*2.4. Tribometer*

The change in the tribological performance (friction and wear) of the grease with water contamination was studied using a tribometer setup, shown in Figure 5. The setup consisted of a stationary disk with projection sliding against a rotating disk with a groove (see Figure 5). The tribometer setup was designed for performing pin-on-disk; However, to perform disk-on-disk tests, a disk holder was designed and built (see Figure 5).

The stationary disk was fastened to the disk holder and connected to a dual load sensor through the suspension. Similarly, the rotating disk was fastened to a lubricating cup and then to the driven pulley. The driven pulley was connected to the motor using the driving pulley through a belt-pulley drive system. The dual load sensor was attached to the motion control drive to measure the applied load in the vertical direction and frictional force in the horizontal direction. Using the motion control drive, the required displacement in the vertical as well as horizontal motion was achieved. Inbuilt software was used to control the motions of the motor and control drive. The additional details of the setup are available in [24,25].

The mean diameter and thickness in the stationary part were 30 and 2 mm, respectively. The depth, mean diameter, and thickness of the groove in the rotating part were 1, 30, and 8 mm, respectively. Experiments were performed at 30 N load and 0.126 m/s for 3 h. The weight loss was determined using a weighing gauge having an accuracy of 0.1 mg.

**Figure 5.** Tribometer setup.
