Roller kiln transmission uses pressureless sintered silicon carbide thick wall roller rod and its preparation method
Patent Information
- Application Number
- CN202610995688.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-07-06
- Publication Date
- 2026-09-15
AI Technical Summary
[0015] The beneficial effects of the pressureless sintered silicon carbide thick-walled rollers for roller kiln transmission and their preparation method provided by this invention are as follows: This invention provides a method for preparing pressureless sintered silicon carbide thick-walled rollers for roller kiln transmission. By preparing two types of clay with different compositions and combining them with bilayer co-extrusion molding and subsequent densification sintering, high-purity, high-density thick-walled rollers are manufactured. The core clay and surface clay, prepared from two different slurries respectively, are co-extruded using a bilayer composite extrusion die. During extrusion, both clays are in a relatively wet and plastic state, merging and extruding synchronously within the die, resulting in a continuous, tight, and seamless bond between the surface clay and the core clay in a wet state, avoiding the weak interface defects common in layered processes. In the subsequent pressureless sintering process, due to the pre-set differences in the composition of the two clay materials, their high-temperature sintering behaviors are different. The surface clay material tends to densify faster and the grain growth is suppressed, thus forming a fine-grained layer; while the core clay material allows the grains to grow moderately, forming a relatively coarse-grained layer, ultimately obtaining a silicon carbide thick-walled roller bar with a dense fine-grained outer layer, a coarse-grained inner layer, and overall high purity and high density.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of roller kiln technology, and in particular to a pressureless sintered silicon carbide thick-walled roller bar for roller kiln transmission and its preparation method. Background Technology
[0002] Roller kilns are high-temperature continuous firing equipment widely used in ceramics, lithium battery cathode materials, magnetic materials, and other fields. The rollers in their transmission system are the core components for carrying and conveying the green bodies. Under high-temperature conditions above 1200℃, the rollers need to possess excellent high-temperature strength, thermal shock resistance, wear resistance, and oxidation resistance. Silicon carbide ceramics, due to their high thermal conductivity, low thermal expansion, high hardness, and excellent high-temperature mechanical properties, have become the preferred material for manufacturing high-end rollers. Among them, pressureless sintered silicon carbide, compared to reaction-sintered silicon carbide, has a purer phase composition and higher high-temperature strength stability, making it particularly suitable for the harsh environment of ultra-high temperature roller kilns.
[0003] Currently, the main methods for preparing pressureless sintered silicon carbide rollers are extrusion molding and cold isostatic pressing. Extrusion molding is efficient and low-cost, suitable for continuous production of long-length tubes and rods. However, most extruded rollers in existing technologies have a homogeneous structure, and their key problems are: to obtain good extrusion molding performance, a large amount of organic binder is often required, resulting in high residual porosity and decreased density after sintering; if the powder particle size is refined to improve density, it will cause excessive sintering shrinkage and a reduced yield. Some technologies have attempted to use layered or multi-layer composite processes, but conventional layering methods usually combine two preformed blanks through physical bonding or secondary coating, resulting in insufficient interfacial bonding strength. This easily leads to defects such as delamination and cracking during drying or sintering, seriously affecting the service life and reliability of the rollers. In addition, existing silicon carbide rollers, in thick-walled specifications, struggle to achieve both surface densification and sufficient core sintering, resulting in poor overall mechanical properties. Summary of the Invention
[0004] This invention provides a pressureless sintered silicon carbide thick-walled roller for roller kiln transmission and its preparation method, in order to solve the problems mentioned in the background art.
[0005] This invention provides a method for preparing pressureless sintered silicon carbide thick-walled rollers for roller kiln transmission, comprising the following steps: S1: Prepare the core slurry and surface slurry; S2: Spray granulation is performed on the core slurry and the surface slurry to obtain core granulated powder and surface granulated powder respectively; S3: Mix the core granulation powder with organic additives and water to obtain core mud, and mix the surface granulation powder with organic additives and water to obtain surface mud. After obtaining the mud, knead and age it. S4: Using a double-layer composite extrusion die, the surface clay and core clay after kneading are extruded together to form a double-layer roller blank with the outer layer being surface clay and the inner layer being core clay. S5: Dry the roller blank; S6: The dried green blank is subjected to cold isostatic pressing; S7: The green blank after cold isostatic pressing is sintered without pressure in an inert atmosphere, and the roller bar is obtained after cooling.
[0006] Optionally, the core slurry in S1 comprises a first silicon carbide powder, boron carbide, phenolic resin, organic additives, and water; the surface slurry comprises a second silicon carbide powder, boron carbide, phenolic resin, organic additives, and water; the average particle size of the second silicon carbide powder is smaller than the average particle size of the first silicon carbide powder, and the mass percentage of boron carbide in the surface slurry is higher than the mass percentage of boron carbide in the core slurry.
[0007] Optionally, when preparing the core slurry and the surface slurry, the raw materials are put into a ball mill for stirring and ball milling, and the water volume is adjusted during ball milling so that the solid content of the slurry is 45%-55%.
[0008] Optionally, the D50 particle size of the first silicon carbide powder in S1 is 0.8-1.2 μm, and the D50 particle size of the second silicon carbide powder is 0.3-0.6 μm; the amount of boron carbide added in the core slurry is 0.2-0.5 wt% of the mass of the first silicon carbide powder, and the amount of boron carbide added in the surface slurry is 0.6-1.0 wt% of the mass of the second silicon carbide powder.
[0009] Optionally, the amount of phenolic resin added in S1 is 1-3 wt% of the corresponding silicon carbide powder mass, and the organic additives are polyvinyl alcohol and polyethylene glycol, with the amount of each polyvinyl alcohol and polyethylene glycol being 1-2 wt% of the corresponding silicon carbide powder mass.
[0010] Optionally, during granulation in S2, the core slurry and the surface slurry are spray-granulated at an inlet temperature of 210-220℃ and an atomizing disc speed of 8000-13000 r / min, respectively, to obtain a D50 of 50-200 μm and a bulk density of 0.8-1.2 g / cm³. 3 Core granulated powder and surface granulated powder.
[0011] Optionally, the organic additives in S3 are sodium carboxymethyl cellulose and polyethylene oxide; based on the mass of granulated powder, the amount of sodium carboxymethyl cellulose added is 3-6%, the amount of polyethylene oxide added is 1-1.5%, and the amount of water added is 14-16%.
[0012] Optionally, in S3, the vacuum degree of vacuum plowing is ≤-0.08MPa, the plowing is circulated 4-6 times, and cooling water at 12-16℃ is introduced; after plowing, the plow material is aged at 20-25℃ and 50-60% humidity for 24-48 hours.
[0013] Optionally, in S5, the drying process is as follows: first, the green blank is air-dried at 30-35℃ and 40-50% humidity for 48 hours, and then dried in an oven at a gradually increasing temperature to 150℃; in S6, the pressure of the cold isostatic pressing treatment is 100-200MPa, and the holding time is 5-15min; in S7, the temperature of the pressureless sintering is 2100-2200℃, and the holding time is 1-2h.
[0014] The present invention also provides a pressureless sintered silicon carbide thick-walled roller for roller kiln drive, which is prepared by the above-described method.
[0015] The beneficial effects of the pressureless sintered silicon carbide thick-walled rollers for roller kiln transmission and their preparation method provided by this invention are as follows: This invention provides a method for preparing pressureless sintered silicon carbide thick-walled rollers for roller kiln transmission. By preparing two types of clay with different compositions and combining them with bilayer co-extrusion molding and subsequent densification sintering, high-purity, high-density thick-walled rollers are manufactured. The core clay and surface clay, prepared from two different slurries respectively, are co-extruded using a bilayer composite extrusion die. During extrusion, both clays are in a relatively wet and plastic state, merging and extruding synchronously within the die, resulting in a continuous, tight, and seamless bond between the surface clay and the core clay in a wet state, avoiding the weak interface defects common in layered processes. In the subsequent pressureless sintering process, due to the pre-set differences in the composition of the two clay materials, their high-temperature sintering behaviors are different. The surface clay material tends to densify faster and the grain growth is suppressed, thus forming a fine-grained layer; while the core clay material allows the grains to grow moderately, forming a relatively coarse-grained layer, ultimately obtaining a silicon carbide thick-walled roller bar with a dense fine-grained outer layer, a coarse-grained inner layer, and overall high purity and high density. Detailed Implementation
[0016] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are also within the scope of protection of the present invention.
[0017] This invention provides a method for preparing pressureless sintered silicon carbide thick-walled rollers for roller kiln transmission, comprising the following steps: S1: Prepare the core slurry and surface slurry; S2: Spray granulation is performed on the core slurry and the surface slurry to obtain core granulated powder and surface granulated powder respectively; S3: Mix the core granulation powder with organic additives and water to obtain core mud, and mix the surface granulation powder with organic additives and water to obtain surface mud. After obtaining the mud, knead and age it. S4: Using a double-layer composite extrusion die, the surface clay and core clay after kneading are extruded together to form a double-layer roller blank with the outer layer being surface clay and the inner layer being core clay. S5: Dry the roller blank; S6: The dried green blank is subjected to cold isostatic pressing; S7: The green blank after cold isostatic pressing is sintered without pressure in an inert atmosphere, and the roller bar is obtained after cooling.
[0018] This invention provides a method for preparing pressureless sintered silicon carbide thick-walled rollers for roller kiln transmission. By preparing two types of clay with different compositions and combining them with bilayer co-extrusion molding and subsequent densification sintering, high-purity, high-density thick-walled rollers are manufactured. Core clay and surface clay, prepared from two different slurries, are co-extruded using a bilayer composite extrusion die. During extrusion, both clays are in a relatively wet and plastic state, converging and extruding synchronously within the die. This results in a continuous, tight, and seamless bond between the surface and core clays in a wet state, avoiding the weak interface defects common in laminated processes. In the subsequent pressureless sintering process, due to the pre-defined differences in the compositions of the two clays, their high-temperature sintering behaviors differ. The surface clay tends to densify more quickly, and grain growth is inhibited, forming a fine-grained layer; the core clay, on the other hand, allows for moderate grain growth, forming a relatively coarse-grained layer. Ultimately, a silicon carbide thick-walled roller with a dense, fine-grained outer layer, a coarse-grained inner layer, and overall high purity and high density is obtained.
[0019] Further, the core slurry in S1 comprises first silicon carbide powder, boron carbide, phenolic resin, organic additives, and water; the surface slurry comprises second silicon carbide powder, boron carbide, phenolic resin, organic additives, and water; the average particle size of the second silicon carbide powder is smaller than that of the first silicon carbide powder, and the mass percentage of boron carbide in the surface slurry is higher than that in the core slurry. Further, the D50 particle size of the first silicon carbide powder in S1 is 0.8-1.2 μm, and the D50 particle size of the second silicon carbide powder is 0.3-0.6 μm; the amount of boron carbide added to the core slurry is 0.2-0.5 wt% of the mass of the first silicon carbide powder, and the amount of boron carbide added to the surface slurry is 0.6-1.0 wt% of the mass of the second silicon carbide powder.
[0020] Both slurries consist of silicon carbide powder, boron carbide, phenolic resin, organic additives, and water. The main differences lie in the particle size of the silicon carbide powder and the amount of boron carbide used. The average particle size of the second silicon carbide powder is smaller than that of the first, meaning the silicon carbide powder used in the surface slurry is finer. This difference in particle size directly translates into a difference in sintering activity. Finer powder has a larger specific surface area and higher surface energy, resulting in a stronger thermodynamic driving force for densification at high temperatures. Therefore, under the same sintering regime, the surface material will densify earlier. Simultaneously, the boron carbide mass ratio in the surface slurry is higher than that in the core slurry. At a higher concentration, boron carbide can inhibit grain growth, resulting in finer grains in the surface rollers. Excess boron will segregate at the silicon carbide grain boundaries, producing a "solute dragging" effect, or precipitate nanoscale second-phase particles, producing a "Zener pinning" effect, thus strongly hindering grain boundary migration. Therefore, the higher boron carbide content in the surface layer endows it with strong inhibitory capabilities.
[0021] Furthermore, during the preparation of the core slurry and the surface slurry, the raw materials are fed into a ball mill for stirring and ball milling. During ball milling, the water volume is adjusted so that the solid content of the slurry is 45%-55%.
[0022] Furthermore, the amount of phenolic resin added in S1 is 1-3 wt% of the corresponding silicon carbide powder mass, and the organic additives are polyvinyl alcohol and polyethylene glycol, with each of the polyvinyl alcohol and polyethylene glycol added being 1-2 wt% of the corresponding silicon carbide powder mass.
[0023] Furthermore, during granulation in S2, the core slurry and the surface slurry are spray-granulated at an inlet temperature of 210-220℃ and an atomizing disc speed of 8000-13000 r / min, respectively, to obtain a D50 of 50-200 μm and a bulk density of 0.8-1.2 g / cm³. 3 Core granulated powder and surface granulated powder.
[0024] Furthermore, the organic additives in S3 are sodium carboxymethyl cellulose and polyethylene oxide; based on the mass of granulated powder, the amount of sodium carboxymethyl cellulose added is 3-6%, the amount of polyethylene oxide added is 1-1.5%, and the amount of water added is 14-16%. Among them, the viscosity of sodium carboxymethyl cellulose is 3000 mPa·s, and the molecular weight of polyethylene oxide is 3.5 million.
[0025] Furthermore, in S3, the vacuum degree of vacuum plowing is ≤-0.08MPa, the plowing is circulated 4-6 times, and cooling water at 12-16℃ is introduced; after plowing, the plow material is aged at 20-25℃ and 50-60% humidity for 24-48 hours.
[0026] Furthermore, in S5, the drying process is as follows: first, the green blank is air-dried at 30-35℃ and 40-50% humidity for 48 hours, and then dried in an oven at a gradually increasing temperature of 150℃; in S6, the pressure of the cold isostatic pressing treatment is 100-200MPa, and the holding time is 5-15min; in S7, the temperature of the pressureless sintering is 2100-2200℃, and the holding time is 1-2h.
[0027] The present invention also provides a pressureless sintered silicon carbide thick-walled roller for roller kiln drive, the roller being prepared by the above-described method.
[0028] The present invention will be further described in detail below with reference to specific embodiments.
[0029] Example 1
[0030] S1: Preparation of core and surface slurries: The core slurry consists of silicon carbide powder with a D50 particle size of 1 μm, boron carbide accounting for 0.3% of the mass of the silicon carbide powder, phenolic resin accounting for 2% of the mass of the silicon carbide powder, and polyvinyl alcohol and polyethylene glycol each accounting for 1.5% of the mass of the silicon carbide powder. The materials required for the core slurry are then fed into a ball mill for stirring and ball milling. During ball milling, the water volume is adjusted to achieve a slurry solids content of 50%.
[0031] The surface slurry consists of second silicon carbide powder with a D50 particle size of 0.4 μm, boron carbide accounting for 0.8% of the mass of the second silicon carbide powder, phenolic resin accounting for 2% of the mass of the second silicon carbide powder, and polyvinyl alcohol and polyethylene glycol each accounting for 1.5% of the mass of the second silicon carbide powder. The materials required for the surface slurry are then fed into a ball mill for stirring and ball milling. During ball milling, the water volume is adjusted to achieve a slurry solids content of 50%.
[0032] S2: Spray granulation is performed on the core slurry and the surface slurry separately to obtain core granulated powder and surface granulated powder. The core slurry and the surface slurry were spray-granulated at an inlet temperature of 215℃ and an atomizing disc speed of 10000 r / min to obtain a D50 of 100 μm and a bulk density of 1 g / cm³. 3 Core granulated powder and surface granulated powder.
[0033] S3: Mix the core granulation powder with 4% sodium carboxymethyl cellulose, 1.3% polyethylene oxide and 15% water by mass to obtain the core mud. Mix the surface granulation powder with 4% sodium carboxymethyl cellulose, 1.3% polyethylene oxide and 15% water by mass to obtain the surface mud. After obtaining the mud, circulate and knead the mud 5 times under a vacuum of ≤-0.08MPa. During the kneading process, 15℃ cooling water is introduced into the heat exchange jacket of the kneading machine for cooling.
[0034] After the clay is kneaded, it is aged at 23℃ and 55% humidity for 36 hours.
[0035] S4: A double-layer composite extrusion die is used to extrude the surface clay and core clay after kneading, resulting in a double-layer roll blank with the outer layer being surface clay and the inner layer being core clay. The outer diameter of the roll blank is 60mm, the wall thickness is 14mm, and the surface layer thickness is about 3.5mm.
[0036] S5: The roll bar blank is air-dried at 33℃ and 45% humidity for 48 hours, and then dried in an oven at a gradually increasing temperature of 150℃.
[0037] S6: Perform cold isostatic pressing on the dried green blank: The pressure of cold isostatic pressing is 150MPa, and the holding time is 10min.
[0038] S7: The cold isostatically pressed green blank is sintered at 2150℃ under an inert atmosphere for 1.5 hours without pressure. After cooling, the roller bar is obtained.
[0039] Example 2
[0040] S1: Preparation of core and surface slurries: The core slurry consists of silicon carbide powder with a D50 particle size of 0.8 μm, boron carbide accounting for 0.2% of the mass of the silicon carbide powder, phenolic resin accounting for 1% of the mass of the silicon carbide powder, and polyvinyl alcohol and polyethylene glycol each accounting for 1% of the mass of the silicon carbide powder. The materials required for the core slurry are then fed into a ball mill for stirring and ball milling. During ball milling, the water volume is adjusted to achieve a slurry solids content of 45%.
[0041] The surface slurry consists of second silicon carbide powder with a D50 particle size of 0.3 μm, boron carbide accounting for 0.6% of the mass of the second silicon carbide powder, phenolic resin accounting for 1% of the mass of the second silicon carbide powder, and polyvinyl alcohol and polyethylene glycol each accounting for 1% of the mass of the second silicon carbide powder. The materials required for the surface slurry are then fed into a ball mill for stirring and ball milling. During ball milling, the water volume is adjusted to achieve a slurry solids content of 45%.
[0042] S2: Spray granulation is performed on the core slurry and the surface slurry separately to obtain core granulated powder and surface granulated powder. The core slurry and the surface slurry were spray-granulated at an inlet temperature of 210℃ and an atomizing disc speed of 8000 r / min, respectively, to obtain a D50 of 50 μm and a bulk density of 0.8 g / cm³. 3 Core granulated powder and surface granulated powder.
[0043] S3: Mix the core granulation powder with 3% sodium carboxymethyl cellulose, 1% polyethylene oxide and 14% water by mass to obtain core mud. Mix the surface granulation powder with 3% sodium carboxymethyl cellulose, 1% polyethylene oxide and 14% water by mass to obtain surface mud. After obtaining the mud, circulate and knead the mud 4 times under a vacuum of ≤-0.08MPa. During the kneading process, 16℃ cooling water is introduced into the heat exchange jacket of the kneading machine for cooling.
[0044] After the clay is kneaded, it is aged at 20℃ and 50% humidity for 24 hours.
[0045] S4: A double-layer composite extrusion die is used to extrude the surface clay and core clay after kneading, resulting in a double-layer roll blank with the outer layer being surface clay and the inner layer being core clay. The outer diameter of the roll blank is 60mm, the wall thickness is 14mm, and the surface layer thickness is about 3.5mm.
[0046] S5: Air-dry the roll bar blank at 30℃ and 40% humidity for 48 hours, and then dry it in an oven at a gradually increasing temperature of 150℃.
[0047] S6: Perform cold isostatic pressing on the dried green blank: The pressure of cold isostatic pressing is 100MPa and the holding time is 15min.
[0048] S7: The cold isostatically pressed green blank is sintered at 2100℃ under an inert atmosphere for 2 hours without pressure. After cooling, the roller bar is obtained.
[0049] Example 3
[0050] S1: Preparation of core and surface slurries: The core slurry consists of silicon carbide powder with a D50 particle size of 1.2 μm, boron carbide accounting for 0.5% of the mass of the silicon carbide powder, phenolic resin accounting for 3% of the mass of the silicon carbide powder, and polyvinyl alcohol and polyethylene glycol each accounting for 2% of the mass of the silicon carbide powder. The materials required for the core slurry are then fed into a ball mill for stirring and ball milling. During ball milling, the water volume is adjusted to achieve a slurry solids content of 55%.
[0051] The surface slurry consists of second silicon carbide powder with a D50 particle size of 0.6 μm, boron carbide accounting for 1.0% of the mass of the second silicon carbide powder, phenolic resin accounting for 3% of the mass of the second silicon carbide powder, and polyvinyl alcohol and polyethylene glycol each accounting for 2% of the mass of the second silicon carbide powder. The materials required for the surface slurry are then fed into a ball mill for stirring and ball milling. During ball milling, the water volume is adjusted to achieve a slurry solids content of 55%.
[0052] S2: Spray granulation is performed on the core slurry and the surface slurry separately to obtain core granulated powder and surface granulated powder. The core slurry and the surface slurry were spray-granulated at an inlet temperature of 220℃ and an atomizing disc speed of 13000 r / min, respectively, to obtain a D50 of 200 μm and a bulk density of 1.2 g / cm³. 3 Core granulated powder and surface granulated powder.
[0053] S3: Mix the core granulation powder with 6% sodium carboxymethyl cellulose, 1.5% polyethylene oxide and 16% water by mass to obtain the core mud. Mix the surface granulation powder with 6% sodium carboxymethyl cellulose, 1.5% polyethylene oxide and 16% water by mass to obtain the surface mud. After obtaining the mud, circulate and knead the mud 6 times under a vacuum of ≤-0.08MPa. During the kneading process, 12℃ cooling water is introduced into the heat exchange jacket of the kneading machine for cooling.
[0054] After the clay is kneaded, it is aged at 25℃ and 60% humidity for 48 hours.
[0055] S4: A double-layer composite extrusion die is used to extrude the surface clay and core clay after kneading, resulting in a double-layer roll blank with the outer layer being surface clay and the inner layer being core clay. The outer diameter of the roll blank is 60mm, the wall thickness is 14mm, and the surface layer thickness is about 3.5mm.
[0056] S5: The roll bar blank is air-dried at 35℃ and 50% humidity for 48 hours, and then dried in an oven at a gradually increasing temperature of 150℃.
[0057] S6: Perform cold isostatic pressing on the dried green blank: The pressure of cold isostatic pressing is 200MPa, and the holding time is 5min.
[0058] S7: The cold isostatically pressed green blank is sintered at 2200℃ under an inert atmosphere for 1 hour. After cooling, the roller bar is obtained.
[0059] Example 4
[0060] S1: Preparation of core and surface slurries: The core slurry consists of first silicon carbide powder with a D50 particle size of 1 μm, boron carbide accounting for 0.4% of the mass of the first silicon carbide powder, phenolic resin accounting for 2% of the mass of the first silicon carbide powder, and polyvinyl alcohol and polyethylene glycol each accounting for 1.5% of the mass of the first silicon carbide powder. The materials required for the core slurry are then fed into a ball mill for stirring and ball milling. During ball milling, the water volume is adjusted to achieve a slurry solids content of 50%.
[0061] The surface slurry consists of second silicon carbide powder with a D50 particle size of 0.4 μm, boron carbide (1% by weight of the second silicon carbide powder), phenolic resin (2% by weight of the second silicon carbide powder), and polyvinyl alcohol and polyethylene glycol (2% by weight of the second silicon carbide powder, respectively). The materials required for the surface slurry are then fed into a ball mill for stirring and ball milling. During ball milling, the water volume is adjusted to achieve a slurry solids content of 50%.
[0062] S2: Spray granulation is performed on the core slurry and the surface slurry separately to obtain core granulated powder and surface granulated powder. The core slurry and the surface slurry were spray-granulated at an inlet temperature of 215℃ and an atomizing disc speed of 10000 r / min to obtain a D50 of 100 μm and a bulk density of 1 g / cm³. 3 Core granulated powder and surface granulated powder.
[0063] S3: Mix the core granulation powder with 4% sodium carboxymethyl cellulose, 1.2% polyethylene oxide and 15% water by mass to obtain the core mud. Mix the surface granulation powder with 5% sodium carboxymethyl cellulose, 1.5% polyethylene oxide and 15% water by mass to obtain the surface mud. After obtaining the mud, circulate and knead the mud 6 times under a vacuum of ≤-0.08MPa. During the kneading process, 12℃ cooling water is introduced into the heat exchange jacket of the kneading machine for cooling.
[0064] After the clay is kneaded, it is aged at 20℃ and 60% humidity for 30 hours.
[0065] S4: A double-layer composite extrusion die is used to extrude the surface clay and core clay after kneading, resulting in a double-layer roll blank with the outer layer being surface clay and the inner layer being core clay. The outer diameter of the roll blank is 60mm, the wall thickness is 14mm, and the surface layer thickness is about 3.5mm.
[0066] S5: The roll bar blank is air-dried at 35℃ and 40% humidity for 48 hours, and then dried in an oven at a gradually increasing temperature of 150℃.
[0067] S6: Perform cold isostatic pressing on the dried green blank: The pressure of cold isostatic pressing is 200MPa and the holding time is 13min.
[0068] S7: The cold isostatically pressed green blank is sintered at 2100℃ under an inert atmosphere for 1.5 hours without pressure. After cooling, the roller bar is obtained.
[0069] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that only a single core slurry is used, followed by single-layer extrusion, while the rest of the processes are the same.
[0070] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that only a single surface slurry is used, followed by single-layer extrusion, while the rest of the processes are the same.
[0071] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the D50 particle size of silicon carbide powder in both the core slurry and the surface slurry is 1 μm.
[0072] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that the amount of boron carbide used in the surface slurry is 2% of the mass of the second silicon carbide powder.
[0073] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that no organic additives were used in S3 when preparing the core clay and the surface clay.
[0074] The performance of the rollers obtained in Examples 1-4 and Comparative Examples 1-5 was tested, and the test results are shown in Table 1: Table 1
[0075] As can be seen from the data in Table 1, the density distribution of the four embodiments ranges from 3.06 to 3.09 g / cm³. 3 The apparent porosity was ≤0.05% for all samples, and the flexural strength at 1200℃ was in the range of 380-420 MPa. This data indicates that, within the process parameters defined in this invention, high-density, high-purity silicon carbide rollers with excellent high-temperature mechanical properties can be stably prepared. The minor differences between the various embodiments mainly stem from variations in particle size, sintering temperature, and holding time.
[0076] Comparative Example 1 used only a single core slurry for single-layer extrusion, with a density of 3.08 g / cm³. 3 The apparent porosity was 0.03%, comparable to Example 1, indicating that the densification degree was not affected. However, its flexural strength at 1200°C was only 361 MPa, a decrease of approximately 12.6% compared to 413 MPa in Example 1. This is because the product of Comparative Example 1 has a homogeneous coarse-grained structure without the protection of a fine-grained layer on the surface. Coarse-grained surfaces are more prone to stress concentration and crack propagation, resulting in a significantly lower strength than Example 1, which has an outer fine-grained protective layer.
[0077] Comparative Example 2 used only a single surface slurry for extrusion, and its density was only 2.93 g / cm³. 3The apparent porosity was 2.84%, and the flexural strength at 1200℃ was only 212 MPa, all three indicators being far lower than those of Example 1. This is mainly because the surface slurry used ultrafine powder with D50=0.4μm and a high boron carbide content of 0.8wt%, resulting in extremely high sintering activity but inhibiting grain growth. In a homogeneous single-layer thick-walled structure, pores cannot be completely eliminated through grain boundary migration, leaving a large number of closed pores.
[0078] Comparative Example 3: The silicon carbide powder particle size of the core and surface slurry was uniformly set to 1 μm, resulting in a roller density of 3.06 g / cm³. 3 The apparent porosity was 0.06%, but the flexural strength at 1200℃ was 364 MPa, lower than that of Example 1. This is because the elimination of particle size differences weakened the difference in sintering driving force between the two slurries. Although the difference in boron carbide content alone can still produce a certain grain size difference, this difference is reduced, and the surface grains do not reach an ideal state, thus weakening the surface strengthening effect.
[0079] Comparative Example 4 increased the amount of surface boron carbide to 2%, resulting in a roller density reduced to 2.84 g / cm³. 3 The apparent porosity increased to 5.53%, and the strength was only 145 MPa. This was due to the excessive boron carbide addition, which formed a large amount of boride second phase during sintering. These second phases not only excessively pinned grain boundaries, hindering densification, but were also brittle phases, becoming crack initiation points. Simultaneously, excessive grain suppression on the surface layer led to a severe mismatch in sintering shrinkage between the surface and the core, inducing microcracks between the layers.
[0080] Comparative Example 5, which did not add organic additives in step S3, had a density of only 2.71 g / cm³. 3 The apparent porosity is as high as 12.06%, and the strength is only 107 MPa. This is because there is no sodium carboxymethyl cellulose and polyethylene oxide, so the granulated powder cannot form a plastic clay when mixed with water. During extrusion molding, the clay lacks binding and fluidity, and a large number of microcracks and uneven density areas are generated inside the green body. After drying and sintering, these develop into large-scale cracking and pores.
[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
Claims
1. A method for preparing pressureless sintered silicon carbide thick-walled rollers for roller kiln transmission, characterized in that, Includes the following steps: S1: Prepare the core slurry and surface slurry; S2: Spray granulation is performed on the core slurry and the surface slurry to obtain core granulated powder and surface granulated powder respectively; S3: Mix the core granulation powder with organic additives and water to obtain core mud, and mix the surface granulation powder with organic additives and water to obtain surface mud. After obtaining the mud, knead and age it. S4: Using a double-layer composite extrusion die, the surface clay and core clay after kneading are extruded together to form a double-layer roller blank with the outer layer being surface clay and the inner layer being core clay. S5: Dry the obtained roller blank; S6: The dried green blank is subjected to cold isostatic pressing; S7: The cold isostatically pressed green blank is sintered without pressure under an inert atmosphere, and the roller bar is obtained after cooling.
2. The method for preparing pressureless sintered silicon carbide thick-walled rollers for roller kiln transmission according to claim 1, characterized in that, The core slurry in S1 comprises a first silicon carbide powder, boron carbide, phenolic resin, organic additives, and water; the surface slurry comprises a second silicon carbide powder, boron carbide, phenolic resin, organic additives, and water. The average particle size of the second silicon carbide powder is smaller than that of the first silicon carbide powder, and the mass percentage of boron carbide in the surface slurry is higher than that in the core slurry.
3. The method for preparing pressureless sintered silicon carbide thick-walled rollers for roller kiln transmission according to claim 2, characterized in that, When preparing the core slurry and the surface slurry, the raw materials are put into a ball mill for stirring and ball milling. During ball milling, the water volume is adjusted so that the solid content of the slurry is 45%-55%.
4. The method for preparing pressureless sintered silicon carbide thick-walled rollers for roller kiln transmission according to claim 2, characterized in that, The first silicon carbide powder in S1 has a D50 particle size of 0.8-1.2 μm, and the second silicon carbide powder has a D50 particle size of 0.3-0.6 μm; The amount of boron carbide added to the core slurry is 0.2-0.5 wt% of the mass of the first silicon carbide powder, and the amount of boron carbide added to the surface slurry is 0.6-1.0 wt% of the mass of the second silicon carbide powder.
5. The method for preparing pressureless sintered silicon carbide thick-walled rollers for roller kiln transmission according to claim 2, characterized in that, The amount of phenolic resin added in S1 is 1-3 wt% of the corresponding silicon carbide powder mass, and the organic additives are polyvinyl alcohol and polyethylene glycol, with each of the polyvinyl alcohol and polyethylene glycol added being 1-2 wt% of the corresponding silicon carbide powder mass.
6. The method for preparing pressureless sintered silicon carbide thick-walled rollers for roller kiln transmission according to claim 1, characterized in that, During granulation in step S2, the core slurry and the surface slurry are spray-granulated at an inlet temperature of 210-220℃ and an atomizing disc speed of 8000-13000 r / min, respectively, to obtain a D50 of 50-200 μm and a bulk density of 0.8-1.2 g / cm³. 3 Core granulated powder and surface granulated powder.
7. The method for preparing pressureless sintered silicon carbide thick-walled rollers for roller kiln transmission according to claim 6, characterized in that, The organic additives in S3 are sodium carboxymethyl cellulose and polyethylene oxide; based on the mass of granulated powder, the amount of sodium carboxymethyl cellulose added is 3-6%, the amount of polyethylene oxide added is 1-1.5%, and the amount of water added is 14-16%.
8. The method for preparing pressureless sintered silicon carbide thick-walled rollers for roller kiln transmission according to claim 1, characterized in that, In step S3, the vacuum degree of vacuum plowing is ≤-0.08MPa, the plowing is circulated 4-6 times, and cooling water at 12-16℃ is introduced; after plowing, the plow material is aged at 20-25℃ and 50-60% humidity for 24-48 hours.
9. The method for preparing pressureless sintered silicon carbide thick-walled rollers for roller kiln transmission according to claim 1, characterized in that, In step S5, the drying process is as follows: the green blank is first air-dried at 30-35℃ and 40-50% humidity for 48 hours, and then dried in an oven at a gradually increasing temperature to 150℃; in step S6, the pressure of the cold isostatic pressing treatment is 100-200MPa, and the holding time is 5-15min; in step S7, the temperature of the pressureless sintering is 2100-2200℃, and the holding time is 1-2h.
10. A pressureless sintered silicon carbide thick-walled roller bar for roller kiln transmission, characterized in that, The roller is prepared by the method described in any one of claims 1-9.