Air jet head for rail air cooling quenching with high and uniform heat exchange and design method thereof

Abstract

This invention relates to the field of jet nozzles for rail heat treatment, and particularly to a jet nozzle for air-cooled quenching of rails with strong and uniform heat exchange, and its design method. The jet nozzle has a three-cavity structure, comprising a top central cavity, a first side cavity, and a second side cavity. Each cavity consists of a contraction section, a throat, and an expansion section. The top central cavity corresponds to the top surface of the rail head, while the first and second side cavities correspond to the middle positions of the sides of the rail head. Based on aerodynamic principles, this invention employs a method of truncating the supersonic contour nozzle at a position corresponding to the arc angle of the rail head. Through the design of the three-cavity structure, it simultaneously improves the jet cooling capacity and cooling uniformity.

Description

Technical Field

[0001] This invention relates to the field of air nozzles for heat treatment of rails, and particularly to an air nozzle for air-cooled quenching of rails with strong and uniform heat exchange, and its design method. Background Technology

[0002] Railways are one of the main modes of land transportation, and steel rails are one of the main consumable components of railways, bearing the full pressure of train operation. The construction of new railways and the replacement of old rails result in a huge annual demand for steel rails. Furthermore, the development trend of high-speed and heavy-haul railways and the high-density transportation organization mode place higher demands on the performance of steel rails. 100-meter standard-length pearlitic steel rails are the main type of steel rail for my country's high-speed and heavy-haul railways, and heat treatment is the main means of strengthening and toughening pearlitic steel rails. Online low-speed air-cooling quenching is the main heat treatment method for 100-meter pearlitic steel rails: the high-temperature steel rails (700~900℃) in the austenitic state after rolling are directly fed into the heat treatment unit, and pressurized air is sprayed onto the surface of the rail head using a blower to accelerate cooling, ultimately obtaining a lamellar pearlitic structure.

[0003] Currently, the air-cooled quenching process for rails uses three circular air nozzles to spray air onto the top and sides of the rail head for cooling, which has prominent problems such as weak cooling capacity and poor cooling uniformity.

[0004] Taking U75V rails as an example, on the one hand, the critical cooling rate for heat treatment of U75V rails is 6~9℃ / s, but the cooling rate of the currently used air jets can only reach about 3~4℃ / s, severely limiting the optimization space for U75V rail processes. On the other hand, due to the length of the rails (hundreds of meters), the moving speed of the rails within the heat treatment unit cannot be too fast due to limitations in cooling rate and the length of the heat treatment production line. This results in the rear end of the rail (the end that enters the heat treatment unit later in the length direction) experiencing a longer natural air cooling time than the front end, leading to inconsistent initial cooling temperatures. Currently, the moving speed of U75V rails during heat treatment is approximately 1.4 m / s, and the initial quenching time at the rear end is about 79 seconds later than at the front end. The initial temperature of the rolled rail entering the heat treatment unit is 680~850℃. Studies have shown that the initial quenching temperature affects the properties of pearlitic materials after heat treatment. Increasing the cooling rate during rail heat treatment can shorten the time the rail needs to stay in the heat treatment unit, thereby increasing the rail's movement speed within the unit and reducing the initial quenching temperature difference between the front and rear ends of a 100-meter rail before entering the heat treatment unit. This ultimately improves both production efficiency and the uniformity of rail performance at both ends. On the other hand, the distance between the nozzle outlet and the heat exchange surface affects heat exchange capacity. The arrangement of the three circular nozzles results in varying distances between different positions on the rail head and the nozzle outlet, leading to uneven cooling rates across the rail cross-section (the area directly below the nozzle cools faster than other areas).

[0005] Existing technologies for addressing the prominent problems in current air-cooled quenching of steel rails include:

[0006] 1. Regarding improving cooling capacity, the use of supersonic jets to increase the jet velocity and thus enhance the cooling capacity of the nozzle has yielded positive results, demonstrating that supersonic air jets can significantly improve the cooling capacity of air-cooled quenching. However, currently used circular supersonic nozzles are all circular or have rectangular outlet structures. Due to the irregular cross-section of the rail, the distance between different positions on the rail and the nozzle outlet is not equal. Furthermore, the increased local cooling capacity further exacerbates the uneven cooling of the rail cross-section.

[0007] 2. Regarding improving cooling uniformity, existing technologies generally involve air jets designed according to the shape of the rail head. For example, air boxes are installed at the top and sides of the rail head, with closely spaced small circular air outlets on the surfaces of the air boxes opposite the rail head to reduce differences in the fluid characteristics of the jets hitting the rail surface at different locations. Other methods include using contoured multi-hole array air jets, variable-diameter multi-hole plate air jets, and plum-blossom-shaped circular hole air jets based on the rail head shape to control the cooling intensity of different parts of the rail.

[0008] The existing technologies described above only improve cooling capacity or cooling uniformity. To balance both cooling capacity and uniformity, Chinese patent document CN102643971A discloses a "Solid Rail Online Heat Treatment Device" which uses a slotted nozzle. This device arranges small-diameter, densely packed circular supersonic air outlets at opposite positions on the top and sides of the rail head, thus improving both cooling capacity and uniformity. However, it has a large number of nozzles; over 500 air outlets are set on a 500mm long air box. The frictional resistance between the air and the walls of each nozzle can affect heat exchange efficiency to some extent. Under the same process conditions, its cooling capacity for the rail is not as good as that of the circular supersonic nozzle. Summary of the Invention

[0009] To overcome the shortcomings of existing technologies, this invention provides a heat exchange nozzle for air-cooled quenching of steel rails with strong and uniform heat exchange, and its design method. It combines both heat exchange capacity and heat exchange uniformity, solving the prominent problems of weak cooling capacity and poor cooling uniformity in the air-cooled quenching process of steel rails caused by existing heat exchange nozzles.

[0010] To achieve the above objectives, the present invention employs the following technical solution:

[0011] A heat exchange nozzle for air-cooled quenching of steel rails, characterized by strong and uniform heat exchange, comprises a three-cavity structure with three cavities: a top central cavity, a first side cavity, and a second side cavity. Each cavity consists of a contraction section, a throat, and an expansion section. The top central cavity corresponds to the top surface of the rail head, while the first and second side cavities correspond to the middle positions of the sides of the rail head. The inlet walls of the contraction sections and the outlet walls of the expansion sections in the first and second side cavities are straight lines, with the outlet wall angle of the expansion section being 90°. The junction between the throat and the contraction section, and the junction between the throat and the expansion section, are smoothly transitioned. The nozzle is a modular design, with the nozzle cavity divided into two parts along a symmetrical plane in the width direction, forming a first half-nozzle and a second half-nozzle. The first half-nozzle and the second half-nozzle are detachably connected as a whole, and sealed at the joint surface outside the nozzle cavity.

[0012] Furthermore, the first half of the nozzle and the second half of the nozzle are assembled into an integral nozzle by screws, and a sealing ring is used to seal the mating surface outside the nozzle cavity.

[0013] Furthermore, the first half-spray head and the second half-spray head are provided with a horizontal connecting plate at the top, a groove in the middle corresponding to the shape of the rail head, and bolt holes on both sides.

[0014] The design method for the jet nozzle used for air-cooled quenching of rails with strong and uniform heat exchange is as follows: height of contraction section A1, mm; throat height A2, mm; height of expansion section A3, mm; width of contraction section inlet B1, mm; width of throat B2, mm; width of expansion section outlet B3, mm; length of contraction section inlet L1, mm; center length of throat L2, mm; length of expansion section outlet L3, mm; length of straight section of side outlet L4, mm; outlet wall angle a3, °; included angle of contraction section a1, °; included angle of expansion section a2, °; and jet height H.

[0015] The design method specifically includes the following steps:

[0016] Step 1) Using the top and two side profiles of the rail head section as the design reference for the nozzle expansion section outlet and throat profile curve, the rail head curve is proportionally transformed at equal intervals according to the jet height H to obtain the shape of the expansion section outlet length L3 curve.

[0017] Correspondingly, the rail head curve is transformed by equal intervals according to H+A3+0.5A2 to obtain the curve shape of the throat center length L2;

[0018] Step 2) Determine the cross-sectional area S2 of the nozzle throat (mm) based on production requirements. 2 ;

[0019] Step 3) Design the cross-sectional area S3 of the expansion section outlet, mm 2 :

[0020] Based on the required jet velocity and S2, calculate S3 using the following formula:

[0021] (1)

[0022] Where: K is the gas specific volume ratio; Ma is the jet velocity at the nozzle outlet, Mach, 1 Mach = 0.3403 km / s;

[0023] Step 4) Design the jet height H, throat width B2, and throat center length L2:

[0024] B2≥0.5mm, H≥4mm; Calculate L2 based on the determined H, B2 and S2, L2=S2 / B2;

[0025] Step 5) Design the throat height A2:

[0026] (2)

[0027] Step 6) Design the side outlet straight section length L4, outlet wall angle a3, expansion section height A3, expansion section outlet width B3, and expansion section outlet length L3: The expansion section outlet length L3 includes the length of the curved section in the middle of the expansion section outlet L3c (mm) and the length of the straight section on both sides of the side outlet, L4, i.e.:

[0028] (3)

[0029] (4)

[0030] In the formula: a4, a5 and a6 are the angles corresponding to each arc segment of the rail head, in °; L5, L6 and L7 are the arc lengths of each arc segment of the rail head.

[0031] The formula for calculating the central length L2 of the larynx is:

[0032] (5)

[0033] In the formula: L2c is the length of the curved segment at the center of the throat, mm; L2s is the length of the straight segments on both sides of the center of the throat, mm.

[0034] (6)

[0035] The relationship between L2s and L4 is as follows:

[0036] (7)

[0037] Step 7) Design the inlet cross-sectional area S1 of the contraction section, mm 2The length L1 of the contraction section inlet (mm) and the width B1 of the contraction section inlet:

[0038]

[0039] Step 8) Design the height A1 of the contraction section:

[0040] (9)

[0041] Step 9) Change the nozzle after design parameters to a three-cavity structure: cut off the nozzle cavity along the upper end of L4 parallel to the nozzle outlet wall, change the curved parts of L1 and L3 of the cut-off cavity to straight lines, and change a3 to 90°. Then move the cut-off cavity down to the middle position of the side of the rail head.

[0042] Further, in step 2), S2 is the cross-sectional area at the minimum point of the existing type of nozzle; or it is determined according to the air supply capacity of the air compressor on site. If the air supply capacity of the air compressor is A, mm³ / s, and the number of nozzles is N, then: 340×S2×N≤A.

[0043] Furthermore, step 6) is subject to three constraints:

[0044] Constraint ①: L2s≥0;

[0045] Constraint ②:

[0046] (8)

[0047] In the formula: L8 is the length of the straight section on the side of the rail head, in mm;

[0048] Constraint ③: a2>0, that is: B3>B2.

[0049] Furthermore, it also includes step 10), which smoothly transitions the throat to the junction of the contraction and expansion segments.

[0050] Compared with existing methods, the beneficial effects of the present invention are:

[0051] 1. The cavity of this invention consists of a contraction section, a throat, and an expansion section. After compressed air enters the contraction section through the inlet, the airflow velocity increases due to the gradual decrease in cross-sectional area. When it reaches the throat, the velocity reaches the local speed of sound. From the throat outlet to the expansion section, the airflow expands due to the gradual increase in cross-sectional area, and the airflow velocity further increases, eventually generating a supersonic jet. Using a supersonic air jet can significantly improve the cooling capacity of air jet quenching.

[0052] 2. The cross-sectional area ratios of the components of a supersonic jet nozzle are limited by the designed outlet velocity and inlet pressure, and influenced by the shape of the rail head. Using conventional contour-following design methods that involve simple equidistant transformations of the rail head, it is difficult to achieve a supersonic jet with uniform velocity and pressure at the rail head. This is because a supersonic jet nozzle requires its throat cross-sectional area to be smaller than the outlet cross-sectional area of ​​the expansion section to allow sufficient space for the sonic airflow to expand and generate a supersonic jet. When designing the nozzle using the equidistant transformation method, assuming a simple equidistant transformation formula based on the rail head shape, the formula for calculating the length of curve L3 at the nozzle's expansion section outlet should be:

[0053]

[0054] The formula for calculating the length of curve L2 at the center of the throat should be:

[0055]

[0056] Clearly, L2 will always be greater than L3, which contradicts the design principle of supersonic nozzles. Although the method of setting an angle α3 at the nozzle cross-section (as shown in the attached diagram) can be used... Figure 1 (As shown) can effectively alleviate the contradiction between supersonic speed and isometric transformation contouring.

[0057] Figure 10 , 11 Figures 1 and 12 show the jet flow field, jet pressure field, and rail head temperature of a 900℃ rail cooled for 100 seconds using a supersonic contour nozzle designed using a traditional simple equidistant transformation method, respectively. Figure 10 It can be seen that the highest flow velocity in the nozzle occurs near the outlet of the nozzle expansion section. When the compressed air reaches the throat through the nozzle inlet, its velocity increases significantly, reaching the speed of sound (approximately 340 m / s) relatively uniformly. As the airflow passes through the outlet expansion section, its velocity also increases significantly, reaching supersonic speeds. However, the acceleration is not uniform at different locations. At the position opposite the rail head tread, the velocity increase is close to the design value, reaching approximately Mach 1.35. At the positions opposite the two sides of the rail head, the velocity increase is greater, reaching a maximum of approximately Mach 1.73. The velocity increase at the positions opposite the two curved surfaces of the rail head is insufficient, reaching only approximately Mach 1.2 to 1.3. When the jet impacts the vicinity of the rail surface, the velocity decreases sharply. The most significant velocity decrease occurs at the rail head tread. The reason is that the outlet at the position opposite to the side of the nozzle has a larger relative expansion cross-sectional area than other positions. Therefore, the airflow expands more fully here, resulting in a greater cooling rate. However, at the position opposite to the arc surface of the rail head, the airflow expands more to both sides, resulting in insufficient speed increase at this position.

[0058] according to Figure 11 It can be seen that the airflow pressure is relatively uniform and stable in most areas of the inlet section. The inlet pressure is lower near the two side walls of the nozzle, possibly because the outlet cross-sectional area on both sides of the nozzle is larger than at other locations, resulting in excessive expansion and causing the pressure in the corresponding inlet contraction section to fail to stabilize at the design value. After passing through the throat and expansion section, the airflow pressure decreases significantly due to the expansion effect, with the pressure drop being more pronounced near the two side walls of the nozzle. The pressure drop is smaller at the location corresponding to the rail head arc surface than at other locations. When the jet approaches the rail surface, the pressure value increases significantly again, with the highest pressure value near the rail head arc surface, followed by the pressure value near the rail head tread surface, and the pressure value gradually decreases from top to bottom on the side of the rail head.

[0059] according to Figure 12 It can be seen that the pressure distribution trend of the jet on the rail head tread is consistent with the distribution trend of its cooling rate. The temperature of the cooled rail head tread and rail head arc surface is lower than that of the rail head side. The cooling capacity for the rail head side is clearly insufficient.

[0060] Based on the above analysis, it can be seen that the cooling capacity of the rail head side is weaker than that of other positions. Although the jet has a high flow velocity when it reaches the vicinity of the rail head side, its impact pressure on the rail surface is small. The fundamental reason is that the two side walls of the nozzle have an angle a3, which makes the expansion of its relative position with the rail head side greater than that of other positions. In addition, the relative distance between the rail head side and the SP nozzle outlet gradually increases from top to bottom.

[0061] Therefore, based on aerodynamic principles, this invention employs a three-section cavity structure for the nozzle. By truncating the supersonic contour nozzle at a position corresponding to the railhead's arc angle, the three-cavity structure design simultaneously enhances both jet cooling capacity and cooling uniformity. Firstly, by truncating the section with the strongest cooling capacity corresponding to the railhead's arc, L3 can be shortened more than L2 without significantly reducing cooling capacity, allowing for an increase in the cavity cross-sectional area at the corresponding position on the railhead side. Secondly, by changing a3 to 90°, the nozzle jet at this point can be perpendicularly sprayed onto the rail surface, reducing the relative distance between the nozzle outlet at different locations and the rail surface, thus resulting in more uniform cooling.

[0062] 3. In this invention, the junction between the throat and the contraction section is smoothly transitioned, as is the junction between the throat and the expansion section. This reduces air resistance and thus improves heat exchange capacity.

[0063] 4. This invention is a modular design, where the first and second half of the nozzle are assembled into a single nozzle using screws, and a sealing ring is used to seal the mating surfaces outside the nozzle cavity. This simplifies manufacturing and reduces production costs. Attached Figure Description

[0064] Figure 1 This is a front view of the cavity and design parameters of the present invention.

[0065] Figure 2 This is a side view of the cavity and design parameters of the present invention.

[0066] Figure 3 This is a schematic diagram of the three-dimensional structure of the cavity and rail head of the present invention.

[0067] Figure 4 This is a schematic diagram of the three-dimensional structure of the first half of the nozzle of the present invention.

[0068] Figure 5 This is a three-dimensional structural schematic diagram of the present invention.

[0069] Figure 6 This is a schematic diagram showing the location of the test point for the rail head temperature in the experiment of this invention.

[0070] Figure 7 This is a schematic diagram of the jet velocity field of the present invention.

[0071] Figure 8 This is a schematic diagram of the jet pressure field of the present invention.

[0072] Figure 9 This is a schematic diagram of the numerical simulation results of the temperature field of the rail cross section after cooling a U75V rail at a high temperature (900℃) for 100 seconds.

[0073] Figure 10 This is a schematic diagram of the jet flow field of a supersonic contour nozzle applied to a rail, designed using the traditional simple isometric transformation method.

[0074] Figure 11 This is a schematic diagram of the jet pressure field of a supersonic contour nozzle applied to a rail, designed using a traditional simple isometric transformation method.

[0075] Figure 12 This is a schematic diagram of the rail head temperature when a supersonic contour nozzle designed using the traditional simple equidistant transformation method cools a 900℃ rail for 100 seconds.

[0076] In the diagram: A1 - Height of the contraction section, A2 - Height of the throat, A3 - Height of the expansion section, B1 - Width of the contraction section inlet, B2 - Width of the throat, B3 - Width of the expansion section outlet, L1 - Length of the contraction section inlet, L2 - Center length of the throat, L3 - Length of the expansion section outlet, L4 - Length of the straight section of the side outlet, L5 - Arc length of the first circular arc segment, L6 - Arc length of the second circular arc segment, L7 - Arc length of the third circular arc segment, L8 - Length of the straight section of the rail head side, a1 - Angle of the contraction section, a2 - Angle of the expansion section, a3 - Angle of the outlet wall, a4 - Radius of the first circular arc segment, a5 - Radius of the second circular arc segment, a6 - Radius of the third circular arc segment, H - Jet height, 1 - Top cavity, 2 - First side cavity, 3 - Second side cavity, 4 - First half-jet head, 5 - Second half-jet head, 6 - Groove, 7 - Connecting plate, 8 - Bolt hole, 9 - Rail head. Detailed Implementation

[0077] This invention discloses a heat exchange nozzle for air-cooled quenching of steel rails with strong and uniform heat exchange, and its design method. Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this invention. The methods and applications of this invention have been described through preferred embodiments. Those skilled in the art can clearly modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0078] The embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples, examples of which are shown in the drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0079] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0080] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" 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 direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0081] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

[0082] like Figure 1-9 As shown, a heat exchange nozzle for air-cooled quenching of steel rails, characterized by strong and uniform heat exchange, is designed as a combination for ease of processing. It consists of a first half-nozzle head 4 and a second half-nozzle head 5. The first half-nozzle head 4 and the second half-nozzle head 5 have the same shape, size, and structure, and are symmetrical in width. A horizontal connecting plate 7 is provided at the top of the first half-nozzle head 4 and the second half-nozzle head 5, with mounting bolt holes 8. A groove 6, corresponding to the shape of the rail head 9, is provided in the middle of the vertical surface. Corresponding bolt holes 8 are provided on both sides of the vertical surface of the first half-nozzle head 4 and the second half-nozzle head 5. The vertical surfaces of the first half-nozzle head 4 and the second half-nozzle head 5 are connected as a whole by screws, and an O-ring seal is used at the mating surface outside the nozzle cavity.

[0083] The blower head has a three-cavity structure, consisting of three cavities: a top central cavity 1, a first side cavity 2, and a second side cavity 3. Each cavity comprises a contraction section, a throat, and an expansion section. The top central cavity 1 corresponds to the top surface of the rail head 9, while the first side cavity 2 and the second side cavity 3 correspond to the middle positions of the sides of the rail head 9.

[0084] The inlet walls of the contraction sections and the outlet walls of the expansion sections of both the first side cavity 2 and the second side cavity 3 are straight lines, and the outlet wall angle of the expansion section is 90°. The junction between the throat and the contraction section is smooth, and the junction between the throat and the expansion section is also smooth.

[0085] A design method for a jet nozzle used in the air-cooled quenching of steel rails, characterized by strong and uniform heat exchange, comprising the following steps:

[0086] like Figure 1 , Figure 2 As shown, the main design parameters of the blower head are as follows:

[0087] Contraction section height A1, mm; throat height A2, mm; expansion section height A3, mm; contraction section inlet width B1, mm; throat width B2, mm; expansion section outlet width B3, mm; contraction section inlet length L1, mm; throat center length L2, mm; expansion section outlet length L3, mm; side outlet straight segment length L4, mm; first arc segment arc length L5, mm; second arc segment arc length L6, mm; third arc segment arc length L7, mm; expansion section outlet mid-section curve L3c, mm; contraction section included angle a1, °; expansion section included angle a2, °; outlet wall angle a3, °; first arc segment radian a4, °; second arc segment radian a5, °; third arc segment radian a6, °; contraction section inlet cross-sectional area S1, mm² 2 Throat cross-sectional area S2, mm 2 Expansion section outlet cross-sectional area S3, mm 2 And the jet height H.

[0088] Step 1: Using the top and side profiles of the rail head section as the design reference for the outlet and throat profile curves of the jet head expansion section, the rail head curve is proportionally transformed at equal intervals according to the jet height H to obtain the L3 curve shape. Correspondingly, the rail head curve is proportionally transformed at equal intervals according to H+A3+0.5A2 to obtain the L2 curve shape.

[0089] Step 2: Determine the cross-sectional area S2 of the nozzle throat based on production requirements:

[0090] To ensure comparability, the same throat cross-sectional area (the smallest cross-sectional area of ​​the nozzle) as the existing nozzle was selected.

[0091] Step 3: Design the cross-sectional area S3 of the expansion section outlet:

[0092] Based on the required jet velocity and S2, the outlet cross-sectional area S3 is calculated using the following formula:

[0093] (1)

[0094] In the formula: K is the specific volume ratio of the gas;

[0095] Ma is the design Mach number for the jet velocity at the nozzle outlet.

[0096] Step 4: Design the jet height H, throat width B2, and throat center length L2:

[0097] Because the profiled nozzle has a long and narrow cross-section, the throat width B2 cannot be too small to reduce the impact of frictional resistance between the air and the nozzle wall; it is generally not less than 0.5 mm. Furthermore, the distance between the actual production rail and the nozzle outlet (jet height H) cannot be too close, and is generally not less than 4 mm. Based on the determined H, B2, and S2, L2 = S2 / B2 can be calculated.

[0098] Step 5: Design throat height A2: To ensure stable airflow, A2 should be greater than B2 and less than three times B2, that is:

[0099] (2)

[0100] Step 6: Design the straight section length L4 of the nozzle side outlet, the outlet wall angle a3, the expansion section height A3, the expansion section outlet width B3, and the expansion section outlet length L3. L3 includes the curved section L3c in the middle of the expansion section outlet and the straight section length L4 of the side outlets on both sides, i.e.: (3)

[0101] In the formula:

[0102] (4)

[0103] Where: a4, a5, and a6 are the angles corresponding to each arc segment of the rail head, in °; L5, L6, and L7 are the arc lengths of each arc segment of the rail head (e.g., ...). Figure 1 , Figure 2 (As shown).

[0104] The formula for calculating the central length L2 of the larynx is:

[0105] (5)

[0106] Where: L2c, mm, and L2s mm are the lengths of the curve segment and the straight line segments on both sides of L2, respectively.

[0107] (6)

[0108] The relationship between L2s and L4 is as follows:

[0109] (7)

[0110] Constraint (1): In order to ensure the cooling effect on the side of the rail head, L2s should not be less than zero.

[0111] Constraint (2): In selecting angle a3, the extension of the line connecting the lower endpoint of the straight segment L2s of the throat curve and the lower endpoint of the straight segment L4 of the expansion section exit curve should be lower than the lower endpoint of the straight segment on the side of the rail head. That is:

[0112] (8)

[0113] Constraint (3): Both A3 and a3 affect the aspect ratio of each section of the nozzle, which in turn affects the flow field of the jet and ultimately the heat transfer capacity. For example, the smaller the value of A3, the smaller L2c, and the larger B2 for the same cross-sectional area. Also, when L2c and A3 are fixed, the larger a3 is, the smaller L3 is, and the larger B3 is for the same cross-sectional area. To ensure the effective heat transfer area of ​​the nozzle in the width direction, a2 > 0, i.e., B3 > B2.

[0114] Step 7: Design the inlet cross-sectional area S1, inlet length L1, and inlet width B1 of the contraction section:

[0115] To ensure stable airflow, S1 should be greater than S3, generally selected as 1.5 to 2 times, i.e.:

[0116] (9)

[0117] Step 8: Design the height A1 of the contraction section:

[0118] When selecting A1, the angle a1 of the contraction segment should be between 5 and 10°, that is:

[0119] (10)

[0120] Step 9: To ensure cooling capacity on the side of the rail head, the nozzle, after being designed with parameters, is modified into a three-chamber structure: The nozzle cavity is cut off along the upper end of L4, parallel to the nozzle outlet wall. The curved sections of L1 and L3 of the cut-off cavities are straightened, and a3 is changed to 90°. Then, the cut-off cavities are moved downwards to the middle position on the side of the rail head. The final nozzle cavity design for air-cooled quenching of rails, which combines heat exchange capacity and uniformity, is shown in the diagram. Figure 3 As shown.

[0121] Step 10: To reduce air resistance, make a smooth transition at the junction of the throat with the contraction and expansion sections.

[0122] [Example]:

[0123] Taking the most widely used 60kg / m U75V steel rail as an example, a blower head for air-cooled quenching of steel rails is designed to combine heat exchange capacity and heat exchange uniformity:

[0124] Currently, the smallest diameter of the shrink-type nozzle used in production is 7mm, and the total cross-sectional area of ​​three nozzles at the same cross-section of the rail head is 115.395 mm². 2 Therefore, the S2 of the nozzle is determined to be 115.395 mm. 2 .

[0125] Using 1.35 Ma as the design exit Mach number, S3 is calculated to be 125.67 mm according to formula (1). 2 .

[0126] According to relevant research results, the optimal jet height for heat exchange capacity of supersonic jet is close to H / B2=5. Therefore, we select H=5 mm and B2=0.95 mm, and the length of L2 is: L2=S2 / B2=121.47 mm.

[0127] According to formula (2), the throat height A2 is taken as 2 mm. According to my country's rail quality inspection standard "TB / T 2344.1-2020", the dimensions of the rail head curve section of a 60kg / m rail are: L5=16.71 mm, L6=15.84 mm, L7=19.35 mm, a4=73.65 °, a5=11.34 ° and a6=3.69 °. Combining constraint 1 and formulas (3)-(7), A3≤7.503mm is calculated.

[0128] In the initial design, A3 was set to 5 mm. According to constraint 2, a3 ≤ 31.24°. According to formulas (4) and (7), L3c = 94.6 mm and L4 = 16.2 mm were calculated. At this time, B3 = S3 / L3 = 1.03 mm, which satisfies the requirements of constraint 3.

[0129] According to formula (9), S1 = 2S3 = 251.34 mm² is selected. Combining with formula (10), A1 = 5 mm is selected, then L1 = 118.18 mm, B1 = 2.13 mm, and a1 = 6.7 °, which meets the design standard of 5-10 °.

[0130] The nozzle cavity is cut off along the upper end of L4, parallel to the nozzle outlet wall. The curved sections of L1 and L3 of the cut-off cavity are straightened, and a3 is changed to 90°. Then, the cut-off cavity is moved downwards to the middle position of the rail head side. The final nozzle cavity for air-cooled quenching of rails with both heat exchange capacity and heat exchange uniformity is shown in the figure. Figure 3 As shown.

[0131] To reduce air resistance, the throat is smoothly transitioned at the junction of the contraction and expansion sections.

[0132] The surface temperature of the rail was measured using a SIRL2-2ML infrared thermometer (measurement temperature range 300-1300 ℃, spectral response 1.6 μm, response time 5 ms, repeatability ±0.3%). The experiment was repeated three times, and the average value was taken. The locations of the temperature test points TP1, TP2, and TP3 are shown below. Figure 6 As shown in the figure, the "*" marks the locations of rail cross-section hardness monitoring points as required by my country's railway industry standard "TB / T 2344.1-2020". The first point is 5 mm from the rail surface, and the remaining points are spaced 5 mm apart. The distance between lines D and E and the lower jaw of the rail head is 5 mm. Lines B and C are the angle bisectors of lines A, D, and A, E.

[0133] Table 1 shows the cooling rates at different locations on the surface of a 900 ℃ rail after 100 s using different types of nozzles. In the table, CR, SR, and CP nozzles represent a constant-speed contraction nozzle, a supersonic circular nozzle, and a constant-speed contour nozzle, respectively. The average cooling rate at each test point is used to characterize the cooling capacity of the nozzle; Dev is the standard deviation of the temperature at each test point, used to characterize the uniformity of the cooling rate at each test point on the railhead, and is calculated using the following formula:

[0134]

[0135] In the formula: X i The value of Dev represents the cooling rate at test point i. A smaller Dev value indicates a smaller deviation from the average value and better cooling uniformity among the test points on the rail head. It can be seen that the jet nozzle of this invention significantly improves both cooling capacity and cooling uniformity compared to other types of jet nozzles. Regarding cooling speed, the test points on the rail cooled using the jet nozzle of this invention show improvements compared to other types of jet nozzles, with the average rail head cooling speed increasing by 54.22%, 13.88%, and 47.01% compared to CR, SR, and CP jet nozzles, respectively. Regarding cooling uniformity, the Dev value decreases by 31.11%, 31.11%, and 6.06% compared to CR, SR, and CP jet nozzles, respectively.

[0136] Table 1. Cooling rate of rail surface after 100s for different types of air nozzles at 900℃.

[0137]

[0138] Table 2 shows the temperatures at various test points on the rail head when cooling a 900 ℃ rail for 100 s using different types of air nozzles. It can be seen that, within the same cooling time, the air nozzle of this invention can lower the rail head surface temperature to a lower level. According to literature research, the surface cooling end temperature for under-speed quenching of U75V rail steel should not exceed 500 ℃. Using constant-speed air nozzles (CR and CP nozzles), the time required to lower the temperature at all test points on the rail surface to below 500 ℃ exceeds 100 s; using an SR nozzle, the time is 74 s; and using the air nozzle of this invention, the time is 43 s. The air nozzle of this invention can significantly shorten the cooling time required for air-cooled quenching of rails.

[0139] Table 2. Temperature at various test points when different types of nozzles cool a 900 ℃ rail for 100 s.

[0140]

[0141] Figures 7-9 The images show the flow field of the jet and the temperature field cloud map of the rail cross section when a jet nozzle for air-cooled quenching of rails (900℃) with a heat exchange capacity and uniformity, obtained using numerical simulation methods, is used to cool a 60kg / m U75V rail for 100s. It can be seen that the compressed air velocity increases significantly when it reaches the throat position through the contraction section of the SP nozzle, reaching sonic speed (approximately 340 m / s) relatively uniformly. Furthermore, the fluid velocity increases further, reaching supersonic speed, when the airflow passes through the expansion section of the outlet. The compressed air pressure is stable at the nozzle inlet section, providing a continuous and stable inlet pressure. When the jet impacts the vicinity of the rail surface, the velocity decreases sharply while the pressure increases. The rail temperature decreases in a ring shape from the center of the rail head outwards. The temperature in the low-temperature zone near the rail head surface is relatively uniform, and the temperature at the arc surface of the rail head is slightly lower than at other locations, indicating that the absence of the nozzle cavity at this point does not affect the cooling effect of the nozzle on the rail.

[0142] The cavity of this invention consists of a contraction section, a throat, and an expansion section. Compressed air enters the contraction section through the inlet, and the airflow velocity increases due to the gradual decrease in cross-sectional area. Upon reaching the throat, the velocity reaches the local speed of sound. From the throat outlet to the expansion section, the airflow expands due to the gradual increase in cross-sectional area, further increasing the airflow velocity and ultimately generating a supersonic jet. Using a supersonic air jet significantly improves the cooling capacity of jet quenching. The junctions between the throat and the contraction section, and between the throat and the expansion section, are smoothly transitioned. This reduces air resistance and thus improves heat exchange capacity. This invention is a modular design; the first half-jet head 4 and the second half-jet head 5 are assembled into a single jet head using screws, and a sealing ring is used to seal the mating surfaces outside the jet head cavity. This facilitates manufacturing and reduces production costs.

[0143] The cross-sectional area ratios of the components of a supersonic jet nozzle are limited by the designed outlet velocity and inlet pressure. Influenced by the shape of the rail head, it is difficult to achieve a supersonic jet with uniform velocity and pressure at the rail head using conventional contouring design methods that involve simple equidistant transformations of the rail head. This is because a supersonic jet nozzle requires its throat cross-sectional area to be smaller than the outlet cross-sectional area of ​​the expansion section to allow sufficient space for the sonic airflow to expand and generate a supersonic jet. When designing the nozzle using the equidistant transformation method, assuming a simple equidistant transformation formula based on the rail head shape, the formula for calculating the length of curve L3 at the nozzle's expansion section outlet should be:

[0144]

[0145] The formula for calculating the length of curve L2 at the center of the throat should be:

[0146]

[0147] Clearly, L2 will always be greater than L3, which contradicts the design principle of supersonic nozzles. Although the method of setting an angle α3 at the nozzle cross-section (as shown in the attached diagram) can be used... Figure 1 (As shown) can effectively alleviate the contradiction between supersonic speed and isometric transformation contouring.

[0148] Figure 10 , 11 Figures 1 and 12 show the jet flow field, jet pressure field, and rail head temperature of a 900℃ rail cooled for 100 seconds using a supersonic contour nozzle designed using a traditional simple equidistant transformation method, respectively. Figure 10 It can be seen that the highest flow velocity in the nozzle occurs near the outlet of the nozzle expansion section. When the compressed air reaches the throat through the nozzle inlet, its velocity increases significantly, reaching the speed of sound (approximately 340 m / s) relatively uniformly. The airflow also experiences a significant velocity increase as it passes through the outlet expansion section, reaching supersonic speeds. However, the acceleration is not uniform at different locations. At the position opposite the rail head tread, the velocity increase is close to the design value, reaching approximately Mach 1.35. At the positions opposite the two sides of the rail head, the velocity increase is greater, reaching a maximum of approximately Mach 1.73. The velocity increase at the positions opposite the two curved surfaces of the rail head is insufficient, reaching only approximately Mach 1.2 to 1.3. When the jet impacts the vicinity of the rail surface, the velocity decreases sharply. The velocity reduction is most pronounced at the rail head tread. The reason is that the outlet at the position opposite to the side of the nozzle has a larger relative expansion cross-sectional area than other positions. Therefore, the airflow expands more fully here, resulting in a greater cooling rate. However, at the position opposite to the arc surface of the rail head, the airflow expands more to both sides, resulting in insufficient speed increase at this position.

[0149] according to Figure 11 It can be seen that the airflow pressure is relatively uniform and stable in most areas of the inlet section. The inlet pressure is lower near the two side walls of the nozzle, possibly because the outlet cross-sectional area on both sides of the nozzle is larger than at other locations, resulting in excessive expansion and causing the pressure in the corresponding inlet contraction section to fail to stabilize at the design value. After passing through the throat and expansion section, the airflow pressure decreases significantly due to the expansion effect, with the pressure drop being more pronounced near the two side walls of the nozzle. The pressure drop is smaller at the location corresponding to the rail head arc surface than at other locations. When the jet approaches the rail surface, the pressure value increases significantly again, with the highest pressure value near the rail head arc surface, followed by the pressure value near the rail head tread surface, and the pressure value gradually decreases from top to bottom on the side of the rail head.

[0150] according to Figure 12 It can be seen that the pressure distribution trend of the jet on the rail head tread is consistent with the distribution trend of its cooling rate. The temperature of the cooled rail head tread and rail head arc surface is lower than that of the rail head side. The cooling capacity for the rail head side is clearly insufficient.

[0151] Based on the above analysis, it can be seen that the cooling capacity of the rail head side is weaker than that of other positions. Although the jet has a high flow velocity when it reaches the vicinity of the rail head side, its impact pressure on the rail surface is small. The fundamental reason is that the two side walls of the nozzle have an angle a3, which makes the expansion of its relative position with the rail head side greater than that of other positions. In addition, the relative distance between the rail head side and the SP nozzle outlet gradually increases from top to bottom.

[0152] Therefore, this invention, based on aerodynamic principles, employs a three-section cavity structure for the nozzle. By truncating the supersonic contour nozzle at a position corresponding to the railhead's arc angle, the three-cavity structure design simultaneously enhances both jet cooling capacity and cooling uniformity. Firstly, by truncating the section with the strongest cooling capacity corresponding to the railhead's arc, L3 can be shortened by a greater degree than L2 without significantly reducing cooling capacity. This allows for increasing the cross-sectional area of ​​the cavity at the corresponding position on the railhead side. Secondly, by changing a3 to 90°, the nozzle jet at this point can be perpendicularly sprayed onto the rail surface, reducing the relative distance difference between the outlet at different locations and the rail surface, thus resulting in more uniform cooling.

[0153] This invention combines heat exchange capacity and heat exchange uniformity, and can solve the prominent problems of weak cooling capacity and poor cooling uniformity in the air-cooled quenching process of rails caused by existing air nozzles.

[0154] 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 inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A blower head for air-cooled quenching of steel rails with strong and uniform heat exchange, characterized in that, The blower head has a three-cavity structure, consisting of three cavities: a top central cavity, a first side cavity, and a second side cavity. Each of the three cavities is composed of a contraction section, a throat, and an expansion section. The top central cavity corresponds to the top surface of the rail head, while the first and second side cavities correspond to the middle positions of the sides of the rail head. The inlet wall of the contraction section and the outlet wall of the expansion section of the first side cavity and the second side cavity are both straight lines, and the angle of the outlet wall of the expansion section is 90°. The junction between the throat and the contraction section is smoothly transitioned, and the junction between the throat and the expansion section is also smoothly transitioned. The nozzle is in a combined form, with the nozzle cavity divided into two parts along the width direction symmetrical plane to form a first half nozzle and a second half nozzle; the first half nozzle and the second half nozzle are connected as a whole by disassembly, and sealed at the joint surface outside the nozzle cavity.

2. The air nozzle for air-cooled quenching of rails with strong and uniform heat exchange as described in claim 1, characterized in that, The first half of the nozzle and the second half of the nozzle are assembled into a whole nozzle by screws, and the mating surface outside the nozzle cavity is sealed with a sealing ring.

3. The air nozzle for air-cooled quenching of rails with strong and uniform heat exchange as described in claim 1, characterized in that, The first and second half of the nozzles are provided with horizontal connecting plates at the top, with a groove in the middle corresponding to the shape of the rail head, and bolt holes on both sides.

4. A design method for a jet nozzle for air-cooled quenching of steel rails, characterized by strong and uniform heat transfer as described in any one of claims 1 to 3, wherein... The design parameters are as follows: contraction section height A1, mm; throat height A2, mm; expansion section height A3, mm; contraction section inlet width B1, mm; throat width B2, mm; expansion section outlet width B3, mm; contraction section inlet length L1, mm; throat center length L2, mm; expansion section outlet length L3, mm; side outlet straight section length L4, mm; outlet wall angle a3, °; contraction section included angle a1, °; expansion section included angle a2, °; and jet height H. The design method specifically includes the following steps: Step 1) Using the top and two side profiles of the rail head section as the design reference for the nozzle expansion section outlet and throat profile curve, the rail head curve is proportionally transformed at equal intervals according to the jet height H to obtain the shape of the expansion section outlet length L3 curve. Correspondingly, the rail head curve is transformed by equal intervals according to H+A3+0.5A2 to obtain the curve shape of the throat center length L2; Step 2) Determine the cross-sectional area S2 of the nozzle throat (mm) based on production requirements. 2 ; Step 3) Design the cross-sectional area S3 of the expansion section outlet, mm 2 : Based on the required jet velocity and S2, calculate S3 using the following formula: （1） Where: K is the gas specific volume ratio; Ma is the jet velocity at the nozzle outlet, Mach, 1 Mach = 0.3403 km / s; Step 4) Design the jet height H, throat width B2, and throat center length L2: B2≥0.5 mm, H≥4 mm; Calculate L2 based on the determined H, B2 and S2, L2= S2 / B2; Step 5) Design the throat height A2: （2） Step 6) Design the side outlet straight section length L4, outlet wall angle a3, expansion section height A3, expansion section outlet width B3, and expansion section outlet length L3: The expansion section outlet length L3 includes the length of the curved section in the middle of the expansion section outlet L3c (mm) and the length of the straight section on both sides of the side outlet, L4, i.e.: （3） （4） In the formula: a4, a5 and a6 are the angles corresponding to each arc segment of the rail head, in °; L5, L6 and L7 are the arc lengths of each arc segment of the rail head. The formula for calculating the central length L2 of the larynx is: （5） In the formula: L2c is the length of the curved segment at the center of the throat, mm; L2s is the length of the straight segments on both sides of the center of the throat, mm. （6） The relationship between L2s and L4 is as follows: （7） Step 7) Design the inlet cross-sectional area S1 of the contraction section, mm 2 The length L1 of the contraction section inlet (mm) and the width B1 of the contraction section inlet: Step 8) Design the height A1 of the contraction section: （9） Step 9) Change the nozzle after design parameters to a three-cavity structure: cut off the nozzle cavity along the upper end of L4 parallel to the nozzle outlet wall, change the curved parts of L1 and L3 of the cut-off cavity to straight lines, and change a3 to 90°. Then move the cut-off cavity down to the middle position of the side of the rail head.

5. The design method of a jet nozzle for air-cooled quenching of steel rails with strong and uniform heat exchange according to claim 4, characterized in that, In step 2), S2 is the cross-sectional area at the minimum point of the existing type of nozzle; or it is determined according to the air supply capacity of the air compressor on site. If the air supply capacity of the air compressor is A, mm³ / s, and the number of nozzles is N, then: 340×S2×N≤A.

6. The design method of a blower head for air-cooled quenching of steel rails with strong and uniform heat exchange according to claim 4, characterized in that, Step 6) has three constraints: Constraint ①: L2s≥0; Constraint ②: （8） In the formula: L8 is the length of the straight section on the side of the rail head, in mm; Constraint ③: a2>0, that is: B3>B2.

7. The design method of a jet nozzle for air-cooled quenching of steel rails with strong and uniform heat exchange according to claim 4, characterized in that, It also includes step 10), which smoothly transitions the throat to the junction of the contraction and expansion segments.

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