TASK 70-21-00-110-051
1 . General.
Chemical cleaning is a process used for removing surface contaminants such as oil, grease, carbon deposits, oxidizing agents and corrosion. It is employed to clean surfaces prior to visual inspection, prior to crack detection using fluorescent-penetrant or magnetic-particle inspection methods, and prior to making repairs.
2 . Choice of Cleaning Method.
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A.The choice of cleaning method is dictated by the type of contaminant to be removed and by the metal(s) in the part being cleaned. Oil and grease are removed by cleaning methods using chlorinated solvents in liquid or vapor phase. Rust and carbon deposits are eliminated by the use of acid and alkaline baths that are continually maintained and monitored.
NOTE:
The effectiveness of some cleaning processes may be improved by manually assisting the process using various types of fiber bristle brushes and/or polishing pads. Obey all applicable safety cautions for the cleaning processes including cautions regarding contact with skin, eyes, and clothing.
3 . Presentation.
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B.The information is presented as Processes, Products, and Solutions.
(1)Processes - Mentioned under this heading are the baths or solutions to be employed; these are fully described in the instructions and in the solution sheets beginning with TASK 70-00-99-800-000, Solution Sheets.
(2)Products - Used either on their own or in solution, are covered in the Consumable Products List Chapter 70-80-XX.
(3)Solutions - These (as well as the products) are each identified by a No. It is preceded by:
(a)SXXXX for solutions.
(b)CXX-XXX for products (consumable products).
C.The chemical cleaning processes are to be used in conjunction with the Engine/Shop Manual, which should cover the operations or special handling of parts that precede and follow the application of the particular process.
D.Many of the chemical cleaning solutions and products can be dangerous to human skin and clothes. It is essential that personnel involved in the cleaning of parts take effective precautions against any direct contact by wearing protective equipment and clothing, when the operation is preceded by a WARNING note similar to the following examples.
WARNING:
ALKALINE SOLUTIONS ARE VERY ACTIVE AND CAUSE SERIOUS BURNS. AVOID CONTACT WITH SKIN, EYES, AND CLOTHING. IF CONTACT OCCURS, WASH IMMEDIATELY WITH ABUNDANT QUANTITY OF WATER. AVOID BREATHING VAPORS.
OPERATOR SHOULD WEAR FACE SHIELD, GLOVES, PROTECTIVE CLOTHING, AND PROTECTIVE SHOES.
WARNING:
ACID SOLUTIONS ARE VERY ACTIVE AND CAUSE SERIOUS BURNS. AVOID CONTACT WITH SKIN, EYES, AND CLOTHING. AVOID BREATHING OF VAPORS. IF CONTACT OCCURS, WASH IMMEDIATELY WITH ABUNDANT QUANTITY OF WATER.
OPERATOR SHOULD WEAR FACE SHIELD, GLOVES, PROTECTIVE CLOTHING, AND PROTECTIVE SHOES.
WARNING:
HYDROFLUORIC ACID SOLUTIONS ARE VERY DANGEROUS AND POISONOUS. PREVENT CONTACT WITH SKIN, EYES, AND CLOTHING. PREVENT INHALATION OF VAPORS. IF INCIDENT OCCURS, WASH IMMEDIATELY WITH ABUNDANT QUANTITY OF WATER AND OBTAIN IMMEDIATE MEDICAL ASSISTANCE.
OPERATOR SHOULD WEAR FACE SHIELD, GLOVES, PROTECTIVE CLOTHING, AND PROTECTIVE SHOES.
WARNING:
SOLVENT IS FLAMMABLE. TAKE PRECAUTIONS AGAINST FIRE. AVOID CONTINUED OR REPEATED INHALATION OF VAPORS. OPERATOR SHOULD USE ONLY IN WELL VENTILATED AREAS.
WARNING:
SOLVENT IS TOXIC. AVOID INHALATION OF VAPORS. AVOID PROLONGED CONTACT WITH EYES, SKIN, OR CLOTHING. OPERATOR SHOULD USE ONLY IN WELL VENTILATED AREA.
E.Be sure you read, understand, and obey all WARNINGS in this manual.
4 . Special Recommendations.
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F.Parts made entirely or partially out of titanium must not be degreased with chlorinated solvents.
G.Blasting or thermal treatment is to be used as specified in the Engine/Shop Manual, for parts that cannot easily be degreased or otherwise cleaned.
H.To ensure parts are thoroughly cleaned, the instructions of the cleaning process below must be strictly followed.
(1)Parts of intricate shape or made from honeycomb and having blind holes difficult to rinse must not be cleaned in acid baths. These parts should be cleaned using a spray of a water/additive mix.
(2)Intermediate rinsing has a great influence on the final result. Correct rinsing requires immersion of the part in water and agitation of the part or the water. This procedure avoids contaminating the next bath by removing all traces of the products used in the bath before rinsing. Components with recessed pockets or blind holes should be rinsed with a pressure jet (air-water nozzle). In addition, the use of a 2000 psi water pressure lance is permitted to assist in the removal of conditioned oxide scale following chemical cleaning steps. Maximum cleaning effectiveness is obtained by using both chemical and intermediate pressure assisted rinsing processes. The water required is defined in TASK 70-00-05-800-006, Water Types.
(3)Agitate the cleaning solution to improve the cleaning action.
(a)The preferred method to agitate cleaning solutions is the mechanical method.
(b)Air Agitation has several disadvantages.
1Carbonic gas in the air of hot alkaline solutions causes the formation of carbonates.
2Foaming increases when surfactants are incorporated in the cleaner.
3Air agitation cools down the solution temperature and makes solution temperature difficult to control.
(4)After the pressure water rinse and immersion in agitated cold water, the parts should be rinsed in a hot water bath of minimum 150°F (66°C).
(5)Proper drying of the part is necessary for subsequent inspection operations such as fluorescent-penetrant inspection. Parts can be flash dried or oven dried. To flash dry the part, keep the part submerged until the part reaches a temperature sufficient to provide for flash drying. The time required will vary with part size, water temperature and tank size. Proper flash drying is indicated by seeing the water on the surface of a part start to "flash" or "whisk" off as the part is being removed from the hot water tank. Remove the part from the tank and drain the excess water. Use repositioning, suction, blotting with a clean, absorbent material, or by blowing off with an oil and water filtered shop air gun to remove excess water.
(6)You can substitute drying the part in an air re-circulating oven for the dwell time in the hot water. Remove the part from the hot water tank and remove excess water by repositioning, suction, blotting with a clean absorbent material, or blowing the water off with an oil and water filtered shop air gun. Move the part to the oven and dry at 200°F ± 25°F (93°C ± 14°C) until the part reaches the oven temperature and all traces of surface water are removed.
I.In many of the following cleaning procedures we recommend stainless steel tanks. In general these should be made from 316 stainless steel. Sometimes optional polypropylene liners are required to give additional protection to the stainless steel. Certain acids (such as hydrochloric acid) can cause pitting of stainless steel tanks. Other solutions can become aggressive and damage stainless steel if the chloride levels from make-up water get too high. Follow the advice of your chemical supplier and tank manufacturer.