| PLASTIC MEDIA
BLASTING (PMB) PAINT STRIPPING
phenylic acid, benzophenol, hydroxybenzene, C6H5OH; chloracetic acid, MCA Revision: 9/96 monochloroacetic acid, CH2ClCOOH; methylene dichloride Process Code: Navy and Marine Corps: ID-01-99; Air Force: ST01; Army: DPT Usage List: Navy: High; Marine Corps: High; Army: High; Air Force: High Substitute for: Chemical Paint Stripping/Sand Blasting dichloromethane, CH2Cl2 Applicable EPCRA Targeted Constituents: Toluene (CAS: 108-88-3), Xylenes (CAS: 1330-20-7), Methyl Ethyl Ketone (CAS: 78-93-3), Acetone (67-64-1), n-Butyl Alcohol (CAS: 71-36-3), Lead (CAS: 7439-92-1), Chromium (CAS: 7440-47-3), Zinc Compounds, Phenols (CAS: 108-95-2), Chloroacetic Acids (CAS: 79-11-8), Methylene Chloride (CAS: 75-09-2) Overview: Methyl benzene, phenylmethane, C6H5CH3; dimethylbenzene,
C6H4(CH3)2; Plastic Media Blasting (PMB) is a dry abrasive blasting process, designed to replace chemical paint stripping operations and conventional sand blasting. This process uses soft, angular plastic particles as the blasting medium. ethyl methyl ketone, 2-butanone, MEK, CH3COCH2CH3; PMB is performed in a ventilated enclosure such as a small cabinet (glove box), a walk-in booth, a large room, or airplane hanger. The PMB process blasts the plastic media at a much lower pressure (less than 40 psi) than conventional blasting. PMB is well suited for stripping paints, since the low pressure and relatively soft plastic medium have minimal effect on the surfaces beneath the paint. dimethylketone, 2-propanone, CH3COCH31-butanol, butyric alcohol, After blasting, the media is passed through a reclamation system that
consists of a cyclone centrifuge, a dual adjustable air wash, multiple
vibrating classifier screen decks, and a magnetic separator. In addition,
some manufacturers provide dense particle separators as a reclamation
system. The denser particles, such as paint chips, are separated from the
reusable blast media, and the reusable media is returned to the blast pot.
Typically, media can be recycled ten to twelve times before it becomes too
small to remove paint effectively. Waste material consists of blasting
media and paint chips. The waste material may be classified as a RCRA
hazardous waste because of the presence of metals. An alternative solution
to handling a potential hazardous waste is to locate a vendor that would
"lease" the blast media to the base and then recycle the media to
recapture the metals. CH3(CH2)2CH2OH; plumbum, Pb; Cr; carboxyic acid Plastic media are manufactured in 6 types and a variety of sizes and
hardnesses. A military specification (MIL-P-85891) has been developed for
plastic media. The specification provides general information on the types
and characteristics of plastic media. The plastic blasting media types
are: Type I Polyester (Thermoset) Type II Urea formaldehyde (Thermoset) Type III Melamine formaldehyde (Thermoset) Type IV Phenol formaldehyde (Thermoset) Type V Acrylic (Thermoplastic) Type VI Poly(allyl diglycol carbonate) (Thermoset) PMB facilities typically use a single type of plastic media which they
use for all of their PMB work. The majority of DOD PMB facilities use
either Type II or Type V media. Type V media is not as hard as Type II
media and is gentler on substrates. Type V media is more commonly used on
aircraft. Type II is better for steel-only surfaces. An option with PMB is to lease the plastic media. Under the lease
program, the used plastic media is picked up by the leasing company for
recycling. This option eliminates media waste from the PMB facility
wastestream. The effect that this technology has on pollution prevention is that
reusing the blasting media greatly reduces the volume of spent media
generated as compared to sand blasting. When compared to chemical paint
stripping, this technology eliminates the generation of waste solvent. PMB is being used at Puget Sound, Charleston, and Portsmouth Naval
shipyards; Naval Aviation depots (NADEPs) San Diego, Norfolk, and Cherry
Point; and Naval Surface Warfare Center (NSWC) Indian Head, as well as
other Navy activities and throughout the Army and Air Force. Plastic media
glove boxes and enclosed blasting booths have been installed at aircraft
maintenance activities to remove paint from support equipment and
components. A blast media lease and recycle program is currently in place
at NADEP Cherry Point. A more detailed list of organizations within the
DOD depot maintenance community that have implemented PMB operations is
provided in Appendix III of Joint Paint Removal Study; Final Report
Plastic Media Blast, Joint Depot Maintenance Analysis Group,
Technology Assessment Division, June 1994. Materials Compatibility: Storage and handling of plastic media and blast waste associated with
this process pose no compatibility problems. Prior to using plastic media
for depainting operations, personnel should check applicable military
specifications [such as (MIL-P-85891)] and operations manuals for the PMB
systems. Plastic media cannot be used with a system designed for other
types of media. Some military specifications do not allow PMB for
depainting certain types of materials (i.e. fiberglass, certain
composites, honeycomb sandwich structures, and some applications with
thin-skinned aircraft components). In certain cases, PMB can inhibit crack
detection on some of the softer alloys used for aircraft components (i.e.
magnesium). Safety and Health: As with any blasting operations, airborne dust is a major safety and
health concern. Proper precautions should be taken to ensure that
personnel do not inhale dust/particulate matter. Additional protective
measures should be taken when stripping lead chromate- or zinc
chromate-based paints, as these compounds may be hazardous. Inhalation of
lead and zinc compounds can irritate the respiratory tract, and some
compounds are known to be carcinogenic. Inhalation of paint solvents can
irritate the lungs and mucous membranes. Prolonged exposure can affect
respiration and the central nervous system. Operators must wear continuous
flow airline respirators in accordance with OSHA requirements as specified
in 29 CFR 1910.94 when blasting operations are in progress. Consult your local industrial health specialist, your local health and
safety personnel, and the appropriate MSDS prior to implementing this
technology. Benefits:
Disadvantages:
Economic Analysis: PMB systems can range in cost from $7,000 for a small portable unit to
$1,400,000 for a major facility for aircraft stripping. The following
information on investment costs and costs/payback for PMB systems at Hill
AFB, Utah, was provided in Joint Paint Removal Study; Final Report;
Plastic Media Blast, Joint Depot Maintenance Analysis Group,
Technology Assessment Division, June 1994. In 1987, Hill AFB gathered data during the stripping of F-4 aircraft
using chemical stripping and PMB. Assumptions:
PMB and Chemical Stripping
Economic Analysis Summary Annual Savings for PMB: $846,200 Capital Cost for Diversion Equipment/Process: $1,400,000 Payback Period for Investment in Equipment/Process: < 2 years Approving Authority: Navy: PMB is not authorized for use on aluminum and magnesium
components that require a fluorescent penetrant inspection. NAVAIR has
authorized PMB use on metal substrates under specific process control
parameters at depot activities. NAVAIR has not authorized PMB for
depainting composites, other non-metal substrates, or honeycomb sandwich
structures. This recommendation should be implemented only after
engineering approval has been granted by cognizant authority. Points of Contact: Charles Tittle Greg Piner Butch Green Vendors: The following is a list of PMB manufacturers. This is not meant to be a
complete list, as there may be other manufacturers of this type of
equipment. Pauli & Griffin Schlick-America Inc. Leasing Services: Solidstrip, Inc., Composition Materials L.S. Solutions, Incorporated Sources: Joint Paint Removal Study; Final Report; Plastic Media Blast, Joint Depot Maintenance Analysis Group, Technology Assessment Division, Dayton, Ohio; June 1994; (513) 296-8296. N.E. Wasson, Jr., P.E., "Dry Stripping the C-5 and B-52 in the World's Largest Dry Stripping Installation", Proceedings of the Second Annual AF Worldwide Pollution Prevention Conference, June 2, 1993. Butch Green, LMTCE Code 343, Naval Aviation Depot, Naval Air Station Jacksonville, June 1996. Mark Meno, NADEP Cherry Point, July 1996. Brian Lund, Solidstrip, Inc., June
1996. |