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Ted Mooney, P.E. RET
Pine Beach, NJ
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for Metal Finishing since 1989
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Salt spray test before or after assembly?
Q. I am the quality manager for a fastener manufacturer. I have a question about a pin we manufacture which is zinc and clear chromate electroplated (approx .0004" thickness) I think it is generally understood that the salt spray requirements for fasteners is tested after the plating operation but before much handling occurs. I have been told it is good practice to allow the parts to "cure" for 24 hours and to handle with gloves to avoid any oil/lotion/contaminants from human hands to affect the test. My customer and I agree that the parts pass testing when tested in this manner. They contend that the part should pass salt spray after the parts are assembled. In this particular application after the plating occurs the parts are electronically sorted by us through a vibratory bowl and placed in a box. They are then loaded into vibratory bowls at their assembly operation and assembled into a door handle with a spring riding on the pin. I contend that:
1. The testing is understood to be performed before handling. The sorting and packaging operation is developed by us so we do bear some responsibility for "reasonable handling" but by the same token the validity of the process as a whole has to be considered.
2. Each handling/assembly operation will degrade the barrier coating slightly and the salt spray will be affected.
3. That a stainless steel spring on zinc plating may be affected by bi-metallic corrosion.
4. Because the whole door handle is being tested (and is placed into the chamber as it would be in a vehicle) that liquid is pooling in the spring causing premature failures.
I am looking or any information/articles/standards on when the appropriate time to test parts is, how handling damage affects salt spray and how an ASTM A313 stainless steel part on a zinc plated part may affect salt spray. Any feedback would be GREATLY appreciated.
Quality Manager - Grand Rapids, Michigan, USA
October 22, 2010
A. You can look at this issue in one of two ways. The first is to start with the EXACT requirements that you have been given, which would be in the form of a mutually agreed upon engineering drawing and any other specifications that have been given to you as part of a larger Statement of Requirements, etc. Does the part drawing say anything about corrosion testing of fasteners in the assembled condition? Is there a note or separate specification that documents these supposed requirements? I sincerely doubt this. Instead, what is likely indicated on the drawing is a one line note about plating type, thickness, and salt spray performance, maybe in the form of an industry standard such as ASTM B633, ASTM F1941/F1941M-16, etc. Unless the drawing or another specification requires you as the fastener supplier to perform corrosion testing of an assembled fastener (together with stainless steel springs, etc.), then this is not much of an argument.
The second way is to reference standards like ASTM F1941/F1941M-16 and SAE USCAR1-3 that describe fastener coatings and corrosion testing, and which only describe testing plated fasteners, not fasteners that have been assembled with other parts. Both of these standards specifically address parameters such as the angle of the fastener during salt spray testing because local accumulation of the salt-water mixture can significantly increase the corrosion rate. I recommend contacting your plating supplier as well as their chemical vendor about technical articles, etc. on this subject. It is well understood, if not extensively documented in the public domain, that salt spray testing of galvanically coupled components will result in rapid corrosion which is considerably in excess of typical requirements listed in consensus standards.
Automotive module and component supplier - Michigan, USA
October 25, 2010
A. It is well defined is standards that parts shall be tested before any handling or mechanical operation.
If the testing is done after any operation the coating will be ruptured and the components will not qualify in SST.
Thanks & Regards.
- PUNE, Maharashtra, India
January 2, 2011
Q. Is there an actual spec that indicates the SST results are only valid before excessive handling or assembly? I have a customer who rejected some parts a couple weeks after we shipped them citing that their independent lab tested them and they failed the SST. The parts passed our plater's SST. I'd like a spec to cite. Thank you!
Josie Brusatori- Detroit, Michigan United States
August 31, 2016
A. Hi Josie. Not trying to be facile, just let readers benefit from experience: "accepted practices" are a will-o-the-wisp, so the time to mention specific standards is at the quotation stage, rather than the contract dispute stage :-(
What standards, if any, did you agree to plate to and to test to? Dissimilar salt spray results are a common issue; furthermore, in some cases you don't even test the actual parts but representative coupons. The starting point has to be exactly what you and the customer actually agreed to, not expectations. Please get back to us with what kind of plating you are doing and what standards if any were part of the work. Thanks.
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
A. Josie,
Were any parts that underwent SST shipped to the customer? If so, could they have used any of those same parts for their SST?
How badly did the parts fail the customer's SST? Did they at least make it most of the way to the required number of test hours?
Ray Kremer
Stellar Solutions, Inc.
McHenry, Illinois
September 13, 2016
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