Isothermal constant velocity production process of extruded micro-channel aluminum flat tube

Abstract

The present application relates to a kind of extrusion microchannel aluminum flat tube isothermal constant speed production process, by installing multiple liquid nitrogen rapid cooling units outside extrusion die to the microchannel aluminum flat tube section in extrusion die for cooling cooling, extrusion die side wall is provided with several liquid nitrogen cooling holes, liquid nitrogen rapid cooling unit is sent liquid nitrogen to the microchannel aluminum flat tube section in extrusion die through liquid nitrogen cooling hole and carries out cooling cooling;By using thermal imager outside extrusion die to the microchannel aluminum flat tube section surface temperature in extrusion die is monitored, and microchannel aluminum flat tube section surface temperature signal is sent to control module, and the flow of liquid nitrogen at liquid nitrogen cooling hole is adjusted by control module.The isothermal constant speed production process of the present application is close to " isothermal constant speed", product appearance quality is high, the qualified rate can reach 97.6% or more, extrusion rate can reach 107m / min or more, extrusion rate is high, the modification of extrusion die is small, effectively improve production efficiency and capacity, and application value is high.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of isothermal constant speed production process of extrusion microchannel aluminum flat tube, belong to microchannel aluminum flat tube extrusion molding technical field. BACKGROUND

[0002] Microchannel aluminum flat tube (also known as "parallel flow aluminum flat tube") is a kind of thin-walled porous flat tube material made of refined aluminum bar through hot extrusion and surface zinc spraying corrosion prevention treatment, mainly used in various refrigerant air conditioning systems as a pipeline component carrying new environmental protection refrigerant, and it is the key material of new generation parallel flow microchannel air conditioner heat exchanger using new environmental protection.

[0003] In the extrusion production process, in addition to the key role of the die size, extrusion temperature and speed also play an important role in the size of the extruded flat tube, so under the condition of ensuring the size of the die is qualified, isothermal constant speed extrusion is the key to ensure the consistency of the size.

[0004] In the conventional metal hot extrusion process, the temperature and deformation of the billet are very uneven, which leads to unevenness in the size, shape, organization and performance of the product, and isothermal extrusion can reduce these unevenness, which is an ideal extrusion process. The feature of isothermal extrusion is to ensure that the temperature of the metal in the deformation zone near the die hole remains constant or basically constant throughout the extrusion process, and to maintain the uniformity of the metal deformation resistance and metal flow as much as possible, so that the die face pressure remains unchanged or basically unchanged, thereby obtaining a higher extrusion speed, and the shape and size of the extruded profile are accurate, and the uniformity of the organization and performance along the cross section and length direction is also improved. Therefore, the implementation of isothermal extrusion is of great significance to improve the productivity and quality of the extruded products.

[0005] There are many methods to achieve isothermal extrusion of aluminum or aluminum alloy, among which the main methods can be roughly divided into four categories:

[0006] The first method is to change the temperature distribution of the billet along the length direction to compensate (offset) the temperature rise caused by deformation heat or the temperature drop caused by the cooling effect of the tool, which can be called billet gradient temperature extrusion. This method mainly includes billet gradient temperature heating method and billet gradient temperature cooling method, which has the advantages of simple method and easy implementation, but has the disadvantages of small control range and low precision.

[0007] The second method is to control the temperature of the tool to ensure that the temperature of the metal in the deformation zone near the die hole and the product flowing out of the die hole remains basically unchanged, which can be called tool temperature control extrusion. This method mainly includes extrusion cylinder partition heating method, extrusion cylinder partition cooling method, die cooling method and gasket temperature control method, which has the advantages of strong controllability and high control precision, but has the disadvantages of complex tool structure (except gasket temperature control method) and difficult control.

[0008] The third type of method involves comprehensively optimizing various process parameters that affect the temperature (heat flow) balance during the extrusion process, aiming to maintain a relatively constant temperature when the product exits the die. This can be called the process parameter optimization control isothermal extrusion method. The advantages of this method are that it can achieve isothermal extrusion under conditions of uniform billet heating and constant extrusion speed, and the process is simple. However, it has disadvantages such as limited parameter matching conditions for achieving isothermal extrusion and its unfavorability in obtaining the highest possible extrusion speed for alloys with good extrudability.

[0009] The fourth type of method involves controlling the extrusion speed to maintain a relatively constant temperature as the profile exits the die. Speed-controlled isothermal extrusion is further divided into two types: speed model control and online closed-loop speed control. Speed ​​model control involves establishing a temperature-speed model of the extrusion process and controlling the speed through programmed control to ensure that the temperature of the product exiting the die remains relatively constant during extrusion; this can be called simulated isothermal extrusion. The advantages of this method are its simplicity, ease of implementation, and ability to achieve higher control accuracy than the first type of method. The disadvantages are the difficulty in establishing a correct model, the challenge in accurately reflecting actual changes in process parameters and boundary conditions during extrusion, and the need for extensive empirical data accumulation.

[0010] Online closed-loop control of extrusion speed involves detecting temperature changes in the product at the die exit and adjusting relevant process parameters online to achieve online closed-loop control of temperature and speed. This type of method is an ideal isothermal extrusion method that can achieve relatively ideal control results, but it is difficult to implement and requires advanced technology and equipment.

[0011] The temperature rise principle of microchannel aluminum flat tube extrusion is as follows: In the profile extrusion production process, when a profile casting is extruded into a profile through a die, the heat of plastic deformation of the casting is concentrated near the die; during extrusion, there is metal-to-metal frictional heat between the profile surface and the die surface. Since both heat sources are located near the die, the outlet temperature of the extruded profile exceeds the heating temperature of the casting, and the die temperature is constantly rising. When the extrusion speed is too high, surface defects are easily formed in the profile, and the excessively high die temperature shortens the die's service life. Therefore, from this extrusion production perspective, controlling additional heating and effectively cooling the die are crucial.

[0012] Because extrusion production is a continuous process, the surface temperature of the profile within a single die cannot be measured quickly and accurately. Currently, temperature sensors are used at the exit of the die's working belt for measurement. However, the temperature measured and fed back to the profile temperature inside the die differs greatly. It is impossible to guarantee in real time and with 100% certainty that the temperature of any section of the profile inside the die is the same. It can only be infinitely close to "isothermal constant rate". Therefore, some surface defects still exist on the surface of the extruded profile, which prevents the profile qualification rate from being improved further. For example, the isothermal extrusion system for aluminum profiles disclosed in Publication No. CN106694595B includes an extrusion cylinder, an extrusion cylinder, and an aluminum profile outlet temperature detection mechanism. The piston rod of the extrusion cylinder passes through the material extrusion chamber and connects to the extrusion pad. A pad mold is provided at the right end of the extrusion cylinder, and a through groove communicating with the material extrusion chamber is provided on the pad mold. The aluminum profile outlet temperature detection mechanism includes a vertical cylinder and a temperature sensor. The vertical cylinder is located at the right end of the extrusion cylinder, and a temperature sensor is provided at the bottom of the piston rod of the vertical cylinder. A cooling channel is also formed on the cylindrical surface of the extrusion cylinder. The beneficial effects of this invention are: compact structure, efficient control of aluminum profile outlet temperature, improved aluminum profile production efficiency, and guaranteed product quality; the production process is simple. However, this invention suffers from the aforementioned problems.

[0013] Based on this, the present invention is proposed. Summary of the Invention

[0014] This invention addresses the shortcomings of existing technologies by providing an isothermal constant-rate production process for extruding microchannel aluminum flat tubes. The specific technical solution is as follows:

[0015] An isothermal constant-rate production process for extruding microchannel aluminum flat tubes includes the following steps:

[0016] Multiple liquid nitrogen rapid cooling units are installed outside the extrusion die to cool the microchannel aluminum flat tube profile inside the extrusion die, with adjacent liquid nitrogen rapid cooling units staggered.

[0017] The side wall of the extrusion die is provided with a number of liquid nitrogen cooling holes, and the liquid nitrogen rapid cooling unit delivers liquid nitrogen to the microchannel aluminum flat tube profile inside the extrusion die through the liquid nitrogen cooling holes for cooling and temperature reduction.

[0018] The surface temperature of the microchannel aluminum flat tube profile inside the extrusion die is monitored by a thermal imager outside the extrusion die, and the surface temperature signal of the microchannel aluminum flat tube profile is transmitted to the control module, which then adjusts the flow rate of liquid nitrogen at the liquid nitrogen cooling hole.

[0019] In a further improvement, the liquid nitrogen rapid cooling unit includes a heat insulation groove fixedly installed on the outside of the extrusion die, a liquid nitrogen delivery pipe connected to the liquid nitrogen source, and an electric cylinder. The groove opening of the heat insulation groove is sealed to the outer wall of the extrusion die, and a liquid nitrogen flow cavity is formed between the heat insulation groove and the extrusion die. An adjustment head is provided in the liquid nitrogen flow cavity. The adjustment head is driven by the electric cylinder to perform translational reciprocating motion along the forward direction of the microchannel aluminum flat tube profile.

[0020] The outer side of the extrusion die is provided with multiple protrusions and grooves arranged adjacent to the protrusions. Both the protrusions and grooves are located in the liquid nitrogen flow chamber. The liquid nitrogen cooling hole includes a first through hole provided at the protrusion and a second through hole provided at the groove. A gap is provided between the adjusting head and the protrusion. The liquid nitrogen delivery pipe is connected to the liquid nitrogen flow chamber.

[0021] In a further improvement, the adjusting head includes a conch-shaped head and a conical part integrated with the head. The surface of the head is provided with a logarithmic spiral thread, and a guide rod is connected to the tip of the conical part.

[0022] In a further improvement, the electric cylinder includes a cylinder seat installed outside the heat insulation groove and a telescopic rod coaxially connected to the guide rod. One side of the heat insulation groove is provided with an installation hole for the telescopic rod to enter and exit. A heat insulation sleeve is also installed on one side of the heat insulation groove. The heat insulation sleeve is fixedly installed inside the heat insulation groove and is sleeved on the outside of the guide rod.

[0023] In a further improvement, a third through hole connected to the liquid nitrogen delivery pipe is provided on the other side of the heat insulation tank. The axis of the third through hole, the axis of the mounting hole, and the axis of the adjusting head are coaxial.

[0024] In a further improvement, the liquid nitrogen cooling hole includes a large circular hole, a conical hole, and a small circular hole. The small circular hole is located inside the extrusion die, the large circular hole is located outside the extrusion die, and the conical hole is located between the large circular hole and the small circular hole. The large circular hole, the conical hole, and the small circular hole are interconnected.

[0025] In a further improvement, the diameter of the small round hole is 5-10 mm, and the diameter of the large round hole is 25-35 mm.

[0026] In a further improvement, the cone angle of the cone portion is 122° to 126°.

[0027] A further improvement is made: when the direction of movement of the adjusting head is the same as the direction of movement of the microchannel aluminum flat tube profile, the forward speed of the microchannel aluminum flat tube profile is v0, and the speed of movement of the adjusting head is v1, 0.32v0≤(v0-v1)≤0.36v0;

[0028] When the direction of movement of the adjusting head is opposite to the direction of movement of the microchannel aluminum flat tube profile, the forward speed of the microchannel aluminum flat tube profile is v0, and the speed of movement of the adjusting head is v2, 0.11v0≤(v0-v2)≤0.13v0.

[0029] A further improvement is that the fit between the telescopic rod and the mounting hole is a clearance fit.

[0030] The beneficial effects of this invention are:

[0031] When producing microchannel aluminum flat tubes using the isothermal constant-speed extrusion process described in this invention, the process is made to approximate the "isothermal constant-speed" condition. This results in microchannel aluminum flat tubes with good dimensional consistency, high appearance quality, and a pass rate exceeding 97.6%. The extrusion rate can reach over 107 m / min. This high extrusion rate requires minimal modification to the extrusion die, effectively improving production efficiency and capacity, and demonstrating high application value. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the liquid nitrogen rapid cooling unit described in this invention;

[0033] Figure 2 This is an internal schematic diagram of the liquid nitrogen rapid cooling unit described in this invention;

[0034] Figure 3 This is a schematic diagram of the structure of the adjusting head described in this invention. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0036] In the description of this invention, it should be noted that, unless otherwise stated, "a plurality of" means two or more; the terms "upper," "lower," "left," "right," "inner," "outer," "front end," "rear end," "head," "tail," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. Furthermore, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0037] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0038] Example 1

[0039] An isothermal constant-rate production process for extruding microchannel aluminum flat tubes includes the following steps:

[0040] Multiple liquid nitrogen rapid cooling units 50 are installed outside the extrusion die 10 to cool the microchannel aluminum flat tube profile 40 inside the extrusion die 10. Figure 1 As shown, two adjacent liquid nitrogen rapid cooling units are staggered.

[0041] The side wall of the extrusion die 10 is provided with a number of liquid nitrogen cooling holes. The liquid nitrogen rapid cooling unit delivers liquid nitrogen to the microchannel aluminum flat tube profile 40 inside the extrusion die 10 through the liquid nitrogen cooling holes for cooling.

[0042] The surface temperature of the microchannel aluminum flat tube profile 40 inside the extrusion die 10 is monitored by a thermal imager outside the extrusion die 10, and the surface temperature signal of the microchannel aluminum flat tube profile 40 is transmitted to the control module, which then adjusts the flow rate of liquid nitrogen at the liquid nitrogen cooling hole.

[0043] First, a thermal imager is used to obtain a qualitative understanding of the temperature at different locations within the microchannel aluminum flat tube profile 40 inside the extrusion die 10 (relative to the theoretical actual temperature). The temperature measurement error using the thermal imager is within ±2℃. However, if only the temperature value at the outlet of the extrusion die 10 is used and the actual temperature value at a certain point on the microchannel aluminum flat tube profile 40 is used, the value can reach more than ±10℃. Therefore, using a thermal imager to measure the temperature at different locations on the microchannel aluminum flat tube profile 40 will yield better results.

[0044] As for why a temperature sensor such as a temperature probe is not installed at the liquid nitrogen cooling hole for temperature measurement, it is impractical because the microchannel aluminum flat tube profile 40 will rub against the temperature probe at high speed, which will not only cause the temperature probe to be damaged in a short time, but also cause a lot of scratches and grooves on the microchannel aluminum flat tube profile 40.

[0045] Using non-contact temperature measurement, such as installing an infrared thermometer at the liquid nitrogen cooling hole or other temperature measuring holes, is impractical. This is because the infrared rays emitted by the infrared thermometer are affected by the hot airflow inside the measuring hole, causing drastic fluctuations and temperature errors that can reach ±16℃ or more in a short period of time, making it inaccurate and therefore unusable.

[0046] Example 2

[0047] like Figures 1 to 3 As shown, the liquid nitrogen rapid cooling unit 50 includes a heat insulation groove 51 fixedly installed on the outside of the extrusion mold 10, a liquid nitrogen delivery pipe 30 connected to the liquid nitrogen source, and an electric cylinder 20. The groove opening of the heat insulation groove 51 is sealed to the outer wall of the extrusion mold 10, and a liquid nitrogen flow cavity 52 is formed between the heat insulation groove 51 and the extrusion mold 10. An adjustment head 60 is provided in the liquid nitrogen flow cavity 52. ​​The adjustment head 60 is driven by the electric cylinder 20 to perform translational reciprocating motion along the forward direction of the microchannel aluminum flat tube profile 40.

[0048] The outer side of the extrusion die 10 is provided with a plurality of protrusions 13 and grooves 14 arranged adjacent to the protrusions 13. Both the protrusions 13 and the grooves 14 are located in the liquid nitrogen flow chamber 52. The liquid nitrogen cooling hole includes a first through hole 11 provided at the protrusion 13 and a second through hole 12 provided at the groove 14. A gap is provided between the adjusting head 60 and the protrusions 13. The liquid nitrogen delivery pipe 30 is connected to the liquid nitrogen flow chamber 52.

[0049] like Figure 3 As shown, the adjusting head 60 includes a conch-shaped head 61 and a cone 62 integrally connected to the head 61. The surface of the head 61 is provided with a logarithmic spiral thread 611, and a guide rod 22 is connected to the tip of the cone 62.

[0050] The electric cylinder 20 includes a cylinder seat 21 installed outside the heat insulation groove 51 and a telescopic rod coaxially connected to the guide rod 22. One side of the heat insulation groove 51 is provided with an installation hole for the telescopic rod to enter and exit. A heat insulation sleeve 23 is also installed on one side of the heat insulation groove 51. The heat insulation sleeve 23 is fixedly installed inside the heat insulation groove 51 and is sleeved on the outside of the guide rod 22.

[0051] Liquid nitrogen is pumped into the liquid nitrogen flow chamber 52 through the liquid nitrogen delivery pipe 30 by the liquid nitrogen pump, and then flows into the extrusion die 10 through the first through hole 11 and the second through hole 12 to continue cooling the microchannel aluminum flat tube profile 40 that has been formed in the extrusion die 10. The temperature of the corresponding area of ​​the microchannel aluminum flat tube profile 40 has been detected by the thermal imager to see if it has dropped to the expected target.

[0052] The adjusting head 60 is driven by the electric cylinder 20 to perform a reciprocating translational motion along the forward direction of the microchannel aluminum flat tube profile 40. Since the other side of the heat insulation groove 51 is provided with a third through hole 511 connected to the liquid nitrogen delivery pipe 30, the axis of the third through hole 511, the axis of the mounting hole, and the axis of the adjusting head 60 are coaxially arranged. By controlling the moving speed of the adjusting head 60 in the liquid nitrogen flow chamber 52, the flow rate of liquid nitrogen through the first through hole 11 and the second through hole 12 can be easily adjusted, thereby facilitating the adjustment of the cooling rate of the liquid nitrogen on the microchannel aluminum flat tube profile 40.

[0053] The electric cylinder 20 is used to drive the adjusting head 60 to move, which is more suitable for harsh environments such as liquid nitrogen.

[0054] The protrusions 13 and 14, along with the movement of the adjusting head 60, allow the flow velocity difference between two adjacent liquid nitrogen cooling holes to reach 0.06 m / s. Observations and experiments show that when the flow velocity difference between two adjacent liquid nitrogen cooling holes is greater than 0.05 m / s, the incidence of moss-like dark spots decreases by more than 73%. The incidence of moss-like dark spots is calculated by statistically analyzing the number of such defects in 1000 finished products. For example, if the flow velocity difference between two adjacent liquid nitrogen cooling holes is less than 0.01 m / s, the incidence of moss-like dark spots is 5.7%, with no other defects found; while when the flow velocity difference between two adjacent liquid nitrogen cooling holes reaches 0.06 m / s, the incidence of moss-like dark spots is 1.5%, with no other defects found.

[0055] As a supplement to common knowledge, the reason why the method of drilling holes in the surface of the extrusion die 10 and then pouring in liquid nitrogen for cooling is not currently adopted. Because liquid nitrogen cools very rapidly and the thermal expansion and contraction at the liquid nitrogen cooling holes is very intense, some liquid nitrogen may erode the surface of the microchannel aluminum flat tube profile 40, resulting in a large number of moss-like dark spots on the surface of the microchannel aluminum flat tube profile 40. This would increase the probability of moss-like dark spots from 3.2% to more than 6%.

[0056] If conventional liquid nitrogen valves are used to control the flow rate or volume at the corresponding first through hole 11 and second through hole 12, at least two sets of valves are required. Furthermore, due to the long pipeline, the control and feedback cycle is long, resulting in poor real-time control performance.

[0057] The present invention has found that if the difference in liquid nitrogen flow rate between the first through hole 11 and the second through hole 12 can reach a certain level, and the microchannel aluminum flat tube profile 40 is constantly moving forward, the erosion rate of the surface of the microchannel aluminum flat tube profile 40 by liquid nitrogen in the dynamic process will gradually become more uniform, so as not to cause a large number of moss-like dark spots to appear due to excessive cooling in a certain area.

[0058] Because the movement direction of the adjusting head 60 is different, there is a speed difference between its movement speed and the forward speed of the microchannel aluminum flat tube profile 40. This speed difference will also cause the diffusion rate of liquid nitrogen entering the extrusion die 10 to be different. Therefore, it is necessary to strictly control the movement speed of the adjusting head 60. The results of a large number of experiments are summarized as follows:

[0059] When the movement direction of the adjusting head 60 is the same as the forward movement direction of the microchannel aluminum flat tube profile 40, the forward speed of the microchannel aluminum flat tube profile 40 is v0, and the movement speed of the adjusting head 60 is v1, where 0.32v0≤(v0-v1)≤0.36v0. If the value of (v0-v1) is too small, such as equal to 0.1v0, the surface temperature difference of the microchannel aluminum flat tube profile 40 observed by the thermal imager is within ±3℃, with little variation. However, the incidence of moss-like dark spot defects increases by 26% in the later stages. If the value of (v0-v1) is too large, it can also lead to other defects (such as channel twisting defects, segregation defects, etc.).

[0060] When the movement direction of the adjusting head 60 is opposite to the forward movement direction of the microchannel aluminum flat tube profile 40, the forward speed of the microchannel aluminum flat tube profile 40 is v0, and the movement speed of the adjusting head 60 is v2, where 0.11v0 ≤ (v0-v2) ≤ 0.13v0. Similarly, if the value of (v0-v2) is too large, such as (v0-v2) = 0.3v0, it may lead to other defects (such as channel twisting defects, segregation defects, etc.).

[0061] Based on the temperature data fed back by the thermal imager, the movement of the adjusting head 60 within the liquid nitrogen flow chamber 52 is controlled by the electric cylinder 20 using PLC negative feedback closed-loop control technology. When liquid nitrogen is no longer needed, the third through hole 511 can be blocked by the adjusting head 60, thereby stopping the liquid nitrogen pump and immediately preventing liquid nitrogen from flowing into the extrusion mold 10.

[0062] In contrast, if the head 61 is also a conical structure and does not have a logarithmic spiral thread 611, then even in the process of moving in the same direction, when 0.32v0≤(v0-v1)≤0.36v0, the velocity difference between two adjacent liquid nitrogen cooling holes will not reach 0.03m / s.

[0063] In contrast, if the head 61 is a cylindrical structure, then even in the opposite direction of travel, when 0.11v0≤(v0-v2)≤0.13v0, the velocity difference between two adjacent liquid nitrogen cooling holes will not reach 0.02m / s.

[0064] Example 3

[0065] Based on Embodiment 2, the liquid nitrogen cooling hole includes a large circular hole 113, a conical hole 112, and a small circular hole 111. The small circular hole 111 is located inside the extrusion die 10, the large circular hole 113 is located outside the extrusion die 10, and the conical hole 112 is located between the large circular hole 113 and the small circular hole 111. The large circular hole 113, the conical hole 112, and the small circular hole 111 are interconnected.

[0066] Because the diameter of the small circular hole 111 is 5-10 mm, if the diameter of the small circular hole 111 is too large, such as equal to 2 cm, it will bring various appearance defects (channel distortion defects, segregation defects, etc.); however, it cannot be too small, otherwise the number of openings will increase exponentially in order to achieve the corresponding cooling effect. The diameter of the large circular hole 113 is 25-35 mm, which is mainly to facilitate the inflow of liquid nitrogen.

[0067] Example 4

[0068] It should be noted that when the movement direction of the adjusting head 60 is opposite to the forward direction of the microchannel aluminum flat tube profile 40, the main function is to perform secondary compression and retraction of the already injected liquid nitrogen. Therefore, it is unnecessary to provide a corresponding threaded groove on the cone 62, otherwise it would be detrimental to the retraction of the liquid nitrogen. Considering the retraction effect of the liquid nitrogen, the cone angle of the cone 62 is 122°~126°.

[0069] Example 5

[0070] The telescopic rod and the mounting hole are fitted with a clearance fit to maximize sealing and mobility. By installing the insulation sleeve 23, the leakage of liquid nitrogen from the liquid nitrogen flow chamber 52 to the outside of the insulation groove 51 can be further reduced. It should be noted that a small amount of liquid nitrogen overflowing into the insulation groove 51 will not significantly affect the temperature of the outer side of the extrusion die 10, because cooling water is also circulated to the outer side of the extrusion die 10 for cooling; therefore, a small amount of liquid nitrogen overflow has little impact.

[0071] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An isothermal constant-rate production process for extruding microchannel aluminum flat tubes, characterized in that... Includes the following steps: Multiple liquid nitrogen rapid cooling units are installed outside the extrusion die (10) to cool the microchannel aluminum flat tube profile (40) inside the extrusion die (10), with adjacent liquid nitrogen rapid cooling units staggered. The side wall of the extrusion die (10) is provided with a number of liquid nitrogen cooling holes. The liquid nitrogen rapid cooling unit delivers liquid nitrogen to the microchannel aluminum flat tube profile (40) inside the extrusion die (10) through the liquid nitrogen cooling holes for cooling. The surface temperature of the microchannel aluminum flat tube profile (40) inside the extrusion die (10) is monitored by a thermal imager outside the extrusion die (10), and the surface temperature signal of the microchannel aluminum flat tube profile (40) is transmitted to the control module, and the flow rate of liquid nitrogen at the liquid nitrogen cooling hole is adjusted by the control module. The liquid nitrogen rapid cooling unit includes a heat insulation groove (51) fixedly installed on the outside of the extrusion mold (10), a liquid nitrogen delivery pipe (30) connected to the liquid nitrogen source, and an electric cylinder (20). The groove of the heat insulation groove (51) is sealed to the outer wall of the extrusion mold (10), and a liquid nitrogen flow cavity (52) is formed between the heat insulation groove (51) and the extrusion mold (10). An adjusting head (60) is provided in the liquid nitrogen flow cavity (52). The adjusting head (60) is driven by the electric cylinder (20) to move back and forth along the forward direction of the microchannel aluminum flat tube profile (40). The outer side of the extrusion die (10) is provided with a plurality of protrusions (13) and a groove (14) arranged adjacent to the protrusions (13). The protrusions (13) and the groove (14) are both located in the liquid nitrogen flow chamber (52). The liquid nitrogen cooling hole includes a first through hole (11) provided at the protrusion (13) and a second through hole (12) provided at the groove (14). A gap is provided between the adjusting head (60) and the protrusion (13). The liquid nitrogen delivery pipe (30) is connected to the liquid nitrogen flow chamber (52). The adjusting head (60) includes a conch-shaped head (61) and a cone (62) integrally connected to the head (61). The surface of the head (61) is provided with a logarithmic spiral thread (611), and a guide rod (22) is connected to the tip of the cone (62). When the direction of movement of the adjusting head is the same as the direction of movement of the microchannel aluminum flat tube profile, the forward speed of the microchannel aluminum flat tube profile is v0, and the speed of movement of the adjusting head is v1. 0.32 v0≤(v0- v1) ≤0.36 v0; When the direction of movement of the adjusting head is opposite to the direction of movement of the microchannel aluminum flat tube profile, the forward speed of the microchannel aluminum flat tube profile is v0, and the speed of movement of the adjusting head is v2. 0.11 v0≤(v0- v2) ≤0.13 v0.

2. The isothermal constant-rate production process for extruded microchannel aluminum flat tubes according to claim 1, characterized in that: The electric cylinder (20) includes a cylinder seat (21) installed outside the heat insulation groove (51) and a telescopic rod coaxially connected to the guide rod (22). The heat insulation groove (51) has an installation hole on one side for the telescopic rod to enter and exit. The heat insulation groove (51) is also equipped with a heat insulation sleeve (23) on one side. The heat insulation sleeve (23) is fixedly installed inside the heat insulation groove (51) and is sleeved on the outside of the guide rod (22).

3. The isothermal constant-rate production process for extruded microchannel aluminum flat tubes according to claim 2, characterized in that: The other side of the heat insulation tank (51) is provided with a third through hole (511) that is connected to the liquid nitrogen delivery pipe (30). The axis of the third through hole (511), the axis of the mounting hole, and the axis of the adjusting head (60) are coaxial.

4. The isothermal constant-rate production process for extruded microchannel aluminum flat tubes according to claim 1, characterized in that: The liquid nitrogen cooling hole includes a large circular hole (113), a conical hole (112), and a small circular hole (111). The small circular hole (111) is located inside the extrusion die (10), the large circular hole (113) is located outside the extrusion die (10), and the conical hole (112) is located between the large circular hole (113) and the small circular hole (111). The large circular hole (113), the conical hole (112), and the small circular hole (111) are interconnected.

5. The isothermal constant-rate production process for extruded microchannel aluminum flat tubes according to claim 4, characterized in that: The diameter of the small round hole (111) is 5~10mm, and the diameter of the large round hole (113) is 25~35mm.

6. The isothermal constant-rate production process for extruded microchannel aluminum flat tubes according to claim 1, characterized in that: The cone angle of the cone (62) is 122°~126°.

7. The isothermal constant-rate production process for extruded microchannel aluminum flat tubes according to claim 2, characterized in that: The fit between the telescopic rod and the mounting hole is a clearance fit.

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