ASTM F2329 – Coating Properties
The ASTM F2329/F2329M - 15 standard specifies the requirements for hot-dip zinc coating applied to carbon and alloy steel fasteners. This specification is specifically designed for items that are centrifuged or otherwise handled to remove excess galvanizing bath metal, ensuring clear and functional threads after processing. The coating process involves immersing fasteners in a molten zinc bath to form an iron-zinc alloy layer topped with a pure zinc surface. Key technical requirements include:
- Applicability: Covers bolts, screws, washers, nuts, and special threaded fasteners; notably, it excludes nails and rivets.
- Operational Parameters: Normal galvanizing occurs between 820°F and 900°F [435°C to 480°C], while high-temperature processes range from 990°F to 1040°F [530°C to 560°C].
- Quality Control: The standard enforces a "zero defects" acceptance criterion for all process control inspections.
- Mechanical Integrity: It provides critical safeguards against hydrogen embrittlement and thermal alteration of fastener mechanical properties.
Coating Properties
The quality of the coating is evaluated based on thickness, adhesion, and appearance. Coating thickness is measured on non-threaded portions of the fastener, requiring a minimum of five readings per specimen to determine the average. Adhesion must be tenacious, ensuring the zinc does not peel or flake from the base metal under standard testing.
| Zinc Coating Thickness | |||
|---|---|---|---|
| Dimension | Minimum Thickness on Surface | ||
| Average Thickness of All Specimens Tested (Production Lot) | Average Thickness of All Specimens Tested (Batch Lot) | Average Thickness of Individual Specimen | |
| Fasteners and nuts over 3/8 in. [M10] in diameter Washers 3/16 in. [4.7 mm] and over in thickness |
0.0020 in. [50 µm] | 0.0017 in. [43 µm] | 0.0017 in. [43 µm] |
| Fasteners and nuts 3/8 in. [M10] and under in diameter Washers under 3/16 in. [4.7 mm] in thickness |
0.0017 in. [43 µm] | 0.0015 in. [38 µm] | 0.0015 in. [38 µm] |
| Process Control of Batch Lot Sampling Plan | |||
|---|---|---|---|
| Batch Lot Size | Average Coating Thickness (Sample Size) | Adhesion (Sample Size) | Appearance (Sample Size) |
| 5 to 25 | 1 | 1 | 1 |
| 26 to 50 | 1 | 1 | 2 |
| 51 to 150 | 2 | 1 | 2 |
| 151 and over | 2 | 2 | 2 |