FED-STD-791D
hanger made from stainless steel or nichrome wire. The hanger shall have two hooks at one end
permitting one elastomeric specimen to be hung from each hook. The two specimens shall hang
parallel and 1.3 cm (1/2 in) apart. Attach the wire specimen hanger to a standard size number 19
cork and fit with two lengths of 0.8 cm Pyrex glass tubing (chimneys). Insert one chimney, 7.6
cm (3 in) in length, through the cork such that the chimney extends 1.3 cm (1/2 in) above the top
of the cork. Insert the second chimney 12.7 cm (5 in) in length, through the cork such that the
chimney extends 8.9 cm (3 1/2 in) above the top of the cork. Place the cork fitted with the
chimneys, specimen hanger and specimens into the pre-heated test tube containing the test oil.
Adjust the length of the specimen hanger so that when the cork is placed tightly into the test
tube, the specimens will hang with equal distance of test lubricant above and below the
specimens using 140 mL of test lubricant. Hang only two elastomeric specimens in one tube and
adjust cork such that specimens do not contact the side of the test tube.
6.6 Remove the elastomeric specimens from the test tube after 72 h with the time starting
when tubes are first inserted into the bath. Place the elastomeric specimens in a beaker of fresh
test lubricant which is at room temperature and allow to cool for a minimum of 30 min. Remove
the specimens from the cooling oil and place them into a beaker of acetone for a minimum of 14
and a maximum of 20 s. Dry the specimens with filter paper by blotting. Determine volume
swell, hardness, elongation and tensile strength of the elastomeric specimens.
6.7 Determine a base line for elongation and tensile strength measurements for each
batch of standard elastomer stock. Cut eight specimens in accordance with 6.3 with no more
than two specimens being cut from any one sheet. Determine the elongation and tensile strength
of each untreated specimen in accordance with method ASTM D 412 using a 2.5 cm (1 in) bench
marker. Use the average of these values in determining elongation change and tensile strength
change of the oil treated specimens.
6.8 Weigh each oil treated specimen in air and in water in accordance with method
ASTM D 472 and calculate percent volume swell for each specimen. Calculate the percent
volume swell of the test lubricant as the average of four individual volume swell determinations.
6.9 Determine hardness readings on the specimens as described in 6.3. Calculate
hardness change for the test lubricant as the difference between the initial hardness and the final
hardness.
6.10 Determine elongation and tensile strength of the four specimens in accordance with
method ASTM D 412 using a 2.54-cm (1-in) bench marker. Average the four elongations
measurements. Calculate the percent change in elongation, see 7.1.
6.11 Determine the tensile strength of the four specimens in accordance with method
ASTM D 412 and average the four readings. Calculate the percentage change in tensile strength,
see 7.2.
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