TASK 70-23-28-110-801
1 . General.
CAUTION:
FOR STRIPPING THERMAL SPRAY COATINGS FROM INCO 718 MATERIALS, DO NOT USE THIS PROCEDURE. USE TASK 70-23-22-110-041, STRIPPING OF THERMAL BARRIER TOP COATINGS AND NICKEL-CHROMIUM-ALUMINUM-YTTRIA BOND COATINGS.
CAUTION:
THIS PROCEDURE REQUIRES SHOTPEENING PER TASK 70-47-01-380-016 AFTER STRIPPING PROCESS. FOLLOW THE SHOT PEEN REQUIREMENTS SPECIFIED FOR APPROPRIATE SEAL SERRATION COATINGS REPLACEMENT REPAIR PROCEDURE.
A.The method first lets the top coat (aluminum oxide) to be grit blasted and then the bond coat is chemically stripped off. This stripping method to be used on parts made of Rene 88DT.
2 . Materials.
Subtask 70-23-28-110-001
 
Consumable Product
No.
 
Acid Stripping Solution
S1206
 
Maskant
C10-014
 
Solvent, General
C04-001
 
Solvent, General
C04-003
 
Tape, Platers
C10-067
 
Tape, Specialty Duct
C10-063
3 . Procedure.
Subtask 70-23-28-110-002
WARNING:
THIS IS STRONG ACID. WEAR FACE SHIELD AND PROTECTIVE CLOTHING. IF SOLUTION CONTACTS SKIN OR EYES, FLUSH IMMEDIATELY WITH CLEAR WATER AND OBTAIN MEDICAL AID.
CAUTION:
DO NOT GRIT BLAST EXCESSIVELY, PARTICULARLY IF THE COATING IS SPALLED OR MISSING IN PATCHES.
CAUTION:
AIR AGITATION SHALL NOT BE USED FOR THIS PROCESS. ONLY MECHANICAL AGITATION CAN BE USED TO IMPROVE THE STRIPPING ACTION.
A.Mask adjacent to seal coating with C10-067   platers tape or C10-063   duct tape to prevent grit blasting any basis metal adjacent to the coated area. Refer to TASK 70-21-04-120-A01, Cleaning Method No. 4 - Dry Abrasive Blast Cleaning, Method No. 4A, using 220 mesh aluminum oxide, maintain air pressure at 30-45 psi (206-310 kPa) for direct pressure equipment or at 60-90 psi (414-621 kPa) for suction-type equipment with gun distance of 6-8 inches (152-203 mm) from the part with a recommended angle to the surface being blasted of 50 to 70 degrees.
B.Mask any metal sprayed areas that are not to be stripped as follows:
(1)Mask metal sprayed areas to be stripped with masking tape, and seal all part opening with C10-067   platers tape.
(2)Dip the entire part into C10-014   maskant, and let it dry. Repeat until a minimum of 3 coats have been applied.
(3)Trim by cutting through the masking tape and the maskant around areas to be stripped. Expose only the area to be stripped by peeling away tape and maskant, but do not remove the alkaline resistant tape/maskant from the opening.
C.Immerse the part in stripping solution S1206 for 2 hours at room temperature. Refer to TASK 70-00-99-801-803, S1206 - Acid Stripping Solution for Nickel-Chrome-Aluminum-Yttrium Plasma Coatings on Rene 88DT.
D.Rinse the part in cold water and brush the coating with a soft bristle brush and inspect for removal. Repeat paragraphs 3.C and 3.D until the coating is removed, it can not be more than 4 hours in the acid stripping solution.
E.Remove masking if needed by peeling away from the part. Use C04-003   acetone or C04-001   methyl-ethyl-ketone to remove any maskant or tape that does not peel away readily.
F.Rinse by immersion in hot water at minimum 150°F (66°C).
G.Dry the part using either of the following procedures:
(1)Alternative Procedure Available. Remove excess water by using a suction device or a blast of clean, compressed air, and then let the part air dry.
(2)Alternative Procedure: Oven dry: Move the part to an oven and dry at 175 to 225°F (79 to 107°C) until the part reaches the oven temperature and all traces of surface water are removed.
H.If necessary, refer to TASK 70-21-03-160-001, Cleaning Method No. 3 - Steam Cleaning, TASK 70-21-05-120-A02, Cleaning Method No. 5 - Wet Abrasive Blast Cleaning, Method No. 5A, and then follow with a pure steam “rinse” to remove residue from the stripped area.