(2)
Place part in a standard sandblast cabinet.
CAUTION: KEEP SANDBLAST NOZZLE IN MOTION TO PREVENT BLAST FROM
DWELLING ON ONE SPOT.
(3)
Set equipment air pressure at 15 to 30 psig (103,4 to 206,8 kPa), then subject part to sandblast using sand (120 Grit) (MIL-A-22262) (SECTION VII). Air pressure may be reduced as required, to control action on base metal of part.
(4)
Remove part from sandblast cabinet.
(5)
Rinse part free of sand, using running tap water.
(6)
Dry part by placing in an oven, preheated to 175 to 225F (79 to 107C). Allow part to remain in oven for one hour.
(7)
Coat part with corrosion-preventive compound (MIL-C-6529, Type III) (SECTION VII).
C. Method No. 405C: Seal Diameter (Lip Seal Surface) Repair Using Glass Bead Peening
NOTE: Repair shall not be undertaken if damage cannot be removed without reducing seal diameter to less than minimum specified in applicable manual for unit in work.
Repair damaged or worn lip seal surface to restore sealing surface as follows:
(1)
Mask off areas not to be processed.
NOTE: The peening process produces a more compatible surface for mating with lip seal and will prolong life and improve function of seal.
(2)
Mix glass beads in liquid carrier in quantities as follows:
(a)
Mix glass beads (Screen No. 100-230 (130 Grit) Class IV, Size AF or AG) (SECTION VII) and garnet grit (Screen No. 100-200 (150 Grit) Class III, Size AF or AG) (SECTION VII) in equal parts by volume.
(b)
Disperse glass bead and garnet grit mix in ten times the volume of tap water that has been inhibited with 0.25 percent sodium dichromate/bichromate (liquid carrier) (SECTION VII).
(c)
Use mixture in peening chamber (Perfecto-Peen Cabinet) (SECTION VII).
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WARNING: USE CORRECT PERSONAL PROTECTION. COMPRESSED AIR WILL CAUSE LOOSE PARTICLES THAT CAN GET IN YOUR EYES. COMPRESSED AIRFLOW CAN CAUSE CUTS, DO NOT POINT IT AT YOUR SKIN.
(3)
Peen sealing surface specified using machine process. Use setup, pressure, nozzle distance, rotating speed and impingement time as specified in Overhaul Manual covering part being peened to obtain uniform surface texture free of wear rings, nicks, dings and gouges when viewed under 3X to 7X magnification.
(4)
Demask and rinse part in clean water to remove peening material, then allow part to air dry.
(5)
Dimensionally inspect peened surfaces. Repaired surfaces shall meet dimensional requirement specified in applicable Overhaul Manual.
(6)
Coat parts with lubricating oil MIL-L-23699.
6. Repairing Magnesium Parts
A. Method No. 406A: Minor Damage Repair
NOTE: See Method No. 403L for repair of paint coatings for magnesium parts.
Repair minor damage to magnesium-alloy parts as follows:
WARNING: WHENEVER MAGNESIUM-ALLOY PARTS ARE REWORKED, CARE MUST BE EXERCISED TO REMOVE ALL DUST, FILLINGS, TURNINGS, AND SHAVINGS AS THEY ARE FORMED. MAGNESIUM IN THESE FORMS IS HIGHLY FLAMMABLE, AND UNDER CERTAIN CONDITIONS, EXPLOSIVE. PERSONNEL SHALL WEAR PROTECTIVE COVERING AT ALL TIMES.
(1)
Burrs, scratches, and galling shall be smoothed out using abrasive cloth (Federal Specification P-C-451) (SECTION VII) and oil.
(2)
Areas on magnesium parts which are corroded, or where original surface treatment is no longer effective, shall be treated as follows:
(a) Where close tolerances are not required, remove corrosion with wire brush or abrasive cloth (Federal Specification P-C-451) (SECTION VII).
WARNING: USE CORRECT PERSONAL PROTECTION. THIS CHEMICAL SOLUTION CAN CAUSE SKIN, EYE AND LUNG DAMAGE. THE DANGER AND PRECAUTIONS FOR EACH CHEMICAL IS DIFFERENT.
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