FED-STD-791D
storage precautions, emergency treatment and measures, and spill practices of each chemical are
explained.
6. PROCEDURE
6.1 Compute the cross sectional area of the end of the slot (see 7.1).
6.2 Clean template, microscope slide and cover glass, and spatulas.
6.3 Prepare the sample for examination as follows:
a. Open a fresh container of grease to be tested, and with a clean spatula, scrape off and
discard the surface layer.
b. Hold the template by the unslotted end, and place it against the clean microscope slide.
Using another clean spatula fill the slot with the test grease. Make sure the corners are
filled and the surface of the grease is level with, or slightly above the sides of the slot.
Then press the side of the slot firmly against the slide.
c. Place the slide and template in the vacuum chamber for 10 to 15 min to remove bubbles
or voids from the grease in the slot. (See Note 2).
NOTE 2:
Vacuum exposure may be omitted if the grease is free from entrained air.
d. Slide the clean cover glass onto the template to shear off surplus grease. Then press the
cover glass firmly against the template until it is parallel to the microscope slide.
6.4 Mount the assembled slide on the stage of the microscope. Adjust the illumination
so that light passes straight up through the grease in the slot, as well as straight across the surface
of the grease.
6.5 Determine the size and number of opaque particles.
a. Adjust the stage and micrometer eyepiece so that the micrometer scale coincides with
one side of the slot, and so that one end of the scale coincides with one corner of the
slot.
b. Move the stage slowly, so that the slot passes across the field of view. Count each
opaque inclusion having a size of 25 m or more. Particle size is determined by
measuring along the largest dimension of the particle.
c. Record the count in three columns headed: "25 to 75 m", "75 to 125 m", and "over
125 m".
d. When the micrometer scale has reached the opposite side of the slot, move the stage
along the axis of the slot for a distance equal to the length of the scale. (Use a minor
irregularity on the wall of the slot, or a specific particle in the grease, as a point of
reference.) Scan this section completely across the slot.
e. Continue scanning successive sections in the slot until approximately three-quarters of
the area (1 1.5 cm) of the slot has been inspected.
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