Customized Steam Turbine Journal Bearing with Babbitt Alloy Liner and Oil-film

The journal bearing serves as the load-bearing foundation for rotating components of steam turbines. Though seemingly unremarkable, it directly determines the stable operation of the turbine rotor. If the steam turbine rotor is compared to a high-speed-running athlete, the journal bearing is the track that supports it. Once the track malfunctions, the safe operation of the entire unit will be threatened.

The primary roles of journal bearings are to support the weight of steam turbine rotors and reduce frictional resistance during rotation. A turbine rotor may weigh tens or even hundreds of tons and run at rated speeds up to 3000 rpm (or other specified speeds). Journal bearings must steadily sustain such heavy loads while enabling flexible rotor rotation. Through the lubricating oil film, they absorb vibration generated during rotor operation and suppress vibration transmission and amplification, maintaining stable rotor operation and preventing equipment damage caused by excessive vibration.

The journal bearing features a relatively simple structure, yet each component fulfills critical functions:

• Bearing shell: Outer housing generally made of cast iron or cast steel with sufficient strength and rigidity to transfer rotor weight to the bearing pedestal
• Bearing liner: Part in direct contact with the rotor journal, mostly manufactured from babbitt alloys (tin-base babbitt alloy, lead-base babbitt alloy). Soft and ductile babbitt alloy compensates minor out-of-roundness of the journal and provides good wear resistance and embeddability to trap contaminants
• Oil inlet and oil groove: Oil inlet feeds lubricating oil into the clearance; oil grooves distribute lubricant evenly for complete oil-film formation
• Positioning devices: Including locating pins, shims and others that fix the relative position between bearing shell and bearing pedestal, preventing bearing rotation or displacement during operation

Stable support and friction reduction of journal bearings rely on lubricating oil-film formation. When the rotor stands still, the journal makes direct contact with the bearing liner. As the rotor starts rotating, lubricating oil flows into the clearance via the oil inlet. With rising rotating speed, the journal drives lubricant to circulate, building a wedge-shaped oil film between journal and bearing liner.

Pressurized oil film slightly lifts the journal, separating it physically from the liner and establishing liquid-friction status. The rotor weight is fully balanced by oil-film pressure, greatly reducing frictional resistance and minimizing wear on both bearing and journal as well as energy loss. Oil-film quality is closely related to lubricant viscosity, oil supply pressure, rotor speed and other parameters.

Proper maintenance of journal bearings is essential for turbine safe operation. Daily attention shall be paid to the following items:

• Lubricant quality inspection: Regularly test viscosity, moisture, impurity content and other indexes to satisfy specification requirements
• Oil level and oil-pressure monitoring: Keep oil tank level within normal range and maintain stable oil supply pressure
• Temperature monitoring: Normally operating temperature generally shall not exceed 90°C (subject to unit specifications)
• Periodic disassembly inspection: During major overhaul, disassemble bearings to examine liner conditions and verify journal-liner clearance