ASTM F2833 Zinc Rich Base Coated Fasteners

Stud Bolts, Nuts, Screws, Threaded Rod & Washers

ASTM F2833 Specification covers the basic requirements for chromium-free fastener coatings that combine an inorganic Zinc Rich basecoat with an aluminum-rich topcoat that contains an integrated lubricant. These coatings are applied by conventional dip-spin, dip-drain, or spray methods to ferrous parts which can be handled through a cleaning, or phosphate, coating, and baking operation. Phosphating or shot blast is required to clean and prepare the surface of the steel. These coatings are bake cured at temperatures up to 500°F.

ASTM F2833 Classifications

When the zinc phosphate option is used, its coating weight shall be in the range of 8-20 g/square meter. If used, phosphate to be used in accordance to Specification F1137 grade 0.
These coatings are classified into 5 different types :

• ASTM F2833 Grade 1 - requires a minimum basecoat thickness of 0.27 mils applied in one coat. An organic topcoat with an integrated lubricant is applied at a minimum thickness of 0.20 mils in one coat and ; with no additional layers.
• ASTM F2833 Grade 2 - requires a minimum basecoat thickness of 0.27 mils applied in two coats bulk or one coat sprayed. An organic topcoat with an integrated lubricant is applied at a minimum thickness of 0.20 mils in one coat; with no additional layers.
  
• ASTM F2833 Grade 3 - requires a minimum basecoat thickness of 0.27 mils applied in one coat. This basecoat is dark gray in color. A black organic topcoat with an integrated lubricant is applied at a minimum thickness of 0.20 mils in two coats bulk or one coat sprayed; with no additional layers.
  
• ASTM F2833 Grade 4 - requires a minimum basecoat thickness of 0.27 mils applied in one coat. An inorganic topcoat with an integrated lubricant is applied at a minimum thickness of 0.20 mils and an integrated lubricant in one coat; with no additional layers.
  
• ASTM F2833 Grade 5 - requires a minimum basecoat thickness of 0.27 mils applied in one coat. An organic pigmented topcoat with an integrated lubricant is applied at a minimum thickness of 0.20 mils in one coat for additional corrosion protection with no additional layers.

ASTM F2833 Performance Requirements

Appearance

The coating shall have a uniform appearance free from tears and other discontinuities which may affect the appearance or performance, or both, of the coating.

Adhesion

When practical, the coating shall show less than 5 % removal following the tape adhesion test in 6.3. Due to the nature of the coating, some removal is expected, but removal of the coating that exposes the substrate indicates poor adhesion and is cause for rejection.

Corrosion Resistance

The coating shall be capable of withstanding exposure to salt spray test (SST) for the minimum hours (h) specified in Table 1. Unless otherwise defined, acceptable corrosion resistance shall be Rust ASTM F2833 Grade 6 or higher (see Test Method D610 for definition) on significant surfaces (see Terminology F1789 for definition).

Blisters

There shall be no signs of blisters after testing in accordance.

Thread Fit

The coating shall not have an adverse effect on normal installation and removal practices as determined by the proper GO thread gauge. The thickness of the coating is limited by the basic thread size (3A GO gauge for external threads 6h for metric product, 2B GO gauge for internal threads, 6H for metric product). Where greater thickness is necessary, the internal threads may be produced oversized (before coating) providing the finished product (after coating) meets all the specified mechanical properties. Where mechanical properties are not specified, oversizing is subject to the approval of the purchaser.

ASTM F2833 Test Methods

Corrosion

Corrosion resistance shall be tested in accordance with Practice B117 followed by Test Method D610 to rate the amount of corrosion.

Coating Thickness

The coating thickness shall be determined by magnetic induction, X-ray fluorescence spectroscopy, microscopic examination of a cross-section taken perpendicular to the significant surfaces, or weigh-strip-weigh method. When using magnetic induction, or X-ray fluorescence, an average of ten measurements on the flat surface of one part shall be used. NOTE : The weigh-strip-weigh method involves weighing the test specimen before and after the coating is stripped. The method requires a reagent that does not attack the base metal (for example, 20 % NaOH).

Adhesion

Where practical, adhesion of the coating shall be tested in accordance with Test Methods D3359 Scribe-Grid Test. Determination if base material is exposed may be done by visually inspecting the part, or exposing the part to salt spray test (see Practice B117) for 96 h and observing if red rust occurs.

Hydrogen Embrittlement

When specified in the purchase order, testing shall be conducted in accordance with Test Methods F606/F606M, or F1940.
In the event that hardness reductions occur in test specimens due to coating curing times and temperatures, testing per shall be conducted alternatively in accordance with F1624.