Phosphating is a common chemical surface treatment technique for fasteners, primarily used for screws and blots. This process involves immersing the metal workpiece in an acidic solution containing phosphoric acid, phosphates, and an accelerator (such as nitrates, sodium nitrite, or chlorates). A chemical reaction occurs at a specific temperature, forming a water-insoluble, crystalline phosphate conversion coating on the metal surface. The coating typically has a thickness of 1–20 μm, offers some insulation properties, and is heat-resistant up to 400°C.
The coating typically has a thickness of 1–20 μm, offers some insulation properties, and is heat-resistant up to 400°C. Common colors include gray and black.
The primary purposes of phosphating :
1.To improve corrosion resistance, especially when combined with a sealing treatment.
2.To enhance adhesion for subsequent coatings like powder coating.
3.To provide some abrasion resistance and act as a base for oil absorption or rust preventive oils.
This process is widely used on steel, galvanized steel, and aluminum (with specialized phosphating solutions for the latter). Common applications in manufacturing include automotive components, steel furniture, pipes, hardware, and notably—fasteners like screws and drywall nails.
For drywall nails and other screws, phosphating offers key advantages:
The coating is relatively thick (typically 1–50 μm, often 5–20 μm) and provides good insulation and moderate protection. Its micro-porous structure allows for excellent paint, oil, or wax adhesion, making it ideal for coated screws. It offers decent rust prevention by forming a physical barrier against moisture and oxygen.
Phosphate treatment for 48% of our factory applications. This is particularly true for drywall screws, 75% of which are treated for seawater treatment. Phosphate treatment is also used for other fasteners that require additional corrosion resistance or paint. Compared to passivation (a thin coating typically applied to stainless steel) or simple oiling, phosphate treatment provides a stronger and more paint-friendly surface.
Overall, phosphate treatment is a practical and cost-effective treatment that effectively improves the rust resistance and coating adhesion of metal fasteners. but it should be noted that phosphate treatment has limited rust protection, typically lasting up to 48 hours in a salt spray test. It is suitable for dry, non-corrosive environments. For example, drywall screws are used in gypsum board ceilings. Home renovation environments are typically dry, so the phosphate treatment process should be selected based on the actual construction environment. For more information on phosphate treatment, please feel free to contact us.
Post time: Aug-27-2025