Elements and Design of Kingsbury Thrust Bearings
Beginning with a fundamental review of the Kingsbury thrust bearing, this section lists basic bearing elements and how they work, as well as design options and accessories.
How Kingsbury's Thrust Bearing Works
A thrust bearing transmits axial loads to the foundation or machine support of rotating machinery.
Our equalizing thrust bearing actually transmits the load through a self-renewing film of oil during operation and a unique force-balancing action distributes the load across the shoes. Working surfaces touch each other only during start-up and shut-down. Otherwise, these surfaces are separated by the fluid film, so surface wear is minimal, and bearing life dramatically lengthened.
The Kingsbury thrust bearing offers many operating advantages, including:
Here is a quick review of the basic elements in a Kingsbury equalizing fluid film thrust bearing:
Rotating Thrust Collar The forged steel collar, which is rigidly attached to the shaft or rotor, transmits the thrust load from the rotating shaft to the bearing shoes.
The collar faces are ground, then lapped flat and smooth to reduce frictional loss and increase load capacity.
Stationary Pivoted Shoes
The shoes (also known as pads or blocks) in our thrust bearings have three parts:
Shoe Body Shoe thickness has been selected to reduce the amount of thermal and elastic deformation. For a center-pivoted shoe, a certain amount of thermal or elastic crowning is necessary for the thrust shoe to carry load, whereas excessive crowning reduces load-carrying capacity. Therefore, we have carefully optimized our designs so that the elastic or thermal crowning of a Kingsbury thrust shoe yields maximum load-carrying capacity.
Babbitt Face The thickness of the babbitt has also been optimized to increase compressive strength of the babbitt while maintaining the very desirable embedability characteristic of babbitt. This material allows small amounts of foreign particles that are in the lubricating oil to embed themselves in the babbitt rather than score or damage the rotating collar.
Shoe Support The spherical pivot on Kingsbury thrust shoes allows the shoe to tilt not only in the direction of rotation but also in the radial direction, compensating for some misalignment between the thrust bearing face and the rotating thrust collar. The ability of a shoe to pivot as well as to tilt increases load-carrying capability at all shaft speeds. The thrust shoe pivot, or shoe support, and the upper leveling plate where the thrust shoe pivot makes contact, are both made of high carbon steel, heat-treated to Rockwell 50C, to prevent damage to the pivot contact areas.
Design Options: While the standard position of the hardened steel support is at the center of the shoe, this support can be offset in the direction of rotation. For details, contact the Kingsbury's Engineering Department.
Special shoe body materials, such as copper alloy, can be supplied to improve thermal performance. If necessary, the shoes can be retained to facilitate installation.
Stationary Base Ring and Leveling Plate Assembly
Made of cast, plate, or forged steel, the base ring holds the shoes and leveling plates in their operating positions. An oil inlet annulus, at the back of the base ring, distributes oil to radial slots in the ring's back face.
This assembly uses the equalizing principle developed by Dr. Albert Kingsbury to distribute the load equally over the bearing shoes and transmit the load to the bearing housing.
Design Options: Bearing load can be measured by inserting strain gauge load cells in the upper leveling plates or thrust shoes. This feature can be retrofitted to installations in the field.
The base ring may be drilled and tapped for mounting shim packs or filter plates, if necessary. Contact Kingsbury for full details.
Leveling Plates The equalizing feature of the Kingsbury thrust bearing allows each shoe to carry an equal amount of the total thrust load and prevent failure of the babbitted surface and contact areas between critical components. The leveling plates, combined with the spherical shoe support, ensure that the thrust bearing face becomes perfectly aligned with the rotating thrust collar.
Number of Thrust Shoes The standard Kingsbury thrust bearing usually has six or eight pivoted thrust shoes held in the base ring, although there may be as many as 20 shoes in exceptional cases. In equalized thrust bearings, there are upper leveling plates and lower leveling plates installed beneath the shoes to equalize the thrust load.
The thrust bearings in this catalog have been designed to be used with many types of machines or applications. With center pivoted shoes, the same bearing can be used for shafts rotating clockwise, counterclockwise or bidirectionally. These bearings can be used with almost any type of oil, and due to the equalizing capability of the bearings, only reasonable care has to be taken in assembly to assure that the bearings are aligned properly. We manufacture many of these bearings in sufficient quantities to provide economical advantages to the user, and we stock them at our Philadelphia, PA and Oshkosh, WI plants to facilitate prompt delivery.
Thrust bearings without spherically pivoted shoes and the equalizing feature of leveling plates have a substantially reduced factor of safety margin compared with Kingsbury’s EQH design. This is because proper alignment of the bearing and housing relative to the thrust collar is difficult, and because accumulated manufacturing tolerances cannot permit the fine precision necessary to accommodate higher loads.
Kingsbury bearings, on the other hand, have been designed so that they offer not only maximum load capacity for the lifetime of the machine in which they are installed, but also a series of refinements that add versatility to their application.
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