FED-STD-791D
Method 3005.4
September 30, 1986
DIRT CONTENT OF GREASE
1. SCOPE
1.1 This method is used for determining the size and concentration of foreign particles in
lubricating greases.
2. SUMMARY
2.1 The test consists of applying a known quantity of grease to a microscope slide, and
examining the slide with a microscope to determine the size and number of particles present.
3. SAMPLE SIZE
3.1 Approximately l mL of grease to be tested.
4. REFERENCES, STANDARDS, AND APPARATUS
4.1 Microscope, mechanical stage, 60 diameter magnification, with eyepiece micrometer
(not filar) calibrated against suitability ruled, stage micrometer.
4.2 Slide, microscope, approximately 2.5
5.0 cm with cover glass.
4.3 Template (Fig. 1), steel (shim stock), 0.01 cm thick, approximately 2.5 5.0 cm,
slotted from one end for a distance of approximately 2.0 cm with a slot width of approximately
1.0 mm. The template thickness and slot width are accurately measured so that the end area of
the slot can be calculated. (A hemacytometer may be used in place of the template). See Note 1.
NOTE 1:
Calculation of test results will be simplified if the template is ground to such
thickness, or the slot width is adjusted so that the end area of the slot is 0.01 cm2.
4.4 Vacuum chamber, 1.0 cm of mercury (absolute), or lower (to accommodate
microscope slide).
4.5 Spatulas (2)
5. MATERIALS
5.1 CAUTION - SOME MATERIALS ARE TOXIC AND HAZARDOUS. The
materials references and standards listed in this section must be handled carefully. Federal Test
Method 10000, Material Handling Safety Precautions, is a reference which lists all toxic and
hazardous materials cited in FTMS 791. The synonyms, life hazard, flammability, handling and
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