MIL-DTL-27426C
d. The thrust load, based on groove yield, can be found with the following
equation:
Thrust load, lbs.
Shaft or housing diameter,
in.
Mean depth of groove, in.
Allowable angle of deflection, deg.
φ
Pt = A
Sy
D1
Tan
(0.073)K
Factor of safety
Yield strength of groove material, psi
This equation is valid only if the load is applied through a retained part which
applies the load very close to the shaft or bore diameter and where the load is of a
static nature.
e. Minimum distance between outer groove wall and end of shaft should be three
times the groove depth at a minimum.
(Y > 3D1)
f. Centrifugal capacity : Proper functioning of an external retaining ring
depends upon the ring remaining seated on the groove bottom. Centrifugal loading can
overcome cling of the ring. To calculate allowable steady state speed of the retaining
ring the equation is:
Min ring cling to
groove bottom
Ring radial
1/2
wall, in.
Speed, rpm
E3
1012
X
N=
0.466
C1
Rn3
(1+C1) (Ro3 Ri3)
Free outside ring
Free neutral ring
radius, in.
Free inside ring
radius, in.
radius, in.
g. Rotation between parts : When a spiral ring retains a rotating part, rotation
will be limited to one direction only and to applications involving light thrust loads.
The ring is to be wound in the direction of rotation of the rotating part, in the case
of external rings, or against the direction of rotation for internal rings, failure to
follow these criteria could cause the ring to wind out of its groove.
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