Docstoc

Powder Coating - PDF

Document Sample
Powder Coating - PDF Powered By Docstoc
					    60
                            Powder Coating
                            The NDCEE has extensive technical expertise with powder coating. The technology is an
Technologies

                            integral aspect of the NDCEE Demonstration Facility where it has been used for nearly a
                            decade by DoD and industrial facilities to explore the technology’s viability for their site-
                            specific needs. Once the technology has been validated to be technically and
                            economically beneficial for a facility, the NDCEE provides implementation and training
                            assistance to the facility. Most recent beneficiaries of NDCEE powder coating knowledge
                            have been TYAD, Rock Island Arsenal, and Lake City Army Ammunition Plant. Past
                            recipients have included CCAD, Naval Air Depot–Jacksonville, and the Joint Group on
                            Pollution Prevention.
                            Technology Description
                            Powder coating technology is an environmentally friendly alternative to the use of
                            conventional solvent-based, waterborne, or high-solids painting processes. It provides a
                            durable coating and reduces operating costs while eliminating HAPs, VOCs, and solvents.
                            The four basic powder coating application methods are electrostatic spraying, flame spray,
                            fluidized bed, and electrostatic fluidized bed. Electrostatic spraying is the most frequently
                            used method. For all four methods, surface preparation (i.e., cleaning and conversion
                            coating) is required to develop a good coating adhesion substrate. Characteristics of each
                            method are described below.
                            In electrostatic spraying, an electrical charge is applied to the dry powder particles while
                            the component that is to be coated is electrically grounded. The charged powder and
                            grounded workpiece create an electrostatic field that attracts and holds the paint particles
                            to the workpiece. The coated workpiece is placed in a curing oven where the paint
                            particles are melted onto the surface, fused into a film, and then chemically crosslinked into
                            a cured film.
                               The flame-spray technique was developed primarily for application of thermoplastic
                               powder coatings. After being fluidized by compressed air, the thermoplastic powder is
       ESOH Need               fed into a flame gun where it is injected through a flame of propane, melting the powder.
                               The molten coating then is deposited on the workpiece, forming a film on solidification.
      Environmentally          Because no direct heating of the workpiece is required, this technique is suitable for
     compliant coatings        applying coatings to most substrates, including metal, wood, rubber, and masonry. It also
          system               is useful for coating large or permanently fixed objects such as steel frames, railcars, and
                               large diameter pipes.
                                                     In a fluidized bed, an air stream keeps powder particles in
                                                     suspension until they come in contact with a preheated workpiece,
                                                     at which point, they melt and adhere to the workpiece surface.
                                                     Coating thickness is dependent on the temperature and heat
                                                     capacity of the workpiece and its residence time in the bed.
                                                     Typically, post heating is not required to cure thermoplastic powder
                                                     coatings, but it is required to cure thermoset powder coatings
                                                     completely.
                                                     With electrostatic fluidized beds, the air stream is electrically
                                                     charged as it enters the bed. The ionized air then charges the
                                                     powder particles, which cover the grounded workpiece as it enters
                                                     the chamber. Unlike with the conventional fluidized bed, this
                                                     technique does not require a preheated workpiece, but curing of the
                                                     coating is necessary. This technology is most suitable for coating
 Automated powder application to 105-millimeter
 artillery projectiles                               small objects with simple geometry.


NDCEE www.denix.osd.mil
Powder coatings are individually formulated to meet specific finishing needs (e.g., desired                       61
properties) and fall into two basic categories: thermoplastic and thermosetting. Generally,
thermosetting powders use epoxy, polyester, and acrylic resins and are more suitable for




                                                                                                                Technologies
thicker coatings, providing increased durability. Thermoplastic powders are often used
when comparatively thin coatings are desired such as decorative coatings. They primarily
contain polyethylene, polyvinyl, nylon, and fluoropolymer resins.
In comparison to conventional painting techniques, powder coating provides improved
safety and working conditions as well as cost savings in labor, materials, handling, and
disposal of waste. It eliminates most waste streams, such as spent cleaning solvents, air
emissions, and waste streams, that are generated from air emission control equipment.
Cleanup time is faster because the powder is dry when sprayed, allowing overspray to be
readily retrieved and reclaimed for reuse. Consequently, powder usage efficiency can
approach 98% because the overspray powder is separated from the air stream by various
vacuum and filtering methods and returned to a feed hopper for reuse.
Technology Benefits and Advantages
    •   Eliminates the use of VOCs and HAPs that are used as typical solvents in liquid
        paints and thereby eliminates hazardous air emissions
    •   Improves worker health conditions and minimizes safety risks
    •   Can be implemented in high-production facilities with highly automated application
        systems or on low-volume, manual-batch applications
    •   Results in nearly 98% usage efficiencies because overspray can be captured and
        reclaimed
    •   Can use specialty coating formulations that provide powder coating cure by high-
        intensity infrared exposure and thermal melt/ultraviolet-crosslinking film formation
    •   Reduces booth ventilation energy requirements by recycling spray booth air instead
        of venting to the atmosphere to remove solvent emissions
    •   Provides significant cost savings in labor, materials, and handling and disposal of
        waste
    •   Provides protection as a barrier if primers or pretreatments are not used, and
        prevents corrosion as long as the coating remains intact and undamaged
Technology Limitations
    •   As with other coatings, adequate booth ventilation must be maintained to eliminate
        explosion hazards (accumulation of suspended particulate). Integrated application
        equipment controls and fire sensors significantly limit these risks.
    •   System configurations are partially application specific, but not severely limited.
    •   Depending on the coating requirements, some applications may be restricted by
        complex geometry and component assembly.
    •   Typically, workpieces that can be oven-heated to 400°F (204°C) are suitable for
        powder coating application methods. The temperatures that are required to cure
        the coating are too high for many materials that are used in aerospace structures
        (primarily aluminum and magnesium); however, recently developed formulations
        allow baking as low as 250°F (121°C), which enables the use of powder coating on
        most materials. Also, infrared flash cure powder coating technology has been
        developed for curing more sensitive substrates (i.e., materials that must be baked
        at less than 180°F) or, conversely, for rapid curing of high volume parts production
        such as small-caliber ammunition projectiles.




                                                                                      Transferring Technology Solutions
    62           NDCEE FY04 Accomplishments
                 The NDCEE produced a Final Report on Task N.301, Subtask R3-8 accomplishments. These
                 accomplishments included:
Technologies

                     • Tested and evaluated candidate powder coatings (MIL-P-53030 epoxy primer and
                        MIL-PRF-22750 epoxy topcoat) for potential use on select components to replace
                        the current paint system that is used at TYAD. In general, the results show that no
                        single candidate passed all test requirements for TYAD, including the baseline
                        coatings. The NDCEE recommended that the test requirements be prioritized to
                        further identify top performers for a specific application.
                     • Developed a powder coating line specification for TYAD that is based upon the
                        facility’s needs, available space, and support of new maintenance activities and
                        processes. This specification can be used as a basis to request vendor quotations.
                 Economic Analysis
                 The typical capital costs for a powder coating system can range from $20,000 to greater
                 than $4 million. In comparison to a solvent-based system, the powder coating technology
                 generally has lower labor costs as a result of no paint mixing requirements and reduced
                 cleanup requirements. In addition, waste disposal costs are typically lower because less
                 waste is generated.
                 Suggested Implementation Applications
                 Powder coatings are commonly used on a wide assortment of products from ammunition to
                 park benches to automobiles. To ensure that powder coating is their best coating option,
                 DoD production and maintenance coating facilities should conduct a technical and
                 economic evaluation prior to implementation.
                 Points of Contact
                     •   Charles Painter, NSWC-IHDiv, (301) 744-6772, charles.r.painter@navy.mil
                     •   Patrick Tierney, TYAD, (570) 895-6724, Patrick.Tierney@tobyhanna.army.mil
                     •   Michael Docherty, NDCEE/CTC, (814) 269-6462, docherty@ctc.com
                 Applicable NDCEE Task
                 Sustainable Green Manufacturing (Task N.301, Subtask R3-8)




NDCEE www.denix.osd.mil

				
DOCUMENT INFO
Shared By:
Categories:
Tags: Powder, Coating
Stats:
views:72
posted:6/23/2010
language:English
pages:3
Description: Powder Coating