ASTM D7803-12
(Practice)Standard Practice for Preparation of Zinc (Hot-Dip Galvanized) Coated Iron and Steel Product and Hardware Surfaces for Powder Coating
Standard Practice for Preparation of Zinc (Hot-Dip Galvanized) Coated Iron and Steel Product and Hardware Surfaces for Powder Coating
SIGNIFICANCE AND USE
4.1 This practice describes the methods of preparation of hot-dip galvanized surfaces prior to the application of powder coating. The key to achieving proper adhesion between powder coatings and galvanized steel is surface preparation. The surface must be entirely free from metal oxides prior to powder coating. Any metal oxides that remain on the surface of the galvanized steel can potentially retain air or moisture. Upon heating during the curing stages of the powder application, the oxides may release water vapor or air, which can expand and penetrate the powder coating, causing blisters or voids.
4.2 The zinc coating is constantly in a state of change. From the time the steel part is removed from the galvanizing kettle, the exposed zinc coating interacts with the environment to form, first zinc oxides and zinc hydroxides, and then zinc carbonates.4 The process of complete conversion of the outer layer of zinc carbonates can take up to two years of exposure to the environment, depending on the local weather and moisture conditions.
4.3 The zinc surface after full weathering is very resistant to atmospheric corrosion because the tight patina that is formed (zinc oxide, zinc hydroxide and zinc carbonate) is dense and tenacious. However, during the formative stages of patina development, the oxide/hydroxide layer is poorly adhered and must be removed in order for the powder coating to adhere properly to the galvanized coating. The second is pinholing/blistering of the coating which can severely limit its potential performance, especially in aggressive chloride environments. Entrapped gasses developed during the galvanizing process escape the surface through the coating as it cures at high temperatures. If these volatile materials are not removed through an outgassing process prior to the baking of the powder, then pinholing or blistering can occur. The presence of pinholes gives chlorides and other corrosive agents access to the zinc substrate consequently prod...
SCOPE
1.1 This practice describes methods of preparing surfaces of hot-dip galvanized iron and steel for powder coating and the application of powder coating materials.
1.1.1 Powder coating is a dry finishing process which uses finely ground particles of pigment and resin, electrostatically charged, and sprayed onto a part to be coated. The parts are electrically grounded so that the charged particles projected at them adhere to the surface and are held there until melted and fused into a smooth coating in the curing oven.
1.1.2 Hot-dip galvanized iron or steel is produced by the immersion of fabricated or un-fabricated products in a bath of molten zinc, as specified in Specification A123/A123M or A153/A153M. This practice covers surface preparation and thermal pretreatment of iron and steel products and hardware which have not been painted or powder coated previously (Practice D6386). Galvanized surfaces may have been treated with protective coatings to prevent the occurrence of wet storage stain. This practice neither applies to sheet galvanized steel products nor to the coil coating or continuous roller coating processes.
1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
General Information
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Standards Content (Sample)
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Designation: D7803 − 12
Standard Practice for
Preparation of Zinc (Hot-Dip Galvanized) Coated Iron and
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Steel Product and Hardware Surfaces for Powder Coating
This standard is issued under the fixed designation D7803; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope A123/A123M Specification for Zinc (Hot-Dip Galvanized)
Coatings on Iron and Steel Products
1.1 This practice describes methods of preparing surfaces of
A153/A153M Specification for Zinc Coating (Hot-Dip) on
hot-dip galvanized iron and steel for powder coating and the
Iron and Steel Hardware
application of powder coating materials.
A780 Practice for Repair of Damaged and Uncoated Areas
1.1.1 Powder coating is a dry finishing process which uses
of Hot-Dip Galvanized Coatings
finely ground particles of pigment and resin, electrostatically
B201 Practice for Testing Chromate Coatings on Zinc and
charged, and sprayed onto a part to be coated. The parts are
Cadmium Surfaces
electrically grounded so that the charged particles projected at
D4285 Test Method for Indicating Oil or Water in Com-
them adhere to the surface and are held there until melted and
pressed Air
fused into a smooth coating in the curing oven.
D6386 Practice for Preparation of Zinc (Hot-Dip Galva-
1.1.2 Hot-dip galvanized iron or steel is produced by the
nized) Coated Iron and Steel Product and Hardware
immersion of fabricated or un-fabricated products in a bath of
Surfaces for Painting
molten zinc, as specified in Specification A123/A123M or
D7091 Practice for Nondestructive Measurement of Dry
A153/A153M. This practice covers surface preparation and
Film Thickness of Nonmagnetic Coatings Applied to
thermal pretreatment of iron and steel products and hardware
Ferrous Metals and Nonmagnetic, Nonconductive Coat-
which have not been painted or powder coated previously
ings Applied to Non-Ferrous Metals
(Practice D6386). Galvanized surfaces may have been treated
E376 Practice for Measuring Coating Thickness by
with protective coatings to prevent the occurrence of wet
Magnetic-Field or Eddy-Current (Electromagnetic) Test-
storage stain. This practice neither applies to sheet galvanized
ing Methods
steel products nor to the coil coating or continuous roller
F21 Test Method for Hydrophobic Surface Films by the
coating processes.
Atomizer Test
1.2 The values stated in SI units are to be regarded as the
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2.2 Society for Protective Coatings Specifications:
standard. The values given in parentheses are for information
Surface Preparation Specification No. 1 Solvent Cleaning
only.
Surface Preparation Specification No. 2 Hand Tool Cleaning
1.3 This standard does not purport to address all of the
Surface Preparation Specification No. 3 Power Tool Clean-
safety concerns, if any, associated with its use. It is the
ing
responsibility of the user of this standard to establish appro-
Surface Preparation Specification No. 12 Surface Prepara-
priate safety and health practices and determine the applica-
tion and Cleaning of Metals by Water-Jetting Prior to
bility of regulatory limitations prior to use.
Recoating
Surface Preparation Specification No. 16 Brush-Off Blast
2. Referenced Documents
Cleaning of Coated and Uncoated Galvanized Steel,
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Stainless Steels, and Non-Ferrous Metals
2.1 ASTM Standards:
3. Summary of Practice
3.1 This practice describes the procedures that can be used
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This practice is under the jurisdiction of ASTM Committee D01 on Paint and
to prepare surfaces for powder coating application on new,
Related Coatings, Materials, and Applications and is the direct responsibility of
Subcommittee D01.46 on Industrial Protective Coatings.
partially weathered, and fully weathered zinc-coated surfaces
Current edition approved June 1, 2012. Published June 2012. DOI: 10.1520/
on after-fabrication iron and steel products. These procedures
D7803-12.
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For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
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Standards volume information, refer to the standard’s Document Summary page on Available from Society for Protective Coatings (SSPC), 40 24th St., 6th Floor,
the ASTM website. Pittsburgh, PA 15222-4656, http://www.sspc.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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D7803 − 12
improve the bond of the powder coating to the zinc surface hence they do not necessarily yield identical results when
providing for long life. powder coatings are subsequently applied. The age o
...
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