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Aqueous Alternatives for Cleaning Measurement
Instrumentation
Process Background
Rosemount Aerospace Inc. is a large
manufacturer of air data instrumentation used on both commercial
and military aircraft. The instrumentation measures parameters
such as air speed and altitude. This intern project consisted
of testing aqueous alternatives to the chlorinated solvents
that Rosemount Aerospace currently uses for cleaning two key
components of the instrumentation: temperature sensors and
pitot static tubes.
Sensors are lightweight components
that come in various sizes, ranging from one-half to two inches
in diameter. Each sensor is constructed with metal and glass.
To fabricate this part, glass is cleaned with CFC-113 (TMS)
and then melted onto the metal. After a sensor is assembled,
it comes in contact with silicone oil during testing. 1,1,1-trichloroethane
(TCA) is used to remove silicone oil before a soldering process.
Pitot static tubes deliver
air pressures from outside an aircraft to the sensors to help
determine an aircraft's velocity, altitude and angle of attack.
Rosemount Aerospace manufactures hundreds of different pitot
static tube models. The majority of the metal tubes are four
to 15 inches long, with a few models 2.5 feet in length. TCA
is used in a vapor degreaser to remove coolants and cutting
oils that accumulate on the tubes during turning and drilling
operations.
Incentive
for Change
Rosemount Aerospace wanted to find alternative cleaning
systems to TCA and CFC-113 degreasing due to the 1990 Clean
Air Act's production phase-out of ozone-depleting chemicals
scheduled for January 1, 1996. TCA and CFC-113 are two of
the many chlorinated solvents on the list to be eliminated.
Prior to this intern project,
Rosemount Aerospace had already started reducing the amount
of TCA used. Between 1989 and 1992, the company's annual TCA
use dropped from 23,000 pounds to 15,000 pounds, primarily
through conservation. To further reduce use of chlorinated
solvents, the company assembled a Degreaser Replacement Team
to identify objectives for replacing their current degreasing
practices in their machining and assembly areas.
Intern
Activities
A MnTAP intern worked closely with the Degreaser Replacement
Team in testing various cleaning methods. The primary focus
of the testing was on aqueous immersion methods. The MnTAP
intern evaluated different cleaning chemistries and different
types of agitation. Aqueous cleaners were targeted for research
because of their low toxicity and nonflammability. In addition,
three types of agitation were tested: simple mechanical, flushing
solution through tube, and ultrasonics.
Pitot
Tube Project
Samples of pitot static tubes were taken to the machining
area, filled with either a waterbased coolant or a cutting
oil, then cleaned in an aqueous solution. A number of tubes
were cleaned with various aqueous solutions and agitation
methods, followed by "smoke" cleanliness testing.
Since each pitot static tube
is fitted with an internal heating coil, these sample parts
were tested for cleanliness by heating the tube assembly,
and observing any smoke. The presence of smoke indicated uncleaned
residue inside the tube.
Results: Pitot Tube Project
Most aqueous cleaners, even with simple agitation, yielded
smoke-free tubes when the soil was a waterbased coolant.
However, when the soil was cutting oil, the aqueous cleaners
did not clean the inside of the tubes as well as the outside
of the tubes. This was especially true when testing simple
mechanical and flush-through agitation. These tests did not
yield smoke-free parts.
Results with ultrasonic agitation
were highly dependent on the equipment and method used. For
these tests, the ultrasonic power density and the tube orientation
were critical variables. Also, better results were achieved
when the tubes were allowed to drain and refill multiple times
throughout the ultrasonic immersion cycle.
Sensor
Project
The intern also tested aqueous and semi-aqueous cleaners
for removing light soils and finger oils from sample sensors
prior to glass fusing, and for removing silicon oil prior
to soldering. The cleanliness test for the former was observing
the quality of the resulting glass, and for the latter, a
water-break test followed by soldering and inspection of the
solder joint.
Results: Sensor Project
All eight aqueous and semi-aqueous cleaners tested on
the sensors removed light oils and fingerprints at least as
well as the existing vapor degreasing system. Three aqueous
cleaners, Fremont Industries 410 (Shakopee, MN, 952/445-4121),
LPS Precision Clean (Tucker, GA, 800/241-8334), and Micro
International Products Corporation (Burlington, NJ, 609/386-8770),
also effectively removed silicon oil from sensors. This was
demonstrated by favorable results in soldering tests.
Additional
Information
For more information about aqueous cleaning alternatives,
or to receive technical assistance with managing your industrial
waste, contact MnTAP at 612.624.1300 or 800.247.0015 from
greater Minnesota.
This project was conducted in
1993 by MnTAP intern Josh Hackney.
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