Influence of the heat transfer field on anomalous lubricant film formation in elastohydrodynamic lubrication conditions

The influence of the heat transfer field on anomalous film formation under elastohydrodynamic lubrication (EHL) conditions was studied. Liquid lubricant film shapes between a transparent disc and steel ball friction pair were investigated by white light optical interferometry. 1-Dodecanol was used as the representative lubricant to develop anomalous film shapes. A sapphire disc and glass disc, which have different thermal conductivities, were used as the transparent bounding surface. The heat transfer field significantly influenced the formation of anomalous film shapes. The anomalous film shapes approximated the shape of a conventional EHL film with increasing ambient temperature. However, a thickened part of the lubricant film remained, although the phase diagram of 1-dodecanol suggested it to be in the liquid state.

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.

Discrepancy in oil film distribution observed in ZEV reciprocating motion

Purpose This study aims to present the discrepancy in oil film distribution in reciprocating motion experimentally with zero entraining velocity (ZEV) on a conventional ball-disk test rig with oil lubrication. Design/methodology/approach Driven independently by two individual servomotors, a steel ball and a sapphire disc move at equal speed but in opposite directions in a triangle wave. The oil film images between the ball and the disc were recorded by a camera. After the experiments, the mid-section film thickness was evaluated by using a dichromatic interference intensity modulation approach. Findings The dimpled oil film in transient condition is shallower than that at steady state with the same load and velocities, and the transient dimple depth decreases with the decrease of time. The increase of the applied load offers a beneficial effect on lubrication. Boundary slippage happens in ZEV reciprocating motion. The slippage at the interface is related to the transient effect and applied load. Originality/value This study reveals the significant difference of the oil film variation in ZEV reciprocating motion, especially the complex boundary slippage at the interface of the oil and the sapphire disc. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-01-2020-0021

Direct Observation of Surface Transition During Scuffing in Dry Condition

This study investigates surface changes during scuffing in a dry condition. In the test a ball-on-disc apparatus was used, in which a rotating sapphire disc was loaded to a stationary steel ball. The contact area was directly observed and recorded by a digital camera attached to a microscope during the test. The variations in frictional force were synchronously measured with the capturing of images of the camera. After the test, the hardness of the scuffed steel ball were measured at different points in the contact area. The direct observation of the contact area shows that areas of macro plastic flow appeared from the trailing side of the contact area with a dramatic increase in frictional force. The macro plastic flow areas were changed, resulting in a dramatic expansion of the contact area. During the dramatic expansion, the friction coefficient kept a high constant value of about 0.4. The hardness distributions of the scuffed steel ball showed that the hardness was smaller at the tailing side of the contact area, in which macro plastic flows started, than that at the leading side. On the other hand the temperature rise calculated by a simple temperature estimation model was insufficient to cause the hardness reduction.

Synchronous Observation With Friction Measurement Prior to and During Occurrence of Scuffing

In the current work, scuffing phenomenon was investigated by a direct observation of a contact area. A ball-on-disc test rig was used, which produced a point contact area between a rotating sapphire disc and a stationary steel ball. Sequence of the friction and photograph in the contact area was synchronously obtained prior to and during occurrences of scuffing. Experiments were conducted in a dry condition and a lubricated condition with hexadecane. In the lubricated condition, wear debris accumulated in the inlet zone entered suddenly into the contact area to sharply increase the friction coefficient. On the other hand, macro plastic flow occurred in the whole contact area in the dry condition during a rapid increase in friction coefficient.