TASK 70-23-09-100-002
1 . General.
NOTE:
TASK 70-23-23-330-008, Removal of Coatings by High Pressure Water Stripping, is an acceptable alternative to the process listed in this procedure, provided that the self-substantiation requirements of the TASK are met.
A.When specified in the overhaul manual, this method will effectively remove tungsten carbide thermal sprayed coating from parts.
NOTE:
Before beginning this procedure any RTV or solid film lubricant must be removed. Remove copper-nickel-indium from dovetails per TASK 70-23-12-110-027, Stripping Thermal Sprayed Coating.
2 . Method 1. Enstrip A/TL.
Subtask 70-23-09-100-021
A.Materials. Refer to TASK 70-00-99-800-003, Solution S0003.
B.Procedure. Strip coating as follows:
WARNING:
THIS STRIPPING SOLUTION IS STRONGLY ALKALINE. WEAR PROTECTIVE CLOTHING AND FACE SHIELD OR GOGGLES WHEN IMMERSING OR REMOVING PARTS. IF SOLUTION CONTACTS THE SKIN OR EYES, FLUSH AT ONCE WITH CLEAR WATER.
(1)Immerse part, completely or partially as required, in the stripping solution for about 7 hours at 150°-160°F (66°-71°C). Stripping time will vary, depending upon the thickness of the coating.
(2)Rinse part thoroughly in clean running water. Blow dry with clean shop air.
(3)If required, grit blast to remove adhering traces of coating. Do not remove parent metal. Use 150-mesh aluminum oxide grit. Grit blast nozzle should be about 3 inches (76.2 mm) from surface of part, and air pressure should be about 40 psi (275.8 kPa).
(4)Blow all residual grit from part, using clean, dry shop air.
3 . Method 2. Enstrip GT-317 (C04-156)
Subtask 70-23-09-100-022
WARNING:
ENSTRIP GT-317A AND GT-317C C04-156   ARE ACIDIC. ENSTRIP GT-317B C04-156   CONTAINS HYDROGEN PEROXIDE WHICH IS A STRONG OXIDIZING AGENT AND VERY CORROSIVE. WEAR FACE SHIELD, RUBBER GLOVES, PROTECTIVE SHOES, AND PROTECTIVE CLOTHING WHEN PREPARING AND USING THE STRIPPING SOLUTION. IN CASE OF CONTACT WITH THE SKIN OR EYES FLUSH WITH LARGE AMOUNTS OF COOL, CLEAN WATER AND GET IMMEDIATE MEDICAL ATTENTION. STORE ENSTRIP GT-317B IN A COOL, DRY PLACE AWAY FROM HEAT, SPARKS OR OPEN FLAMES. KEEP ENSTRIP GT-317B AWAY FROM COMBUSTIBLE MATERIALS SUCH AS WOOD, SAWDUST, PAPER OR CLOTH AND AWAY FROM CHEMICAL REDUCING AGENTS AND ORGANIC MATERIALS.
NOTE:
This method may not remove an underlying bond coat if one is present.
A.Materials. Refer to TASK 70-00-99-801-138, Solution S1138.
B.Procedure. Strip coating as follows:
CAUTION:
ALL PARTS SHOULD BE INDIVIDUALLY RACKED AND PREVENTED FROM CONTACTING EACH OTHER. IF AN INDIVIDUAL PART IS NOT COMPLETELY IMMERSED, MASKING OF THE AIR/LIQUID INTERFACE IS REQUIRED.
(1)Mix solution thoroughly prior to part immersion.
(2)Maintain and control the bath temperature at 80-85°F (26.7°-29.4°C). Do not exceed the maximum temperature. If the maximum temperature is exceeded, the effectiveness of the solution will be greatly reduced. The process is exothermic and, as a result of the heat generated, the solution may require cooling.
(3)Immerse each part completely or partially in the stripping solution as required and soak for approximately 7 hours.
NOTE:
Stripping rate will vary depending on coating composition, porosity and service history. Typical strip rate is 0.002 inch (0.05 mm) per hour for conventional coating and 0.001 inch (0.025 mm) or less for D-gun coatings.
(4)Remove parts, rinse and scrub coated area with a stiff-bristle fiber brush.
(5)Inspect for coating removal and degradation.
(6)Repeat paragraphs 3.B.(3) through 3.B.(5) until examination reveals complete coating removal.
NOTE:
This process may take 35-40 hours to complete.
(7)Rinse part by immersion in an overflowing cold tap water rinse tank and/or use an air pressurized water rinse to remove any smut or residual acid solution from part.