Control method for local induction heating of aviation bolt parts
Through the induction heat treatment process of three-stage heating and mobile temperature compensation, the problem of temperature unevenness in induction heating is solved, the uniformity control of the local tempering area of the bolt is achieved, the production quality and efficiency are improved, environmental pollution is avoided, and the performance requirements of aviation parts are met.
Patent Information
- Application Number
- CN202510790837.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-13
- Publication Date
- 2025-09-12
AI Technical Summary
In the existing technology, induction heating has the problem of temperature non-uniformity during the local tempering process of parts, resulting in uneven microstructure and performance. In addition, the traditional lead bath tempering process is easily affected by human factors, resulting in unstable quality and serious environmental pollution.
The induction heat treatment process adopts three-stage heating + mobile temperature compensation. By rotating and moving the induction heater and combining it with spray cooling, the uniformity of the temperature field inside the part is controlled. Including three-stage heating and mobile temperature compensation induction tempering method, the uniformity of the microstructure and performance of the local tempering area of the bolt is ensured.
The temperature uniformity of the local tempering area of the bolt is controlled, which improves production quality and efficiency, reduces the risk of environmental pollution, reduces the impact of human operation, and meets the quality and performance requirements of aviation parts.
Smart Images
Figure CN120624801A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of heat treatment of aircraft parts, and in particular to a control method for local induction heating of aviation bolt parts. Background Art
[0002] Currently, in aviation manufacturing, localized tempering and softening treatment is performed on threads of ultra-high-strength steel bolts to reduce notch sensitivity. The traditional localized tempering process involves lead bath tempering, which is highly susceptible to human influence. Consequently, the quality of the resulting products is often inconsistent, leading to a high rate of rework. Liquid lead is highly toxic, not only polluting the environment but also adversely affecting the health of operators. Furthermore, the lead bath significantly impacts production schedules, requiring the lead to be melted in advance, preventing immediate heating. Induction heating technology offers advantages such as high heating rates, reduced decarburization and oxidation, and fast restart times. Compared to traditional heat treatment, induction heat treatment exhibits high efficiency, excellent stability, and energy-saving and environmental benefits. However, induction heating technology is not widely used for localized tempering of parts. This is primarily because, during the induction heating process, the skin effect and end effect create non-uniform temperature gradients within the heated part. This, in turn, leads to varying degrees of tempering within the material, ultimately resulting in uneven microstructure and properties.
[0003] Therefore, controlling the uniformity of the temperature field within each region of the part during induction tempering is crucial. Using a three-stage induction tempering process with localized heating and mobile heating can reduce the impact of human intervention, improve production efficiency, shorten construction time, and save costs. Summary of the Invention
[0004] To address the shortcomings of localized tempering of bolt components in existing technologies, this paper proposes a three-stage heating method with mobile warming for localized tempering of ultra-high-strength steel bolt components. This method improves the uniformity of microstructure and properties in the localized tempering area of the bolt, ensuring part production quality. The three-stage heating method involves holding the inductor at a temperature slightly below the final heat treatment temperature (average temperature) for a period of time to reduce the core-surface temperature difference, followed by heating to the final induction tempering temperature for two heat treatments. The three-stage heating method with mobile warming involves moving the inductor a certain distance to a cooler area for warming after the three-stage heating process is complete.
[0005] Technical solution of the present invention: A method for controlling local induction heating of an aviation bolt part, wherein the diameter of the aviation bolt part is 10 to 30 mm, comprises the following steps: S1: Fix the bolt on a workbench and then rotate the workbench, use an induction heater to perform a first induction tempering heating on the threaded area of the bolt, and spray cool the non-threaded area of the bolt at the same time; S2: Stop heating the bolt; S3: performing a second tempering heating on the bolt; S4: Stop heating the bolt; S5: performing a third tempering heating on the bolt; S6: Stop heating the bolt and stop spray cooling the non-heating area; S7: moving the induction heater vertically upward by a preset distance to perform a fourth tempering heating on the bolt; S8: Stop heating the bolt and spray cool the entire bolt.
[0006] Furthermore, in step S1, the rotation speed of the workbench is 50-100 rpm, the heating power of the first tempering is 6.5-7.5 kW, the induction coil frequency is 7.5-8 kHz, the heating temperature is 580°C-600°C, the heating time is 20-25 s, and the cooling medium sprayed on the non-threaded area of the bolt is water.
[0007] Furthermore, in steps S2, S4, and S6, the heating stop time is 3 to 8 seconds.
[0008] Furthermore, in step S3, the total heating power of the second tempering is 6.0-8.0 kW, the heating temperature is 550-650° C., and the heating time is 3-10 s.
[0009] Furthermore, in step S5, the total heating power of the third tempering is 6.0-8.0 kW, the heating temperature is 550-650° C., and the heating time is 3-10 s.
[0010] Furthermore, in step S7, the total heating power of the fourth tempering is 6.0-8.0 kW, the heating temperature is 550-650° C., and the heating time is 5-15 s.
[0011] Furthermore, in S7, the induction heater is vertically moved upward by a preset distance, which is 14 to 16 mm.
[0012] Furthermore, in S1, the distance between the outer surface of the bolt thread and the inner side of the induction heater is 10-20 mm.
[0013] The present invention provides a precise control method for localized induction heating of aviation bolt parts, including: 1) using the aforementioned three-stage heating + mobile heating induction tempering process; 2) defining the three-stage heating process parameters and key control factors; and 3) defining the mobile heating induction tempering process parameters and key control factors. This method avoids the difficult-to-control skin effect and end effect during induction heating, overcomes the uneven temperature gradients within the heated part, and addresses the issue of uneven microstructure and properties. The method is simple and efficient to operate, ensuring part production quality. BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The present invention is further described in detail below with reference to examples and accompanying drawings. Those skilled in the art can, through careful consideration, grasp the core of the present invention and further apply it to other similar parts.
[0015] Figure 1 This is a schematic diagram of the three-stage heating induction heat treatment method for bolts; Figure 2 Schematic diagram of the three-stage heating + mobile temperature compensation induction tempering process method.
[0016] Explanation of numbers in the figure: 1 axis of symmetry, 2 bolt, 3 induction heater, 4 water spray device, 5 distance from the lower end of the induction heater to the water spray device, 6 moving distance of the induction heater. DETAILED DESCRIPTION
[0017] The following describes the specific embodiments of the present disclosure in detail. Figure 1 , Figure 1 This is a schematic diagram of the three-stage heating induction heat treatment method for bolts. Fix the position of the bolt part 2, adjust the distance between the induction heater 3 and the part, and strictly maintain the relative state of the part (bolt 2) and the induction heater 3 to ensure relatively uniform heating and cooling.
[0018] Adjust the distance 5 between the induction heater 3 and the water spray device 4 (the distance from the lower end of the induction heater to the water spray device) to ensure that water is sprayed to the cooling position of the part. Turn on the power supply and rotate the part about the symmetry axis 1. First, perform three-stage heating. Hold the temperature slightly below the final heat treatment temperature (average temperature) for a period of time to reduce the temperature difference between the core and the surface. Then, heat it to the final induction tempering temperature for two heat treatments.
[0019] Figure 2 The diagram below shows a three-stage heating + moving temperature compensation induction tempering process. After the three-stage heating is complete, the induction heater is moved at a test speed for a certain distance. The moving distance and speed should be determined through testing. If necessary, reciprocating motion can be used for temperature compensation to achieve a near-constant temperature insulation effect on the part.
[0020] Since the parts, induction heater, and the distance and relative position between the induction heater and the parts are all fixed parameters in the test, the entire induction tempering process is fully automatic when the parts are officially produced, avoiding performance differences caused by human operation and ensuring the quality stability and consistency of the parts.
[0021] An embodiment of the present invention provides a method for controlling local induction heating of an aviation bolt part, wherein the diameter of the aviation bolt part is 10 to 30 mm, and the method comprises the following steps: S1: Fix the bolt on a workbench and then rotate the workbench, use an induction heater to perform a first induction tempering heating on the threaded area of the bolt, and spray cool the non-threaded area of the bolt at the same time; S2: Stop heating the bolt; S3: performing a second tempering heating on the bolt; S4: Stop heating the bolt; S5: performing a third tempering heating on the bolt; S6: Stop heating the bolt and stop spray cooling the non-heating area; S7: moving the induction heater vertically upward by a preset distance to perform a fourth tempering heating on the bolt; S8: Stop heating the bolt and spray cool the entire bolt.
[0022] In step S1, the rotation speed of the workbench is 50-100 rpm, the heating power of the first tempering is 6.5-7.5 kW, the induction coil frequency is 7.5-8 kHz, the heating temperature is 580° C.-600° C., the heating time is 20-25 s, and the cooling medium sprayed on the non-threaded area of the bolt is water.
[0023] In steps S2, S4, and S6, the heating stop time is 3 to 8 seconds.
[0024] In step S3, the total heating power of the second tempering is 6.0-8.0 kW, the heating temperature is 550-650° C., and the heating time is 3-10 seconds.
[0025] In step S5, the total heating power of the third tempering is 6.0-8.0 kW, the heating temperature is 550-650° C., and the heating time is 3-10 seconds.
[0026] In step S7, the total heating power of the fourth tempering is 6.0-8.0 kW, the heating temperature is 550-650°C, and the heating time is 5-15 seconds.
[0027] In S7, the induction heater is vertically moved upward by a preset distance, which is 14 to 16 mm.
[0028] In S1, the distance between the outer surface of the bolt thread and the inner side of the induction heater is 10~20mm.
[0029] Example 1 The chemical composition and mass percentage of an ultra-high strength steel bolt part for aviation are as follows: C: 0.31%, Cr: 1.07%, Mn: 1.25%, Si: 1.11%, Ni: 1.62%, P: 0.017%, S: 0.007%, and the balance is Fe.
[0030] The diameter of the bolt is 24 mm, the entire diameter range of the bolt is the heating zone, the bolt length in the local tempering zone is 40 mm, and the length of the tempering transition zone is 10 mm; the width of the induction coil is 25 mm.
[0031] The bolts underwent a localized induction tempering heat treatment, with the induction coil set 10 mm from the bolt's outer surface and the induction coil's top 6 mm from the bolt's tip. The power was turned on and the automated heat treatment program was set, induction heating the bolt's heating zone while spray cooling the area 50 mm below the bolt's tip with water. The first tempering heat treatment was performed at a temperature of 560°C for 25 seconds, with a first heating pause of 6 seconds. The second tempering heat treatment was performed at a temperature of 580°C for 5 seconds, with a second heating pause of 5 seconds. The third tempering heat treatment was performed at a temperature of 580°C for 6 seconds, with a third heating pause of 5 seconds. The bolts were then moved vertically upward by 15 mm for a fourth tempering heat treatment at a temperature of 570°C for 10 seconds, followed by spray cooling of the entire bolt. The bolts rotated at a speed of 60 rpm throughout the entire treatment process. After the heat treatment, hardness and microstructure tests were carried out. The test results showed that the hardness of the local tempering zone was 37~40HRC, the hardness outside the tempering transition zone was 74.5~75.5HRA, and the microstructure was a uniformly distributed martensite structure, which met the production requirements.
[0032] Example 2 The chemical composition and mass percentage of an ultra-high strength steel bolt part for aviation are as follows: C: 0.32%, Cr: 1.03%, Mn: 1.15%, Si: 1.06%, Ni: 1.75%, P: 0.019%, S: 0.009%, and the balance is Fe.
[0033] The diameter of the bolt heating zone is 14 mm, the length of the local tempering zone is 30 mm, and the length of the tempering transition zone is 10 mm; the width of the induction coil is 25 mm.
[0034] The bolts underwent a localized induction tempering heat treatment, with the induction coil set at a distance of 10 mm from the outer surface of the bolt and the upper end of the inductor 5 mm from the bolt tip. The power was turned on and an automated heat treatment program was set up, induction heating the heated area of the bolt while spray cooling the area below 40 mm from the bolt tip with water. The first tempering heat treatment was performed at a temperature of 555°C for 23 seconds, with a first heating pause of 4 seconds. The second tempering heat treatment was performed at a temperature of 585°C for 6 seconds, with a second heating pause of 5 seconds. The third tempering heat treatment was performed at a temperature of 585°C for 4 seconds, with a third heating pause of 6 seconds. The bolts were then moved vertically upward by 13 mm for a fourth tempering heat treatment at a temperature of 580°C for 9 seconds, followed by spray cooling of the entire bolt. The bolts rotated at a speed of 50 rpm throughout the entire treatment process. After the heat treatment, hardness and microstructure tests were carried out. The test results showed that the hardness of the local tempering zone was 37.5~39.5HRC, the hardness outside the tempering transition zone was 74~76HRA, and the microstructure was a uniformly distributed martensite structure, which met the production requirements.
[0035] 1. This invention provides a localized tempering induction heat treatment process for ultra-high-strength steel bolts, which reduces energy consumption and costs while shortening production cycles. The bolts, made of 30CrMnSiNi2A steel, undergo a suitable localized tempering induction heat treatment process design to meet the design and use requirements of aviation bolts.
[0036] 2. The production process of the present invention is as follows: first, the temperature is kept at a certain temperature (average temperature) slightly lower than the final heat treatment temperature for a period of time to reduce the temperature difference between the core and the surface, and then the temperature is raised to the final induction tempering temperature for heat treatment. The entire heat treatment process includes an initial heating stage with a high heating rate, a heat holding stage, and secondary and tertiary heating stages with low acceleration rates. After the three-stage heating is completed, the induction heater is moved to a lower temperature area for supplementary heating.
[0037] 3. The present invention adopts electromagnetic induction heating to perform local tempering and softening treatment on the threaded part, replacing the traditional local lead bath tempering, avoiding the harm of lead liquid, effectively preventing environmental pollution, and greatly protecting the health of the operator; at the same time, it improves production efficiency, avoids the time of melting lead liquid, and can be put into production at any time.
[0038] The above are preferred implementations of the present invention. Any equivalent conversion using the content of the present invention is within the scope of protection of the patent of the present invention.
Claims
1. A method for controlling local induction heating of aviation bolt parts, characterized in that: The diameter of the aviation bolt parts is 10-30 mm. The following steps are involved: S1: Fix the bolt on a workbench and then rotate the workbench, use an induction heater to perform a first induction tempering heating on the threaded area of the bolt, and spray cool the non-threaded area of the bolt at the same time; S2: Stop heating the bolt; S3: performing a second tempering heating on the bolt; S4: Stop heating the bolt; S5: performing a third tempering heating on the bolt; S6: Stop heating the bolt and stop spray cooling the non-heating area; S7: moving the induction heater vertically upward by a preset distance to perform a fourth tempering heating on the bolt; S8: Stop heating the bolt and spray cool the entire bolt.
2. A method for controlling local induction heating of aviation bolt parts according to claim 1, characterized in that: In step S1, the rotation speed of the workbench is 50-100 rpm, the heating power of the first tempering is 6.5-7.5 kW, the induction coil frequency is 7.5-8 kHz, the heating temperature is 580° C.-600° C., the heating time is 20-25 s, and the cooling medium sprayed on the non-threaded area of the bolt is water.
3. The method for controlling local induction heating of aviation bolt parts according to claim 1, characterized in that: In steps S2, S4, and S6, the heating stop time is 3 to 8 seconds.
4. The method for controlling local induction heating of aviation bolt parts according to claim 1, characterized in that: In step S3, the total heating power of the second tempering is 6.0-8.0 kW, the heating temperature is 550-650° C., and the heating time is 3-10 seconds.
5. The method for controlling local induction heating of aviation bolt parts according to claim 1, characterized in that: In step S5, the total heating power of the third tempering is 6.0-8.0 kW, the heating temperature is 550-650° C., and the heating time is 3-10 seconds.
6. The method for controlling local induction heating of aviation bolt parts according to claim 1, characterized in that: In step S7, the total heating power of the fourth tempering is 6.0-8.0 kW, the heating temperature is 550-650°C, and the heating time is 5-15 seconds.
7. The method for controlling local induction heating of aviation bolt parts according to claim 1, characterized in that: In S7, the induction heater is vertically moved upward by a preset distance, which is 14 to 16 mm.
8. The method for controlling local induction heating of aviation bolt parts according to claim 1, characterized in that: In S1, the distance between the outer surface of the bolt thread and the inner side of the induction heater is 10~20mm.