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Chrome plating cracks: microcracking vs. macrocracking
2007
Q. Hi all,
We are an Engine Valve manufacturing company and do plating in the stem portion (cylindrical portion) for 3 to 7 microns thickness for a length of 50 to 100 mm.
In our plating component we find micro cracks in the Cr. deposit. As per our knowledge it is unavoidable and often desirable.
But we are not sure that whatever we find is micro-crack or macro-crack and the crack is only because of plating process.
So can you help by sending any sample picture of Cr. Plating crack type and the allowable density? And which is considered micro-crack and which considered macro-crack?
And can you tell me what are the parameters will cause the crack?
Some parameters of our bath:
We are using normal Chromic acid bath.
Composition: Chromium: 250-300 gram/litter
Sulphate : 2.5-3 gram/litter
Contamination: < 6 %
Substrate: EN-52 (Ferrous based alloy)
21-4N (Nickel based alloy)
Employee - Hyderabad
A. Step 1. is to find out what your customer specs for the valve. I doubt if your customer is so small that they do not have specs.
I would absolutely look into porous pot technology for reducing your contaminant level. You get poor quality and slower plating at that level.
- Navarre, Florida
2007
A. Chrome is very hard but its elongation is less than 1%. During plating it shrinks more than that. As a result it cracks. Trying to define what is a macro and what a micro crack is somewhat subjective and conventional. Try to reach an agreement with your customer. Typically, if the cracks do not propagate to the base metal and are well distributed across the surface they are OK. Plating temperature and chemistry influence the crack pattern.
Guillermo MarrufoMonterrey, NL, Mexico
2007
A. Quantity of Micro cracks /unit on hard chrome plated deposits also vary by type of Hard Chrome Process. Could you elaborate on type of Process being used? (conventional sulphate. Mixed fluoride, High speed or other process). Also , what range of cracks /unit is customer spec? We have plated over 24 million IC valve stems /year and may be able to provide some insight.
Tim DeakinNorth Tonawanda, New York
2007
TAM panel won't crack. Is chrome plating too hard?
April 2, 2014Q. Hello,
We are doing some R&D to develop a TAM panel to test the quality of dye penetrant in NDT. The TAM panel description can be found here:
www.ndt-ed.org/EducationResources/CommunityCollege/PenetrantTest/QualityProcess/PerformanceCheck.htm
It consists of stainless steel (around 2 mm thick) panel on which there is about 70 microns hard chrome plating. The stainless steel is indented with hardness tester machines in order to create artificial cracks on the chrome side.
We used 304 stainless steel, MILL FINISH (NOT POLISHED), then conducted chrome plating. Hardness is supposed to be around 75 Vickers.
When we indent, the chrome does not crack. Instead there are a lot of "micro-cracks" that fill all the bulge created by the indentation. However, our objective is to create star-like deep cracks, deeper, wider and more visible than the micro-cracks.
What is the problem with our procedure? Is the chrome plating too hard / not hard enough?
Thank you very much for your help.
- Coventry, UK
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