Constant displacement control method for steel rail flash welding

Abstract

The invention provides a constant displacement control method for steel rail flash welding, and belongs to the technical field of rail welding. The constant displacement control method comprises the steps that steel rail flash welding is divided into a flash heating stage and an upsetting stage, and the flash heating stage is divided into a pulse flash stage and a continuous flash stage; setting a steel rail consumption reference value and a heat input reference value in a flash heating stage; the actual input heat and the first actual displacement of the steel rail are monitored in the pulse flash stage; determining a heat compensation scheme of the continuous flash stage based on the error between the first actual displacement and the steel rail consumption reference quantity; and the second displacement of the steel rail is controlled based on the heat compensation scheme in the continuous flashing stage. According to the constant displacement control method provided by the invention, the problem that the steel rail consumption cannot be accurately controlled when the steel rail closure opening is stretched and welded in the prior art is solved, the application range of flash welding in the field of closure opening welding is greatly widened, and the defects of a site construction technology are effectively made up.

Description

Technical Field

[0001] The present invention relates to the technical field of rail welding, and particularly to a constant displacement control method for flash welding of steel rails. Background Art

[0002] Flash welding of steel rails is an efficient welding method for connecting steel rails and is widely used in the fields of railway construction and maintenance. The process of flash welding of steel rails is that the electrodes clamp the steel rails and connect the power supply of the welding transformer, so that the end faces of the steel rails gradually approach to achieve local contact. The contact points are heated to form liquid metal crossbeams, which burst to generate spark jets, forming continuous flashes. When the flash heating reaches an appropriate temperature, a forging force is quickly applied to squeeze the end faces of the steel rails against each other, cut off the current, and the welding area undergoes strong plastic deformation, and the bonding surfaces intercrystallize to form a welded joint.

[0003] Based on traditional flash welding of steel rails, subsequent heat treatment processes are integrated, and welding and heat treatment are integrated into the same equipment to form an existing integrated flash welding and induction heat treatment machine. While meeting the quality requirements of existing processes, the integration of the two processes of steel rail welding and heat treatment is achieved. The introduction of this equipment has been widely welcomed by the overhaul department, but there is still an obstacle to realizing on-line closing joint locking welding using the integrated flash welding and induction heat treatment machine, that is, the current technology cannot meet the tensile function of the steel rails after welding, so the requirement of restoring the locking rail temperature of the line cannot be achieved.

[0004] Existing flash welding adopts a pulsating flash welding process and controls welding based on current. The process is affected by factors such as current signals, hydraulic signals, equipment lubrication status, and viscosity of hydraulic oil. The heat input during the welding process is unstable, and the amount of steel rail melting varies greatly. The consumption of steel rails fluctuates during the flash flattening, preheating, and continuous melting stages, and the consumption of steel rails cannot be accurately controlled, usually with an error of 5 - 10 mm. For the above errors, in conventional flash welding, one side of the two steel rails to be welded is a free end, and the steel rail can move according to the actual situation of welding. After welding, the joint is locked at the actual position where it is located, and there is no pre-designed specific accurate position for the joint. However, the steel rails on both sides of the closing joint have been locked, and the steel rails cannot move back and forth, and the joint position has been preset accurately. To meet the precise control requirements of the tensile amount (locking rail temperature) for the tensile welding of the closing joint, the consumption of steel rails must be accurately controlled, which also results in the inability to apply the integrated flash welding and induction heat treatment machine in on-line closing joint locking welding construction.

[0005] In view of this, based on years of production design experience in this field and related fields, the inventor has designed a constant displacement control method for flash welding of steel rails through repeated tests, in order to solve the problems existing in the prior art. Summary of the Invention

[0006] The object of the present invention is to provide a constant displacement control method for flash welding of rails, which can accurately control the rail consumption during the flash welding process of rails.

[0007] To achieve the above object of the invention, the present invention provides a constant displacement control method for flash welding of rails, wherein the constant displacement control method includes:

[0008] Dividing the flash welding of rails into a flash heating stage and a upsetting stage, and further dividing the flash heating stage into a pulsating flash stage and a continuous flash stage;

[0009] Setting a reference value for rail consumption and a reference value for heat input in the flash heating stage;

[0010] Monitoring the actual input heat and the first actual displacement of the rail during the pulsating flash stage;

[0011] Determining a heat compensation scheme for the continuous flash stage based on the error between the first actual displacement and the reference rail consumption;

[0012] Controlling the second displacement of the rail based on the heat compensation scheme during the continuous flash stage.

[0013] Compared with the prior art, the present invention has the following characteristics and advantages:

[0014] The constant displacement control method for flash welding of rails proposed by the present invention changes the original flash welding process control method and on-site use method, and adopts the methods of temperature field monitoring and heat compensation. While controlling the constant displacement, it ensures the stability of the temperature field of the welded joint, thereby achieving precise control of rail consumption and ensuring stable and reliable welding quality. The constant displacement control method proposed by the present invention solves the problem that the prior art cannot accurately control rail consumption during the tensile welding of the rail closing joint, greatly expands the application range of flash welding in the field of closing joint welding, and effectively makes up for the deficiencies of on-site construction technology. Even under non-locked rail temperature conditions, it can ensure the welding quality of the rail closing joint and the precise restoration of the line locked rail temperature, and is applicable to various track engineering applications such as high-speed railways, intercity railways, and subways. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The drawings described herein are only for illustrative purposes and are not intended to limit the scope of the disclosure of the present invention in any way. In addition, the shapes and proportional dimensions of the components in the drawings are only schematic and are used to assist in understanding the present invention, rather than specifically limiting the shapes and proportional dimensions of the components of the present invention. Those skilled in the art can select various possible shapes and proportional dimensions according to specific circumstances to implement the present invention under the teaching of the present invention.

[0016] Figure 1 It is a schematic diagram of the flash welding curve and stage division of the present invention;

[0017] Figure 2 Schematic diagram of temperature field compensation and precise control of consumption amount in the flash heating stage of the present invention;

[0018] Figure 3 Schematic diagram of displacement control method in the upsetting stage of the present invention;

[0019] Figure 4 Schematic diagram of heat input and consumption amount setting in the pulsating stage of welding process parameters of the present invention;

[0020] Figure 5 Schematic diagram of the principle of the flash welding process control process of the present invention;

[0021] Figure 6 Schematic diagram of 100s simulation of temperature field during the flash welding process of the present invention;

[0022] Figure 7 Schematic diagram of the temperature distribution along the axial direction of the rail head of the present invention;

[0023] Figure 8 Schematic diagram of the flash welding stage of the constant displacement control method of the present invention;

[0024] Figure 9 Schematic diagram of the upsetting stage of the constant displacement control method of the present invention. Specific embodiments

[0025] Combined with the description of the drawings and the specific embodiments of the present invention, the details of the present invention can be more clearly understood. However, the specific embodiments of the present invention described herein are only for the purpose of explaining the present invention and cannot be understood in any way as a limitation of the present invention. Under the teaching of the present invention, those skilled in the art can conceive any possible variations based on the present invention, and these should all be regarded as belonging to the scope of the present invention.

[0026] The present invention proposes a constant displacement control method for flash welding of rails, including:

[0027] As Figure 1 shown, the flash welding of rails is divided into a flash heating stage and an upsetting stage, and the flash heating stage is divided into a pulsating flash stage and a continuous flash stage;

[0028] Set the reference value of rail consumption amount and the reference value of heat input in the flash heating stage;

[0029] Monitor the actual input heat and the first actual displacement amount of the rail in the pulsating flash stage;

[0030] Determine the heat compensation scheme for the continuous flash stage based on the error between the first actual displacement amount and the rail consumption reference amount;

[0031] Control the second displacement of the rail based on the heat compensation scheme during the continuous flashing stage.

[0032] A constant displacement control method for flash welding of rails proposed by the present invention realizes precise regulation of the welding temperature field stability and rail consumption by controlling the heat input and rail displacement during the flash welding process in stages, effectively avoiding the problems of excessive rail consumption or insufficient heat caused by temperature fluctuations in the traditional process, being able to accurately ensure the rail consumption during the flash welding process, and ensuring that the welding joint quality meets the requirements of the railway industry standards.

[0033] A constant displacement control method for flash welding of rails proposed by the present invention not only maintains the stability of the temperature field in the joint area but also significantly improves the reliability and consistency of the welding quality, especially suitable for railway engineering scenarios where strict control of the locking rail temperature recovery accuracy is required.

[0034] In the present invention, the constant displacement means that the displacement of each joint welded with the same welding parameter is within a certain error range, and then it is determined that the displacement is constant, thereby realizing precise control of the rail consumption.

[0035] Furthermore, this displacement is the difference between the starting displacement and the ending displacement of the flash welding.

[0036] During the flash welding of the rail, this displacement is preferably equal to the reference value of the rail consumption.

[0037] In an optional example of the present invention, the reference value of the rail consumption and the reference value of the heat input are determined by weighted averaging of a large number of joint data during the process test. In an optional implementation manner of the present invention, the temperature field and the second actual displacement of the rail are monitored in real time during the continuous flashing stage.

[0038] Specifically, as Figure 4 shown, the continuous flashing heating stage (i.e., stage 5 - stage 8 in Figure 4 ) is carried out by a control method based on the temperature field. Before entering stage 5 - stage 8, first calculate the errors between the first displacement and the actual heat input data obtained by monitoring and acquisition and the reference value of the rail consumption and the reference value of the heat input, determine the heat compensation scheme required for the continuous flashing stage, decide whether to increase or decrease the consumption compared to the reference according to the calculated difference, the specific value of the increased / decreased consumption, and ensure the stability of the temperature field through burning. During the continuous flashing heating stage, it is necessary to monitor and acquire the data of the temperature field and the displacement, and adjust the compensation scheme in a timely manner if necessary.

[0039] The constant displacement control method proposed by the present invention monitors the temperature field distribution in the welding joint area and the second actual displacement of the rail in real time. The monitoring data of the temperature field can reflect the thermal state of the welding joint, which helps to accurately control the heat input during the welding process and ensure the uniformity and stability of the joint temperature field. At the same time, by obtaining the second actual displacement of the rail in real time, it can be compared with the preset displacement reference value to detect and handle displacement deviations in a timely manner, thereby achieving precise control of the rail consumption.

[0040] In an alternative embodiment of the present invention, the heat compensation scheme includes the expected input heat and the expected secondary displacement.

[0041] Specifically, as Figure 2 shown, in the pulsating flash stage, a conventional time and displacement dual-control method is adopted to ensure a basically stable heat input. However, due to fluctuations in the rail consumption (displacement), this will cause differences in the temperature field. To compensate for these fluctuations, in the continuous flash stage, based on the heat input and the fluctuation error of the rail consumption (i.e., the difference between the actual value and the reference value) in the pulsating flash stage, a heat compensation scheme is determined. This scheme includes the expected input heat and the expected secondary displacement, and in the continuous flash stage, by increasing or decreasing the heat input, the stability of the joint temperature field is ensured, and at the same time, the constancy of the displacement consumption is ensured.

[0042] In an alternative example of this embodiment, in the continuous flash stage, the second actual displacement is made equal to the expected secondary displacement.

[0043] Specifically, as Figure 2 shown, in the continuous flash stage, through an accurate control strategy, it is ensured that the second actual displacement is equal to the expected secondary displacement. Specifically, after the pulsating flash stage, based on the data of the first actual displacement and the actual input heat monitored, they are compared with the preset rail consumption reference value and heat input reference value, and the required expected input heat and the corresponding expected secondary displacement are calculated. In the subsequent continuous flash stage, by adjusting the heat input, the rail is burned out according to the expected secondary displacement, so as to ensure that the second actual displacement is equal to the expected secondary displacement.

[0044] In an alternative example of this embodiment, the expected secondary displacement is the difference between the rail consumption reference value and the first actual displacement.

[0045] First, monitor the actual input heat and the first actual displacement of the rail during the pulsating flash stage. Then, compare the monitored first actual displacement with the preset rail consumption reference value, calculate the difference between the two, and this difference is the expected secondary displacement. During the continuous flash stage, adjust the heat input according to this expected secondary displacement to ensure that the second actual displacement of the rail can reach the expectation.

[0046] In an alternative example of the present invention, after the continuous flash stage is completed, the joint temperature field is stable, and the total displacement during the joint flash heating stage and the continuous flash heating stage is the rail consumption, which is the same as the rail consumption reference amount.

[0047] In an alternative embodiment of the present invention, during the pulsating flash welding section, keep the actual input heat constant.

[0048] In an alternative example, as Figure 4 shown, in stages 1 - 4, that is, the pulsating flash heating stage of the flash heating stage, the conventional dual control method of displacement and time is adopted. The dual control of displacement and time means that during the welding process, when either the displacement amount or the time reaches first, it enters the next stage. Although this control method is not a pure displacement control, resulting in certain fluctuations in the total displacement amount of stages 1 - 4, the dual control method can try to ensure that the welding quality does not fluctuate greatly due to the control of one quantity. By adopting the conventional dual control method of time and displacement, a basically stable heat input can also be ensured. By using the dual control method of time and displacement to ensure a basically stable heat input and precisely control parameters such as current and hydraulic pressure during the welding process, it helps to establish a stable basic temperature field at the initial stage of welding and prepares for the subsequent continuous flash stage.

[0049] According to the actual needs at the welding site, select an appropriate rail consumption and the range of fluctuation accuracy to be controlled. According to the range of rail consumption fluctuation accuracy, set an error threshold. When the error between the first actual displacement and the rail consumption reference amount is within the set error threshold range, there is no need to continue compensation during the continuous flash stage, and the flash welding heating stage ends and enters the upsetting stage.

[0050] In an alternative embodiment of the present invention, the constant displacement control method further includes: setting a reference value for the upsetting amount in the upsetting stage, and dividing the upsetting stage into the early upsetting stage and the late upsetting stage; monitoring the actual displacement amount in the early stage of the rail during the early upsetting stage; determining the expected displacement amount in the late upsetting stage based on the reference value of the upsetting amount and the actual displacement amount in the early stage; the upsetting speed in the late upsetting stage is less than 1 mm / s, and control the fourth displacement amount of the rail according to the expected displacement amount.

[0051] Specifically, as Figure 4As shown, Stages 1 - 4 are the pulsating flash heating stages of the flash heating stage, and Stages 5 - 8 are the continuous flash heating stages of the flash heating stage, followed by the upsetting stage. The upsetting is carried out in a displacement control mode. First, it upsets quickly and then slowly to ensure a constant displacement (upsetting amount) throughout the upsetting process. The total displacement at the end of the early upsetting stage and the late upsetting stage is constant. There may be certain fluctuations in the quick upsetting because the speed is relatively fast, but corrections can be made during the slow upsetting for compensation.

[0052] Among them, the upsetting speed in the late upsetting stage is less than 1 mm / s. The servo valve is used to control the upsetting speed, and the upsetting speed is adjusted by regulating the flow rate of the servo valve. The servo valve can adjust the flow rate and can also be adjusted to a smaller value.

[0053] Furthermore, the fourth displacement of the rail is accurately controlled according to the expected displacement amount to ensure high precision during the upsetting process.

[0054] It should be noted that during the upsetting stage, increasing the rated upsetting force can achieve upsetting during the welding process and stretching the long rail to restore the locked rail temperature. However, since the locked rail temperature difference (ΔT / ℃) changes with the environment, the required tensile force also changes, while the rated upsetting force remains unchanged. Therefore, the actual upsetting force acting on the joint will continuously change with the locked rail temperature difference (ΔT / ℃), and the actual upsetting amount and upsetting effect will also change continuously.

[0055] In an alternative example of this embodiment, the stage before the first 10 mm of the upsetting amount reference value is divided into the early upsetting stage.

[0056] In the constant displacement control method proposed by the present invention, the upsetting stage is clearly divided into the early upsetting stage and the late upsetting stage. The early upsetting stage specifically refers to the stage of the first 10 mm of the upsetting displacement. During this stage, a quick upsetting method is adopted, specifically the large flow rate mode in which the servo valve and the directional control valve work together, enabling the rail to quickly reach the predetermined early displacement amount and laying the foundation for subsequent upsetting.

[0057] In an alternative example, the upsetting speed in the early upsetting stage is greater than the upsetting speed in the late upsetting stage.

[0058] Specifically, in the late upsetting stage, a slow upsetting method is adopted, with an upsetting speed less than 1 mm / s, such as the small flow rate mode controlled by a servo valve. In the late upsetting stage, through a displacement feedback closed-loop control system, as Figure 4 shown, the fourth displacement of the rail is accurately regulated according to the expected displacement amount to ensure high precision during the upsetting process. This difference in speed settings enables the quick approach to the target displacement in the early upsetting stage and fine adjustment in the late upsetting stage to ensure the accuracy of the upsetting amount.

[0059] Furthermore, the upsetting speed in the early upsetting stage is greater than or equal to 5 mm / s.

[0060] Specifically, in the early stage of upset forging, a rapid upset forging method is adopted, through the large flow mode of the collaborative work of the servo valve and the directional control valve. As a switching valve, the directional control valve has no flow control and can make the upset forging speed reach about 5 mm / s. Its rapid upset forging method can quickly push the rail to reach the predetermined pre-displacement in the early stage of upset forging, laying a foundation for the subsequent upset forging process. By setting the upset forging speed in the early stage of upset forging to be greater than or equal to 5 mm / s, the welding efficiency can be significantly improved on the premise of ensuring the welding quality.

[0061] In an optional example, after improvement, the same upset forging amount can be achieved for long rails, long rails in the stretched state (with increased upset forging force), and short rails. The upset forging amounts are the same, the actual welding data are the same, and the quality is comparable.

[0062] In an optional example of this embodiment, a mobile rail flash welding machine is used to implement the pulsating flash welding process, and welding is carried out with the current as the control reference. The process is affected by factors such as current signals, hydraulic signals, equipment lubrication status, and the viscosity of hydraulic oil. The heat input during the welding process is unstable, and the amount of rail melting varies greatly. As Figure 5 shown, the consumption of the rail fluctuates during the flash flattening, preheating, and continuous melting stages, and generally, the consumption of the rail is controlled within a certain range.

[0063] The rail flash welding process consists of two parts: the flash heating stage (flash melting amount) and the upset forging stage. The flash melting amount of rail flash welding is generally about 25 mm - 45 mm, which consists of the flash melting amount and the upset forging amount.

[0064] It should be noted that if the existing technology is adopted, assuming the rail consumption range is 25 - 35 mm (taking a certain welding machine as an example), for the same welding machine and the same welding process parameters, the error of the rail consumption can reach 10 mm. The 10 - mm error cannot meet the requirement of precise control of the stretching at the closure gap (generally, when the rail is stretched by 10 °C, it is also 10 mm, and if the existing process is used, the stretching error range can reach 100%). When welding with the existing process, the welding at the closure gap and the effect of rail temperature stretching recovery cannot be guaranteed. To meet the normal welding at the closure gap and the requirement of normal rail temperature recovery in the inserted welding section.

[0065] In this embodiment, the displacement is used to control the welding process, which can achieve the purpose of precise melting.

[0066] As Figure 6 shown, the pulsating flash welding process is mainly controlled by time. The time is equivalent, the heat input is equivalent, and the temperature field in the early stage of upset forging is equivalent. This is mainly because the stability of the welding process in the free state ensures the stability of the heat input and indirectly ensures the stability of the joint temperature field. However, when the welding process in the stretched state changes greatly, it is difficult to ensure the stability of the heat input and the rail consumption.

[0067] In an alternative embodiment of the present invention, based on the characteristics of the joint temperature field (the state before upsetting), a large number of simulation tests and calculations were carried out, and the performance tests of the joint were also conducted.

[0068] From the results of the simulation tests, as Figure 6 shown, it can be seen that the temperature transition along the axial direction of the rail is non-uniform, which is due to the complex shape of the rail and the non-uniform surface heat dissipation; the highest temperature at the end face of the rail reaches 1544 °C, exceeding the melting point of the rail steel, but the range is small, which also explains the reason for the very thin decarburized layer in the final weld. There is convective heat dissipation between the rail surface and the air, and the higher the temperature, the faster the heat dissipation, so the outer surface temperature is lower than that of the core.

[0069] As Figure 7 shown, through the analysis of the data from the simulated finite element and the test, as shown in Table 1, Table 1:

[0070]

[0071] By comparing the five groups of data, it can be obtained that the highest value of the highest temperature at the end face is 1544.9 °C, the lowest value is 1544.1 °C, and the range is 0.8 °C; the highest value of the average temperature at the end face is 1401.1 °C, the lowest value is 1379.8 °C, and the range is 21.3 °C; the highest value of the average temperature in the 20 mm range is 1054.4 °C, the lowest value is 1030.1 °C, and the range is 24.3 °C. The temperature change is relatively small and within the controllable range of parameter adjustment. By adjusting the heat input and time parameters, a uniform temperature field can be formed under the parameters of a smaller heat input and a longer heating time (18842 W, 120 s) as well as a larger heat input and a shorter time (21680 W, 80 s). The simulation results can prove that it has a theoretical basis to control the welding process with displacement to achieve precise melting.

[0072] The detailed explanations for the above embodiments are only for the purpose of explaining the present invention so as to better understand the present invention. However, these descriptions cannot be construed as limitations on the present invention for any reason. In particular, the various features described in different embodiments can be arbitrarily combined with each other to form other embodiments. Unless there are clear and contrary descriptions, these features should be understood to be applicable to any one of the embodiments and not limited to the described embodiments.

Claims

1. A constant displacement control method for flash welding of steel rails, characterized in that, The constant displacement control method includes: Dividing the flash welding of the rail into a flash heating stage and a upsetting stage, and dividing the flash heating stage into a pulsating flash stage and a continuous flash stage; Setting a reference value for the rail consumption and a reference value for the heat input in the flash heating stage; Monitoring the actual input heat and the first actual displacement of the rail in the pulsating flash stage; Determining a heat compensation scheme for the continuous flash stage based on the error between the first actual displacement and the reference rail consumption; Controlling the second displacement of the rail based on the heat compensation scheme in the continuous flash stage.

2. The constant displacement control method for flash welding of steel rails according to claim 1, characterized in that Monitoring the temperature field and the second actual displacement of the rail in real time in the continuous flash stage.

3. The constant displacement control method for flash welding of steel rails according to claim 1 or 2, characterized in that, The heat compensation scheme includes the expected input heat and the expected secondary displacement.

4. The constant displacement control method for flash welding of steel rails according to claim 3, characterized in that, In the continuous flash stage, making the second actual displacement equal to the expected secondary displacement.

5. The constant displacement control method for flash welding of steel rails according to claim 3, characterized in that, The expected secondary displacement is the difference between the reference value of the rail consumption and the first actual displacement.

6. The constant displacement control method for flash welding of steel rails according to claim 1, characterized in that In the pulsating flash welding section, keeping the actual input heat constant.

7. The constant displacement control method for flash welding of steel rails according to claim 1, characterized in that, The constant displacement control method further includes: Setting a reference value for the upsetting amount in the upsetting stage and dividing the upsetting stage into a pre-upsetting period and a post-upsetting period; Monitoring the actual displacement in the pre-upsetting period of the rail; Determining the expected displacement in the post-upsetting period based on the reference value of the upsetting amount and the actual displacement in the pre-upsetting period; The upsetting speed in the post-upsetting period is less than 1 mm / s, and controlling the fourth displacement of the rail according to the expected displacement.

8. The constant displacement control method for flash welding of steel rails according to claim 7, characterized in that, Dividing the stage before 10 mm before the reference value of the upsetting amount into the pre-upsetting period.

9. The constant displacement control method for flash welding of steel rails according to claim 8, characterized in that, The upsetting speed in the pre-upsetting period is greater than the upsetting speed in the post-upsetting period.

10. The constant displacement control method for flash welding of steel rails according to claim 9, characterized in that, The upsetting speed in the pre-upsetting period is greater than or equal to 5 mm / s.

Images