Purpose The cleaning of food production equipment using cleaning detergents may contaminate the lubricant of the bearings, thereby reducing the bearing service life. The purpose of this paper is to investigate the cause and mechanism of such damage of bearings lubricated by cleaning detergent/water-in-oil emulsions. Design/methodology/approach The emulsion was prepared by adding a mixture of cleaning detergent and water in one base oil. A self-designed ball-on-disc optical interference test rig was applied to examine the effect of emulsion on lubrication and wear of bearing contacts under pure sliding conditions. Findings The emulsion reduced lubricating film thickness at a relatively low-sliding speed but only when the water concentration (20%) in emulsion was high. Water droplets were trapped around the ball-on-disc contact area under static conditions because of a high capillary force. The emulsion can induce damages on the soft surface in the startup mainly due to the presence of water around the contact. Originality/value The basic lubrication behaviour of water/oil emulsions containing cleaning detergent under pure sliding was experimental studied and the mechanism of bearing damage in food production equipment was investigated. Based on the study, the solution to avoid such damage was proposed.

As a common phenomenon in elastohydrodynamic lubrication, cavitation has an effect on the completeness of the oil film in the contact area. Many studies have therefore been conducted on cavitation. Experimental researches on cavitation usually rely on optical interference observation, which offers a limited resolution and observation range. In this paper, an infrared thermal camera is used to observe the cavity bubbles on a ball-on-disc setup under sliding/rolling conditions. The results show that the cavity length increases with an increases of the entrainment speed and the viscosity of the lubricants. These observations are explained by a numerical model based on Elrod's algorithm. Effects of entrainment speed and lubricant viscosity on the breakup of cavitation bubbles and the cavitation states are investigated. Both the simulation and experimental results show that a negative pressure area is present behind the Hertzian contact area. The ambient pressure plays a role in maintaining cavitation state 1. The cavitation pressure is close to the vacuum pressure when the entrainment speed is low and to the ambient pressure instead when the entrainment speed is high.

Temperature has a significant effect on the performance of elastohydrodynamic lubrication (EHL), and this topic has been extensively covered in many studies. These studies are focused on how temperature affects lubrication performance, without considering the effect of temperature on the deformation and the subsurface stress of the contact bodies. However, there will be a significant rise in temperature in the contact area under such conditions as high speeds, heavy loads, and high slide-roll ratios. This will generate significant thermal stress inside the solid, thus inhibiting the elastic deformation of the contact surface and impairing the lubrication performance in the contact area. In such cases, it is essential to consider the effects of solid thermal stress and thermal expansion on thermal elastohydrodynamic lubrication (TEHL). In this paper, a TEHL model that consider solid thermal expansion and thermal stress to solve point contact problems is developed. The effects of solid thermal expansion and thermal stress on pressure, film thickness, temperature, and subsurface stress are investigated. The results show that solid thermal expansion partially inhibits the elastic deformation of the contact surface, resulting in a decrease in film thickness and an increase in pressure. It is also found that solid thermal stress causes the subsurface von Mises stress of the upper contact body to increase and that of the lower contact body to decrease.

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An electrohydrodynamic lubrication (EHL) model in point contacts with consideration of surface coating is presented. The disturbance displacement caused by the coating on the surfaces is calculated using the finite element method (FEM). The effects of coating’s hardness and thickness on oil film pressure, thickness, and subsurface von Mises stresses are investigated. The results show that hard coating causes a significant increase in the oil film pressure, while soft coating has the opposite effect. A significant stress concentration occurs at the subsurface when there is a hard coating. And when the thickness of the coating reaches a certain value, the subsurface stress reaches its maximum. While when there is a soft coating, the maximum stress on the subsurface is slightly reduced.