This is the standard surface treatment usually applied to carbon steel disc springs; this finish is usually sufficient to prevent corrosion in unexposed applications and during transportation and storage. However in applications where the disc springs will be subjected to the elements a higher level of protection would be required.
Put spring into phosphate solution containing manganese, iron, zinc, and the method of the metal surface to form a water-insoluble phosphate film called phosphate. Phosphate film appearance was dark gray, gray or dark gray, not shiny. The thickness of the phosphate film is generally 10 ~ 15μm. Salt spray test is generally from 48 hours to 72 hours.
A mechanical plating process that allows a substantial thickness of zinc to be applied to the surface of the disc spring without the risk of hydrogen embrittlement associated with normal electroplating. A passivation would then be applied to seal the plating.
The layer thickness is around 12μm, and salt spray test is around 120 hours.
Chemical nickel plating also know as electroless nickel plating is a high quality coating that is wear-resistant and decorative while providing protection against corrosion. Specific process means, under certain conditions, an aqueous solution of metal ions is a reducing agent, and to a solid substrate surface precipitation process.
The layers with a thickness of 15 to 30μm
This is an inorganic silver-grey metallic coating of zinc and aluminium flakes in a chromatic compound. Dacromet-treated springs exhibit excellent resistance in a salt spray test. With the usual processing technology there is absolutely no possibility of hydrogen embrittlement.
The layer thickness is around 5μm, and salt spray test is around 200 hours.