Pre-stressed porcelain part of insulator and its preparation method

Abstract

The application provides a pre-stress insulator porcelain piece and a preparation method thereof, and belongs to the technical field of power equipment. The pre-stress insulator porcelain piece comprises the following components in percentage by weight: calcined industrial alumina 15-30%, quartz powder 5-15%, potassium feldspar 12-25%, and clay 30-60%. The pre-stress insulator porcelain piece has a density gradient in the inner and outer layers of the blank, which can essentially offset the tensile stress of the whole porcelain piece caused by the isostatic pressing and extrusion process, has excellent mechanical properties, and has important significance for meeting the demand of increasing the voltage grade of power transmission and transformation lines.

Description

Technical Field

[0001] This invention relates to the field of power equipment technology, and in particular to a pre-stressed insulator ceramic component and its preparation method. Background Technology

[0002] With the development of the power industry, the voltage levels of transmission and transformation lines are gradually increasing, placing increasingly higher demands on the mechanical properties of porcelain insulators. For suspension porcelain insulators, all mechanical forces during grid operation are borne by the head of the insulator porcelain component. While increasing the wall thickness of the porcelain head can improve its resistance to mechanical forces, this inevitably increases the mass of a single porcelain insulator, thus affecting the stress state and design of the entire line. Therefore, without altering existing conditions, it is necessary to improve the mechanical properties of the insulator porcelain component, specifically its tensile (bending) strength.

[0003] Existing extrusion methods produce clay segments with a certain density gradient in the radial direction (the density gradually decreases from the center to the edge of the clay segment). This density difference is even more pronounced in ultra-high voltage transmission line porcelain products with higher voltage levels (the clay segment diameter can even exceed 300 mm).

[0004] Using clay segments with density gradients to form ceramic blanks, and firing them using existing firing techniques (selecting the highest firing temperature within the firing temperature range and holding it at the highest temperature for a period of time), the final sintering temperature of the inner and outer layers of the blank is consistent, resulting in a basically uniform sintering state between the inner and outer layers. However, due to the density gradient within the blank, a density gradient also exists within the sintered ceramic piece. Specifically, compared to the edges, the center of the ceramic piece has a lower bulk density, higher porosity, and lower compactness. For ceramic materials, as porosity increases, the coefficient of thermal expansion decreases. Therefore, if the porosity in the center of the ceramic piece is higher than that at the edges, the coefficient of thermal expansion in the center will be lower than that at the edges. The ceramic piece as a whole is in a state of tensile stress, so it can withstand less applied tensile stress, resulting in lower tensile (bending) strength.

[0005] Existing technology involves applying a layer of compressive glaze to the surface of the ceramic part, controlling the glaze's coefficient of expansion to be lower than that of the ceramic part. This allows the glaze layer to apply favorable compressive stress to the ceramic part after firing, thereby improving the overall tensile (bending) strength of the ceramic part. If the glaze and the body have good compatibility, the overall tensile (bending) strength of the ceramic part can be further improved. However, if the clay segment prepared using the extrusion process has a large radial density gradient (large clay segment diameter), and this density gradient cannot be effectively eliminated in subsequent processes, the sintered ceramic part will inevitably be in a state of tensile stress. Since the glaze layer on the surface of the insulator ceramic part is relatively thin (generally between 0.2 and 0.5 mm), the compressive stress applied by the glaze layer is insufficient to offset the tensile stress generated inside the ceramic part due to structural differences. Therefore, the glazed ceramic part fired after glazing will still be in a state of tensile stress and cannot achieve the effect of compressive glaze.

[0006] In summary, in order to meet the higher requirements for the mechanical properties of suspension insulators due to the increased voltage levels of transmission and transformation lines, it is urgent to design a pre-stressed insulator that can fundamentally offset the tensile stress state of the porcelain component caused by the extrusion process, and to develop its preparation method. Summary of the Invention

[0007] The purpose of this invention is to provide a pre-stressed insulator porcelain component and its preparation method, which can essentially offset the tensile stress state of the porcelain component as a whole caused by the extrusion process, improve the mechanical properties of the insulator porcelain component, and is of great significance for meeting the requirements of increasing the voltage level of transmission and transformation lines.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0009] The present invention provides a pre-stressed insulator porcelain component comprising the following components by weight percentage: 15-30% calcined industrial alumina, 5-15% quartz powder, 12-25% potassium feldspar, and 30-60% clay.

[0010] Furthermore, the particle size of the quartz powder is ≤325 mesh.

[0011] The present invention also provides a method for preparing pre-stressed insulator ceramic parts, comprising the following steps: preparing a mixture by weight percentage, and sequentially subjecting the mixture to ball milling, sieving, iron removal, pressure filtration, coarse refining, aging, vacuum refining, extrusion, drying, and firing.

[0012] Furthermore, the ball mill operates at a speed of 20–50 rpm, and the material-to-water ratio is 0.5–1.2:1–2:1–2.

[0013] Of these, materials with a particle size ≤10μm account for 65-75 wt% of all materials.

[0014] Furthermore, in the sieving process, the sieve mesh size is 200 to 300 mesh.

[0015] Furthermore, the pressure of the filter press is ≤1.8MPa.

[0016] Furthermore, the aging process involves a humidity of ≥90%, a temperature of 20–40°C, and a time of ≥48 hours.

[0017] Furthermore, the vacuum degree of the vacuum plowing process is ≤-0.094MPa;

[0018] The drying process is a segmented drying process. The temperature of the first stage is 30–50°C, and the heating rate from room temperature to the first stage temperature is 0.8–1.2°C / h, with an ambient humidity of 65–75%. The temperature of the second stage is 55–65°C, and the heating rate from the first stage temperature to the second stage temperature is 1.5–2.5°C / h, with an ambient humidity of 45–55%. The temperature of the third stage is 90–110°C, and the heating rate from the second stage temperature to the third stage temperature is 3.5–4.5°C / h, with an ambient humidity of 3–5%. The fourth stage maintains the temperature of the third stage for 1.5–3 hours, with an ambient humidity of 1–2%. The temperature of the fifth stage is room temperature, and the cooling rate from the fourth stage temperature to room temperature is 4–7°C / h, with an ambient humidity of 0.8–1.8%.

[0019] Furthermore, the firing process involves staged heating. The temperature of the first stage is 250–350°C, with a heating rate of 0.5–2°C / min from room temperature to the first stage temperature, and a holding time of 0.2–0.8 h. The temperature of the second stage is 850–1000°C, with a heating rate of 1–2°C / min from the first stage temperature to the second stage temperature, and a holding time of 2–5 h. The temperature of the third stage is 1200–1300°C, with a heating rate of 3–5°C / min from the second stage temperature to the third stage temperature, and a holding time of ≤5 min. The temperature of the fourth stage is 1300–1400°C, with a heating rate of 8–15°C / min from the third stage temperature to the fourth stage temperature, and a holding time of ≤5 min.

[0020] The beneficial effects of this invention are:

[0021] In this invention, due to the rapid heating rate during the high-temperature stage and the absence or extremely short holding period at the highest temperature, coupled with the low thermal conductivity of the ceramic, a significant temperature difference exists between the edge and center of the ceramic during the high-temperature firing stage. The temperature at the edge is significantly higher than that at the center. Consequently, the quartz particles at the edge melt more thoroughly, resulting in smaller and fewer residual quartz particles and a higher content of the glassy phase after firing. Conversely, the quartz particles at the center melt relatively less, resulting in larger and more numerous residual quartz particles and a lower content of the glassy phase after firing. Therefore, in the ceramic of this invention, there is less residual quartz at the edge compared to the center. Since the coefficient of thermal expansion of quartz crystals is greater than that of quartz glass, the coefficient of thermal expansion at the edge is less than that at the center, and the coefficient of thermal expansion gradually increases from the edge to the center.

[0022] During the firing process of ceramic parts, when the firing temperature is within the firing temperature range, the bulk density, compactness, and true porosity of the fired ceramic parts are the highest. However, when the firing temperature exceeds the firing temperature range, the bulk density and compactness of the ceramic parts gradually decrease with increasing firing temperature, while the true porosity increases. In this invention, because the heating rate is very rapid during the high-temperature stage, and there is no holding process or the holding process at the highest temperature is extremely short, a significant temperature difference exists between the edges and the center of the ceramic part during the high-temperature firing stage. By controlling the highest temperature to be 50-100°C higher than the upper limit of the firing temperature range of the ceramic parts, the edges of the ceramic parts are overfired, while the center remains within the firing temperature range. This results in the bulk density and compactness of the ceramic parts at the edges being lower than those at the center, and the true porosity at the edges being higher than that at the center. For ceramic materials, increased porosity leads to a decrease in the coefficient of thermal expansion. Therefore, the coefficient of thermal expansion of ceramic pieces fired in this way is lower at the edges than at the center, and the coefficient of thermal expansion gradually increases from the edges to the center.

[0023] The ceramic component of this invention has a gradually increasing coefficient of thermal expansion from the edge to the center, thereby creating pre-compression stress throughout the entire ceramic component. When pre-compression stress exists inside the ceramic component, the applied tensile stress must first overcome the pre-compression stress before the ceramic component is subjected to tensile stress that could cause damage. Therefore, when pre-compression stress exists inside the ceramic component, it can improve the tensile (bending) strength of the ceramic body to a certain extent. Attached Figure Description

[0024] Figure 1 This is a micrograph of the edge of the pre-stressed insulator porcelain part obtained in Example 1 after polishing;

[0025] Figure 2 This is a micrograph of the central part of the pre-stressed insulator porcelain component obtained in Example 1 after polishing;

[0026] Figure 3 A micrograph of the polished edge of the ceramic insulator obtained in Comparative Example 1;

[0027] Figure 4 A micrograph of the polished central part of the insulator porcelain component obtained in Comparative Example 1;

[0028] Figure 5 A micrograph of the polished edge of the insulator porcelain part obtained in Comparative Example 2;

[0029] Figure 6 A micrograph of the polished central part of the insulator porcelain component obtained in Comparative Example 2;

[0030] Figure 7 This is a micrograph of the edge of the prestressed insulator porcelain part obtained in Example 1 after corrosion.

[0031] Figure 8 This is a micrograph of the central part of the pre-stressed insulator porcelain component obtained in Example 1 after corrosion.

[0032] Figure 9 The image shows a micrograph of the edge of the insulator porcelain part obtained in Comparative Example 1 after corrosion.

[0033] Figure 10 A micrograph of the central part of the insulator porcelain component obtained in Comparative Example 1 after corrosion.

[0034] Figure 11 This is a micrograph of the edge of the insulator porcelain part obtained in Comparative Example 2 after corrosion.

[0035] Figure 12 This is a micrograph of the central part of the insulator porcelain component obtained in Comparative Example 2 after corrosion. Detailed Implementation

[0036] The present invention provides a pre-stressed insulator porcelain component comprising the following components by weight percentage: 15-30% calcined industrial alumina, 5-15% quartz powder, 12-25% potassium feldspar, and 30-60% clay.

[0037] In the pre-stressed insulator ceramic component of the present invention, the calcined industrial alumina is preferably 17-25%, and more preferably 22%;

[0038] In the pre-stressed insulator ceramic component of the present invention, the quartz powder is preferably 7-12%, more preferably 10%;

[0039] In the pre-stressed insulator ceramic component of the present invention, potassium feldspar is preferably 15-20%, more preferably 18%;

[0040] In the prestressed insulator porcelain component of the present invention, the clay content is preferably 40-52%, and more preferably 50%.

[0041] In this invention, the clay is preferably Jilin Grade 1 ball clay from Jilin Qianfeng Ceramic Materials Co., Ltd. and / or clay from Xinhui Jiayao Ceramic Raw Materials Co., Ltd., and more preferably, the weight ratio of the two clays is 1 to 3:1, and more preferably 1.6:1.

[0042] In this invention, the particle size of the quartz powder is ≤325 mesh.

[0043] In this invention, 5-15% quartz powder (≤325 mesh) is added to the ceramic formulation. If the quartz particles are too fine, the quartz particles at the edges and center of the ceramic piece will completely melt after firing, resulting in a ceramic piece with the desired phase composition. If the quartz particles are too coarse, the remaining quartz particles in the center of the ceramic piece will be too coarse, and these large residual quartz particles are prone to developing transcrystalline cracks during the cooling stage. This is because during the cooling process in the firing stage, the residual quartz in the ceramic piece undergoes a crystal transformation at 573°C. Due to the sudden change in volume, a large shrinkage stress is generated inside the quartz particles (the larger the quartz particles, the greater the shrinkage stress), leading to through-cracks inside the quartz particles, and even causing them to explode. The cracks present in the large residual quartz particles in the ceramic piece can become the source of fracture under external force, which is detrimental to the strength of the ceramic piece.

[0044] The present invention also provides a method for preparing pre-stressed insulator ceramic parts, comprising the following steps: preparing a mixture by weight percentage, and sequentially subjecting the mixture to ball milling, sieving, iron removal, pressure filtration, coarse refining, aging, vacuum refining, extrusion, drying, and firing.

[0045] In this invention, the mixture obtained after vacuum kneading is extruded to obtain test strips, and the preferred specifications of the test strips are φ24mm×150mm.

[0046] In this invention, the rotational speed of the ball mill is 20-50 rpm, preferably 25-40 rpm, more preferably 30 rpm, and the material-to-ball-to-water ratio is 0.5-1.2:1-2:1-2, preferably 0.8-1.1:1.2-1.7:1.3-1.7, more preferably 1:1.5:1.5;

[0047] The material with a particle size ≤10μm accounts for 65-75 wt% of the total material, preferably 68-72 wt%, and more preferably 70 wt%.

[0048] In this invention, the sieve mesh size is 200-300 mesh, preferably 230-280 mesh, and more preferably 270 mesh.

[0049] In this invention, the sieving is performed multiple times, preferably through three sieves in sequence. The mesh size of the first sieve is preferably 200 mesh, the mesh size of the second sieve is preferably 230 mesh, and the mesh size of the third sieve is preferably 270 mesh.

[0050] In this invention, the pressure of the filter press is ≤1.8MPa, preferably ≤1.3MPa, and more preferably ≤1.2MPa.

[0051] In this invention, during the pressure filtration process, the pressure gradually increases from small to large.

[0052] In this invention, the aging humidity is ≥90%, preferably ≥92%, and more preferably ≥95%; the temperature is 20-40℃, preferably 25-35℃, and more preferably 30℃; and the time is ≥48h, preferably ≥60h, and more preferably ≥72h.

[0053] In this invention, the vacuum degree of the vacuum slurry is ≤-0.094MPa, preferably ≤-0.1MPa, and more preferably ≤-0.5MPa;

[0054] The drying is a segmented drying process. The temperature of the first stage is 30-50°C, preferably 35-45°C, and more preferably 40°C. The heating rate from room temperature to the temperature of the first stage is 0.8-1.2°C / h, preferably 1°C / h. The ambient humidity is 65-75%, preferably 68-72%, and more preferably 70%.

[0055] The temperature of the second stage is 55-65℃, preferably 58-62℃, and more preferably 60℃. The heating rate from the temperature of the first stage to the temperature of the second stage is 1.5-2.5℃ / h, preferably 1.8-2.2℃ / h, and more preferably 2℃ / h. The ambient humidity is 45-55%, preferably 48-52%, and more preferably 50%.

[0056] The temperature of the third stage is 90-110℃, preferably 95-105℃, and more preferably 100℃. The heating rate from the second stage to the third stage is 3.5-4.5℃ / h, preferably 3.8-4.2℃ / h, and more preferably 4℃ / h. The ambient humidity is 3-5%, preferably 4%.

[0057] The fourth stage maintains the temperature of the third stage, with a holding time of 1.5 to 3 hours, preferably 2 hours, and an ambient humidity of 1 to 2%, preferably 1.5%.

[0058] The temperature of the fifth stage is preferably room temperature, and the cooling rate from the temperature of the fourth stage to room temperature is 4 to 7 °C / h, preferably 4.5 to 6 °C / h, and more preferably 5 °C / h. The ambient humidity is 0.8 to 1.8%, preferably 1 to 1.5%, and more preferably 1.0%.

[0059] In this invention, the firing process involves staged heating. The temperature of the first stage is 250–350°C, preferably 270–320°C, and more preferably 300°C. The heating rate from room temperature to the temperature of the first stage is 0.5–2°C / min, preferably 0.8–1.5°C / min, and more preferably 1°C / min. The holding time is 0.2–0.8 h, preferably 0.3–0.7 h, and more preferably 0.5 h.

[0060] The temperature of the second stage is 850–1000℃, preferably 870–980℃, more preferably 900–970℃, and even more preferably 960℃; the heating rate from the temperature of the first stage to the temperature of the second stage is 1–2℃ / min, preferably 1.2–1.7℃ / min, and even more preferably 1.5℃ / min; the holding time is 2–5h, preferably 2.5–4h, and even more preferably 3h.

[0061] The temperature of the third stage is 1200-1300℃, preferably 1230-1270℃, more preferably 1240-1260℃, and even more preferably 1250℃; the heating rate from the temperature of the second stage to the temperature of the third stage is 3-5℃ / min, preferably 3.5-4.5℃ / min, and even more preferably 4℃ / min; the holding time is ≤5min, preferably ≤3min, more preferably ≤1min, and even more preferably 0min;

[0062] The temperature of the fourth stage is 1300-1400℃, preferably 1320-1370℃, more preferably 1340-1360℃, and even more preferably 1350℃; the heating rate from the temperature of the third stage to the temperature of the fourth stage is 8-15℃ / min, preferably 9-13℃ / min, and even more preferably 10℃ / min; the holding time is ≤5min, preferably ≤3min, even more preferably ≤1min, and even more preferably 0min.

[0063] In this invention, the cooling process after firing is a segmented cooling process. The temperature of the first stage is 980-1020°C, preferably 1000°C, and the cooling rate from the firing temperature to the first stage temperature is 200-300°C / h, preferably 230-270°C / h, and more preferably 250°C / h.

[0064] The temperature of the second stage is 870-880℃, preferably 872-878℃, and more preferably 875℃. The cooling rate from the first stage temperature to the second stage temperature is 40-60℃ / h, preferably 45-55℃ / h, and more preferably 50℃ / h. The holding time is 1-2h, preferably 1.3-1.7h, and more preferably 1.5h.

[0065] The temperature of the third stage is 800-820℃, preferably 805-815℃, and more preferably 810℃. The cooling rate from the second stage temperature to the third stage temperature is 20-30℃ / h, preferably 23-27℃ / h, and more preferably 25℃ / h. The holding time is 2-3h, preferably 2.3-2.7h, and more preferably 2.5h.

[0066] The temperature of the fourth stage is 540-560℃, preferably 545-555℃, and more preferably 550℃. The cooling rate from the temperature of the third stage to the temperature of the fourth stage is 20-30℃ / h, preferably 23-27℃ / h, and more preferably 25℃ / h.

[0067] The fifth stage is to reduce the temperature from the fourth stage to room temperature at a rate of 20-40℃ / h, preferably 25-35℃ / h, and more preferably 30℃ / h.

[0068] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0069] Example 1

[0070] The composition is based on 20% calcined industrial alumina, 15% 325-mesh quartz powder, and 17% potassium feldspar (Na₂O mass percentage is 0.6 wt%). K2O :m Na2O =18), clay 48% (the mass ratio of clay from Xinhui Jiayao Ceramic Raw Materials Co., Ltd. to Jilin Grade 1 ball clay is 1:0.6) were mixed to obtain a mixture. The mixture was ball-milled at a material-to-ball-to-water ratio of 1:1.5:2 and a rotation speed of 30 rpm to obtain a mixture with a particle size ≤10μm of 70wt%. The mixture was then passed through 200 mesh, 230 mesh and 270 mesh sieves in sequence for iron removal, pressure filtration and coarse sizing. During the pressure filtration process, the pressure was gradually increased, and the maximum pressure of the plunger pump pressure gauge was 1.4MPa. Subsequently, the mixture was aged for 48 hours at a humidity of 90% and a temperature of 30℃. Afterwards, it was vacuum sizing under a vacuum degree of -0.094MPa and then extruded to obtain test strips with a specification of φ24mm×150mm.

[0071] The test strips were dried in stages. In the first stage, the temperature was increased from room temperature to 40℃ at a rate of 1℃ / h, and the ambient humidity in the drying chamber decreased from 80% to 70%. In the second stage, the temperature was increased from 40℃ to 60℃ at a rate of 2℃ / h, and the ambient humidity decreased from 70% to 50%. In the third stage, the temperature was increased from 60℃ to 100℃ at a rate of 4℃ / h, and the ambient humidity decreased from 50% to 5%. In the fourth stage, the temperature was maintained at 100℃ for 2 hours, and the ambient humidity decreased from 5% to 1.5%. In the fifth stage, the temperature was decreased from 100℃ to room temperature at a rate of 5℃ / h, and the ambient humidity was maintained at 1.0%.

[0072] After drying, the material is fired. First, the temperature is increased from room temperature to 300℃ at a rate of 2℃ / min and held for 0.5h (first stage). Then, the temperature is increased to 960℃ at a rate of 2℃ / min and held for 3h (second stage). Next, the temperature is increased to 1270℃ at a rate of 4℃ / min (third stage). Finally, the temperature is increased to 1350℃ at a rate of 10℃ / min (fourth stage).

[0073] Finally, the temperature inside the kiln is reduced to 1000℃ at a cooling rate of 300℃ / h, then reduced to 880℃ at a cooling rate of 50℃ / h, and held for 1 hour; then reduced to 810℃ at a cooling rate of 30℃ / h, and held for 2.5 hours; then reduced to 550℃ at a cooling rate of 25℃ / h, and finally reduced to room temperature at a cooling rate of 35℃ / h, to obtain the pre-stressed insulator porcelain part.

[0074] Example 2

[0075] The composition is based on calcined industrial alumina (15%), 300-mesh quartz powder (25%), potassium feldspar (20%) (Na₂O mass percentage: 0.5 wt%), m K2O :m Na2O =20), clay 40% (the mass ratio of clay from Xinhui Jiayao Ceramic Raw Materials Co., Ltd. to Jilin Grade 1 ball soil is 1:0.6) were mixed to obtain a mixture. The mixture was ball-milled at a material-to-ball-to-water ratio of 0.5:2:1.5 and a rotation speed of 20 rpm, so that the proportion of the mixture with a particle size ≤10μm was 75wt%. The mixture was then passed through 200 mesh, 230 mesh and 270 mesh sieves in sequence for iron removal, pressure filtration and coarse sizing. During the pressure filtration process, the pressure was gradually increased, and the maximum pressure of the plunger pump pressure gauge was 1.8MPa. Subsequently, the mixture was aged for 64 hours at a humidity of 95% and a temperature of 40℃. Afterwards, it was vacuum sizing under a vacuum degree of -0.1MPa and then extruded to obtain test strips with a specification of φ24mm×150mm.

[0076] The test strips were dried in stages. In the first stage, the temperature was increased from room temperature to 30℃ at a rate of 0.8℃ / h, and the humidity in the drying chamber decreased from 80% to 75%. In the second stage, the temperature was increased from 30℃ to 55℃ at a rate of 1.5℃ / h, and the humidity decreased from 75% to 50%. In the third stage, the temperature was increased from 55℃ to 110℃ at a rate of 4.5℃ / h, and the humidity decreased from 50% to 3%. In the fourth stage, the temperature was maintained at 110℃ for 1.5h, and the humidity decreased from 3% to 1.5%. In the fifth stage, the temperature was decreased from 110℃ to room temperature at a rate of 5℃ / h, and the humidity was maintained at 0.8%.

[0077] After drying, the material is fired. First, the temperature is increased from room temperature to 250℃ at 0.5℃ / min and held for 0.8h (first stage). Then, the temperature is increased to 850℃ at 2℃ / min and held for 2h (second stage). Next, the temperature is increased to 1200℃ at 3℃ / min and held for 5min (third stage). Finally, the temperature is increased to 1300℃ at 8℃ / min and held for 1min (fourth stage).

[0078] Finally, the temperature inside the kiln is reduced to 1000℃ at a cooling rate of 300℃ / h, then reduced to 880℃ at a cooling rate of 50℃ / h, and held for 1 hour; then reduced to 810℃ at a cooling rate of 30℃ / h, and held for 2.5 hours; then reduced to 550℃ at a cooling rate of 25℃ / h, and finally reduced to room temperature at a cooling rate of 35℃ / h, to obtain the pre-stressed insulator porcelain part.

[0079] Example 3

[0080] The composition is based on 20% calcined industrial alumina, 5% 325-mesh quartz powder, and 25% potassium feldspar (Na₂O mass percentage is 0.6 wt%). K2O :m Na2O =18), clay 50% (the mass ratio of clay from Xinhui Jiayao Ceramic Raw Materials Co., Ltd. to Jilin Grade 1 ball clay is 1:0.6) were mixed to obtain a mixture. The mixture was ball-milled at a material-to-ball-to-water ratio of 1.2:2:1 and a rotation speed of 50 rpm to obtain a mixture with a particle size ≤10μm of 75wt%. The mixture was then passed through 230 mesh, 270 mesh and 300 mesh sieves in sequence for iron removal, pressure filtration and coarse sizing. During the pressure filtration process, the pressure was gradually increased, and the maximum pressure of the plunger pump pressure gauge was 1.0MPa. Subsequently, the mixture was aged for 72h at a humidity of 92% and a temperature of 20℃. Afterwards, it was vacuum sizing under a vacuum degree of -0.15MPa and then extruded to obtain test strips with a specification of φ24mm×150mm.

[0081] The test strips were dried in stages. In the first stage, the temperature was increased from room temperature to 50℃ at a rate of 1.2℃ / h, and the ambient humidity in the drying chamber decreased from 80% to 75%. In the second stage, the temperature was increased from 50℃ to 65℃ at a rate of 2.5℃ / h, and the ambient humidity decreased from 75% to 45%. In the third stage, the temperature was increased from 65℃ to 90℃ at a rate of 4.5℃ / h, and the ambient humidity decreased from 45% to 5%. In the fourth stage, the temperature was maintained at 90℃ for 3 hours, and the ambient humidity decreased from 5% to 2%. In the fifth stage, the temperature was decreased from 110℃ to room temperature at a rate of 5℃ / h, and the ambient humidity was maintained at 1.8%.

[0082] After drying, the material is fired. First, the temperature is increased from room temperature to 320℃ at a rate of 4℃ / min and held for 0.2h (first stage). Then, the temperature is increased to 1000℃ at a rate of 5℃ / min and held for 0.5h (second stage). Next, the temperature is increased to 1400℃ at a rate of 7℃ / min and held for 1min (third stage). Finally, the temperature is increased to 1500℃ at a rate of 10℃ / min and held for 3min (fourth stage).

[0083] Finally, the temperature inside the kiln is reduced to 1000℃ at a cooling rate of 300℃ / h, then reduced to 880℃ at a cooling rate of 50℃ / h, and held for 1 hour; then reduced to 810℃ at a cooling rate of 30℃ / h, and held for 2.5 hours; then reduced to 550℃ at a cooling rate of 25℃ / h, and finally reduced to room temperature at a cooling rate of 35℃ / h, to obtain the pre-stressed insulator porcelain part.

[0084] Comparative Example 1

[0085] Unlike Example 1, in the firing step, the temperature was first increased from room temperature to 300°C at 3°C / min and held for 0.5 hours, then increased to 960°C at 3°C / min and held for 1 hour, and then increased to 1270°C at 4°C / min and held for 1 hour.

[0086] Comparative Example 2

[0087] Unlike Example 1, in the firing step, the temperature was first increased from room temperature to 300°C at 3°C / min and held for 0.5 hours, then increased to 960°C at 3°C / min and held for 1 hour, then increased to 1270°C at 4°C / min, and then increased to 1350°C at 10°C / min and held for 1 hour.

[0088] As can be seen from the above embodiments, the present invention provides a pre-stressed insulator ceramic component and its preparation method. The pre-stressed insulator ceramic component obtained in Example 1 and the insulator ceramic components obtained in Comparative Examples 1 and 2 were polished and then subjected to corrosion tests. The corrosion test method is as follows:

[0089] (1) Sample corrosion: At an ambient temperature of ≤25℃, the polished sample was placed in a plastic beaker, and 40% hydrofluoric acid solution (enough to cover the sample) was added to the beaker for corrosion for 30s.

[0090] (2) Sample cleaning: Place the etched sample into a beaker, rinse it with water 3 times, add anhydrous ethanol to the beaker (enough to cover the sample), and ultrasonically clean it for 10 minutes at room temperature.

[0091] (3) Sample drying: After cleaning, the sample is placed in a forced-air drying oven at 120℃ for 10 minutes.

[0092] (4) Gold sputtering of samples: The dried sample is fixed on the sample stage with conductive adhesive. The fixed sample is placed in the ion sputtering instrument and the sputtering time is 90s.

[0093] Figure 1 This is a micrograph of the edge of the pre-stressed insulator porcelain part obtained in Example 1 after polishing. Figure 2 This is a micrograph of the central part of the pre-stressed insulator porcelain component obtained in Example 1 after polishing. Figure 3 This is a micrograph of the polished edge of the insulator porcelain part obtained in Comparative Example 1. Figure 4 This is a micrograph of the central part of the insulator porcelain component obtained in Comparative Example 1 after polishing. Figure 5 This is a micrograph of the polished edge of the insulator porcelain part obtained in Comparative Example 2. Figure 6 This is a micrograph of the polished central portion of the insulator porcelain component obtained in Comparative Example 2. Figure 7 This is a micrograph of the edge of the prestressed insulator porcelain component obtained in Example 1 after corrosion. Figure 8 This is a micrograph of the central part of the pre-stressed insulator porcelain component obtained in Example 1 after corrosion. Figure 9 This is a micrograph of the edge of the insulator porcelain part obtained in Comparative Example 1 after corrosion. Figure 10 This is a micrograph of the central part of the insulator porcelain component obtained in Comparative Example 1 after corrosion. Figure 11 This is a micrograph of the edge of the insulator porcelain part obtained in Comparative Example 2 after corrosion. Figure 12 This is a micrograph of the central portion of the insulator porcelain component obtained in Comparative Example 2 after corrosion. Figure 1 and Figure 2 As can be seen, the pre-stressed insulator ceramic component obtained in Example 1 has significantly more pores at the edge and significantly fewer quartz particles at the center. A portion of the melted quartz will ultimately exist in the ceramic component as a glassy phase. Therefore, the more quartz melted, the higher the glassy phase content in the ceramic component, and consequently, the lower the coefficient of thermal expansion (the higher the crystalline phase content in the ceramic component, the greater the coefficient of thermal expansion). From... Figures 3-4 and Figures 9-10It can be seen that the number of pores at the edge and center of the insulator porcelain part obtained in Comparative Example 2 is similar, as is the number of quartz particles. From Figures 5-6 and Figures 11-12 As can be seen, the number of pores on the edge and center of the ceramic piece in Comparison Scheme 2 is similar, as is the number of residual quartz particles on the edge and center of the ceramic piece in Comparison Scheme 2.

[0094] Samples were taken from the edges and center of the ceramic pieces in Example 1 and Comparative Examples 1-2, respectively, and their bulk density and coefficient of thermal expansion were tested. The samples were ground into ceramic powder with a particle size ≤63μm, and the true density of the ceramic powder was tested using a true density meter. The true porosity was calculated as (1 - bulk density / true density) * 100%. The phase composition of the ceramic powder after the true density test was performed using an XRD diffractometer. The three-point bending strength test was conducted according to GB8411.2-2008 standard.

[0095] Table 1 shows the test results of bulk density, porosity, coefficient of thermal expansion, and three-point bending strength of the ceramic parts obtained in Example 1 and Comparative Examples 1-2.

[0096]

[0097]

[0098] Table 2. Quartz phase and glass phase content of the edge and center parts of the ceramic pieces obtained in Example 1 and Comparative Examples 1-2.

[0099]

[0100] The ceramic part obtained in Example 1 gradually increases in bulk density and decreases in porosity from the edge to the center (the highest temperature is higher than the upper limit of the firing temperature range, and the surface is overfired). The content of residual fine quartz particles gradually increases (no heat preservation, there is a temperature difference inside the ceramic part, and the theoretical melting temperature of quartz is above 1700℃). The coefficient of expansion gradually increases, so that there is pre-compression stress inside the entire ceramic part. Therefore, the bending strength of the ceramic part is increased by more than 25% compared with Comparative Examples 1-2.

[0101] In Comparative Example 1 and Comparative Example 2, the bulk density, porosity, and expansion coefficient of the ceramic parts at the edge and center are not significantly different, and the three-point bending strength is relatively low, at 148 MPa and 143 MPa, respectively.

[0102] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A pre-stressed insulator porcelain piece, characterized in that, It includes the following components by weight percentage: 15-30% calcined industrial alumina, 5-15% quartz powder, 12-25% potassium feldspar, and 30-60% clay; The method for preparing the pre-stressed insulator ceramic component includes the following steps: The ingredients are mixed according to the weight percentage to obtain a mixture. The mixture is then subjected to ball milling, sieving, iron removal, filter pressing, coarse grinding, aging, vacuum plowing, extrusion, drying and firing in sequence. The firing process involves staged heating. The first stage temperature is 250–350°C, with a heating rate of 0.5–2°C / min from room temperature to the first stage temperature, and a holding time of 0.2–0.8 h. The second stage temperature is 850–1000°C, with a heating rate of 1–2°C / min from the first stage temperature to the second stage temperature, and a holding time of 2–5 h. The third stage temperature is 1200–1300°C, with a heating rate of 3–5°C / min from the second stage temperature to the third stage temperature, and a holding time of ≤5 min. The fourth stage temperature is 1300–1400°C, with a heating rate of 8–15°C / min from the third stage temperature to the fourth stage temperature, and a holding time of ≤5 min.

2. The pre-stressed insulator porcelain member according to claim 1, wherein The particle size of the quartz powder is ≤325 mesh.

3. The method for preparing the pre-stressed insulator ceramic component according to claim 1 or 2, characterized in that, Includes the following steps: The ingredients are mixed according to the weight percentage to obtain a mixture. The mixture is then subjected to ball milling, sieving, iron removal, filter pressing, coarse grinding, aging, vacuum plowing, extrusion, drying and firing in sequence. The firing process involves staged heating. The first stage temperature is 250–350°C, with a heating rate of 0.5–2°C / min from room temperature to the first stage temperature, and a holding time of 0.2–0.8 h. The second stage temperature is 850–1000°C, with a heating rate of 1–2°C / min from the first stage temperature to the second stage temperature, and a holding time of 2–5 h. The third stage temperature is 1200–1300°C, with a heating rate of 3–5°C / min from the second stage temperature to the third stage temperature, and a holding time of ≤5 min. The fourth stage temperature is 1300–1400°C, with a heating rate of 8–15°C / min from the third stage temperature to the fourth stage temperature, and a holding time of ≤5 min.

4. The method of claim 3, wherein the pre-stressed insulator porcelain piece is prepared by the steps of: The ball mill operates at a speed of 20–50 rpm, and the material-to-ball-to-water ratio is 0.5–1.2:1–2:1–2. Of these, materials with a particle size ≤10μm account for 65-75 wt% of all materials.

5. The method for preparing pre-stressed insulator ceramic parts according to claim 4, characterized in that, In the sieving process, the sieve mesh size is 200-300 mesh.

6. The method for preparing pre-stressed insulator ceramic components according to claim 4 or 5, characterized in that, The pressure of the filter press is ≤1.8MPa.

7. The method for preparing pre-stressed insulator ceramic parts according to claim 6, characterized in that, The aging process involves a humidity level of ≥90%, a temperature of 20–40°C, and a time of ≥48 hours.

8. The method for preparing pre-stressed insulator ceramic parts according to claim 7, characterized in that, The vacuum degree of the vacuum slurry is ≤-0.094MPa; The drying process is a staged drying process. The temperature of the first stage is 30–50°C, and the heating rate from room temperature to the first stage temperature is 0.8–1.2°C / h. The ambient humidity is 65–75%. The temperature in the second stage is 55–65℃, and the heating rate from the first stage to the second stage is 1.5–2.5℃ / h, with an ambient humidity of 45–55%. The temperature in the third stage is 90–110℃, and the temperature rise rate from the second stage to the third stage is 3.5–4.5℃ / h, with an ambient humidity of 3–5%. The fourth stage maintains the temperature of the third stage, with a holding time of 1.5–3 hours and an ambient humidity of 1–2%. The fifth stage temperature is room temperature. The cooling rate from the fourth stage temperature to room temperature is 4-7℃ / h, and the ambient humidity is 0.8-1.8%.

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