NOTE: On surfaces that were previously chrome plated, all old chrome plating shall be removed.
(b)
After grinding or machining operation, surface finish shall be 32 microinches (0,8128 micromters) or better. Dimensions shall allow for plating thickness specified in applicable manual or as indicated in the note at the beginning of this procedure.
(c)
Perform fluorescent penetrant or magnetic particle inspection (SECTION III), as specified for part being plated, to ensure that grinding or machining operation has caused no surface cracks. No cracks are permissible.
(d)
Thoroughly clean part to remove all contamination and other residue, in accordance with SECTION II.
(e)
Mask all surfaces of part that are not to be plated.
(2) Apply chrome plating.
CAUTION: WHEN THE BASE METAL IS ROCKWELL C40 OR HARDER, THE PART SHALL BE STRESS-RELIEVED AT 300F (149C) FOR TWO HOURS PRIOR TO PLATING.
(a) Apply chrome plating to surfaces of part in accordance with AMS2406 or Federal Specification QQ-C-320B.
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CAUTION: WHEN THE BASE METAL IS ROCKWELL C40 OR HARDER, THE PART SHALL BE HYDROGEN-EMBRITTLEMENT-RELIEVED WITHIN FOUR HOURS AFTER PLATING.
(b)
If required, in accordance with applicable manual, relieve chrome plating on part for three hours minimum at 350 to 400F (177 to 204C).
WARNING: USE CORRECT PERSONAL PROTECTION. PROCEDURES THAT NEED GRIND/MACHINE WORK WILL CAUSE LOOSE PARTICLES THAT CAN GET IN YOUR EYES.
(c)
Machine or hone part to finished dimensions specified. Remove excess plating and any sharp edges using a soft stone.
(d)
Vapor degreases part in accordance with SECTION II, to remove all residue.
NOTE: Use only fluorescent penetrant method for inspection, do not use magnetic particle method. Chrome plated surfaces often show a network on fluorescent penetrant; this indication is typical and is not cause for rejection.
(e)
Perform fluorescent penetrant inspection (SECTION III) on part. No cracks are permissible. Cracks indicate chipping, flaking, or separation, which indicates faulty binding of the plating to the base metal and the part shall be rejected.
(f)
Thoroughly clean part (SECTION II) to remove any residue from fluorescent penetrant inspection. Thoroughly dry part.
(g)
Perform reverse plating for improved wear properties after honing. No measurable dimensional change is allowable. For Class A, chrome plate, reverse after eight to twelve seconds in plating bath with the same fixtures used and at the same current density.
(h)
If part is to be stored, apply a thin coat of corrosion-preventive compound (MIL-C-6529, Type III) (SECTION VII) to part and wrap in paper, barrier material (MIL-B-131B) (SECTION VII).
D. Method No. 403D: Metal Spray Repair
Method 1 Parts not meeting manual limits may be processed by applying molybdenum spray in accordance with EMS52432 using EMS57738 powder. Coating thickness limitations are 0.002 to 0.010 inch thick per surface. Coating temperature limitation is 600°F maximum service temperature. Coating hardness is approximately 40 HRC, and grinding is recommended for finishing.
Method 2 Parts not meeting manual limits may be processed by applying nickel/aluminum material in accordance with EMS52432, Class XX. Coating thickness limitations are 0.002 to 0.010 inch thick per surface. Coating temperature limitation is 1500°F maximum continuous service temperature. Coating hardness is approximately 75 HRB, and may be finished by single-point machining or grinding.
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