Tribology of Lubricants

This chapter covers the tribological properties of different types of oil, greases, solid lubricants, and metalworking and traction fluids. It explains how lubricants are made, how they work, and how they are applied and tested. It also discusses the fundamentals of lubrication and friction control, the relationship between viscosity and breakaway friction, and the factors that affect load-carrying capacity and service life.

Traction behaviour of elastohydrodynamic lubrication films with anomalous shapes

This study describes traction behaviours of lubricant films having anomalous shapes under elastohydrodynamic lubrication conditions. The traction generated at a point contact area between a glass or sapphire disc and a steel ball was measured by changing the slide-to-roll ratio. Three alcohols, 1-dodecanol, ethylene glycol and glycerol, and two alkanes of n-tetradecane and n-hexadecane were used as lubricants. Lubricants developing anomalous film shapes exhibited a solid-like behaviour with a sharp traction peak at low slide-to-roll ratios. On the contrary, other lubricants having conventional film shapes indicated a gradual increase in traction coefficient with increasing slide-to-roll ratios. The similarity of the traction behaviour to that of traction fluids supports the solidification of the film, which developed anomalous film shapes.

Improved Temperature Mapping of EHL Contacts

An effective means of studying lubricant film rheology within EHL contacts is by detailed mapping of the temperature of the fluid and the bounding surfaces within the lubricated contact area. This provides a way of directly measuring the rheology of lubricant films under true EHL conditions. Furthermore, temperature measurement itself provides a very effective means of testing and validating computer simulations. In the current work, the experimental approach initially developed by Sanborn and Winer [1] and then by Spikes and co-workers [2], has been advanced to include a high specification infrared (IR) camera and microscope. This is a similar approach to that taken by Yagi and Kyogoku [3]. As well as the instantaneous capture of full field measurements, this has the advantage of increased sensitivity and higher spatial resolution than previous systems used. The increased sensitivity enables a much larger range of testable operating conditions; namely lower loads, speeds and reduced sliding. In addition, the range of test lubricants can be extended beyond high shearing traction fluids. One additional advantage of instantaneous full field measurements is that the weak infrared optical interference caused by the film can be observed and can used to exactly locate the centre of the contact in the resulting temperature maps. These new possibilities have been used to investigate and compare the rheological properties and compression cooling effects exhibited by a PAO, a group II mineral oil, and a traction fluid.

Traction of Synthetic Traction Fluids and Its Related Rheological Properties

The traction μsp in the transverse direction due to spin was experimentally determined for commercially available traction oils. An increase in contact pressure increased μsp because of an increase in elastic strain, while a decrease in the radius of the roller in the transverse direction increased μsp owing to an increase in the effective shear modulus. Then, the effect of contact pressure on the maximum traction coefficient μmax in the rolling direction was studied. Under a constant temperature, μmax increased with increasing contact pressure, and then it decreased after reaching a peak value. The calculated results by the thermal solution based on an elastic-plastic model, using the limiting shear stress as a quadratic equation of pressure, agreed well with the experimental traction curves. This suggested that a peak value of μmax was brought about by less than a proportional increase in the limiting shear stress with pressure.

CVT Rolling Traction Drives—A Review of Research Into Their Design, Functionality, and Modeling

In this paper we detail a review of the current state of published work regarding the modeling of rolling traction drive Continuously Variable Transmissions (CVTs). An overview of CVTs operating by traction through small contact areas is performed, the layouts and kinematics of leading examples are reviewed, including the factors affecting design optimization. Properties of the traction contacts are considered in detail, with particular attention to elastohydrodynamic lubrication and asperity contact. Factors affecting the traction coefficient are reviewed and fundamental empirical predictions are contrasted with modern modeling computations. Finally measurements of the rheology of traction fluids are considered, leading to a definition of ideal properties and the development of proprietary fluids.

Application of Acoustic Emission for High-Pressure Short Time Solidification of Traction Fluids

The lubricating oils solidify at quasi-static high-pressure as the amorphous or glassy solids are verified by a number of studies. However, solidification of lubricating oil under the dynamic condition as the rolling bearings and the traction CVT is not clear. The high-pressure short time solidification of traction fluids is examined by the analysis of dent after the impact tests and AE analysis under impact loads. The intensity of each impact collision is measured by means of an acoustic emission (AE) sensor. The dimensionless AE r.m.s value is investigated by based on phase diagram of testing oils. It was recognized the solidification of oil under the dynamic high-pressure condition almost corresponded to the static condition.