Need to improve salt spray duration of zinc plating

+++

Dear sir,

We are hydraulic hose assembly manufacturers, we are currently doing zinc plating with yellow passivation which withstands 120 hrs of salt spray,(end fittings). Please tell me how my components will witstand 500 hrs of salt spray.

Sudesh.t.s
ist tier automotive - Bangalore, Karnataka, India

1st of two simultaneous responses--Dec +++

Dear Mr Sudesh,

In order to increase your salt-spray corrosion resistance, I would recommend installing a solution on your process line which will leach the hexavalent chromium out or the passivate film and seal the surface. A solution I used was one by the name of JS500 from MacDermid in Birmingham, England, which I operated at 12% strength and gave salt-spray results which exceeded 500 hours before the onset of white corrosion and 720 hours before the onset of red corrosion. Such solutions you should be able to source. They are not difficult to analyse. Good luck in solving your problem!

Nigel Gill,B.Sc. MIMF
- Blantyre, South Lanarkshire, Scotland

2nd of two simultaneous responses-- Dec +++

Mr Suresh.

For 500 hours of neutral SST there are alternatives open to you.

1) Zinc Iron plate to minimum 15 microns, Black Passivate, seal with topcoat or sealant.

2) Zinc Nickel Plate, Blue or yellow chromate, seal .

3) Zinc Cobalt alloy plate , blue or yellow chromate, seal.

2 is the costliest and most corossion resistant.

3 is a middle of the road answer.

1 is the least expensive and is good for black chromate only.

The best Chromate is trivalent blue. Or a Trivalent Black. There is a Yellow 2 step which is basically a dye to follow the Tri blue.

All three find use in the automotive world today.