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topic 4965

WET ADHESION OF ZINC PLATED PASSIVATED FILM


(2000)

Our customers require wet adhesion of passivated film. the components are MS Tubular shaped used in the automobile industry and are plated with 8-10 microns from a warm rack Acid Zinc Bath ( 35 degree C)( KCl Based bath )followed by full iridescent passivation using proprietary liquid passivation concentration chromic acid based.

As the components are bent, formed / pressed after plating. The specification demands, that the passivated film should not get ruptured/broken during normal handling of wet work and also during drying and transportation. The solution is being regularly analysed and the brightener additions are kept to the minimum level as stipulated and we consciously avoid excessive brightener additions.

Please advise if a post plating / post passivation dip can be used to improve the adhesion of passivated film which can withstand light mechanical working like bending / forming / pressing without quaring and also scratch resistance after drying and during storage and transport.

Dilip Thakur
- Mumbai, India


(2000)

Dilip I will attempt to answer your question.

First, zinc electroplate is a corrosion protective layer. Chromate (or passivate) following zinc protects the zinc from corrosion. Together they are a "sacrificial coating". Clear chromate is very thin and becomes part of the zinc. Yellow generally coats the zinc. Zinc is not an "engineered" coating designed to be stamped, crimped or machined. When you scratch the surface it destroys the chromate. Can these parts be plated following all mechanical forming operations?

When shipping parts that have been plated, if they are apt to rub against each other during transit they must be boxed to prevent this from happening.

Bill Hemp
tech svc. w/ chemical supplier - Grand Rapids, Michigan


(2000)

Dear Mr Dilip, Mr Hemp correctly sums up the limitations Zinc plated coatings. We all have clients making some demand or the other and one of my clients has some success in using GW's Aquaguard 300 or is it 600 (?) for a post plating crimping to which it stands up quite well. regards,

Khozem Vahaanwala
Khozem Vahaanwala
Saify Ind supporting advertiser
Bangalore, Karnataka, India

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