A multi-machine flash butt welding process for steel rails

Abstract

The application discloses a steel rail multi-machine flash butt welding process and belongs to the technical field of steel rail welding, and aims at at least one of the problems of low production efficiency and production qualified rate and serious damage of equipment in the prior art. The process comprises the following steps: flash flattening treatment is performed on the section of the steel rail to be welded; the section of the steel rail after the flash flattening treatment is subjected to multiple preheating flash butt welding; after the preheating flash butt welding is completed, the dynamic frame of the welding machine drives the dynamic side steel rail to perform reciprocating instantaneous contact and separation movement relative to the static side steel rail, and pulse flash butt welding is performed; after the pulse flash butt welding is completed, the dynamic side steel rail is controlled to continuously advance to the static side steel rail, continuous flash butt welding is performed, and the liquid metal beam between the dynamic side steel rail and the static side steel rail always exists and is not broken during the continuous flash butt welding; after the continuous flash butt welding is completed, a upsetting force is applied to the section of the steel rail and the upsetting is kept, and the welding is completed. The application can be used for steel rail welding.

Description

Technical Field

[0001] This invention belongs to the field of rail welding technology, and particularly relates to a multi-mechanism flash welding process for rails. Background Technology

[0002] The basic principle of rail flash welding (also known as resistance welding) is as follows: the rail parts to be welded are clamped together to form a butt joint, the power is turned on, and the cross-sections are gradually moved closer to achieve local contact. The resistance heat is used to heat these contact points (generating flashes), which melts the cross-section metal until the end reaches a predetermined temperature within a certain depth range. Then, a forging force is quickly applied to complete the welding.

[0003] In the field of rail welding, flash welding processes are divided into three categories: continuous flash welding, pulsed flash welding, and preheating flash welding.

[0004] Currently, the common method is to use a combination of preheating flash welding and continuous flash welding.

[0005] However, because preheating flash welding operates at a relatively low temperature, typically between 600 and 800°C, the rail cross-sectional temperature is also usually maintained at this range. When transitioning from preheating flash welding to continuous flash welding, the displacement needs to be continuously increased. Due to the low rail cross-sectional temperature after preheating, the flash cannot be effectively and promptly ignited, leading to large-area adhesion of the hot metal on the rail cross-section and prolonged short-circuit current, resulting in welding failure and even severe equipment damage, impacting welding efficiency. In practical applications, the welding failure rate can even reach 5%, severely affecting welding production efficiency and yield. Summary of the Invention

[0006] In view of the above analysis, the present invention aims to provide a multi-mechanism flash welding process for rails to solve at least one of the following problems in the prior art: when transitioning from preheated flash welding to continuous flash welding using a combination of preheated flash welding and continuous flash welding, there is large-area adhesion of hot metal on the rail cross section and long-term short-circuit current leading to low production efficiency and production qualification rate, and serious equipment damage.

[0007] The objective of this invention is mainly achieved through the following technical solutions: This invention provides a multi-mechanism flash welding process for steel rails, comprising the following steps: Step 1: Perform flash leveling on the cross-section of the rail to be welded; Step 2: Perform multiple preheating flash welding operations on the rail section after flash leveling; Step 3: After the preheating flash welding is completed, the welding machine is controlled to drive the moving side rail to reciprocate and momentarily contact and separate relative to the stationary side rail to perform pulsed flash welding. Step 4: After the pulsed flash welding is completed, control the moving side rail to move continuously towards the stationary side rail to perform continuous flash welding. During the continuous flash welding process, the liquid metal crossbeam between the moving side rail and the stationary side rail always exists and does not break. Step 5: After continuous flash welding is completed, apply upsetting force to the rail section and maintain upsetting to complete the welding.

[0008] Furthermore, in step 2, the preheating flash welding temperature is 600~800℃, and the heating depth of the rail is 5~10cm.

[0009] Furthermore, in step 3, the contact time is 0.01~0.02s, the heating temperature of the pulsed flash welding is 1100~1300℃, and the heating depth of the pulsed flash welding is 1~5cm.

[0010] Furthermore, in step 4, the heating temperature for continuous flash welding is 2000~3000℃.

[0011] Furthermore, the following steps are included between steps 3 and 4: The control welding machine gantry drives the moving side rail from the reciprocating speed of the pulsed flash welding stage, through the speed transition stage, to the starting forward speed of the continuous flash welding stage; during the speed transition stage, the forward speed of the moving side rail gradually decreases from the final speed of the pulsed stage through at least one intermediate speed gradient to the starting speed of the continuous flash welding, and the speed reduction method is a step-like speed reduction or a continuous curve speed reduction.

[0012] Furthermore, the stepped deceleration divides the speed transition process into 2 to 5 speed levels, each lasting 0.2 to 0.5 seconds, with the speed decreasing progressively between each level.

[0013] Furthermore, in step 3, the pulsed flash welding employs closed-loop motion control based on current feedback.

[0014] Furthermore, the closed-loop motion control based on current feedback includes the following steps: Four current thresholds I1, I2, I3, and I4 are preset, with I1 < I2 < I3 < I4; the actual current value i in the welding circuit is acquired in real time, and i is compared with I1, I2, I3, and I4. The movement state of the welding gantry is controlled based on the comparison results. If i < I1, then control the welding gantry to move forward at a speed of V1 toward the stationary side rail until the current value of the next acquisition cycle is compared again. If I1≤i<I2, then control the welding machine to move forward at a speed of V2 toward the stationary side rail until the current value of the next acquisition cycle is compared again. If I2≤i<I3, then control the welding gantry to pause its movement for 0.01s, and wait for the current value of the next acquisition cycle to be compared again. If I3≤i<I4, then control the welding machine to retreat at a speed V3 away from the stationary side rail until the current value of the next acquisition cycle is compared again. If i≥I4, then control the welding machine to retreat at a speed V4 away from the stationary side rail until the current value of the next acquisition cycle is compared again. V1>V2, V4>V3, and V1>0, V2>0, V3<0, V4<0.

[0015] Furthermore, the following steps are included before step 1: Determine the welding process parameters for the rails to be welded.

[0016] Furthermore, the welding process is applicable to rails to be welded with the following composition by mass percentage: C 0.71~0.80, Si 0.50~0.80, Mn 0.75~1.05, S≤0.025, P≤0.025, V 0.04~0.12, Al≤0.004.

[0017] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: A) The multi-mechanism flash welding process for rails provided by this invention adds pulsed flash welding between preheating flash welding and continuous flash welding. Since the heating temperature of pulsed flash welding is between that of preheating flash welding and continuous flash welding, it can effectively supplement the heat of the rail section after preheating flash welding, so that the temperature of the rail section after pulsed flash welding can reach 1100~1300℃. This effectively stimulates the flash during the continuous flash welding stage, alleviates the large-area adhesion of hot metal on the rail section, and basically avoids the problem of long-term short-circuit current. This can reduce the probability of welding failure, ensure welding efficiency and production qualification rate, and also reduce equipment damage caused by long-term short-circuit current, thus extending the service life of the equipment.

[0018] B) The multi-mechanism flash welding process for rails provided by this invention, through the addition of pulsed flash welding, can achieve the effect of deep heat storage, mid-layer activation, and concentrated surface heat gradient growth. Preheating flash welding (600~800℃) can perform deep volume heating of 5~10cm on the rail cross-section, establishing a heat reserve of a certain depth for subsequent processes. This ensures that the instantaneous contact of only 0.01~0.02s in each pulsed flash welding is no longer just surface sparks, but can be rapidly heated to 1100~1300℃ with the help of the heat reserve achieved by preheating flash welding.

[0019] C) The multi-mechanism flash welding process for rails provided by this invention creates uniformly distributed micro-protrusions and a temperature field of 1100~1300℃ on the rail cross-section through reciprocating contact during the pulsating stage. This result can create ideal discharge conditions for continuous flash welding. When the moving side rail begins to advance continuously, these high-temperature micro-protrusions will be preferentially broken down to form a dense and stable liquid metal beam. At the same time, the cross-section as a whole has sufficient heat reserve. Continuous flash welding can directly skip the beam establishment stage and instantly enter a steady-state flash at 2000~3000℃, thereby effectively solving the problem of long-term short-circuit current caused by cold start in traditional processes.

[0020] D) The multi-mechanism flash welding process for rails provided by this invention has three completely different heating depths (the heating depth of preheating flash welding is 5~10cm, the heating depth of pulsed flash welding is 1~5cm, and the heating depth of continuous flash welding is the surface layer). The superposition of the three heating depths can form a temperature gradient buffer zone from the inside to the outside on the rail cross-section. This can ensure the smooth release of thermal expansion stress during welding, and also ensure that the high temperature of continuous flash welding only acts on the very thin surface layer, while the deep and middle layers of metal remain in a plastic state. Ultimately, this results in a weld with a narrow heat-affected zone and a smooth hardness transition, significantly reducing the risk of hardening brittle fracture.

[0021] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0022] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0023] Figure 1 The current, voltage, displacement, and upsetting force curves of the multi-mechanism flash welding process for rails provided in Embodiment 1 of the present invention. Detailed Implementation

[0024] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0025] In a first aspect, the present invention provides a multi-mechanism flash welding process for steel rails, comprising the following steps: Step 1: Perform flash flattening on the cross-section of the rail to be welded to remove 2-5mm of impurities and provide initial heat to the cross-section of the rail to be welded. It should be noted that the above-mentioned flash leveling process uses a pulsed method to achieve flash leveling; Step 2: Perform multiple preheating flash welding on the rail section after flash leveling. The preheating flash welding temperature is 600~800℃, and the heating depth of the rail is 5~10cm. Step 3: After the preheating flash welding is completed, control the welding machine to drive the moving side rail to reciprocate with the stationary side rail in a momentary contact (e.g., contact time of 0.01~0.02s) and separation motion to perform pulsed flash welding. The heating temperature of the pulsed flash welding is 1100~1300℃, and the heating depth of the pulsed flash welding is 1~5cm. Step 4: After the pulsed flash welding is completed, control the moving side rail to move continuously towards the stationary side rail to perform continuous flash welding. During the continuous flash welding process, the liquid metal crossbeam between the moving side rail and the stationary side rail always exists and is not broken. The heating temperature for continuous flash welding is 2000~3000℃. Step 5: After continuous flash welding is completed, apply upsetting force to the rail section and maintain upsetting to complete the welding.

[0026] It should be noted that preheating flash welding and pulsed flash welding are used to achieve deep heating of the rail, while continuous flash welding is used to heat the cross-section of the rail.

[0027] Compared with existing technologies, the multi-mechanism flash welding process for rails provided by this invention adds pulsed flash welding between preheating flash welding and continuous flash welding. Since the heating temperature of pulsed flash welding is between that of preheating flash welding and continuous flash welding, it can effectively replenish the heat of the rail section after preheating flash welding, so that the temperature of the rail section after pulsed flash welding can reach 1100~1300℃. This effectively stimulates the flash during the continuous flash welding stage, alleviates the large-area adhesion of hot metal on the rail section, and basically avoids the problem of long-term short-circuit current. This reduces the probability of welding failure, ensures welding efficiency and production qualification rate, and also reduces equipment damage caused by long-term short-circuit current, extending the service life of the equipment.

[0028] Specifically, on the one hand, the addition of pulsed flash welding can achieve the effect of deep heat storage, mid-layer activation, and concentrated surface heat gradient growth. Preheating flash welding (600~800℃) can heat the rail cross-section to a depth of 5~10cm, establishing a heat reserve of a certain depth for subsequent processes. This means that the instantaneous contact of only 0.01~0.02s in each pulsed flash welding is no longer just surface sparks, but can be rapidly heated to 1100~1300℃ with the help of the heat reserve achieved by preheating flash welding.

[0029] On the other hand, the pulsating stage creates uniformly distributed micro-protrusions and a temperature field of 1100~1300℃ on the rail cross-section through reciprocating contact. This result can create ideal discharge conditions for continuous flash welding. When the moving side rail begins to advance continuously, these high-temperature micro-protrusions will be preferentially broken down to form a dense and stable liquid metal lintel. At the same time, the cross-section has sufficient heat reserves. Continuous flash welding can directly skip the lintel establishment stage and instantly enter a steady-state flash at 2000~3000℃, thereby effectively solving the problem of long-term short-circuit current caused by cold start in traditional processes.

[0030] On the other hand, the heating depths of the three types of flash welding are completely different (the heating depth of preheating flash welding is 5~10cm, the heating depth of pulsed flash welding is 1~5cm, and the heating depth of continuous flash welding is the surface layer). The superposition of the three heating depths can form a temperature gradient buffer zone from the inside to the outside on the rail cross section. This can ensure the smooth release of thermal expansion stress during welding, and also ensure that the high temperature of continuous flash welding only acts on the very thin surface layer, while the deep and middle layers of metal remain in a plastic state. Ultimately, this results in a weld with a narrow heat-affected zone and a smooth hardness transition, which greatly reduces the risk of hardening brittle fracture.

[0031] For example, the above is particularly applicable to rails to be welded with the following composition by mass percentage: C 0.71~0.80, Si 0.50~0.80, Mn 0.75~1.05, S≤0.025, P≤0.025, V 0.04~0.12, Al≤0.004.

[0032] It should be noted that preheating flash welding provides the necessary preheating buffer for the rails to be welded with the above-mentioned components, preventing hardening; pulsed flash welding acts on the vanadium carbonitride dissolution-sensitive area with a precisely controlled temperature range, limiting its thermal damage to a minimum; continuous flash welding efficiently removes low-melting-point impurities such as sulfur and phosphorus, as well as oxide inclusions, with instantaneous ultra-high temperature. The synergy of these three methods enables the weld seam of the rails to be welded with the above-mentioned components to maintain its hardness, toughness, and defects.

[0033] Specifically, carbon (0.71~0.80%): High carbon content gives the rails extremely high strength and wear resistance, but it also leads to a high tendency to harden and grain boundary segregation. By using preheating flash welding to gently preheat the deep layer, the cooling rate of the welding thermal cycle is effectively buffered, alleviating the hardened structure caused by rapid cooling. At the same time, the high temperature of the continuous flash welding stage only acts on the very thin surface area, which rapidly melts the enriched carbides and removes them with the flash spatter, which can reduce the accumulation of grain boundary carbides and ensure the toughness of the weld.

[0034] Silicon (0.50~0.80%): Silicon is a deoxidizer and solid solution strengthening element. However, a high content can reduce the thermal conductivity of steel, making it difficult for heat to be conducted deep into the base material during welding, which can easily cause localized overheating on the surface. The reciprocating contact mechanism of pulsed flash welding can effectively break the dense oxide film formed by silicon on the surface, ensuring that the newly exposed metal can receive continuous and uniform heating, and alleviating the problem of uneven temperature distribution caused by poor thermal conductivity.

[0035] Manganese (0.75~1.05%): Manganese improves hardenability and strength; however, high-manganese steel is prone to MnS inclusions during welding, and their distribution along grain boundaries significantly reduces low-temperature impact toughness. The intense flash and spatter effects of the pulsed flash welding stage can squeeze out the MnS inclusions floating in the liquid metal along with the molten metal, while the stable liquid metal bridging in the continuous flash welding stage can ensure sufficient stirring and venting of the molten pool, resulting in a significant reduction in the number of inclusions in the final weld.

[0036] Sulfur (≤0.025%) and Phosphorus (≤0.025%): Sulfur and phosphorus are harmful impurities in steel. Sulfur causes hot brittleness, and phosphorus causes cold brittleness. The triple flash welding mechanism (flash leveling to remove surface contaminants, preheating and pulsation to melt and float deep impurities, and continuous flashing to concentrate and remove impurities) creates a step-by-step purification effect. In particular, the heating temperature of 1100~1300℃ in the pulsating flash welding stage is just above the FeS eutectic melting point (about 988℃), which allows sulfides to be fully liquefied and removed with the flash, effectively reducing the sensitivity of the weld to hot cracking.

[0037] Vanadium (0.04~0.12%): Vanadium is a microalloying element that plays a role in grain refinement and precipitation strengthening by forming VC and VN carbonitrides. However, the high welding temperature (>1000℃) causes these precipitates to dissolve and aggregate, leading to a significant decrease in the strength of the heat-affected zone (softening). Through gradient heating of deep heat storage, intermediate transition, and surface burst, and by strictly controlling the width of the high-temperature region exceeding the dissolution temperature of vanadium carbonitrides (approximately 950~1000℃), vanadium carbonitrides are retained in most of the heat-affected zone and dissolve only near a very narrow fusion line, thus maximizing the preservation of the original grain refinement strengthening effect of the rail.

[0038] During the pulsating phase, both the forward and backward speeds are relatively fast, generally greater than 1 mm / s (e.g., 2 mm / s). However, the distance between the two rail surfaces being welded is typically around 1-3 mm. If the forward speed during the pulsating phase is too fast, and the initial forward speed during the continuous phase is relatively slow, usually only 0.8 mm / s, lacking an intermediate speed transition, excessive speed at such a small surface distance can easily cause momentary forward sticking, resulting in flash termination and welding failure. Alternatively, excessive momentary backward movement can cause the liquid crossbeam to break, resulting in flash termination and welding failure. Therefore, the following steps are also included between steps 3 and 4 above: The control welding machine gantry drives the moving side rail from the reciprocating speed of the pulsed flash welding stage, through the speed transition stage, to the starting forward speed of the continuous flash welding stage; during the speed transition stage, the forward speed of the moving side rail gradually decreases from the final speed of the pulsed stage through at least one intermediate speed gradient to the starting speed of the continuous flash welding, and the speed reduction method is a step-like speed reduction or a continuous curve speed reduction.

[0039] For example, the stepped deceleration divides the speed transition process into 2 to 5 speed levels, each lasting 0.2 to 0.5 seconds, with the speed decreasing progressively between each level.

[0040] In this way, by setting a smooth speed transition step, a smooth connection from pulsed flash welding to continuous flash welding can be achieved, reducing the problem of instantaneous sticking or flash interruption caused by sudden speed changes, further reducing the probability of welding failure and improving the stability of the welding process.

[0041] Furthermore, in order to solve the problem that the fixed speed mode cannot adapt to drastic changes in the flash state, in step 3 above, the pulsed flash welding adopts closed-loop motion control based on current feedback.

[0042] Specifically, closed-loop motion control based on current feedback includes the following steps: Four current thresholds I1, I2, I3, and I4 are preset, with I1 < I2 < I3 < I4; the actual current value i in the welding circuit is acquired in real time, and i is compared with I1, I2, I3, and I4. The movement state of the welding gantry is controlled based on the comparison results. If i < I1, then control the welding machine to move forward at a speed of V1 toward the stationary side rail, so that the distance between the two rail sections decreases rapidly until the current value of the next acquisition cycle is compared again. If I1≤i<I2, then control the welding machine to move forward at a speed of V2 toward the stationary side rail, so that the distance between the two rail sections decreases slowly until the current value of the next acquisition cycle is compared again. If I2≤i<I3, then control the welding gantry to pause its movement for 0.01s, and wait for the current value of the next acquisition cycle to be compared again. If I3≤i<I4, then control the welding machine to retreat at a speed V3 away from the stationary side rail, so that the distance between the two rail sections increases slowly until the current value in the next acquisition cycle is compared again. If i≥I4, then control the welding machine to retreat at a speed V4 away from the stationary side rail, so that the distance between the two rail sections increases rapidly until the current value in the next acquisition cycle is compared again. Among them, V1>V2, V4>V3, and V1>0, V2>0, V3<0, V4<0.

[0043] In this way, by dividing the actual welding current into four threshold ranges and matching them with five speed responses—fast forward, slow forward, pause, slow retreat, and fast retreat—real-time adaptive adjustment of the moving side rail's movement speed to the flash state is achieved during pulsed flash welding. Specifically, when the current is too low, it quickly approaches to replenish heat; when the current is too high, it moderately retreats to dissipate heat; and when the current is moderate, it maintains a steady state. This effectively alleviates welding short circuits and flash failures caused by the mismatch between the fixed speed mode and the dynamic flash state, ensuring stable combustion of the liquid metal bridge throughout the entire pulsed process. At the same time, this closed-loop feedback control makes the cross-sectional heating temperature uniform and controllable, providing an ideal temperature field and surface condition for the subsequent continuous flash welding stage. This significantly improves the first-pass success rate and joint quality consistency of the welding process, and reduces equipment wear and rework costs caused by welding failures.

[0044] The second aspect provides a multi-mechanism flash welding process for rails, which is basically the same as the multi-mechanism flash welding process for rails provided in the first aspect, except that: The addition of pulsed flash welding can effectively improve the adaptability of the welding process to rails of different hardness.

[0045] Furthermore, in order to address the problem of low production efficiency and yield caused by the inability to effectively select process parameters for pulsed flash welding based on the hardness of the rail, the following steps are included before step 1 above: Determine the welding process parameters for the rails to be welded.

[0046] Specifically, determining the welding process parameters for the rails to be welded includes the following steps: Step a: Provide multiple sets of test rails with the same hardness, with two test rails in each set; Step b: Preheating flash welding, continuous flash welding and upsetting use the same process parameters, while pulsed flash welding uses different process parameters to weld multiple sets of test rails; Step c: Test the welds of multiple sets of test rails after welding to obtain the weld with the best performance. The preheating flash welding, pulsed flash welding, continuous flash welding and upsetting process parameters corresponding to the weld with the best performance are taken as the optimal process parameters. Step d: Change the hardness of the test rail and repeat steps a to c to obtain a table comparing different hardnesses with the optimal process parameters; Step e: Based on the hardness of the rail to be welded and the comparison table of different hardnesses and optimal process parameters, determine the optimal process parameters of the rail to be welded, and use the optimal process parameters of the rail to be welded as the welding process parameters.

[0047] Compared with existing technologies, the multi-mechanism flash welding process for rails provided by this invention, on the one hand, through systematic comparative experiments, fixes the preheating flash welding, continuous flash welding, and upsetting parameters, and only changes the pulsed flash welding parameters for orthogonal comparison. Using weld performance as the sole evaluation index, the optimal combination of pulsed parameters for rails with specific hardness is screened out in reverse. Based on this, a comparison table of hardness and optimal process parameters is established. This is equivalent to improving the selection of pulsed flash welding parameters from manual experience judgment to table lookup, thereby significantly reducing the interference of human factors on welding quality.

[0048] On the other hand, by calibrating each rail according to its hardness grade, once the reference table is established, all rails of the same hardness grade can directly apply the optimal process parameters without repeated testing. This significantly improves welding efficiency and first-pass yield during mass production. Furthermore, when introducing new models or new hardness grades of rails, only a set of calibration tests needs to be performed according to steps a to c to quickly expand the reference table. This enables the welding equipment to adapt to rails of different hardness, solving the problems of lag in parameter adjustment and poor adaptability in traditional processes, and laying a data foundation for intelligent production of flash welding of rails.

[0049] Thirdly, the present invention provides a multi-mechanism flash welding process for rails, which is basically the same as the multi-mechanism flash welding process for rails provided in the first aspect, except that: The addition of pulsed flash welding can effectively improve the adaptability of the welding process to rails of different hardness.

[0050] Furthermore, in order to address the problem of low production efficiency and yield caused by the inability to effectively select process parameters for pulsed flash welding based on the hardness of the rail, the following steps are included before step 1 above: Determine the welding process parameters for the rails to be welded.

[0051] Specifically, determining the welding process parameters for the rails to be welded includes the following steps: Step A: Obtain the specific heat capacity of the rail to be welded in the range of 20~1300℃ by referring to the table based on the rail grade. c(T) ,density ρ(T) and thermal conductivity λ(T) ; Step B: Calculate the total heat required for pulsed flash welding. The calculation formula is as follows:

[0052] In the formula: Q t The total heat required for pulsed flash welding, in J; The average volumetric specific heat capacity over the temperature range, J / (mm²).3 ·℃); V h The volume of the heating zone is in mm. 3 , V h = A · h , A The cross-sectional area of ​​the rail is in mm. 2 , h Heating depth, in mm; for pulsed flash welding, it is 10~50mm. T t To obtain a target value between 1100 and 1300℃, ℃; T i The temperature of the rail section after preheating flash welding (approximately 600~800℃) is ℃.

[0053] Step C: Within the given total pulsation time t z pulsation frequency f Under the condition of (number of contacts per second), the heating time for a single contact is t p ≈0.01~0.02s, total number of pulses N ≈ t z · f， Assuming the effective value of the current is constant, and the average contact resistance and internal resistance can be obtained from empirical values ​​or estimated using formulas, then the required effective value of the current is:

[0054] In the formula: I r The effective value of the required current is in A; Q t The total heat required for pulsed flash welding, in J; N This represents the total number of pulses. N ≈ t z · f,t z Given the total pulsation time s, f The pulsation frequency is expressed in Hz. t p The heating time for a single contact is in seconds. R c The contact resistance is expressed in Ω. Rw is the internal resistance of the rail base metal itself, in Ω.

[0055] Compared with the prior art, the multi-mechanism flash butt welding process for rails provided in this embodiment, on the one hand, realizes the precision and quantifiability of parameter selection for pulsating flash welding. Starting from the thermophysical properties of the material, the total heat required in the pulsation stage is accurately calculated based on the inherent parameters such as specific heat capacity and density of the rail within the target temperature range, and then the required effective current value is derived inversely using the Joule heat formula, which can effectively greatly improve the reliability of welding parameters.

[0056] On the other hand, as long as the grade and hardness of the rail to be welded are known, the core parameters such as the required pulsating flash welding current and time can be quickly solved, which can not only significantly shorten the process commissioning cycle and improve production efficiency, but also provide core algorithm support for the subsequent construction of a rail flash welding process expert system or adaptive control system.

[0057] Embodiment 1 A hot-rolled rail of WISCO U75V is welded, with its chemical composition meeting the requirements of TB / T2344: 0.76% C, 0.70% Si, 0.93% Mn, 0.002% S, 0.012% P, 0.048% V, 0.0028% Al. The rail has a Brinell hardness of 313HBW (10 / 3000), a Rockwell hardness of 31HRC, a tensile strength of 1074MPa, and an elongation after fracture of 10%.

[0058] The process parameters are shown in Table 1, and the welding curve is shown in Figure 1 .

[0059] Table 1 Table of various process parameters of Embodiment 1

[0060] The welding process parameters for the WISCO U75V hot-rolled rail are commissioned. The rail is welded by adjusting the welding process parameters, and the welded joints are subjected to ultrasonic flaw detection. After confirming that the flaw detection is qualified, the joints are subjected to a drop weight test, with a drop height of 5.2 meters and a hammer weight of 1000 kilograms. 25 consecutive joints do not break in the drop weight test. Small notches are cut on the rail bottoms of 15 of the joints, which are then broken again by the drop hammer to inspect the area of the gray spot defect on the fracture surface. The gray spot defect area of the 15 fracture surfaces is qualified and does not exceed the standard requirements. The commissioned welding process parameters pass the drop weight test and fracture inspection of the welding type test, and all remaining items of the type test are qualified, meeting the standard requirements.

[0061] The welding curves show that the displacement curves in the pulsating stages 04 and 05 have very small slopes, indicating that the heat loss from the rail flash during these stages is minimal. The heat from each instantaneous short-circuit contact remains on the surface without being dissipated by flash spatter. The current curves in stages 04 and 05 exhibit a larger range of fluctuations compared to the smaller overall fluctuations in stages 07, 08, and 09, suggesting that the pulsating welding in stages 04 and 05 was effective.

[0062] 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 changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A multi-mechanism flash welding process for steel rails, characterized in that, Includes the following steps: Step 1: Perform flash leveling on the cross-section of the rail to be welded; Step 2: Perform multiple preheating flash welding operations on the rail section after flash leveling; Step 3: After the preheating flash welding is completed, the welding machine is controlled to drive the moving side rail to reciprocate and momentarily contact and separate relative to the stationary side rail to perform pulsed flash welding. Step 4: After the pulsed flash welding is completed, control the moving side rail to move continuously towards the stationary side rail to perform continuous flash welding. During the continuous flash welding process, the liquid metal crossbeam between the moving side rail and the stationary side rail always exists and does not break. Step 5: After continuous flash welding is completed, apply upsetting force to the rail section and maintain upsetting to complete the welding.

2. The multi-mechanism flash welding process for rails according to claim 1, characterized in that, In step 2, the preheating flash welding temperature is 600~800℃, and the heating depth of the rail is 5~10cm.

3. The multi-mechanism flash welding process for rails according to claim 1, characterized in that, In step 3, the contact time is 0.01~0.02s, the heating temperature of the pulsed flash welding is 1100~1300℃, and the heating depth of the pulsed flash welding is 1~5cm.

4. The multi-mechanism flash welding process for rails according to claim 1, characterized in that, In step 4, the heating temperature for continuous flash welding is 2000~3000℃.

5. The multi-mechanism flash welding process for rails according to claim 1, characterized in that, The following steps are also included between step 3 and step 4: The control welding machine gantry drives the moving side rail from the reciprocating speed of the pulsed flash welding stage, through the speed transition stage, to the starting forward speed of the continuous flash welding stage; during the speed transition stage, the forward speed of the moving side rail gradually decreases from the final speed of the pulsed stage through at least one intermediate speed gradient to the starting speed of the continuous flash welding, and the speed reduction method is a step-like speed reduction or a continuous curve speed reduction.

6. The multi-mechanism flash welding process for rails according to claim 5, characterized in that, The stepped deceleration divides the speed transition process into 2 to 5 speed levels, each lasting 0.2 to 0.5 seconds, with the speed decreasing progressively between each level.

7. The multi-mechanism flash welding process for rails according to claim 1, characterized in that, In step 3, the pulsed flash welding employs closed-loop motion control based on current feedback.

8. The multi-mechanism flash welding process for rails according to claim 7, characterized in that, The closed-loop motion control based on current feedback includes the following steps: Four current thresholds I1, I2, I3, and I4 are preset, with I1 < I2 < I3 < I4; the actual current value i in the welding circuit is acquired in real time, and i is compared with I1, I2, I3, and I4. The movement state of the welding gantry is controlled based on the comparison results. If i < I1, then control the welding gantry to move forward at a speed of V1 toward the stationary side rail until the current value of the next acquisition cycle is compared again. If I1≤i<I2, then control the welding machine to move forward at a speed of V2 toward the stationary side rail until the current value of the next acquisition cycle is compared again. If I2≤i<I3, then control the welding gantry to pause its movement for 0.01s, and wait for the current value of the next acquisition cycle to be compared again. If I3≤i<I4, then control the welding machine to retreat at a speed V3 away from the stationary side rail until the current value of the next acquisition cycle is compared again. If i≥I4, then control the welding machine to retreat at a speed V4 away from the stationary side rail until the current value of the next acquisition cycle is compared again. V1>V2, V4>V3, and V1>0, V2>0, V3<0, V4<0.

9. The multi-mechanism flash welding process for rails according to claim 1, characterized in that, The following steps precede step 1: Determine the welding process parameters for the rails to be welded.

10. The multi-mechanism flash welding process for rails according to any one of claims 1 to 9, characterized in that, The welding process is applicable to rails to be welded with the following composition by mass percentage: C 0.71~0.80, Si 0.50~0.80, Mn 0.75~1.05, S≤0.025, P≤0.025, V 0.04~0.12, Al≤0.004.

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