Post on 24-May-2020
METHYLENE CHLORIDE FREE PAINT STRIPPERS
RICK BARNES
NAVAL AVIATION DEPOT JACKSONVILLE
The effort at NADEP JACKSONVILLE to eliminate the use of
methylene chloride paint strippers began in March of 1990. At
that time, the driver was the threat of OSHA exposure limits
being changed from 500ppm to 25ppm.
protect our employees, comply with the proposed requirement,
Our concerns were how to
and continue to remove paint from naval aircraft.
Protecting the employees seemed easy ; simply put the
worker in a TYVEK suit with a breathing helmet and the problem is
solved. However, there were certain environmental difficulties
that arose:
- Employee safety and fatigue - Methylene chloride saturated the hangar area, limiting other operations in the area.
MAN L I-IACTURING TECH NOLOGY LOW VOC SURFACE COATINGS
JUNE, 1993 STATUS
MAJOR ACCOMPLISHMENTS
- COMPLETED FIRST A/C (7002 RAF, FUSELAGE ONLY) WITH NEW
- ESTABLISHED FIRM CUTOVER DATE (JULY 1,1993) FOR POLYURETHANE PAINT SCHEME
FACILITY WIDE C'ONVERSION TO POLYURETHANE TOPCOAT
IMPLEMENTATION ISSUES ,,./---\ 17 i, /'/ ,L ,
--- POLYURETHANE PAINT FOR RAF 1.f ' c ; r: 6'J LACQUER STENCILS DIRECTLY OVER
BASE TOPCOAT n
CORRECTIVE ACTIONS
- THIN PAINT TO EXTEND POT LIFE - APPLY MIST COAT OF PRIMER BETWEEN BASE POLY COAT
AND LACQUER STENCILS Y
The first issue was as serious as the second. The worker
was required to pull an air hose and stripper hose while moving
up and down steep ladders, all this action in a non
air-conditioned space. We were able to do away with most of the
ladders when high lifts were purchased, this made the job safer
and much less fatiguing.
The methylene chloride fumes in the hangar were still a
problem, as they’continue to be today.
reduce these fumes was to eliminate the source; procurement of
We viewed the best way to
new ventilation equipment was years away. At that point, the
search for a non-methylene chloride paint stripper began, TYVEK
suits and breathing helmets were considered an intermediate
solution for worker safety.
We investigated several acid based paint removers and
tested some on selected aircraft components with good results.
However, the risk of hydrogen embrittlement of high strength
steel was too great and acid strippers were rejected as a viable
option.
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The question was begged - What about plastic media blast?
The answer to that one was easy. We simply did not have full
facilities capability . There were also other considerations
with plastic media blasting large aircraft:
- Increased Process Turnaround Time - Increased Manpower Requirements
Essentially, we determined that it was important to press
\? on with our inquiries and search for a methylene chloride free
chemical paint stripper that would:
a. Not damage the aircraft structure
b. Remove Navy paint systems in a timely fashion
c. Be environmentally acceptable
d. Be safer for use
e. Be compatible with our paint stripping equipment
The first four criteria were considered as the most important . As events unfolded OSHA was the impetuous for change but
the Clean Air Act was the driver. Most of you know that the
Environmental Protection Agency is beginning to set emission
standards for the aerospace industry. Several round table
discussions have been held with the EPA and industry
representatives to control and limit hazardous air pollutants
(HAPS).
elimination of methylene chloride in the aerospace industry.
The direction that the national standards is taking is
Are there any substitutes that we can use?
are they? Or is chemical stripping a thing of the past?
If so, what
There are several chemical paint stripper substitutes
These products vary significantly in their available.
effectiveness, physical appearance, odor, and paint system
affected.
while others look like thick colored pastes. The odors range
Some products appear similar to a thick amber liquid,
from no odor to the pungent sting of ammonia.
the formulation of the product they can be effective against
Depending on
epoxies, polyurethanes, and polysulfides. The primary constituent
of the most effective non-methylene chloride strippers is benzyl
alcohol. When working with these products we must keep in mind
some of the problems and constraints these materials impose on
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us.
One of the problems with the benzyl alcohol strippers is
that they take longer to remove the paint.
statement on the'surface; however, it becomes more complex when
one considers the variance of strip times encountered in testing.
That is a simple
1 The table below illustrates the variance in strip times and
effectiveness.
I Stripper 2 hrs 3 hrs 6 hrs 19 hrs 24 hrs
EZE 541 0% 0%
EZE 542 0% 0%
10%
30%
CB 1092A 0% 0% 0%
100%
Our tests were conducted on aluminum panels treated with
chromate conversion coating, water borne epoxy primer, and grey
polyurethane top coat.
stripper would not drain off.
The panels were laid flat so the paint
When the panels were inclined
,*-
sixty degrees there was a problem with drain off of the product. ", ;
This required several applications of stripper for it to act on
the paint system.
This drain off characteristic of the other strippers does not
make them desirable for use on aircraft. However, these products
are in their developmental infancy and can be improved upon.
Based on favorable results from the effects on metals
The exception to this was the T-6813 product.
testing done by the Naval Aviation Warfare Center at Trenton, New
Jersey, and permission from the Naval Air Systems Command, we
performed prototype testing on a production aircraft.
The aircraft chosen for testing was a P-3 Orion. This
aircraft has seven thousand seven hundred square feet of exterior
surface area requiring paint removal. The paint system was a r-- -+.-, # 1
chromated epoxy primer and a polyurethane topcoat.
thickness was approximately .006 inch.
The coating
Chemical strippers are applied by pumping the stripper
through a nozzle and directing it on to the surface to be
stripped. As easy as this sounds it belies the technique
required to apply it.
altered to suit the product.
In this case the spray technique had to be
The difference was in the speed of
application and the coverage.
Essentially, if too much T-6813 is applied, it rolls off
the aircraft. There is a critical amount that can be applied
before the stripper begins to slip off the surface.
the limit is not exceeded, the product adheres and effectively
However, if
attacks the paint system. When properly applied, the usage of
stripper is approximately twenty-five percent less than methylene
chloride strippers.
The ambient air temperature was 72 degrees F on the day
the P3 was stripped. During lab tests we found that the benzyl
alcohol strippers were not effective below 70 degrees F.
degrees F we anticipated a slow strip rate . However, within
*. 'I-
At 72 - -
eight hours 95 percent of the paint was removed. This is slower
than the traditional paint stripper but still acceptable. Using 110 c)
a methylene chloride paint stripper the time is usually three to
four hours. These times include the spray up and the complete
removal.
Removal of the stripper after the dwell time was achieved
by using high pressure water. This is the method we normally use
to remove stripper at our facility. The T-6813 was easily
removed with water and left no residue.
The safety of the product was a concern, since methylene
chloride is not a pleasant material to be near and has specific
hazards. In addition to benzyl alcohol, T-6813, contains
ammonium hydroxide, which has a very pungent odor. While the
workers must wear respirators with ammonia cartridges, the whole
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hangar does not have to be cleared. We also found that with
minimal ventilation, odors from the T-6813 dissipate rapidly and
the product is much safer to handle.
During the stripping operation, we noticed that the
stripper dropped to the surface of the aircraft; as opposed to
some drifting through the air and stinging passersby and
workers, as experienced with chloride strippers.
Overall, T-6813, preformed well enough to be considered a
substitute for methylene chloride paint stripper.
other benzyl alcohol paint strippers on the market that may suit
your particular needs better than T-6813. The point is that
there are several benzyl alcohol products available for use.
one does not perform satisfactorily for your needs investigate
another.
There are
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