Observations of Liquid Droplet Behavior and Oil Film Formation in O/W Type Emulsion Lubrication

The behavior of liquid droplets in O/W type emulsions flowing between a flat glass plate and a metal roller was observed by means of a microscope. The behavior of the droplets introduced into the EHL film was found to be related to the streamlines of the continuous water phase in the vicinity of the inlet zone. It was observed that the oil droplets which penetrated into the EHL zone formed an oily pool (an oily film zone) containing water droplets in the inlet zone close to the EHL zone. This oily pool was a W/O emulsion rich in oil caused by phase inversion. The effects of oil concentration, emulsifier content and rolling speed on the area of the oily pool were investigated, and it was found that the extent of the oily pool was influenced by the rolling speed as well as oil concentration. The EHD film thickness was measured by means of optical interferometry with use of two wavelengths, and the measured results were compared with the calculated ones employing the starvation theory of Wolveridge et al. and the empirical equation of Wymer and Cameron for the region of the oil pool. It was found that course droplets play an important role in film formation by causing the formation of the oily pool in the low speed range. In the high speed range, however, a fine O/W emulsion forms the film.