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  for Metal Finishing since 1989
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Shock rod macrocracks in chrome plating

We are a shock absorber manufacturer and we have a chrome plating process to protect the shock rod. We had a problem of microcracks on some rods. I already know that micro cracks are supposed to exist in chrome plating and we have an specification of 100 to 400 micro cracks per centimeter which we can see in a microscope after etching the sample. However in this case we can see them with a magnification of 100x without etching. The are causing the shock to leak oil. Some operators have described them as "Chicken wire". We are also considering them macrocracks instead of micro. I would like to know the potential causes and the remedy.

Best regards,

Carlos A. Fedosi
Quality Engineer 1st tier automotive - Lavras, MG, Brazil
2004

Carlos.

How has your shock rod been handled before plating by machining, shot peening and heat treatment. Micro cracks can be found with a magnification 100 x. I believe that you can see is macro cracks and they will be around 1-20 cm2 and from a Sargent's chrome solution and from a SRHS chrome solution about 300-800 cm2.

regards

Anders Sundman
4th Generation Surface Engineering
Consultant - Arvika,
Sweden
2004

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HI,

PISTON ROD FOR SHOCK ABSORBER SHOULD PASS THE 120 H SALT SPRY AND 1000 HV HARDNESS. THE MORE THE MICROCRACK DENSITY THE MORE HOURS SALT SPRAY TEST. IF You WANT TO KNOW THE CRACKS TYPE SEND YOUR HARD CR PLATED PISTON WITH 30 MIC THICKNESS TO SALT SPRAY TEST . IF IT PASSES 100 H OR MORE BE SURE THE CRACKS ARE MICRO TYPE OTHER VISE MACRO CRACK EXISTED. ANOTHER WAY TO SEE MACROCRACKS IS PLATING CUPER ON CROSS SECTION OF ROD , CRACKS OF MACRO TYPE EXTEND TO SUBSTRATE.

BUFFING AFTER HARD CR INCREASE CRACK DENSITY,FOR HARD STEEL THESE MICRO CHANGE TO MACRO UNLESS POST PLATING BAKING ADMITTED.

Hadi Khosravi
- Tehran, Iran
2004