DEGREASING AND PAINT STRIPPING USING SPONGE BLASTING
blasting systems incorporate various grades of water-based urethane-foam
cleaning media in order to clean and prepare surfaces. Non-abrasive media
grades are used to clean more delicate substrates. Abrasive media grades,
consisting of grit-impregnated foam, are used to remove surface contaminants,
paints, protective coatings, and rust from a variety of surfaces. In addition,
the abrasive grades can be used to roughen concrete and metallic surfaces,
if desired. The abrasive media may contain a variety of grit including aluminum
oxide, steel, plastic, and garnet, depending upon the application.
The foam cleaning media is absorptive and can be used either dry or wetted with various cleaning agents and surfactants to capture, absorb, and remove a variety of surface contaminants such as oils, greases, lead compounds, chemicals, and radionuclides. The capability of using the foam cleaning media wetted also provides for dust control without excess damping of the surface being cleaned. The equipment consists of three transportable modules, which include the feed unit, the classifier unit, and the wash unit.
The feed unit is pneumatically powered for propelling the foam cleaning media. The unit is portable and is produced in several sizes (depending on the capacity required). A hopper, mounted at the top of the unit, holds the foam media. The media is fed into a metering chamber that mixes the foam cleaning media with compressed air. By varying the feed unit air pressure and type of cleaning media used, sponge blasting can remove a range of coatings from soot on wallpaper to high-performance protective coatings on steel and concrete surfaces.
The classifier unit is used to remove large debris and powdery residues from the foam media after each use. The used media is collected and placed into an electrically powered sifter. The vibrating sifter classifies the used media with a stack of progressively finer screens. Large contaminants, such as paint flakes, rust particles, etc., are collected on the coarsest screens. The reusable foam media are collected on the corresponding screen size. The dust and finer particles fall through the sifter and are collected for disposal. After classifying, the reclaimed foam media can be reused immediately in the feed unit. The abrasive media can be recycled approximately six times and the non-abrasive media can be recycled approximately 12 times.
During degreasing applications, the foam media must be washed every three to five cycles. The washing of the foam media takes place in the wash unit, which is a portable centrifuge, closed-cycle device. The contaminated wash water is collected, filtered, and reused within the wash unit.
This system removes paint, surface coatings, and surface contaminants from a variety of surfaces. Waste streams produced from this system include blast process contaminants, such as paint flakes, rust particles; dust and finer particles, and the concentrated residue from the bottom of the wash unit.
The effect that this technology has on pollution prevention is that the stripping media can be recycled (10-15 events) and the quantity of wastewater that is typically generated using conventional methods (chemical stripping) is greatly reduced.
Use of sponge blasting paint stripping as a replacement for chemical paint strippers results in the following compliance benefits:
Compliance benefits include: 1) elimination of recordkeeping and reporting requirements under the Clean Air Act Title V Operating Permit Program, NESHAPs, and SARA programs, 2) reduce administrative burden associated with hazardous waste (i.e., tracking, plans, reports, training), and 3) reduced administrative burden associated with OSHA (i.e., training and recordkeeping).
The compliance benefits
listed here are only meant to be used as a general guideline and are not
meant to be strictly interpreted. Actual compliance benefits will vary
depending on the factors involved, e.g. the amount of workload involved.
|Safety and Health:||
As with any blasting operations, airborne dust is a major safety and health concern. Proper precautions should be taken to avoid inhalation of 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 solvent vapor can irritate the lungs and mucous membranes. Prolonged exposure can affect respiration and the central nervous system. Proper personal protective equipment should be used.
Consult your local industrial health specialist, your local health and safety personnel, and the appropriate MSDS prior to implementing this technology.
cost elements of a Sponge-Jet stripping system are compared to chemical
Sponge Jet and Chemical Stripping
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Unless locally controlled, no major claimant has endorsed this technology for use on aircraft components without subsequent additional treatment to ensure that the substrate is completely free of blast media. This process should be implemented only after cognizant authority has granted engineering approval.
For Air Force applications, degreasing and paint stripping using sponge blasting must not be used on any aircraft or weapon systems without the knowledge and approval of the appropriate system manager, office(s) having engineering authority on the specific airframe(s) and the Air Force Corrosion Prevention and Control Office. This process requires significant engineering evaluation and must be approved by the engineering authority of the specific Weapon system Manager or Equipment Item Manager within the Air Force.
|Points of Contact:||
The following is a list of sponge blasting manufacturers. This is not meant to be a complete list, as there may be other manufacturers of this type of equipment.
GSA Contract No.:
Sponge-Jet, May 1996.