MIL-DTL-27426C
Table VIII.
C=0 Sampling Plan AQL Levels
Key Characteristics
AQL Levels
Diameter
Cpk 1.67 and above:
1.0
Cpk 1.66 to 1.00:
.25
Cpk less than 1.00:
100% inspection
Major Characteristics
4.0
Thickness
4.0
Radial Wall
4.0
Burr
4.0
Dish
4.0
Misalignment
4.0
Crimp
Minor Characteristics
Notch Radius
10.0*
*Controlled by the tooling used.
4.2.4.1 Hardness test. Prior to forming the ring, a sample of each lot of raw
material to be used in the retaining rings shall be tested for conformance to the
hardness requirements specified in 3.2. The samples shall be tested for hardness using
the Test Method ASTM E18.
4.2.4.2 Performance. Retaining rings shall be capable of being inserted and
removed from grooves conforming to the dimensions and tolerances of the grooves for
which the ring was designed without showing indications of cracks, excessive permanent
set or distortion or other conditions detrimental to use of the rings. Sample ring
shall be inserted and removed a minimum of (5) times from a fixture with a groove
diameter conforming to the dimension and tolerance for which the ring was designed.
Upon completion of the test, the ring shall be visually and dimensionally checked. Any
indications of cracks or distoriton shall be cause for rejection. The amount of
permanent set acceptable for the ring shall be determined from the following formulas
shown below. Rings not meeting the minimum requirements for interference fits between
ring and groove shall be rejected.
H≥ 0.003(∅C)
Where:
FOR EXTERNAL RINGS: H = ∅C ∅G
H = Minimum interference fit between ring and groove after performance test.
∅G = Maximum I. D. of ring as measured after performance test.
∅C = Minimum groove diameter, external ring.
FOR INTERNAL RINGS: H = ∅G ∅C
H = Minimum interference fit between ring and groove after performance test.
∅G = Minimum O.D. of ring as measured after performance test.
∅C = Maximum groove diameter, internal ring.
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