Precision Cleaning of Aerospace Hardware at Martin
Spacecraft/satellite propulsion components require high
levels of cleanliness to ensure reliability in their operating environment.
Typical components and their respective cleanliness levels are shown in Table
2 . Cleanliness levels of MIL-STD-1246 25A and 50A have also been required
in several systems and have been achieved.
Table 2 Propulsion Components and Cleanliness Requirements
Precision cleaning of these
components has been by ultrasonic immersion in CFC 113 followed by a low
pressure CFC 113 or alcohol spray rinse. Medium and large object precision
cleaning was accomplished by spray rinsing CFC 113 over a large object
ultrasonic cleaner located in a Class 100,000 clean room. Small details and
assemblies were precision cleaned with CFC 113 or isopropyl alcohol on a Class
100 laminar flow bench which exhausts to the outside. Filtering of the CFC
113/alcohol (isopropyl) was accomplished using a 10, 5, 2, and 0.2 micron
filtration bank (prefilters) and a 0.2 micron filter at the nozzle. These
operations were performed in an open spray booth.
Final cleaning of medium and large assemblies is much more difficult and
typically accomplished by flow through of CFC 113 or alcohol followed by
gaseous nitrogen purges for up to 8 hours. Use of a vacuum drying oven to
assist drying was also occasionally used. Cleanliness verification for
particulate and non- volatile residue (NVR) was made prior to drying. The
purpose of this cleaning scenario is to precision clean the hardware at a low
assembly level such that high precision cleanliness levels can still be met
for the end product.
The current cleaning process consists of an ultrasonic
aqueous degreaser preclean, followed by water rinse and gaseous nitrogen purge
(for drying) and finally an isopropyl alcohol (IPA) spray rinse for final
cleaning. The use of CFC 113 and other ozone depleting substances in the
cleaning process have been eliminated. This process is illustrated in Figure 1
described in more detail in the next section.