Oil Film Breakdown Research Articles

ERRATA

Title: Proposition of Thermal-Diffusion-Induced Spiral Model for the Rapid Oil-Film Breakdown Process during Scuffing

Proposition of Thermal-Diffusion-Induced Spiral Model for the Rapid Oil-Film Breakdown Process during Scuffing

Proposition of Thermal-Diffusion-Induced Spiral Model for the Rapid Oil-Film Breakdown Process during Scuffing

Friction Properties of Waste Cooking Oil with Banana Peel Broth

The aim of this study is to investigate the friction properties of waste cooking oil (WCO) with banana peel broth. The WCO was purified using a physical technique. Several weight percentages of 15 wt.%, 30 wt.% and 45 wt.% of banana peel broth was dispersed in WCO using ultrasonic homogenizer. Span 80, as a surfactant, were added to the blends. The tribological test was performed using a four-ball tribometer according to the ASTM standards. At early stage, between 0-1200 seconds, it was found that the presence of banana peel broth in WCO reduces the friction coefficient. However, after a certain time, the oil film breakdown and instantly increased the friction coefficient. By observation of worn surfaces, it can be suggested that WCO with 30 wt.% banana peel broth could be a good blends for this study. As a conclusion, this study proposes that the banana peel broth could improve the tribological properties of WCO in mild conditions.

Study of Contact Condition under Squeeze Film Formation.

This study was carried out to investigate the contact condition, between impacting hammer and oiled anvil. To estimate the contact condition during impact, the anvil sputtered with gold film was used. Oil film break down was evaluated by a electric resistance method. It was found that the pattern of impact prints left on a sputtered Au film were roughly divided into three kinds, a circle pattern, concentric circles pattern and random pattern. The ratio of diameter of impact print that seemed white to that of Hertzian contact circle was fairly small as compared with the dry contact condition. The squeeze film prevents from metallic contact according to the oil property. Most oils showed perfect separation due to the existence of squeeze film. As far as the relation between oil film breakdown and the kind of pattern is concerned, oil film breakdown is likely to occur when a circle pattern was recognized.

Influence of surface roughness on normal-sliding lubrication

Contact between machine components can involve normal, sliding and rolling motion, either singly or in combination. Combined normal and sliding motion, which occur for example in the meshing of gear teeth and in heavily-loaded rolling elements, can present problems for lubrication. The purpose of the present experimental study was to investigate how surface roughness affects the lubricant film characteristics under conditions of combined normal and sliding motion. The experimental arrar gement consisted of a rotating roller which impacted a stationary ball in the presence of a lubricant. Under the same conditions of normal surface approach, increasing the surface roughness significantly decreased the level of roller sliding that could occur without breakdown of the lubricating film. This behaviour was similar to a step function. Of the several surface roughness parameters investigated, only those which involved the maximum peak-to-valley height correlated well with experimental results. In general, surface roughness had a greater effect on oil film breakdown than did either viscosity or load.

A simplified solution to the combined squeeze-sliding lubrication problem

The unfavourable elastohydrodynamic lubrication situation in combined squeeze and sliding motion has been analysed both theoretically and experimentally. In experiments a rotating roller impacted and rebounded on a lubricated surface. It was found that oil film breakdown always occurs at the end of the impact time, when the contact force is low. It has also been found that there exists an upper limit for the sliding velocity. Below this limiting velocity no oil film breakdown occurs. This paper is an initial attempt to explain theoretically why oil film breakdown takes place towards the end of the impact, and why an increasing sliding velocity reduces the capability of the oil film to separate the lubricated surfaces. If the oil film's elastic and damping behaviour are taken into consideration it can be shown that a considerable phase shift between maximum contact force and oil film breakdown will arise. It has been found that the squeeze action dominates the pressure formation in the contact and thus the hydrodynamic effect of sliding motion is moderate. Furthermore, several effects, such as non-newtonian behaviour, surface roughness, temperature rise, starvation and deformations, which are not included in the theoretical model, may decrease the oil film thickness if the sliding velocity increases.

Lubrication of machine elements during combined squeeze and sliding motion

The motion when two parts in a machine come into contact can be a normal, sliding or rolling approach, or a combination of the three. The case of combined normal and sliding motion can be very unfavourable from the point of view of lubrication. Nevertheless, this situation does occur, for example in a gear mesh and in heavily loaded rolling-element bearings. The following factors in the case of lubrication of machine elements during combined normal and sliding motion were studied experimentally: oil viscosity, surface texture, shear strength of oil and maximum pressure. The pressure also involves the parameters normal force, Young's modulus, Poisson's ratio and surface curvature. Based on the experimental results, an equation has been deduced which describes how the above-mentioned factors influence the permissible limiting sliding velocity V sl without oil film breakdown: V sl = 0.127 × 10 − 6 ( v 0.1 − 1.575 ) ( ψ − 13.1 − 1.707 ) ( 3840 − p max ) This equation agrees well with results from experiments carried out by other authors, and is valid if combined sliding and impact between the machine elements, resulting in a limited contact time, are present.

Antifoaming Properties of Lubricating Oils

Antifoaming properties of lubricating oils are reviewed. There are two types of foaming in lubricating oils. One is surface foaming and another is air bubbles in oils. Surface foaming causes overflow of the oil from the reservoir, and air bubbles in oils promote cavitation erosion and wear brought about breakdown of oil film by bubbles. Usually antifoaming agents are added into lubricating oils. However, effects of antifoaming additives are influenced by base oils and other additives or mixing methods. In this review, effects of these several factors on antifoaming properties are summarized.

High-speed video photographs of lubrication breakdown in squeeze-sliding contact

Using photographs from a high-speed video camera it was confirmed that the main part of breakdown of a lubricating film will appear at the end of the contact time for a contact simultaneously subjected to squeeze and sliding motion. This corresponds with earlier findings using totally different equipment for electric detection of the asperity contact. The present investigation used glass and steel as the lubricated surfaces, instead of steel and steel as was the case in the earlier investigation. In combination with far less stiff equipment, the new materials gave longer contact time and larger elastic deformations of the contact bodies. It was also verified that increased surface roughness, increased sliding velocity and decreased viscosity increase the risk of oil film breakdown.

Mixed lubrication

If the simplest rheological model of a lubricant, the newtonian model, is used in the calculation of oil film thickness between elastohydrodynamically lubricated smooth or rough surfaces, oil film breakdown is never experienced. As soon as the oil film thickness over an asperity becomes thin enough, a local pressure will be built up there, squeezing the asperity into the surface and making sure that no metal-to-metal contact takes place. Oil film breakdown and surface contact through the oil film can be explained only if the behaviour of the oil is non-newtonian. In this paper, the influence of the limited lubricant shear strength on the asperity behaviour in the high-pressure zone of an elastohydrodynamic lubrication contact is studied theoretically, experimentally and numerically.

Relation between oil-film-formation and vibration-acceleration in spur gear.

To certify the effect of the dynamic load on the oil-film-formation under partial elastohy-drodynamic condition in spur gears, the cross-correlation function Rxy(τ) was measured between the insulating voltage of oil-film and the vibration-acceleration in circumferential direction. The measured cross-correlation functions show clearly that the breakdown of oil-film is apt to occur at the maximum of vibration-acceleration. Under a light tangential load, the coefficients of correlations R (O) were minus and their absolute values were large owing to large fluctuation of dynamic load, compared with the case of a heavy tangential load. In the case of a pair of hobbed gears, Rxy(0) had a higher absolute value in comparison with the case of ground gears. However, after the oil-film was almost completely formed by running-in, or when some pittings occurred at gear teeth, the crosscorrelation functions were distorted and the absolute values of Rxy(0) became small.