C. D.Wolbach and C McDonald
United States
Wastewater Environmental Protection Research
Cincinnati OH 45268
NWEPA/600/SA-8710141987
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
On economics, the environmental Impact, and the quality of the product. ....fly. largo 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 at this study was to determine If the PMB mod" Is applicable to Army communications sheltered and 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 shelter 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 point 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 Me 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 prevention.
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 some title (a" Project Report ordering information at back)
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 composite SW is very difficult to use on soft alloys and light. thin materials. Chemical Stripping generates large 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. The report its results of a study competing 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 ....... we a hold between October 23 and November 1, 1985, at the Sacramento Army Depot (SAAD). The same type of equipment was depainted at both facilities.
a PMB process is an economically and environmentally viable alternatively 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. a 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 project was conducted in two phases. The first phase entails( 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 communication., 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 WV by 2.1 in wide by 2.0 m tail. Both size shelters are constructed of an aluminum composite laminate with an outer skin thickness of about 1.0 mm and an inns, 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 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 Me 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 attributed media dust. The residue. however, is a dry solid that must be treated as a hazardous waste. The volume of waste is significantly lower Mm MM generated during sandblasting or chemical stripping-
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.
See document source for Table.
Does not include required hand sanding.
See document source for Table.
Fines collected in air vent.
C. D. Wolbarh and C. McDonald are with Acurex Corporation.
Mountain View, CA 94039.
Char)" 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. PS 87-154 480/AS; Cost. $18.95, subject to range) will be available only from:.
National Technical Informabon
5285 Port Royal Road
Silver Spring, VA 22167
Telephone: 703-487-4650
The EPA Office can be contacted at:
Water Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
The Army Pollution Prevention Office can be contacted at:
U.S. Office of Toxic and Hazardous Materials Agency
Aberdeen Proving Ground, MD 21010
Last Updated: February 22, 1996