and the extrusion shoe: according to the formula Calculate the gap amount And adjusted to 0.8-1.2mm, among which Let E be the yield strength of the aluminum alloy round rod at the extrusion temperature, expressed in MPa, and let E be the elastic modulus of the aluminum alloy round rod at the extrusion temperature, expressed in MPa. The clearance adjustment coefficient is 0.08-0.12, dimensionless, and d is the diameter of the round rod in mm. The radial clearance between the extrusion roller and the extrusion shoe is in mm;

[0060] Coupled control of extrusion temperature and rotation speed: according to formula Calculate the heat of deformation per unit time and adopt the formula The steady-state thermal balance equation determines the required cooling flow rate q to maintain the extrusion temperature at 370-420℃, where... The heat conversion efficiency during plastic deformation is taken as 0.90-0.95, dimensionless. The flow stress of the aluminum alloy is expressed in MPa. The average strain rate is in units of V is the unit of volume for the deformation zone: m³. The unit of deformation heat power is W. For frictional heat power, according to the Coulomb friction model Calculation, where The coefficient of friction is 0.2-0.4. The unit for normal stress is W. The density of the aluminum alloy is taken as 2700 kg / m³, c is the specific heat capacity of the aluminum alloy is taken as 900 J / (kg·℃), and q is the flow rate of the cooling medium. To reduce the temperature rise, a temperature of 5-10℃ is selected. The actual temperature T is made to meet the condition of 370℃≤T≤420℃ by adjusting the extrusion wheel speed n and the cooling flow rate q.

[0061] Flow stress calculation: based on hyperbolic equation Calculate flow stress ,in , is a parameter, and the unit is , Strain rate, unit: Q is the deformation activation energy, taken as 156 kJ / mol; R is the molar gas constant, taken as 8.314 J / (mol·K); T is the absolute temperature in K; A, n, Let A be a material constant, and for 6063 aluminum alloy, take A= n=4.2 = , The unit for flow stress is MPa;

[0062] Extrusion pressure control: according to the formula Calculate the required extrusion pressure P, and control the actual pressure within the range of 45-55 MPa. The unit for flow stress is MPa. The extrusion ratio is dimensionless. The coefficient of friction is dimensionless. The normal stress of the extrusion wheel groove wall is expressed in MPa. The effective contact arc length between the billet and the extrusion wheel is in mm, d is the diameter of the round rod in mm, and P is the extrusion pressure in MPa.

[0063] Extrusion molding: Under controlled parameters, cleaned aluminum alloy round rods are formed into microchannel aluminum flat tubes through a continuous extrusion press and a die.

[0064] In a specific embodiment of the present invention, the working belt length coefficient k is 1.8, and the wall thickness t is 0.6-0.9 mm;

[0065] Gap adjustment coefficient Take 0.10, yield strength Its strength is 80-100 MPa, and its elastic modulus E is 69-71 GPa;

[0066] coefficient of friction The surface roughness Ra of the extrusion wheel groove was measured according to the formula. Online correction, where Ra is the surface roughness of the extrusion wheel groove in μm, ranging from 0.4 to 1.6 μm. The coefficient of friction is dimensionless.

[0067] Effective contact arc length ,in The wrap angle of the billet within the extrusion roller groove, measured in rad, ranges from 0.8 to 1.2 rad. The nominal radius of the extrusion wheel is in mm.

[0068] Specifically, during the extrusion process in step S4, fluctuations in the extrusion pressure P and extrusion temperature T are monitored online using the formula... The deviation criterion is used to judge the process stability when When the speed exceeds 10%, adjust the extrusion roller speed n, where To set the extrusion pressure, a value of 50 MPa is selected. To set the extrusion temperature, a value of 395℃ was selected. The deviation unit for comprehensive evaluation is %.

[0069] In a specific embodiment of the invention, the stability criterion integrates multi-dimensional parameter fluctuations into a single index, avoiding the limitations of single-parameter control. Real-time monitoring enables process anomalies to be detected and corrected early, effectively preventing prolonged production of defective products due to temperature or pressure drift. Rapid adjustment of the extrusion roller speed ensures process stability and product consistency, making it particularly suitable for high-volume production scenarios requiring long-term continuous operation, significantly improving production efficiency and yield.

[0070] Specifically, step S5 includes:

[0071] Establish a nonlinear relationship between zinc spraying current and extrusion speed: according to the formula Set zinc spraying current The relationship between the microchannel aluminum flat tube extrusion speed v and the extrusion speed v is a quadratic function, where v is the extrusion speed of the microchannel aluminum flat tube in m / min. The unit of the zinc spraying current is A, corresponding to the extrusion speed. a, b, c, and d are fitting constants related to the zinc spraying equipment and zinc wire specifications, a = 160, b = -1, c = 176, and d = 740.

[0072] Setting deviation threshold and delay time: Setting the current deviation threshold The range is 1-3A, and the delay time t is set to 1-2s;

[0073] Real-time monitoring and comparison: During the zinc spraying process, the actual extrusion speed of the microchannel aluminum flat tube is continuously collected. According to the formula Calculate the corresponding set current Simultaneously, the actual zinc spraying current of the arc spray gun is collected in real time. The control system determines whether the deviation condition is met. If it is met, the current zinc spraying parameters are maintained; otherwise, the timing is started.

[0074] Closed-loop adjustment: When the duration of non-compliance reaches the delay time t, the control system automatically adjusts the actual zinc spraying current. to bring it closer to the set value The adjusted current will be used as the new actual zinc spraying current to continue zinc spraying;

[0075] High-frequency vibration-assisted densification: During the zinc spraying process, a high-frequency self-vibration mechanism is used to clamp the microchannel aluminum flat tube and apply high-frequency vibration to the flat tube. The parameters of the high-frequency vibration are: the excitation frequency along the length of the flat tube is 3200-3300 Hz, the maximum amplitude is 8 mm, the excitation frequency along the width of the flat tube is 95-105 Hz, and the maximum amplitude is 1 mm. At the same time, the flat tube is rotated at a speed of 10-12 r / min to make the zinc layer uniform and dense.

[0076] Zinc spraying process: A six-axis robot drives an arc spraying machine to spray zinc onto the surface of the microchannel aluminum flat tube according to the current parameters and high-frequency vibration parameters, controlling the zinc spraying thickness to be 6-10 g / m².

[0077] In a specific embodiment of the present invention, the fitting constants a, b, c, and d are calibrated in the following way: under the conditions of a fixed zinc spraying distance of 150 mm, a compressed air pressure of 5.5 MPa, and a wire feeding speed of 68-72 mm / s, the optimal zinc spraying current I corresponding to different extrusion speeds v is measured and obtained by quadratic curve fitting.

[0078] Deviation threshold Choose 2 A, and set the delay time t to 1.5 s.

[0079] The high-frequency self-vibration mechanism includes a chuck, a square plate, two sets of excitation mechanisms, a turntable, and a drive mechanism. The excitation mechanisms are arranged along the length and width of the square plate, and each set includes an exciter and a damper. The chuck is fixed in the center of the square plate and is used to clamp the microchannel aluminum flat tube. The turntable supports the square plate through a central movable column and four auxiliary columns, and rotates the flat tube under the drive mechanism.

[0080] The arc current of the electric arc spraying machine is 85 A, the arc voltage is 27 V, the spraying distance is 150 mm, the compressed air pressure is 5.5 MPa, and the wire feeding speed is 68-72 mm / s.

[0081] Specifically, before zinc spraying in step S5, the surface of the microchannel aluminum flat tube is cleaned to remove oil and oxide scale, and preheated to 30-40℃. After zinc spraying, a cooling jacket and spiral baffles are used for forced cooling. The cooling airflow direction is opposite to the moving direction of the flat tube, and the airflow speed gradually increases along the cooling jacket to achieve rapid solidification of the zinc sprayed layer.

[0082] In a specific embodiment of the invention, preheating eliminates moisture absorption on the surface of the flat tube and improves the fluidity of the molten zinc upon contact, significantly enhancing the bonding strength between the zinc layer and the aluminum substrate. Countercurrent gradient forced cooling after zinc spraying accelerates zinc layer solidification, inhibits grain coarsening and dendrite growth, resulting in a finer and more uniform zinc layer structure. It also reduces porosity and voids that may result from slow natural cooling. The spiral baffles improve heat exchange efficiency, ensuring sufficient cooling even under high-speed production conditions.

[0083] Specifically, step S6 includes:

[0084] Cooling step: The zinc-sprayed microchannel aluminum flat tube is moved through the cooling zone at a speed v and cooled to the target temperature using water cooling. The target temperature is set at 25-40℃, according to the formula. Calculate the required cooling water flow rate Q, where For the density of aluminum alloy, take... , For the specific heat capacity of aluminum alloy, take... A represents the cross-sectional area of ​​the flat tube, in units of... , The unit for the speed of the flat tube movement is . , The measured temperature of the flat tube upon entering the cooling zone is in °C. The target cooling temperature is expressed in °C. For the density of cooling water, take... , To determine the specific heat capacity of cooling water, take... , The unit for cooling water inlet temperature is °C. The unit for cooling water outlet temperature is °C. The heat transfer efficiency coefficient has a range of values. Q represents the cooling water flow rate, in units of... ;

[0085] Eddy current testing procedure: An online flaw detection process is performed on the cooled microchannel aluminum flat tube using a through-type eddy current coil, according to the formula... Determine the frequency of flaw detection ,in Let be the magnetic permeability of the aluminum alloy, and take . , Let be the electrical conductivity of the aluminum alloy, and take . , To determine the standard skin depth, take the thickness of the flat tube wall. The unit is m, and f is the flaw detection frequency, with the unit being Hz;

[0086] Inkjet marking procedure: Based on the flaw detection results, inkjet mark the flat pipe section with defects, specifying the delay distance between the inkjet marking position and the defect position. According to the formula Calculate, where v is the moving speed of the flat tube in m / s. The total delay time from the triggering of the flaw detection signal to the execution of the inkjet printing is expressed in seconds. The distance to the location of the inkjet printing position lag defect is in meters;

[0087] Winding process: The inspected and marked microchannel aluminum flat tube is wound on a winding machine with winding tension... According to the formula Taper control is performed as the roll diameter changes, where The initial winding tension is in N, and D is the current winding diameter in m. The initial roll diameter is in meters. The maximum roll diameter is in meters (m), and k is the taper coefficient, ranging from 0.1 to 0.3. This represents the current winding tension, in N.

[0088] In a specific embodiment of the present invention, the heat transfer efficiency coefficient Based on the thickness of the zinc coating on the flat tube surface Online correction, when For 6-10 hour, Take 0.90, when Below 6 or higher than 10 hour, The corresponding decrease is 0.02;

[0089] Eddy current testing employs simultaneous excitation at multiple frequencies, including low frequency. and high frequency Two frequencies: low frequency During calculation Take half the wall thickness of the flat tube for detecting internal defects, high frequency. During calculation One-third of the flat tube wall thickness is used to detect surface defects; the two channels are processed differentially to determine the defect type.

[0090] The marking uses a high-speed inkjet printer. The marking content includes at least the defect type code, defect location coordinates, and production batch number. The inkjet printer communicates with the eddy current flaw detector via an RS485 bus, with a total delay time of [missing information]. It consists of a fixed delay and a dynamic compensation that varies with velocity, and is calculated according to equation (V):

[0091]

[0092] in The inherent response delay of the inkjet printer is taken as 0.05-0.1s. The unit for compensation of the fixed distance between the inkjet printer and the flaw detection coil is meters (m), and v is the moving speed of the flat tube in meters per second (m / s). Total delay time, in seconds;

[0093] The taper coefficient k depends on the wall thickness of the flat tube. Adjustment: When When the thickness is 0.5-0.8 mm, k is taken as 0.20. When the value is greater than 0.8 mm, k is taken as 0.15. When the thickness is less than 0.5mm, k is set to 0.25 to prevent indentation or deformation during the winding of thin-walled flat tubes.

[0094] Specifically, in step S6, the flat tube moving speed v is synchronized with the extruder outlet speed by the main control PLC, with a synchronization accuracy of ±0.5%. The cooling water flow rate Q is controlled by adjusting the opening of the electric regulating valve, with an adjustment cycle of 0.5s. The sampling frequency of the eddy current flaw detector is 2000Hz. The coiler uses a torque motor to control the tension, with a tension feedback accuracy of ±2%.

[0095] In a specific embodiment of the invention, high-precision speed synchronization ensures seamless connection of each post-processing stage on a continuous production line, avoiding accumulation or tensile deformation caused by speed mismatch. A 0.5s adjustment cycle allows cooling water flow to be quickly corrected according to temperature fluctuations, maintaining stable cooling performance. A 2000Hz sampling frequency can capture defect signals below the millimeter level, significantly improving flaw detection reliability. ±2% tension feedback accuracy minimizes winding tension fluctuations, further ensuring winding quality and flat tube shape accuracy, meeting the stringent requirements of high-end air conditioning heat exchangers for microchannel aluminum flat tubes.

[0096] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and its improved concept, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing continuously extruded microchannel aluminum flat tubes, characterized in that, include: S1. Raw material preparation: Provide aluminum alloy round rods, wherein the chemical composition of the aluminum alloy, by mass percentage, is Mn 0.95%-1.20%, Si≤0.20%, Fe≤0.20%, Cu 0.02%-0.05%, Ti 0.06%-0.12%, with the balance being Al and unavoidable impurities; S2. Straightening: Straighten the aluminum alloy round rod, controlling the curvature to ≤2mm / m; S3. Surface cleaning: The straightened round rod is then ultrasonically cleaned, rinsed with hot water, and dried in sequence. S4. Continuous extrusion: The cleaned round rod is fed into a continuous extrusion press and extruded into shape using a die. S5. Zinc spraying treatment: Zinc is sprayed onto the surface of the extruded microchannel aluminum flat tube; S6. Cooling, Flaw Detection, Marking and Winding: After zinc spraying, the flat tube is cooled, and after eddy current flaw detection and inkjet marking, it is wound into a reel.

2. The method for preparing a continuously extrudable microchannel aluminum flat tube according to claim 1, characterized in that, Step S1 includes: Based on the target chemical composition, according to Calculate the proportion coefficient of each alloying element relative to pure aluminum, where i represents the i-th alloying element. The mass percentage of the i-th alloying element in the target aluminum alloy is expressed in %. The sum of the target mass percentages of all alloying elements, expressed in %. is the mass ratio coefficient of the i-th alloying element to pure aluminum, dimensionless, and based on the actual mass of the molten aluminum. According to the formula Calculate the required mass of raw materials to be added for each alloying element. Where M is the mass of molten aluminum in the smelting furnace, in kg. The mass percentage of the i-th alloying element in the added raw materials is expressed in %. The mass of raw material required to be added for the i-th alloying element, in kg; According to the calculation Mn source, Si source, Fe source, Cu source and Ti source are added to aluminum liquid respectively and stirred evenly to obtain an aluminum alloy melt with chemical composition satisfying Mn 0.95%-1.20%, Si≤0.20%, Fe≤0.20%, Cu0.02%-0.05%, Ti0.06%-0.12%, with the balance being Al and unavoidable impurities; The obtained aluminum alloy melt is refined, degassed, and allowed to stand before being cast into round rods, which are then used as raw materials for continuous extrusion.

3. The method for preparing a continuously extrudable microchannel aluminum flat tube according to claim 1, characterized in that, Step S2 includes: Determine the straightening inflection radius: based on the yield strength of the aluminum alloy round rod. , elastic modulus E and radius of the round rod According to the formula Calculate the theoretical inflection radius Where E is the elastic modulus of the aluminum alloy round rod, with the unit being MPa. The radius of the round rod is in mm. The yield strength of an aluminum alloy round rod is measured in MPa. To account for the inverse curvature ratio of the neutral layer offset, a dimensionless value is used, ranging from 1.0 to 1.

5. The theoretical inflection radius is expressed in mm. Setting the straightening roller parameters: A two-roll straightener is used, which consists of a concave roller and a convex roller, with the concave roller waist radius... and the waist radius of the convex roller All are 30-50mm, with a difference in roller waist radius. The angle between the axis of the straightening roller and the axis of the round rod is 2-5mm. ,in The distance between the two points of contact between the round rod and the straightening roller, projected along the axis of the straightening roller, is expressed in mm. The radius of the straightening roller at the contact point is in mm. The angle between the cross-section of the straightening roller and the plane of the roller waist is expressed in degrees. The angle between the axis of the straightening roller and the axis of the round rod is in degrees. When calculating the angle of the concave roller, use a combination of +, - and + signs. When calculating the angle of the convex roller, use a combination of -, + and - signs. Set the initial roll gap value: according to the formula Calculate the initial roll gap ,in This represents the maximum deflection applied to the concave roller, in mm. r is the contact state correction factor, with a value ranging from 1.0 to 1.

3. The initial roll gap value is in mm; Straightening operation: The aluminum alloy round rod is fed into the straightening machine and repeatedly bent and straightened under the determined parameters, and the curvature of the round rod after straightening is controlled to be ≤2mm / m.

4. The method for preparing a continuously extrudable microchannel aluminum flat tube according to claim 1, characterized in that, In step S3, during the ultrasonic cleaning process, the ultrasonic frequency f, ultrasonic pulse duty cycle R, ultrasonic power P, cleaning fluid temperature T, and ultrasonic cleaning time are determined and adjusted in real time based on the diameter D of the rod and the surface oil contamination level G. Cleaning parameters: In step S3, the hot water rinsing step, the rinsing temperature is adjusted by a PID controller to set the temperature. Take 65℃, proportionality coefficient Pick Integral coefficient Pick Differential coefficients Pick The rinsing time is fixed at 2.5 seconds; In the drying step, compressed air is used for purging, with a purging pressure of 0.4-0.6 MPa, a purging angle of 45° to the axis of the round rod, and a purging time of 3-5 seconds.

5. The method for preparing a continuously extrudable microchannel aluminum flat tube according to claim 1, characterized in that, Step S4 includes: Extrusion ratio preset: based on the cross-sectional area of ​​the round rod raw material. The cross-sectional area of ​​the target microchannel aluminum flat tube According to the formula Calculate the actual extrusion ratio and set Within the range of 1.0-7.5; Mold parameter settings: The width of the upper mold flow divider bridge is fixed at 10.0mm, and the length of the lower mold working belt is... The value is determined based on the wall thickness t of the flat tube, ranging from 1.15 to 1.30 mm, where t is the wall thickness of the microchannel aluminum flat tube in mm, k is the working zone length coefficient, ranging from 1.5 to 2.0, and L is the length of the lower die working zone in mm. Setting the radius of the bottom arc of the extrusion wheel groove: radius of the bottom arc of the extrusion wheel groove The value is determined based on the diameter d of the round rod, and ranges from 3.5 to 5.0 mm. Extrusion roller and extrusion shoe clearance control: according to formula Calculate the gap amount And adjusted to 0.8-1.2mm, among which Let E be the yield strength of the aluminum alloy round rod at the extrusion temperature, expressed in MPa, and let E be the elastic modulus of the aluminum alloy round rod at the extrusion temperature, expressed in MPa. The clearance adjustment coefficient is 0.08-0.12, dimensionless, and d is the diameter of the round rod in mm. The radial clearance between the extrusion roller and the extrusion shoe is in mm; Coupled control of extrusion temperature and rotation speed: according to formula Calculate the heat of deformation per unit time and adopt the formula The steady-state thermal balance equation determines the required cooling flow rate q to maintain the extrusion temperature at 370-420℃, where... The heat conversion efficiency during plastic deformation is taken as 0.90-0.95, dimensionless. The flow stress of the aluminum alloy is expressed in MPa. The average strain rate is in units of V is the unit of volume for the deformation zone: m³. The unit of deformation heat power is W. For frictional heat power, according to the Coulomb friction model Calculation, where The coefficient of friction is 0.2-0.

4. The unit for normal stress is W. The density of the aluminum alloy is taken as 2700 kg / m³, c is the specific heat capacity of the aluminum alloy is taken as 900 J / (kg·℃), and q is the flow rate of the cooling medium. To reduce the temperature rise, a temperature of 5-10℃ is selected. The actual temperature T is made to meet the condition of 370℃≤T≤420℃ by adjusting the extrusion wheel speed n and the cooling flow rate q. Flow stress calculation: based on hyperbolic equation Calculate flow stress ,in , is a parameter, and the unit is , Strain rate, unit: Q is the deformation activation energy, taken as 156 kJ / mol; R is the molar gas constant, taken as 8.314 J / (mol·K); T is the absolute temperature in K; A, n, Let A be a material constant, and for 6063 aluminum alloy, take A= n=4.2 = , The unit for flow stress is MPa; Extrusion pressure control: according to the formula Calculate the required extrusion pressure P, and control the actual pressure within the range of 45-55 MPa. The unit for flow stress is MPa. The extrusion ratio is dimensionless. The coefficient of friction is dimensionless. The normal stress of the extrusion wheel groove wall is expressed in MPa. The effective contact arc length between the billet and the extrusion wheel is in mm, d is the diameter of the round rod in mm, and P is the extrusion pressure in MPa. Extrusion molding: Under controlled parameters, cleaned aluminum alloy round rods are formed into microchannel aluminum flat tubes through a continuous extrusion press and a die.

6. The method for preparing a continuously extrudable microchannel aluminum flat tube according to claim 5, characterized in that, In step S4, during the extrusion process, the fluctuations of the extrusion pressure P and extrusion temperature T are monitored online using the formula... The deviation criterion is used to judge the process stability when When the speed exceeds 10%, adjust the extrusion roller speed n, where To set the extrusion pressure, a value of 50 MPa is selected. To set the extrusion temperature, a value of 395℃ was selected. The deviation unit for comprehensive evaluation is %.

7. The method for preparing a continuously extrudable microchannel aluminum flat tube according to claim 1, characterized in that, Step S5 includes: Establish a nonlinear relationship between zinc spraying current and extrusion speed: according to the formula Set zinc spraying current The relationship between the microchannel aluminum flat tube extrusion speed v and the extrusion speed v is a quadratic function, where v is the extrusion speed of the microchannel aluminum flat tube in m / min. The unit of the zinc spraying current is A, corresponding to the extrusion speed. a, b, c, and d are fitting constants related to the zinc spraying equipment and zinc wire specifications, a = 160, b = -1, c = 176, and d = 740. Setting deviation threshold and delay time: Setting the current deviation threshold The range is 1-3A, and the delay time t is set to 1-2s; Real-time monitoring and comparison: During the zinc spraying process, the actual extrusion speed of the microchannel aluminum flat tube is continuously collected. According to the formula Calculate the corresponding set current Simultaneously, the actual zinc spraying current of the arc spray gun is collected in real time. The control system determines whether the deviation condition is met. If it is met, the current zinc spraying parameters are maintained; otherwise, the timing is started. Closed-loop adjustment: When the duration of non-compliance reaches the delay time t, the control system automatically adjusts the actual zinc spraying current. to bring it closer to the set value The adjusted current will be used as the new actual zinc spraying current to continue zinc spraying; High-frequency vibration-assisted densification: During the zinc spraying process, a high-frequency self-vibration mechanism is used to clamp the microchannel aluminum flat tube and apply high-frequency vibration to the flat tube. The parameters of the high-frequency vibration are: the excitation frequency along the length of the flat tube is 3200-3300 Hz, the maximum amplitude is 8 mm, the excitation frequency along the width of the flat tube is 95-105 Hz, the maximum amplitude is 1 mm, and the flat tube is rotated at a speed of 10-12 r / min to make the zinc layer uniform and dense. Zinc spraying process: A six-axis robot drives an arc spraying machine to spray zinc onto the surface of the microchannel aluminum flat tube according to the current parameters and high-frequency vibration parameters, controlling the zinc spraying thickness to be 6-10 g / m².

8. The method for preparing a continuously extrudable microchannel aluminum flat tube according to claim 7, characterized in that, Before zinc spraying in step S5, the surface of the microchannel aluminum flat tube is cleaned to remove oil and oxide scale, and preheated to 30-40℃. After zinc spraying, forced cooling is performed using a cooling jacket and spiral baffles. The cooling airflow direction is opposite to the moving direction of the flat tube, and the airflow speed gradually increases along the cooling jacket to achieve rapid solidification of the zinc sprayed layer.

9. The method for preparing a continuously extrudable microchannel aluminum flat tube according to claim 1, characterized in that, Step S6 includes: Cooling step: The zinc-sprayed microchannel aluminum flat tube is moved through the cooling zone at a speed v and cooled to the target temperature using water cooling. The target temperature is set at 25-40℃, according to the formula. Calculate the required cooling water flow rate Q, where For the density of aluminum alloy, take... , For the specific heat capacity of aluminum alloy, take... A represents the cross-sectional area of ​​the flat tube, in units of... , The unit for the speed of the flat tube movement is . , The measured temperature of the flat tube upon entering the cooling zone is in °C. The target cooling temperature is expressed in °C. For the density of cooling water, take... , To determine the specific heat capacity of cooling water, take... , The unit for cooling water inlet temperature is °C. The unit for cooling water outlet temperature is °C. The heat transfer efficiency coefficient has a range of values. Q represents the cooling water flow rate, in units of... ; Eddy current testing procedure: An online flaw detection process is performed on the cooled microchannel aluminum flat tube using a through-type eddy current coil, according to the formula... Determine the frequency of flaw detection ,in Let be the magnetic permeability of the aluminum alloy, and take . , Let be the electrical conductivity of the aluminum alloy, and take . , To determine the standard skin depth, take the thickness of the flat tube wall. The unit is m, and f is the flaw detection frequency, with the unit being Hz; Inkjet marking procedure: Based on the flaw detection results, inkjet mark the flat pipe section with defects, specifying the delay distance between the inkjet marking position and the defect position. According to the formula Calculate, where v is the moving speed of the flat tube in m / s. The total delay time from the triggering of the flaw detection signal to the execution of the inkjet printing is expressed in seconds. The distance to the location of the inkjet printing position lag defect is in meters; Winding process: The inspected and marked microchannel aluminum flat tube is wound on a winding machine with winding tension... According to the formula Taper control is performed as the roll diameter changes, where The initial winding tension is in N, and D is the current winding diameter in m. The initial roll diameter is in meters. The maximum roll diameter is in meters (m), and k is the taper coefficient, ranging from 0.1 to 0.

3. This represents the current winding tension, in N.

10. A method for preparing a continuously extrudable microchannel aluminum flat tube according to claim 9, characterized in that, In step S6, the flat tube moving speed v is synchronized with the extruder outlet speed by the main control PLC, with a synchronization accuracy of ±0.5%. The cooling water flow rate Q is controlled by adjusting the opening of the electric regulating valve, with an adjustment cycle of 0.5s. The sampling frequency of the eddy current flaw detector is 2000Hz. The coiler uses a torque motor to control the tension, with a tension feedback accuracy of ±2%.

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