Not only for swaged types, but also for other spherical bearings, certain torque and play values are required: no-load breakaway torque for PTFE lined bearings, and both radial and axial play for metal/metal bearings.
Torque for PTFE type
The no load breakaway is measured by fixing the ball aligned with the axis of a torque meter. The race or Rod End body shall be held securely by hand or tool but without any force. The ball shall be rotated a few times prior to torque measuring. Torque value shall be read when ball rotates. Standard torque requirement of PTFE type bearings is 0.049~1.96N • m {0.5~20kgf • cm}, which is relatively high comparing with ball bearings. Although it is possible to manufacture PTFE type bearings with 0.02N • m {0.2kgf • cm} or less torque, it should allow approx. 0.05mm play as well. The torque value may increace with aging, and this is because:
- Observed moisture changes the thickness of liner, and
- Residual stress from swaging may cause small deformation of race to change its form.
Radial & Axial Play for metal/metal type
The clearance in radial or axial direction between ball and race, or ball and body is called radial or axial play. Based on MIL-standard, radial/axial play for self-aligning bearings is measured as relative motion of race and ball when 24.5N{2.5kgf} load is applied from two opposite directions. The method of radial play measurement of spherical bearings is shown in Figure 16. Table 16 shows the standard radial play values.
Figure 16: Method of measuring Radial Play
(1) Set the dial to "O" during 24.5N load is applied from one direction.
(2) Release the 24.5N load, and re-apply from opposit direction read the value.
Table 16: Standard Radial Play
| | Standard Radial Play |
|---|---|
| Spherical Bearing | 0.051mmMAX |
| 3 Piece Rod End | 0.051mmMAX |