PSI - Issue 83

Iman Onsa et al. / Procedia Structural Integrity 83 (2026) 273–279

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The wear factor for WBMs is 14.24 at 1000 N and 19.22 at 1400 N. It offers approximately 35% increase, whereas the wear factor for OBMs only rises from 5.91 (1000N) to 7.10 (1400N), therefore offering approximately 20% increase over the same load range. Thus, indicating that load is a significant operating parameter, it also shows that the impact of load is greater under poor lubricating conditions. 3.3. OBM vs WBM comparison For the same load (and speed), WBM caused more casing wear than OBM, which is consistent with WBM having a greater coefficient of friction and thus greater frictional shear at the casing – TJ interface. The difference in casing wear between the two lubricant types diverged more rapidly as the side load increases, showing that lubrication effects are magnified by increasing the severity of contact.

Table 2: WBM vs OBM wear factor and depth at 115rpm, 1000N

Parameter

WBM 0.23 12.48 0.311

OBM 0.18 5.11 0.188

COF

Wear factor (× 10 -9 MPa -1 ) Max. final wear depth (mm)

Compared to WBMs, OBM provides significantly less wear at all applied loads (Figure 4): • 1000 N: 14.24 (WBM) vs 5.91 (OBM) → OBM ~59% lower than WBM • 1200 N: 16.80 (WBM) vs 6.21 (OBM) → OBM ~63% lower than WBM • 1400 N: 19.22 (WBM) vs 7.10 (OBM) → OBM ~63% lower than WBM

WBM vs OBM

25

19.22

20

16.8

14.24

15

WBM OBM

10

7.1

6.21

5.91

5

Wear Factor (MPa^-1)

0

1000

1200

1400

Force (N)

Figure 4: OBM vs WBM: changing the load under the same rotational speed of 115RPM

This large reduction in wear is consistent with OBMs typically producing less friction and having better lubricity than WBMs; therefore, by reducing the friction at the tool-casing joint OBM reduces both the severity of the surface contact between the two surfaces and material removal rate as wear occurs at Fe surface.