TRI Align-A-Pad® Bearings
The TRI Align-A-Pad® tilting pad journal bearings are state of the art. The heavy duty operating performance characteristics result from advanced design detail and careful selection of materials. The Align-A-Pad tilt pad bearings are designed for ease of installation, alignment, and maintenance by customers’ in-house personnel.
The design details which make the Align-A-Pad journal bearings so successful are the direct result of many years of analytical, diagnostic and in-place optimization efforts by Turbo Research in its consulting work with turbomachinery users around the world.
TRI supplies all types of journal bearings, including elliptical journal bearings, pressure dam journal bearings, circular bore journal bearings, and film-damper journal bearings with pressure fed lubrication. Either standard or undersize bore are available. For fans and similar equipment, TRI supplies journal bearings with either oil ring and/or pressure fed lubrication. Our objective is to supply the journal bearings that are proper for the customers’ requirements. Journal bearings with lift oil pockets and lift oil pumping systems are also designed and provided.
There are many factors that have to be addressed in the design of bearings for high-speed (3600 rpm) turbine rotors for Steam Turbine-Generators. Among these factors are the following: Vertical forces from rotor weights and vertical misalignments across couplings; Lateral forces on the High-Pressure turbine rotors from steam emanating from the entrance nozzles from the “Nozzle Block”; temperatures of the journals, temperatures of the housings surrounding the bearings, and even the temperature distribution throughout the foundation for a turbine-generator.
It is clearly not satisfactory to assume that the only weight to be used in calculating bearing performance is the cold static weight carried by the bearing when the centerline of the rotor train has the shape of the ideal catenary from one end of the train to the other end. This is one case, and may be the first case studied, but others need to be considered depending upon the circumstances of the application. The designer must be well aware of all of the forces acting on the bearings, the temperature distributions through the machine, both transient and static, and other influences such as the range of lube oil temperatures expected.
TRI Align-A-Pad® bearings are extremely effective for High Pressure and the Intermediate Pressure Rotors with journals from 6 inches to 20 inches. The typical designs are 5-pad or 6-pad configurations depending upon bearing reaction forces and speeds.
Many existing Low Pressure Turbine Bearings are fixed bore with a spherical OD fitted to an outer bearing ring that has “saddle blocks” or alignment pads on the OD. If the turbine rotors show a tendency to exhibit vibrations of substantial amplitude and are unreliable when being balanced, a choice is to redesign the bore geometry to stiffen the film and to suppress the rotor vibration amplitudes.
It should be noted that today, the price for a new TRI Align-A-Pad® Bearing which has self-aligning pads and has “saddle blocks” or alignment pads on the OD is almost the same as for a new fixed bore bearing with spherical OD and an outer bearing ring with “saddle blocks” or alignment pads on the OD. This is how an improved technology can be very cost effective for new or refurbished machines.
An issue for the HP and IP turbines that have very hot steam conditions is the heating of the standards adjacent to the turbines. When the standards get hot, they expand more than the bearings that are being cooled by colder lube oil, so the bearings can become loose. TRI has numerous methods to design bearings to remain tightly mounted in standards that get hot.
Steady Rest Bearings (extension shaft bearings)
Many turbines have long extension shafts, often approximately 6 feet long or longer, that are attached to the HP Turbine rotor and extend through the front standard. In almost all cases, the overspeed bolt and the main oil pump are mounted on this shaft, and in some cases, the thrust bearing runner is included as well.
For many reasons, at 3600 rpm and generally due to unbalance of the rotors and marginal control of the resulting rotor vibrations, these extension shafts vibrates excessively, causing wear to the seal rings (aka “wear rings”) of the main oil pumps.
A number of turbines have extension shafts that extend through the front standard and drive large high powered fluid drives through flexible couplings. Westinghouse turbines use steady rest bearings to support the end of the extension shafts for these applications. The Westinghouse steady rest bearing design uses four small tilting-pads with small diameter rod supports that often pound out within a short time from being installed, whether new or after being renewed. Another extension shaft application that occurs with increasing frequency today has to do with the collector extension shafts outboard of generators. This occurs because rotating exciters that supported these collector extension shafts are being removed and solid-state excitation systems are being installed. This leaves these extension shafts unsupported or inadequately supported at the ends so they experience high amplitude vibrations. Serious consequences are that the collector brushes wear rapidly and the collector rings wear in a non-uniform pattern, often with a 2 per rev wear pattern, due to the two-pole design of the generator rotors with the inherent 2 per rev bending stiffness.
TRI’s solution is to provide heavy-duty bearings and supporting pedestals of appropriate designs. TRI has manufactured numerous steady rest bearings and associated pedestals for the extension shafts of Westinghouse turbines. TRI now has a repertoire of parts from which an assembly of parts is selected. Certain TRI bearing designs bolt right onto the front walls where the existing 4-pad Westinghouse bearings are attached.
Where there is no fluid drive, the extension shaft is wholly within the front standard and a new pedestal extending from the floor to the new TRI bearing is required. These have proven to suppress the rotor vibrations to the point of eliminating wear of the pump seal rings, one of the most common causes of reduced availability of turbine-generators.
If desirable, TRI can manufacture and supply new extension shafts, and if desired, with an integral multi-tooth wheel for electronic speed and overspeed control.
TRI’s solutions for solving the vibration issues of collector extension shafts generally include these activities:
- Assuring that there is a journal surface that is concentric to the extension shaft and collector rings. This may involve “in-place machining” of the existing rotor, or adding on a short extension shaft with a qualified round and concentric journal surface.
- A TRI Tilting pad bearing of heavy duty design.
- A pedestal that extends from the new TRI bearing down to a sole plate.
- A sole plate, if necessary.
TRI also provides Technical Direction service for installation of our Bearings and other products.
- Tech Note March 2005: Solutions For Common Problems of Extension Shafts, Oil Pumps and Steady Rest Bearings For Westinghouse Large Steam Turbine Generators
- Tech Note June 2016: Pressure Dam & Elliptical Bore Bearings
- Tech Note November 2007: How changes to condenser back pressure and condensate temperature can effect LP turbine rotor vibrations
- Tech Note March 2005: Solutions for common Problems for Westinghouse Steam Turbine Generators
- Tech Note June 2003: Solutions for over-heating and vibration
- Tech Note July 1996: 750 MW Westinghouse Turbine-Generator Improved