A fuse for an energy storage system and a method of manufacturing the same
By adopting a separable upper and lower ceramic shell structure and laser welding technology, the problem of low production efficiency in the fuse manufacturing process has been solved, achieving integrated packaging and consistent electrical performance of the fuse, and supporting automated production.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHAANXI SUYUAN RUINENG NEW ENERGY TECH CO LTD
- Filing Date
- 2026-02-09
- Publication Date
- 2026-06-02
Smart Images
Figure CN121687787B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of fuse manufacturing technology, and more specifically, to a fuse for energy storage systems and its manufacturing method. Background Technology
[0002] As a core supporting facility of the new energy industry, energy storage systems place extremely high demands on the reliability, stability and production efficiency of circuit protection components. As a key overcurrent protection device in energy storage systems, the positioning accuracy and sealing performance of the internal fuse directly determine the electrical performance and service life of the fuse, while the efficiency of the manufacturing process affects the cost and capacity of large-scale production.
[0003] Current fuse manufacturing processes typically employ a separate welding and encapsulation logic for the upper and lower end caps. This involves multiple discrete steps, including solder ring placement, lower end cap fixing, fuse terminal assembly installation, quartz sand pouring, upper end cap docking, and separate welding of the upper and lower end caps. In this traditional fuse manufacturing model, the encapsulation process is carried out in steps, with each step requiring independent positioning and operation. This not only results in a cumbersome process and long production cycle but also makes the encapsulation process prone to abnormalities due to errors in process connection, affecting fuse production efficiency. Furthermore, the processes in traditional fuse manufacturing are highly interconnected and difficult to operate in parallel. The next process can only begin after the previous one is completed, leading to low overall production efficiency. This makes it impossible to meet the large-scale production capacity demands brought about by the rapid expansion of the energy storage industry and hinders the realization of automated production. Summary of the Invention
[0004] In view of the problems in related technologies, the present invention proposes a fuse for energy storage systems and a method for manufacturing the same, so as to overcome the above-mentioned technical problems existing in the existing related technologies.
[0005] Therefore, the specific technical solution adopted by the present invention is as follows:
[0006] A method for manufacturing a fuse for an energy storage system, the method comprising the following steps:
[0007] S1. The copper foil roll is fed into a precision high-speed punch press, and the progressive die is used to continuously punch and cut the sheet to obtain the molten sheet. The stamped sheet is then sent to an ultrasonic cleaner to clean it with anhydrous ethanol to remove the stamping oil stains. After that, it is dried in an 80°C circulating hot air drying oven for 15 minutes to obtain the target molten sheet.
[0008] S2. Place the lower ceramic shell and the upper ceramic shell into the cleaning basket respectively, clean them with anhydrous ethanol in an ultrasonic cleaner for 5 minutes, and dry them for later use.
[0009] S3. For the pre-assembled lower cover, fusible strip and upper cover fusible terminal assembly, align the lower edges of the lower cover and upper cover and press them into the pre-set slots at both ends of the lower half ceramic shell. Ensure that the slots of the lower half ceramic shell are tightly engaged with the lower cover and upper cover to obtain the lower half shell assembly. Arrange the lower half shell assembly with the opening facing upward on the vacuum sand filling machine fixture. Start the equipment to evacuate the cavity. Then open the sand valve to add the dried quartz sand and start the high-frequency micro-vibrator. Vibration makes the quartz sand fill tightly. After the vibration stops, use a mechanical scraper to scrape off the excess quartz sand on the top surface of the shell so that the sand surface is 0.5-1.0mm lower than the pipe opening.
[0010] S4. Align the upper ceramic shell with the lower ceramic shell, and make the slots at both ends of the bottom surface of the upper ceramic shell fit tightly with the upper and lower covers. After the upper and lower ceramic shells are fitted together, place them in a laser welding workstation. Under a high-purity nitrogen protective atmosphere, use a laser beam to perform circumferential scanning and melting along the upper and lower shell joint. After welding, keep the nitrogen protective atmosphere and cool to below 50°C before removing the fuse.
[0011] In a preferred embodiment, the stamping speed in S1 is 300 times / minute, the mold accuracy is required to be ±5μm, and the height of the punched burrs is required to be less than 10μm.
[0012] In a preferred embodiment, the ultrasonic frequency of the ultrasonic cleaner in S1 is set to 40kHz, and the cleaning time of the ultrasonic cleaner is 3 minutes.
[0013] In a preferred embodiment, the ultrasonic frequency for ultrasonic cleaning in step S2 is set to 40kHz, the drying temperature is set to 80-100℃, and the drying duration is 10 minutes.
[0014] In a preferred embodiment, the pressing force of the upper and lower covers in S3 is 20-30N, and the vacuum degree of the cavity evacuated by starting the equipment is less than 5×10. -2 Pa, the vibration frequency of the high-frequency micro-vibrator is 100Hz, and the vibration time is 20 seconds.
[0015] In a preferred embodiment, the quartz sand filling density between the molten sheets in S3 is 1.6±0.05g / cm³, and the quartz sand mesh size is 40-70 mesh. The lower cover and the upper cover are respectively fixedly connected to one side with a contact knife, and the other side is respectively welded to both ends of the molten sheet. The axial deviation of the molten sheet alignment is required to be less than ±0.2mm.
[0016] In a preferred embodiment, the laser power in S4 is 100-200W, the laser scanning speed is 10-20mm / s, the purity of high-purity nitrogen is ≥99.999%, the flow rate of nitrogen is 10-15L / min, and the weld depth needs to penetrate the butt joint of the outer shell to form an airtight seal.
[0017] In a preferred embodiment, the upper half of the ceramic shell has slots at both ends on the bottom surface that are adapted to the upper edge of the upper cover and the lower cover in S4, and the slots at both ends of the lower half of the ceramic shell are adapted to the lower edge of the upper cover and the lower cover and the outer contour.
[0018] A fuse for an energy storage system specifically includes a lower ceramic shell, an upper ceramic shell, and a fusible terminal assembly. The fusible terminal assembly consists of a lower cover, an upper cover, a fusible element, and a contact blade. The lower cover and the upper cover are respectively fixedly connected to the middle position of one side, and the other side is respectively welded to both ends of the fusible element. The fusible terminal assembly is snapped into the slots of the lower ceramic shell and the upper ceramic shell, and the interior is filled with quartz sand.
[0019] The beneficial effects of this invention are as follows:
[0020] This invention employs separable upper and lower ceramic shells, with the fusible terminal assembly pre-attached inside the lower shell and the upper shell serving as a cover for subsequent connection. The encapsulation logic is transformed into an integrated seal from the center outwards. That is, all internal components are pre-assembled and positioned in the lower shell. After filling with quartz sand, the upper shell only needs to be covered and sealed once along the seams to complete the fuse manufacturing process. This achieves the integration and one-step encapsulation process, improving the actual fuse production efficiency.
[0021] This invention, by changing the packaging logic of the fuse, eliminates the steps of placing the solder ring and welding the upper and lower end covers separately, thus shortening the actual fuse production time. Furthermore, the pre-assembly of the fuse terminal assembly and the lower half-shell can be carried out in parallel as an independent workstation, resulting in smoother connection with the preceding and following processes and enhanced functionality. At the same time, the fuse terminal assembly is fixed by the mechanical slot of the lower half-shell, and its axial and radial positions are defined from the beginning of assembly, improving the positioning accuracy of the fuse element in the fuse terminal assembly and ensuring the consistency of electrical performance. Attached Figure Description
[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, 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.
[0023] Figure 1This is a flowchart of a method for manufacturing a fuse for an energy storage system according to an embodiment of the present invention. Detailed Implementation
[0024] To further illustrate the various embodiments, the present invention provides accompanying drawings, which are part of the disclosure of the present invention. These drawings are mainly used to illustrate the embodiments and can be used in conjunction with the relevant descriptions in the specification to explain the operating principles of the embodiments. With reference to these drawings, those skilled in the art should be able to understand other possible implementation methods and the advantages of the present invention. The components in the drawings are not drawn to scale, and similar component symbols are generally used to represent similar components.
[0025] According to an embodiment of the present invention, a fuse for an energy storage system and a method for manufacturing the same are provided.
[0026] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments:
[0027] Example 1: As Figure 1 As shown, a method for manufacturing a fuse for an energy storage system according to an embodiment of the present invention includes the following steps:
[0028] S1. The copper foil roll is fed into a precision high-speed punch press and punched continuously through a progressive die to obtain a molten sheet. The punched molten sheet is then sent to an ultrasonic cleaner and cleaned with anhydrous ethanol to remove the stamping oil stains. After that, it is dried in an 80°C circulating hot air drying oven for 15 minutes to obtain the target molten sheet.
[0029] The stamping speed in S1 is 300 times / minute, the die accuracy requirement is ±5μm, and the burr height requirement is less than 10μm.
[0030] The ultrasonic frequency of the ultrasonic cleaner in S1 is set to 40kHz, and the cleaning time is 3 minutes.
[0031] S2. Place the lower ceramic shell and the upper ceramic shell into the cleaning basket respectively, clean them with anhydrous ethanol in an ultrasonic cleaner for 5 minutes, and dry them for later use.
[0032] In S2, the ultrasonic frequency for ultrasonic cleaning is set to 40kHz, the cleaning time of the ultrasonic cleaner is 5 minutes, the drying temperature is set to 80-100℃, and the drying duration is 10 minutes.
[0033] S3. For the pre-assembled lower cover, fusible strip and upper cover fusible terminal assembly, align the lower edges of the lower cover and upper cover and press them into the pre-set slots at both ends of the lower half ceramic shell. Ensure that the slots of the lower half ceramic shell are tightly engaged with the lower cover and upper cover to obtain the lower half shell assembly. Arrange the lower half shell assembly with the opening facing upward on the vacuum sand filling machine fixture. Start the equipment to evacuate the cavity. Then open the sand valve to add the dried quartz sand and start the high-frequency micro-vibrator. Vibration makes the quartz sand fill tightly. After the vibration stops, use a mechanical scraper to scrape off the excess quartz sand on the top surface of the shell so that the sand surface is 0.5-1.0mm lower than the pipe opening.
[0034] It should be noted that the fuse terminal assembly is pre-clamped into the precise slot of the lower half shell, ensuring that its position is absolutely fixed during the sand filling and final encapsulation process. This avoids displacement of internal components due to vibration or sand filling pressure during the sand filling process, which would affect the subsequent use of the fuse.
[0035] The upper and lower covers of S3 require a pressing force of 20-30N. When the equipment is started, the vacuum level of the cavity should be less than 5×10⁻⁶. -2 Pa, the vibration frequency of the high-frequency micro-vibrator is 100Hz, and the vibration time is 20 seconds;
[0036] It should be noted that by drawing a vacuum, air trapped between quartz sand particles and around the fused flakes in the lower half of the complex cavity can be removed. Under vacuum, the air pressure inside the cavity is low. When the sand valve is opened, the quartz sand will quickly fill the cavity under the action of external atmospheric pressure to better wrap the internal structure and fill every gap.
[0037] It should be noted that since the lower shell is a stable container with its opening fixed upwards, it is easy to control the vacuum sand filling and vibration compaction process, resulting in a highly uniform density of quartz sand filling throughout the cavity. At the same time, the same lower shell base module can be used to quickly generate products with different current specifications by combining different pre-assembled fuse terminal assemblies, which enhances the convenience of the actual fuse manufacturing process.
[0038] The density of the quartz sand filling between the molten plates in S3 is 1.6±0.05g / cm³, and the mesh size of the quartz sand is 40-70 mesh. The lower cover and the upper cover are respectively fixedly connected to one side with a contact knife, and the other side is respectively welded to both ends of the molten plate. The axial deviation of the molten plate is required to be less than ±0.2mm.
[0039] S4. Align the upper ceramic shell with the lower ceramic shell, and make the slots at both ends of the bottom surface of the upper ceramic shell tightly engage with the upper and lower covers, so that the upper and lower ceramic shells fit together. After the upper and lower ceramic shells fit together, place them in a laser welding workstation and use a laser beam to perform circumferential scanning and melting along the upper and lower shell joint under a high-purity nitrogen protective atmosphere. After welding, keep the nitrogen protective cooling to below 50°C and remove it to obtain the fuse.
[0040] In S4, the laser power is 100-200W, the laser scanning speed is 10-20mm / s, the high-purity nitrogen gas has a purity of ≥99.999%, the nitrogen flow rate is 10-15L / min, and the weld depth needs to penetrate the outer shell butt joint to form an airtight seal.
[0041] The upper half of the ceramic shell in S4 has slots at both ends on the bottom surface that are adapted to the upper edge of the upper cover and the lower cover. The slots at both ends of the lower half of the ceramic shell are adapted to the lower edge of the upper cover and the lower cover and the outer contour.
[0042] It should be noted that the snap-fit positioning and one-time peripheral sealing are suitable for robot gripping, vision alignment and automatic welding, laying the foundation for realizing a fully automated production line.
[0043] Example 2: A fuse for an energy storage system, specifically including a lower ceramic shell, an upper ceramic shell, and a fusible terminal assembly. The fusible terminal assembly consists of a lower cover, an upper cover, a fusible element, and a contact blade. The lower cover and the upper cover are respectively fixedly connected to the middle of one side, and the other side is respectively welded to both ends of the fusible element. The fusible terminal assembly is snapped into the slots of the lower ceramic shell and the upper ceramic shell, and the interior is filled with quartz sand.
[0044] Example 3: A fuse for an energy storage system, the specific process and manufacturing flow are as follows:
[0045] The first step is to feed the copper foil roll into a precision high-speed punch press at a punching speed of 300 times / minute, with a die accuracy requirement of ±5μm and a punching burr height requirement of less than 10μm. The punching is completed continuously through a progressive die to obtain a molten sheet. The punched molten sheet is then sent to an ultrasonic cleaner with an ultrasonic frequency of 40kHz. It is cleaned with anhydrous ethanol for 3 minutes to remove the punching oil stains. After that, it is dried in an 80℃ circulating hot air drying oven for 15 minutes to obtain the target molten sheet.
[0046] Step 2: Place the lower ceramic shell and the upper ceramic shell into the cleaning basket respectively, clean them with anhydrous ethanol at an ultrasonic cleaning frequency of 40kHz for 5 minutes in an ultrasonic cleaner, and dry them at 80℃ for 10 minutes.
[0047] Step 3: For the pre-assembled lower cover, fusible link, and upper cover fusible terminal assembly, align the lower edges of the lower and upper covers and simultaneously press them into the pre-set slots at both ends of the lower ceramic shell with a force of 20N. Ensure that the slots of the lower ceramic shell are tightly engaged with the lower and upper covers to obtain the lower shell assembly. Arrange the lower shell assembly with the opening facing upwards on the vacuum sand filling machine fixture, start the equipment, and evacuate the cavity to a vacuum level of less than 5 × 10⁻⁶. -2 Pa, then open the sand valve to add the dried quartz sand and start the high-frequency micro-vibrator. The high-frequency micro-vibrator vibrates at a frequency of 100Hz for 20 seconds to make the quartz sand fill tightly. The density of the quartz sand filling between the fused plates is 1.55g / cm³, and the mesh size of the quartz sand is 40 mesh. After the vibration stops, use a mechanical scraper to scrape off the excess quartz sand on the top surface of the shell so that the sand surface is 0.5mm lower than the pipe opening.
[0048] Step 4: Align the upper ceramic shell with the lower ceramic shell, ensuring the slots at both ends of the bottom surface of the upper ceramic shell are tightly engaged with the upper and lower covers, allowing the upper and lower ceramic shells to fit together. After the upper and lower ceramic shells are fitted together, place them in a laser welding workstation. Under a high-purity nitrogen protective atmosphere, use a laser beam to perform circumferential scanning and melting along the upper and lower shell joint. The laser power is set to 100W, the laser scanning speed is 10mm / s, the high-purity nitrogen purity is ≥99.999%, and the nitrogen flow rate is 10L / min. The weld depth must penetrate the shell joint to form a gas-tight seal. After welding, keep the nitrogen protective atmosphere and cool to below 50℃ before removing the fuse.
[0049] Example 4: A fuse for an energy storage system, the specific process and manufacturing flow are as follows:
[0050] The first step is to feed the copper foil roll into a precision high-speed punch press at a punching speed of 300 times / minute, with a die accuracy requirement of ±5μm and a punching burr height requirement of less than 10μm. The punching is completed continuously through a progressive die to obtain a molten sheet. The punched molten sheet is then sent to an ultrasonic cleaner with an ultrasonic frequency of 40kHz. It is cleaned with anhydrous ethanol for 3 minutes to remove the punching oil stains. After that, it is dried in an 80℃ circulating hot air drying oven for 15 minutes to obtain the target molten sheet.
[0051] Step 2: Place the lower ceramic shell and the upper ceramic shell into the cleaning basket respectively, clean them with anhydrous ethanol at an ultrasonic cleaning frequency of 40kHz for 5 minutes in an ultrasonic cleaner, and dry them at 100℃ for 10 minutes.
[0052] Step 3: For the pre-assembled lower cover, fusible link, and upper cover fusible terminal assembly, align the lower edges of the lower and upper covers and simultaneously press them into the pre-set slots at both ends of the lower ceramic shell with a force of 30N. Ensure that the slots of the lower ceramic shell are tightly engaged with the lower and upper covers to obtain the lower shell assembly. Arrange the lower shell assembly with the opening facing upwards on the vacuum sand filling machine fixture, start the equipment, and evacuate the cavity to a vacuum level of less than 5 × 10⁻⁶. -2 Pa, then open the sand valve to add the dried quartz sand and start the high-frequency micro-vibrator. The high-frequency micro-vibrator vibrates at a frequency of 200 Hz for 20 seconds to make the quartz sand fill tightly. The density of the quartz sand filling between the fused plates is 1.65 g / cm³, and the mesh size of the quartz sand is 70 mesh. After the vibration stops, use a mechanical scraper to scrape off the excess quartz sand on the top surface of the shell so that the sand surface is 1 mm lower than the pipe opening.
[0053] Step 4: Align the upper ceramic shell with the lower ceramic shell, ensuring the slots at both ends of the bottom surface of the upper ceramic shell are tightly engaged with the upper and lower covers, thus fitting the upper and lower ceramic shells together. After the upper and lower ceramic shells are fitted together, place them in a laser welding workstation. Under a high-purity nitrogen protective atmosphere, use a laser beam to perform circumferential scanning and melting along the upper and lower shell joint. The laser power is set to 200W, the laser scanning speed is 20mm / s, the high-purity nitrogen purity is ≥99.999%, and the nitrogen flow rate is 15L / min. The weld depth must penetrate the shell joint to form a gas-tight seal. After welding, keep the nitrogen protective atmosphere and cool to below 50℃ before removing the fuse.
[0054] In summary, this invention employs separable upper and lower ceramic shells, with the fusible terminal assembly pre-attached inside the lower shell and the upper shell serving as a cover for subsequent connection. The encapsulation logic is transformed into an integrated seal from the center outwards. That is, all internal components are pre-assembled and positioned in the lower shell. After filling with quartz sand, the upper shell only needs to be covered and sealed once along the seams to complete the fuse manufacturing process. This achieves the integration and one-step process of the encapsulation action, improving the actual fuse production efficiency.
[0055] By changing the fuse packaging logic, the processes of placing the solder ring and welding the upper and lower end covers separately are eliminated, thus shortening the actual fuse production time. Furthermore, the pre-assembly of the fuse terminal assembly and the lower half-shell can be carried out in parallel as an independent workstation, resulting in smoother integration with the preceding and following processes and enhanced functionality. At the same time, the fuse terminal assembly is fixed by the mechanical slot of the lower half-shell, and its axial and radial positions are defined from the beginning of assembly, improving the positioning accuracy of the fuse element in the fuse terminal assembly and ensuring the consistency of electrical performance. Through the integrated structural design, the intermediate welding steps for fixing and conducting electricity in the traditional process are eliminated. Through precision mechanical positioning and one-time laser sealing, the process flow is simplified from assembly, welding, reassembly, and rewelding to one-time assembly and one-time sealing, thereby improving the actual fuse production efficiency, consistency, and reliability.
[0056] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. 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 manufacturing a fuse for an energy storage system, characterized in that, The method includes the following steps: S1. The copper foil roll is fed into a precision high-speed punch press, and the progressive die is used to continuously punch and cut the sheet to obtain the molten sheet. The stamped sheet is then sent to an ultrasonic cleaner to clean it with anhydrous ethanol to remove the stamping oil stains. After that, it is dried in an 80°C circulating hot air drying oven for 15 minutes to obtain the target molten sheet. S2. Place the lower ceramic shell and the upper ceramic shell into the cleaning basket respectively, clean them with anhydrous ethanol in an ultrasonic cleaner for 5 minutes, and dry them for later use. S3. For the pre-assembled lower cover, fusible strip and upper cover fusible terminal assembly, align the lower edges of the lower cover and upper cover and press them into the pre-set slots at both ends of the lower half ceramic shell. Ensure that the slots of the lower half ceramic shell are tightly engaged with the lower cover and upper cover to obtain the lower half shell assembly. Arrange the lower half shell assembly with the opening facing upward on the vacuum sand filling machine fixture. Start the equipment to evacuate the cavity. Then open the sand valve to add the dried quartz sand and start the high-frequency micro-vibrator. Vibration makes the quartz sand fill tightly. After the vibration stops, use a mechanical scraper to scrape off the excess quartz sand on the top surface of the shell so that the sand surface is 0.5-1.0mm lower than the pipe opening. S4. Align the upper ceramic shell with the lower ceramic shell, and make the slots at both ends of the bottom surface of the upper ceramic shell tightly engage with the upper and lower covers, so that the upper and lower ceramic shells fit together. After the upper and lower ceramic shells fit together, place them in a laser welding workstation and use a laser beam to perform circumferential scanning and melting along the upper and lower shell joint under a high-purity nitrogen protective atmosphere. After welding, keep the nitrogen protective cooling to below 50°C and remove it to obtain the fuse. The upper and lower covers in S3 are pressed in with a force of 20-30N, and the vacuum level of the cavity is less than 5×10 when the equipment is started. -2 Pa, the vibration frequency of the high-frequency micro-vibrator is 100 Hz, and the vibration time is 20 seconds; In S4, the laser power is 100-200 W, the laser scanning speed is 10-20 mm / s, the high-purity nitrogen gas has a purity of ≥99.999%, the nitrogen gas flow rate is 10-15 L / min, and the weld depth needs to penetrate the outer shell butt joint to form an airtight seal. In the S4, the bottom surface of the upper half ceramic shell has slots at both ends that are adapted to match the upper edge of the upper cover and the lower cover, and the slots at both ends of the lower half ceramic shell are adapted to match the lower edge of the upper cover and the lower cover and the outer contour.
2. The manufacturing method of a fuse for an energy storage system according to claim 1, characterized in that, The stamping speed in S1 is 300 times / minute, the mold accuracy requirement is ±5μm, and the burr height requirement is less than 10μm.
3. The manufacturing method of a fuse for an energy storage system according to claim 2, characterized in that, In S1, the ultrasonic frequency of the ultrasonic cleaner is set to 40 kHz, and the cleaning time of the ultrasonic cleaner is 3 minutes.
4. The manufacturing method of a fuse for an energy storage system according to claim 1, characterized in that, In S2, the ultrasonic frequency for ultrasonic cleaning is set to 40 kHz, the drying temperature is set to 80-100℃, and the drying duration is 10 minutes.
5. A method for manufacturing a fuse for an energy storage system according to claim 1, characterized in that, The density of the quartz sand filling between the molten plates in S3 is 1.6±0.05g / cm³, and the mesh size of the quartz sand is 40-70 mesh. The lower cover and the upper cover are respectively fixedly connected to one side with a contact knife, and the other side is respectively welded to both ends of the molten plate. The axial deviation of the molten plate is required to be less than ±0.2mm.
6. A fuse for an energy storage system, characterized in that, The fuse is prepared by the method described in any one of claims 1-5, specifically including a lower ceramic shell, an upper ceramic shell, and a fusible terminal assembly. The fusible terminal assembly consists of a lower cover, an upper cover, a fusible element, and a contact blade. The lower cover and the upper cover are respectively fixedly connected to the middle position of one side of each of them, and the other side is respectively welded to both ends of the fusible element. The fusible terminal assembly is snapped into the slots of the lower ceramic shell and the upper ceramic shell, and the interior is filled with quartz sand.