What’s Babbitt Metal?

Babbitt metal is a low melting point soft phase and hard particle phase bearing alloy alloyed tin, lead, antimony, copper. It was invented by Babbitt, an American metallurgical engineer. The density of babbitt alloy is 7.38 kg/m, which is usually obtained by casting, spraying or coating methods. It can be divided into tin-based babbitt alloy, lead-based babbitt alloy and cadmium base babbitt alloy according to its chemical elements.

 

Microstructure of  Babbitt alloy


Most Babbitt alloys are used for plain bearings manufacturing. The sliding bearing strongly rubs against the high-speed heavy load shaft at work, which requires the alloy structure to have soft matrix hardpoints and hard matrix soft points. The soft phase matrix makes the alloy have very good embeddability, compliance and anti-bite property. After running-in, the soft matrix is concave in the inner part and convex in the outer part of the hardpoint, so that a small gap is formed between the sliding surfaces, which is conducive to the storage of lubricating oil and reduces friction. The hardpoint on the convex is supported, which is beneficial to bearing.

 

TIN BABBITT ALLOY

Tin Babbitt alloys are tin-based alloys with 3%~15% antimony, 2%~6%copper and cadmium less than 1%. The soft phase matrix of the tin bearing alloy is a solid solution containing antimony in the tin, and the hardpoints are metal compounds such as SnSb and Cu3Sn. Tin base babbitt alloy offers good plasticity and thermal conductivity, small coefficient of friction and coefficient of expansion, but low fatigue strength and low working temperature, mainly used for pouring large machinery bearing, such as high-power high-speed steam engine, steam turbine and machine tool spindle bearing.

 

LEAD BABBITT ALLOY

Lead-based babbitt alloys contain 10% ~ 20% antimony, 5% ~ 15% tin, a small amount of arsenic, copper and other alloy elements to prevent segregation and refine grains. The soft matrix of the lead-based bearing alloy is a solid solution containing antimony in lead, and the hardpoints are metal compounds such as SnSb and Cu3Sn. The strength and hardness of lead base babbitt alloy is not as good as that of tin-based babbitt alloy, the large friction coefficient and low impact resistance but a low price is generally used for the bearing with the operating temperature not exceeding 120℃, no obvious impact load, such as motors, crushers, compressors and vacuum pumps.

 

Tin alloy has high strength and hardness ratio and better corrosion resistance than lead alloy, so it is more popular in industrial applications, and its commonly used brands are ZSnSb11Cu6, ZSnSb8Cu4, ZSnSb8Cu8 and so on. Many customers still choose lead-based alloys due to their economy, such as ZPbSb16Sn16Cu2, ZPbSb10Sn6, etc (GB/T 1174). Other standards like 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.

 

Babbitt alloys cannot withstand large pressures because their strength is relatively low, so a thin and uniform lining (<0.1mm) is often formed by centrifugal pouring on the steel bearing shell. Babbitt alloy is mainly used in large machinery spindle bearing bush, bearing, shaft lining, shaft sleeve application in cement, steel, chemical, paper, petroleum, ships, coal mines, coal mine equipment, etc., can also be used in large machine tools to replace brass. In addition to the manufacture of plain bearings, babbitt alloy is often used for its soft texture and low strength.