MIL-DTL-3533C
Table III. Conformance tests
Applicable type
Property
ASTM D2240
Types I and II
a. Hardness
ASTM D412
Types I and II
b. Tensile Strength
ASTM D412
Types I and II
c. Ultimate Elongation
ASTM D412
Types I and II
d. Tensile Stress
ASTM D624
Type II
e. Tear Resistance
see 4.4.3
Type I
Type II
ASTM D395
f.
Compression Set
Type I
see 4.4.4
g.
Crush Test
Type II
ASTM D412
h.
Tension Set
Type I
see 4.4.5
i.
Permanent Set
Type I
see 4.4.6
j.
Temperature Retraction
Type II
see 4.4.7
k.
Low Temperature Flexibility
Type II
see 4.4.8
l.
Adhesion & Corrosion
Types I and II
see 4.4.10.3
m.
Volume Change
4.4.1 Hardness. Hardness of the compound shall be determined as specified in Table III
except that test samples shall be three compression molded discs .250 ± .005 (6.35 ± .127 mm)
inch thick and not less than one inch in diameter. Hardness checks shall not be made on actual
gaskets.
4.4.2 O-Ring tests. Tests specified for O-Rings (Type I material) shall be performed on the
actual samples of rings submitted for acceptance testing, when possible.
4.4.3 Tear resistance. Tear resistance shall be measured in two planes on separate
samples; one with the mold seam and the second at right angles to the mold seam. A minimum
of two samples shall be tested. In conducting the test, the O-Ring shall first be severed to open
the ring. A cut shall then be made through the center of the cross sectional diameter of one end.
Lengthwise, this cut shall be about 1.25 inches (31.75 mm), sufficient to allow the two halves
formed to be inserted into the jaws of a testing machine (Scott tester, or equivalent). The tear
resistance shall be calculated as follows :
Tear resistance, pounds per inch of thickness = F
T
where: F = minimum tearing force in lbs. and
T = the thickness of the specimen in inches.
4.4.4 Crush test (Type I only). Three O-Rings shall be selected at random for testing. They
shall be twisted (inside out) one-half turn about the central axis of the cross section and then
placed in separate locations between two rigid steel plates having a surface roughness of 32 to
63 inches (812.8 to 1600.2 mm) rms. (in accordance with standard ASME B46.1). An axial
compression load of 16,800 pounds (7620.35 Kg) (or 5600 (2540.12 Kg) pounds for each ring in
the layer) shall be applied. The plates shall be secured to maintain this load for 20 hours by a
suitable means (mechanical fixture). The rings shall then be removed and inspected immediately
for cracking or disintegration. Following this inspection, the rings shall be stored at room
temperature in the free condition and the percent recovery of the ring cross section determined at
the end of six hours. No cracking or disintegration shall be evident and the cross sectional
dimensions of the O-Rings shall have attained the values specified in Table II in respect to the "as
manufactured" size at the thinnest section.
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