Solvent Cleaners
In general, solvent cleaners used in aircraft cleaning must have a flashpoint of not less than 105 °F, if explosion proofing of equipment and other special precautions are to be avoided. Chlorinated solvents of all types meet the nonflammable requirements, but are toxic. Safety precautions must be observed in their use. Use of carbon tetrachloride is to be avoided. The SDS for each solvent must be consulted for handling and safety information.
AMTs must review the SDS available for any chemical, solvent, or other materials they may come in contact with during the course of their maintenance activities. In particular, solvents and cleaning liquids, even those considered “environmentally friendly,” can have varied detrimental effects on the skin, internal organs, and/or nervous system. Active solvents, such as methyl ethyl ketone (MEK) and acetone, can be harmful or fatal if swallowed, inhaled, or absorbed through the skin in sufficient quantities.
Particular attention must be paid to recommended protective measures including gloves, respirators, and face shields. A regular review of the SDS keeps the AMT updated on any revisions that may be made by chemical manufacturers or government authorities.
Dry Cleaning Solvent
Stoddard solvent is the most common petroleum base solvent used in aircraft cleaning. Its flashpoint is slightly above 105 °F and can be used to remove grease, oils, or light soils. Dry cleaning solvent is preferable to kerosene for all cleaning purposes, but like kerosene, it leaves a slight residue upon evaporation that may interfere with the application of some final paint films.
Aliphatic and Aromatic Naphtha
Aliphatic naphtha is recommended for wipe down of cleaned surfaces just before painting. This material can also be used for cleaning acrylics and rubber. It flashes at approximately 80 °F and must be used with care. Aromatic naphtha must not be confused with the aliphatic material. It is toxic, attacks acrylics and rubber products, and must be used with adequate controls.
Safety Solvent
Safety solvent, trichloroethane (methyl chloroform), is used for general cleaning and grease removal. It is nonflammable under ordinary circumstances and is used as a replacement for carbon tetrachloride. The use and safety precautions necessary when using chlorinated solvents must be observed. Prolonged use can cause dermatitis on some persons.
Methyl Ethyl Ketone (MEK)
MEK is also available as a solvent cleaner for metal surfaces and paint stripper for small areas. This is a very active solvent and metal cleaner with a flashpoint of about 24 °F. It is toxic when inhaled, and safety precautions must be observed during its use. In most instances, it has been replaced with safer to handle and more environmentally-friendly cleaning solvents.
Kerosene
Kerosene is mixed with solvent emulsion-type cleaners for softening heavy preservative coatings. It is also used for general solvent cleaning, but its use must be followed by a coating or rinse with some other type of protective agent. Kerosene does not evaporate as rapidly as dry cleaning solvent and generally leaves an appreciable film on cleaned surfaces that may actually be corrosive. Kerosene films may be removed with safety solvent, water emulsion cleaners, or detergent mixtures.
Cleaning Compound for Oxygen Systems
Cleaning compounds for use in the oxygen system are anhydrous (waterless) ethyl alcohol or isopropyl (antiicing fluid) alcohol. These may be used to clean accessible components of the oxygen system, such as crew masks and lines. Fluids must not be put into tanks or regulators.
Do not use any cleaning compounds that may leave an oily film when cleaning oxygen equipment. Instructions of the manufacturer of the oxygen equipment and cleaning compounds must be followed at all times.
Emulsion Cleaners
Solvent and water emulsion compounds are used in general aircraft cleaning. Solvent emulsions are particularly useful in the removal of heavy deposits, such as carbon, grease, oil, or tar. When used in accordance with instructions, these solvent emulsions do not affect good paint coatings or organic finishes.
Water Emulsion Cleaner
Material available under Specification MIL-C-22543A is a water emulsion cleaning compound intended for use on both painted and unpainted aircraft surfaces. This material is also acceptable for cleaning fluorescent painted surfaces and is safe for use on acrylics. However, these properties vary with the material available. A sample application must be checked carefully before general uncontrolled use.
Solvent Emulsion Cleaners
One type of solvent emulsion cleaner is nonphenolic and can be safely used on painted surfaces without softening the base paint. Repeated use may soften acrylic nitrocellulose lacquers. It is effective, however, in softening and lifting heavy preservative coatings. Persistent materials are to be given a second or third treatment as necessary.
Another type of solvent emulsion cleaner has a phenolic base that is more effective for heavy-duty application, but it also tends to soften paint coatings. It must be used with care around rubber, plastics, or other nonmetallic materials. Wear rubber gloves and goggles for protection when working with phenolic base cleaners.
Soaps and Detergent Cleaners
A number of materials are available for mild cleaning use. In this section, some of the more common materials are discussed.
Cleaning Compound, Aircraft Surfaces
Specification MIL-C-5410 Type I and II materials are used in general cleaning of painted and unpainted aircraft surfaces for the removal of light to medium soils, operational films, oils, or greases. They are safe to use on all surfaces, including fabrics, leather, and transparent plastics. Nonglare (flat) finishes are not to be cleaned more than necessary and must never be scrubbed with stiff brushes.
Nonionic Detergent Cleaners
These materials may be either water-soluble or oil-soluble. The oil-soluble detergent cleaner is effective in a 3 to 5 percent solution in dry cleaning solvent for softening and removing heavy preservative coatings. This mixture’s performance is similar to the emulsion cleaners mentioned previously.
Mechanical Cleaning Materials
Mechanical cleaning materials must be used with care and in accordance with directions given, if damage to finishes and surfaces is to be avoided.
Mild Abrasive Materials
No attempt is made in this section to furnish detailed instructions for using various materials listed. Some “do’s and don’ts” are included as an aid in selecting materials for specific cleaning jobs.
The introduction of various grades of nonwoven abrasive pads has given the AMT a clean, inexpensive material for the removal of corrosion products and for other light abrasive needs. The pads can be used on most metals (although the same pad should not be used on different metals) and are generally the first choice when the situation arises. A very open form of this pad is also available for paint stripping when used in conjunction with wet strippers.
Powdered pumice can be used for cleaning corroded aluminum surfaces. Similar mild abrasives may also be used.
Impregnated cotton wadding material is used for removal of exhaust gas stains and polishing corroded aluminum surfaces. It may also be used on other metal surfaces to produce a high reflectance.
Aluminum metal polish is used to produce a high luster, long lasting polish on unpainted aluminum clad surfaces. It must not be used on anodized surfaces, because it removes the oxide coat.
Three grades of aluminum wool, coarse, medium, and fine are used for general cleaning of aluminum surfaces. Impregnated nylon webbing material is preferred over aluminum wool for the removal of corrosion products and stubborn paint films and for the scuffing of existing paint finishes prior to touchup.
Lacquer rubbing compound material can be used to remove engine exhaust residues and minor oxidation. Avoid heavy rubbing over rivet heads or edges where protective coatings may be worn thin.
Abrasive Papers
Abrasive papers used on aircraft surfaces must not contain sharp or needlelike abrasives that can imbed themselves in the base metal being cleaned or in the protective coating being maintained. The abrasives used must not corrode the material being cleaned. Aluminum oxide paper, 300 grit or finer, is available in several forms and is safe to use on most surfaces. Type I, Class 2 material under Federal Specification P-C-451 is available in 11⁄2" and 2" widths. Avoid the use of carborundum (silicon carbide) papers, particularly on aluminum or magnesium. The grain structure of carborundum is sharp and the material is so hard that individual grains penetrate and bury themselves, even in steel surfaces. The use of emery paper or crocus cloth on aluminum or magnesium can cause serious corrosion of the metal by imbedded iron oxide.
Chemical Cleaners
Chemical cleaners must be used with great care in cleaning assembled aircraft. The danger of entrapping corrosive materials in faying surfaces and crevices counteracts any advantages in their speed and effectiveness. Any materials used must be relatively neutral and easy to remove. It is emphasized that all residues must be removed. Soluble salts from chemical surface treatments, such as chromic acid or dichromate treatment, liquefy and promote blistering in the paint coatings.
Phosphoric-citric Acid
A phosphoric-citric acid mixture (Type I) for cleaning aluminum surfaces is available and is ready to use as packaged. Type II is a concentrate that must be diluted with mineral spirits and water. Wear rubber gloves and goggles to avoid skin contact. Any acid burns may be neutralized by copious water washing, followed by treatment with a diluted solution of baking soda (sodium bicarbonate).
Baking Soda
Baking soda may be used to neutralize acid deposits in lead-acid battery compartments and to treat acid burns from chemical cleaners and inhibitors. Baking soda may be used to neutralize acid deposits in lead-acid battery compartments and to treat acid burns from chemical cleaners and inhibitors.
