PTFE type Spherical Bearing
PTFE types are mainly targeted where slow fluctuation velocity applies. Under slow fluctuation velocity, PTFE abrasion determines the life of Spherical Bearings. PTFE Liner deformation also decides the performance ability under static load.
Definition of Load
Static Limit Load
This is the load, with which the permanent deformation does not exceed the value in Table 8 below.
Table 8 : Permanent deformation under static load
| Maximum value | |
|---|---|
| Radial Static Limit Load | 0.076mm |
| Axial Static Limit Load | 0.127mm |
Static Ultimate Load
The load 1.5 times the static limit load. It can be applied to Spherical Bearings without distracting them.
Oscillating Load
The test is conducted based on MIL-specification. After 25,000 cycles, the wear shall not exceed 0.152mm under this load. Figure 9 shows the association of surface pressure and life cycle of bearing from this test. Test conditions are ± 25° oscillation angle, 10cpm cycle, and constant load condition. Figure 9 shall be taken as a guideline, as the actual figure may be influenced by other factors such as temperature, load, velocity, oscillation angle, and so on.
Figure 9: PTFE Liner Allowable Stress
Calculation of load capacity
Radial projected area
The projected area is basically the same as of metal/metal types. The edge of PTFE Liner, however, shall be taken into consideration.
Allowable stress (σ)
Based on several examinations, the allowable stress is set as indicated in Table 9 below.
Table 9 : PTFE Liner Allowable Stress
| X-1118 X-1276 X-1276F |
X-1820 | |
|---|---|---|
| Radial Static Limit Load | 482N/mm2 { 49.2kgf/mm2 } | 541N/mm2 { 55.2kgf/mm2 } |
| Axial Static Limit Load | 309N/mm2 { 31.6kgf/mm2 } | 309N/mm2 { 31.6kgf/mm2 } |
| Oscillation Load | 220N/mm2 { 22.5kgf/mm2 } | 275N/mm2 { 28.1kgf/mm2 } |