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Ceramic Bearings Information
Ceramic ball bearings are a typical example of engineering ceramics widely used in industrial fields, receiving significant attention from many engineers. In high-speed precision bearings, hybrid ceramic ball bearings are the most commonly used, featuring hot-pressed Si3N4 ceramic balls while the bearing rings remain steel. These bearings are highly standardized, require minimal changes to machine structure, and are easy to maintain, making them particularly suitable for high-speed operations. High-speed electric spindles equipped with these bearings offer advantages such as high speed, high rigidity, high power, and long life.
1.Corrosion Resistance: Ceramic rolling bearings are ideal for operating in harsh conditions filled with corrosive media as ceramics are almost impervious to corrosion.
2.Low Density and Lightweight: Ceramic balls have a lower density compared to steel, significantly reducing centrifugal force on the outer ring during rotation by up to 40%, thus extending the bearing’s lifespan.
3.Thermal Stability: Ceramics are less affected by thermal expansion and contraction compared to steel, allowing bearings to operate in environments with significant temperature fluctuations.
4.High Modulus of Elasticity: Ceramics’ higher modulus of elasticity means less deformation under load, which helps increase operational speed and achieve higher precision.
Comparison of Bearing Materials
Here’s a comparison of performance characteristics among AISI 52100 (GCr15), stainless steel AISI 440 (9Cr18), silicon nitride (Si3N4), and zirconia (ZrO2):
| Material | Density (g/cm³) | Thermal Expansion Coefficient (10^-6/°C) | Young’s Modulus (GPa) | Hardness (HV) | Compressive Strength (MPa) | Flexural Strength (MPa) | Fracture Toughness (MPa.m^1/2) | Thermal Conductivity (W/m·K) | Specific Heat (J/kg·K) | Max Operating Temp (°C) | Electrical Insulation | Durability |
| GCr15 | 7.8 | 11 | 208 | 800 | 2400 | 20 | 30-40 | 30-40 | 450 | 120 | Non-insulating | Weak |
| 9Cr18 | 7.9 | 17 | 200 | 700 | 2600 | 25 | 30-40 | 15 | 450 | 150 | Non-insulating | Moderate |
| Si3N4 | 3.2 | 3.2 | 320 | 1700 | 900 | 7.0 | 3.5-5.5 | 15 | 800 | 100 | Insulating | Strong |
| ZrO2 | 6.0 | 10.5 | 210 | 1300 | 3500 | 10.5 | 2.5-3.5 | 2.5 | 400 | 800 | Insulating | Strong |
Types of Ceramic Bearings
Full ceramic bearings are characterized by magnetic insulation, wear and corrosion resistance, self-lubrication, high and low-temperature resistance, making them suitable for extreme environments and special working conditions. The rings and rolling elements use zirconia (ZrO2) ceramic materials, with PTFE as the standard cage material. Other materials such as fiberglass reinforced nylon 66 (RPA66-25), engineering plastics (PEEK, PI), stainless steel (AISISUS316), and brass (Cu) are also used.
Silicon nitride full ceramic bearings use silicon nitride (Si3N4) ceramic materials for rings and rolling elements. Other materials like RPA66-25, PEEK, PI, and phenolic laminated tubes can also be used. Compared to ZrO2, Si3N4 bearings are suitable for higher speeds, load capacities, and environmental temperatures. High-precision ceramic bearings for high-speed, high-rigidity spindles are available, with precision up to P4 to UP grades.
Full Complement Ball Bearings
These bearings use a cage-free design, allowing ceramic balls to be incorporated, increasing load capacity and avoiding limitations due to cage materials. However, they are unsuitable for high-speed applications and should be installed with the gap side facing the non-axial load-bearing end.
Ceramic balls, especially silicon nitride, have low density, high hardness, low friction coefficient, wear resistance, self-lubrication, and rigidity, making them ideal for high-speed, high-precision, and long-life hybrid bearings (with metal inner and outer rings). The inner and outer rings typically use bearing steel (GCr15) or stainless steel (AISI440C), while ceramic balls can be made of ZrO2, Si3N4, or SiC materials.
Manufacturing Process of Ceramic Bearings
Ceramic bearings are high-tech products widely used in modern industry. Their manufacturing process includes raw material preparation, forming, sintering, and precision machining.
Raw Material Preparation
The main materials are alumina and silicon nitride. The powders are strictly screened and measured to ensure proper particle size and proportion. Raw materials undergo drying and ball milling for better flow and filling during forming.
Mixing
Ceramic powder is mixed with other additives to improve performance and processability. Grinding and mixing ensure uniform particle size and stable composition.
Forming
The mixed raw materials are pressed into molds. Ceramic products can be divided into plasma spray products and press/injection molded products. Plasma spray products require high technical demands and are produced on a smaller scale, while press/injection molded products use preform blanks, providing high production efficiency but requiring stringent quality control.
Sintering
The formed ceramic blanks are sintered in high-temperature environments, forming dense structures and increasing strength and hardness.
Precision Machining
Sintered ceramics have high surface hardness and wear resistance but are prone to cracking. Precision machining (turning, grinding, etc.) is necessary, involving multiple inspections and polishing to ensure the bearings’ appearance and internal quality.
Assembly
Precision-machined ceramic bearings are assembled, involving the inner ring, outer ring, and balls. Assembly requires professional equipment and thorough quality checks to ensure all specifications are met.
Quality Control
Ceramic materials have high strength, temperature, wear resistance, and chemical stability but are brittle. Strict quality control is essential during manufacturing, with common methods including X-ray and metallographic microscope inspections.
Applications of Ceramic Bearings
Ceramic bearings are used in environments and conditions demanding high temperature, corrosion resistance, electrical insulation, self-lubrication, and high-speed performance. They are widely applied in aerospace, chemical, mechanical, medical, and electronic fields.
Aerospace
Ceramic bearings are used in turbines, engines, rudder machines, and propellers of aircraft, rockets, and satellites, handling high speeds and large loads. They offer higher strength, better wear resistance, and corrosion resistance, improving fuel efficiency and reducing environmental impact.
Chemical Industry
Ceramic bearings are ideal for equipment exposed to corrosive gases or liquids. They provide excellent corrosion resistance in environments with strong acids, alkalis, and saltwater, making them widely used in acid washing machines, chemical pumps, etc.
Mechanical Manufacturing
In mechanical manufacturing, ceramic bearings are used in motors, pumps, centrifuges, high-speed hydraulic pumps, and machine tools, reducing noise, increasing speed, and extending lifespan. They maintain stability in high-speed and high-temperature environments and reduce maintenance costs. They are also used in special equipment like high-temperature furnaces and vacuum furnaces due to their strong corrosion and temperature resistance.
Medical Field
Ceramic bearings are used in various medical equipment such as surgical devices and dialysis machines, ensuring precision and reliability while reducing maintenance time and costs.
Conclusion
Ceramic ball bearings are essential mechanical components with unparalleled performance compared to metal bearings. Their widespread use across various fields significantly enhances bearing lifespan and speed, providing foundational components for developing high-speed, high-precision machinery. Their applications in high-temperature, corrosive, insulating, and vacuum environments have also yielded excellent results, offering greater vitality for future development.