Low-voltage varistor and preparation method thereof

Abstract

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

Description

Technical Field

[0001] This application relates to the technical field of varistors, and particularly relates to a low-voltage varistor and a preparation method thereof. Background Art

[0002] A low-voltage varistor refers to a varistor with a breakdown voltage less than or equal to 68 V, which is mainly used in control instruments, communications, railway control signals, industrial control, robots, lightning protection fields, automotive electronics, etc.

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

[0004] Ultimately, the analysis shows that this is due to the relatively low level of formula research and development and production process technology of the above-mentioned low-voltage varistors. In addition, the exploration of new materials and new processes for low-voltage varistors is still very limited. For the accelerated aging life of low-voltage varistors, the current industry can only claim to achieve 1000 hours, and its corresponding actual service life is about 10 years. However, many application fields require a longer service life.

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

[0006] To solve the problems of the existing technology mentioned in the above background art, this application provides a low-voltage varistor, and its technical solution is as follows: The low-voltage varistor provided by this application includes 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 (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 3000:(50 - 60); the weight ratio of the binder to ZnO is 15:100.

[0007] In some embodiments, the aluminum nitrate is Al(NO3)3·9H2O.

[0008] In some embodiments, the binder is a PVA or PEG system.

[0009] This application also provides a method for preparing a low-voltage varistor as described above, which includes the following steps: Ingredient preparation: By weight, mix 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 silver nitrate, and 0.2 - 0.6 parts of H3BO3 powder raw materials to form a mixed powder; mix the mixed powder with water and perform sand grinding to obtain mixture M; Abrasive material preparation: Mix mixture M with ZnO powder and a dispersant, and continue sand grinding to obtain a slurry; wherein, 50 - 60 parts of the dispersant are added; the weight ratio of ZnO to Bi2O3 is 3000:(50 - 60); Granulation: Add a binder to the slurry and stir, then perform spray granulation to make a dry powder; wherein, the weight ratio of the binder to ZnO is 15:100; Forming: Press the dry powder into a green body; Debinding: Perform debinding treatment on the green body, and then cool it to room temperature; Sintering: Perform sintering treatment on the product after debinding, and cool it to obtain a low-voltage varistor ceramic sheet; Silver printing and silver firing: Brush silver paste on both sides of the low-voltage varistor ceramic sheet and perform silver firing treatment to obtain a varistor chip with electrodes; Welding, encapsulation, and curing: Weld leads on both sides of the varistor chip, then encapsulate with epoxy resin, and after curing, the low-voltage varistor is obtained.

[0010] In some embodiments, in the ingredient preparation step, add the mixed powder and the water into a sand mill for sanding treatment for (25 - 35) min.

[0011] In some embodiments, in the abrasive material preparation step, mix mixture M with ZnO powder and a dispersant in a sand mill, and perform sanding treatment for (10 - 20) min to obtain a slurry.

[0012] In some embodiments, in the forming step, press the dry powder into green bodies with φ14 and φ20 specifications respectively using a press; wherein, the target thickness is calculated according to a gradient of 25 - 30 V / mm.

[0013] 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 temperature of the debinding treatment is (500 - 550) °C and the heat preservation time is (2 - 3) h.

[0014] In some embodiments, in the sintering step, the product after debinding is sintered at (1100 - 1200) °C, and after the sintering heat preservation time of (2 - 5) h and cooling, a low-voltage varistor ceramic chip is obtained.

[0015] In some embodiments, in the silver printing and silver firing steps, silver paste is brushed on both sides of the low-voltage varistor ceramic chip by screen printing, and then silver firing treatment is carried out at (600 - 650) °C for heat preservation of (25 - 35) min to obtain a varistor chip with electrodes.

[0016] In some embodiments, in the welding, encapsulation and curing steps, tinned copper wires are welded on both sides of the varistor chip, and then epoxy resin is encapsulated. After curing, the low-voltage varistor is obtained.

[0017] The low-voltage varistor provided by the present application has the following beneficial effects compared with the existing technology: The solution of the present application can effectively improve the current-carrying capacity and aging life of the low-voltage varistor, and it has good comprehensive varistor performance. Description of the Drawings

[0018] Figure 1 It is a process flow chart of the preparation method of the low-voltage varistor provided by the present application.

[0019] Figure 2 It is a schematic diagram of the lattice defect reaction. Detailed Embodiments

[0020] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. Apparently, the described embodiments are some, but not all, of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the protection scope of the present application.

[0021] An operation example of the preparation method of a long-life low-voltage varistor provided by the present application is as Figure 1 shown and includes the following steps: Step 1: Batching By weight, 50 to 60 parts of Bi2O3, 1.2 to 1.4 parts of Sb2O3, 20 to 25 parts of MnCO3, 25 to 30 parts of Co2O3, 11 to 18 parts of NiO, 3 to 5 parts of TiO2, 0.1 to 0.4 parts of Gd2O3, 0.4 to 0.5 parts of aluminum nitrate, 0.2 to 0.5 parts of AgNO3, and 0.2 to 0.6 parts of H3BO3 are mixed to form a mixed powder, and then poured into a sand mill together with pure water and milled for (25 to 35) min.

[0022] Among them, since the pure water will be dried and volatilized in the subsequent steps. Therefore, for the weight of the pure water, as long as it is sufficient in the milling and abrasive steps to enable the material to be fully milled, those skilled in the art can make adaptive adjustments according to actual needs, and the present application does not impose excessive restrictions.

[0023] Among them, optionally, the aluminum nitrate is Al(NO3)3·9H2O.

[0024] Step Two: Abrasive After the powder is ground in Step One, ZnO powder is added. The weight of the ZnO powder is 50 to 60 times that of Bi2O3. At the same time, a dispersant with the same weight as Bi2O3 is added, and sand milling is continued for (10 to 20) min to obtain a slurry.

[0025] Step Three: Granulation A binder is added to the above slurry and stirred, and then spray granulated into dry powder. Among them, the weight ratio of the binder to the ZnO is 15:100.

[0026] Among them, the function of the binder is to improve the fluidity of the granulated powder and enable the powder particles to better combine into a green body with a certain strength during the forming process. Optionally, the binder is a PVA or PEG system, including but not limited to BP05, PEG20000, etc.

[0027] Step Four: Forming The above dry powder is pressed into green blanks with φ14 and φ20 specifications respectively by a press, and the target thickness is calculated according to the gradient of 25 to 30 V / mm.

[0028] Step Five: Debinding The above green blanks are placed in a debinding furnace for debinding. The maximum temperature of the debinding treatment is (500 to 550) °C, and the holding time is (2 to 3) h, and then cooled to room temperature.

[0029] Step Six: Sintering The product after debinding is sintered at (1100 to 1200) °C, and the sintering holding time is (2 to 5) h. After cooling, a low-voltage varistor ceramic sheet is obtained.

[0030] Step Seven: Silver Printing and Silver Firing The silver paste is brushed on both sides of the low-voltage varistor ceramic chip by screen printing, and then it is kept at a temperature of (600 - 650)°C for (25 - 35) minutes to obtain a varistor chip with electrodes.

[0031] Step Eight: Welding, encapsulation and curing Tin-coated copper wires are welded on both sides of the varistor chip, and then epoxy resin is encapsulated. After curing, the finished low-voltage varistor is obtained.

[0032] Step Nine: Testing For the low-voltage varistors with φ14 and φ20 specifications produced by the above method, the three parameters are tested with a varistor three-parameter tester, and then the maximum current-carrying capacity is tested with an 8 / 20 μs waveform impulse current generator. Aging test is carried out at an applied voltage Uc and an ambient temperature of 105°C for 2000 hours.

[0033] The present application also provides the following examples and comparative examples to verify the effect of the present application: Example 1 Step One: Batching By weight, the powder raw materials shown in Table 1 are mixed to form a mixed powder, and then poured into a sand mill together with pure water 20 times the total weight of the powder and ground for 30 minutes.

[0034] Step Two: Add ZnO powder to the sand mill. The weight of the ZnO powder is 60 times that of Bi2O3. At the same time, a dispersant with the same weight as Bi2O3 is added, and sand milling is continued for 15 minutes to obtain a slurry.

[0035] Step Three: Add PVA glue accounting for 15% of the weight of ZnO to the above slurry and stir for 60 minutes, and then spray granulate into dry powder.

[0036] Step Four: The above dry powder is respectively pressed into green bodies with φ14 and φ20 specifications by a press, and the target thickness is calculated according to the gradient of 25 V / mm.

[0037] Step Five: Put the above green bodies into a debinding furnace for debinding. The highest debinding temperature is 500°C, and the heat preservation time is 3 hours. Finally, it is cooled to room temperature.

[0038] Step Six: The debound product is sintered at a temperature of 1100°C, and the sintering heat preservation time is 5 hours. After cooling, the low-voltage varistor ceramic chip is obtained.

[0039] Step Seven: The silver paste is brushed on both sides of the low-voltage varistor ceramic chip by screen printing, and then it is kept at 600°C for 30 minutes to obtain a varistor chip with electrodes.

[0040] Step Eight: Tin-coated copper wires are welded on both sides of the varistor chip, and then epoxy resin is encapsulated. After curing, the finished low-voltage varistor is obtained.

[0041] Step 9: For the low-voltage varistors with specifications of φ14 and φ20 produced by this method, test the three parameters with a varistor three-parameter tester, and then use an 8 / 20 μs waveform impulse current generator to test the maximum current-carrying capacity. Test the aging at 105 °C for 1000 h or 2000 h according to the applied voltage Uc.

[0042] Example 2-11 The difference between Example 2-11 and Example 1 is only that their raw material component formulations are inconsistent. See the difference points in Table 1-2 for details. Other steps and conditions are the same as those in Example 1.

[0043] Comparative Example 1-20 The difference between Comparative Example 1-20 and Example 1 is only that their raw material component formulations are inconsistent. See the difference points shown in Table 3-7: Comparative Example 1: Gd2O3 and TiO2 were not added; Comparative Example 2: The addition amounts of Gd2O3 and TiO2 were 1 part and 8 parts respectively, exceeding the scope defined in this application; Comparative Example 3: AgNO3 and H3BO3 were not added; Comparative Example 4: The addition amounts of AgNO3 and H3BO3 were 0.8 part and 1 part respectively, exceeding the scope defined in this application; In Comparative Example 5 and Comparative Example 6, the addition amounts of Bi2O3 were 20 parts and 80 parts respectively, exceeding the scope defined in this application; among them, the weight ratio of ZnO powder, dispersant, and PVA glue remained unchanged; In Comparative Example 7 and Comparative Example 8, the addition amounts of Sb2O3 were 0.5 part and 2 parts respectively, exceeding the scope defined in this application; In Comparative Example 9 and Comparative Example 10, the addition amounts of MnCO3 were 15 parts and 30 parts respectively, exceeding the scope defined in this application; In Comparative Example 11 and Comparative Example 12, the addition amounts of Co2O3 were 20 parts and 40 parts respectively, exceeding the scope defined in this application; In Comparative Example 13 and Comparative Example 14, the addition amounts of NiO were 5 parts and 24 parts respectively, exceeding the scope defined in this application; In Comparative Example 15 and Comparative Example 16, the addition amounts of Al(NO3)3·9H2O were 0 part and 1 part respectively, not added, exceeding the scope defined in this application; In Comparative Example 17-20, AgNO3, H3BO3, Gd2O3, and TiO2 were not added respectively.

[0044] The specific other steps and conditions of Comparative Example 1-20 are the same as those in Example 1.

[0045] See Table 1-7 for the data sheet of the raw material formulation: Table 1

[0046] Table 2

[0047] Table 3

[0048] Table 4

[0049] Table 5

[0050] Table 6

[0051] Table 7

[0052] The products obtained in the above-mentioned examples and comparative examples were subjected to performance tests, and the test results are as follows: Table 8 Comprehensive Performance of φ20-Size Products in Examples

[0053] Table 9 Comprehensive Performance of φ20-Size Products in Comparative Examples

[0054] Table 10 Comprehensive Performance of φ14-Size Products in Examples

[0055] Test standards or methods: For the three-parameter (varistor voltage, leakage current, non-linearity coefficient) test, the standard in 6.6 of IEC61051-1 was adopted, and a varistor three-parameter instrument was used for the test. Then, the maximum discharge current was tested with an 8 / 20 μs waveform impulse current generator according to the standard in 8.3.1 of IEC 61643-331:2003; the accelerated aging test conditions were applying voltage Uc and testing for aging for 1000 h or 2000 h in an environment of 105°C.

[0056] Data Analysis of Test Results 1. It can be seen from the data of the examples of this application that: The products obtained in the examples have a high non-linearity coefficient, low leakage current, and improved discharge current and aging life, and the performance is significantly improved compared with products of the same specification in the industry. The performance of the long-life low-voltage varistors of this application and the currently optimal products in the world is shown in Table 11 below: Table 11

[0057] 2. It can be seen from the comparison of the data in the examples and comparative examples that: (1) The addition of Gd2O3 and TiO2 and the design of their specific addition ratios in the solution of this application can improve the current-carrying capacity and anti-aging performance of the product. See Comparative Examples 1, 2, 19, and 20 in Table 9.

[0058] (2) The addition of AgNO3 and H3BO3 and the design of their specific addition ratios in the solution of this application can further improve the anti-aging performance. See Comparative Examples 3, 4, 17, and 18 in Table 9. The addition of AgNO3 and H3BO3 in the solution of this application can improve the anti-aging performance, but if their addition amounts exceed the specific limited range of this application, other performances will decline.

[0059] (3) The design of the specific addition ratio ranges of the raw materials Bi2O3, Sb2O3, MnCO3, Co2O 3、 NiO, and Al(NO3)3·9H2O in this application can endow the product with good comprehensive varistor performance, with good current-carrying capacity and anti-aging performance.

[0060] (4) When Gd2O3, TiO2, AgNO3, or H3BO3 is not added, it will respectively lead to a reduction in lightning strike resistance and anti-aging performance. Without TiO2, a low-voltage varistor cannot be made, and its varistor voltage is as high as 68V.

[0061] (5) When Gd2O3 and TiO2, or AgNO3 and H3BO3 are not added in pairs, it will lead to a reduction in anti-aging performance.

[0062] In summary, the solution of this application has at least the following design concepts and beneficial effects: The solution of this application provides an optimized formula combination that can improve the current-carrying capacity and aging life of low-voltage varistors. Its performance exceeds the international best performance (see Table 11 for details), and its production process is simple, suitable for large-scale industrial production.

[0063] The technical description of the design concept of the solution of this application is as follows: On the basis of the conventional varistor formula, this application adds Gd2O3, TiO2, AgNO3, and H3BO3 in the corresponding weight ratios of the technical solution according to specific addition ratios. The principle for the solution of this application to achieve the desired effect may be as follows: Among them, the ionic radius of Gd 3+ (0.0938 nm) is slightly larger than that of Zn 2+ (0.074 nm). Some Gd replaces Zn in the ZnO grains, thereby generating lattice defects. Therefore, the potential barrier can be increased, so the current-carrying capacity and aging performance of the varistor can be enhanced.

[0064] Among them, the specific lattice defect reactions are as follows Figure 2 As shown, it can be seen from the formula that: Gd · Zn is a positively charged Gd ion that replaces the Zn lattice site, V″ Zn is a negatively charged Zn vacancy, O X O is a neutral oxygen at the oxygen lattice site. The generated oxygen in the formula affects the donor concentration. Therefore, as the content of Gd2O3 increases, the donor concentration decreases because of the increase in oxygen partial pressure. As the content of Gd2O3 increases, the barrier width increases and the interface state density decreases. Since the degree of decrease in donor concentration is greater than the degree of decrease in interface states, the barrier height also increases according to the Poisson equation. However, if the doping amount of Gd2O3 is too large and exceeds the scope defined in this application, Gd2O3 is mainly distributed in the grain boundary layer, existing alone or forming the Bi3GdO6 phase to play a pinning role to prevent the growth of zinc oxide particles, thereby rapidly increasing the varistor voltage, which is contrary to the low voltage of the low-voltage varistor obtained in this application. The addition of Gd2O3 will also affect the discharge of pores, resulting in an increase in pores, promoting a decrease in the density of the varistor, and thus a decrease in the current-carrying capacity. Therefore, in this application, the amount of Gd2O3 is controlled not to be too high or too low, and is strictly limited within the scope of this application.

[0065] In addition, by adding TiO2 to inhibit the pinning effect of Gd2O3, while reducing the varistor voltage, the high barrier of the varistor is maintained. TiO2 can chemically react with Bi2O3 to generate the Bi2Ti2O7 liquid phase, increasing the solubility of ZnO in the liquid phase, promoting sintering, and enabling grain growth. In addition, Ti belongs to unstable transition metals and has a strong electron affinity, which is conducive to solid-state mass transfer and can also promote grain growth, further reducing the varistor voltage, and at the same time driving the movement of pores at the grain boundaries. Small pores merge and grow and are discharged from the ceramic body, thereby improving the density of the varistor and increasing the current-carrying capacity. However, if the amount of TiO2 is too large, it will lead to a decrease in the non-linear coefficient of the varistor and a sharp increase in leakage current. Therefore, it is necessary to find a suitable amount in matching with Gd2O3. In this application, the addition amount of TiO2 is strictly limited within the scope of the scheme, so that the product can achieve the required effect.

[0066] This application also adds an appropriate amount 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, inhibiting the distortion or deterioration of the Schottky barrier, and improving the aging characteristics. However, Ag +Excessive content (beyond the scope defined in this application) will also cause the varistor voltage to rise and the non-linear coefficient to decrease. B doping can significantly inhibit 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 to improve the aging characteristics. However, within the scope of this application, the elements Ag and B are not the more the better. Excessive amounts (beyond the scope defined in this application) will cause the non-linear coefficient to decrease, the leakage current to increase, and the aging performance to decline.

[0067] In summary, in the solution of this application, by adding Gd2O3 and TiO2 and designing their specific addition ratios, the current-carrying capacity and aging resistance of the product are effectively improved; and by adding AgNO3 and H3BO3 and designing their specific addition ratios, the aging resistance can be further improved, and at the same time, their addition amounts are strictly controlled within the specific scope defined in this application to avoid the decline of other properties of the product. In addition, by designing the specific addition ratio ranges of the raw materials Bi2O3, Sb2O3, MnCO3, Co2O3, NiO, and Al(NO3)3·9H2O in this application, the product can have good comprehensive varistor performance, with good current-carrying capacity and aging resistance.

[0068] In summary, the solution of this application provides an optimal formula combination for a low-voltage varistor, which can effectively improve the current-carrying capacity and aging life of the low-voltage varistor, and the product has good comprehensive varistor performance.

[0069] It should be noted that: In this article, "~" is used to represent a numerical range, and the two endpoint values are included within the represented range.

[0070] In addition to the actual selections reflected in the above specific embodiments, when implementing this application specifically, using the above formula ranges is feasible, including but not limited to the above embodiment solutions.

[0071] The specific parameters or some common reagents or raw materials in the above embodiments are specific embodiments or preferred embodiments under the concept of this application, rather than limitations on it; those skilled in the art can make adaptive adjustments within the concept and protection scope of this application.

[0072] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of this application, rather than to limit it; although this application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A low voltage varistor, characterized in that: Its components include Bi2O3, Sb2O3, MnCO3, Co2O3, NiO, TiO2, Gd2O3, aluminum nitrate, AgNO3, H3BO3, ZnO, dispersant and binder; The weight ratio of 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 to the Bi2O3 is 3000:(50-60); the weight ratio of the binder to the ZnO is 15:

100.

2. The low voltage varistor according to claim 1, characterized in that: The aluminum nitrate is Al(NO3)3·9H2O; The binder is a PVA or PEG system.

3. A method for preparing a low voltage varistor according to any one of claims 1 to 2, characterized in that: The following steps are involved: Ingredients: 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 powder raw materials are mixed to form a mixed powder; the mixed powder is mixed with water and sand-milled to obtain a mixture M; Abrasive: Mix the mixture M with ZnO powder and dispersant, and continue sand grinding to obtain slurry; wherein the added dispersant is 50-60 parts; the weight ratio of the ZnO to the Bi2O3 is 3000: (50-60); Granulation: adding a binder to the slurry and stirring, and then spraying and granulating to form a dry powder; wherein the weight ratio of the binder to the ZnO is 15:100; Molding: pressing the dry powder into a green compact; Debinding: Debinding the green body, and then cooling it to room temperature; Sintering: The product after debinding is sintered and cooled to obtain a low-voltage varistor ceramic sheet; Silver printing and silver burning: brushing silver paste on both sides of the low-voltage varistor ceramic sheet and performing silver burning 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. After curing, the low-voltage varistor is obtained.

4. The method for preparing a low voltage varistor according to claim 3, characterized in that: In the batching step, the mixed powder and the water are added into a sand mill and sanded for (25-35) minutes.

5. The method for preparing a low voltage varistor according to claim 3, characterized in that: In the grinding step, the mixture M is mixed with ZnO powder and a dispersant in a sand mill and subjected to sand grinding for (10 to 20) minutes to obtain a slurry.

6. The method for preparing a low voltage varistor according to claim 3, characterized in that: In the molding step, the dry powder is pressed into green compacts of φ14 and φ20 specifications by a press, respectively; wherein the target thickness is calculated based on a gradient of 25 to 30 V / mm.

7. The method for preparing a low voltage varistor according to claim 3, characterized in that: 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)°C, and the holding time is (2-3) hours.

8. The method for preparing a low voltage varistor according to claim 3, characterized in that: In the sintering step, the debinding product is sintered at (1100-1200)°C, and the sintering and heat preservation time is (2-5) hours. After cooling, a low-voltage varistor ceramic sheet is obtained.

9. The method for preparing a low voltage varistor according to claim 3, characterized in that: In the silver printing and silver burning steps, silver paste is brushed on both sides of the low-voltage varistor ceramic sheet by screen printing, and then the silver is burned at (600-650)°C for (25-35) minutes to obtain a varistor chip with electrodes.

10. The method for preparing a low voltage varistor according to claim 3, characterized in that: In the welding, encapsulation and curing steps, tinned copper wires are welded on both sides of the varistor chip, and then encapsulated with epoxy resin. After curing, the low-voltage varistor is obtained.

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