Powder Metallurgy Bearing Characteristics
Powder metallurgy bearings are capable of producing high precision and high strength products with uniform density and less porosity. Combining well-chosen lubricants with the structural characteristics of powder metallurgy bearings, such bearings can handle up to 10 times or even 100 times the load of general bearing products. Furthermore, due to process characteristics of powder metallurgical bearings, they can facilitate high speed motion, reduce friction, achieve low noise emission, and possess excellent lubrication on-site steadiness.
Powder metallurgy bearings are extensively used as aerospace industrial components, automobile parts, and precision machinery devices. Bearings are formed chiefly by sintering and infiltration of the corresponding powder mixtures. Since the materials used in powder metallurgy bearings typically can reach higher strength and more uniform material distribution, such bearings offer more reliable performance than general sintered bearings. In addition, powder metallurgical bearing manufacturing processes are also highly robust and controllable regardless of tolerance, shape, and time of manufacture. These design and process characteristics have made powder metallurgical bearings ideal components for numerous high-speed and high-precision transportation applications.
The primary materials used for producing powder metallurgical bearings are usually powders of abutment metals, lubricants, and alloys. The first step of powder metallurgy bearing production involves mixing the pre-alloyed powder with the lubricant, which is usually applied for the bearing’s specific purposes. At the beginning of the powder bearing production, the powder of the abutment metal and lubricant are in a dry form. These dry powder ingredients must first be blended with other additives and lubricants in a planetary mixer, and then transferred to a vacuum chamber where the blended powder is uniformly dispersed into a powder bed while being vacuum-sintered. After the powder has been vacuum-sintered, it is transferred to a pressurized mold. This mold is pressed at a preset pressure and temperature level. This process usually requires a heating and cooling cycle to complete both sintering and infiltration processes. Post-sintering operations such as grinding, testing, and post-heat treatments are performed to ensure quality and compliance of the manufactured product.
Powder metallurgy bearings differ in their tolerances and surface finishes depending on the application. Usually, a higher level of tolerance is required for bearings in aerospace applications, while a certain level of tolerance is desirable but not essential in automotive applications. This is because higher tolerances are required during production of aerospace components in order to withstand high velocity loads. For example, during operation in potential bearing failure areas, tolerances of less than 30 micrometers are extremely important in order to maintain proper lubrication and pressure between the bearings and their orientation within the aircraft. In automotive applications, a certain tolerance is desirable to ensure adequate bearing performance, but not necessarily for optimal performance. These tolerances help to reduce friction and noise and vibration, but the automobile does not necessarily require the highest tolerance levels. Generally, the surface finish of a powder metallurgy bearing is usually around 2 to 4 microns.
The lubricants used for lubricating powder metallurgical bearings are chosen for their ability to resist high temperatures and loads. The lubricants used can be either inorganic or organic, depending on the bearing’s application. Generally, organic lubricants are used when minimal friction is desired or when medium temperatures or loads are expected. Inorganic lubricants are used generally in applications wherein high temperature and high load bearance is essential. The most common organic lubricants used in powder metallurgy bearings include molybdenum disulfide and graphite, while commonly used inorganic greases are lithium soap and calcium soap.
In summary, powder metallurgy bearings offer superior high-speed and high-precision performance due to their robust and controllable manufacturing processes, wide variety of materials and finishes, and wide range of reliable lubricants. The precise material distribution that they achieve provides remarkable strength and reliability over standard bearing systems, making them ideal components in various industrial and automotive applications.
