Local induction tempering controlled cooling method for sealing head circular seam

Abstract

The invention discloses an end socket circular seam local induction tempering controlled cooling method, and aims to optimize the welding heat treatment process through induction heating and controlled cooling technologies, improve the welding quality and ensure the mechanical property of a welding seam area. The method specifically comprises the steps that a follow-up trolley is guided to move in the annular direction through an annular guide rail, and it is ensured that an induction coil and a controlled cooling cover installed on the trolley can accurately control the heating and cooling processes; the temperature sensor array is combined with the contact type thermocouple and the non-contact type infrared probe to monitor the temperature of the workpiece, and it is guaranteed that the temperature difference is controlled within the specified range in the heat treatment process. A water cooling and fan system is matched with a temperature control cover, it is ensured that a weld joint area reaches a specified tempering temperature window, and the temperature and the cooling rate are accurately adjusted in the heat preservation and controlled cooling stages. And through zoning treatment and arrangement of overlapping regions, the uniformity of heat treatment is ensured, and the temperature gradient does not exceed 5 DEG C / cm. The whole process is automatically monitored and adjusted by the control unit, and a quality report is generated for final quality release.

Description

Technical Field

[0001] This invention relates to the field of welding technology, specifically to a method for controlled cooling of local induction tempering in the circumferential seam of a head. Background Technology

[0002] In industrial manufacturing, especially in the production of large welded components such as pressure vessels and heat exchangers, the quality of the welding process directly affects the strength, durability, and safety of the product. Controlling heat input during the welding process is crucial for weld quality, particularly in the welding of heads and cylinders, where the control of welding stress, heat-affected zone, and residual stress is especially important due to their large welding area and complex shapes.

[0003] Currently, traditional butt welding processes for end caps and cylinders mostly employ either overall heating and annealing or local heating and annealing. While overall heating and annealing can effectively reduce welding stress, it is not widely used in practice due to its high equipment and operating costs and low efficiency in large-scale production. Local heating and annealing, although reducing heat input, suffers from imprecise temperature control, potentially leading to excessively large or small local heat-affected zones, thus affecting the weld strength and fatigue resistance.

[0004] Furthermore, the controlled cooling stage in traditional welding processes is also a crucial step, as controlling the cooling rate is essential to prevent cracking and embrittlement of the weld metal. In existing technologies, most processes cannot precisely control the cooling rate, especially for large welded components, making it difficult to achieve uniform cooling, resulting in localized overcooling or overheating, which can further lead to structural deformation or defects.

[0005] Therefore, it is necessary to design a local induction tempering controlled cooling method for the end cap circumferential seam to address these issues. Summary of the Invention

[0006] The purpose of this invention is to provide a method for controlled cooling of local induction tempering in the circumferential seam of a head, so as to solve the problems mentioned in the background art.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for controlled cooling of local induction tempering in the circumferential seam of a head, comprising the following steps: (a) After the end cap is connected to the cylinder, a circumferential guide rail is installed on the outer wall of the cylinder along the circumferential direction and the circumferential guide rail is fixed to the outer wall of the cylinder by bolts; (b) The follower trolley is connected to the circumferential guide rail by rollers and is only allowed to move in a single degree of freedom in the circumferential direction. The follower trolley is equipped with a partitioned induction coil and a cooling cover. The partitioned induction coil maintains a radial gap of 3 to 8 mm between itself and the outer surface of the workpiece, and the cooling cover maintains a gap of 2 to 5 mm between itself and the outer wall of the workpiece. It also covers an area of ​​40 to 60 mm on both sides of the weld centerline in the axial direction. (c) The temperature sensor array consists of contact thermocouples and non-contact infrared temperature probes. The sensor array is fixed on the outer wall of the cylinder by a bracket. The thermocouple measuring points are 10-20 mm away from the outside of the weld toe, and a group is arranged every 50-100 mm along the circumference. The infrared probe is directly facing the weld toe area. (d) An adjustable baffle is provided under the cooling cover. The fan is connected to the air outlet of the cooling cover through a flexible air duct. The fan adjusts the air volume through the control unit to keep the temperature difference gradient within a limited range. (e) The water cooling system is connected to the induction coil via a water-cooled cable to provide circulating cooling water. Flow and temperature sensors are installed on the inlet and outlet water pipes to ensure that the cooling water flow and temperature difference meet the requirements.

[0008] According to the above technical solution, the temperature control window for induction tempering is 620-680℃, the heating rate is 2-5℃ / min, the holding time is 2-4 hours, the cooling rate is 1-3℃ / min, and the temperature difference gradient when cooled to 300℃ does not exceed 5℃ / cm.

[0009] According to the above technical solution, the speed of the trolley running in the circumferential direction is 50-120 mm / min. The control unit compares the deviation between the temperature and the target curve in real time and adjusts the sensing power and the speed of the trolley accordingly.

[0010] According to the above technical solution, during the heat preservation stage, the induction power maintains the temperature within the tempering temperature window through small pulses, and the cooling hood is slightly opened to guide the flow, and the fan runs at low speed to keep the temperature difference between zones no more than 25°C.

[0011] According to the above technical solution, before the process is implemented, the deviation between the guide rail and the center line of the weld is no more than 1 mm, and the gap between the induction coil and the outer surface of the workpiece is adjusted. The thermocouple and infrared probe are calibrated, and the calibration deviation is no more than ±5℃.

[0012] According to the above technical solution, the cooling process is controlled by the control unit, which adjusts the fan speed and the opening of the baffle based on the real-time measurement values ​​of the thermocouple and infrared probe, to ensure that the temperature of each zone is controlled within the specified range.

[0013] According to the above technical solution, the temperature gradient between the treated area and the untreated area is no greater than 5℃ / cm, and the overlapping area ensures a seamless transition between adjacent zones.

[0014] According to the above technical solution, during the entire heat treatment process, all temperature curves, power, speed and air volume data are automatically archived by the control unit and a quality report is generated as the basis for release.

[0015] Compared with existing technologies, the beneficial effects achieved by this invention are as follows: By setting up a circumferential guide rail and a follow-up trolley, this invention ensures the precise positioning and movement trajectory of the induction coil and the cooling control cover, thereby achieving uniformity and high-precision control of the local induction tempering and cooling process of the weld. Through the optimized layout of the temperature sensor array, combined with dual measurement methods of contact thermocouples and non-contact infrared temperature probes, real-time monitoring and feedback adjustment of the workpiece temperature can be achieved, effectively avoiding welding defects caused by excessive temperature differences. The cooperation between the cooling control cover and the fan system further ensures that the temperature gradient in the weld area during cooling does not exceed 5℃ / cm, thereby improving the mechanical properties and stability after welding. Compared with traditional methods, this invention has higher heat treatment uniformity, more precise temperature control, and a more efficient cooling system, significantly improving workpiece quality and shortening processing time. Attached Figure Description

[0016] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Fig. 1 This is a process flow diagram of a method for controlled cooling of local induction tempering in the circumferential seam of a head proposed in this invention; Fig. 2 This is a schematic diagram of the overall structure of the end cap and the cylinder in an embodiment of the present invention. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] Reference Figs. 1-2 This embodiment provides a method for controlled cooling of local induction tempering in the circumferential weld of a head. After the head is joined to the cylinder, a circumferential guide rail is installed on its outer wall along the circumferential direction. The circumferential guide rail is fixed to the outer wall of the cylinder by bolts. A follow-up trolley cooperates with the circumferential guide rail via rollers, allowing only single-degree-of-freedom movement along the circumferential direction. A partitioned induction coil and a controlled cooling cover are installed on the trolley. A radial gap of 3-8 mm is maintained between the partitioned induction coil and the outer surface of the workpiece, and a gap of 2-5 mm is maintained between the controlled cooling cover and the outer wall of the workpiece, covering an area of ​​40-60 mm on both sides of the weld centerline axially.

[0019] The temperature sensor array consists of contact thermocouples and non-contact infrared temperature probes, both fixed to the outer wall of the cylinder by a bracket. The thermocouple measuring points are 10-20 mm from the outer side of the weld toe, arranged in groups every 50-100 mm along the circumference. The infrared probes are directly facing the weld toe area. The sensor signals are connected to the data acquisition and control unit. The induction power supply is connected to the induction coil via a water-cooled cable. The cooling system provides circulating cooling water, with flow and temperature sensors installed on the inlet and outlet water pipes. A variable frequency fan is connected to the airflow inlet of the cooling shroud via a flexible air duct and is equipped with adjustable baffles to form a controllable convection channel. If necessary, an insulation cover or blanket is added to the inside or back of the workpiece to suppress the temperature difference between the inner and outer walls.

[0020] Before implementation, the guide rail needs to be calibrated to ensure its deviation from the weld centerline is no more than 1 mm; adjust the gap between the induction coil and the outer surface of the workpiece, and arrange thermocouples and infrared probes to complete the calibration of the two temperature measurement methods, with a calibration deviation of no more than ±5℃. After the cooling cover is in place, check the opening and sealing of the guide baffle, and ensure the fan performance meets design requirements. Flow water through the water cooling system and check whether the flow rate and inlet / outlet water temperature difference meet the specifications in the process card.

[0021] To ensure uniform heat treatment, the full circumferential weld is divided into multiple zones, each with an arc length of 300–600 mm, and adjacent zones have a 10%–20% overlap. The process parameters are: tempering temperature window 620–680℃, heating rate 2–5℃ / min, holding time 2–4 hours, and cooling rate 1–3℃ / min to 300℃. The temperature gradient between the treated and untreated zones is specified to be no greater than 5℃ / cm.

[0022] During the heating phase, the trolley travels at a low speed of 50–120 mm / min along the circumference. The control unit compares the temperature deviation from the target curve in real time and adjusts the induction power and trolley speed accordingly. When the temperature reaches the set window and the temperature difference between zones is no greater than 25°C, the trolley stops and enters the heat preservation phase. During the heat preservation phase, the induction power maintains the temperature within the window with small pulses, the cooling shroud slightly opens its airflow outlet, and the variable frequency fan runs at low speed to keep the temperature gradient within the specified range.

[0023] After the heat preservation is completed, the controlled cooling stage begins. The induction power is cut off, and the fan is turned on to reduce the zone temperature from the tempering zone to 300℃ according to the set cooling curve, maintaining a cooling rate of 1-3℃ / min. During the controlled cooling process, the control unit adjusts the fan speed and the opening of the baffle in real time based on the measurements from the thermocouple and infrared probe to ensure that the temperature gradient does not exceed 5℃ / cm.

[0024] Each zone undergoes heat treatment sequentially, ensuring a seamless transition in overlapping areas. After the entire ring is completed, once the workpiece has cooled to room temperature, residual stress is measured at points on the weld toe and weld cap area, with a maximum value not exceeding 120 MPa. Hardness is tested on the weld metal and heat-affected zone, with a hardness value not exceeding 240 HV10. Simultaneously, roundness, ovality, and axial deformation are checked, and the results should all conform to the drawing tolerances.

[0025] The temperature curve, power, speed, and air volume data of the entire process are automatically archived by the control unit, and a quality report is generated as the basis for release.

[0026] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0027] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for controlled cooling of local induction tempering in the circumferential seam of a head, characterized in that: The method includes the following steps: (a) After the end cap is connected to the cylinder, a circumferential guide rail is installed on the outer wall of the cylinder along the circumferential direction and the circumferential guide rail is fixed to the outer wall of the cylinder by bolts; (b) The follower trolley is connected to the circumferential guide rail by rollers and is only allowed to move in a single degree of freedom in the circumferential direction. The follower trolley is equipped with a partitioned induction coil and a cooling cover. The partitioned induction coil maintains a radial gap of 3 to 8 mm between itself and the outer surface of the workpiece, and the cooling cover maintains a gap of 2 to 5 mm between itself and the outer wall of the workpiece. It also covers an area of ​​40 to 60 mm on both sides of the weld centerline in the axial direction. (c) The temperature sensor array consists of contact thermocouples and non-contact infrared temperature probes. The sensor array is fixed on the outer wall of the cylinder by a bracket. The thermocouple measuring points are 10-20 mm away from the outside of the weld toe, and a group is arranged every 50-100 mm along the circumference. The infrared probe is directly facing the weld toe area. (d) An adjustable baffle is provided under the cooling cover. The fan is connected to the air outlet of the cooling cover through a flexible air duct. The fan adjusts the air volume through the control unit to keep the temperature difference gradient within a limited range. (e) The water cooling system is connected to the induction coil via a water-cooled cable to provide circulating cooling water. Flow and temperature sensors are installed on the inlet and outlet water pipes to ensure that the cooling water flow and temperature difference meet the requirements.

2. The method for controlled cooling of local induction tempering in the circumferential seam of a head according to claim 1, characterized in that: The temperature control window for induction tempering is 620–680°C, the heating rate is 2–5°C / min, the holding time is 2–4 hours, the cooling rate is 1–3°C / min, and the temperature gradient when cooled to 300°C does not exceed 5°C / cm.

3. The method for controlled cooling of local induction tempering in the circumferential seam of a head according to claim 1, characterized in that: The trolley travels at a low speed of 50-120 mm / min in the circumferential direction. The control unit compares the deviation between the temperature and the target curve in real time and adjusts the sensing power and the trolley speed accordingly.

4. The method for controlled cooling of local induction tempering in the circumferential seam of a head according to claim 1, characterized in that: During the heat preservation stage, the induction power maintains the temperature within the tempering temperature window through small pulses, and the cooling hood is slightly opened to guide the airflow, while the fan runs at low speed to keep the temperature difference between zones no more than 25°C.

5. The method for controlled cooling of local induction tempering in the circumferential seam of a head according to claim 1, characterized in that: Before the process is implemented, the deviation between the guide rail and the center line of the weld is no more than 1 mm, and the gap between the induction coil and the outer surface of the workpiece is adjusted. The thermocouple and infrared probe are calibrated, and the calibration deviation is no more than ±5℃.

6. The method for controlled cooling of local induction tempering in the circumferential seam of a head according to claim 1, characterized in that: The cooling process is controlled by a control unit that adjusts the fan speed and the opening of the baffle based on real-time measurements from thermocouples and infrared probes to ensure that the temperature of each zone is controlled within the specified range.

7. The method for controlled cooling of local induction tempering in the circumferential seam of a head according to claim 1, characterized in that: The temperature gradient between the treated and untreated areas is no greater than 5℃ / cm, and seamless transition between adjacent zones is ensured through overlapping areas.

8. The method for controlled cooling of local induction tempering in the circumferential seam of a head according to claim 1, characterized in that: Throughout the entire heat treatment process, all temperature curves, power, speed, and airflow data are automatically archived by the control unit, and a quality report is generated as the basis for release.

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