Analysis and Comparison of Hydrodynamic Features in Liftoff Seals

Abstract Dynamic seals are often used in the aerospace industry for sealing fluids in gearboxes, turbo pumps, engine main shafts, and industrial compressor applications. Dynamic seals consist of two pieces, a rotating mating ring (rotor) that is attached to the shaft and a static, non-rotating carbon face seal (stator). During operation, the mating ring rubs against the carbon face, generating heat from friction. In applications where temperature, leakage, or life requirements demand higher performance, hydrodynamic non-contacting (liftoff) seals are generally employed. Mating rings are designed with features on the contacting surface that enable the development of a film of air between the mating ring and carbon seal face above certain operating speeds. This film significantly reduces the heat generated from friction compared to a contacting face seal as there is no contact between components when non-contacting is achieved. There are multiple ways to design and manufacture a hydrodynamic non-contacting seal. A major part of the manufacturing of such seals consists of proprietary processes used to manufacture the hydrodynamic features. This work aims to characterize two of the processes, features manufactured with a laser, and features manufactured with media blasting. There are several characteristics used to determine when to use one process or the other. The testing outlined here will help determine when one process is advantageous to use over the other. This work aimed to characterize the performance differences between these two types of hydrodynamic feature manufacturing methods by studying the speed at which the seals operate in a non-contacting mode, the operating temperatures, and resultant seal leakage. Three of the four mating ring configurations were tested, including seals designed for each process that were manufactured using either process. These experiments showed a direct performance comparison between the configurations. The chosen manufacturing method, laser etching or media blasting, has a relatively small impact on seal performance (operating temperatures, leakage, and non-contacting speed). Seals designed for a particular process performed similarly with both manufacturing methods.