1. Performance requirements for bearing alloys
Sliding bearings are parts used in mechanical manufacturing industries such as automobiles, tractors, and machine tools to support shafts for operation. They are composed of bearing shells and shaft sleeves. The wear-resistant alloy used to manufacture bearing shells and liners is called bearing alloy. When the shaft rotates at high speed in the bearing shell, strong friction inevitably occurs, and the bearing shell also has to bear the periodic load transmitted to it by the journal. Therefore, it will inevitably cause wear on the shaft and bearing. Axes are usually expensive and it is uneconomical to replace them frequently. Choosing bearing alloys that meet certain performance requirements can ensure minimal wear of the shaft.
The properties that bearing alloys should possess:
① Wear resistant and have a low coefficient of friction to reduce shaft wear.
② Has high fatigue strength and compressive strength to withstand large cyclic loads.
③ Has sufficient shaping and toughness to resist impact and vibration, and improve the running in performance of the shaft and bearing.
④ It has good thermal conductivity and corrosion resistance to prevent the bearing and shaft from biting due to strong friction and heating, and can resist the erosion of lubricating oil.
In the alloy structure, if hard points of a certain size are uniformly distributed on the soft matrix (or soft particles are distributed on the hard matrix), the above performance requirements can be basically met. When the shaft runs in the bearing, the soft matrix (or particles) are prone to wear and indentation, while the hard matrix (or particles) protrudes to provide load-bearing and wear-resistant functions. In this way, the contact area between the shaft and the bearing shell is reduced, and the gap between them can store lubricating oil, reducing the friction coefficient between the shaft and the bearing and reducing wear. A soft matrix or particle can withstand impact and vibration and allow the shaft and bearing to break in well. In addition, soft matrices or particles can embed foreign hard points that accidentally enter to prevent scratching the shaft neck.
Commonly used bearing alloys can be divided into tin based, lead based, aluminum based, copper based, and iron-based according to their main chemical compositions. Among them, tin based and lead based bearing alloys, also known as Babbitt alloys, are widely used bearing alloys.
2. Tin based bearing alloy
Tin based bearing alloy is an alloy mainly composed of tin with a small amount of antimony, copper and other elements added. The commonly used tin based bearing alloy for Z is ZSnSb11Cu6, which contains approximately 11% Sb in WSb, 6% Cu in WCu, and the remaining Sn. The alpha solid solution of Sb and Cu dissolved in Sn is a soft matrix (black part in Figure 1), while the compounds Cu3Sn (white needle shaped or star shaped in Figure 1) and SnSb (white square or polygonal) formed by Sn, Sb, and Cu are hard dots. When WCu=6%, a high melting point compound Cu3Sn is formed, which can prevent SnSb based solid solutions from floating in the solution, prevent specific gravity segregation, and also improve the wear resistance of the alloy.
Figure 1 Microstructure of ZSnSb11Cu6 alloy
Tin based bearing alloy has a low friction coefficient, good plasticity and thermal conductivity, and is an excellent anti friction material. It is applied to Z important bearings, such as high-speed bearings used for casting heavy machinery such as steam turbines, engines, and compressors, with a working temperature not exceeding 150 ℃.
The strength, especially fatigue strength, of tin based bearing alloys is low. In production, bimetallic bearings are often used, that is, centrifugal casting method is used to pour a thin layer of tin based bearing alloy on low-carbon steel bearing shells, which improves the strength and service life of the bearings and saves a lot of tin based bearing alloy.
3. Lead based bearing alloy
Lead based bearing alloy is an alloy mainly composed of lead with a small amount of antimony, tin, copper and other elements added, which can be used as a substitute for tin based bearing alloy. Among them, Pb Sb alloy has a wide range of applications.
The phase diagram of Pb Sb binary alloy (Figure 2) exhibits eutectic transformation. The WSb content in the eutectic composition is 11.2%. The room temperature microstructure of the alloy with Sb content between 17.5% and 20% in the figure is composed of primary β - phase hard points and (α+β) eutectic soft matrix. However, due to the severe segregation of binary Pb Sb alloys, as well as the brittleness and fragility of the β phase, the matrix is too soft and prone to wear, other elements such as Cu and Sn are also added to Pb Sb alloys. Adding Cu can form Cu3Sn, prevent specific gravity segregation, and also form Cu2Sb hard spots, improving the wear resistance of the alloy. Adding Sn can form metal compound SnSb hard spots, which can dissolve in lead in large quantities and strengthen the matrix, thus improving the strength and wear resistance of the alloy. ZPbSb16Sn16Cu2 is a commonly used lead based bearing alloy in industry, with a WSb of 16% WSn=16%,WCu=2%, Belongs to hypereutectic alloys. The (α+β) eutectic in its organization is a soft matrix, the white square is the compound SnSb, and the white needle shaped crystal is the compound Cu3Sn. The newly formed β - compounds Cu2Sn and SnSb are hard spots in the alloy (see Figure 3).
Figure 2 Phase diagram of Pb Sb alloy
Figure 3 Microstructure of ZPbSb16Sn16Cu2
Lead based bearing alloys can be made into double-layer or three-layer metal structures. Although their strength, hardness, and wear resistance are lower than tin based bearing alloys, the cost is reduced due to the decrease in tin content. In addition, it has good casting performance and wear resistance, and is generally used to manufacture medium and low load bearing shells, such as crankshaft bearings for automobiles and tractors.
4. Aluminum based bearing alloy
Aluminum based bearing alloy is a new type of anti friction material developed in the 1960s. China has gradually replaced tin based, lead based, and copper based bearing alloys with it, thus saving a large amount of industrial copper. Aluminum bearing alloys have abundant resources, low prices, high fatigue strength, good thermal conductivity, and their corrosion resistance is no less than that of tin antimony Babbitt alloy. Therefore, aluminum based bearing alloys are widely used in diesel engine bearings for automobiles and tractors that operate at high speeds and high loads.
The commonly used aluminum based bearing alloys include Al Sb bearing alloy and Al Sn bearing alloy.
(1) Al Sb bearing alloy
Its composition includes WSb=3.5%~5% WMg=0.3%~0.7%, The rest is Al. As shown in Figure 4, AlSb with WSb=4% transforms into flakes, improving the plasticity, toughness, and strength of the alloy. The microstructure of Al Sb alloy consists of metal compounds AlSb and Mg3Sb2, with hard points uniformly distributed on a soft aluminum based solid solution. This alloy uses low-carbon steel as the backing, and Al Sb Mn bearing alloy is poured onto the steel backing to make bimetallic bearings, or rolled together with low-carbon steel strip to form bimetallic steel strips.
Figure 4 Phase diagram of Al Sb alloy
Al Sb bearing alloy has high fatigue resistance and wear resistance, but its load-bearing capacity is not large, and it is used in medium load internal combustion engines.
(2) Al Sn bearing alloy
High tin aluminum based bearing alloys have higher load-bearing capacity and fatigue strength. It is rolled together with low-carbon steel to form a bimetallic bearing, which can work under a pressure of 28MPa and a sliding linear velocity of 13m/s. Its anti bite performance is comparable to that of Babbitt alloy. The chemical composition of high tin aluminum based bearing alloy is: WSn=20%,WCu=1%, The rest is Al. Tin has extremely low solubility in aluminum. The eutectic structure of Al Sn alloy with WSn=20% is more abundant, and tin surrounds the aluminum crystal in a network, greatly reducing the mechanical properties of the alloy. In order to eliminate the network eutectic, after pouring, it can be rolled together with the steel back and annealed at 350 ℃ for 3 hours to spheroidize the tin. Therefore, the actual structure of the alloy is uniformly distributed with soft granular tin particles on a hard aluminum matrix.
Adding Cu and Ni to Al Sn alloy, as they can dissolve in Al, can further enhance the strength of the matrix.
High tin aluminum based bearing alloys are easy to produce and cost-effective. They have been widely used in diesel engine bearings for medium and high-speed vehicles and tractors in China, replacing Babbitt alloy and other bearing materials in many machines. However, when producing this type of bearing, if the alloy layer is not firmly bonded to the steel back, it will cause early peeling of the alloy layer during use. In order to firmly bond the high tin aluminum based bearing alloy with the steel back, this type of bearing is currently rolled from a three-layer alloy consisting of steel strip, Al Sn alloy, and an intermediate layer of aluminum foil. During the rolling process, the oxide film on the aluminum surface is broken due to elongation, and the remaining oxide film is spheroidized by subsequent recrystallization annealing, greatly improving the bonding strength with the steel back.
2025 March 2nd Week Marginal Product Recommendation:
Plastic Self-lubricating Bearings:
Filament wound self-lubricating bearings,High strength glass fiber with epoxy resin baked with PTFE and special fiber as bearing lining, the back material provides high load capacity and bearing lining offers low friction under dry condition. Therefore, this special structure offered an outstanding anti-wear feature and anti-impact performance, suitable for high load with high corrosion resistance application like lifting machinery, logistic machinery, agricultural machinery, and port machinery etc. This special structure offered an outstanding anti-wear feature and anti-impact performance, suitable for high load with high corrosion resistance application like lifting machinery, logistic machinery, agricultural machinery, and port machinery etc,.
