Pressurized environments directly influence friction and wear of dry steel contacts - Investigations in a novel high fluid pressure tribometer

To reduce the usage of classical lubricants in deep drawing, a new tribological system based on volatile lubricants was developed. Therefore, a volatile medium is injected under high pressure into the interstice between drawing tool and sheet metal. Depending on temperature and pressure, the temporary lubricant may exist in its gaseous or liquid phase. In this study, a novel high fluid pressure tribometer was designed to investigate the friction and wear of dry steel contacts under comparable conditions like in dry deep drawing. Therefore, a new ball-on-disc tribometer was designed and integrated into a high-pressure vessel. To specifically investigate the effects of different environments (technical air, liquid and gaseous carbon dioxide, nitrogen, argon) at atmospheric and high pressure (0.1 MPa, 6 MPa) on tribology, the specimens and all components were operating unlubricated. During the experiments, the friction was measured continuously. Results show that the highest friction occurs in air and the lowest in carbon dioxide environment. Subsequent to the experiments, the wear of the specimens was assessed along with changes in surface chemistry related to tribochemical reactions. Therefore, the tribology of the dry sliding contacts is correlated to changes of the surface chemistry. Also differences as well as similarities regarding the different fluid environments are shown. As the results show, the differences between the media used are most pronounced at elevated pressure. Concluding, this work gives clear indications on the suitability of volatile lubricants in dry friction or rather gas lubrication, especially for dry deep drawing.