An electromagnetic induction local heating device for R corner region of high-strength steel square tube

Abstract

The application discloses an electromagnetic induction local heating device for R-angle area of high-strength steel square tube, and relates to the technical field of metal pipe forming processing.The device comprises a partition temperature control unit, a passive dust removal unit and a stress uniform unit.The partition temperature control unit adopts an electromagnetic induction coil matched with the R-angle contour to locally heat the R-angle to 500-750 DEG C, and simultaneously controls the straight wall of the square tube to 60-120 DEG C through a cooling assembly, so that the yield strength difference between the R-angle and the straight wall is eliminated, and the forming quality and the dimensional stability of the R-angle area of the square tube after cold bending forming are improved; the passive dust removal unit drives a deformation plate to reciprocatingly bend relying on the coil residual heat, so that directional blowing airflow is generated to remove dust in the heating gap; and the stress uniform unit utilizes an alternating magnetic field to drive a magnetic response medium to generate micro vibration, and homogenizes the residual stress of the R-angle section under the residual heat of the pipe.The application eliminates the stress concentration of the R-angle, improves the pipe forming precision and the yield rate, and reduces the cracking risk in subsequent processing.

Description

Technical Field

[0001] This invention relates to the field of metal tube forming and processing technology, and more specifically, to an electromagnetic induction local heating device for the R-angle region of high-strength steel square and rectangular tubes. Background Technology

[0002] High-strength steel square and rectangular tubes, with their advantages of high strength, good structural rigidity, and strong load-bearing capacity, are widely used in heavy-duty structural fields such as steel structure buildings, engineering machinery, bridge supports, and special equipment frames. Square and rectangular tubes are mostly manufactured using a flat plate cold-bending extrusion forming process. The edges and corners of the sheet metal are bent and extruded to form a rounded R-corner structure. The R-corner area is a key core component for load-bearing in square and rectangular tubes; its material uniformity and mechanical property stability directly determine the overall structural strength and service safety of the tube.

[0003] Existing traditional cold-bending forming processes rely solely on mechanical force to forcibly compress and bend the radius (R) of high-strength steel square and rectangular tubes. During the forming process, the metal fibers in the R-corner area are subjected to intense stretching, compression, and bending, resulting in concentrated material deformation and highly uneven plastic deformation. This easily leads to severe stress concentration at the R-corner location. Furthermore, residual tensile stress remains in the R-corner after forming. Due to the high hardening sensitivity of high-strength steel, both cold bending deformation and residual tensile stress after forming cause significant work hardening in the R-corner area. This results in a significant difference in yield strength between this area and the straight edge area of ​​the tube, drastically reducing the overall consistency of the tube's mechanical properties.

[0004] The aforementioned technical defects will bring many adverse effects: residual stress concentration at the R-angle will cause deformation, warping, and cracking risks in square and rectangular tubes during subsequent cutting, welding, and heavy-duty service; while the difference in yield strength between the R-angle and the straight edge will lead to uneven deformation and load displacement of the tube under stress, and local micro-deformation and fatigue damage are likely to occur, which will significantly reduce the overall structural stability and fatigue life of the square and rectangular tubes, and cannot meet the high precision, high consistency, and high reliability requirements of high-strength steel square and rectangular tubes for high-load engineering.

[0005] Currently, the industry lacks precise, localized, and efficient heat treatment devices for the radius (R) corners of square and rectangular tubes. Conventional overall heating methods are energy-intensive, can damage the overall substrate properties of the tube, and cannot achieve localized stress relief and homogenization of mechanical properties at the R corners. Therefore, there is an urgent need to design an electromagnetic induction localized heating device for the R corner area of ​​high-strength steel square and rectangular tubes to precisely improve R corner forming defects, eliminate stress concentration, and balance the mechanical properties of the tube. This is the research background and core objective of this invention. Summary of the Invention

[0006] The purpose of this invention is to provide an electromagnetic induction local heating device for the R-corner region of high-strength steel square and rectangular tubes, so as to solve the technical problem of being unable to achieve local stress elimination and mechanical property homogenization at the R-corner.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: an electromagnetic induction local heating device for the R-corner region of a high-strength steel square and rectangular tube, comprising a zoned temperature control unit having a heating cavity for accommodating the square and rectangular tube, for locally heating the R-corner region of the external square and rectangular tube and cooling the straight wall, so as to form a zoned temperature field on the cross-section of the tube. The zone temperature control unit includes: An outer shell surrounds and forms the heating cavity, which carries the electromagnetic induction coil and the cooling assembly, and shields against heat diffusion; A cooling component, which is thermally coupled to the flat wall region, is used to absorb and remove heat from the flat wall through fluid circulation in order to maintain it within a preset low temperature range. An electromagnetic induction coil is disposed in the heating cavity to generate an alternating magnetic field for induction heating of the R-angle region. The shape of the electromagnetic induction coil is adapted to the R-angle profile and is used to pass in a high-frequency current to generate an eddy current effect to heat the R-angle. A passive dust removal unit is located inside the partition temperature control unit. It is used to absorb the waste heat generated by the partition temperature control unit and deform to form a directional blowing airflow to remove dust from the heating gap.

[0008] Preferably, the cooling assembly includes a connecting frame with an internal cavity for the flow of cooling medium, and its outer wall is used to fit the straight wall area of ​​the rectangular tube.

[0009] Preferably, the passive dust removal unit includes: A displacement plate, which is disposed inside the outer shell, has a component that can reciprocate with temperature changes, and is used to generate displacement during the process of absorbing the residual heat of the induction heating component and dissipating heat. The two sides of the displacement plate are connected to the outer shell by heat insulation strips. An airflow control assembly, together with the displacement plate, is used to control the direction of airflow intake and exhaust during deformation.

[0010] Preferably, the displacement plate comprises: The deformation plate, made of a thermodeformable material, has a corrugated cross section, the crests of which are used to contact the induction heating component to absorb residual heat and bend when the deformation threshold is reached. A flat plate, which is connected to the deformation plate, is used to transmit displacement and serve as an installation base.

[0011] Preferably, the airflow control component includes: A one-way vent valve is located in the channel between the outer casing and the external environment, allowing gas to flow in only one direction. A sealing insert plate, which is connected between the connecting plate and the inner wall of the protective housing, is used to separate different air pressure zones during movement.

[0012] Preferably, the passive dust removal unit further includes an airbag component, which has one-way valves at both ends. One end is connected to the heating gap, and the other end is connected to an external air source. The airbag component is connected to the plate so that it is stretched and sucked in when the deformed plate is bent, and compressed and exhausted into the heating gap when the deformed plate rebounds.

[0013] Preferably, a stress-uniforming unit is also provided on one side of the outer shell; The waste heat vibration aging unit includes a vibration generating component containing a medium that responds to a magnetic field or heat, used to generate random motion under the action of the magnetic field generated by the zoned temperature control unit and the waste heat of the pipe. A vibration transmission and constraint component is used to support the vibration generating component and transmit its vibration to the R-angle surface, while constraining the vibration amplitude.

[0014] Preferably, the vibration generating component includes: A sphere, which has a cavity inside; The sensing element, which is filled inside the hollow uniform sphere, is a magnetorheological elastomer or a thermomagnetic dual-response fluid, and is used to generate irregular micro-motions under alternating magnetic or thermal fields.

[0015] Preferably, the vibration transmission and constraint component includes: An arc plate, the curvature of which is the same as the radius of the R-angle, is used to fit the R-angle surface, and a ball groove is provided on it to accommodate the uniform ball; A fluctuation gap, formed between the equalizing ball and the inner wall of the ball groove, is used to limit the vibration amplitude within a preset range.

[0016] Preferably, the zoned temperature control unit heats the R-corner area to 500-750°C and controls the straight wall area at 60-120°C, and the fluctuation gap constrains the vibration amplitude to 0.3-1.2 mm.

[0017] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention employs an electromagnetic induction coil adapted to the R-angle profile, paired with a 304 non-magnetic stainless steel outer shell and a connecting frame with a cooling cavity. It can individually heat the R-angle to 500-750℃ to enhance plasticity, while simultaneously maintaining a constant temperature of 60-120℃ for the straight sidewalls of the pipe. The high temperature of the R-angle can weaken the stress concentration during cold bending, release some residual tensile stress, and reduce deformation resistance. Continuous water cooling of the straight wall blocks the diffusion of high temperature, avoids the softening of the sidewalls during low-temperature tempering, locks in the original high-strength characteristics of the base material, eliminates the difference in yield strength between the R-angle and the straight edge, and completes differentiated hot and cold zoning online simultaneously. It eliminates the need for high-temperature heating of the entire pipe, significantly reducing energy consumption and avoiding the pipe twisting and springback dispersion defects caused by overall heating. It unifies the mechanical properties of the pipe from the forming source, solving the core problems of hardening and uneven performance of traditional cold-bent R-angles.

[0018] 2. This invention features a passive dust removal unit composed of a glass fiber reinforced polyimide composite deformation plate. The material is non-magnetic and insulated, unaffected by continuous heating from alternating magnetic field eddy currents. It utilizes residual heat from the coil to achieve a stable cycle of bending in 0.4–0.8 seconds and rebounding in 0.6–1.2 seconds. During the bending process, the deformation plate compresses the air within the cavity, and the airflow is directed through a one-way valve to purge the gap between the coil and the radius (R-angle), continuously removing iron oxide scale, magnetic yoke powder debris, and carbonized lubricating oil dust. The outer shell only has a pre-exhaust gap, which, together with the sealing strip and sealing plate, forms a sealed cavity, preventing external dust from entering the workshop. The entire structure requires no external power source such as fans or motors, enabling long-term continuous dust removal. It prevents ferromagnetic dust from disrupting the magnetic field distribution, avoids localized overheating of the radius (R-angle) and coil arcing / erosion, and ensures long-term stable and controllable induction heating temperature.

[0019] 3. This invention adds multiple sets of airbag components with bidirectional one-way valves to the middle of the displacement plate, which, in conjunction with the hot and cold deformation of the deformation plate, form a secondary dust removal system. When the deformation plate absorbs heat and bends inward, the displacement plate stretches and the airbags expand, drawing in clean air from the outside under negative pressure to complete air storage. When the deformation plate cools down and rebounds to its original position, the displacement plate squeezes the airbags, and the stored air is sprayed at high speed into the dead corner of the coil gap, achieving a two-stage impact purging during bending and resetting. This compensates for the insufficient cleaning power and dust residue of a single deformation airflow. The overall enclosed structure of the outer shell, combined with multi-layer sealing components, significantly blocks external dust from entering the heating chamber. The internal passive dust removal unit continuously circulates and self-cleans, constructing a closed-loop system of "external dust prevention + internal two-stage purging," further reducing the probability of dust accumulation, extending the service life of the induction coil and magnetic yoke, and reducing equipment maintenance frequency and production costs.

[0020] 4. The present invention is equipped with a stress uniformity unit on the discharge side. The hollow uniform sphere is filled with a magnetorheological elastomer or a thermomagnetic dual-response fluid induction element. Relying on the inherent alternating magnetic field of the electromagnetic coil, it continuously generates irregular global micro-vibrations. The fluctuation gap 603 stably constrains the vibration amplitude to 0.3-1.2mm, which will not scratch the R-corner forming surface. After the pipe is induction heated, it carries the residual heat of 400-600℃ into the structure. At high temperature, the dislocation slip resistance of the steel is greatly reduced. The alternating micro-cyclic stress transmitted by the uniform sphere can break up the local high stress clusters in the R-corner, uniformly disperse the residual tensile stress of cold bending, and reduce the difference in mechanical properties between the R-corner and the straight edge. The whole structure has no additional vibration driving components, and the residual heat vibration aging is completed online synchronously, eliminating the offline annealing process, shortening the production line process, and reducing the overall energy consumption of heat treatment.

[0021] 5. This invention integrates four major modules: zoned hot and cold temperature control, passive self-circulating dust removal, airbag secondary purging, and magneto-induced residual heat micro-vibration aging. Each structure relies on the residual heat of the coil and the passive linkage of the alternating magnetic field, eliminating the need for additional equipment such as electrical control, motors, and sensors. It is suitable for continuous high-speed pipe production lines. First, zoned hot and cold heating eliminates the problem of uneven plasticity during molding. Then, a double-layer dust removal system ensures long-term stable heating accuracy. Finally, residual heat micro-vibration is used to homogenize the residual stress of the cross-section online. This progressively solves the multiple composite defects of traditional high-strength steel square and rectangular tubes, such as stress concentration at the R-angle, mechanical inconsistency, easy cracking, and high equipment dust loss. The final product has no banded performance transition zone and low residual stress, making it less prone to warping and fatigue cracking during subsequent welding and heavy-duty service. It significantly improves the dimensional accuracy, mechanical consistency, and long-term service life of pipe fittings, meeting the stringent usage standards of high-end heavy-duty fields such as engineering machinery and steel structures. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is a schematic diagram of the outer protective shell in this invention; Figure 3 This is a half-sectional view of the outer casing in the undriven state of the present invention. Figure 4 This is a half-sectional view of the outer casing in the driving state in this invention. Figure 5 This is a schematic diagram of the connection structure of the passive dust removal unit in this invention; Figure 6 This is a schematic diagram of the displacement plate in this invention; Figure 7 This is a schematic diagram of the airbag component in this invention; Figure 8 This is a schematic diagram of the stress uniformity unit in this invention; Figure 9 This is a half-section structural diagram of the stress uniformity unit in this invention; Figure 10 For the present invention Figure 9 A magnified structural diagram of the structure at point A in the middle.

[0023] Explanation of the labels in the diagram: 1. Outer shell; 11. Exhaust gap; 2. Connecting frame; 3. Electromagnetic induction coil; 4. Passive dust removal unit; 41. Displacement plate; 411. Deformation plate; 412. Flat plate; 413. Sealing strip; 402. Heat insulation strip; 403. Sealing insert plate; 5. Airbag component; 6. Stress equalization unit; 601. Arc plate; 602. Stress equalization ball; 603. Fluctuation gap; 604. Sensing component. Detailed Implementation

[0024] like Figures 1 to 10 As shown in the figure, an electromagnetic induction local heating device for the R-corner area of ​​a high-strength steel square and rectangular tube according to an embodiment of the present invention includes multiple outer shells 1, with a connecting frame 2 connecting adjacent sides of the multiple outer shells 1. The outer shells 1 are made of metal and are designed to fit the flat surface of the square and rectangular tube. Exhaust gaps 11 for exhaust are provided on both sides of the outer shells 1 near the R-corner. An electromagnetic induction coil 3 is installed inside the outer shell 1. The connecting frame 2 has a cavity inside, which is connected to an external cooling system. The connecting frame 2 and the external cooling system form a cooling assembly. Here, it is only necessary to connect to the existing cooling system, so it will not be described in detail. This allows for temperature control of the flat edge near the R-corner, avoiding excessive temperature difference from affecting quality. The electromagnetic induction coil 3 is designed to be compatible with the R-corner.

[0025] Working principle: During operation, an alternating high-frequency current is passed through the electromagnetic induction coil 3 inside the outer casing 1, which is adapted to the R-corner contour of the tube. Relying on the skin effect of electromagnetic eddy currents, the coil precisely heats only the four R-corners of the rectangular tube, raising the R-corners to the plastic range of 500-750℃. This significantly reduces the deformation resistance of the R-corners, weakens the tensile stress peak generated by cold bending, and alleviates the problems of stress concentration and work hardening at the R-corners. The alternating magnetic field generated by the coil is constrained by the outer casing 1 and the matching magnetic yoke, and the magnetic field is concentrated only on the rounded corner area, reducing magnetic field leakage to the straight tube wall. At the same time... External cooling medium is continuously introduced into the internal cavity of the connecting frame 2. The low-temperature cooling medium circulates within the frame cavity, continuously exchanging heat with the inner wall of the outer shell 1 corresponding to the straight sidewall of the square and rectangular tube. This forces constant-temperature cooling of the four straight walls of the tube, stabilizing the straight sidewalls within the range of 60–120°C. This effectively blocks the high temperature at the R-angle from being conducted and diffused along the edge of the tube to the straight wall, preventing low-temperature tempering of the straight wall. It ensures that the flat section of the tube retains its original high-strength mechanical properties, eliminates the additional thermal stress caused by the temperature difference between the hot and cold sides of the tube, and suppresses the formation of band-shaped areas with uneven mechanical properties at the edges.

[0026] The entire structure completes two core processes online and simultaneously: local softening and heating of the R-corner and constant temperature control of the straight wall. Differentiated hot and cold zone control reduces residual stress in the R-corner forming by local hot forming on the one hand, and avoids defects such as pipe twisting, dimensional springback dispersion, and inconsistent mechanical properties caused by heating the whole pipe and excessive temperature difference on the other hand. During continuous material feeding production, the stress distribution of the square and rectangular tube cross section is continuously homogenized, improving the forming quality and long-term service stability of the pipe.

[0027] Furthermore, during electromagnetic induction heating, the radius (R) is heated to 500–750°C, causing oxidation of the steel surface with air, generating micron-sized Fe2O3 and Fe3O4 ferromagnetic oxide scales. As the pipe continues to feed and vibrates slightly, the oxide layer peels off and floats in the 2–5 mm gap between the coil and the radius, continuing to deposit. The U-shaped manganese-zinc ferrite yoke is pulverized by long-term alternating hot and cold temperatures, and the mica heat-insulating coating peels off at high temperatures, forming insulating fine powder that mixes into the gaps. The lubricating oil from the production line is carbonized by heat, and rust and grinding wheel dust in the air are adsorbed by the magnetic field and accumulate in the heating gaps.

[0028] To address the issue of dust accumulation in the gaps, a passive dust removal unit 4 is also installed inside the outer shell 1. This unit divides the interior of the outer shell 1 into two side spaces. The passive dust removal unit 4 utilizes heat changes to generate a deformation effect. It includes a displacement plate 41, with heat-insulating strips 402 connecting the two sides of the displacement plate 41 to the outer shell 1. The heat-insulating strips 402 are made of heat-insulating material. The displacement plate 41 consists of two deformation plates 411 and a flat plate 412, with the flat plate 412 positioned at the center. The two deformation plates 411 and the flat plate... The two sides of 412 are connected, and the deformation plate 411 is in a wavy shape. The crest of the deformation plate 411 can contact the electromagnetic induction coil 3. The displacement plate 41 is fixed with sealing strips 413 on both sides near the outer shell 1. At least one sealing insert 403 is installed on the outer side of the plate 412. This embodiment adopts two symmetrical designs. The sealing insert 403 can pass through the outer shell 1 and be tightly attached to the periphery of the outer shell 1. A one-way valve is installed on the heat insulation strip 402. The one-way valve can only release air in the direction of the electromagnetic induction coil 3.

[0029] The deformation plate 411 is selected as a glass fiber reinforced polyimide thermotropic bicrystalline composite board (PI glass fiber composite board, thickness 0.8-1.5mm). The board has a medium thermal conductivity, and the thermal expansion difference of the oriented glass fiber layer results in a fast response. The time to complete bending and forming is 0.4-0.8s. The PI insulating substrate has no eddy current heat storage, only its own stored heat release, and the air convection cooling speed is fast. The time to complete rebound and stretching is 0.6-1.2s. It is suitable for continuous material feeding in the production line, with a stable circulation frequency and continuous output of directional blowing airflow. Alternatively, the material can also be selected as a mica-based ceramic fiber thermotropic composite elastic board (inorganic insulating board). It should be noted that the deformation of the selected material is regular, ensuring that the deformation position is stable each time.

[0030] The outer shell 1 can be made of 304 austenitic non-magnetic stainless steel plate. 304 austenitic stainless steel is non-magnetic and has a resistivity much higher than that of carbon steel / pure aluminum. When the high-frequency alternating magnetic field of the induction coil passes through the shell, the induced eddy current loss is extremely low and the temperature will not rise due to continuous self-heating of the magnetic field. The shell temperature is determined only by the radiation heat of the tube R angle and the conduction heat of the coil. The temperature is controllable and stable, and there will be no unexplained continuous high temperature of the shell, ensuring the normal switching of hot and cold cycles of the deformation plate 411.

[0031] Working principle: When the electromagnetic induction coil 3 is working, it will simultaneously heat the outer shell 1. At the same time, the heat is transferred to the deformation plate 411 through the contact point of the wave crest. After the plate reaches the deformation threshold, it will bend inward steadily along the preset trajectory within 0.4 to 0.8 seconds. The two deformation plates 411 will simultaneously retract towards the coil side, and the displacement plate 41 will be squeezed inward as a whole. The volume of the inner coil heating cavity will shrink rapidly. The mixed gas in the cavity, which contains iron oxide powder, insulating debris, carbonized oil dust, etc., will be compressed and can only be sprayed directionally through the one-way valve on the heat insulation strip 402 towards the gap between the electromagnetic induction coil 3 and the R angle. The high-speed airflow blows along the tangent of the R angle, dispersing and carrying away the various dusts deposited in the gap, thus preventing the dust from staying in the shielding magnetic field for a long time.

[0032] After the deformation plate 411 bends inward, the sealing plate 403 on the outside of the flat plate 412 moves inward synchronously. The ventilation groove on the outside of the outer shell 1 is vented with room temperature air. The cold air contacts the deformation plate 411 to achieve rapid convection heat dissipation. The PI substrate has no additional eddy current heat source and relies solely on its own stored heat for heat dissipation. It can fully rebound and stretch in 0.6 to 1.2 seconds. The displacement plate 41 resets outward, and the volume of the inner coil cavity increases to form a negative pressure. Clean air from the outside is replenished to the outer air storage cavity through the exhaust gap 11 and the gap of the sealing plate 403 to complete the air storage. An ultrafiltration screen can be designed at the air inlet to prevent external dust from entering.

[0033] Under the condition that the coil is continuously energized and heated and the pipe is continuously transported, the deformation plate 411 continuously cycles through the action of "heat absorption, bending, extrusion and air supply - air cooling, rebound and negative pressure air replenishment", forming a periodic directional blowing airflow to continuously clean up various dusts accumulated between the coil and the R-corner. The entire structure relies on the residual heat of the coil itself to drive the deformation, without the need for external power components such as motors, electrical controls, and fans. Moreover, the material of the deformation plate 411 is not affected by the alternating magnetic field, and there will be no problem of continuous high temperature jamming and inability to rebound. It eliminates the hidden defects such as uneven heating, coil ablation, and magnetic yoke failure caused by dust accumulation from the source, ensuring uniform and stable local induction heating of the R-corner.

[0034] Furthermore, in order to enhance the dust removal effect, multiple airbag components 5 are connected between the center of the flat plate 412 and the outer shell 1. One end of the airbag component 5 passes through the area of ​​the flat plate 412 and the electromagnetic induction coil 3, and the other end of the airbag component 5 is fixed to the side of the outer shell 1. Both ends of the airbag component 5 are equipped with one-way valves, so that when the airbag component 5 is inflated, it will draw in the gas from the area away from the electromagnetic induction coil 3, and when it is exhausted, it will exhaust the gas towards the area of ​​the electromagnetic induction coil 3.

[0035] Working principle: When the electromagnetic induction coil 3 continues to release heat, the deformation plate 411 absorbs heat and rises to a temperature above 130°C, causing it to bend inward. This drives the entire displacement plate 41 to move horizontally towards the side of the electromagnetic induction coil 3. Simultaneously, the flat plate 412 moves towards the coil, stretching the airbag component 5 to expand its capacity. The one-way valves at both ends of the airbag component 5 operate synchronously, with only the outer one-way valve open and the inner one-way valve closed. During the expansion of the airbag, negative pressure is applied to the air storage chamber on the side of the outer shell 1 away from the coil, drawing in the pre-stored clean cooling air into the airbag to complete the storage and energy storage. During this stage, the deformation plate 411 compresses the airflow in the cavity to complete the first round of dust blowing.

[0036] After the deformation plate 411 is bent into place, the crest separates from the coil. Room temperature air is introduced into the exhaust gap 11 of the outer shell 1 for convection heat exchange. The temperature of the deformation plate 411 gradually drops to below 80°C and rebounds and resets along the original path. Simultaneously, the displacement plate 41 moves backward outward, forming an axial compression on the airbag component 5. The airbag's volume shrinks under pressure, the outer one-way valve closes, and the inner one-way valve connecting the coil area opens. The high-pressure air stored inside the airbag is rapidly and directionally sprayed towards the narrow gap between the electromagnetic induction coil 3 and the R angle, forming a second wave of impact airflow. This supplements the blowing during the reset phase of the deformation plate 411, and performs a secondary flushing of the dust accumulated in the dead corner of the gap. This compensates for the insufficient blowing force and incomplete cleaning of the single deformation compression airflow, achieving continuous dust removal in both bending and reset stages.

[0037] The entire outer shell 1 is an integrally enclosed structure, with only the exhaust gap 11 reserved for heat exchange. The remaining positions are sealed by the sealing strip 413 and the sealing plate 403, which greatly reduces the probability of external dust, grinding wheel iron powder, and rust particles in the air entering the heating gap through the shell gap, thus reducing the amount of dust added. The periodic deformation air supply of the passive dust removal unit 4, combined with the airbag component 5 for dual-stage air extraction and exhaust, forms a continuously circulating composite airflow cleaning system that removes various magnetic dust and insulation debris around the coil in all directions, avoiding dust accumulation that disturbs the induction magnetic field, causes uneven heating of the R-angle, and causes coil arcing and burning defects, thus continuously ensuring uniform and stable local electromagnetic induction heating of the R-angle.

[0038] Furthermore, to achieve uniform stress, a stress-uniforming unit 6 is arranged near the discharge direction of the outer shell 1. The stress-uniforming unit 6 includes an arc plate 601 with the same radius as the radius of the R-angle. Multiple spherical grooves are formed on the arc plate 601, and stress-uniforming spheres 602 are arranged in the spherical grooves. A fluctuation gap 603 is provided between the arc plate 601 and the stress-uniforming spheres 602. The fluctuation gap 603 constrains the vibration amplitude to 0.3-1.2 mm. The stress-uniforming spheres 602 are hollow and contain a sensing element 604. The sensing element 604 can be moved by an alternating magnetic field. For example, the sensing element 604 is selected as an MRE magnetorheological elastomer. The magnetic particles inside the alternating magnetic field are repeatedly arranged and reorganized, and the material continuously twists and vibrates slightly, generating irregular and disordered micro-movements. Filling the cavity inside the hollow sphere, the magnetic field continuously acts to cause uninterrupted global disturbance, resulting in uniform vibration without a fixed direction, which is suitable for all-round stress dispersion.

[0039] The sensing element 604 can also be a thermomagnetic dual-response material, such as high-temperature resistant nano-manganese ferrite dispersed high-temperature lubricating grease, filling the entire hollow sphere; residual heat reduces the viscosity of the medium, and the alternating magnetic field drives the magnetic particles to continuously roll and convect, so that the fluid is permanently disordered in the sealed sphere, continuously transmitting small disturbance vibrations, without hard collisions, and will not scratch the inner wall of the sphere, and can achieve 360° all-round micro-vibration transmission.

[0040] Working principle: Under the action of the alternating magnetic field of the coil, the magnetic particles inside the elastic body are continuously reorganized and arranged, and the material continuously undergoes irregular twisting and micro-vibration throughout the entire area, which drives the hollow uniform strain ball 602 to move and vibrate in all directions within the fluctuation gap 603. If a high-temperature resistant nano-manganese ferrite magnetothermal fluid is selected as the sensing element 604, the residual heat of the tube reduces the viscosity of the fluid, and the alternating magnetic field drives the internal magnetic particles to continuously roll and convect. The fluid turbulence drives the uniform strain ball 602 to continuously and irregularly reciprocate micro-movements.

[0041] The 602 ball is closely attached to the outer wall of the high-temperature R-corner of the square and rectangular tube. Its disordered micro-vibrations are continuously transmitted to the R-corner area through the spherical surface. At this time, the R-corner maintains a residual heat range of 400-600℃, the dislocation slip resistance of the steel is greatly reduced, and the alternating micro-cyclic stress generated by the micro-vibration can break up the local high stress concentration area of ​​the R-corner, evenly disperse the residual tensile stress of the forming, weaken the yield strength difference between the R-corner and the straight sidewall of the tube, and avoid warping and fatigue micro-cracks in the tube during subsequent welding and heavy-load service.

[0042] The entire structure relies on the inherent alternating magnetic field of the heating coil to drive the induction element 604 to move autonomously. The amplitude of the uniform ball 602 is controlled only by the fluctuation gap 603. Online vibration aging is completed simultaneously during the residual heat stage of the pipe, eliminating the need for offline annealing. This can significantly balance the stress distribution of the R-angle section of the square and rectangular tubes, improving the consistency of the mechanical properties of the pipes and their long-term service stability.

[0043] The embodiments disclosed in this invention are preferred embodiments, but are not limited thereto. Those skilled in the art can easily understand the spirit of this invention based on the above embodiments and make different extensions and variations, but as long as they do not depart from the spirit of this invention, they are all within the protection scope of this invention.

Claims

1. An electromagnetic induction local heating device for the radius (R) region of high-strength steel square and rectangular tubes, characterized in that, It includes a zoned temperature control unit, which has a heating cavity for accommodating a rectangular tube, for locally heating the R-corner region of the rectangular tube and cooling the straight wall, so as to form a zoned temperature field on the tube cross-section; The zone temperature control unit includes: An outer shell (1) surrounds and forms the heating cavity, which carries the electromagnetic induction coil (3) and the cooling assembly, and shields against heat diffusion; A cooling component, which is thermally coupled to the flat wall region, is used to absorb and remove heat from the flat wall through fluid circulation in order to maintain it within a preset low temperature range. An electromagnetic induction coil (3) is disposed in the heating cavity and is used to generate an alternating magnetic field to inductively heat the R-angle region. The shape of the electromagnetic induction coil (3) is adapted to the R-angle profile and is used to pass in a high-frequency current to generate an eddy current effect to heat the R-angle. The passive dust removal unit (4) is located inside the partition temperature control unit and is used to absorb the residual heat generated by the partition temperature control unit and deform to form a directional blowing airflow to remove dust in the heating gap.

2. The electromagnetic induction local heating device for the R-angle region of high-strength steel square and rectangular tubes according to claim 1, characterized in that, The cooling assembly includes a connecting frame (2), which has a cavity inside for the flow of cooling medium, and its outer wall is used to fit the straight wall area of ​​the rectangular tube.

3. The electromagnetic induction local heating device for the R-angle region of high-strength steel square and rectangular tubes according to claim 1, characterized in that, The passive dust removal unit (4) includes: The displacement plate (41) is located inside the outer shell (1) and has a component that can reciprocate with temperature changes. It is used to generate displacement during the process of absorbing the residual heat of the electromagnetic induction coil (3) and dissipating heat. The two sides of the displacement plate (41) are connected to the outer shell (1) through heat insulation strips (402). An airflow control component, which is linked to the displacement plate (41), is used to control the direction of airflow intake and exhaust during deformation.

4. The electromagnetic induction local heating device for the R-angle region of high-strength steel square and rectangular tubes according to claim 3, characterized in that, The displacement plate (41) includes: The deformation plate (411) is made of a thermo-deformable material and has a corrugated cross section, the crests of which are used to contact the induction heating component to absorb residual heat and bend when the deformation threshold is reached. A flat plate (412), which is connected to the deformation plate (411), is used to transmit displacement and serve as an installation base.

5. The electromagnetic induction local heating device for the R-angle region of high-strength steel square and rectangular tubes according to claim 4, characterized in that, The airflow control component includes: A one-way vent valve is provided in the channel between the outer casing (1) and the external environment, allowing gas to flow in only one direction; A sealing insert (403) is disposed between the flat plate (412) and the inner wall of the outer shell (1) to separate different gas zones during movement.

6. An electromagnetic induction local heating device for the R-angle region of a high-strength steel square or rectangular tube according to claim 4 or 5, characterized in that, The passive dust removal unit (4) also includes an airbag component (5). The airbag component (5) is provided with one-way valves at both ends. One end is connected to the heating gap, and the other end is connected to the air storage chamber inside the outer shell (1). The airbag component (5) is connected to the plate (412) so that it is stretched and sucked in when the deformation plate (411) is bent, and compressed and discharged into the heating gap when the deformation plate (411) rebounds.

7. The electromagnetic induction local heating device for the R-angle region of high-strength steel square and rectangular tubes according to claim 1, characterized in that, A stress uniform unit (6) is also provided on one side of the outer shell (1); The stress uniformity unit (6) includes: a vibration generating component containing a medium that responds to a magnetic field or heat, used to generate random motion under the action of the magnetic field generated by the partition temperature control unit and the residual heat of the pipe; A vibration transmission and constraint component is used to support the vibration generating component and transmit its vibration to the R-angle surface, while constraining the vibration amplitude.

8. The electromagnetic induction local heating device for the R-angle region of high-strength steel square and rectangular tubes according to claim 7, characterized in that, The vibration generating component includes: The sphere (602) has a cavity inside; The sensing element (604), which is filled in the hollow uniform sphere (602), is a magnetorheological elastomer or a thermomagnetic dual-response fluid, and is used to generate irregular micro-motions under alternating magnetic field or thermal field.

9. An electromagnetic induction local heating device for the R-angle region of a high-strength steel square or rectangular tube according to claim 8, characterized in that, The vibration transmission and constraint component includes: An arc plate (601) with the same arc as the radius of the R-angle is used to fit the R-angle surface and is provided with a ball groove for accommodating the uniform ball (602); A ripple gap (603), formed between the uniform ball (602) and the inner wall of the ball groove, is used to limit the vibration amplitude within a preset range.

10. An electromagnetic induction local heating device for the R-angle region of a high-strength steel square or rectangular tube according to claim 9, characterized in that, The zoned temperature control unit heats the R-corner area to 500-750°C and controls the straight wall area at 60-120°C. The fluctuation gap (603) constrains the vibration amplitude to 0.3-1.2 mm.

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