Frictional behaviour of trimethylolpropane (TMP) oleate at different regimes of lubrication / A.F. Maarof ... [et al.]

Trimethylolpropane (TMP) esters possess good frictional properties,
portraying good potential as alternative bio-lubricants. However, the most
common TMP ester, which is TMP oleate, is found to be widely used only for
hydraulics application. Therefore, to explore its potential usage in
automotive applications, the present study determines the frictional
behaviour of TMP oleate at different operating lubrication regimes. Friction
forces for TMP oleate lubricated conjunction, consisting of cast iron pin
being rotated against a stainless-steel disk, are measured using a pin-on-disk
type tribometer. The applied normal load is 3 kg while the disk rotational
speed is varied between 20 rpm and 2000 rpm. Along fluid film and boundary
lubrication regimes, the average coefficients of friction for TMP oleate
lubricated conjunction are measured to be 0.074 and 0.101, respectively.
Along fluid film lubrication regime, with the maximum Hertzian pressure
being calculated to be 1.1 GPa, the contact is expected to be elastohydrodynamic in nature. Transitions of lubrication regimes, similar to
the classical Stribeck curve, are also observed between sliding velocities of
1.8 m.s-1 and 2.7 m.s-1
. Hence, the measured Stribeck curve demonstrates the
potential use of TMP oleate for automotive applications, where a large range
of operating lubrication regimes is required.