Zinc Phosphating

Phosphating (or phosphatization) mainly concerns the protection of ferrous metals (alloy steels and cast irons).

Phosphating is a surface conversion process (1) where, unlike painting or galvanic plating, the base metal participates in the chemical reaction and is a constituent of the surface layer. The first stage of the phosphating reaction consists of micro-corrosion of the base metal by the phosphating bath, acid for phosphoric acid. In the second phase, the formation of the crystalline phosphate layer occurs, which restores the corroded layer and also creates a further deposit.

The products we use for this treatment guarantee compact and uniform microcrystalline phosphate layers with a thickness of 14 to 18 g/m² (approximately 7–9 µ), providing greater corrosion resistance after impregnation with a highly protective emulsifiable oil.

Any deviations from these values may depend on the material’s level of reactivity. In specific cases, we can provide an alternative oil-free finish.

Reference standards

UNI EN ISO 9717:2017 = Fe/Znph/T4

(UNI EN 12476)

ASTM F 1137 (corrispondente a UNI 3740/6)

DIN-50942

Special Applications

Pre-Painting Phosphating

An excellent pre-painting conversion treatment, especially when a low coating weight is required to improve mechanical resistance and combined impact and corrosion resistance. Zinc phosphating prepares metal surfaces to receive and retain paint by exerting chemical-physical forces between the metal surface and the primer or paint itself. The phosphate layer is non-conductive and therefore insulates the metal from electrochemical corrosion, while still favoring electrophoretic painting. The corrosion resistance of a painted part increases significantly when phosphating is applied. It prevents any chemical reaction between the paint components and the metal itself. The dielectric insulating power, microcrystallinity, and structural uniformity of the phosphate layer inhibit the rapid propagation of corrosion from one area to another, even if the corrosion process has already begun.

Pre-Teflon phosphating

Zinc phosphating is used to prepare metal surfaces for the application of Teflon, providing a highly bonding layer. Compared to sandblasting, the phosphate coating ensures both excellent adhesion and good corrosion protection, even in the event of partial deterioration of the Teflon layer. Furthermore, this also ensures corrosion protection for any parts not covered by the Teflon coating. A typical application involves the Teflon coating of tie rods for the petrochemical industry.

Pre-Gumming Phosphating

Zinc phosphating is used to prepare metal surfaces for rubber application, providing a highly bonding layer. Compared to sandblasting, the phosphate coating ensures excellent adhesion and corrosion protection for parts not covered by the rubber coating. A typical application is the manufacturing of anti-vibration mounts.

Preparation for cold extrusion and molding

Zinc phosphating is used to prepare metal surfaces for cold extrusion and stamping operations. The phosphate layer provides an excellent substrate for the application of additives such as stearates, lubricating oils, and waxes, which are retained on the metal surface. This prevents the metal from undergoing surface "melting" processes during extrusion, which would cause it to stick to the dies, thus increasing their durability. A typical application is the stamping of socket wrench slots.

Zinc Phosphating

Reference standards

Special Applications

Pre-Painting Phosphating

Pre-Teflon phosphating

Pre-Gumming Phosphating

Preparation for cold extrusion and molding

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