Discussion: “The Present State of Lubrication and Its Relation to Rheology” (Appeldoorn, J. K., 1968, ASME J. Lubr. Technol., 90, pp. 526–530) and “The Significant Rheological Characteristics of Lubricants” (Metzner, A. B., 1968, ASME J. Lubr. Technol., 90, pp. 531–539)

Abstract

After the presentation of Appeldoorn's and Metzner's introductory papers [1, 2], 2 the session was opened for discussion. Much of the discussion at this time was of a general nature concerning the content of both papers and is summarized here.RICHARD S. FEIN. 3 Mr. Appeldoorn has covered the broad aspects of the relation of the present state of lubricant rheology to lubrication in commendable fashion. This discussion is intended to supplement two of his points with somewhat greater detail.First, in discussing elastohydrod3 r namic (ehd) lubrication, Mr. Appeldoorn suggests that rheologists can point out where unusual rheological properties might be expected to have an effect, and what the direction and magnitude of these effects might be. I concur in this and would like to emphasize the severity of the conditions to which the lubricant is subjected. Table 1 gives some deformation and stress parameters for a typical ehd film between gear teeth under moderately severe operating conditions. 4 It is apparent that the lubricant in the ehd film is rapidly subjected to extreme deformations and stresses. Not only are shear rates, shear stresses, and pressures on the elastohydrodynamic film many times higher than those which have generally been studied bj r rheologists but the rate of change of these parameters is also extremely high. It is evident from the fairly typical numbers shown here why the understanding of lubrication requires guidance from the rheologists.