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Letter 27050
Shock rod macrocracks in chrome plating
[Brazil]
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We are a shock absorber manufacturer and we have a chrome platting
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
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Carlos.
How has your shock rod been handled before plating by machining,
shootpeening and heatreatment. Micro cracks can be found with a
magnification 100 x. I belive 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 abouth 300-800 cm2.
regards
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Anders Sundman
surface finishing engineer
Sweden
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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 U 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 ADDMITED.
Hadi Khosravi
- Tehran, Iran
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