Experimental Study On Thickness Distribution Of Grease-Lubricated EHL Film

In this paper,the changing process of grease film under non-steady state conditions were studied.The whole thesis is mainly divided into three parts: the influence of start-stop on surface dimple under pure sliding condition,the grease film distribution under ZEV reciprocating motion and the effect of slide/roll ratio on grease distribution in contact zone.All of the experiments in this paper were carried out on a self-developed optical EHL test rig.After obtaining the interferograms,the thickness of the oil film and its variations were measured using a self-developed measurement software.The movement of steel ball and disk in the experiment can be controlled by two PLC programs respectively,creating the prerequisite for the experiment of reverse reciprocating motion.First of all,in the process of start-stop,the PB680 lubricating oil with higher viscosity was used to study the dimple transformation between "temperature-viscosity wedge" dimple and squeezing effect dimple to understand the formation mechanism of "temperature-viscosity wedge" dimple.In the study by a sudden stop,the main condition load and speed were changed.While at the start-up process,the main conditions load and acceleration were changed.The study found that both the load and the speed have a certain influence on the conversion process between the "temperature-viscosity wedge" dimple and the squeezing effect dimple.Secondly,the change of grease film under ZEV reciprocating motion was studied.In this experiment,the steel ball and sapphire disk were used and the changes in grease film under various stroke length for a variety of commercial greases was also studied.In one stroke during the reverse reciprocating motion,the film thicknesses of the acceleration and deceleration process are obviously different.Moreover,the properties of grease and the length of the stroke can affect the length of the starvation cycle in the contact area.Finally,the effect of slide/roll ratio on the presence of grease fiber clusters in the contact area was studied.The change in load does not have a significant effect on the presence time of the thickener fiber in the contact area.With the same slide/roll ratio,the lower the ball speed,the longer the time for the presence of grease in the contact area.In addition,when the slide/roll ratio is close to 0,fresh grease enters the contact area after the grease in the contact area is pushed out of the contact area.After a number of cycles,thickener fiber in the contact area are flattened and tiled in the contact area.