MIL-DTL-17901C(SH)
TABLE I. Physical requirements for bearing facing material.
Units of
Test in
Class II
Class III
Class IV
Class V
Property
measurement
accordance with
Tensile strength
Method A of
LB/IN2
1500 min
1500 min
1500 min
1500 min
before aging
ASTM D412
Method A of
Elongation before
150 min
150 min
150 min
150 min
Percent
ASTM D412
aging
Instantaneous
ASTM D2240,
65 min
80 min
65 min
80 min
Hardness
Shore A
Type A
75 max
90 MAX
75 max
90 max
Method A of
Tensile strength after
LB/IN2
1/
1/
1/
1/
ASTM D412
aging
Method A of
Elongation after
Percent
1/
1/
1/
1/
ASTM D412
aging
Surface finish
Microinches Ra
4.5.2.1
64 max
64 max
64 max
64 max
Percent increase in
4.6.4
+5%, -0%
+5%, -0%
+5%, -0% +5%, -0%
Volume change
volume
1/
After being subjected to the oven aging test as specified in 4.6.2.1 the rubber material shall not vary more than 25
percent from the initial tensile strength and elongation.
3.2.2 Metal parts for class II bearings. Metal parts for class II bearings shall be casting or tubing. Casting and
tubing shall be in accordance with the chemical requirements of UNS C85700, C90300, or C92200 according to
ASTM B271, B505, or B584 (static, centrifugal, or continuous casting), or C46400 (ASTM B21 or QQ-B-639).
3.2.3 Nonmetallic backing for class III bearing staves, class IV cylindrical bearings, and class V partial-arc
bearings. Non-metallic backing for class III bearing staves, class IV cylindrical bearings, and class V partial-arc
bearings shall meet the physical requirements in accordance with Table II.
TABLE II. Physical requirements for nonmetallic backing.
(class III, class IV, and class V bearings only)
Class III
Class IV
Class V
Test in
Units of
required test
required test
required test
accordance
Remarks
Property
measurement
value
value
value
with
Sample size
64 min
70 min
70 min
ASTM D2240
Hardness
Shore D
per Table VI
85 max
100 max
100 max
15,000 min in
hoop direction
Tensile
LB/IN2
3900 min
24,000 min
ASTM D638
----
strength
2500 min in
axial direction1/
LB/IN2
Yield
2600 min
----
----
ASTM D638
----
Secant
1900000 min in
modules
hoop direction
45,000 at
Flexural
----
ASTM D790
----
measured at a
73 °F min
modules
500000 min in
max 1 percent
axial direction2/
strain LB/IN2
4
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