The effect of macroscopic wear on friction in lubricated systems
I. Crãcãoanu and D.J. Schipper
Phone +31-(0)53-4892476, e-mail i.cracaoanu@utwente.nl University of Twente, Faculty of Engineering Technology,
Laboratory for Surface Technology and Tribology, P.O. Box 217, NL 7500 AE Enschede
Introduction
Wear is a dynamic and complex phenomenon that leads to a change in functional behav-iour, in particular friction, of lubricated system.
Objective
Understanding of the effect of macroscopic wear on the friction in lubricated systems.
Test method
Friction of worn systems was measured using a pin-on-disc tribometer.
Fig.1: Pin-on-disc tribometer.
Experimental conditions: Load F = 10 [N]
Temperature T = 21 [0C]
Sliding velocity v = 0.001 to 1 [m/s] Sliding distance s = 72 to 216 [m] Lubricant viscosity 0 = 0.078 [Pa·s]
Results
10X Dw = 0.25 [mm] 4 h Dw = 0.34 [mm] 8 h Dw = 0.37 [mm] 12 h 5X 2a = 0.35 [mm] 8 h 2a = 0.63 [mm] 16 h 2a = 0.84 [mm] 40 h 2b = 0.17 [mm] 2b = 0.27 [mm] 2b = 0.35 [mm]Fig. 2: Wear evolution in point (above) and elliptical contacts (below).
Friction in lubricated systems can be best rep-resented in the generalized Stribeck curve, i.e. the coefficient of friction is depicted as a function of velocity. In Fig. 3 and 4 the results are given. 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.001 0.01 0.1 1 10 Velocity [m/s] C oe ff ic ie nt o f f ri ct io n, f [-] after 4 h after 8h after 12 h BL ML EHL wear
Fig. 3: Experimental Stribeck curve – point contact. 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.001 0.01 0.1 1 10 Velocity [m/s] C oe ff ic ie nt o f f ri ct io n, f [-] after 8h after 16h after 40h BL ML EHL wear
Fig. 4: Experimental Stribeck curve – elliptical contact.
Conclusion
Based on these experiments it is concluded that wear improves the lubrication situation of Force Closed Systems.
The contact geometry modification due to wear leads to changes on operating regimes of the lubricated systems (Fig. 3 and 4).
Future work
Validation of the experimental results.
elastic joint Circular contacts
Elliptical contacts F arm pin Rx = 4 [mm] Ry = 26.67 [mm] AISI 52100 H = 63 HRC R = 5 [mm]
