Seals perform an important and at times overlooked function in a lubricant system. They prevent or minimize the movement of the lubricant between two surfaces and also minimize the level of contamination in the system. Seals are divided into static and dynamic types. Static seals operate in systems where the mating surfaces do not move relative to each other. In contrast, dynamic seals operate under conditions where the mating surfaces are in relative motion with each other. A previous TLT article discussed a second-generation engine oil seal prepared from polytetrafluoroethylene.1 This seal represented an improvement over a first-generation material because it was installed without an installation aid. Performance testing showed the benefit of having a reduced length and more grooves in the seal lip. Evaluation testing demonstrated that additional grooves led to a reduction in friction in the engine.
Acoustic emissions (AE) technique was applied to rolling contact fatigue tests of two radially loaded rollers running under constant load and velocity to detect the incipient damage and damage location. Signals detected from contacts were processed using signal conditioning and enhancement techniques by an AE source locator to bring out the difference between the signals from the sound and damaged rollers. It was found that AE hit count pulse observations by the AE source locator can provide an indication of the damage at its initial stage. The conventional AE parameters and the AE signal features were studied and correlated with the AE source locator counts. The results demonstrated the successful use of the combination of the AE monitoring and the AE source locator as a new technique for detecting the incipient damage and forecasting the position of the damage in the roller, and this technique could allow the user to monitor the rate of deterioration of the rolling elements.
Many phosphorus-based antiwear films, including those formed by zinc dialkyl dithiophosphates (ZDDP), cause a significant increase in friction in thin film, high-pressure, lubricated contacts. This can have a deleterious effect on engine oil fuel efficiency. Previous work has shown that friction is increased not under boundary, but under mixed lubrication conditions and it has been suggested that this phenomenon results from an effective roughening of the rubbing surfaces by the formation of unevenly distributed reaction films.In the current paper it is shown that, when other additives commonly used in engine oils are added to ZDDP solutions, quite smooth ZDDP reaction films can result. Despite this, the ZDDP still produces a marked increase in friction in mixed lubrication conditions, which suggests that surface roughening is not the main origin of friction enhancement by ZDDP reaction films. In a companion paper, Part H, it is shown that ZDDP reaction films, whether rough or smooth, enhance friction by inhibiting the entrainment of liquid lubricant into rubbing contacts, thereby reducing the elastohydrodynamic oil film thickness (13).
In a companion paper, Part I, it was shown that the friction enhancement produced in mixed lubrication conditions by ZDDP reaction films is not due to surface roughening as has previously been supposed. Instead, optical measurement of elastohydrodynamic film thickness shows that the presence of a ZDDP reaction layer inhibits the entrainment of liquid lubricant into rolling/sliding contacts. As a result, these contacts operate in boundary lubrication, with consequently high friction, up to higher speeds than would otherwise be the case and the attainment of full film elastohydrodynamic lubrication is also postponed. Possible mechanisms by which ZDDP reaction films might inhibit fluid entrainment are discussed.
