The selection is usually made step by step, repeated if necessary, by comparing -

1. the load ratio involved with the normal minimum values for that ratio;
2. the forces affecting the bearing and the maximum permitted load of the bearing proposed;
3. the maximum surface pressure and the surface pressure on the proposed bearings;
4. the maximum glide speed and the glide speed involved of the bearing proposed;
5. the specific performance of the bearing involved with the published catalogue limits.

Re 1:
The load ratio (C/F) is a value for a specific use of a bearing according to formula (5):

The common minimum values for (C/F) for different antifriction surfaces as listed in table 3, can be used to establish the required dynamic load rating C in accordance with formula (5a) by changing formula (5). By this means a suitable bearing size can be selected from the tables of this catalogue.

Table 3: Typical load ratios

Re 2:
When the existing force affecting the bearing is a static load, it can be used as is for a comparison. When it is a dynamic load, it can be calculated by using formula (2), (3) or (4).

When a Rod End is mounted with a locking nut or retransfer with two nuts, the additional tensile stress at the male thread or the connecting rod has to be taken into consideration.

However the static or dynamic load must always be smaller than the maximum permitted load, which is calculated from the static load rating C_o using formula (6).This might have to be further reduced by the load factor f_B (picture1) and the temperature factor f_T (table 4).

Table 4: Temperature factor F_T

If no bearing size is given in the application the required static load rating can be established by changing formula (6) and a Rod End can be selected from the tables accordingly.

Re 3:
The load on a mating surface can be worked out by using formula (8). It must be less than the standard value for surface load according to the antifriction combination of materials, selected as listed in table (1).

P_max acc. to table1, F acc. to formula (2), (3) or (4)

Re 4:
The existing average glide speed v_m is calculated according to formula (9) using the frequency of rotation of the crank K and the glide distance of the Spherical Plain Bearing G. (At one rotation of K it corresponds to the double arc b between the centres 1 and 2 in Picture 5 and thus to the double maximum oscillating angle ß).

Picture 5: Oscillating angle ß relative to crank rotation

Diameter of ball d_K [mm] (page 17) and f [1/min]

In case where the bearing rotates fully ß needs to be substituted by 180°. The slip speed has to be less than the speed permissible listed in table 5.

Table 5: Maximum slip speed

Re 5:
The product p · v can be defined as a specific bearing performance P_L (see formula 10). Thus, an estimated value for the heat build-up per mm² of the Spherical Plain Bearing surface is available, mainly dependent on the antifriction material combination, the lubrication/ cooling applied and the surface pressure and glide speed. By increasing temperate the allowable surface pressure of maintenance free bearings is decreasing (picture 1 and 4).

Slip speed v according to (9)
Surface pressure p according to (8)

After the selection of the bearing the following is valid: P_{L, exist} ^≤ P_{L, max}

Table 6: Maximum specific bearing performance

Ball diameter for Rod Ends and Spherical Plain Bearings