Low-voltage varistor and method for manufacturing the same

Abstract

The application relates to the technical field of pressure-sensitive resistors, in particular to a low-voltage pressure-sensitive resistor and a preparation method thereof. The components of the low-voltage pressure-sensitive resistor include Bi2O3, Sb2O3, MnCO3, Co2O3, NiO, TiO2, Gd2O3, aluminum nitrate, AgNO3, H3BO3, ZnO, a dispersing agent and a binder; the weight ratio of Bi2O3, Sb2O3, MnCO3, Co2O3, NiO, TiO2, Gd2O3, aluminum nitrate, AgNO3, H3BO3 and the dispersing agent is (50-60):(1.2-1.4):(20-25):(25-30):(11-18):(3-5):(0.1-0.4):(0.4-0.5):(0.2-0.5):(0.2-0.6):(50-60); the weight ratio of ZnO and Bi2O3 is 3000:(50-60); and the weight ratio of the binder and ZnO is 15:100. The application scheme can effectively improve the flow capacity and aging life of the low-voltage pressure-sensitive resistor, and the product has good pressure-sensitive comprehensive performance.

Description

Technical Field

[0001] This application relates to the field of varistor technology, and in particular to a low-voltage varistor and its preparation method. Background Technology

[0002] Low-voltage varistors refer to varistors with a varistor voltage of less than or equal to 68 V. They are mainly used in control instruments, communications, railway control signals, industrial control, robotics, lightning protection, automotive electronics, etc.

[0003] For a long time, the maximum current carrying capacity of low-voltage varistors has been generally low. Taking a low-voltage varistor with a varistor voltage of 22V as an example, the best φ14mm specification can reach 2kA, and the best φ20mm specification can reach 4.5kA.

[0004] Ultimately, the problem stems from the relatively low level of research and development in the formulation and manufacturing technology of the aforementioned low-voltage varistors. Furthermore, exploration of new materials and processes for low-voltage varistors is still very limited. Regarding the accelerated aging lifespan of low-voltage varistors, the industry currently only claims a lifespan of 1000 hours, corresponding to an actual service life of approximately 10 years; however, many application fields require a much longer service life.

[0005] Therefore, the industry urgently needs to develop a low-voltage varistor with higher current carrying capacity and longer aging life. Summary of the Invention

[0006] To address the problems of the prior art mentioned in the background section, this application provides a low-voltage varistor, the technical solution of which is as follows:

[0007] The low-voltage varistor provided in this application comprises Bi2O3, Sb2O3, MnCO3, Co2O3, NiO, TiO2, Gd2O3, aluminum nitrate, AgNO3, H3BO3, ZnO, a dispersant, and a binder; the weight ratio of Bi2O3, Sb2O3, MnCO3, Co2O3, NiO, TiO2, Gd2O3, aluminum nitrate, AgNO3, H3BO3 to the dispersant is as follows: The weight ratio of ZnO to Bi2O3 is 3000:(50-60):(1.2-1.4):(20-25):(25-30):(11-18):(3-5):(0.1-0.4):(0.4-0.5):(0.2-0.5):(0.2-0.6):(50-60); the weight ratio of ZnO to Bi2O3 is 15:100.

[0008] In some embodiments, the aluminum nitrate is Al(NO3)3·9H2O.

[0009] In some embodiments, the adhesive is a PVA or PEG system.

[0010] This application also provides a method for preparing the low-voltage varistor as described above, which includes the following steps:

[0011] Ingredients: By weight, mix 50-60 parts Bi₂O₃, 1.2-1.4 parts Sb₂O₃, 20-25 parts MnCO₃, 25-30 parts Co₂O₃, 11-18 parts NiO, 3-5 parts TiO₂, 0.1-0.4 parts Gd₂O₃, 0.4-0.5 parts aluminum nitrate, 0.2-0.5 parts AgNO₃, and 0.2-0.6 parts H₃BO₃ powder to form a mixed powder; mix the mixed powder with water and mill it to obtain mixture M;

[0012] Abrasive: The mixture M is mixed with ZnO powder and dispersant, and then milled to obtain a slurry; wherein the added dispersant is 50-60 parts; the weight ratio of ZnO to Bi2O3 is 3000:(50-60).

[0013] Granulation: The binder is added to the slurry and stirred, and then spray granulation is performed to produce dry powder; wherein the weight ratio of the binder to the ZnO is 15:100;

[0014] Molding: The dry powder is pressed into a green body;

[0015] Debinding: The green body is debinded and then cooled to room temperature;

[0016] Sintering: The product after debinding is sintered and cooled to obtain a low-voltage varistor ceramic sheet;

[0017] Silver printing and silver firing: Silver paste is brushed onto both sides of the low-voltage varistor ceramic sheet and silver firing is performed to obtain a varistor chip with electrodes.

[0018] Soldering, encapsulation and curing: Pins are soldered to both sides of the varistor chip, then encapsulated with epoxy resin, and after curing, the low-voltage varistor is obtained.

[0019] In some embodiments, during the batching step, the mixed powder and water are added to a sand mill for grinding (25-35) min.

[0020] In some embodiments, during the abrasive step, the mixture M is mixed with ZnO powder and a dispersant in a sand mill and then sand milled for (10-20) min to obtain a slurry.

[0021] In some embodiments, during the molding step, the dry powder is pressed into green blanks of φ14 and φ20 specifications using a press; wherein the target thickness is calculated based on a gradient of 25 to 30 V / mm.

[0022] In some embodiments, in the debinding step, the green body is placed in a debinding furnace for debinding treatment, and then cooled to room temperature; wherein the debinding treatment temperature is (500~550)℃, and the holding time is (2~3)h.

[0023] In some embodiments, during the sintering step, the product after debinding is sintered at (1100-1200) °C, and after sintering and holding for (2-5) h, a low-voltage varistor ceramic sheet is obtained.

[0024] In some embodiments, during the silver printing and silver firing steps, silver paste is applied to both sides of the low-voltage varistor ceramic sheet using screen printing, and then silver firing is performed at (600-650)℃ for (25-35) min to obtain a varistor chip with electrodes.

[0025] In some embodiments, during the welding, encapsulation, and curing steps, tin-plated copper wires are welded onto both sides of the varistor chip, and then epoxy resin is encapsulated. After curing, the low-voltage varistor is obtained.

[0026] The low-voltage varistor provided in this application has the following advantages compared with existing technologies:

[0027] The proposed solution can effectively improve the current carrying capacity and aging life of low-voltage varistors, and it has good overall varistor performance. Attached Figure Description

[0028] Figure 1 A process flow diagram for the low-voltage varistor fabrication method provided in this application.

[0029] Figure 2 This is a schematic diagram of lattice defect reactions. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be described clearly and completely below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0031] An operational example of a method for fabricating a long-life, low-voltage varistor provided in this application is as follows: Figure 1 As shown, it includes the following steps:

[0032] Step 1: Ingredients

[0033] By weight, 50-60 parts of Bi2O3, 1.2-1.4 parts of Sb2O3, 20-25 parts of MnCO3, 25-30 parts of Co2O3, 11-18 parts of NiO, 3-5 parts of TiO2, 0.1-0.4 parts of Gd2O3, 0.4-0.5 parts of aluminum nitrate, 0.2-0.5 parts of AgNO3, and 0.2-0.6 parts of H3BO3 are mixed to form a mixed powder, which is then poured into a sand mill along with pure water and ground for (25-35) min.

[0034] Since the pure water will be dried and evaporated in subsequent steps, the amount of pure water only needs to be sufficient for the grinding and abrasive steps to ensure thorough grinding of the material. Those skilled in the art can make adaptive adjustments according to actual needs, and this application does not impose excessive restrictions.

[0035] Optionally, aluminum nitrate is Al(NO3)3·9H2O.

[0036] Step 2: Abrasive

[0037] After grinding the powder in step one, ZnO powder is added, with the weight of ZnO powder being 50 to 60 times that of Bi2O3. At the same time, a dispersant of the same weight as Bi2O3 is added, and the mixture is further milled for (10 to 20) min to obtain a slurry.

[0038] Step 3: Granulation

[0039] The binder is added to the above slurry and stirred, then spray-granulated into dry powder. The weight ratio of the binder to the ZnO is 15:100.

[0040] The binder serves to improve the flowability of the granulated powder and to better bind the powder particles into a green body with a certain strength during the molding process. Optionally, the binder is a PVA or PEG system, including but not limited to BP05, PEG20000, etc.

[0041] Step 4: Molding

[0042] The above dry powder was pressed into green blanks of φ14 and φ20 specifications using a press, and the target thickness was calculated based on a gradient of 25 to 30 mm.

[0043] Step 5: Remove glue

[0044] The above-mentioned green blanks are placed in a debinding furnace to remove the glue. The maximum temperature for debinding is (500~550)℃, and the holding time is (2~3)h. Then the temperature is lowered to room temperature.

[0045] Step Six: Sintering

[0046] The product after debinding is sintered at (1100~1200)℃ for (2~5)h, and after cooling, a low-voltage varistor ceramic sheet is obtained.

[0047] Step Seven: Printing and Refurbishing Silver

[0048] Silver paste was applied to both sides of a low-voltage varistor ceramic sheet using screen printing, and then kept at (600~650)℃ for (25~35) min to obtain a varistor chip with electrodes.

[0049] Step 8: Soldering, Encapsulation and Curing

[0050] Tinned copper wires are soldered onto both sides of the varistor chip, then encapsulated with epoxy resin, and after curing, a low-voltage varistor product is obtained.

[0051] Step Nine: Testing

[0052] The φ14 and φ20 low-voltage varistors produced according to the above method were tested for their three parameters using a varistor three-parameter tester, and then their maximum current carrying capacity was tested using an 8 / 20μs waveform inrush current generator. They were then subjected to an aging test at 105℃ for 2000 hours with power applied (Uc).

[0053] This application also provides the following embodiments and comparative examples to verify the effectiveness of this application:

[0054] Example 1

[0055] Step 1: Ingredients

[0056] By weight, the powder raw materials as shown in Table 1 are mixed to form a mixed powder, and then poured into a sand mill with 20 times the total weight of pure water and ground for 30 minutes.

[0057] Step 2: Add ZnO powder to a sand mill, with the weight of ZnO powder being 60 times that of Bi2O3. Simultaneously add a dispersant of the same weight as Bi2O3, and continue sand milling for 15 minutes to obtain a slurry.

[0058] Step 3: Add 15% by weight of ZnO PVA adhesive to the above slurry and stir for 60 minutes, then spray granulate into dry powder.

[0059] Step 4: Press the above dry powder into green blanks of φ14 and φ20 specifications respectively using a press. The target thickness is calculated based on a gradient of 25 V / mm.

[0060] Step 5: Place the above green body into the debinding furnace to debind the glue. The maximum debinding temperature is 500℃, the holding time is 3 hours, and finally the temperature is reduced to room temperature.

[0061] Step 6: The product after debinding is sintered at 1100℃ for 5 hours. After cooling, a low-voltage varistor ceramic sheet is obtained.

[0062] Step 7: Apply silver paste to both sides of the low-voltage varistor ceramic sheet using screen printing, and then heat at 600℃ for 30 minutes to obtain a varistor chip with electrodes.

[0063] Step 8: Solder tinned copper wires to both sides of the varistor chip, then encapsulate it with epoxy resin, and after curing, obtain the finished low-voltage varistor.

[0064] Step Nine: For the low-voltage varistors of φ14 and φ20 specifications produced according to this method, test the three parameters using a varistor three-parameter tester, and then test the maximum current carrying capacity using an 8 / 20μs waveform impulse current generator. Then, perform an aging test at 105℃ for 1000h or 2000h with power applied (Uc).

[0065] Example 2-11

[0066] The only difference between Examples 2-11 and Example 1 is that their raw material composition formulas are different, as detailed in Table 1-2. The other steps and conditions are the same as in Example 1.

[0067] Comparative Examples 1-20

[0068] The only difference between Comparative Examples 1-20 and Example 1 is their raw material composition formulation, as detailed in Table 3-7:

[0069] Comparative Example 1: No Gd2O3 or TiO2 was added;

[0070] Comparative Example 2: The amounts of Gd2O3 and TiO2 added were 1 part and 8 parts, respectively, which exceeded the limits of this application;

[0071] Comparative Example 3: AgNO3 and H3BO3 were not added;

[0072] Comparative Example 4: The amounts of AgNO3 and H3BO3 added were 0.8 parts and 1 part, respectively, which exceeded the limits of this application;

[0073] In Comparative Examples 5 and 6, the amounts of Bi2O3 added were 20 parts and 80 parts, respectively, which exceeded the limits of this application; however, the weight ratios of ZnO powder, dispersant, and PVA adhesive remained unchanged.

[0074] The amounts of Sb2O3 added in Comparative Examples 7 and 8 were 0.5 parts and 2 parts, respectively, which exceeded the limits of this application.

[0075] The amounts of MnCO3 added in Comparative Example 9 and Comparative Example 10 were 15 parts and 30 parts, respectively, which exceeded the limits of this application.

[0076] In Comparative Examples 11 and 12, the amounts of Co2O3 added were 20 parts and 40 parts, respectively, which exceeded the limits of this application.

[0077] The amounts of NiO added in Comparative Examples 13 and 14 were 5 parts and 24 parts, respectively, which exceeded the limits of this application.

[0078] In Comparative Examples 15 and 16, the amounts of Al(NO3)3·9H2O added were 0 parts and 1 part, respectively, which were not added and exceeded the scope of this application.

[0079] Comparative Examples 17-20 did not contain AgNO3, H3BO3, Gd2O3, or TiO2.

[0080] The other specific steps and conditions for Comparative Examples 1-20 are the same as those for Example 1.

[0081] For detailed raw material formula data, please refer to Table 1-7:

[0082] Table 1

[0083]

[0084] Table 2

[0085]

[0086] Table 3

[0087]

[0088] Table 4

[0089]

[0090] Table 5

[0091]

[0092] Table 6

[0093]

[0094] Table 7

[0095]

[0096] The products obtained in the above embodiments and comparative examples were subjected to performance tests, and the test results are as follows:

[0097] Table 8. Overall performance of the φ20 specification product in the examples

[0098]

[0099] Table 9. Overall performance of the φ20 specification product in the comparative example

[0100]

[0101] Table 10 Overall performance of φ14 specification products in the examples

[0102]

[0103] Test standards or methods: The three parameters (varistor voltage, leakage current, and nonlinear coefficient) are tested according to standard 6.6 of IEC 61051-1 using a varistor three-parameter tester. Then, the maximum current carrying capacity is tested using an 8 / 20 μs waveform impulse current generator according to standard 8.3.1 of IEC 61643-331:2003. The accelerated aging test conditions are: power-on Uc, aging at 105℃ for 1000h or 2000h.

[0104] Test Result Data Analysis

[0105] 1. As can be seen from the data in the embodiments of this application:

[0106] The product obtained in the embodiment has a high nonlinear coefficient, low leakage current, and improved current carrying capacity and aging life, showing a significant performance improvement compared to similar products in the industry. The performance of the long-life, low-voltage varistor of this application and the best existing international products are shown in Table 11 below:

[0107] Table 11

[0108]

[0109] 2. A comparison of the data from the examples and comparative examples shows that:

[0110] (1) The addition of Gd2O3 and TiO2 and their specific addition ratio design in this application can improve the flow rate and aging resistance of the product, as shown in Table 9 Comparative Examples 1, 2, 19 and 20.

[0111] (2) The addition of AgNO3 and H3BO3 and their specific addition ratio design in this application can further improve the aging resistance performance, as shown in Comparative Examples 3, 4, 17 and 18 in Table 9. The addition of AgNO3 and H3BO3 in this application can improve the aging resistance performance, but if the amount added exceeds the specific limit of this application, it will lead to a decline in other properties.

[0112] (3) The raw materials of this application are Bi2O3, Sb2O3, MnCO3, and Co2O 3、 The specific addition ratio range of NiO and Al(NO3)3·9H2O is designed to give the product good overall pressure-sensitive performance, good flow rate and aging resistance.

[0113] (4) When Gd2O3, TiO2, AgNO3 or H3BO3 are not added, the lightning protection performance and aging resistance performance will be reduced respectively. Without TiO2, low voltage varistor cannot be made, and its varistor voltage is as high as 68V.

[0114] (5) When Gd2O3 and TiO2, AgNO3 and H3BO3 are not added in pairs, the aging resistance will be reduced.

[0115] In summary, the proposed solution has at least the following design concepts and beneficial effects:

[0116] This application provides an optimized formulation combination that can improve the flow rate and aging life of low-voltage varistors, and its performance surpasses the best international performance (see Table 11 for details). Moreover, its production process is simple and suitable for mass industrial production.

[0117] The technical description of the design concept of this application is as follows:

[0118] This application, based on a conventional pressure-sensitive formulation, adds Gd₂O₃, TiO₂, AgNO₃, and H₃BO₃ in specific weight proportions as required in the technical solution. The principle behind achieving the desired effect in this application's solution may be: Gd₂O₃, TiO₂, AgNO₃, and H₃BO₃ are added in specific proportions according to the weight requirements of the technical solution. 3+ Ionic radius (0.0938 nm) is greater than that of Zn. 2+ With a slightly larger ionic radius (0.074 nm), some Gd replaces Zn in ZnO grains, resulting in lattice defects. This can increase the potential barrier, thereby enhancing the current-carrying capacity and aging performance of the varistor.

[0119] Among them, specific lattice defect reactions are as follows Figure 2 As shown in the figure, it can be seen from the formula that: Gd · Zn It is the Gd ion that replaces the positively charged Zn lattice position. V″ Zn These are negatively charged Zn vacancies. O X OThis refers to neutral oxygen at the oxygen lattice sites. The oxygen generated in the formula affects the donor concentration. Therefore, the donor concentration decreases with increasing Gd2O3 content due to the increase in oxygen partial pressure. With increasing Gd2O3 content, the barrier width increases and the interface state density decreases because the decrease in donor concentration is greater than the decrease in interface state density; according to the Poisson equation, the barrier height also increases. However, if the Gd2O3 doping amount is too high, exceeding the limits of this application, Gd2O3 will mainly be distributed in the grain boundary layer, either alone or forming the Bi3GdO6 phase, which acts as a pinning agent to prevent zinc oxide particles from growing, thus causing a rapid increase in varistor voltage. This contradicts the low voltage of the low-voltage varistor obtained in this application. The addition of Gd2O3 will also affect the discharge of pores, leading to an increase in pores and a decrease in varistor density, thus reducing the flow rate. Therefore, this application strictly limits the amount of Gd2O3 within the limits of this application.

[0120] Furthermore, by adding TiO2, the pinning effect of Gd2O3 is suppressed, reducing the varistor voltage while maintaining a high potential barrier. TiO2 can chemically react with Bi2O3 to form a Bi2Ti2O7 liquid phase, increasing the solubility of ZnO in the liquid phase, promoting sintering, and facilitating grain growth. Additionally, Ti, being an unstable transition metal, has strong electron affinity, which is beneficial for solid-phase mass transfer and also promotes grain growth, further reducing the varistor voltage. Simultaneously, it drives the movement of pores at grain boundaries, causing small pores to merge, grow, and exit from the ceramic body, thereby improving the compactness of the varistor and increasing the current throughput. However, excessive TiO2 can lead to a decrease in the varistor's nonlinear coefficient and a sharp increase in leakage current. Therefore, it is necessary to find a suitable amount in combination with Gd2O3. This application strictly limits the amount of TiO2 added within the specified range to achieve the desired effect.

[0121] This application also incorporates appropriate amounts of Ag and B elements to further enhance the aging performance of the varistor. Ag + Ions can act as acceptor ions, increasing the Schottky barrier height, reducing the donor density, suppressing Schottky barrier distortion or degradation, and improving aging properties. However, Ag... + Excessive content (beyond the limits of this application) can also lead to an increase in varistor voltage and a decrease in nonlinear coefficient. Boron doping can significantly suppress the formation of oxygen vacancies and zinc interstitials inside the sample, thereby reducing the concentration of intrinsic defects and inhibiting the migration of zinc interstitial ions, thus improving aging characteristics. However, within the scope of this application, more Ag and B elements are not necessarily better; excessive amounts (beyond the limits of this application) will cause a decrease in nonlinear coefficient, an increase in leakage current, and a decrease in aging performance.

[0122] In summary, the present application effectively improves the flow rate and aging resistance of the product through the addition of Gd2O3 and TiO2 and their specific addition ratio design. Furthermore, the addition of AgNO3 and H3BO3 and their specific addition ratio design further improves the aging resistance, while the amount added is strictly controlled within the specific limits of this application to avoid degradation of other product properties. In addition, the specific addition ratio range of the raw materials Bi2O3, Sb2O3, MnCO3, Co2O3, NiO, and Al(NO3)3·9H2O designed in this application enables the product to have good overall pressure-sensitive performance, possessing excellent flow rate and aging resistance.

[0123] In summary, this application provides an optimal formulation combination for low-voltage varistors, which can effectively improve the current carrying capacity and aging life of low-voltage varistors, and the product has good overall varistor performance.

[0124] It should be noted that:

[0125] In this article, “~” is used to represent the range of values, and the range of values ​​represented by this expression includes two endpoint values.

[0126] Apart from the specific choices embodied in the above embodiments, any formulation range described above may be used in the specific implementation of this application, including but not limited to the above embodiment schemes.

[0127] The specific parameters or some commonly used reagents or raw materials in the above embodiments are specific embodiments or preferred embodiments under the concept of this application, and are not intended to limit them; those skilled in the art can make adaptive adjustments within the concept and protection scope of this application.

[0128] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A low voltage varistor, characterized by: The components include Bi2O3, Sb2O3, MnCO3, Co2O3, NiO, TiO2, Gd2O3, aluminum nitrate, AgNO3, H3BO3, ZnO, dispersant and binder; The weight ratio of the Bi2O3, Sb2O3, MnCO3, Co2O3, NiO, TiO2, Gd2O3, aluminum nitrate, AgNO3, H3BO3 and dispersant is (50-60):(1.2-1.4):(20-25):(25-30):(11-18):(3-5):(0.1-0.4):(0.4-0.5):(0.2-0.5):(0.2-0.6):(50-60); The weight ratio of the ZnO and the Bi2O3 is 3000:(50-60); the weight ratio of the binder and the ZnO is 15:

100.

2. The low voltage varistor of claim 1, wherein: The aluminum nitrate is Al(NO3)3·9H2O; The binder is PVA or PEG system.

3. A method of producing a low-voltage varistor as claimed in any one of claims 1-2, characterized in that, The method comprises the following steps: Batching: 50-60 parts of Bi2O3, 1.2-1.4 parts of Sb2O3, 20-25 parts of MnCO3, 25-30 parts of Co2O3, 11-18 parts of NiO, 3-5 parts of TiO2, 0.1-0.4 parts of Gd2O3, 0.4-0.5 parts of aluminum nitrate, 0.2-0.5 parts of AgNO3, 0.2-0.6 parts of H3BO3 powder raw materials are mixed to form a mixed powder; the mixed powder is mixed with water and sand ground to obtain a mixture M; Grinding: the mixture M is mixed with ZnO powder and dispersant and continues to be sand ground to obtain a slurry; wherein the added dispersant is 50-60 parts; the weight ratio of the ZnO and the Bi2O3 is 3000:(50-60); Granulation: a binder is added into the slurry and stirred, and then spray granulation is performed to prepare a dry powder; wherein the weight ratio of the binder and the ZnO is 15:100; Molding: the dry powder is pressed into a green body; Glue removal: the green body is subjected to glue removal treatment, and then cooled to room temperature; Sintering: the product after glue removal is subjected to sintering treatment, and then cooled to obtain a low-voltage varistor ceramic sheet; Silver printing and silver firing: silver paste is brushed on both sides of the low-voltage varistor ceramic sheet and subjected to silver firing treatment to obtain a varistor chip with electrodes; Welding, encapsulation and curing: pins are welded on both sides of the varistor chip, and then encapsulated with epoxy resin, and after curing, the low-voltage varistor is obtained.

4. The method of claim 3, wherein: In the batching step, the mixed powder and the water are added into a sand mill for sand grinding treatment for 25-35 min.

5. The method of claim 3, wherein the low-voltage varistor is prepared by the steps of: In the grinding step, the mixture M, ZnO powder and dispersant are mixed in a sand mill and subjected to sand grinding treatment for 10-20 min to obtain a slurry.

6. The method of claim 3, wherein: In the molding step, the dry powder is pressed into φ14 and φ20 specification green bodies by a press; wherein the target thickness is calculated according to a gradient of 25-30 V / mm.

7. The method of claim 3, wherein the low-voltage varistor is prepared by the steps of: In the glue discharging step, the green body is put into a glue discharging furnace for glue discharging treatment, and then cooled to room temperature; wherein the glue discharging treatment temperature is (500-550) ℃, and the holding time is (2-3) h. ​ 8. The method of claim 3, wherein: In the sintering step, the product after glue discharging is sintered at (1100-1200) ℃, and the sintering holding time is (2-5) h, and then cooled to obtain the low-voltage varistor ceramic sheet.

9. The method of claim 3, wherein the low-voltage varistor is prepared by the steps of: In the silver printing and silver sintering step, silver paste is brushed on both sides of the low-voltage varistor ceramic sheet by using silk screen printing, and then silver sintering treatment is carried out at (600-650) ℃ for (25-35) min, to obtain the varistor chip with electrodes. ​ 10. The method of claim 3, wherein: In the welding, encapsulation and solidification step, tinned copper wires are welded on both sides of the varistor chip, then encapsulated with epoxy resin, and after solidification, the low-voltage varistor is obtained.

Images