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 slip speed and the slip 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 anti-friction 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.

Tabelle 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 not or retransfered 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 (Illustration 1) and the temperature factor f_T (Table 4).


Illustration 1: Load Factors - check f_B

Table 4: Temperature Factor F_T

If no bearing size is given on 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.

(7)

[kN]

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 anti-friction combination of
of materials, selected as listed in table (1).

Table 1: Maximum surface pressure

P_max  according to table (1), F according to formula (2), (3) or (4)

re 4:
The existing average slip speed V_m is calculated according to formula (9) using the
frequency of rotation of the crank K and the slip part of the Spherical Plain Bearing G.
(At one rotation of K it corresponds to the double arc b between the center 1 and 2 in
Illustration 5 and thus to the double maximum oscillating angle b).


Illustration 5: Oscillating angle b relative to crank rotation

(9)

[m/s]

Diameter of Ball d_K [mm] (Table 12) and f [1/min]

In case where the bearing rotates fully b needs to be substituted by 180^o 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 (Formula10).
Thus, an estimated value for the heat build-up per pro mm² of the Spherical Plain
Bearing's surface is available, mainly dependent on the anti-friction material
combination, the lubrication/cooling applied and the surface pressure and slip
speed.

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

After the selection of the bearing the following table 6 is valid: P_{L, exist} ^≤ P_{L, max}

Table 6: Maximum specific bearing performance

Table 12: Ball diameter for Rod Ends and Spherical Plain Bearings