I. Introduction to Bus Alloy Bushings

Babbitt bearing bushings are sliding bearing components lined with Babbitt alloy—a type of bearing alloy characterized by a low-melting-point, soft matrix based on tin (Sn) or lead (Pb), uniformly embedded with hard particles. Primarily designed to work in conjunction with journal bearings, they are widely used in the rotating systems of large-scale machinery. Their applications span across various heavy industrial sectors, including cement machinery (such as cement ball mills), steel machinery (like fans in steel plants), chemical processing equipment, paper-making machinery (e.g., drying cylinder machines), petroleum equipment, marine machinery (such as propeller shaft sleeves for ships), compression machinery, coal mining equipment, and mineral-processing systems. Additionally, these bushings are essential components in critical parts like bearings, shaft sleeves, and shaft liners found in large machine tools, hydro turbines, steam turbines, and power generation units.

II. Core Characteristics and Material Classification of Babbitt Alloy Bearings

1. Material Classification and Composition Characteristics

• Tin-based Babbitt alloy: Its main components are tin, antimony, and copper, with trace amounts of lead added in some cases. A typical composition (by mass fraction) includes 3% to 15% antimony, 2% to 6% copper, and 1% cadmium (with the remainder being tin). In China, this alloy is designated by the grade "ZChSnSb," such as ZChSnSb11-6. The microstructure consists of a soft-phase matrix (α solid solution) and hard-phase particles (intermetallic compounds like SnSb, as well as star- or strip-shaped Cu6Sn5 compounds), giving it excellent friction-reducing properties, wear resistance, corrosion resistance, and thermal conductivity. It is particularly well-suited for high-speed, heavy-load operating conditions.
• Lead-based Babbitt alloy: Based on lead as the matrix, it contains elements such as antimony and tin, making it relatively low in cost. It is suitable for medium-to-low speed, light-load operating conditions, though its overall performance is slightly inferior to tin-based alloys.
• Cadmium-based Babbitt alloy: Less commonly used, primarily for specific corrosive environments.

2. Performance Advantages

Friction-reducing and wear-resistant properties: After initial running-in when the soft matrix wears down, the hard-phase particles help support the journal, maintaining a low coefficient of friction while also exhibiting excellent conformability and embeddability (capable of accommodating minute impurities).

Mechanics and Environmental Adaptability: Exhibits excellent conformability (adapting to journal eccentricity), anti-galling properties, robust resistance to vibration and compression, as well as superior performance under extreme temperatures and in corrosive environments.

Excellent embeddability: The soft matrix allows tiny hard particles (such as dust or metal debris) to become embedded within it, preventing scratches on the journal bearing.

Good compliance: Capable of slight deformation to accommodate minor shaft deflection or misalignment.

Anti-galling properties: Exhibits a lower coefficient of friction compared to steel journal bearings, making it less prone to cold welding (seizing).

Good oil affinity/wettability: Easily establishes and maintains a lubricating oil film.

Certain fatigue resistance: Capable of withstanding cyclic loads (especially tin-based alloys).

3. Key Points of Manufacturing Process

Bearing Bush Cleaning: Place the steel-shell bearing bush in a 10%-15% cleaning agent solution to remove rust, then rinse thoroughly with 80°C hot water. Finally, use 70°C hot water to eliminate any remaining contaminants. Never touch the cleaned inner surface with your hands.

Centrifugal casting: This process uses centrifugal casting technology to ensure an even alloy layer is uniformly bonded to the steel shell, eliminating porosity and shrinkage cavities for a strong, durable bond. The thickness of the alloy layer must be adjusted according to the specific operating conditions: thicker coatings are required for applications involving high loads, high rotational speeds, elevated temperatures, or corrosive environments, while thinner coatings are sufficient under less demanding circumstances.

III. Main Application Scenarios

Babbitt alloy bearings (especially tin-based ones) are widely used in medium-to-high-speed, medium-to-heavy-load sliding bearings that require high reliability, low friction, excellent impact resistance, and effective journal protection.

For example: Large power machinery—such as steam turbines, gas turbines, hydro turbines, main bearings for large generators and compressors, as well as connecting rod bearings.

Marine Power: Diesel engine crankshaft bearings, crosshead bearings, and thrust bearings.

Heavy machinery: Bearings for rolling mills and mining equipment.

Internal combustion engines: (some older or large diesel engines are still in use). Precision machine tool spindle bearings

Common Damages and Repair Methods

• Causes of damage include primarily bearing burn-out (caused by poor lubrication or overload), vibrational wear, and corrosion fatigue; in severe cases, the damaged area can exceed one-third of the total bearing surface.
• Repair method: Cast and refurbish damaged bearing shells by re-casting Babbitt alloy to restore their performance, making it suitable for repairing bearing shells in equipment such as drying cylinders and blowers.

IV. Usage and Maintenance Recommendations

Regular inspections: Monitor the condition of bearing bushings to prevent equipment downtime caused by the escalation of localized damage.

Lubrication Management: Ensure proper lubrication to prevent severe failures such as bearing seizure.

Temperature Control: Avoid prolonged operation in high-temperature environments exceeding the alloy's tolerance range to maintain the stability of its microstructure.