Understanding More about the Process of Zinc Phosphate Coating

30/07/2015 02:55

A Zinc Phosphate Coating is being used to improve the corrosion resistance. The process of Zinc Phosphating involves converting the metal surface to where it is being applied into the nonmetallic and polycrystalline coating that consists of manganese, iron and nickel, as well as zinc phosphate. The process of Zinc Phosphate Coating can be used in treating metals individually or treating metals in mixed production.  Aside from providing corrosion resistance, the process of Zinc Coating can help to improve the appearance of the finished goods by means of creating uniform black or gray appearance. The process is also considered a cost effective alternative to painting or plating, most specifically on hidden metal parts.

Uses of Zinc Phosphating

In those operations where the corrosion resistance of the finished work pieces is essentially high, the conversion coatings are being applied by means of Zinc Phosphate Coating. Such approach is commonly used in the automotive industry and on certain sectors of the electronics and appliance industries. In the same way, the Zinc Phosphating is often specified by the armed services, especially for equipment that is being exposed to severe environments. In addition, a lot of operations that make use of electro coating or powder coatings, more particularly with a one coat finish is going to be exposed to the weather while the pretreated work pieces are exposed to Zinc Phosphate.

Immersion Process

The cleaning of Zinc Phosphate Coating is often based on alkaline or the strongly alkaline solution in the concentration range of one to five percent and a pH value of 10 to 13. As compared to the cleaners used in a spray mode, the cleaners used for the immersion contains larger amount of silicate and sodium hydroxide. The surfactants that are being used will usually include the anionic types often mixed with the nonionic varieties. Activation is necessary for Zinc Phosphating and on its absence, due to the reasonably high pH values that are involved, and a coarse and thick crystalline coating is being created which is quite unsuitable for the succeeding painting. Conditions for the post rinse, rinse and drying stages will greatly differ from spray Phosphating.

Spray Process

In the event of spray Phosphating, the main differences are to be found on the process sequences for the Zinc Phosphate process and the Alkali metal Phosphate systems. Zinc Phosphate Coating lines are often based on a five to six stage plants. They slightly differ on the pre Phosphating stages. The five stage type will include a rinse in between cleaning and Phosphating steps. On the case of the six stage type, there are either two cleaning and one rinse stages, or perhaps, one cleaning and two rinsing steps.

It is normal to dry the phosphated work right before the conventional plants are applied and in the event of electro coating paint, this is recommended. The circulating air ovens that operate at 120 to 180 degree Celsius and with a drying time of 5 to 15 minutes are often being used for such drying in the process of Zinc Phosphate Coating.
 


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