Preparation method of silicon carbide ceramic ball

Abstract

The invention provides a silicon carbide ceramic ball preparation method, and belongs to the technical field of silicon carbide ceramic ball preparation, and the method comprises the following steps: preparing a matrix material, and preparing a silicon carbide green body ball through a method of combining low-pressure mold pressing pre-pressing and isostatic pressing final pressing; the preparation method comprises the following specific steps: (1) preparing granulation powder; (2) mold pressing and pre-pressing forming; (3) preparing an isostatic pressing auxiliary tool; (4) vacuumizing and sealing; (5) isostatic compaction; (6) sintering; and (7) post-processing. By utilizing an integrated innovative process, the preparation process of the high-performance silicon carbide ceramic ball is simplified, the production efficiency of the high-performance silicon carbide ceramic ball is improved, the yield is improved, the production cost is reduced, and the preparation method is particularly suitable for preparing the high-performance silicon carbide ceramic ball.

Description

Technical Field

[0001] The invention relates to the technical field of silicon carbide ceramic ball preparation, and in particular to a method for preparing a silicon carbide ceramic ball. Background Art

[0002] Silicon carbide ceramics have excellent properties such as high hardness, high strength, high temperature resistance, oxidation resistance, corrosion resistance, wear resistance, thermal shock resistance, and good chemical stability, making them an ideal material for preparing high-energy ceramic balls. Ceramic balls prepared using the excellent properties of silicon carbide ceramics have better performance than traditional metal balls and plastic balls, and are particularly suitable for harsh industrial and mining conditions such as strong corrosion, high speed, heavy load, and high temperature.

[0003] However, silicon carbide ceramics are hard and brittle, and are difficult to process. The sintered ceramic balls are hard and brittle, and can only be post-processed through grinding and polishing processes to achieve the required size and precision. This is not only time-consuming and labor-intensive, but also expensive, far higher than the material cost. Therefore, it is necessary to choose the appropriate molding and sintering methods to ensure product quality, improve production efficiency, reduce production costs, and improve product market competitiveness. At present, the commonly used molding methods for silicon carbide ceramic balls are mainly molding, isostatic pressing, and turning.

[0004] Although the molding method has high molding efficiency, it is generally only suitable for the preparation of ceramic balls with a diameter of less than 30mm. Since a large molding pressure needs to be applied, a ring band of a certain height will generally be formed, resulting in poor roundness of the green ceramic ball. Moreover, the greater the molding pressure, the greater the ring band height, the worse the roundness of the green ball, resulting in a larger processing volume and lower processing efficiency of the ceramic ball after sintering. In addition, the consistency and uniformity of the ceramic balls produced by the molding method are poor. Generally, the density at the crown of the green ball is greater than that at the ring band, resulting in large differences in strength and hardness at different positions of the ceramic ball. Moreover, the strength, hardness and other properties of the ceramic balls produced by the molding method are also relatively low, making them unsuitable as high-performance ceramic bearing balls.

[0005] Isostatic pressing can prepare ceramic balls of various specifications, and the consistency and uniformity of the ceramic balls are good, and the strength, hardness and other properties are also high, which is particularly suitable for preparing high-performance ceramic balls. This method generally first loads the powder into a flexible mold and then isostatically presses it. Smaller ceramic balls generally adopt the "one mold and multiple balls" loading method (such as patent CN202280050744.7), and larger ceramic balls (diameter greater than 30mm) generally adopt the "one mold and one ball" loading method. On the one hand, the isostatic pressing method has low loading efficiency, especially the "one mold and one ball" process, which requires many molds, and each mold needs to be separately loaded with powder, sealed, vacuumed, and isostatically pressed. Moreover, the process is relatively complex and not easy to realize automation, resulting in low production efficiency, high labor cost, and high production cost; on the other hand, the shape of the green body is easily affected by the mold design and manufacturing level, the number of mold uses, and the powder filling technology, resulting in large differences in the shape and size of the green body ball. In addition, although the performance of isostatically pressed ceramic balls is better, the roundness of the ceramic ball green body is generally poor, whether it is one ball per mold or multiple balls per mold, and the workload of post-processing is large.

[0006] The turning method is to turn the pressed (dry pressing or cold isostatic pressing) material rod into a green body of suitable size as required. This method can produce green balls with good roundness and less post-processing work after sintering, but it is easy to introduce microcracks or cracks during the turning process. The cracking of the green body causes the green ball to be scrapped, reducing the qualified rate of the ceramic ball. The microcracks in the green body are difficult to find in the green body inspection, but they will be further amplified during the sintering process, resulting in relatively obvious surface microcracks, surface cracks or internal cracks in the ceramic ball after sintering. The surface microcracks and cracks cause the ceramic ball to be scrapped after sintering, which not only increases the sintering cost, but also further reduces the qualified rate of the ceramic ball. The internal cracks of the ceramic ball after sintering cannot be detected by the naked eye. Some of them cause the ceramic ball to crack and be scrapped during the grinding and polishing process, which not only increases the grinding and polishing processing cost, but also further reduces the qualified rate of the ceramic ball. If the dark cracks that have been left until the end are not detected before delivery, it will leave hidden dangers and reduce the reliability of the product service. Summary of the invention

[0007] The object of the present invention is to provide a method for preparing a silicon carbide ceramic ball to solve the problems raised in the above background technology.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] A method for preparing a silicon carbide ceramic ball, characterized in that the matrix material for preparing the silicon carbide ceramic ball comprises, by weight: 100 parts of silicon carbide micropowder, 0.5-3 parts of boron carbide micropowder, 5-15 parts of an adhesive, 0.5-3 parts of a surfactant, and 0.5-2 parts of a dispersant;

[0010] The specific preparation method comprises the following steps:

[0011] (1) Preparation of granulated powder

[0012] Weigh the above matrix material, add deionized water, the amount of deionized water is 0.9-1.5 times the mass of silicon carbide micropowder, and then ball mill for 8-20 hours to obtain silicon carbide ceramic slurry; then spray granulate the silicon carbide ceramic slurry to obtain granulated powder, and sieve the final granulated powder, the moisture content of the granulated powder is 0.8-1.5%, and the mass ratio of the particle size of 60-180 mesh in the granulated powder is greater than 90%;

[0013] (2) Pre-molding

[0014] Weigh the granulated powder in step (1), put it into a spherical mold, and press it into a silicon carbide green ball at a pressure of 10-30 MPa; the pressed silicon carbide green ball has a certain strength and will not loosen when moving, so as to reduce the unevenness of the silicon carbide green ball caused by molding and improve the roundness of the silicon carbide green ball;

[0015] (3) Preparation of isostatic pressing auxiliary tooling

[0016] A plurality of cylindrical holes are processed on the PE foam, the thickness of the foam is 0.1-0.3 times the diameter of the silicon carbide green ball, the diameter of the cylindrical hole is 0.5-0.9 times the diameter of the silicon carbide green ball, and the center distance between two adjacent holes is 1.2-1.5 times the diameter of the silicon carbide green ball;

[0017] (4) Vacuum sealing

[0018] The auxiliary tooling prepared in step (3) is placed on a smooth flat support plate, and then the silicon carbide green ball pressed in step (2) is placed into the cylindrical hole of the auxiliary tooling, and the auxiliary tooling and the silicon carbide green ball are sent into a sealed bag using the flat support plate, and then the flat support plate is pulled out, and the sealed bag is evacuated and sealed using a vacuum sealer;

[0019] (5) Isostatic Pressing

[0020] The sealed bag vacuum-sealed in step (4) is placed in a cold isostatic press and maintained at 180-250 MPa for 5-30 minutes. After the pressure is maintained, the sealed bag is opened, the isostatically pressed silicon carbide green ball is taken out, and it is dried at 50-80° C. for 1-5 hours to avoid cracking caused by rapid volatilization of water during sintering. The density of the dried silicon carbide green ball is not less than 1.7 g / cm 3 ;

[0021] (6) Sintering

[0022] The silicon carbide green ball dried in step (5) is rolled in boron nitride powder to make a thin layer of boron nitride adhere to its surface to prevent the silicon carbide green ball from sticking during sintering, and then placed in a vacuum sintering furnace and sintered at 2100-2200° C. for 1-7 hours to obtain a sintered silicon carbide ceramic ball;

[0023] (7) Post-processing

[0024] The silicon carbide ceramic ball sintered body is processed after grinding and polishing to obtain the silicon carbide ceramic ball of required specifications.

[0025] Preferably, in step (1), the D of the silicon carbide powder is 50 The D of the boron carbide powder is 0.5±0.2μm. 50 1.50±1μm.

[0026] Preferably, in step (1), the adhesive is phenolic resin, polyvinyl alcohol or carboxymethyl cellulose; the surfactant is stearic acid or fatty acid glyceride; and the dispersant is tetramethylammonium hydroxide or polyacrylic acid.

[0027] Preferably, in step (2), the density of the pre-pressed silicon carbide green ball is controlled to be 1.4-1.5 g / cm 3 .

[0028] Preferably, in step (4), the flat pallet is made of high-strength material, so that it can carry a large weight with a small thickness.

[0029] Preferably, the flat pallet is made of stainless steel, wood or engineering plastic.

[0030] Preferably, in step (4), the sealed bag is a commercially available vacuum sealed bag.

[0031] Preferably, the commercially available vacuum sealing bag is a heat-sealed plastic bag or a heat-sealed aluminum-plastic composite bag.

[0032] The beneficial effects of the above technical solution of the present invention are as follows:

[0033] 1. The present invention adopts a method combining low-pressure pre-pressing with isostatic final pressing to prepare silicon carbide green balls. Low-pressure pre-pressing improves the performance uniformity, roundness and dimensional consistency of the green balls, reduces the amount of post-processing of the sintered body, and has the advantages of high automation and high production efficiency; isostatic final pressing further improves the uniformity, consistency, hardness, strength and other properties of the green balls. This method combines the advantages of the two molding methods, solves the problems of poor roundness, poor consistency and low performance of single molding, and also solves the problems of poor roundness, low production efficiency and high cost of flexible molds of single isostatic pressing.

[0034] 2. The present invention adopts perforated PE foam as auxiliary isostatic pressing tooling, which can limit the silicon carbide green balls and prevent the silicon carbide green balls from shifting during the movement, vacuum sealing and isostatic pressing processes, thereby preventing the green balls from breaking, deforming, stacking and other problems. It can also improve the production efficiency and pass rate of isostatically pressed silicon carbide green balls.

[0035] 3. Compared with the conventional process of loading materials into flexible molds, bagging, vacuum sealing and then isostatic pressing, the present invention adopts direct bagging, vacuum sealing and then isostatic pressing to prepare silicon carbide ceramic balls. The process is simpler, the production efficiency is higher, and the expensive flexible mold costs are saved.

[0036] 4. Before sintering, the silicon carbide green ball is rolled in boron nitride powder so that a thin layer of boron nitride adheres to its surface, thereby avoiding the problem of silicon carbide ceramic balls being scrapped due to adhesion of the silicon carbide green ball during sintering.

[0037] 5. The present invention utilizes an integrated innovative process to simplify the preparation process of high-performance silicon carbide ceramic balls, improves its production efficiency, increases the yield rate, and reduces production costs, and is particularly suitable for preparing high-performance ceramic balls. DETAILED DESCRIPTION

[0038] Example:

[0039] A method for preparing a silicon carbide ceramic ball. The matrix material for preparing the silicon carbide ceramic ball comprises, by weight, 100 parts of silicon carbide micropowder, 0.5-3 parts of boron carbide micropowder, 5-15 parts of an adhesive, 0.5-3 parts of a surfactant and 0.5-2 parts of a dispersant.

[0040] The specific preparation method comprises the following steps:

[0041] (1) Preparation of granulated powder

[0042] The matrix material is weighed, deionized water is added in an amount of 0.9-1.5 times the mass of the silicon carbide micropowder, and then ball milled for 8-20 hours to obtain silicon carbide ceramic slurry; the silicon carbide ceramic slurry is spray granulated to obtain granulated powder, and the final granulated powder is sieved, the moisture content of the granulated powder is 0.8-1.5%, and the mass ratio of the particle size of 60-180 mesh in the granulated powder is greater than 90%.

[0043] (2) Pre-molding

[0044] The granulated powder in step (1) is weighed, loaded into a spherical mold, and pressed into a silicon carbide green ball at a pressure of 10-30 MPa; the pressed silicon carbide green ball has a certain strength and will not loosen when moved, so as to reduce the unevenness of the silicon carbide green ball caused by molding and improve the roundness of the silicon carbide green ball.

[0045] (3) Preparation of isostatic pressing auxiliary tooling

[0046] Several cylindrical holes are processed on the PE foam cotton, the thickness of the foam cotton is 0.1-0.3 times the diameter of the silicon carbide green ball, the diameter of the cylindrical hole is 0.5-0.9 times the diameter of the silicon carbide green ball, and the center distance between two adjacent holes is 1.2-1.5 times the diameter of the silicon carbide green ball.

[0047] On the premise of meeting the above requirements, the number of cylindrical holes processed on the PE foam should be as large as possible to increase the loading capacity of the silicon carbide green balls and improve production efficiency; the prepared auxiliary tooling is used to position the silicon carbide green balls to prevent the silicon carbide green balls from rolling during movement or vacuuming, resulting in uneven positioning, adhesion, etc.

[0048] (4) Vacuum sealing

[0049] Place the auxiliary tooling prepared in step (3) on a smooth flat pallet, then place the silicon carbide green ball pressed in step (2) into the cylindrical hole of the auxiliary tooling, use the flat pallet to send the auxiliary tooling and the silicon carbide green ball into a sealed bag, then remove the flat pallet, and use a vacuum sealer to evacuate the sealed bag and seal it.

[0050] The surface of the flat support plate remains smooth, and after the auxiliary tooling and the silicon carbide green ball are placed into the sealing bag, they can be easily withdrawn without affecting the position of the silicon carbide green ball on the auxiliary tooling and without damaging the silicon carbide green ball and the sealing bag.

[0051] (5) Isostatic Pressing

[0052] The sealed bag vacuum-sealed in step (4) is placed in a cold isostatic press and maintained at 180-250 MPa for 5-30 minutes. After the pressure is maintained, the sealed bag is opened, the isostatically pressed silicon carbide green ball is taken out, and it is dried at 50-80° C. for 1-5 hours to avoid cracking caused by rapid volatilization of water during sintering. The density of the dried silicon carbide green ball is not less than 1.7 g / cm 3 ;

[0053] (6) Sintering

[0054] The silicon carbide green ball dried in step (5) is rolled in boron nitride powder to make a thin layer of boron nitride adhere to its surface to prevent the silicon carbide green ball from sticking during sintering, and then placed in a vacuum sintering furnace and sintered at 2100-2200° C. for 1-7 hours to obtain a sintered silicon carbide ceramic ball;

[0055] (7) Post-processing

[0056] The silicon carbide ceramic ball sintered body is processed after grinding and polishing to obtain the silicon carbide ceramic ball of required specifications.

[0057] In step (1), the D of silicon carbide powder is 50 The D of boron carbide powder is 0.5±0.2μm. 50 The particle size is 1.50±1μm; the adhesive is phenolic resin, polyvinyl alcohol or carboxymethyl cellulose, the surfactant is stearic acid or fatty acid glyceride, and the dispersant is tetramethylammonium hydroxide or polyacrylic acid.

[0058] In step (2), the density of the pre-pressed silicon carbide green ball is controlled to be 1.4-1.5 g / cm 3 .

[0059] In step (4), the flat tray is made of high-strength material, such as stainless steel, wood or engineering plastic, so that it can carry a large weight with a small thickness, and the auxiliary tooling carrying the silicon carbide green balls can be stably delivered into the sealed bag; the sealed bag is a commercially available vacuum sealed bag, such as a heat-sealed plastic bag or a heat-sealed aluminum-plastic composite bag.

[0060] Embodiment 1:

[0061] Silicon carbide ceramic balls are prepared according to the above preparation method, wherein in step (1), the matrix materials are weighed, and the weight ratio is as follows: 100 parts of silicon carbide powder, 0.8 parts of boron carbide powder, 8 parts of phenolic resin, 0.5 parts of stearic acid, and 0.5 parts of tetramethylammonium hydroxide;

[0062] The matrix material was added to 100 parts of deionized water, ball-milled in a drum ball mill for 10 hours, and then spray-granulated in a centrifugal spray tower to obtain granulated powder;

[0063] The moisture content of the granulated powder was measured to be 1.0%, and the mass ratio of the granulated powder with a particle size of 60-180 mesh was 92.8%.

[0064] In step (2), the silicon carbide green ball is pressed with a pre-pressing pressure of 15 MPa, and the diameter of the silicon carbide green ball is measured to be 35 mm, and the volume density is 1.42 g / cm 3 .

[0065] In step (3), the size of the PE foam is selected to be 300×200×4 mm, the diameter of the processed cylindrical hole is 18 mm, and the center distance between two adjacent holes is 43 mm.

[0066] In step (4), the flat support plate is made of stainless steel, and the sealing bag is an aluminum-plastic composite sealing bag.

[0067] In step (5), a cold isostatic press is used for isostatic pressing, and the pressure is maintained at 200 MPa for 10 minutes. Then, the isostatically pressed silicon carbide ceramic ball is dried at 55°C for 3 hours. The volume density of the dried silicon carbide ceramic ball green body is measured to be 1.85 g / cm 3 .

[0068] In step (6), the dried silicon carbide ceramic ball green body is placed in a vacuum sintering furnace and sintered at 2120°C for 4 hours to obtain a silicon carbide ceramic ball sintered body. The maximum diameter of the silicon carbide ceramic ball sintered body is measured to be 26.3 mm, the minimum diameter is 26.1 mm, and the relative error is 0.77%.

[0069] In step (7), the silicon carbide ceramic ball sintered body is ground and polished to obtain a silicon carbide ceramic ball of required specifications.

[0070] After testing, the relative density of the obtained silicon carbide ceramic ball is 98.8%, and the Vickers microhardness is 26.2 GPa.

[0071] Embodiment 2:

[0072] Silicon carbide ceramic balls are prepared according to the above preparation method, wherein in step (1), the matrix materials are weighed, and the weight ratio is as follows: 100 parts of silicon carbide powder, 1 part of boron carbide powder, 9 parts of phenolic resin, 0.5 parts of stearic acid, and 0.5 parts of tetramethylammonium hydroxide;

[0073] The above matrix material was added to 105 parts of deionized water, ball-milled in a drum ball mill for 9 hours, and then spray-granulated using a centrifugal spray tower to obtain granulated powder;

[0074] The moisture content of the granulated powder was measured to be 1.05%, and the mass ratio of the particle size of 60-180 mesh in the granulated powder was 93.2%.

[0075] In step (2), the silicon carbide green ball is pressed with a pre-pressing pressure of 20 MPa, and the diameter of the silicon carbide green ball is measured to be 50 mm, and the volume density is 1.44 g / cm 3 .

[0076] In step (3), the size of the PE foam is selected to be 500×300×5.5 mm, the diameter of the processed cylindrical hole is 30 mm, and the center distance between two adjacent holes is 65 mm.

[0077] In step (4), the flat support plate is made of stainless steel, and the sealing bag is an aluminum-plastic composite sealing bag.

[0078] In step (5), a cold isostatic press is used for isostatic pressing, and the pressure is maintained at 220 MPa for 8 minutes. Then, the isostatically pressed silicon carbide ceramic ball is dried at 55°C for 4 hours. The volume density of the dried silicon carbide ceramic ball green body is measured to be 1.86 g / cm 3 .

[0079] In step (6), the dried silicon carbide ceramic ball green body is placed in a vacuum sintering furnace and sintered at 2150°C for 4 hours to obtain a silicon carbide ceramic ball sintered body. The maximum diameter of the silicon carbide ceramic ball sintered body is measured to be 37.7 mm, the minimum diameter is 37.4 mm, and the relative error is 0.80%.

[0080] In step (7), the silicon carbide ceramic ball sintered body is ground and polished to obtain a silicon carbide ceramic ball of required specifications.

[0081] After testing, the relative density of the obtained silicon carbide ceramic ball is 99.1%, and the Vickers microhardness is 26.5 GPa.

[0082] Example 3

[0083] Silicon carbide ceramic balls are prepared according to the above preparation method, wherein in step (1), the matrix materials are weighed, and the weight ratio is as follows: 100 parts of silicon carbide powder, 1.2 parts of boron carbide powder, 10 parts of phenolic resin, 2 parts of stearic acid, and 1.5 parts of tetramethylammonium hydroxide;

[0084] The matrix material was added to 110 parts of deionized water, ball-milled in a drum ball mill for 10 hours, and then spray-granulated in a centrifugal spray tower to obtain granulated powder;

[0085] The moisture content of the granulated powder was measured to be 1.2%, and the mass ratio of the granulated powder with a particle size of 60-180 mesh was 93.5%.

[0086] In step (2), the silicon carbide green ball is pressed with a pre-pressing pressure of 25 MPa, and the diameter of the silicon carbide green ball is measured to be 50 mm, and the volume density is 1.48 g / cm 3 .

[0087] In step (3), the size of the PE foam is selected to be 600×400×5.5 mm, the diameter of the processed cylindrical hole is 36 mm, and the center distance between two adjacent holes is 65 mm.

[0088] In step (4), the flat support plate is made of stainless steel, and the sealing bag is an aluminum-plastic composite sealing bag.

[0089] In step (5), a cold isostatic press is used for isostatic pressing, and the pressure is maintained at 250 MPa for 5 minutes. Then, the isostatically pressed silicon carbide ceramic ball is dried at 50° C. for 5 hours. The volume density of the dried silicon carbide ceramic ball green body is measured to be 1.88 g / cm 3 .

[0090] In step (6), the dried silicon carbide ceramic ball green body is placed in a vacuum sintering furnace and sintered at 2160°C for 5 hours to obtain a silicon carbide ceramic ball sintered body. The maximum diameter of the silicon carbide ceramic ball sintered body is measured to be 37.8 mm, the minimum diameter is 37.6 mm, and the relative error is 0.53%.

[0091] In step (7), the silicon carbide ceramic ball sintered body is ground and polished to obtain a silicon carbide ceramic ball of required specifications.

[0092] After testing, the relative density of the obtained silicon carbide ceramic ball is 99.3%, and the Vickers microhardness is 27.5 GPa.

[0093] Comparative Example 1:

[0094] The difference between this comparative example and Example 1 is that isostatic pressing is not performed, and only the molding method is used to produce silicon carbide ceramic balls, and the preparation method thereof is as follows:

[0095] The granulated powder in Example 1 was weighed and loaded into a spherical mold, and a silicon carbide green ball was pressed with a pressure of 200 MPa. The obtained silicon carbide green ball was a spherical ball with an annular zone. The maximum size of the green ball was 38.5 mm (in the height direction of the annular zone) and the minimum size was 35 mm.

[0096] The silicon carbide green ball was dried at 50°C for 5 hours, and its volume density after drying was measured to be 1.84 g / cm 3 .

[0097] The dried silicon carbide green ball was rolled in boron nitride powder to adhere a thin layer of boron nitride on its surface, and then sintered at 2120°C for 4 hours to obtain a silicon carbide ceramic ball sintered body. The maximum size of the silicon carbide ceramic ball sintered body was measured to be 31.2mm, the minimum diameter was 28.8mm, and the relative error was 8.33%.

[0098] The silicon carbide ceramic ball sintered body is processed by grinding and polishing to obtain a silicon carbide ceramic ball of required specifications; after testing, the relative density of the obtained silicon carbide ceramic ball is 98.6%, and the Vickers microhardness is 25.7 GPa.

[0099] The relative error of the diameter of the sintered body of silicon carbide ceramic balls obtained by this preparation method is relatively large, resulting in an increase in the amount of post-processing, a large amount of waste of raw materials, and low production efficiency.

[0100] Comparative Example 2:

[0101] The difference between this comparative example and Example 1 is that the pre-pressing is not performed by molding, the isostatic pressing auxiliary tooling is not processed, and the isostatic pressing auxiliary tooling is not used during isostatic pressing. The isostatic pressing is performed directly by using a flexible mold, and each flexible mold forms one green ball at a time. The preparation method is as follows:

[0102] The granulated powder in Example 1 was weighed and loaded into a flexible mold, which was then placed in a cold isostatic press and maintained at 200 MPa for 10 minutes to obtain a silicon carbide green ball. The green ball diameter was measured to be 40 mm.

[0103] The silicon carbide green ball was dried at 50°C for 5 hours, and its volume density after drying was measured to be 1.85 g / cm 3 .

[0104] The dried silicon carbide green ball was rolled in boron nitride powder to adhere a thin layer of boron nitride on its surface, and then sintered at 2120°C for 4 hours to obtain a silicon carbide ceramic ball sintered body. The maximum diameter of the silicon carbide ceramic ball sintered body was measured to be 33.1 mm, the minimum diameter was 32.8 mm, and the relative error was 0.91%.

[0105] The silicon carbide ceramic ball sintered body is processed by grinding and polishing to obtain a silicon carbide ceramic ball of required specifications; after testing, the relative density of the obtained silicon carbide ceramic ball is 98.8%, and the Vickers microhardness is 26.3 GPa.

[0106] The relative error of the diameter of the product obtained by this preparation method is slightly larger than that of Example 1, and the amount of post-processing will increase slightly; in addition, the price of the flexible mold is relatively high, and only one silicon carbide green ball can be formed at a time, so its production efficiency is low and the labor cost is high.

[0107] Comparative Example 3:

[0108] The technical solution refers to Example 1.

[0109] The difference is that the isostatic pressing auxiliary tooling is not processed, the isostatic pressing auxiliary tooling is not used during isostatic pressing, and the silicon carbide green balls pre-pressed in step (2) are directly loaded into the aluminum-plastic composite sealing bag, and only one is loaded into each aluminum-plastic composite sealing bag.

[0110] The rest is the same as Example 1.

[0111] After testing, the maximum diameter of the sintered silicon carbide ceramic ball is 26.3mm, the minimum diameter is 26.0mm, and the relative error is 0.77%. After grinding and polishing, the sintered silicon carbide ceramic ball has a relative density of 98.8% and a Vickers microhardness of 26.2GPa.

[0112] The performance of the product prepared by this preparation method is basically similar to that of Example 1. However, it was found in production that: this process reduces the utilization rate of the aluminum-plastic composite sealed bag. Although the method of reducing the size of the aluminum-plastic composite sealed bag to match the green ball can be adopted, the average single ball cost of the aluminum-plastic composite sealed bag is significantly increased; in addition, this process increases the number and time of isostatic pressing bagging and sealing, resulting in a significant reduction in production efficiency.

[0113] Comparative Example 4

[0114] The technical solution refers to Example 1.

[0115] The difference is that the isostatic pressing auxiliary tooling is not processed, and the isostatic pressing auxiliary tooling is not used during isostatic pressing. The silicon carbide green balls pre-pressed in step (2) are directly loaded into the aluminum-plastic composite sealing bag, and each aluminum-plastic composite sealing bag is loaded with a plurality of pre-pressed silicon carbide green balls. The silicon carbide green balls are manually separated by a suitable distance and then vacuum-sealed.

[0116] The rest is the same as Example 1.

[0117] After testing, the maximum diameter of the sintered silicon carbide ceramic ball is 26.4mm, the minimum diameter is 26.1mm, and the relative error is 1.15%. After grinding and polishing, the sintered silicon carbide ceramic ball has a relative density of 98.7% and a Vickers microhardness of 26.0GPa.

[0118] The performance of the product obtained by this preparation method is slightly worse than that of Example 1. In addition, it was found in production that: during the vacuum sealing process, the green balls are easily displaced, resulting in contact and damage between the green balls; the green balls that have not been displaced during the sealing process will still have some green balls displaced during the isostatic pressing process, resulting in several green balls being isostatically pressed together and causing serious damage; in addition, it is time-consuming to manually separate the green balls, and reliability and stability are not easy to ensure. As a result, the yield rate of green balls is reduced, and the production efficiency is also greatly reduced.

[0119] Result analysis: By comparing Example 1 with Comparative Examples 1-4, it can be seen that the technical solution of the present invention adopts low-pressure molding pre-pressing and isostatic pressing, and uses auxiliary tooling and sealing bags for final pressing during the isostatic pressing process to prepare silicon carbide green balls. This method can prepare multiple silicon carbide green balls at one time, and the prepared silicon carbide green balls have good uniformity and consistency, and the performance of the sintered body is superior. The relative error of the diameter of the sintered body of the silicon carbide green ball is small, which reduces the amount of post-processing, improves production efficiency, and reduces production costs.

[0120] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Other modifications or equivalent substitutions made to the technical solution of the present invention by ordinary technicians in the field should be included in the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for preparing a silicon carbide ceramic ball, characterized in that: The matrix material for preparing the silicon carbide ceramic ball includes, by weight: 100 parts of silicon carbide micropowder, 0.5-3 parts of boron carbide micropowder, 5-15 parts of adhesive, 0.5-3 parts of surfactant and 0.5-2 parts of dispersant; The specific preparation method comprises the following steps: (1) Preparation of granulated powder Weigh the above matrix material, add deionized water, the amount of deionized water is 0.9-1.5 times the mass of silicon carbide micropowder, and then ball mill for 8-20 hours to obtain silicon carbide ceramic slurry; then spray granulate the silicon carbide ceramic slurry to obtain granulated powder, and sieve the final granulated powder, the moisture content of the granulated powder is 0.8-1.5%, and the mass ratio of the particle size of 60-180 mesh in the granulated powder is greater than 90%; (2) Pre-molding Weigh the granulated powder in step (1), put it into a spherical mold, and press it into a silicon carbide green ball at a pressure of 10-30 MPa; the pressed silicon carbide green ball has a certain strength and will not loosen when moving, so as to reduce the unevenness of the silicon carbide green ball caused by molding and improve the roundness of the silicon carbide green ball; (3) Preparation of isostatic pressing auxiliary tooling A plurality of cylindrical holes are processed on the PE foam, the thickness of the foam is 0.1-0.3 times the diameter of the silicon carbide green ball, the diameter of the cylindrical hole is 0.5-0.9 times the diameter of the silicon carbide green ball, and the center distance between two adjacent holes is 1.2-1.5 times the diameter of the silicon carbide green ball; (4) Vacuum sealing The auxiliary tooling prepared in step (3) is placed on a smooth flat support plate, and then the silicon carbide green ball pressed in step (2) is placed into the cylindrical hole of the auxiliary tooling, and the auxiliary tooling and the silicon carbide green ball are sent into a sealed bag using the flat support plate, and then the flat support plate is pulled out, and the sealed bag is evacuated and sealed using a vacuum sealer; (5) Isostatic Pressing The sealed bag vacuum-sealed in step (4) is placed in a cold isostatic press and maintained at 180-250 MPa for 5-30 minutes. After the pressure is maintained, the sealed bag is opened, the isostatically pressed silicon carbide green ball is taken out, and it is dried at 50-80° C. for 1-5 hours to avoid cracking caused by rapid volatilization of water during sintering. The density of the dried silicon carbide green ball is not less than 1.7 g / cm 3 ; (6) Sintering The silicon carbide green ball dried in step (5) is rolled in boron nitride powder to make a thin layer of boron nitride adhere to its surface to prevent the silicon carbide green ball from sticking during sintering, and then placed in a vacuum sintering furnace and sintered at 2100-2200° C. for 1-7 hours to obtain a sintered silicon carbide ceramic ball; (7) Post-processing The silicon carbide ceramic ball sintered body is processed by grinding and polishing to obtain the silicon carbide ceramic ball of required specifications.

2. The method for preparing a silicon carbide ceramic ball according to claim 1, characterized in that: In step (1), the silicon carbide powder has a D 50 The D of the boron carbide powder is 0.5±0.2μm. 50 1.50±1μm.

3. The method for preparing a silicon carbide ceramic ball according to claim 1, characterized in that: In step (1), the adhesive is phenolic resin, polyvinyl alcohol or carboxymethyl cellulose; the surfactant is stearic acid or fatty acid glyceride; and the dispersant is tetramethylammonium hydroxide or polyacrylic acid.

4. The method for preparing a silicon carbide ceramic ball according to claim 1, characterized in that: In step (2), the density of the pre-pressed silicon carbide green ball is controlled to be 1.4-1.5 g / cm 3 .

5. The method for preparing a silicon carbide ceramic ball according to claim 1, characterized in that: In step (4), the flat pallet is made of high-strength material, which is convenient for carrying a large weight with a small thickness.

6. The method for preparing a silicon carbide ceramic ball according to claim 5, characterized in that: The flat tray is made of stainless steel, wood or engineering plastic.

7. The method for preparing a silicon carbide ceramic ball according to claim 1, characterized in that: In step (4), the sealed bag is a commercially available vacuum sealed bag.

8. The method for preparing a silicon carbide ceramic ball according to claim 7, characterized in that: The commercially available vacuum sealing bag is a heat-sealed plastic bag or a heat-sealed aluminum-plastic composite bag.