United States
Environmental Protection
Agency
Water Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-87/014 June 1987
&EPA Project Summary
Reduction of Total Toxic
Organic Discharges and VOC
Emissions from Paint Stripping
Operations Using Plastic Media
Blasting
C. D.Wolbach and C. McDonald
Three depainting methods were
compared for their ability to strip
Army communications shelters:
chemical stripping, sandblasting, and
plastic media blasting (PMB). Each
process was studied with respect to
the economics, the environmental
impact, and the quality of the
product Currently, large pieces of
military equipment constructed of
various alloys and composite
materials are either sandblasted or
chemically stripped. These methods
have economic and environmental
drawbacks. PMB is being evaluated
by the U.S. Air Force for depainting
military aircraft, and is currently
being introduced to commercial
aviation. The purpose of this study
was to determine if the PMB method
is applicable to Army
communications shelters and
whether it would be advantageous
for the Army to convert to this
procedure both from the perspective
of process efficiency and pollution
reduction.
Chemical stripping of
communications shelters was
studied at McClellan Air Force Base,
Sacramento Air Logistics Center
(SAALC). Sandblasting and PMB
were studied at the Sacramento
Army Depot (SAAD). Each process
was studied for paint removal
efficiency, surface quality equipment
requirements, labor and material
costs, and quantities and type of
waste pollutants generated.
The PMB process was determined
superior to the chemical stripping
process and marginally better than
sandblasting based upon the
evaluation criteria. This report
presents study results of the three
methods evaluated and compares
their respective efficiencies,
processing costs, and waste
generation.
This Project Summary was
developed by EPA's Water Engineering
Research Laboratory, Cincinnati, OH,
to announce key findings of the
research project conducted in
cooperation with the U.S. Army Toxic
and Hazardous Materials Agency and
is fully documented in a separate
report of the same title (see Project
Report ordering information at back).
Introduction
Until recently there have been three
main methods for depainting large
equipment - sandblasting, vegetable-
matter blasting, and chemical stripping.
Vegetable-matter blasting has
decreased significantly in use because it
generates dust with a high explosive
potential and does not perform well
against many of the newer paints.
Sandblasting cannot be used on many
composites and is very difficult to use on
soft alloys and light, thin materials.
Chemical stripping generates large
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quantities of contaminated waste waters
that are classified as hazardous under
the Resource Conservation and
Recovery Act (RCRA). Plastic Media
Blasting (PMB) has been identified as a
viable paint removal method for aircraft
and other equipment constructed of soft
metal alloys such as aluminum alloys.
Ths report presents the results of a study
comparing the technical performance,
the economics, and the environmental
costs of PMB. chemical stripping, and
sandblasting.
EPA has promulgated an effluent
regulation governing the discharge of
liquid waste from metal-finishing
operations. Under RCRA other forms of
waste discharge have also come under
increasing regulatory pressure including
paint-stripping discharges. The U.S.
Army operates several metal-finishing
facilities that have large depainting
operations. Thus, the Army is
investigating methods of reducing
hazardous waste from these facilities.
The U.S. Army Toxic and Hazardous
Materials Agency jointly conducted a
study with EPA specifically for the
purpose of determining if PMB could be
a viable substitute in performance and
environmental safety for the Army's
paint-stripping processes now used for
U.S. Army communications shelters.
The study of the various paint-
removing methods took place between
July and November 1985. The
observations of chemical stripping were
held at McClellan Air Force Base
(SAALC) between July 24 and July 26,
1985. The observations of sandblasting
and demonstration test of the PMB
process were held between October 23
and November 1, 1985, at the
Sacramento Army Depot (SAAD). The
same type of equipment was depainted
at both facilities.
Conclusions and
Recommendations
• PMB process is an economically and
environmentally viable alternative
technology to chemical stripping and
sandblasting for depainting major
pieces of equipment fabricated from
aluminum. In particular, it is a viable
and desirable replacement for the
current methods of depainting military
communication shelters, which are
typically minimally corroded aluminum.
• PMB's economic superiority to
sandblasting is predominate only when
the hand sanding necessary with
sandblasting is taken into
consideration. PMB generates a much
smaller volume of waste in a more
easily handled form than does
sandblasting or chemical stripping.
• The economics of the PMB process
are strongly dependent on the recycle
rate of the media through the process.
• PMB will not clean heavy corrosion
(such as rust).
• The PMB process requires a slightly
higher skill level than sandblasting.
• Although the plastic media is normally
considered inert, it is recommended
that a study be undertaken to establish
the toxicity and hazard potential of the
dust from the PMB process.
• Several other questions with respect to
treatability should also be addressed.
They include:
- Can the waste material be
incinerated?
- What are the products of
incineration?
- Can heavy metals from the entrained
paint waste be pacified or
recovered?
- Can the waste material be cofired as
a fuel supplement?
Process Descriptions
The project was conducted in two
phases. The first phase entailed
preparing a summary of current activity
in the PMB field. The second phase
included a comparative study of three
major methods of depainting army
communications shelters.
In Phase II, observations were made
on each depainting process as it was
applied to similar communications
shelters. A list of the equipment, the area
depainted, and the time required is given
in Table 1. Small communications
shelters resemble pickup campers and
measure approximately 1.8 m long by 1.8
m wide by 2.0 m tall. Medium-size
shelters resemble a large box on skids
measuring approximately 3.5 m long by
2.1 m wide by 2.0 m tall. Both size
shelters are constructed of an aluminum
composite laminate with an outer skin
thickness of about 1.0 mm and an inner
skin thickness of 0.8 mm. The core is
foamed plastic resin to which the skins
are bonded.
Chemical stripping involves applying a
liquid solvent to the object by spraying,
painting, or dipping. The stripper is
allowed to set until the paint softens. The
softened paint is then removed either by
scrubbing with brushes or spraying with
high pressure water. The process is
completed when the surface has been
Table 1. Equipment Cleaned in Project
Equipment Item
Total Area Cleaned (m2) Total Clean Time (min)
Rate (m2/min)
Chemical Stripping
Sandblasting
Hand Sanding
PMB
1"
2
3
4
5
6"
7
8'
9
10
11
12"
13
14
IS"
16"
31.8
16.8
35.9
17.6
17.6
17.6
22.2
22.2
22.2
6.6
3.35
61.0
33.0
33.0
68.8
33.0
702
1126
1345
24.4
26.7
66.0
33.0
67.3
23.8
97.1
50.0
440
221
230
258
160
0.045
0.015
0.027
0.725
0.662
0.268
0.673
0.330
0.934
0.068
0.067
0.139
0.150
0.144
0.266
0.206
* Item painted in camouflage pattern.
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cleaned to the bare metal, rinsed, and
dried. The water used to wash off the
paint and stripper is one of the waste
products from this process. The liquid
waste will contain high levels of toxic
organic chemicals as well as paint
sludge. It is also estimated that >90% of
the solvents in chemical paint stripper
volatilize to the air. Thus the chemical
stripping process results in air, water,
and solid waste pollution.
Sandblasting is the process of
impacting sand onto a surface using
pneumatic pressure. Sand is usually
blasted at about 4.9 to 5.6 kg/cm2
pressure when used on aluminum.
Sandblasting relies on the abrasive
nature of the sand to break the paint
layer and erode the paint from the
substrate. The residual sand and paint
dust combination is collected and
disposed of in landfills. Dependent upon
the concentration of toxic metal pigments
in the sand, it may be considered a
hazardous waste. An additional
environmental contaminant is suspended
dust that may escape the blasting facility.
PMB is similar to sandblasting
although blasting takes place at a much
lower pressure (1.4 to 2.8 kg/cm2). The
blasted media can be recovered and
recycled, thus leaving for disposal a
residue of only paint dust and chips and
a few percent by weight of blasted media
from attrited media dust. The residue,
however, is a dry solid that must be
treated as a hazardous waste. The
volume of waste is significantly lower
than that generated during sandblasting
or chemical stripping.
Results
A summary of results of the study
based on area cleaned, process costs,
waste generated, and cleaning rate (in
m2/min) is presented in Table 2. Waste
disposal quantities were estimated by
measuring the amount of waste
generated and normalizing to 100 m2
depainted. These costs were obtained by
contacting disposal companies. The
results are shown in Table 3. Finally,
Table 4 presents the results of chemical
analysis for heavy metals of the solids
from sandblasting and PMB. The high
levels of chromium, lead, and zinc mark
the paint waste and are the items of
concern which warrant additional study.
The full report was submitted in
fulfillment of Contract No. 68-02-3993
by Acurex Corporation, under the
sponsorship of the U.S. Environmental
Protection Agency.
Table 2. Summary of Results
Process
Area (m2)
Cost (S/100 m2)
Waste (kg/100m2)
Rate (m2/min)
Chemical Stripping
Sandblasting
Plastic Media
85
120
229
4,856
818
634
95,500
545
120
0.029
0.53"
0.18
* Does not include required hand sanding.
Table 3.
Method
Waste Costs by Process for 100 m2
Waste Product
Amount (per 100 m2)
Cost of Disposal ($/iOO m2)
Chemical Stripping
Sandblasting
PMB
Water
Sludge
Sand/Paint
PMB/Paint
95,000 L
550 L
545kg
120 kg
120"
I12t
6.4*
17.5§
" 0.125?/L(0.50/gal).
t $35/175 L drum.
*$2.100 for90 tons.
§ $35/175 L (50 gal drum with a plastic media density of 1.5 kg/I).
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Table 4. Chemical Analysis of Sand, Clean PMB, and Waste Samples (mg/kg) for Heavy Metals.
Average PMB t
Clean Sand Used Sand Clean PMB PMB Floor Dust Tunnel Dust" "
Antimony < 0.2 2.4 < 1 4 13
Arsenic 1.8 1 < 1 < 1 < i
Cadmium < 0.2 28 5 16 16
Chromium 7.4 240 5 72 120
Copper 3.8 6.6 2 4 4
Lead 1.2 160 < 1 64 330
Mercury < 0.05 0.75 < 0.01 < 0.01 0.2
Nickel 5.2 8.6 37 81 30
Silver < 0.02 1.8 < 1 < 1 < 1
Zinc 4.8 340 490 570 980
* Fines collected in air vent.
C. D. Wolbach and C. McDonald are with Acurex Corporation, Mountain View,
CA 94039.
Charles Darvin is the EPA Project Officer (see below).
D. E. Renard is the Army Project Officer (see below).
The complete report, entitled "Reduction of Total Toxic Organic Discharges and
VOC Emissions from Paint Stripping Operations Using Plastic Media Blasting, "
(Order No. PB 87-154 4801 AS; Cost: $18.95, subject to change) will be
available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Water Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
The Army Project Officer can be contacted at:
U.S. Army Toxic and Hazardous Materials Agency
Aberdeen Proving Ground, MD 21010
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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