TASK 70-32-16-250-001
1 . General.
A.This procedure gives the instructions to make an inspection of the fan mid shaft (FMS) for serviceability. This procedure is necessary when a visual inspection shows that rubs have occurred during engine operation. The procedure includes preparation of the shaft surface for etching, the etching process, and an analysis of the results.
NOTE:
The aluminized paint on the shaft will polish when the shaft is turned in the transportation fixtures. These indications are not operational rubs and it is not necessary to inspect them to the limits of this procedure.
B.The FMS must be removed from the engine to complete this inspection. It is not necessary to remove the center vent tube.
NOTE:
You can do this procedure more easily if you set the shaft so that you can turn the area to be polished and etched to the top vertical position.
2 . Equipment.
Subtask 70-32-16-250-051
A.Standard equipment. None required.
B.Materials:
 
Consumable Product
No.
 
Oil, Preservation
C02-025  
 
Solvent, Methyl-Ethyl-Ketone (Fed. Spec. TT-M-261)
C04-001  
 
Solvent, Acetone
C04-003  
 
Nitric Acid, Technical Grade, 67 to 70 wt %, A-A-59105
C04-072  
 
Alcohol, Methyl
C04-180  
 
Cloth, Abrasive Alumina, Superflexible,80-100 Grit
C10-187  
 
Abrasive Paper, 400 Grit, Silicon Carbide Wet/Dry
C10-190  
 
Swabs, Lint-Free Rayon-Tip
C10-207  
3 . Pre-Inspection Part Preparation.
Subtask 70-32-16-250-052
A.Prepare the surface for the inspection. Refer to Figure 1.
(1)Identify the area to be polished.
(a)The area must be about 1.0 inch (25 mm) wide and 4.0-6.0 inches (101-152 mm) long, as measured in the axial direction.
(b)The inspection area must be moved from the non-rubbed area through the rubbed area and back to the non-rubbed area.
(c)It is important that you polish the rubbed area and a non-rubbed area. This will permit you to compare the part during analysis.
(2)Remove the paint from the area to be polished. Use an 80-100 grit abrasive alumina superflexible cloth C10-187  .
NOTE:
The inspection must be done within 24 hours after you remove the paint because the FMS is easily damaged by corrosion.
(3)Polish the area to be inspected as follows:
(a)Remove machining marks from the inspection area with an abrasive alumina superflexible cloth C10-187   backed with 120-180 grit polishing material.
NOTE:
The removal of machining marks will keep changes in the etch rate to a minimum. These change can cause interference when you examine the etch results.
(b)Wipe the surface with a clean, lint-free cloth.
(c)To remove scratches, polish the surface with an abrasive alumina superflexible cloth C10-187   backed with 220-240 grit polishing material.
(d)Wipe the surface with a clean, lint-free cloth.
(e)To remove all signs of scratches, polish the surface with 400 grit silicon carbide abrasive paper C10-190  .
NOTE:
The etch cannot be done correctly if the surface is not smooth.
(f)Wipe the surface with a clean, lint-free cloth.
(4)Do a visual inspection of the polished area for signs of smeared or transferred metal in the rubbed area.
(5)If there is smeared or transferred metal in the rubbed area, polish the area to be inspected again.
WARNING:
METHYL-ETHYL-KETONE (MEK) OR ACETONE IS FLAMMABLE AND TOXIC TO THE SKIN, EYES, AND LUNGS. YOU MUST USE SKIN AND EYE PROTECTION. AVOID REPEATED OR PROLONGED CONTACT. USE IN A WELL-VENTILATED AREA.
(6)Wipe the surface with a clean, lint-free cloth that is moistened with MEK C04-001   or acetone C04-003  .
NOTE:
To decrease oxidation on the surfaces that have no protection, the etch procedure must be done as soon as possible after the polishing procedure.
B.Etch the polished surface.
WARNING:
NITRIC ACID OR ETCHING SOLUTION IS HIGHLY TOXIC TO SKIN, EYES, AND LUNGS. SKIN AND EYE PROTECTION, AND VAPOR CONTROL ARE NECESSARY.
WARNING:
ALWAYS ADD ACID TO ALCOHOL. NEVER ADD ALCOHOL TO ACID. SKIN AND EYE PROTECTION, AND VAPOR CONTROL ARE NECESSARY.
(1)Prepare an etching solution in a plastic container. Fully mix nitric acid C04-072  , 8-12 percent by volume, in methyl alcohol C04-180  . Keep the solution sealed when it is not in use.
NOTE:
Do not use the etching solution after 24 hours.
(2)Apply the etchant to the polished surface as follows:
(a)Apply the etchant to the polished area with an eye dropper or large lint-free rayon-tip swab C10-207  . The etchant must be smooth and equal on the surface, with no sign of a break in the liquid film.
CAUTION:
DO NOT SWAB THE ETCHANT ONTO THE POLISHED SURFACE. THIS CAN CAUSE A SMEARED ETCHED FIGURE WHICH CAN BLOCK YOUR VIEW OF AREAS THAT HAD AN OVERTEMPERATURE CONDITION.
(b)Apply the etchant for a maximum of 2 minutes, or until the polished area outside the inspection area begins to get dark in color.
NOTE:
You must stop the application immediately when the area begins to get dark in color.
(c)If the polished area outside the inspection area does not begin to get dark after 2 minutes, prepare the surface for the inspection again. Refer to paragraph 3.A.
(d)If you prepare the surface for the inspection again, etch the polished surface again.
(e)Rinse the etchant from the polished surface with a gentle stream of clean, clear water.
NOTE:
The inspection area must be wet when you do the inspection.
* * * FOR ALL
Figure 1   Rubbed Area Inspection
4 . Part Inspection.
Subtask 70-32-16-250-053
A.Do a visual inspection of the etched surface.
(1)An equal dark color that is fully through the etched area shows that the FMS did not have a local overtemperature condition.
(a)If the first etch did not show a local overtemperature condition, do the following:
1Prepare another area that you think has a rub to be etched. Refer to paragraph 3.A. in Subtask 70-32-16-250-052, Pre-inspection Part Preparation.
2Etch the polished surface. Refer to paragraph 3.B. in Subtask 70-32-16-250-052, Pre-inspection Part Preparation.
(b)If the second polished surface that you etched does not show a local overtemperature condition, the FMS is serviceable.
(c)If the second polished surface that you etched shows a local overtemperature condition, the FMS is not serviceable or repairable.
(2)A color that has areas lighter than the adjacent area shows that the FMS had a local overtemperature condition. If this is the condition of the inspection area, the FMS is not serviceable or repairable.
NOTE:
The light-colored areas can be small and separate, or they can be in an area across the etched surface if the rub is very bad. Overtemperature indications are usually very clear and easily seen. A sign of light-colored areas is a cause for rejection of the FMS.
NOTE:
The polishing procedure can result in axial scratches. It is possible that these scratches will be lighter in color than the adjacent area. If this is the only type of indication, it is not a cause for rejection of the FMS.
5 . Part Preservation.
Subtask 70-32-16-250-054
A.After the analysis is complete, apply preservation oil C02-025   to the FMS to prevent corrosion damage.