Preparation method of spherical electrical insulation magnesium oxide powder

Abstract

The invention discloses a preparation method of spherical electrical insulation magnesium oxide powder. The preparation method comprises the following steps: S1, crushing a square crystal magnesium oxide block material into a magnesium oxide particle block material; s2, performing high-pressure airflow crushing on the magnesium oxide granular material to obtain a material with the D75 content of 300-400 microns, performing grading treatment on the material by a grading machine and performing high-speed extraction on the material by a fan to obtain a magnesium oxide granular material; s3, the magnesium oxide granules are subjected to screening, magnetic separation and drying, and spherical magnesium oxide with the specification being 0.03-0.425 mm is obtained; and S4, mixing and stirring the spherical magnesium oxide and a high-temperature-resistant insulating filler to obtain spherical electrical insulation magnesium oxide common powder, mixing the spherical electrical insulation magnesium oxide common powder with an organic silicon insulating material, and sieving to obtain the spherical electrical insulation magnesium oxide powder. A high-pressure airflow crushing method is adopted, the magnesium oxide spheroidizing step is simplified, and the efficiency and the spheroidizing effect are improved; the grader and the fan are used for removing dust, so that the granularity uniformity is ensured, the purity is improved, and the properties such as flowability, tap density and electrical insulating property of the prepared electrical insulating magnesium oxide powder are remarkably improved.

Description

Technical Field

[0001] The invention relates to the technical field of material science and electrical engineering, and in particular to a method for preparing spherical electrical insulating magnesium oxide powder. Background Art

[0002] In the electrical industry, the selection of electrical insulation materials is crucial to ensure the safe operation of equipment and improve overall performance. Electrical insulation magnesium oxide powder, as a high-performance insulation material, is widely used in the manufacture of electric heating elements, mineral insulated cables, mineral insulated heating cables and special high-voltage electric heating elements due to its excellent electrical insulation performance and outstanding thermal conductivity. This type of material can not only provide the necessary electrical isolation to prevent current leakage, but also effectively transfer heat to ensure the efficient and stable operation of electric heating elements.

[0003] In the production process of electrical insulating magnesium oxide powder, the selection and processing of raw materials is one of the key steps. The quality of particle shape has a direct and significant impact on the performance of electrical insulating magnesium oxide powder. Irregularly shaped particles may lead to reduced packing density, affecting the uniformity and density of the insulating layer, thereby reducing electrical insulation performance. In addition, edges and defects may also increase friction and stress concentration between particles, causing the insulating layer to be more prone to cracks and breakage during long-term use, thereby shortening the service life of the electric heating element.

[0004] In order to solve the above problems and improve the performance of electrical insulating magnesium oxide powder, researchers began to explore the use of spherical magnesium oxide as the core raw material. Spherical particles have higher packing density, more uniform particle size distribution and better fluidity, which makes spherical magnesium oxide an ideal choice for preparing high-performance electrical insulating magnesium oxide powder.

[0005] However, conventional methods for preparing spherical magnesium oxide, such as crushing cubic magnesium oxide with an ordinary jaw crusher and supplemented by other shaping or grinding methods, often make it difficult to obtain spherical particles with regular shapes and smooth edges, and a large amount of dust often remains in the final product. At the same time, the particle shape is irregular, which does not meet the strict requirements of high-performance electrical insulation materials for raw materials. Summary of the invention

[0006] In view of the technical problems existing in the prior art, the present invention proposes a method for preparing spherical electrically insulating magnesium oxide powder, which can efficiently prepare spherical magnesium oxide with regular shape and smooth edges, and apply it to the production of electrically insulating magnesium oxide powder to improve the insulation performance and thermal conductivity of electric heating elements.

[0007] A method for preparing spherical electrical insulating magnesium oxide powder comprises the following steps:

[0008] S1: preparing magnesium oxide granules and blocks, and crushing cubic magnesium oxide blocks into magnesium oxide granules and blocks;

[0009] S2: preparing magnesium oxide granules, crushing the magnesium oxide granules with a high-pressure airflow to obtain a material with a D75 content of 300-400 μm, and subjecting the material to classification by a classifier and high-speed extraction by a fan to obtain magnesium oxide granules;

[0010] S3: preparing spherical magnesium oxide, screening, magnetically separating and drying the magnesium oxide particles to obtain spherical magnesium oxide with a specification of 0.03 to 0.425 mm;

[0011] S4: preparing spherical electrically insulating magnesium oxide powder, mixing the spherical magnesium oxide with a high temperature resistant insulating filler to obtain spherical electrically insulating magnesium oxide general powder, mixing the spherical electrically insulating magnesium oxide general powder with an organic silicon insulating material, and sieving to obtain spherical electrically insulating magnesium oxide powder.

[0012] Furthermore, the content of fine powder particles with a particle size less than 20 μm in the magnesium oxide granular material is less than 0.05%.

[0013] Furthermore, the particle size of the magnesium oxide granules is less than 3 mm.

[0014] Furthermore, the cuboidal magnesium oxide is at least one of large-crystal fused magnesium oxide, fused magnesia, and high-purity magnesia.

[0015] Furthermore, the particle size of the cubic magnesium oxide is 1 to 10 mm, the Leeb hardness is 5 to 7, and the magnesium content is 96 to 99.5%.

[0016] Furthermore, the mass ratio of the spherical magnesium oxide to the high temperature resistant insulating filler is 100:0.5-3.

[0017] Furthermore, the high temperature resistant insulating filler is formed by high temperature calcination of filler raw materials, and the composition of the filler raw materials is as follows: the mass ratio of aluminum magnesium spinel, zirconium oxide, silicon oxide and ferric oxide is 3-5:1-2:2-4:0.5-2.

[0018] Furthermore, the high temperature calcination temperature is 600-800° C. and the duration is 40-90 minutes.

[0019] Furthermore, the mass ratio of the spherical electrical insulating magnesium oxide powder to the organic silicon insulating material is 50:0.001-0.04.

[0020] Furthermore, the composition of the organic silicon insulating material is as follows: the mass ratio of methyl silicone oil to silicone resin is 4 to 9:3.

[0021] In summary, the present invention has the following beneficial effects:

[0022] First, the present invention uses high-pressure airflow to crush square crystal magnesium oxide, and effectively achieves crushing through strong impact, collision and friction shear caused by high-speed airflow. At the same time, this process can naturally remove edges and corners and directly form spherical magnesium oxide, which improves production efficiency and spherical effect compared with existing spheroidization treatment methods.

[0023] Second, the present invention uses a classifier and a fan to remove dust from the crushed magnesium oxide particles. The materials are transported to the impeller classification area through the airflow, and the coarse and fine separation is achieved under the action of centrifugal force and suction. The coarse particles are refluxed for further crushing, and the fine particles enter the cyclone collector. This process ensures uniform particle size, and at the same time, the dust is removed by the bag dust collector to improve the purity of the product.

[0024] Third, this technology uses airflow for crushing, grading and dust removal throughout the process, without the need for chemical reagents or complex physical treatment, and has environmental advantages. Efficient grading and dust removal equipment effectively controls dust emissions, purifies gas emissions and reduces environmental pollution. In addition, optimizing the process reduces energy consumption, improves energy utilization efficiency, and achieves green and energy-saving production.

[0025] Fourth, compared with the electrical insulating magnesium oxide powder prepared by conventional methods, the product prepared by the present invention exhibits the following significant advantages: its particle surface is smoother, and the powder fluidity is significantly improved, with an increase of 10%. In addition, the filling of the product is denser, and the tap density is increased by more than 5%; the electrical insulation performance is improved by more than 30%. Due to the substantial improvement in the above-mentioned key performance indicators, the present invention fully optimizes the various electrical performance indicators of the terminal products - electric heating elements and electric heating tubes, thereby comprehensively improving the quality of the overall terminal products. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0027] Figure 1 It is an operation step diagram of the method for preparing spherical electrical insulating magnesium oxide powder of the present invention. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] A method for preparing spherical electrical insulating magnesium oxide powder, such as Figure 1 As shown, the following steps are included:

[0030] S1: preparing magnesium oxide granules and blocks, and crushing cubic magnesium oxide blocks into magnesium oxide granules and blocks;

[0031] S2: preparing magnesium oxide granules, crushing the magnesium oxide granules with a high-pressure airflow to obtain a material with a D75 content of 300-400 μm, and subjecting the material to classification by a classifier and high-speed extraction by a fan to obtain magnesium oxide granules;

[0032] S3: preparing spherical magnesium oxide, screening, magnetically separating and drying the magnesium oxide particles to obtain spherical magnesium oxide with a specification of 0.03 to 0.425 mm;

[0033] S4: preparing spherical electrically insulating magnesium oxide powder, mixing the spherical magnesium oxide with a high temperature resistant insulating filler to obtain spherical electrically insulating magnesium oxide general powder, mixing the spherical electrically insulating magnesium oxide general powder with an organic silicon insulating material, and sieving to obtain spherical electrically insulating magnesium oxide powder.

[0034] In this scheme, high-pressure airflow is used to crush the square crystal magnesium oxide. During the crushing process, the high-speed movement of the airflow causes strong impact collision and friction shear between the particles and between the particles and the wall of the container, thereby achieving the refinement of the square crystal magnesium oxide, removing the edges and irregular shapes produced after the crushing, and achieving the sphericalization of the magnesium oxide material. Compared with the rough crushing, hammering and other spheroidization treatment steps in the prior art, the production efficiency is greatly improved and the sphericalization effect is enhanced.

[0035] During the dust removal process, the crushed particles are transported to the impeller classification area using the rising airflow. Under the action of the centrifugal force of the classification wheel and the suction force of the fan, the coarse and fine particles are separated. The coarse particles return to the crushing chamber according to their own gravity to continue to be crushed. The qualified fine particles enter the cyclone collector with the airflow, and the fine dust is collected by the bag dust collector. The purified gas is discharged by the induced draft fan. In this process, not only the uniformity of the product particle size is ensured, but also impurities are effectively removed and the purity of the product is improved. This precise particle size classification and dust removal technology makes the final spherical magnesium oxide product more in line with application requirements.

[0036] Furthermore, the crushing method in step S1 is jaw crushing.

[0037] This solution optimizes the crushing method based on the high hardness of cubic magnesium oxide. Due to the high hardness of cubic magnesium oxide, it is difficult for general crushing equipment to effectively crush it, which often leads to uneven fragments and excessive dust. The jaw crusher uses a jaw plate made of high-strength alloy material, which can effectively handle high-hardness cubic magnesium oxide blocks. Its large crushing ratio can quickly crush it to the required particle size; at the same time, since there is no dead zone in the crushing chamber, the feeding capacity and output are relatively high, which helps to improve production efficiency.

[0038] Furthermore, the content of fine powder particles with a particle size less than 20 μm in the magnesium oxide granular material is less than 0.05%.

[0039] This solution further limits the content of dust (fine powder particles with a particle size of less than 20 μm) in the magnesium oxide granular material, thereby ensuring the purity and uniformity of the magnesium oxide granular material.

[0040] Furthermore, the particle size of the magnesium oxide granules is less than 3 mm.

[0041] This solution optimizes the particle size of magnesium oxide granules to ensure that the feed particle size is moderate during the high-pressure airflow crushing process, thereby avoiding problems such as low crushing efficiency, long crushing time, and excessive equipment load. At the same time, this solution can also effectively ensure that the crushed material meets the D75 content requirement between 300 and 400 microns.

[0042] Furthermore, the cuboidal magnesium oxide is at least one of large-crystal fused magnesium oxide, fused magnesia, and high-purity magnesia.

[0043] Furthermore, the particle size of the cubic magnesium oxide is 1 to 10 mm, the Leeb hardness is 5 to 7, and the magnesium content is 96 to 99.5%.

[0044] This scheme optimizes the cubic crystal magnesium oxide raw materials and their physical and chemical properties, and uses large crystal fused magnesium oxide, fused magnesium sand and high purity magnesium sand alone or in combination, which significantly improves the purity and uniformity of particle size distribution of spherical magnesium oxide products, enhances chemical and thermal stability, mechanical strength and corrosion resistance. High-purity raw materials reduce impurities, and spherical magnesium oxide improves insulation performance; uniform particle size and moderate hardness promote the formation of spherical magnesium oxide particles and optimize fluidity and distribution.

[0045] Furthermore, the mass ratio of the spherical magnesium oxide to the high temperature resistant insulating filler is 100:0.5-3.

[0046] Furthermore, the high temperature resistant insulating filler is formed by high temperature calcination of filler raw materials, and the composition of the filler raw materials is as follows: the mass ratio of aluminum magnesium spinel, zirconium oxide, silicon oxide and ferric oxide is 3-5:1-2:2-4:0.5-2.

[0047] Furthermore, the high temperature calcination temperature is 600-800° C. and the duration is 40-90 minutes.

[0048] This scheme optimizes the selection, proportion and high-temperature calcination temperature conditions of high-temperature insulation materials, significantly improving the high-temperature resistance and insulation performance of the materials. The introduction of aluminum-magnesium spinel enhances the thermal stability and chemical inertness of the materials, while the reasonable proportion of zirconium oxide, silicon oxide and ferric oxide further optimizes the microstructure and performance of the filler. High-temperature calcination not only removes impurities in the material, but also promotes the crystal phase transformation of the filler, thereby improving its high-temperature resistance and insulation performance.

[0049] At the same time, the mass ratio of spherical magnesium oxide and high temperature resistant insulating filler is optimized. Compared with the electrical insulating magnesium oxide powder prepared by conventional methods, the electrical insulation performance of the spherical electrical insulating magnesium oxide powder product prepared by the scheme of the present invention is improved by more than 20%.

[0050] Furthermore, the mass ratio of the spherical electrical insulating magnesium oxide powder to the organic silicon insulating material is 50:0.001-0.04.

[0051] Furthermore, the composition of the organic silicon insulating material is as follows: the mass ratio of methyl silicone oil to silicone resin is 4 to 9:3.

[0052] The preferred organic silicon insulating material and proportion of this scheme significantly improve the processing performance and mechanical strength of the spherical electrical insulating magnesium oxide powder. Methyl silicone oil has good lubricity and dispersibility, which can reduce the viscosity of the material and improve processing efficiency. The introduction of silicone resin enhances the toughness and mechanical strength of the material, allowing it to withstand greater external forces without being easily damaged. This preferred scheme not only improves the processing performance and mechanical strength of the spherical electrical insulating magnesium oxide powder, but also ensures that it can form a more dense and uniform insulating layer during the filling process, thereby improving the electrical insulation performance and reliability of the overall material.

[0053] At the same time, the mass ratio of spherical electrical insulating magnesium oxide powder and organic silicon insulating material is optimized. Compared with the electrical insulating magnesium oxide powder prepared by the conventional method, the spherical electrical insulating magnesium oxide powder product prepared by the scheme of the present invention has a smoother particle surface, and the powder fluidity is improved by 10%; the filling is denser, and the tap density is increased by 5%.

[0054] Example 1

[0055] Preparation of spherical electrical insulating magnesium oxide powder:

[0056] S1: Preparation of magnesium oxide granules:

[0057] Large crystal fused magnesium oxide with a Leeb hardness of 5-7, a magnesium content of 96-99.5% and a particle size of 1-10 mm is crushed into magnesium oxide granules with a particle size of less than 3 mm by jaw crushing.

[0058] S2: Preparation of magnesium oxide granules:

[0059] The magnesium oxide granules are fed into a high-pressure air flow mill at a feeding speed of 5 to 10 kg / min to be crushed, removed from edges and corners, and spheroidized to obtain a material with a D75 content of 300 to 400 μm. The material is then subjected to classification by a classifier and high-speed extraction by a fan. The dust in the material is removed by utilizing the working principle of the centrifugal force of the classifier wheel and the high-speed extraction by the fan. The dust is fine powder particles with a particle size of less than 20 μm and a content of less than 0.05%. The obtained magnesium oxide granules are raised without visible dust.

[0060] S3: Preparation of spherical magnesium oxide A:

[0061] The magnesium oxide particles are screened by a screening machine, magnetically separated, and dried to obtain spherical magnesium oxide A with a diameter of 0.03 to 0.425 mm.

[0062] S4: Preparation of spherical electrical insulating magnesium oxide powder:

[0063] Aluminum magnesium spinel, zirconium oxide, silicon oxide, and ferric oxide were mixed and stirred at a mass ratio of 4:1:4:1, calcined at 700°C for 60 minutes, and sieved to obtain a high temperature resistant insulating filler. Spherical magnesium oxide A was mixed with the high temperature resistant insulating filler at a mass ratio of 100:2 and stirred for 20 minutes to obtain a spherical electrical insulating magnesium oxide general powder.

[0064] The methyl silicone oil and the silicone resin are mixed in a mass ratio of 2:1 to obtain an organic silicon insulating material, and the spherical electrical insulating magnesium oxide general powder and the organic silicon insulating material are mixed in a mass ratio of 50:0.02, and sieved to obtain the spherical electrical insulating magnesium oxide powder.

[0065] Example 2

[0066] Preparation of spherical electrical insulating magnesium oxide powder:

[0067] S1: Preparation of magnesium oxide granules:

[0068] The fused magnesia with a Leeb hardness of 5-7, a magnesium content of 96-99.5% and a particle size of 1-10 mm is crushed by jaw crushing into magnesium oxide granules with a particle size of less than 3 mm.

[0069] S2: Preparation of magnesium oxide granules:

[0070] The magnesium oxide granules are fed into a high-pressure air flow mill at a feeding speed of 5 to 10 kg / min to be crushed, removed from edges and corners, and spheroidized to obtain a material with a D75 content of 300 to 400 μm. The material is then subjected to classification by a classifier and high-speed extraction by a fan. The dust in the material is removed by utilizing the working principle of the centrifugal force of the classifier wheel and the high-speed extraction by the fan. The dust is fine powder particles with a particle size of less than 20 μm and a content of less than 0.05%. The obtained magnesium oxide granules are raised without visible dust.

[0071] S3: Preparation of spherical magnesium oxide B:

[0072] The magnesium oxide particles are screened by a screening machine, magnetically separated, and dried to obtain spherical magnesium oxide B with a size of 0.03 to 0.425 mm.

[0073] S4: Preparation of spherical electrical insulating magnesium oxide powder:

[0074] Aluminum magnesium spinel, zirconium oxide, silicon oxide, and ferric oxide were mixed and stirred at a mass ratio of 3:2:3:2, calcined at 600°C for 40 minutes, and sieved to obtain a high temperature resistant insulating filler. Spherical magnesium oxide B was mixed with the high temperature resistant insulating filler at a mass ratio of 100:0.5 and stirred for 10 minutes to obtain spherical electrical insulating magnesium oxide general powder.

[0075] The methyl silicone oil and the silicone resin are mixed in a mass ratio of 3:1 to obtain an organic silicon insulating material, and the spherical electrical insulating magnesium oxide powder and the organic silicon insulating material are mixed in a mass ratio of 50:0.001, and sieved to obtain the spherical electrical insulating magnesium oxide powder.

[0076] Example 3

[0077] Preparation of spherical electrical insulating magnesium oxide powder:

[0078] S1: Preparation of magnesium oxide granules:

[0079] High-purity magnesia sand with a Leeb hardness of 5-7, a magnesium content of 96-99.5% and a particle size of 1-10 mm is crushed by jaw crusher into magnesium oxide granules with a particle size of less than 3 mm.

[0080] S2: Preparation of magnesium oxide granules:

[0081] The magnesium oxide granules are fed into a high-pressure air flow mill at a feeding speed of 5 to 10 kg / min to be crushed, removed from edges and corners, and spheroidized to obtain a material with a D75 content of 300 to 400 μm. The material is then subjected to classification by a classifier and high-speed extraction by a fan. The dust in the material is removed by utilizing the working principle of the centrifugal force of the classifier wheel and the high-speed extraction by the fan. The dust is fine powder particles with a particle size of less than 20 μm and a content of less than 0.05%. The obtained magnesium oxide granules are raised without visible dust.

[0082] S3: Preparation of spherical magnesium oxide C:

[0083] The magnesium oxide particles are screened by a screening machine, magnetically separated, and dried to obtain spherical magnesium oxide C with a diameter of 0.03 to 0.425 mm.

[0084] S4: Preparation of spherical electrical insulating magnesium oxide powder:

[0085] Aluminum magnesium spinel, zirconium oxide, silicon oxide, and ferric oxide were mixed and stirred at a mass ratio of 5:2:2.5:0.5, calcined at 800°C for 90 minutes, and sieved to obtain a high temperature resistant insulating filler. Spherical magnesium oxide C was mixed with the high temperature resistant insulating filler at a mass ratio of 100:3 and stirred for 30 minutes to obtain a spherical electrical insulating magnesium oxide general powder.

[0086] The methyl silicone oil and the silicone resin are mixed in a mass ratio of 4:3 to obtain an organic silicon insulating material, and the spherical electrical insulating magnesium oxide general powder and the organic silicon insulating material are mixed in a mass ratio of 50:0.04, and sieved to obtain the spherical electrical insulating magnesium oxide powder.

[0087] Comparative Example 1

[0088] Spherical electrical insulating magnesium oxide powder is prepared using spherical magnesium oxide prepared by conventional methods as raw material:

[0089] S1: Preparation of magnesium oxide granules:

[0090] Large crystal fused magnesium oxide with a Leeb hardness of 5-7, a magnesium content of 96-99.5% and a particle size of 1-10 mm is crushed into magnesium oxide granules with a particle size of less than 3 mm by jaw crushing.

[0091] S2: Preparation of spherical magnesium oxide D:

[0092] The magnesium oxide granules are ground, hammered, sieved by a sieving machine, magnetically separated, and dried to obtain 0.425 mm spherical magnesium oxide D.

[0093] S4: Preparation of spherical electrical insulating magnesium oxide powder:

[0094] Aluminum magnesium spinel, zirconium oxide, silicon oxide, and ferric oxide were mixed and stirred at a mass ratio of 4:1:4:1, calcined at 700°C for 60 minutes, and sieved to obtain a high temperature resistant insulating filler. Spherical magnesium oxide D was mixed with the high temperature resistant insulating filler at a mass ratio of 100:2 and stirred for 20 minutes to obtain a spherical electrical insulating magnesium oxide general powder.

[0095] The methyl silicone oil and the silicone resin are mixed in a mass ratio of 2:1 to obtain an organic silicon insulating material, and the spherical electrical insulating magnesium oxide general powder and the organic silicon insulating material are mixed in a mass ratio of 50:0.02, and sieved to obtain the spherical electrical insulating magnesium oxide powder.

[0096] Comparative Example 2

[0097] Different from Example 1, the spherical magnesium oxide used in step S4 is a mixture of spherical magnesium oxide A prepared in Example 1 and spherical magnesium oxide D prepared in Comparative Example 1, with a mass ratio of 3:7.

[0098] Comparative Example 3

[0099] Different from Example 1, the spherical magnesium oxide used in step S4 is a mixture of spherical magnesium oxide A prepared in Example 1 and spherical magnesium oxide D prepared in Comparative Example 1, with a mass ratio of 6:4.

[0100] The main implementation conditions of each embodiment and comparative example are shown in Table 1:

[0101] Table 1 List of experimental conditions corresponding to each embodiment and comparative example

[0102]

[0103] Test results and analysis

[0104] The present invention implements the technical solutions proposed in Examples 1 to 3 in detail, and provides comparative examples to verify the performance of the spherical electrical insulating magnesium oxide powder prepared in the examples and comparative examples, as shown in Table 2:

[0105] Table 2 Performance comparison of spherical electrical insulation magnesium oxide powder prepared in each embodiment and comparative example

[0106] sample <![CDATA[3 # Flow rate (s / 100g)]]> <![CDATA[Tap density (g / cm 3 )]]> Hot withstand voltage (kV) Hot insulation resistance (MΩ) Example 1 155 2.51 2.6 10.0 Example 2 156 2.49 2.5 10.0 Example 3 155 2.50 2.6 9.0 Comparative Example 1 170 2.38 2.0 1.5 Comparative Example 2 165 2.42 2.2 2.5 Comparative Example 3 162 2.45 2.4 4.0

[0107] During the implementation of the embodiments and comparative examples, the present invention investigated the morphological characteristics of the spherical magnesium oxide prepared in Examples 1 to 3 and Comparative Example 1. From an intuitive visual perspective, there is a significant difference between these samples: the spherical magnesium oxide prepared in Examples 1 to 3 has a round and smooth surface, and no dust or particles visible to the naked eye are observed when the samples are lifted with a tool; on the contrary, the spherical magnesium oxide prepared in Comparative Example 1 exhibits obvious dust flying under the same operation.

[0108] In addition, when preparing electrical insulation grade spherical magnesium oxide in Comparative Examples 2 and 3, the experiment selected a mixture of spherical magnesium oxide A prepared in Example 1 and spherical magnesium oxide D prepared in Comparative Example 1 as the spherical magnesium oxide raw material. After being fully mixed, as the proportion of spherical magnesium oxide A in the mixture increases, the amount of dust generated when the mixture is raised is significantly reduced. Specifically, the phenomenon of dust flying in Comparative Example 2 is alleviated, and only a small amount of suspension appears; while in Comparative Example 3, the dust flying is reduced to a state where a trace amount is visible.

[0109] In terms of fluidity testing, the test adopts 3 # The Ford cup measures the flow rate of 100g of electrically insulating magnesium oxide powder. The test process starts from when the sample is poured into the Ford cup and the timing starts, and ends when the sample passes through the orifice. According to the test data in Table 2: for samples of the same weight, the electrically insulating magnesium oxide powder prepared by conventional methods in Comparative Example 1 all flows out of the Ford cup within 170s. In contrast, the time used for the electrically insulating magnesium oxide powder prepared in Examples 1 to 3 is shortened to about 155 to 156s, showing an improvement in fluidity. In addition, by comparing the data of the embodiments with the comparative examples, it can be found that with the increase in the amount of spherical magnesium oxide A added to the magnesium oxide raw material, the fluidity of the prepared electrically insulating magnesium oxide powder shows a trend of continuous enhancement.

[0110] In terms of tap density, according to the data analysis in Table 2, the average tap density of the electrical insulating magnesium oxide powder prepared in Examples 1 to 3 reached 2.50 g / cm 3 It is worth noting that, under the condition that all other test conditions remain the same, in the tests of Comparative Example 1, Comparative Example 2, Comparative Example 3 and Example 1, the proportion of spherical magnesium oxide raw material A in the spherical magnesium oxide raw material gradually increases from 0 to 100%. As this proportion increases, the tap density data shows an obvious increasing trend, from 2.38 g / cm 3 Gradually increase to about 2.50g / cm 3 This is because the performance of the spherical magnesium oxide product prepared by Example 1 of the present invention is improved compared with the conventional method, and the electrical insulating magnesium oxide powder prepared by using it as a raw material is more densely filled, thereby improving the tap density.

[0111] In terms of the most critical electrical insulation performance of the electrically insulating magnesium oxide powder, the test was conducted under a high temperature of 700°C in terms of hot withstand voltage performance and hot insulation performance. According to the data in Table 2, as the blending ratio of spherical magnesium oxide A in the spherical magnesium oxide raw material continues to increase, the electrical insulation performance of the electrically insulating magnesium oxide powder also shows a trend of significant improvement. Specifically, under the test condition of 0.5mA·2s, the hot withstand voltage strength of the sample is enhanced from 2.0kV to 2.5~2.6kV; at the same time, the hot insulation resistance of the sample also jumped significantly from 1.5MΩ to 10MΩ. Compared with Comparative Example 1, the electrically insulating magnesium oxide powder prepared in Example 1 has achieved significant improvements in both hot withstand voltage performance and hot insulation performance, which is due to the improvement in the performance of the spherical magnesium oxide prepared in Example 1 of the present invention compared with the conventional method.

[0112] In summary, the spherical electrical insulating magnesium oxide powder obtained by the present invention has a smooth particle surface and a 10% improvement in powder fluidity compared with ordinary electrical insulating magnesium oxide powder; the filling is more dense, and the tap density is increased by more than 5%; the electrical insulation performance is improved by more than 30%. Due to the improvement of the above performance indicators, the various electrical performance indicators of the terminal product electric heating element and electric heating tube are fully improved, thereby improving the overall terminal product quality, which is of great significance for improving the reliability and safety of electrical equipment.

[0113] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing spherical electrical insulating magnesium oxide powder, characterized in that: The following steps are involved: S1: preparing magnesium oxide granules and blocks, and crushing cubic magnesium oxide blocks into magnesium oxide granules and blocks; S2: preparing magnesium oxide granules, crushing the magnesium oxide granules with a high-pressure airflow to obtain a material with a D75 content of 300-400 μm, and subjecting the material to classification by a classifier and high-speed extraction by a fan to obtain magnesium oxide granules; S3: preparing spherical magnesium oxide, screening, magnetically separating and drying the magnesium oxide particles to obtain spherical magnesium oxide with a specification of 0.03 to 0.425 mm; S4: preparing spherical electrically insulating magnesium oxide powder, mixing the spherical magnesium oxide with a high temperature resistant insulating filler to obtain spherical electrically insulating magnesium oxide general powder, mixing the spherical electrically insulating magnesium oxide general powder with an organic silicon insulating material, and sieving to obtain spherical electrically insulating magnesium oxide powder.

2. The method for preparing spherical electrically insulating magnesium oxide powder according to claim 1, characterized in that: The content of fine powder particles with a particle size of less than 20 μm in the magnesium oxide granular material is less than 0.05%.

3. The method for preparing spherical electrically insulating magnesium oxide powder according to claim 1, characterized in that: The particle size of the magnesium oxide granules is less than 3 mm.

4. The method for preparing spherical electrically insulating magnesium oxide powder according to claim 1, characterized in that: The prismatic magnesium oxide is at least one of large crystalline fused magnesium oxide, fused magnesia, and high-purity magnesia.

5. The method for preparing spherical electrically insulating magnesium oxide powder according to claim 1, characterized in that: The particle size of the cubic crystal magnesium oxide is 1-10 mm, the Leeb hardness is 5-7, and the magnesium content is 96-99.5%.

6. The method for preparing spherical electrically insulating magnesium oxide powder according to claim 1, characterized in that: The mass ratio of the spherical magnesium oxide to the high temperature resistant insulating filler is 100:0.5-3.

7. The method for preparing spherical electrically insulating magnesium oxide powder according to claim 1, characterized in that: The high temperature resistant insulating filler is formed by high temperature calcining of filler raw materials, and the composition of the filler raw materials is as follows: the mass ratio of aluminum magnesium spinel, zirconium oxide, silicon oxide and ferric oxide is 3-5:1-2:2-4:0.5-2.

8. The method for preparing spherical electrically insulating magnesium oxide powder according to claim 7, characterized in that: The high temperature calcination temperature is 600-800° C. and the duration is 40-90 minutes.

9. The method for preparing spherical electrically insulating magnesium oxide powder according to claim 1, characterized in that: The mass ratio of the spherical electrical insulating magnesium oxide powder to the organic silicon insulating material is 50:0.001-0.

04.

10. The method for preparing spherical electrically insulating magnesium oxide powder according to claim 1, characterized in that: The composition of the organic silicon insulating material is as follows: the mass ratio of methyl silicone oil to silicone resin is 4-9:3.

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