Thrust Bearing Turbine

Thrust bearings are used in turbines that generate clean energy. This includes wind, solar, geothermal, and the energy derived from water currents.

The thrust bearing consists of Babbitt metal lined shoes that run against the rotor shaft collar. It can take radial load but cannot take axial load. Under low speed and idling conditions, it is susceptible to crossover.

Axial Load

The function of a thrust bearing is to take the axial load caused by flow of steam through a turbine. A hydraulically-operated piston within the bearing carries this axial force, which is transmitted to the rotating rotor shaft.

Journal bearings can only take radial loads and cannot withstand axial load, but a thrust bearing is designed to handle both axial and rotary loads. The thrust bearing consists of Babbitt metal lined, stationary shoes that run against the rotor thrust runner. The runner is allowed to float to both axial directions, but the axial shift must not exceed a certain limit or it can damage the rotation and fixed parts of the equipment.

Various types of thrust bearings are available. One type uses a self-equalizing link to handle static misalignment and thermal expansion between the bearing surfaces. This kind of bearing is also known as a flat land, tilting pad or polymer-lined thrust bearing. It is used in turbines that run on clean energy sources, such as wind power and geothermal power.

Axial Clearance

The axial clearance is the distance the shaft can move between the thrust collar and bearing shoes. It allows room for the formation of an oil film and misalignment between the bearings.

During operation the axial load on the thrust collar is often higher than on the bearings. When this occurs it can cause the rotor to tilt about each of its axes. This is known as a rub or impact condition, and can damage the thrust collar or the bearings.

The self-equalizing link design helps to avoid the occurrence of these conditions by allowing the rotor to float or orbit about each axis. This arrangement also prevents the onset of critical speed, which is the point at which the axial force exerted on the rotor changes from an aft direction to a forward direction or vice versa. This condition can lead to failure of the rotor.

Rotor Clearance

Thrust bearings are an integral part of many machines. They help the machines to operate smoothly while avoiding breakdown due to excess weight. Similarly, thrust bearings play an important role in equipment that produces alternative energy.

The thrust bearing consists of several sector-shaped shoes or pads fixed on a pivot. The pivot is inserted between the shoes and the shaft collar. The shoes are free to tilt about the pivot, and oil pressure causes the pad to tilt slightly, thereby creating wedge-shaped regions of pressurized oil between the shoes and collar surface.

Under low or idling speeds, the compressor discharge pressure is biased toward its open position by this biasing force. Therefore, under these conditions, no compressor discharge air is admitted to the cavity 32. This prevents the axial load on the rotor from shifting under these conditions to a forward direction and preventing crossover. This allows the thrust bearing to perform adequately under low or idling speed conditions.

Tilting Shoe

A thrust bearing consists of Babbitt metal lined, stationary shoes that run against the rotor runner. They can take radial load but can’t take axial load. The shaft is allowed to float in both axial directions but only within a certain limit that prevents damage to the rotor and fixed parts.

As shaft speeds and loads increase, gas turbine and steam turbine applications are pushing the safe operating limits of flooded tilting pad journal and thrust bearings. These types of bearings require special design features, such as copper chrome babbitted shoes and assurance of proper pivoting mechanisms. They also use directed lubrication to minimize power losses and reduce bearing surface temperatures.

Tilting pad bearings can include self-equalizing links to handle misalignment between the shoe and collar. They may also be deliberately crowned or deformed to accommodate shaft rotation and to control the distribution of lubricant film thickness. As such, their performance depends not only on tilt parameters but also on the pad geometry and the effects of the tilting pads on lubricant flow within the diverging pad area.