A graded response thermal fuse with double fuse cavities and a preparation method thereof

Abstract

The application discloses a kind of hierarchical response type thermal fuse with double fusing cavity and preparation method thereof, thermal fuse includes: insulating shell, first composite temperature sensing core, welding electrode and second composite temperature sensing core;Wherein: the insulating shell is configured to form first fusing cavity and second fusing cavity;First composite temperature sensing core is arranged in the first fusing cavity, and have multiple temperature sensing layers, the melting point of temperature sensing layer increases gradually from inside to outside;Second composite temperature sensing core is arranged in the second fusing cavity, and have multiple temperature sensing layers, the melting point of temperature sensing layer increases gradually from inside to outside, and the melting point of temperature sensing layer of second composite temperature sensing core is greater than the melting point of temperature sensing layer of first composite temperature sensing core;Welding electrode is arranged in the insulating shell, for connecting the first composite temperature sensing core and second composite temperature sensing core end close to each other.The application has high precision of fusing temperature, high temperature oxidation resistance and very high work reliability.

Description

Technical Field

[0001] This invention relates to the field of electrical safety, and in particular to a graded response thermal fuse with dual fusible cavities and its preparation method. Background Technology

[0002] Thermal fuses, as key overheat protection components in electrical and electronic equipment, are widely used in household appliances, industrial control devices, and high-end medical equipment. Their core function is to reliably cut off the circuit by irreversibly melting the temperature-sensing fuse core when the temperature exceeds the safety threshold due to a system fault or abnormal operating conditions, thereby preventing safety accidents such as fires or equipment damage.

[0003] Traditional thermal fuses typically use low-melting-point alloys (such as Sn-Bi and Sn-Pb alloys) as the thermal fuse element, which usually has the following drawbacks: (1) Wide fusing temperature range (±3℃ or ±2℃). In international and national standards such as IEC 60691 and GB / T 9816.1, GB / T9816.2, GB / T 9816.3, the rated functioning temperature (Tf) is required to be: when the rated functioning temperature is less than 250℃, the temperature tolerance is +0 / -10℃; when the rated functioning temperature is greater than or equal to 250℃, the temperature tolerance is 0 / -20℃. Therefore, the existing alloy type thermal fuses are difficult to meet the protection requirements of high-precision equipment (especially high-end medical equipment). (2) Currently, alloy-type thermal fuses on the market typically use a single fuse core, the surface of which is covered with a special resin. This special resin is a weakly acidic substance. After long-term operation in a high-temperature environment, the single fuse core is easily oxidized. Oxidation of the alloy surface causes the fusing characteristics to drift, and may even prevent normal fusing. Some improved solutions, such as CN108767012A, inhibit oxidation by adding flux, but this does not truly solve the fusing accuracy problem. CN110246732B uses a bimetallic strip structure, but the bimetallic strip is a mechanically resettable product, which makes it difficult to guarantee stable operation when the equipment needs to be reliably disconnected after long-term use. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a graded response thermal fuse with dual fusible cavities and a method for preparing the same, so as to improve the above-mentioned problems.

[0005] This invention provides a graded response thermal fuse with dual fusible cavities, comprising: an insulating shell, a first composite temperature-sensing core, a welding electrode, and a second composite temperature-sensing core; wherein: The insulating outer shell is configured to form a first fusible cavity and a second fusible cavity; The first composite temperature sensing core is disposed in the first fusible cavity and has multiple temperature sensing layers, the melting point of which increases sequentially from the inside to the outside; The second composite temperature sensing core is disposed in the second fusible cavity and has multiple temperature sensing layers. The melting point of the temperature sensing layers increases sequentially from the inside to the outside, and the melting point of the temperature sensing layer of the second composite temperature sensing core is greater than the melting point of the temperature sensing layer of the first composite temperature sensing core. The welding electrode is disposed inside the insulating shell and is used to connect the first composite temperature sensing core and the second composite temperature sensing core at their closest points.

[0006] Preferably, the first composite temperature sensing core is cylindrical and includes a first inner temperature sensing layer, a first middle temperature sensing layer, and a first outer temperature sensing layer from the inside out; wherein the melting point of the first inner temperature sensing layer is 110°C, the melting point of the first middle temperature sensing layer is 112°C, and the melting point of the first outer temperature sensing layer is 125°C.

[0007] Preferably, the first inner temperature sensing layer is made of a bismuth-tin-indium-silver eutectic alloy, and its volume accounts for 50% to 70% of the volume of the first composite temperature sensing core; the first middle temperature sensing layer is made of a tin-bismuth-indium-copper alloy doped with nano-alumina, and its thickness is 10% to 25% of the diameter of the first inner temperature sensing layer; the first outer temperature sensing layer is made of a tin-indium alloy containing the rare earth element cerium.

[0008] Preferably, by mass fraction: The first inner temperature sensing layer contains a bismuth-tin-indium-silver eutectic alloy with the following composition: Bi: 0.5%-10%, Sn: 34%-54%, In: 40-60%, Ag: 0.1-5%, and a diameter of 1.2 mm. In the first temperature-sensing layer, the tin-bismuth-indium-copper alloy contains: Sn: 30%-50%, Bi: 0.1%-12%, In: 40%-60%, Cu: 0.1%-2%, Al2O3 content is 0.3%, and the thickness is 0.2 mm. In the first external temperature sensing layer, the tin-indium alloy has the following composition: Sn: 40%-60%, In: 39%-59%, cerium content: 0.05-0.8%, and thickness: 0.15 mm.

[0009] Preferably, the second composite temperature sensing core is cylindrical and includes a second inner temperature sensing layer, a second middle temperature sensing layer, and a second outer temperature sensing layer from the inside out; wherein the melting point of the second inner temperature sensing layer is 131°C, the melting point of the second middle temperature sensing layer is 135°C, and the melting point of the second outer temperature sensing layer is 140°C.

[0010] Preferably, the second inner temperature sensing layer is made of a tin-indium eutectic alloy, and its volume accounts for 50% to 70% of the volume of the second composite temperature sensing core; the second middle temperature sensing layer is made of a tin-bismuth-indium alloy doped with nano-alumina, and its thickness is 10% to 25% of the diameter of the second inner temperature sensing layer; the second outer temperature sensing layer is made of a tin-bismuth alloy containing the rare earth element cerium.

[0011] Preferably, by mass fraction: In the second inner temperature-sensing layer, the tin-indium eutectic alloy has the following composition: In: 60%-90%, Sn: 10%-40%, and a diameter of 1.2 mm. In the second temperature-sensing layer, the tin-bismuth-indium alloy contains: Bi: 45%-65%, Sn: 30%-50%, In: 0.5%-5%, Al2O3 content is 0.3%, and the thickness is 0.2mm. The second external temperature sensing layer is a tin-bismuth alloy with the following composition: Bi: 40%-60%, In: 40%-60%, cerium content: 0.05-0.8%, and thickness: 0.15 mm.

[0012] Preferably, both the first and second fuse cavities are filled with a special resin and an inert gas at a pressure of 0.05 to 0.1 MPa.

[0013] Preferably, it further includes a first sealing cover for sealing the first fusible cavity and a second sealing cover for sealing the second fusible cavity, wherein the insulating shell, the first sealing cover, and the second sealing cover are made of alumina ceramic.

[0014] Preferably, it further includes a first electrode and a second electrode, wherein the first electrode passes through the first sealing cover and is electrically connected to the first composite temperature sensing core; the second electrode passes through the second sealing cover and is electrically connected to the second composite temperature sensing core, and a sealing resin is provided at the position where the electrode passes through the sealing cover.

[0015] Preferably, the first electrode and the second electrode adopt a copper-plated nickel or copper-plated tin structure, and their contact end with the composite temperature sensing core is designed as a corrugated elastic sheet with a pre-compression force of 0.5 to 1.2 N.

[0016] Preferably, the surface of the insulating shell is coated with a thermochromic coating, which changes color after exceeding a set temperature.

[0017] This invention also provides a method for preparing a graded responsive thermal fuse with dual fusing cavities as described above, comprising: According to the alloy formula corresponding to each inner temperature sensing layer, weigh the corresponding weight of metal material, put it into the melting furnace and melt it under vacuum. After removing oxides and impurities, the inner layer alloy is prepared. The inner alloy is melted and injected into a mold, and then welded together with the leads of the electrodes. After cooling and forming, an inner temperature-sensing layer with electrodes is obtained. According to the alloy formula corresponding to each intermediate temperature sensing layer, weigh the corresponding weight of metal material, mix it with nano Al2O3 by ultrasonic dispersion, spray it onto the surface of the inner temperature sensing layer, and laser remelt it to form the intermediate temperature sensing layer. According to the alloy formula corresponding to each external temperature sensing layer, weigh the corresponding weight of metal material, vacuum melt it and wrap it around the middle temperature sensing layer, then heat it and isostatically press it to form the external temperature sensing layer, thus obtaining the composite temperature sensing core. The composite temperature-sensing core of the fusion welding electrode is placed into an insulating shell, evacuated, and then filled with argon gas. It is then sealed with a sealing cap and sealing resin to obtain a graded response thermal fuse with dual fusing cavities.

[0018] The graded response thermal fuse with dual fuse cavities of the present invention has two composite temperature sensing cores with different operating temperatures, thus enabling this embodiment to operate at two temperatures. After the first composite temperature sensing core breaks, in the event of an emergency such as a super-high current, super-high voltage, or other abnormal temperature rise, the second composite temperature sensing core can activate a second time, ensuring that this embodiment can still reliably break under such circumstances without the risk of failure. Therefore, this embodiment can be applied to high-end medical, new energy, and other new application scenarios with extremely high reliability requirements for overheat protection. Attached Figure Description

[0019] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the structure of a graded response thermal fuse with dual fusible cavities provided in an embodiment of the present invention.

[0021] Figure 2 This is a schematic diagram of the internal structure of the insulating shell provided in an embodiment of the present invention.

[0022] Figure 3 This is a schematic flowchart illustrating the preparation method of a graded responsive thermal fuse with dual fusing cavities provided in an embodiment of the present invention. Detailed Implementation

[0023] 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.

[0024] Please see Figure 1 and Figure 2 The first embodiment of the present invention provides a graded response thermal fuse with dual fusible cavities, comprising: an insulating shell 10, a first composite temperature-sensing core 20, a welding electrode 30, and a second composite temperature-sensing core 40; wherein: The insulating outer shell 10 is configured to form a first fusible cavity 11 and a second fusible cavity 12; The first composite temperature sensing core 20 is disposed in the first fusible cavity 11 and has multiple temperature sensing layers, the melting point of which increases sequentially from the inside to the outside; The second composite temperature sensing core 40 is disposed in the second fusible cavity 12 and has multiple temperature sensing layers. The melting point of the temperature sensing layers increases sequentially from the inside to the outside, and the melting point of the temperature sensing layer of the second composite temperature sensing core 40 is greater than the melting point of the temperature sensing layer of the first composite temperature sensing core 20. The welding electrode 30 is disposed inside the insulating shell 10 and is used to connect the ends of the first composite temperature sensing core 20 and the second composite temperature sensing core 40 that are close to each other.

[0025] In this embodiment, the insulating shell 10 may be a cylindrical shape with openings at both ends, and may be made of an insulating material, such as alumina ceramic.

[0026] like Figure 2 As shown, the interior of the insulating shell 10 can be divided into a first fusible cavity 11 and a second fusible cavity 12 by means of an isolation member 13. The isolation member 13 can be a positioning ring or other isolation structure, which will not be described in detail here.

[0027] In this embodiment, the first composite temperature sensing core 20 is cylindrical in shape and includes a first inner temperature sensing layer 21, a first middle temperature sensing layer 22, and a first outer temperature sensing layer 23 from the inside out; wherein, the melting point of the first inner temperature sensing layer 21 is 110°C, the melting point of the first middle temperature sensing layer 22 is 112°C, and the melting point of the first outer temperature sensing layer 23 is 125°C.

[0028] Specifically, in this embodiment, the first inner temperature-sensing layer 21 may be made of a bismuth-tin-indium-silver eutectic alloy, wherein, by mass fraction: In the bismuth-tin-indium-silver eutectic alloy of the first inner temperature sensing layer 21: Bi: 0.5%-10%, Sn: 34%-54%, In: 40-60%, Ag: 0.1-5%; its volume accounts for 50% to 70% of the volume of the first composite temperature sensing core 21.

[0029] In this embodiment, the first inner temperature sensing layer 22 is made of a tin-bismuth-indium-copper alloy doped with nano-alumina, and its thickness is 10% to 25% of the diameter of the first inner temperature sensing layer; In the first temperature-sensing layer 22, the tin-bismuth-indium-copper alloy contains: Sn: 30%-50%, Bi: 0.1%-12%, In: 40%-60%, Cu: 0.1%-2%, and the content of nano-alumina is 0.3%, with a particle size of 10-60nm. In this embodiment, the first external temperature sensing layer 23 is made of a tin-indium alloy containing the rare earth element cerium.

[0030] In the first outer temperature sensing layer 23, the tin-indium alloy contains: Sn: 40%-60%, In: 39%-59%, and cerium content is 0.05-0.8%.

[0031] In this embodiment, the second composite temperature sensing core 40 is also generally cylindrical, and includes a second inner temperature sensing layer 41, a second middle temperature sensing layer 42, and a second outer temperature sensing layer 43 from the inside out; wherein, the melting point of the second inner temperature sensing layer 41 is 131°C, the melting point of the second middle temperature sensing layer 42 is 135°C, and the melting point of the second outer temperature sensing layer 43 is 140°C.

[0032] In this embodiment, the second inner temperature sensing layer 41 is made of tin-indium eutectic alloy, and its volume accounts for 50% to 70% of the volume of the second composite temperature sensing core 40.

[0033] Of which, by mass fraction: In the tin-indium eutectic alloy of the second inner temperature sensing layer 41: In: 60%-90%, Sn: 10%-40%, diameter 1.2mm; In this embodiment, the second inner temperature sensing layer 42 is made of a tin-bismuth-indium alloy doped with nano-alumina, and its thickness is 10% to 25% of the diameter of the second inner temperature sensing layer 41; In the second temperature-sensing layer 42, the tin-bismuth-indium alloy contains: Bi: 45%-65%, Sn: 30%-50%, In: 0.5%-5%, and Al2O3 content is 0.3%. In this embodiment, the second external temperature sensing layer 43 is made of a tin-bismuth alloy containing the rare earth element cerium.

[0034] Among them, in the tin-bismuth alloy of the second outer temperature sensing layer 43: Bi: 40%-60%, In: 40%-60%, and cerium content is 0.05-0.8%.

[0035] In this embodiment, specifically, both the first fusible cavity 11 and the second fusible cavity 12 are filled with a special resin 14 and an inert gas. The special resin 14 serves to fix and support the composite temperature-sensing core, while the inert gas is used to inhibit the oxidation of the special resin and alloy. Specifically, the inert gas is argon, and its pressure is 0.05 to 0.1 MPa.

[0036] In this embodiment, in particular, it also includes a first sealing cover 15 for sealing the first fusible cavity 11 and a second sealing cover 16 for sealing the second fusible cavity 12.

[0037] The sealing cap is made of the same material as the insulating shell 10 to ensure that the coefficient of thermal expansion matches that of the insulating shell 10.

[0038] In this embodiment, in particular, a first electrode 51 and a second electrode 52 are also included. The first electrode 51 passes through the first sealing cover 15 and is electrically connected to the first composite temperature sensing core 10. The second electrode 52 passes through the second sealing cover 16 and is electrically connected to the second composite temperature sensing core 40. A sealing resin 53 is provided at the position where the electrode passes through the sealing cover.

[0039] In this embodiment, specifically, both the first electrode 51 and the second electrode 52 are copper-plated nickel or copper-plated tin, and their contact ends with the composite temperature-sensing core are designed as corrugated elastic sheets. The corrugated elastic sheets significantly reduce the transmission of vibration waves during device operation to the composite temperature-sensing core, improving the vibration and impact resistance of this embodiment. Furthermore, the pre-compression force of the corrugated elastic sheets is 0.5–1.2 N, which can be used to compensate for thermal expansion and contraction stress, preventing contact failure between the electrodes and the composite temperature-sensing core.

[0040] In this embodiment, in particular, the surface of the insulating shell 10 is coated with a thermochromic coating, which changes color after exceeding a preset temperature.

[0041] For example, the thermochromic coating can be a CoCl2-PVA system, which changes from blue to pink when the sensed temperature exceeds 140°C, thus visually indicating whether the composite temperature sensing core has been activated.

[0042] In this embodiment, the operating temperature of the first composite temperature sensing core 10 is 125°C, and the melting temperature of the second composite temperature sensing core 40 is 140°C, thus giving this embodiment two operating temperatures. Specifically, after the first composite temperature sensing core 10 disconnects, in the event of an emergency such as a super-high current, super-high voltage, or other abnormal temperature rise, the second composite temperature sensing core 40 can activate a second time, ensuring that this embodiment can still reliably disconnect under such circumstances without the risk of failure. Therefore, this embodiment can be applied to high-end medical, new energy, and other new application scenarios with extremely high reliability requirements for overheat protection.

[0043] The application of the present invention will be illustrated below with a specific embodiment.

[0044] Example 2: The first composite temperature sensing core 20 is prepared according to the following proportions. (1) First inner temperature sensing layer 21: Bi: 0.5%-10%, Sn: 34%-54%, In: 40-60%, Ag: 0.1-5% (melting point 110℃), diameter 1.2mm; (2) First temperature-sensing layer 22: Sn: 30%-50%, Bi: 0.1%-12%, In: 40%-60%, Cu: 0.1%-2%+0.3%Al2O3 (melting point 112℃), thickness 0.2mm; (3) First outer temperature sensing layer 23: Sn: 40%-60%, In: 39%-59%+0.2% Ce (melting point 125℃), thickness 0.15mm; Second composite temperature sensing core 40: (1) Second inner temperature sensing layer 41: In: 60%-90%, Sn: 10%-40% (melting point 131℃), diameter 1.2mm; (2) Second temperature-sensing layer 42: Bi: 45%-65%, Sn: 30%-50%, In: 0.5%-5%, doped with nano-alumina (Al2O3, tin-bismuth-indium alloy with particle size (10-60nm) (melting point 135℃), with a thickness of 0.2mm; (3) Second outer temperature sensing layer 43: Bi: 40%-60%, In: 40%-60%, tin-bismuth alloy containing rare earth element cerium (Ce, 0.05-0.8%) (melting point 140℃) to form a dense anti-oxidation shell with a thickness of about 0.15mm.

[0045] Sealing cap: It adopts an alumina ceramic column with a sealing ring and is filled with argon gas at 0.08MPa; First electrode 51 and second electrode 52: are made of C11000 copper plated with nickel.

[0046] Comparison of performance test data based on the graded responsive thermal fuses prepared above:

[0047] In summary, the graded response thermal fuse of the present invention has the following advantages: (1) Improved fusing accuracy: The structure of the composite temperature sensing core with an increased melting point gradient makes the fusing temperature deviation ≤ ±1.5℃, which is higher than the operating temperature accuracy of the traditional thermal fuse. Moreover, the composite temperature sensing core is divided into three layers, which can more effectively sense the ambient temperature and make the operating temperature more accurate. (2) Strong anti-interference: The nano-Al2O3 doping in the middle temperature sensing layer of the composite temperature sensing core can suppress grain boundary diffusion. After aging at 90℃ for 3000h, the melting temperature drift value is <0.8℃. (3) High mechanical reliability: The elastic electrode pins made of corrugated elastic sheets can better absorb vibration energy and pass the random vibration test of IEC 60068-2-64; (4) Faster temperature sensing: The composite temperature sensing core is composed of three alloy layers, and the melting point of the inner layer < the melting point of the middle layer < the melting point of the outer layer. According to the requirements of the international standard IEC 60691 and the Chinese national standard GB / T 9816.1-2023 for thermal fuses, during the operating temperature test, the thermal fuse is first placed in an oil bath or air furnace at the rated operating temperature of -12K. After the temperature stabilizes at a time interval of 5 minutes, and the difference between two consecutive temperature readings does not exceed 1K, the temperature is then increased at a rate of 0.5-1K / minute. During the heating process, the temperature at which the thermal fuse breaks is the actual operating temperature of the thermal fuse. However, when this embodiment is applied to terminal equipment, especially high-power high-end medical equipment and high-power energy storage equipment, the heating rate is very fast when the equipment malfunctions, which is significantly higher than the 0.5-1K / minute specified by the international and national standards. Therefore, the actual breaking temperature of the thermal fuse will be higher than the designed protection temperature. Therefore, the composite temperature sensing core of this embodiment has a three-level temperature gradient. When the equipment heats up abnormally, the inner temperature sensing layer melts first. As the temperature rises, the middle temperature sensing layer also begins to melt. When the operating temperature of the outermost temperature sensing layer is reached, the outer temperature sensing layer also melts quickly. This reduces the melting time of the core when the designed operating temperature is sensed, improves the overall temperature sensing sensitivity, and makes the operating temperature more rapid.

[0048] (5) Graded protection avoids "one-size-fits-all" power outages and improves availability; This embodiment uses two composite temperature sensing cores. When the temperature is too high, the first composite temperature sensing core 20 melts first. When the residual temperature of the equipment continues to rise, the second composite temperature sensing core 40 will continue to melt under the action of abnormal residual heat of the equipment, providing two break points, thereby ensuring that the operation of this embodiment is more reliable. Moreover, the two break points under graded protection can improve the withstand voltage and insulation level of this embodiment. This is because after the operation of a normal thermal fuse, its two poles can only withstand a withstand voltage and insulation of 2 times the rated voltage, while the withstand voltage and insulation level of this embodiment can be increased to 4 times the rated voltage value, which significantly improves the safety and reliability of the electrical equipment.

[0049] (6) Fault traceability: By observing the state of the thermochromic coating on the surface of the insulating shell 10, the temperature level at which the abnormal state of the equipment is felt in this embodiment can be accurately determined, thereby determining whether this embodiment is operating on demand or malfunctioning, providing a basis for repair and maintenance when the equipment is abnormal, and improving the maintainability and predictability of the equipment.

[0050] (7) High integration: The dual-cavity coaxial design is only 15% larger in volume than traditional products; however, the reliability, pressure resistance and insulation performance of this embodiment are greatly improved compared with traditional products.

[0051] Please see Figure 3 The present invention also provides a method for preparing a graded responsive thermal fuse with dual fusible cavities as described above, comprising: S201, according to the alloy formula corresponding to each inner temperature sensing layer, weigh the corresponding weight of metal material, put it into the melting furnace and melt it under vacuum. After removing oxides and impurities, the inner layer alloy is prepared. S202, the inner alloy is melted and injected into the mold, and then welded together with the leads of the electrode, and then cooled and shaped to obtain the inner temperature sensing layer connected with the electrode; S203, according to the alloy formula corresponding to each intermediate temperature sensing layer, weigh the corresponding weight of metal material, mix it with nano Al2O3 by ultrasonic dispersion, spray it on the surface of the inner temperature sensing layer, and laser remelt it to form the intermediate temperature sensing layer. S204, according to the alloy formula corresponding to each external temperature sensing layer, weigh the corresponding weight of metal material, vacuum melt it and wrap it around the middle temperature sensing layer, then heat it and isostatically press it to form the external temperature sensing layer, thus obtaining the composite temperature sensing core. S205 involves placing the composite temperature-sensing core of the fusion welding electrode into an insulating shell, evacuating it, filling it with argon gas, and sealing it with a sealing cap and sealing resin to obtain a graded response thermal fuse with dual fusing cavities.

[0052] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A graded-response thermal fuse with dual fusing cavities, characterized in that, include: The components include an insulating outer shell, a first composite temperature-sensing core, a welding electrode, and a second composite temperature-sensing core; wherein: The insulating outer shell is configured to form a first fusible cavity and a second fusible cavity; The first composite temperature sensing core is disposed in the first fusible cavity and has multiple temperature sensing layers, the melting point of which increases sequentially from the inside to the outside; The second composite temperature sensing core is disposed in the second fusible cavity and has multiple temperature sensing layers. The melting point of the temperature sensing layers increases sequentially from the inside to the outside, and the melting point of the temperature sensing layer of the second composite temperature sensing core is greater than the melting point of the temperature sensing layer of the first composite temperature sensing core. The welding electrode is disposed inside the insulating shell and is used to connect the first composite temperature sensing core and the second composite temperature sensing core at their closest points.

2. The graded response thermal fuse with dual fusing cavities according to claim 1, characterized in that, The first composite temperature sensing core is cylindrical and includes a first inner temperature sensing layer, a first middle temperature sensing layer, and a first outer temperature sensing layer from the inside out; wherein, the melting point of the first inner temperature sensing layer is 110°C, the melting point of the first middle temperature sensing layer is 112°C, and the melting point of the first outer temperature sensing layer is 125°C.

3. The graded response thermal fuse with dual fusing cavities according to claim 2, characterized in that, The first inner temperature sensing layer is made of a bismuth-tin-indium-silver eutectic alloy, and its volume accounts for 50% to 70% of the volume of the first composite temperature sensing core; the first middle temperature sensing layer is made of a tin-bismuth-indium-copper alloy doped with nano-alumina, and its thickness is 10% to 25% of the diameter of the first inner temperature sensing layer; the first outer temperature sensing layer is made of a tin-indium alloy containing the rare earth element cerium.

4. The graded response thermal fuse with dual fusing cavities according to claim 3, characterized in that, By mass fraction: The first inner temperature sensing layer contains a bismuth-tin-indium-silver eutectic alloy with the following composition: Bi: 0.5%-10%, Sn: 34%-54%, In: 40-60%, Ag: 0.1-5%, and a diameter of 1.2 mm. In the first temperature-sensing layer, the tin-bismuth-indium-copper alloy contains: Sn: 30%-50%, Bi: 0.1%-12%, In: 40%-60%, Cu: 0.1%-2%, and nano-alumina content is 0.3%, with a thickness of 0.2 mm. In the first external temperature sensing layer, the tin-indium alloy has the following composition: Sn: 40%-60%, In: 39%-59%, cerium content: 0.05-0.8%, and thickness: 0.15 mm.

5. The graded response thermal fuse with dual fusing cavities according to claim 4, characterized in that, The second composite temperature sensing core is cylindrical and includes a second inner temperature sensing layer, a second middle temperature sensing layer, and a second outer temperature sensing layer from the inside out; wherein, the melting point of the second inner temperature sensing layer is 131°C, the melting point of the second middle temperature sensing layer is 135°C, and the melting point of the second outer temperature sensing layer is 140°C.

6. The graded response thermal fuse with dual fusing cavities according to claim 5, characterized in that, The second inner temperature sensing layer is made of tin-indium eutectic alloy, and its volume accounts for 50% to 70% of the volume of the second composite temperature sensing core; the second middle temperature sensing layer is made of tin-bismuth-indium alloy doped with nano-alumina, and its thickness is 10% to 25% of the diameter of the second inner temperature sensing layer; the second outer temperature sensing layer is made of tin-bismuth alloy containing the rare earth element cerium.

7. The graded response thermal fuse with dual fusing cavities according to claim 6, characterized in that, By mass fraction: In the second inner temperature-sensing layer, the tin-indium eutectic alloy has the following composition: In: 60%-90%, Sn: 10%-40%, and a diameter of 1.2 mm. In the second temperature-sensing layer, the tin-bismuth-indium alloy contains: Bi: 45%-65%, Sn: 30%-50%, In: 0.5%-5%, nano-alumina content is 0.3%, and the thickness is 0.2mm. The second external temperature sensing layer is a tin-bismuth alloy with the following composition: Bi: 40%-60%, In: 40%-60%, cerium content: 0.05-0.8%, and thickness: 0.15 mm.

8. The graded response thermal fuse with dual fusing cavities according to claim 7, characterized in that, Both the first and second fuse cavities are filled with a special resin and an inert gas at a pressure of 0.05 to 0.1 MPa.

9. The graded response thermal fuse with dual fusing cavities according to claim 8, characterized in that, It also includes a first sealing cover for sealing the first fusible cavity and a second sealing cover for sealing the second fusible cavity. The insulating shell, the first sealing cover, and the second sealing cover are made of alumina ceramic. The surface of the insulating shell is coated with a thermochromic coating, which changes color after exceeding a set temperature.

10. The graded response thermal fuse with dual fusing cavities according to claim 9, characterized in that, It also includes a first electrode and a second electrode. The first electrode passes through the first sealing cover and is electrically connected to the first composite temperature sensing core. The second electrode passes through the second sealing cover and is electrically connected to the second composite temperature sensing core. The first electrode and the second electrode adopt a copper-plated nickel or copper-plated tin structure. The contact end with the composite temperature sensing core is designed as a corrugated elastic sheet. The pre-compression force of the corrugated elastic sheet is 0.5 to 1.2 N.

11. A method for preparing a graded responsive thermal fuse with dual fusing cavities as described in claim 10, characterized in that, include: According to the alloy formula corresponding to each inner temperature sensing layer, weigh the corresponding weight of metal material, put it into the melting furnace and melt it under vacuum. After removing oxides and impurities, the inner layer alloy is prepared. The inner alloy is melted and injected into a mold, then fused together with the leads of the electrodes, and then cooled and shaped to obtain an inner temperature-sensing layer connected to the electrodes. According to the alloy formula corresponding to each intermediate temperature sensing layer, weigh the corresponding weight of metal material, ultrasonically disperse and mix it with nano Al2O3, spray it on the surface of the inner temperature sensing layer, and laser remelt it to form the intermediate temperature sensing layer. According to the alloy formula corresponding to each external temperature sensing layer, weigh the corresponding weight of metal material, vacuum melt it and wrap it around the middle temperature sensing layer, then heat it and isostatically press it to form the external temperature sensing layer, thus obtaining the composite temperature sensing core. The composite temperature-sensing core of the fusion welding electrode is placed into an insulating shell, evacuated, and then filled with argon gas. It is then sealed with a sealing cap and sealing resin to obtain a graded response thermal fuse with dual fusing cavities.

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