EFFECTS OF MICRO (ROCKING) VIBRATIONS AND SURFACE WAVINESS ON WEAR AND WEAR DEBRIS

Recent studies have shown that micro-vibrations (10-100 mu m amplitude , 10 to 100 Hz) can reduce sliding wear 50%. especially rigid body roc kings of the slider. In this article, clearances between a carbon brus h (called a carbon sample in this article) and its holder were reduced while sliding over a slightly wavy (8 to 20 mu m) steel surface. Undu lations of the counter surface induced rigid body vibrations of the sl ider, including rocking. Tighter fits restricted rocking, looser fits permitted it, Plotted were wear (mu g s(-1)) rate vs. speed (rpm) with clearance between brush and holder a parameter. Normal and rocking mo tions were measured. We found: (a) Micro-vibrations reduced brush wear on steel: (b) No rocking gave higher levels of wear; (c) An optimal f it (150 to 200 mu m clearance), which kinematically permitted optimum rocking, 10(-3) to 10(-1) degrees, gave maximum wear reduction; (d) Fi ts too loose increased wear beyond smooth rotor levels; (e) Rocking wi th rotation vectors parallel or perpendicular to the sliding direction gave similar wear reduction, 50% or more; (f) Rocking with a rotation vector perpendicular to the sliding direction generated 'chatter', au dible acoustic noise; (g) Rocking with a rotation vector parallel to s liding was quiet: (h) Wear reduction can occur at low waviness amplitu des (8 mu m). Also in this article, wear particles were inspected unde r Scanning Electron Microscope. At low to moderate speeds particles sh ed from wavy and smooth copper counter surfaces were similar. At highe r speeds, smooth surface panicles were larger than wavy surface partic les: often snowball like compactions of sub-particles similar to those shed from the wavy surface. This is consistent with a hypothesis wher ein small weak particles shed from a slider running over a wavy surfac e escape the sliding interface through gaps opened by vibrations; with out gaps, particles become entrapped and compacted. In addition, clear ances optimal for wear reduction correlated to the size of the gaps re quired for particles to escape. (C) 1998 Elsevier Science S.A. All rig hts reserved.