True Stability of Lubricants Determined Using the Ball-on-Disk Test

Figure 4

Surface topography images (2 mm × 2 mm) of the wear tracks on the disk lubricated by the motor oil 5W30 or 5W40. (a, d) fixed point condition and circular geometry, (b, e) migrating point condition and spiral geometry, and (c, f) fixed point-variable speed condition and circular geometry.

(a) Fixed point; 1564 µm² (wear area)

(b) Migrating point; 413 µm²

(c) Fixed point-variable speed; 1585 µm²

(d) Fixed point; 1250 µm² (wear area)

(e) Migrating point; 1866 µm²

(f) Fixed point-variable speed; 360 µm²