Fig. 1 Microstructure of the Class C railway wheel composed of pearlite with some grains of ferrite in the grain boundary. Etching: nital 2%. More

Fig. 2 Schematic drawing of the twin-disc tribometer from the Tribology Laboratory at FEM/UNICAMP: (1) disc actuation motor, (2) disc actuation motor, (3) servo motor that applies the desired load, and (4) disc contact region More

Fig. 3 Representation of the position in which the discs were removed from the wheel More

Fig. 4 Dimensions in millimeters of disc: ( a ) lower and ( b ) upper [ 11 ] More

Fig. 5 Regions used for the analysis of the discs: ( a ) surface roughness, ( b ) circumferential hardness on the face of the disc, and ( c ) radial cut: hardness and transversal cut: OM [ 12 ] More

Fig. 6 ( a ) Coefficient of traction (COT) curves versus the number of cycles for the dry tests with different cycles. ( b ) COT value at the end of the test as a function of the number of cycles. More

Fig. 7 Surface of the disc pairs before the wear test and after the dry test with 500, 1000, 1500, 2000, 3000, 4000, and 5000 cycles More

Fig. 8 Width of the rolling track of discs A and B after the dry tests More

Fig. 9 Images of the rolling track surface of discs A and B after dry tests under the conditions: ( a ) initial with controlled roughness of 0.100 ± 0.004 µ m, ( b ) 500 cycles, ( c ) 1000 cycles, ( d ) 1500 cycles, ( e ) 2000 cycles, ( f ) 3000 cycles, ( g ) 4000 cycles, and ( h ) 5000 cycles. A... More

Fig. 10 Roughness as a function of the number of cycles in the dry test with 1% slip and maximum initial pressure of 2.3 GPa: ( a ) roughness Ra of the discs A and B and ( b ) combined roughness ( RCa and RCz ) of the discs A and B More

Fig. 11 Mass values: disc A, disc B, sum of discs A and B and sum of modules of discs A and B (|A| + |B|) as a function of the number of cycles in the dry test. In the fitting equation, “ x ” represents the number of cycles, and the term “ y ” represents the mass variation which is a function of t... More

Fig. 12 Mass variation per cycle: disc A, disc B, sum of discs A and B, and sum of discs A and B modules (|A| + |B|) in the function of the number of cycles More

Fig. 13 Unit scale of the COT results, combined roughness of the discs ( Ra and Rz ) average of the width of the bearing lane and variation of the mass in the module as a function of the number of cycles in the dry test. In the fitting formula, “ x ” represents the number of cycles, and the term... More

Fig. 1 Lubricating angle and sliding angle More

Fig. 2 Positional relation among vectors n → 1 , V → 12 , V → 1 , and V → 2 More

Fig. 3 Formation of arc-toothed cylindrical worm helical surface More

Fig. 4 Coordinate system used in meshing of worm drive More

Fig. 5 Relative position among vectors ( r → 1 ϕ ) o 1 , ( n → 1 ) o 1 × ( r → 1 ϕ ) o 1 , ( α → V ) o 1 , and ( α → ⊥ ) o 1 More