FERROGRAPHIC EVALUATION OF AH-1 HELICOPTER SWASHPLATE AND SCISSORS AND SLEEVE ASSEMBLY

NAVAIR 17-15-50.3

TM 38-301-3

T.O. 33-1-37-3

CGTO 33-1-37-3

a. The DR ferrograph is an instrument used to measure the concentration of wear metal particles and

other debris in lubricants. The sample passes through a precipitator tube placed in a gradient magnetic field.

The magnetic material contained in the sample is deposited in the tube and measured at two positions. The

readings are indicated as DS (small, 1 - 2 micrometers) and DL (large, 5 micrometers or larger). This operation

takes approximately 5 minutes and provides the information needed to determine if additional analysis is

required. Criteria, with thresholds, are established for a component by evaluating numerous samplings of data

over a period of time. If an established DR threshold is exceeded, the development of a ferrogram and its

examination under the ferroscope is required. The DR ferrograph is not normally used in the analysis of grease

samples.

b. The analytical ferrograph is used to prepare a ferrogram. This procedure involves pumping a lubricant

sample across a substrate which has a non-wetting barrier applied to one side. The slide is mounted at a slight

angle above a magnetic field gradient. Gravitational pull causes the lubricant sample to flow across the slide,

and the ferrous particles in the sample are deposited in strings along the surface of the substrate. The largest

ferrous particles are deposited at the entry area of the barrier on the substrate. Nonferrous particles are usually

contaminated with small amounts of ferrous materials and as a result are attracted to the substrate. Precipitation

also causes nonferrous particles to be deposited on the slide. After the lubricant sample is pumped across the

substrate, a fixer solution is used to clean the substrate and remove any residual lubricant. After the solution

dries, the wear metal particles continue to adhere to the barrier area of the substrate even after being removed

from the magnetic field. The ferrogram is then analyzed under the ferroscope.

c. The ferroscope is a bichromatic microscope with filters and a polarizer to direct both transmitted and

reflected light onto the ferrogram. The ferroscope can be fitted with a Polaroid camera or a 35 millimeter camera

to produce pictures of ferrograms. It can also be fitted with a video monitor for remote viewing of the ferrogram.

When examined with bichromatic light under various magnifications, prepared ferrograms disclose relevant

information about the wear particles. By observing color and shape and by using various lighting and heating

techniques, ferrous and many nonferrous materials can be identified and the mode of wear determined. In order

to analyze the ferrogram, the operator requires special training and experience. Once the evaluator is proficient

in the operation of the ferrograph system and proficient in evaluation procedures and techniques, he can readily

determine the size, shape, type, and amount of wear material. Additional tests such as heat treating and

chemical analysis can be conducted to further determine wear metal particle characteristics when viewed under

the ferroscope.

d. Modified ferrographic oil analysis procedures are used in the analysis of grease samples. The grease

sample is diluted with 14 milliliters of fixer solution to break down the bonding material of the grease. The liquid

is then allowed to flow across the substrate by utilizing gravitational flow.

NOTE

The peristaltic pump in the analytical ferrograph is not used.

The substrate is elevated at the entry end to reduce the amount of initial magnetic attraction of the wear particles

in the diluted grease and to increase the flow rate across the substrate. The magnetic field aligns the ferrous

particles in strings along the slide and the fixer solution is passed across the substrate to remove the residual

grease. After drying, the substrate is analyzed under the ferroscope. Evaluation baselines and criteria are

developed for each type of component analyzed. Evaluation guideline criteria are provided to Army Oil Analysis

Program (AOAP) laboratories in the form of color photographs of samples containing various amounts and types

of wear particles. Grease sample ferrograms are compared to these photographs and a subjective evaluation of

the wear particle content of the ferrogram is made. A more detailed description of the evaluation process is

contained in paragraph 2-7.

2-7. FERROGRAPHIC EVALUATION OF AH-1 HELICOPTER SWASHPLATE AND SCISSORS AND SLEEVE

ASSEMBLY. The ferrographic evaluation of the grease sample is accomplished by comparing the analytical

ferrogram with the evaluation guideline photographs furnished to each laboratory under separate cover. The DR

ferrograph is not used at this time.

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