Project Details
Projekt
Polytetrafluoroethylene lubrication of radial rolling bearings: Control of lubricant transfer by cage design according to material-specific requirements
Subject Area
Engineering Design, Machine Elements, Product Development
Term
since 2018
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 407714666
Rolling bearings are used for guidance and power transmission between components under relative motion. For rolling bearings with solid lubrication, the formation and effect of transfer layers is important. Therefore, the cage or at least parts of the cage are made either from a solid lubricant or from a material doped with a solid lubricant in order to realize a film transfer from the cage to the bearing surfaces. The wear on the cage is determined by the load in the sliding contacts between the cage and the rolling elements. Until now, the operating life of solid-lubricated rolling bearings has been limited because the amount of material removed from the cage required for transfer layer deposition cannot be correctly adjusted. Insufficient lubrication due to insufficient transfer layer thicknesses in the rolling contacts and cage breakage due to excessive cage wear are typical damage patterns. In the first funding period, an experimental method was developed to determine the contact force in the sliding contact, which is required for the transfer in the sliding contact to lubricate a single rolling contact with pure PTFE. Thus, the determination of the operating point-dependent transfer layer generation is possible. However, due to the high wear rates of pure PTFE, the use of a composite such as PTFE/PEEK as a solid lubricant is required.The central hypothesis of the project is that the wear of the PTFE/PEEK reservoir at the cage can be reduced to a minimum value without deteriorating the lubrication effect. The aim of the project is therefore to determine the optimum composition of a PTFE/PEEK composite, considering the manufacturing and operating parameters (roughness, pressure, temperature, relative velocity). Another hypothesis is that the correct deposition rate of the transfer layer over the entire bearing lifetime requires a separation of transferred and guiding surfaces in the cage. Therefore, another goal is to design a bearing cage, in which the transferred and guiding surfaces are separated to allow an optimized lubricant transfer.Using a combination of MD simulations and tribometer measurements, the transfer, friction and wear processes of PEEK/PTFE composites are studied at the atomic level as well as at the single contact level. Parameter variations are used to determine the influences of the composition of the composite, the surface roughness of the contact partners and the operating conditions on friction and wear in sliding and rolling contacts. For a suitable combination of roughness and composition of the composite, the operating point-dependent material removal is determined. Based on this, the conceptual design, development and construction of a cage for radial roller bearings with integrated elements for PTFE/PEEK solid lubrication is carried out. Finally, functional verification is demonstrated in rolling bearing experiments.
DFG Programme
Priority Programmes
