Please introduce the manufacturing process of hybrid ceramic bearings
Hybrid ceramic bearings refer to bearing products with rolling elements made of ceramic materials and inner and outer rings made of metal materials (different from all ceramic bearings), which have the advantages of high rigidity of metal bearings and wear and high temperature resistance of ceramic rolling elements. Their manufacturing process requires strict control of material processing accuracy and component assembly adaptability.
1、 Raw material selection and pretreatment
Metal ring (inner ring+outer ring) raw material
The mainstream materials are high carbon chromium bearing steel (GCr15) or stainless steel (440C/304). The former is suitable for conventional industrial working conditions, while the latter is suitable for corrosion-resistant scenarios.
Preprocessing process: Round steel cutting → Forging (eliminating internal looseness and improving density) → Spheroidizing annealing (reducing hardness for subsequent cutting) → Turning rough machining (preliminary forming of ring blank).
Ceramic rolling element raw materials
Silicon nitride (Si ∝ N ?) ceramics are preferred, followed by zirconia (ZrO ?) ceramics. Silicon nitride has lower density, higher hardness, and wear resistance, making it the mainstream choice for industrial hybrid ceramic bearings.
Preprocessing process: Preparation of ceramic powder (using vapor deposition or solid-state sintering method to ensure uniform particle size) → Powder granulation (adding binder to make compressible granular raw materials).
2、 Core component processing technology
(1) Precision machining of metal rings
Precision machining: Precision machining is carried out on the annealed blank, controlling the dimensional tolerances of the inner diameter, outer diameter, width, etc. of the ring, with an accuracy of within ± 0.005mm.
Heat treatment:
GCr15 bearing steel rings need to undergo quenching and low-temperature tempering treatment to increase their hardness to HRC 60-64, ensuring wear resistance;
Stainless steel rings are treated with solid solution to improve corrosion resistance while maintaining a certain hardness.
Grinding processing: This is the key process that determines the accuracy of the ring, achieved through multiple grinding processes:
Heartless grinding (grinding the outer diameter of the outer ring and the inner diameter of the inner ring) → Double end grinding (grinding the two ends of the ring to ensure parallelism) → Groove grinding (grinding the raceway of the rolling element, strictly controlling the curvature radius of the groove and adapting it to the ceramic rolling element).
Ultra precision machining: Polish the surface of the raceway to reduce surface roughness (Ra ≤ 0.01 μ m) and minimize friction loss between the rolling elements and the raceway.
Cleaning and rust prevention: Ultrasonic cleaning is used to remove residual iron filings and oil stains from processing. Stainless steel rings can be directly dried, while carbon steel rings need to be treated with nickel plating, zinc plating, or rust prevention oil.
(2) Ceramic rolling element forming and sintering
Compression molding: Place the pelletized ceramic powder into a mold and use cold isostatic pressing (CIP) technology to press spherical blanks. The pressure is controlled at 100-300MPa to ensure uniform density of the blanks.
Degreasing treatment: Place the spherical blank into a degreasing furnace, heat it to 400-600 ℃, remove the internal binder, and avoid the formation of bubbles and cracks during sintering.
High temperature sintering: Place the defatted blank in a sintering furnace and heat it to 1600-1800 ℃ (silicon nitride sintering temperature) under a nitrogen or argon protective atmosphere. Hold for 2-4 hours to tightly bond the ceramic particles and form dense ceramic balls.
Grinding and polishing:
Rough grinding: Remove surface defects after sintering and preliminarily correct sphericity;
Fine grinding: using diamond grinding fluid to control the sphericity error of ceramic balls within 0.001mm;
Polishing: The final surface roughness Ra after polishing is ≤ 0.005 μ m, ensuring smoothness during rolling.
3、 Assembly and final inspection process
Processing and assembly of retaining frames
The material of the retaining frame is selected according to the working conditions, commonly using brass, engineering plastic (PA66+fiberglass) or stainless steel; After stamping or injection molding, drilling and chamfering are required to ensure the fitting gap between the pocket hole and the ceramic rolling element.
Assembly process: In a clean and dust-free workshop, evenly install the ceramic rolling elements into the cage pocket holes and assemble them together with the metal inner and outer rings.
Lubrication and Sealing
Normal working conditions: Fill with high-temperature lubricating grease (such as polyurea grease, fluorine grease) to reduce the friction between rolling elements and raceways;
Adverse working conditions (high temperature, dust, corrosive environment): Install metal sealing rings or dust covers to prevent foreign objects from entering and grease loss.
Final inspection and factory delivery
Dimensional testing: Testing key parameters such as bearing inner diameter, outer diameter, and clearance to ensure compliance with industry standards (such as ISO 302);
Performance testing: Conduct rotation accuracy testing, vibration testing, high temperature resistance testing, etc;
Appearance inspection: Check whether there are cracks, scratches and other defects on the surface of the ring and rolling element. After passing the inspection, package and leave the factory.
4、 Key process control points
The sphericity of ceramic rolling elements directly affects the rotational accuracy and vibration value of bearings, and requires strict control through high-precision grinding equipment.
Curvature matching of metal ring raceway: The ratio of raceway curvature radius to ceramic rolling element should be controlled between 1.01-1.05 to ensure uniform contact stress.
Cleanliness control: The entire processing and assembly process should be carried out in a dust-free environment to prevent impurities from entering the bearing and causing operational failure.
