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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1

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

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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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