The core function of a journal bearing (using the sliding journal bearing as an example; rolling journal bearings have similar structures but slightly different component names) is to support the journal and bear radial loads. Its main components and their functions are as follows:
1. Core Load-Bearing Components
Bearing Shell
The bearing shell is a key component that comes into direct contact with the journal. It is typically composed of an upper and a lower half-shell (a split structure), and its material is selected based on operating conditions (e.g., babbitt metal, copper alloy, cast iron, etc.). Its function is to transmit the radial load of the shaft to the bearing seat through sliding or rolling contact with the journal, while also reducing friction losses. The surface of the bearing shell is usually machined with oil grooves to store lubricant, forming an oil film that isolates the journal from the bearing shell and prevents wear caused by direct metal-to-metal friction.
Bearing Seat
The bearing seat serves as the mounting base for the bearing shell, typically made of cast iron or cast steel, and is bolted to the equipment frame. Its primary functions are to secure the bearing shell in place, ensure concentricity between the journal and the bearing shell, bear the radial load transmitted by the bearing shell, and distribute this load to the equipment foundation-preventing excessive localized stress that could cause equipment deformation. Some bearing seats are designed with heat sinks to accelerate heat dissipation, making them suitable for high-speed or heavy-load applications.
2. Auxiliary Components
Lubrication System
It consists of an oil hole, an oil groove, and an oil supply device (such as an oil cup or oil pump):
The oil hole is used to inject lubricating oil between the bearing shell and the journal;
The oil groove (mostly located on the inner surface of the bearing shell) guides the lubricating oil to spread evenly across the contact surface, forming a continuous oil film;
The oil supply device provides continuous or intermittent lubrication according to operating conditions (e.g., a manual oil cup for low-speed conditions and a forced lubrication pump for high-speed conditions). Its core functions are to reduce the friction coefficient, lower operating temperatures, and prevent metal corrosion.
Thrust Device (Select Models)
For journal bearings that require axial displacement control (such as turbine main shaft bearings), a thrust ring or thrust washer is installed between the end of the journal and the bearing seat. Its role is to bear a small amount of axial load, prevent shaft movement caused by excessive axial forces during operation, and ensure the axial positioning accuracy of the shaft system.
Sealing Devices
These include oil seals and sealing rings, installed at both ends of the bearing seat. They prevent lubricant leakage and block external dust, moisture, and impurities from entering the bearing-avoiding lubrication failure and bearing shell wear. (Sealing devices are particularly crucial for extending bearing life in dusty and humid environments.)
Adjusting Shims
Located between the bearing shell and the bearing seat, these are typically thin metal sheets (0.05–0.5mm thick). By increasing or decreasing the number or thickness of the shims, the clearances (radial and axial) between the bearing shell and the journal can be adjusted. This ensures the bearing operates with neither excessive tightness (which would cause overheating) nor excessive looseness (which would cause vibration), thus guaranteeing load-bearing stability.
3. Component Synergy
The operation of a journal bearing relies on the coordinated function of its various components: the bearing seat provides rigid support; the bearing shell contacts the journal via the oil film formed by the lubrication system and transmits loads; the sealing devices protect the lubrication environment; and the adjusting shims optimize clearances to ensure operational accuracy. The failure of any component (such as bearing shell wear, seal leakage, or loose shims) may lead to bearing overheating, increased vibration, or even shaft system damage. Therefore, the performance matching of each component is just as important as routine maintenance.