PERFORMANCE OF A POWDER LUBRICATED JOURNAL BEARING WITH WS2 POWDER - EXPERIMENTAL-STUDY

Previous investigations have demonstrated the principle and feasibilit y of quasi-hydrodynamic lubrication using powders. With conventional l ubricants, the hydrodynamic behavior of a journal bearing can be summa rized in the form of a plot of friction coefficient against a nondimen sional load parameter usually referred to as a Stribeck curve. One of the main features of the curve is that, as the thickness of the lubric ant film increases, the friction coefficient initially decreases until it reaches a minimum and then increases due to shearing of the lubric ant film. Previous tests on a three pad journal bearing using molybden um disulfide powder ns the lubricant showed that its friction/load cha racteristics followed the Stribeck form. The experimental work reporte d herein describes further tests carried out on a three-pad journal be aring to evaluate its thermal stability and long teem went characteris tics using tungsten disulfide powder as the lubricant. Dry tungsten di sulfide powder lubricant has been shown to provide excellent wear resi stance. Its friction properties are similar to molybdenum disulfide bu t it can be used at much higher temperatures. Bearing tests were carri ed out nt speeds up to 30,000 rpm and lends Lip to 236 N. Over the loa d/speed, range stable thermal operation was achieved From friction tor que measurements it was found that the coefficient of friction for the bearing was essentially constant over the range of lends and speeds. Unlike liquids, powders have a limiting shear strength property. When the limiting shear stress is reached in a powder flow, the powder esse ntially shears along a plane and does not pow in a viscous manner. The constant friction coefficient seen with the tungsten disulfide powder suggests that the powder had a low limiting shear strength and that t his dominated the operation of the bearing in the rests. The total acc umulated test time was more than eighteen hours. Periodically, the tes t journal and bearing pads were inspected but there was no measurable wear or visible damage.