The manufacturing process of oil-impregnated bearings is centered on the powder metallurgy method, and its characteristics and challenges are closely related to porous structure control, material performance balance and process precision. The detailed analysis is as follows:
I. Characteristics of Manufacturing Process
Controllability of Porous Structure
Oil-impregnated bearings form a porous framework through sintering in the powder metallurgy process, and the porosity (10%-40%) and pore distribution can be freely adjusted during manufacturing. For example:
High-speed and light-load scenarios: High porosity (above 30%) is required to store more lubricating oil and ensure continuous oil supply;
Low-speed and heavy-load scenarios: Low porosity (below 15%) is required to improve material strength and avoid deformation.
This flexibility enables it to adapt to different working conditions, but it also requires precise control of process parameters (such as powder particle size, compaction pressure, and sintering temperature).
Near-net Shape Forming and High Material Utilization
The powder metallurgy process is directly formed by die compaction without cutting, and the material utilization rate can reach more than 95% (only 50%-70% for traditional cutting processing). For example, the compaction density of iron-based oil-impregnated bearings can be controlled at 6.8-7.2g/cm³, and the shrinkage rate after sintering is stable at 1.2%-1.5%, which significantly reduces the subsequent machining allowance.
Realization of Self-lubricating Performance
The sintered porous structure is filled with lubricating oil (such as mineral oil, synthetic oil) through the vacuum oil impregnation process to form a dynamic lubrication system. During operation, the rising temperature of the bearing causes the lubricating oil to expand and overflow, filling the friction interface; when shutdown, the oil is sucked back into the pores. This process eliminates the need for an external lubrication system, but requires matching affinity between pores and lubricating oil. For example, copper-based bearings need to select lubricating oil with better extreme pressure performance to adapt to heavy-load working conditions.
II. Challenges in Manufacturing Process
Balance between Porosity and Strength
Contradiction: Although high porosity can improve oil storage capacity, it will reduce material density and mechanical strength. For example, when the porosity exceeds 35%, the compressive strength of iron-based bearings may drop from 400MPa to below 200MPa, making it difficult to withstand heavy loads.
Solutions: Optimize the powder formula (such as adding strengthening elements like copper and nickel) or improve the sintering process (such as sectional sintering, hot isostatic pressing) to enhance material density. For example, an enterprise uses copper-iron composite powder to control the porosity at 25% while increasing the compressive strength to 350MPa.
Lubricant Penetration and Retention
Penetration challenge: Lubricating oil needs to uniformly fill micron-scale pores. Poor pore connectivity or excessive surface tension may lead to insufficient oil impregnation. For example, due to the obstruction of oxide film, the oil impregnation rate of aluminum-based oil-impregnated bearings may be 20%-30% lower than that of iron-based bearings.
Retention challenge: Lubricating oil may volatilize or oxidize and deteriorate in high-temperature environments (above 150℃). In a wide temperature range test of -40℃ to 80℃ for oil-impregnated bearings used in wind power gearboxes, it was found that the volatilization rate of ordinary mineral oil increased significantly above 60℃, so synthetic ester oil must be used to extend the service life.
Dimensional Accuracy and Consistency Control
Fluctuation of compaction shrinkage: The random arrangement of particles during powder compaction may cause a difference of ±0.5% in sintering shrinkage, resulting in dimensional deviation. For example, the batch pass rate of micro-motor oil-impregnated bearings (outer diameter 5mm) produced by an enterprise was only 85% due to unstable shrinkage.
Surface defect control: Porous structures are prone to residual powder particles or sintering impurities, so subsequent processes such as ultrasonic cleaning and sandblasting are required to improve surface quality. In a case of automotive air conditioning compressor bearings, after the surface roughness was reduced from Ra1.6μm to Ra0.4μm, the noise was reduced by 5dB and the service life was extended by 30%.
III. Industrial Breakthrough Directions
Material innovation: Develop nano-porous structures (pore size <1μm) to increase oil storage density, or adopt metal-ceramic composite materials to enhance wear resistance.
Process intelligence: Introduce AI algorithms to optimize compaction-sintering parameters and achieve a dynamic balance between porosity and strength.
Green manufacturing: Research bio-based lubricating oil to replace mineral oil and reduce environmental impact; develop short-process processes to reduce energy consumption.
The manufacturing process of oil-impregnated bearings needs to find the optimal solution among porous structure control, material performance balance and process precision. With the advancement of powder metallurgy technology and lubricating material science, its application scenarios are expanding from traditional home appliances and automobiles to high-end equipment (such as industrial robots, new energy vehicle electric drive systems), becoming a key fundamental component for green intelligent manufacturing.
Chinese