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The NASA WSTF evaluated four methods of cleaning that do not involve the use of CFCs and compared the results to current procedures which use CFCs. The cleaning methods investigated were cleaning with an emulsifying agent, steam cleaning, ultrasonic cleaning with an inorganic cleaning agent, and ultrasonic cleaning with an emulsifying agent. Stainless steel components were used in the evaluation. The components were made of 304 stainless steel and were configured as tube elbows, end caps, and straight tubes with female end-fittings. Pieces of each configuration were contaminated with a mixture of particulate, and various greases and oils. The pieces were then cleaned using the WSTF methods, and alternate methods, and the levels of contamination removal, and levels of cleanliness were compared. Results of the evaluation showed that the all of the alternatives were more effective in removing organic contaminants than vapor degreasing with trichloroethane, and some were comparable to the WSTF 3-step process involving CFCs. The most effective alternative was ultrasonic cleaning with an emulsifying agent. The investigation also showed that the verification step of rinsing with Freon 113 is not very effective for determining NVR, and is not an adequate method for determining particulate. In several tests, hardware verified as meeting particulate requirements by a Freon 113 rinse released tens of thousands of additional particles when subjected to ultrasound. Freon 113 was far more effective when combined with ultrasound in the removal of organics and particles.
precision cleaning, chlorofluorocarbons, contamination, cleaning agents, alternative cleaning methods, nonvolatile residue
Section Head of Nonmetallic Materials, NASA Johnson Space Center, Houston, TX
principal scientist, Lockheed Engineering and Sciences Company, Houston, TX
chemist, NASA Johnson Space Center White Sands Test Facility, Las Cruces, NM