A bearing is a component that supports a mechanical rotating shaft, reducing its friction coefficient and ensuring its accuracy. According to the bearing structure and motion, it can be divided into rolling friction bearing (referred to as rolling bearing) and sliding friction bearing (referred to as sliding bearing).
Rolling bearing steel
The rolling bearing is a kind of precise mechanical component of rolling friction between the rotating shaft and shaft seat. The rolling bearing needs to bear a high alternating load in the work, the contact stress between the rolling body and the inner and outer rings is large, and it also works in the lubricant medium. The rolling bearing steel is a type of steel that used to manufacture the rolling body of the rolling bearing, the inner/outer ring, the rolling body, usually used in the quenching condition and the surface hardness should reach HRC60 ~ 65. Rolling bearing steel has high compressive strength and fatigue strength, good toughness, plasticity, wear resistance and corrosion resistance, steel internal structure, composition uniformity and good dimensional stability after heat treatment. The commonly used rolling bearing steels are high carbon and low chromium bearing steels with 0.95% ~ 1.10% carbon and 0.40% ~ 1.60% chromium, such as AISI 52100, 51100, 50100, etc.
Sliding bearings(Plain bearings) steel
Sliding bearings(Plain bearings) are bearings that operate under sliding friction. The plain bearings work smoothly, reliably and noiseless. Under the condition of liquid lubrication, the sliding surface is separated by lubricating oil without direct contact, which greatly reduces the friction loss and surface wear. The part of the shaft supported by the bearing is called the journal, and the matching part is called the bearing bush. The anti-friction material layer cast on the inner surface of the bearing bush in order to improve its friction property is called the bearing liner. Plain bearings are generally used for high speed and light load conditions.
The metal materials used for sliding bearings include Tin/lead-based bearing alloys(Babbitt alloy), copper-bearing alloy, aluminum bearing alloy, zinc bearing alloy, etc. Babbitt alloy is a low melting point soft phase and hard particle phase bearing alloy alloyed tin, lead, antimony, copper. Because it offers good wear resistance, plastic, thermal conductivity, good adsorbability with oil while a low strength, recommended being cast on the bronze, steel strip or cast-iron bush to form a thin coating. Material including ISO 4381 SnSb8Cu4, ASTM B23 Grade 1,2,3, 4,11 for Sn Babbitt, Grade 7,8,13,15 for Pb Babbitt; JIS H 5401 WJ-1 ~ WJ-10; Grade 1-8 of BS 3332; DIN 1703 LgSn80 ~ LgPbSn6Cd, etc.
Copper-based bearing alloy
It usually includes Tin bronze and Lead bronze. Copper-based bearing alloy offers high fatigue strength and bearing capacity, excellent wear resistance, good thermal conductivity, low friction coefficient and can work normally under 250℃. It’s suitable for the manufacture of high speed, heavy-duty work under the bearing, such as high-speed diesel engines, aircraft engine bearings.
Aluminum bases bearing alloy
Aluminum-based bearing alloy is an alloy based on aluminum with tin and other elements added. The alloy is characterized by high thermal conductivity, corrosion resistance, high fatigue strength and high-temperature strength and low price, while there are large expansion coefficient and poor bite resistance. High-tin aluminum-based bearing alloy is the most widely used type and suitable for the manufacture of high-speed (13m/s), heavy load (3200MPa) engine bearings.
In addition, porous metal materials (powder metallurgy materials) and some plastic materials can also be used in the manufacture of sliding bearings. Porous metal is a kind of self - lubricating powder material. However, it’s suitable for smooth non-impact load and medium and small speed conditions due to its small toughness. Plastic bearings have greater compressive strength and wear resistance, can be lubricated with oil and water, also have self-lubricating performance, but poor thermal conductivity. Common bearing plastics include phenolic plastics, nylon, polytetrafluoroethylene, etc.