Effect of Surface Texturing on EHD Lubrication Films Under Transient Speed Condition

Transient EHD lubrication, where operating parameters such as speed, load and surface curvature vary over time, occurs in many machine elements such as cams, gears or roller bearings. The effect of transient speed and surface texturing on EHD lubrication films are investigated by the direct observation. For the purposes of the experiment the speed profile of contact point between cam and follower is used. Most critical part of the operation is when the contact surfaces are running in opposite directions. This effect can cause a lubricant film breakdown and in consequence also damage of contact surfaces. For this reason three types of experiments, for the same speed profile, are carried out for polished surface and for contact surfaces with and without surface texturing. It has enabled us to consider if the texture of micro-dents have any significant influence on film thickness especially in critical parts of the operation. To simplify the problem the concept of cam and follower contact was replaced by EHD contact of the flat surface of chromium coated glass disk and a steel ball. Also only transient speed was taken into account. The method used to measured film thickness was thin film colorimetric interferometry. The experimental results show that micro-dents could increase lubrication efficiency under rolling/sliding condition through the lubricant emitted from micro-dents. It was found that the lubricant emitted from micro-dents helps to separate contact surfaces especially in the case where the contact surfaces moves very slowly in the opposite direction.