Proceedings of SerbiaTrib '13

where P is the load, a – radius of the contactsurface, and r – radius of the sphere.In the friction couple components (see Fig. 9)are made of steel, the quantities of equations (5),(6) and (7) become:p max ≈ 5800 3 P (8)p med ≈ 1700 3 P (9)A1A2a ≈ 0.09 3 P (10)Attention was paid to processing of workingsurfaces of couples. Surface state defined bytopography, microstructure of surface layer andoxidation state has a major influence on the wearprocess.Due to the complexity of processing by abrasionof the surface, the most reliable way to ensure areproductible surface is stringently observance ofall processing phases, which are turning of theform, finishing turning, thermal treatment, andcorrection of profile by polishing andsuperpolishing of working surface.All the operations until smooth processing of theprofile are made by current technology, noting thatthe intensity of the process is kept low to protectthe structure of the surface layer of material.Super-finishing operation using metallographicground slides technique includes:- wet polishing with sandpaper, grain size 32 μmand 17 μm;- polishing with diamont slury, grain size 6 μmand 1 μm;- wet polishing with slury of 2000 Ǻ.Finally, the surfaces are washed with distiledwater, alcohol and then are dried.The maintenance of processed couples is madein closed vessels, on silica gel. Surfaces roughnesswas measured with a roughness tester withparametric transducer and recording. Theinstrument allow recording of surface profile, andalso determination of R a and r.m.s., defined as:Rar.m.s 1ll01ll0ydxy2dx(11)(12)In Fig. 6 (A1-A8) profiles (cross-cut) of thesurfaces used and of microphotographs obtained innormal lighting are presented.A3A5A7Figure 6. Profile and microfotograph of the surface withroughness R a = 0.015 μm (A1-A2), R a = 0.045 μm (A3-A4), R a = 0.075 μm (A5-A6) si R a = 0.19 μm (A7-A8).4. RESULTS AND DISSCUSION4.1. Evolution of the surface state in the wearprocessExperimental determinations were made onthese test conditions:- Load: variabile between P = 20 ÷ 300 N fordetermining of seizure limit. A load of 50 N wasused for wear tests.- Sliding speed: Main speed for determining thewear rate was u = 174 cm/s. To determine theinfluence of speed on the wear, the device allowsachieving speeds:u = 60 cm/s; u = 18 cm/s si u = 3,2 cm/s.- Lubricant: BSF (Body Simulated Fluid) with thedensity 1183 kg/m 3 and vascosity 0.84 Pa s(HyClone, SH30212.03).Using the parameters above mentioned, thecpuple operates in elastohydrodynamic regime.For the minimum thickness of the lubricant film,Archard [8] proposed the relationship:hr00.741 20.0740 u0 Er.84 r P A4A6A8(13)where: h 0 -minimum thickness of lubricant film; r-radius of the sphere; α-pressure coefficient ofvascosity; u-sum velocity; μ 0 -dynamic viscosity at13 th International Conference on Tribology – Serbiatrib’13 335