Vacuum Vapor Degreasing at Raytheon Missile Systems

When Raytheon Missile Systems at Air Force Plant (AFP) 44 in Tucson, AZ decided to upgrade its manual solvent-based cleaning and automated vapor degreasing operations, environmental challenges with the current solvents were laid out on the table to take into consideration, along with the current and future projected cleaning requirements. One challenge was high usage of IPA ( isopropyl alcohol). Use of a 10-year-old IPA vapor degreaser was resulting in nearly one ton of VOC emissions per year. A second challenge was the high usage of MEK (methyl ethyl ketone) during manual cleaning operations and varying cleaning requirements, producing nearly one ton of both HAP and VOC emissions per year. Note: MEK was taken off the federal hazardous air pollutant (HAP) list in December 2005 but still remains an issue in the State for Arizona.

Goals and Requirements

Considering these challenges, the goals for the new degreaser were established that would give Raytheon the most effective cleaning and degreasing process during manufacturing, including implementing an automated vacuum vapor degreasing system using a non-HAP and preferably low-VOC cleaning agent, capable of removing both polar and non-polar contaminants, and continuing to meet “water break free surface” cleanliness requirement prior to painting or bonding. It was important that production areas were given a competitive reason to switch from IPA vapor degreasing and manual MEK-based cleaning processes to a central and automated process. In addition, Raytheon wanted to reduce worker exposure to solvents.

Vacuum vapor degreaser equipment requirements were determined via a Six Sigma, team-based approach. A minimum basket load size of 26.4" x 19.0" x 12.0" was needed to accommodate all projected components entering the work area (see Figure 1). Since both foreign and domestic equipment suppliers were invited to bid, a detailed performance based equipment specification was written. DURR-Ecoclean (Wixom, MI) was selected. Dow’s (Midland, MI) modified alcohol-based cleaning chemistry, DOWCLENE 1601, was also selected. Finally, a factory buyoff of the fully operational system was conducted at DURREcoclean in Stuttgart, Germany using Raytheon-provided missile components. Parts were cleaned to a water break free surface in all cases.

Process Chemistry

Getting back to the cleaning chemistry, Raytheon selected DOWCLENE 1601 from Europe to use in the degreaser. Through some very involved laboratory testing, DOWCLENE 1601 was fully capable of removing both polar and non-polar contaminants, and was more than able to meet a straightforward water break free surface cleanliness requirement prior to painting or bonding. DOWCLENE 1601 was non- HAP and low VOC, and its price per gallon was comparable to similar chemistries on the market and already in use at Raytheon. In turn, DOW agreed to supply the chemistry for the first time in the United States to Raytheon. Figure 2 shows the comparison of DOWCLENE 1601 with IPA.

Programmable Process Sequence

Trying out the programmable process sequence through test washing with DURR-Ecoclean, Raytheon’s trials proved favorable to the cleaning process. Wash #1 consisted of removing all of or the bulk of contaminants, high volume solution circulation (selectable), ultrasonics (selectable), parts load rotation or oscillation (selectable), and vapor degreasing (selectable), while wash #2 provided a much cleaner version of wash #1, with the same criteria, including optional vapor degrease and then vacuum drying at 1 mBar (see Figure 3). Whereas before, Raytheon engineers had to hand clean parts one at a time with MEK, now they could load 48 parts into a degreaser and set a six-minute cleaning cycle. Even though this operation is not large-scale by any means, the overall initial savings have been calculated at over $70,000 per year, making for about a three-year payback for equipment and installation.

Results

Raytheon is very pleased with the vacuum vapor degreasing process using DOWCLENE 1601. It is a better, cheaper, faster, greener and safer process. In addition it eliminates all IPA vapor degreasing except for one legacy missile program component having a critical pyroceramic-to-titanium bond. A closed working system with no solvent emissions, the vacuum vapor degreaser reduced manual cleaning operations, thus reducing the use of MEK and other HAP/VOC containing solvents, and resulted in minimal worker exposure to solvents. A distillation unit significantly reduces hazardous wastes since the cleaning solution is continuously recycled. “Our hats are off to the equipment supplier
DURR-Ecolean and to Dow, as we are very pleased with the results of the new equipment and process,” says Senior Materials and Process Engineer Bruce T. Miller (see Figure 4).


Paul W. Fecsik is a project manager for Raytheon Missile Systems in Tucson, AZ. For more information on this Raytheon Missile Systems’ cleaning process contact him at (520) 794-4105.