# Frictional Behaviour of the Microstructural Surfaces Created by Cylindrical Grinding Processes
## 3 Tribological Performance of Structural Surfaces
### Friction Test and Test Procedure  
The experiments were carried out on a test rig equipped with a servo motor to drive the component (shaft) on a paired cylinder liner (bearing) as shown in Figure 3. The workload was applied to the bearing rod creating a normal force on the sample component. The test sample component was assembled on a shaft that linked to motor through a torque sensor. The outputs from the torque sensor and the load sensor were recorded in a computer for \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**No.** & \(S_{a}\) **(um)** & \(S_{ak}\) **(um)** & \(S_{ku}\) **(um)** & \(S_{k}\) **(um)** & \(S_{ik}\) **(um)** & \(S_{tr}\) & \(S_{al}\) **(um)** & \(R_{pc}\) **(1/mm)** \\ \hline
1 & 0.283 \(\pm\) 0.02 & 0.016 \(\pm\) 0.15 & 4.856 \(\pm\) 0.35 & 0.841 \(\pm\) 0.08 & 0.463 \(\pm\) 0.05 & 0.051 \(\pm\) 0.01 & 9.091 \(\pm\) 3.6 & 38.819 \(\pm\) 1.1 \\
2 & 0.263 \(\pm\) 0.03 & 0.982 \(\pm\) 2.76 & 5.937 \(\pm\) 0.35 & 0.754 \(\pm\) 0.03 & 0.538 \(\pm\) 0.12 & 0.070 \(\pm\) 0.05 & 8.001 \(\pm\) 3.6 & 46.314 \(\pm\) 1.3 \\
3 & 0.255 \(\pm\) 0.01 & 0.661 \(\pm\) 0.55 & 5.046 \(\pm\) 3.17 & 0.755 \(\pm\) 0.08 & 0.521 \(\pm\) 0.32 & 0.062 \(\pm\) 0.01 & 8.324 \(\pm\) 3.3 & 45.053 \(\pm\) 10 \\
4 & 0.269 \(\pm\) 0.06 & 0.546 \(\pm\) 0.53 & 4.792 \(\pm\) 0.89 & 0.815 \(\pm\) 0.05 & 0.471 \(\pm\) 0.05 & 0.055 \(\pm\) 0.01 & 9.391 \(\pm\) 2.6 & 43.828 \(\pm\) 6.2 \\
5 & 0.401 \(\pm\) 0.43 & 0.579 \(\pm\) 0.43 & 5.677 \(\pm\) 0.98 & 1.138 \(\pm\) 0.13 & 0.897 \(\pm\) 0.29 & 0.043 \(\pm\) 0.01 & 13.281 \(\pm\) 3.3 & 42.575 \(\pm\) 4 \\
6 & 0.208 \(\pm\) 0.01 & 0.198 \(\pm\) 0.1 & 9.355 \(\pm\) 1.58 & 0.579 \(\pm\) 0.02 & 0.409 \(\pm\) 0.01 & 0.119 \(\pm\) 0.01 & 2.419 \(\pm\) 0.5 & 53.846 \(\pm\) 1.2 \\
7 & 0.254 \(\pm\) 0.01 & 0.033 \(\pm\) 0.07 & 5.181 \(\pm\) 1.38 & 0.773 \(\pm\) 0.01 & 0.428 \(\pm\) 0.04 & 0.064 \(\pm\) 0.01 & 5.451 \(\pm\) 0.6 & 50.089 \(\pm\) 2.5 \\
8 & 0.263 \(\pm\) 0.16 & 0.204 \(\pm\) 0.04 & 5.313 \(\pm\) 0.57 & 0.793 \(\pm\) 0.14 & 0.485 \(\pm\) 0.13 & 0.061 \(\pm\) 0.01 & 7.448 \(\pm\) 3.2 & 47.584 \(\pm\) 0.1 \\
0 & 0.082 \(\pm\) 0.01 & 0.164 \(\pm\) 0.09 & 4.655 \(\pm\) 0.05 & 0.379 \(\pm\) 0.01 & 0.19 \(\pm\) 0.02 & 0.048 \(\pm\) 0.003 & 3.886 \(\pm\) 0.01 & 43.825 \(\pm\) 0.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Surface roughness parameters of microstructural surfaces measured before tribo-tests. the calculation of the coefficient of friction (COF) that is equal to the ratio of friction force (deduced from the torque) to workload force. The friction tests were conducted on every component under full lubrication conditions. The oil was pumped into the inlet side of the bearing component. Table 4 presents three test condition settings of normal load and spindle rotational speed. The tests under each condition were conducted at least two repetitions for the same component. The experiment procedure of friction tests is described as follows to ensure the tests are stable, repeatable and comparable. First, the component was installed in the cylinder bearing pairs and fresh oil was pumped to the component surface. The test apparatus was controlled by a computer program, so that a series of multiple tests could be executed automatically. The friction tests were performed under the test conditions A, B and C as indicated in Table 4. In each test, the workload was fixed at a defined value, while the sample component was rotating at a selected rotational speed. Meanwhile, the oil temperature between the cylinder bearing pair was monitored. With the initial increase in rotating speed, the oil temperature would gradually rise, which would break the thermal balance in the bearing test system leading to the fluctuation of the COF curve. When the rotating speed reached the working speed and continued running, the thermal balance would re-establish and became stable again. As a result, the variation of the COF decreased, and the COF curve became stable again.