FERROGRAPHY AS A SUPPLEMENTAL OIL ANALYSIS PROCESS

NAVAIR 17-15-50.3

TM 38-301-3

T.O. 33-1-37-3

CGTO 33-1-37-3

a. Evaluation of the swashplate and scissors and sleeve assemblies can be easily accomplished at or

near the entry area using 100x magnification. The most critical type of wear particles found in the evaluation of

these components are caused by spalling (contact stress fatigue) formed from the bearing race and balls. In the

swashplate, these particles average between 50 and 200 micrometers but can reach 500 micrometers. For the

scissors and sleeve assemblies, these particles average between 50 and 150 micrometers, but can be as large

as 350 micrometers. A large increase in size and quantity of the spalling particles from one sample to the next is

the most dangerous wear situation. A maintenance action may be necessary when the abnormal level of

spalling wear (photograph 4) is reached.

b. Rubbing wear is caused by the bearing spinning or fretting and can be very dense in both the

swashplate and scissors and sleeve grease samples. Increases in rubbing wear can be tolerated as long as the

spalling particles do not increase in size and quantity. An example of this is found in photograph 8. The amount

of spalling, marginal to high, makes this a more critical wear situation than that found in photograph 9, which

shows abnormal rubbing wear. A removal recommendation could be based on abnormal rubbing wear, but

generally the component should be closely monitored for a period of time rather than recommending immediate

removal.

c. It is not unusual to see some cuffing wear in both the swashplate and the scissors and sleeve

assemblies. However, an abnormal amount as shown in photograph 10, is cause for a maintenance

recommendation.

d. For determining the presence of any nonferrous wear, evaluation will need to be accomplished at or

near the 30mm - 10 mm (exit) area of the ferrogram. It is unusual to see nonferrous wear in a swashplate

grease sample; however, there have been instances where aluminum has been found (photograph 11). Most of

the time the aluminum originates from the shims or retainer plate. The type of nonferrous wear that occurs most

often in the scissors and sleeve samples is produced as brass chunks that can average from 30 to 100

micrometers in size. The brass wear originates from the bearing cages and caution should be exercised if the

size and quantity of brass wear increases significantly from one sample to the next.

2-8. FERROGRAPHY AS A SUPPLEMENTAL OIL ANALYSIS PROCESS. Ferrography is routinely used as a

supplemental oil analysis process by AOAP laboratories for analyzing suspect aeronautical oil samples. Suspect

oil samples are defined as those for which one or more of the following diagnostic indicators are observed: chip

light; vibration; metal on screens or filters; oil of unusual color, odor, or high solids content; and oil samples

having abnormal spectrometric trends or wear-metal content. Ferrography is not a substitute for spectrometric

analysis, but rather a supplemental analytical tool used to provide additional information in the diagnostic process.

a. The three-step process outlined in paragraph 2-6 is utilized in the ferrogrophic analysis and evaluation

of suspect oil samples. In this process, the direct reading (DR) Ferrograph serves as a screening device to

determine whether or not a complete ferrographic analysis is necessary.

b. DR Ferrograph evaluation guidelines for selected aeronautical components are contained in.

Components having high DR readings or ratios should be monitored closely. When established guidelines are

exceeded, the development of a ferrogram and its examination under the Ferroscope is required.

c. Recommendations which could lead to the removal of a component from service, will not be made on

the basis of DR analysis alone. A complete ferrographic analysis should be performed as a final check before a

recommendation leading to the removal of a component from service is made. This will enhance the laboratory's

ability to pinpoint potential failures as well as help to eliminate the unnecessary removal and teardown of

serviceable components.

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