An electric porcelain glaze for reducing porosity of porcelain parts and a preparation method thereof

Abstract

This invention relates to the field of electrical porcelain production technology, specifically disclosing an electrical porcelain glaze for reducing the porosity of porcelain parts. The glaze comprises, by mass parts: 4-10 parts high-clay, 3-10 parts calcium silicate micropowder, 1-5 parts high-temperature calcined liquid stone powder, 25-35 parts potassium microparticles, 10-30 parts silica micropowder, 10-20 parts hard kaolin, 4-12 parts α-alumina micropowder, 6-10 parts glaze color base, and 0.15-0.25 parts CMC. A method for preparing the electrical porcelain glaze for reducing the porosity of porcelain parts includes: Step 1, formulation development and screening: designing a color glaze formulation and screening a formulation with an initial melting temperature ≥1170℃ as the target formulation; Step 2, pilot testing and production: adding the raw materials weighed according to the target formulation to a ball mill and ball milling to obtain a glaze slurry; testing the fineness of the glaze slurry, followed by a melting temperature test; after passing the test, firing the glaze slurry onto an electrical porcelain blank to obtain the electrical porcelain product. This solution aims to reduce the porosity within ceramic components, thereby addressing the issue of significant performance variation in high-voltage power transmission ceramic products.

Description

Technical Field

[0001] This invention relates to the field of electrical porcelain production technology, specifically to an electrical porcelain glaze for reducing the porosity of porcelain parts and its preparation method. Background Technology

[0002] With the continuous development of ultra-high voltage and extra-high voltage power transmission technologies, extremely stringent requirements have been placed on the electromechanical properties of electrical porcelain products, especially their mechanical strength and insulation reliability. The microstructure of the porcelain is the fundamental factor determining its electromechanical properties, and the gas phase (i.e., pores) within the porcelain is a key factor in reducing product performance. The larger the diameter and the greater the number of pores, the lower the density of the electrical porcelain, leading to decreased strength, deteriorated insulation performance, and an increased risk of moisture absorption and expansion. Ultimately, this may cause the product to exhibit a "zero value" phenomenon, seriously threatening the safe operation of the power system.

[0003] To address the porosity issue, existing technologies primarily focus on increasing the density and strength of the porcelain material. For example, this is achieved by employing finer ball milling processes to minimize the particle size of the porcelain slurry raw materials. The existing fine grinding process for porcelain slurry is as follows: Ingredient preparation stage: Ingredient calculation → Weigh raw materials according to the ratio → Add the weighed raw materials to the ball mill → Add additives → Add an appropriate amount of purified water → Seal the ball mill → Prepare for ball milling.

[0004] Ball milling stage: Start the ball mill → Control the ball milling time → Stop the ball milling when the specified time is reached → Open the slurry discharge valve → Take out the uniformly composed slurry → Prepare for testing.

[0005] Moisture testing stage: Stir the mud to keep it in suspension → Weigh 20 grams of mud → Bake the mud → Bake for no less than 45 minutes → Weigh the mud immediately after drying → Calculate the moisture content → Record the data.

[0006] Fineness testing stage: Weigh 200 grams of mud → Filter all 200 grams of mud through a standard sieve → Filter until clear water is obtained → Pour all the remaining particles on the sieve into an evaporating dish → Pour off the excess water in the evaporating dish → Bake until dry → Weigh the dried remaining particles → Record the data.

[0007] The above process aims to increase the fineness of the powder and enhance the sintering driving force to obtain a denser ceramic blank. This method is highly effective and frequently adopted in the production of ordinary electrical porcelain products with relatively low performance requirements.

[0008] However, through long-term practice, the inventors of this invention discovered that when dealing with electrical porcelain products at higher voltage levels that require rigorous electromechanical testing (e.g., products at 160kN level and above, requiring impact resistance tests of 392kV or higher), simply relying on refining the particle size of the slurry encountered a technical bottleneck: even with the slurry fineness maximized, the porosity of the final fired porcelain still remained above 15%, resulting in significant performance dispersion. (The increased grinding time during fineness improvement reduced efficiency, and the prolonged grinding also caused the grinding medium to be over-ground and mixed into the slurry, affecting the purity of the slurry and negatively impacting the electrical performance of the porcelain.) The pass rate in stringent key tests such as electromechanical damage, impact resistance, and temperature cycling was low, far from meeting the reliability requirements of high-voltage electrical porcelain. Through repeated cross-comparison experiments, the inventors noticed a crucial phenomenon generally overlooked by the industry: there is a significant difference in the internal porosity between unglazed fired blanks and glazed fired porcelain. Summary of the Invention

[0009] The present invention aims to provide an electric porcelain glaze for reducing the porosity of ceramic parts and its preparation method, so as to reduce the porosity inside the ceramic parts and thus solve the problem of large product performance dispersion of electric porcelain products for high voltage power transmission.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: An electric porcelain glaze for reducing the porosity of ceramic parts comprises, by weight parts: 4-10 parts high clay, 3-10 parts calcium silicate micro powder, 1-5 parts high-temperature calcined liquid stone powder, 25-35 parts potassium microcline, 10-30 parts silica micro powder, 10-20 parts hard kaolin, 4-12 parts α-alumina micro powder, 6-10 parts glaze color base, and 0.15-0.25 parts CMC.

[0011] Preferably, as an improvement, the high-clay content is 6-8 parts.

[0012] Preferably, as an improvement, the calcium silicate micro powder comprises 7-9 parts, the silicon micro powder comprises 20-25 parts, and the α-alumina micro powder comprises 6-9 parts.

[0013] Preferably, as an improvement, the hard kaolin clay is 13-16 parts.

[0014] Preferably, as an improvement, the high-temperature calcined liquid stone powder comprises 2-3 parts, and the potassium microcline comprises 28-30 parts.

[0015] Preferably, as an improvement, the glaze color base is any one of green, yellow, or red.

[0016] This invention also provides a method for preparing an electric porcelain glaze that reduces the porosity of ceramic parts, comprising the following steps: Step 1: Formula Development and Screening: Design the color glaze formula, conduct small-scale and comparative tests, and perform melting temperature tests on the screened formulas. Select the formula with an initial melting temperature ≥1170℃ as the target formula; if the melting temperature is lower than 1170℃, it is considered unqualified and the formula needs to be readjusted. Step 2, Pilot Testing and Production: Weigh the raw materials according to the target formula and add them to a ball mill to obtain a glaze slurry; test the fineness of the glaze slurry, and after the fineness is qualified, conduct a melting temperature test; after the initial melting temperature obtained from the melting temperature test is qualified, apply the glaze slurry to the electric porcelain blank for glazing, and then fire it to obtain the electric porcelain product.

[0017] Compared with the prior art, the principles and advantages of this invention are: 1. This invention arose after the inventors, having failed to achieve results through multiple improvements to the electric porcelain formula and numerous experiments with the fine grinding process, noticed the unusual phenomenon of "differences in porosity between unglazed and glazed ceramic pieces." This led them to shift their research focus from the traditional body of the ceramic to the interaction between the body and the glaze during firing. Ultimately, they discovered that in the temperature range of 1100℃ to 1160℃, components such as sulfates in the ceramic body undergo violent decomposition under a reducing atmosphere, producing gases such as sulfur dioxide. If the glaze has already begun to melt and form a dense glassy phase at this temperature, it will seal the pores of the body, preventing the decomposition gases from escaping and causing them to remain inside the ceramic piece, forming numerous closed pores. This invention fundamentally solves this "venting" problem by precisely designing and raising the initial melting temperature of the electric glaze to ≥1170℃, thus preserving a clear venting channel for the peak gas production period during the high-temperature decomposition of the ceramic body. Only when the temperature continues to rise above 1170℃ does the glaze slowly produce a glassy phase, thereby ensuring that the gas is fully expelled. This effectively controls the porosity of the ceramic product from 15% in the prior art to 7%, solving the problems of low electromechanical properties and high dispersion caused by porosity. Furthermore, in the production of 160kN products using the glaze of this invention, the glaze strength is increased by 35MPa, the sand strength is increased by 25MPa, the electromechanical failure load is increased by 29kN, and the radio interference level is significantly optimized.

[0018] 2. This invention introduces α-alumina micropowder, a material rarely used in traditional glazes, as a key functional component into its formulation system. In conventional understanding, α-alumina micropowder is typically used in refractory materials or engineering ceramics. Due to its extremely high melting point and low chemical reactivity, it is rarely used in glaze formulations, as glazes usually prioritize good melt flowability and gloss. However, this invention takes a different approach, introducing it at a significant amount of 4-12 parts, and combining it with a substantially increased amount of hard kaolin (10-20 parts) and silica micropowder (10-30 parts) to jointly construct a "high refractoriness framework." This framework possesses extremely strong chemical and thermal stability, offsetting or even eliminating the negative effects of fluxing components that may be present in the color base of each glaze, ensuring that even with the addition of high-content colorants (6-10 parts), the initial melting temperature of the glaze remains stably maintained above 1170℃.

[0019] 3. The formulation system of this invention is compatible with various color bases such as green, yellow, and red, and can achieve excellent glaze surfaces with uniform color and normal body-glaze bonding. This provides a unified and reliable glaze technology platform for producing high-end electrical porcelain products with different appearance requirements, avoiding the tedious work of developing high refractoriness formulations separately for each color.

[0020] 4. In this invention, in addition to playing a role in stabilizing the skeleton, the α-alumina micro powder also works in combination with the high silica glass formed by the silica micro powder in the later stage of firing, which greatly improves the hardness, wear resistance and overall mechanical strength of the glaze, and realizes the sequential effect of "first degassing and densification, then enhanced reaction".

[0021] 5. In the preparation method of the present invention, a strict "melting temperature test" step is set to ensure that the glaze with high refractoriness and an initial melting temperature of above 1170℃ serves as a quality gate before the glaze slurry flows into the next process. This can effectively prevent batch quality problems caused by abnormal situations such as incorrect material preparation, and ensure the stability of the production process and the product yield. Attached Figure Description

[0022] Figure 1 This is a flowchart illustrating the manufacturing process of an electrical porcelain product according to an embodiment of the present invention. Detailed Implementation

[0023] The following detailed description illustrates the specific implementation method: An electric porcelain glaze for reducing the porosity of ceramic parts comprises, by weight parts: 4-10 parts high-clay, 3-10 parts calcium silicate micropowder, 1-5 parts high-temperature calcined liquid stone powder, 25-35 parts potassium microparticles, 10-30 parts silica micropowder, 10-20 parts hard kaolin, 4-12 parts α-alumina micropowder, 6-10 parts glaze color base, and 0.15-0.25 parts CMC. In this embodiment, the high-clay is Dongsheng high-clay.

[0024] In the preferred formula: The composition includes 6-8 parts of Dongsheng high clay, 7-9 parts of calcium silicate micro powder, 2-3 parts of high-temperature calcined liquid stone powder, 28-30 parts of potassium microcline, 20-25 parts of silica micro powder, 13-16 parts of hard kaolin, 6-9 parts of α-alumina micro powder, and CMC of 0.15-0.2 parts.

[0025] Preferably, the glaze color base is any one of green, yellow, or red color base, and the glaze color base is 6-8 parts.

[0026] In this embodiment, the green, red, and yellow color bases are all composed of stable crystals formed by pre-firing, differing only in the color-developing core minerals. These differences do not affect the physicochemical properties of the glaze. The specific formulation below in this embodiment uses the yellow color base as an example.

[0027] Combination Figure 1 This embodiment also provides a method for preparing an electric porcelain glaze that reduces the porosity of ceramic parts, including the following steps: Step 1: Formula Development and Screening: Design the color glaze formula, conduct small-scale and comparative tests, and perform melting temperature tests on the screened formulas. Select the formula with an initial melting temperature ≥1170℃ as the target formula; if the initial melting temperature is lower than 1170℃, it is considered unqualified and the formula needs to be readjusted. Step 2, Pilot Testing and Production: The raw materials weighed according to the target formula are added to a ball mill and ball milled to obtain a glaze slurry; the fineness of the glaze slurry is tested, and after the fineness is qualified, a melting temperature test is conducted; after the initial melting temperature obtained from the melting temperature test is qualified (that is, the initial melting temperature is ≥1170℃, and the initial melting temperature is also referred to as "refractory temperature" in this article), the glaze slurry is applied to the electric porcelain blank for glazing, and then the electric porcelain product is obtained after firing in a kiln.

[0028] In step two, to further ensure product quality, after the melting temperature test is qualified (i.e., the refractoriness test is qualified), a high-temperature fluidity test of the glaze is required before glazing. The high-temperature fluidity test requires the glaze to have a high-temperature fluidity of 45-55 mm to be considered qualified, with the preferred range being 50-53 mm.

[0029] In this embodiment, the standard for qualified fineness is: ≥90% of particles smaller than 20µm, and D 50 It is 4-6 μm.

[0030] To conduct performance testing on electrical porcelain products, product inspection is also carried out after firing. Product inspection includes electromechanical damage testing, impact resistance testing, and temperature cycling testing of electrical porcelain products.

[0031] To screen for the optimal formula, the inventors designed numerous exploratory experiments. The following are seven representative glaze formulas, with their specific compositions shown in Table 1. The preparation method was standardized as follows: weigh each component according to Table 1, add them to a ball mill, and ball mill for 15 hours to obtain a glaze slurry. Subsequently, various performance tests were conducted.

[0032] Table 1. Composition of electric porcelain glaze (parts by mass)

[0033] The specific requirements for the components in the above table are as follows: 1. Dongsheng high-clay clay requires a bonding strength of over 2.5 MPa, a hydration rate of over 60%, a silica content of over 50%, an alumina content of over 18%, and an iron oxide content of less than 2.5%. 2. The calcium silicate micro powder requires a calcium oxide content greater than 40%, a silicon dioxide content greater than 40%, an iron oxide content less than 1.5%, and a fineness of less than 15% residue on a 500-mesh sieve.

[0034] 3. The high-temperature calcined liquid stone powder must have a magnesium oxide content greater than 30%, a silicon dioxide content greater than 60%, and an iron oxide content less than 1.0%; 4. Potassium microcline requires a potassium oxide to sodium oxide content greater than 13%, an iron oxide content less than 0.7%, and a fineness of less than 15% residue on a 250-mesh sieve. 5. The silica powder must have a silica content greater than 99%, an iron oxide content less than 0.5%, and a fineness of less than 5% residue on a 250-mesh sieve. 6. Hard kaolin powder requires an alumina content greater than 30%, a silica content greater than 50%, an iron oxide content less than 1%, and a fineness of less than 15% residue on a 120-mesh sieve.

[0035] 7. The α-alumina micro powder requires an alumina content greater than 98%, an iron oxide content less than 0.5%, and a fineness of less than 1% residue on a 400-mesh sieve; 8. The glaze color base is yellow.

[0036] Formulas 1 to 3 are comparative examples, and formulas 4 to 7 are embodiments of the present invention.

[0037] The glaze slurry processing performance of the above formulation was tested, and the results are shown in Table 2.

[0038] Table 2 Glaze Slurry Processing Performance

[0039] Further tests were conducted on the glaze appearance, body-glaze bonding quality, refractoriness, and mechanical strength after firing. The results are shown in Tables 3 and 4.

[0040] Table 3. Information on glaze appearance, glaze-body bonding quality, refractoriness, etc.

[0041] Table 4 Mechanical Strength

[0042] Comparative analysis: Formula 1, used as a comparative example simulating conventional fine grinding, involves a large amount of plastic clay and lacks an effective refractory skeleton. It contains as much as 18 parts of Dongsheng high-quality clay and only 1 part of α-alumina micropowder, and no CMC is added. As shown in Table 2-4, due to the high clay content, this formula has the finest glaze fineness among all formulas under the same ball milling time, resulting in high relative viscosity and poor fluidity of the glaze slurry. After firing, the glaze layer is too thick (0.5 mm), leading to poor adhesion between the body and glaze, and surface cracking. With Formula 1, the refractoriness is only 1130℃, far below the threshold of 1170℃, ultimately resulting in a flexural strength of only 137 MPa for the high-strength material test strips.

[0043] Formula 2, as another comparative example, has a high content of silica fume (42 parts), which has high refractoriness, while the content of potassium microcline, the main flux, is relatively low (15 parts), and the amount of glaze color base is only 2 parts. Although the refractoriness reaches 1210℃, the high viscosity at high temperatures prevents the glaze from flowing and spreading sufficiently, resulting in an excessively thin glaze layer and insufficient formation of the intermediate layer between the body and glaze. This leads to glaze peeling and uneven color. This indicates that the accumulation of a single high-refractory component can disrupt the normal formation of the glaze and the bonding between the body and glaze.

[0044] Formula 3 uses 2 parts of α-alumina micro powder, and has a refractoriness of 1160℃, which is close to but does not reach 1170℃.

[0045] Formulas 4 to 7 increase the α-alumina micropowder to 6-9 parts and form a better ratio with Dongsheng high-clay (6-8 parts) and potassium microcline (28-30 parts), constructing a high-refractory skeleton with stable refractoriness at 1190℃-1202℃, creating a generous "time window" for air removal in the green body. This results in a product with uniform color and normal body-glaze bonding.

[0046] In formulations 4 to 7, especially formulation 4, the high-strength material specimens exhibit a flexural strength as high as 200 MPa, which is 46% higher than the 137 MPa of formulation 1. Formulations 5 to 4.3 also maintain a stable high level of 195-198 MPa.

[0047] To comprehensively evaluate the actual effect of this invention on high-voltage electrical porcelain products, formula 4 was used to produce electrical porcelain products. The glaze of formula 4 was applied to the porcelain blank to obtain a 160kN product. It was compared with the 160kN product obtained by applying yellow glaze in the prior art. The measured performance indicators are shown in Table 5 below. The yellow glaze applied to the porcelain blank in the prior art is a commonly used yellow glaze. The formula of the yellow glaze in the prior art is: 20-24 parts potassium feldspar, 6-10 parts sodium feldspar, 13-17 parts quartz powder, 5-7 parts Gulin clay, 3-7 parts Jiangjin clay, 4-8 parts limestone, 3-7 parts calcined talc, 11-15 parts Huatao ceramic powder, and 2-4 parts colorant. The initial melting temperature of the glaze in the prior art formula is 1145℃.

[0048] Table 5 Comprehensive Comparison of Final Product Performance

[0049] Note: The electromechanical failure test applied voltage in the table is 45kV, and the judgment criteria for the electromechanical failure test shall be implemented in accordance with GB / T 1001.1; The temperature cycling test has a temperature difference of ≥70℃. After three cycles and 90 minutes, the sample is not damaged. The impact withstand test requires that the product withstand a breakdown voltage higher than 392kV without breaking down; The porosity test was performed by taking a ceramic block from the sample after the electromechanical destructive test and keeping it under a pressure of 30 MPa for 6 hours. No permeation was observed. Radio interference tests at 10kV and 1MHz require interference voltage ≤50μV.

[0050] Table 5 shows that, while maintaining the same body strength, Formula 4 of the present invention increases the glaze strength by 35 MPa, the sand-coated strength by 25 MPa, and the electromechanical failure load by 29 kN. It also reduces the porosity of the ceramic part from 15% to 7%, and ensures that the produced product transforms from an unreliable state of "micro-red absorption," "48% breakdown," and "52% failure" to fully passing all stringent tests. This ultimately leads to a significant optimization of the radio interference level.

[0051] In summary, the glaze of the present invention not only improves the electromechanical strength and insulation performance of electrical porcelain products, but also effectively reduces the porosity of the porcelain parts, thus solving the problem of large performance dispersion of the products.

[0052] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. An electric porcelain glaze for reducing the porosity of ceramic parts, characterized in that, According to the mass fractions, it includes: 4-10 parts high clay, 3-10 parts calcium silicate micro powder, 1-5 parts high-temperature calcined liquid stone powder, 25-35 parts potassium microcline, 10-30 parts silica micro powder, 10-20 parts hard kaolin, 4-12 parts α-alumina micro powder, 6-10 parts glaze color base, and 0.15-0.25 parts CMC.

2. The electric porcelain glaze for reducing the porosity of ceramic parts according to claim 1, characterized in that: The high-clay clay is 6-8 parts.

3. The electric porcelain glaze for reducing the porosity of ceramic parts according to claim 1, characterized in that: The calcium silicate micro powder consists of 7-9 parts, the silicon micro powder consists of 20-25 parts, and the α-alumina micro powder consists of 6-9 parts.

4. The electric porcelain glaze for reducing the porosity of ceramic parts according to claim 3, characterized in that: The hard kaolin clay is 13-16 parts.

5. The electric porcelain glaze for reducing the porosity of ceramic parts according to claim 1, characterized in that: The high-temperature calcined liquid stone powder consists of 2-3 parts, and the potassium microcline consists of 28-30 parts.

6. The electric porcelain glaze for reducing the porosity of ceramic parts according to claim 1, characterized in that: The glaze color base is any one of green, yellow, or red.

7. A method for preparing an electric porcelain glaze that reduces the porosity of ceramic parts, characterized in that, Includes the following steps: Step 1: Formula Development and Screening: Design the color glaze formula, conduct small-scale and comparative tests, and perform melting temperature tests on the screened formulas. Select the formula with an initial melting temperature ≥1170℃ as the target formula; if the melting temperature is lower than 1170℃, it is considered unqualified and the formula needs to be readjusted. Step 2, Pilot Testing and Production: Weigh the raw materials according to the target formula and add them to a ball mill to obtain a glaze slurry; test the fineness of the glaze slurry, and after the fineness is qualified, conduct a melting temperature test; after the initial melting temperature obtained from the melting temperature test is qualified, apply the glaze slurry to the electric porcelain blank for glazing, and then fire it to obtain the electric porcelain product.

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