Proceedings of SerbiaTrib '13

Figure 3. Modified force acting scheme0.80.70.60.5F D =10000 NParameter a is determining distribution of sideforce F D between inclined and small vertical contactsurface and his value is in the range 0 to 1. It wasadopted a=0.7 in this case. Parameter a influence onfriction coefficient value is very small (about 1%).Figures 4 and 5 gives comparative overview ofall the 6 formulas whereat was adopted F D =10 kN(fig. 4) and F D =0 kN (fig. 5). Inclination angle was10 o . Drawing force is linearly increasing from 0 to9500 N and lies on x axis. Clearly can be seen thatformulas 1, 2 and 3 gives unreal negative frictioncoefficient values for smaller force F intensities.Use of 4 and 4a formulas is solving thisdisadvantage, but at the sliding process beginningfriction coefficient have positive nonzero alsounreal values. Only formula 5 gives frictioncoefficient values which starts from 0. That is inaccordance with ironing process course. At smallerintensities of side force F D friction coefficientvalues are probably higher then real.=10 o Formula 2Proposed formula0.4Formula 4-a0.30.20.10.0-0.1Formula 4 Formula 1-0.2-0.3Formula 3-0.40 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000F, NFigure 4. Friction coefficient dependencies on drawing forceAs a example of formula (5) application inlubricants quality evaluation experiment giving arethe figures 6 and 7. Experimental equipment isbased on tribo model from fig. 1 and describedwith more details in [9]. Sliding process was onephase with side forces 5, 10, 15 and 20 kN. Slidinglength was approximately 60 mm at speed of 100mm/min. Stripe material is low carbon steel sheetwith 2.5 mm thickness. L2 is special dry ecologicallubricant based on wax and metallic soap.Lubricant layer was obtained by dipping into bathwith proper solution and than drying. L3 is lithiumgrease with MoS 2 .13 th International Conference on Tribology – Serbiatrib’13 361