Tilting pad bearing history
Evan Zabawski | TLT From the Editor April 2020
You don't always have to be first to be famous.
Dr. Albert Kingsbury (right) at the 25th anniversary celebration of the installation of his first bearing. Photo courtesy of ASME.
When asked for another name of a tilting pad bearing, the most common answer seems to be Kingsbury and not Michell. Both names refer to their respective manufacturers, which are, in turn, named after their founders—two inventors with an interwoven history.
Anthony George Maldon Michell was an Australian engineer whose major contribution to the field of lubrication was his 1905 publication of a three-dimensional solution to the Reynolds’ equation which considered side leakage. However, in the same year he patented his design of a tilting pad bearing in both Australia and Britain, this was a full five years before Dr. Albert Kingsbury patented a similar design in the U.S.
The first installation of a Michell bearing appears to be a vertical thrust bearing for a centrifugal pump installed on the Murray River in Cohuna, Australia in 1907. This was also a full five years before the first installation of a 48-inch diameter Kingsbury bearing on Unit 5 at the Pennsylvania Water and Power Co. in Holtwood, Pa. When the 10,000 HP unit was started up on June 22, 1912, the bearing wiped—a rather ignoble beginning.
If the official accounts clearly show that Michell preceded Kingsbury, why did the lion’s share of fame go to Kingsbury? This apparent injustice seemingly grows once we see that Michell complexly calculated the pressure distribution to place his bearing’s pivot line off-center and through the point of maximum fluid pressure, yet Kingsbury simply placed his spherical pivot in the geometric center of the bearing—a design consideration so simple as to appear flawed.
The placement was to allow rotation in either direction, a consideration dating back to Kingsbury’s first constructed model of a tilting pad bearing in 1898. The spherical pivot proved to be advantageous by allowing the pad to compensate for misalignment between the pad and rotor, eventually leading to wider adoption of the Kingsbury design over Michell’s.
This is not to suggest that the Michell design is flawed. In fact, when his first bearing was removed from service after five months, the original hand scraper (machining) marks were still visible. It was about this same time that Kingsbury first applied for his patent and was apparently quite upset that it was not immediately awarded due to Michell’s patent.
One document suggests the dispute Kingsbury had with Michell was “legendary,” but details are scarce. What is known is that proof of his 1898 work reversed the patent office’s decision, and even Michell would later admit in a 1929 paper that his bearing was not the first and that “Professor Kingsbury’s work was commenced a few years earlier.”
By this point, Kingsbury likely did not require this vindication because Westinghouse had been undeterred by the failure of his first field installation and had given him a second chance. The failure taught Kingsbury much about tolerances and finishes required for successful operation, leading to proper finishing and fitting before the second attempt. Therefore, by 1929 Kingsbury’s bearing had been operating continuously for 17 years without incident.
To mark the 25th anniversary of the installation, Kingsbury returned to Holtwood and took time away from the ceremony to smear his initials into the oil film of a Kingsbury bearing shoe that had been removed for the occasion. Seven years after his death in 1943, the generator was rebuilt and the original bearing was retained with “not a single part” being replaced. In 1987, the American Society of Mechanical Engineers (ASME) designated the bearing as an International Historical Mechanical Engineering Landmark in celebration of 75 years of continuous service—truly a remarkable feat cementing Kingsbury’s fame for a well-designed bearing.
Evan Zabawski, CLS, is the senior technical advisor for TestOil in Calgary, Alberta, Canada. You can reach him at ezabawski@testoil.com.