Wear scars generated in the plates of the tribological cell and
the corresponding average diameter are shown in Table 3 for
selected lubricating grease samples and conditions. As can be
concluded from the images, wear mechanism is predominantly
abrasive. As expected, the stronger normal load is applied, the
wider wear scar is, as can be seen in the bar diagram in Fig. 8,
which summarizes the evolution of the scar size with the normal
load, at 25 and 125 °C. However, temperature and normal load do
not exert a significant influence when using the lithium grease as
lubricant. Sample CP provide values of the average wear scar
diameter comparable to those found with the commercial greases,
excepting for the highest normal load applied, and generally lower
at high temperature (Fig. 8). In the particular cases of MC and CH,
no wear evidence in the plates was observed, excepting for 20 and
40 N at 125 °C, being especially wide for MC.
Fig. 9 displays the average wear mark diameters obtained from
the steel plates of the tribological cell after performing tests at
0.15, 10 and 400 rpm under 20 N at 25 and 125 °C, respectively. As
can be observed, the increase in wear diameter with the rotational
velocity is the predominant tendency, at both temperatures. Once
again, the samples based on methylcellulose (MC) and chitin (CH)
only provide appreciable wear scars under specific conditions. At
25 °C, steel plates only evidence wear scars at 400 rpm when using
MC sample as lubricant, whereas rather large scar diameters can
be observed at 125 °C under 10 and 400 rpm conditions. In the
case of CH, significant wear evidence can be only detected at
400 rpm and 125 °C.