Lubrication modes and the IRG transition diagram

The relationship between a Lubrication Mode Diagram (LMD) for concentrated contacts (LCC‘s) and the ‘IRG transition’ diaLubrication Modes and the IRG Transition D i ag ram gram has been studied. In addition, scuffing results, obtained by the IRG (International Research Group) have been analysed, as well as the results of scuffing tests performed by different workers using a two-disc apparatus. It has been found that in Region I of the IRG transition diagram, three sub-regions can be distinguished, representing elastohydrodynamic lubrication, mixed lubrication, and boundary lubrication, respectively. Thus, the IRG transition diagram is not comparable to a ‘lubrication mode diagram’. Furthermore, it has been found that failure of LCCs by scuffing most frequently occurs under conditions of mixed 1 ubrication. Therefore, scuffing criteria based upon the assumption that the load at failure is carried entirely by the micro-contacts are doubtful, and probably wrong. Nomenclature E F n H L P R Rat Units Equivalent elasticity modulus for combined surfaces (Pa) Normal force (N) Operational number: H = qi-V,/p (m) Lubrication number: L = H/Rat = qi-VJGRat) Mean contact pressure (Pa) Reduced radius of curvature (m) Combined CLA surface roughness: Rat = (RaI2 + Ra22)*2 (m> Slip or slide-to-roll ratio: S = 2.V$V+ ( I ds> ( Ids) Inlet viscosity (Pa.s) Coefficient of friction refers to properties of individual surfaces Sliding velocity: V = IV, V21 sum velocity: V+ =Vl + V, Lubrication Science 8-1, October 1995. (8) 27 0954-0075 $10.00 + $4.00