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Testing adhesion of electroless nickel plating
Current question and answers:March 26, 2021
Q. There are a lot of conflicts between specifications regarding testing. SAE AMS-C-26074 [affil. link to spec at Techstreet] requires a specimen be bent over a mandrel 4 times the thickness of the specimen and yet in parentheses has (.4" min.). Can anyone explain why the mandrel has to be this thick when the rest of Electroless Nickel specs reference ASTM B571 [affil. link to spec at Techstreet] for testing which only requires 4 times the thickness of the specimen?Gary Smith
- Boston, Massachusetts
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A. Hi Gary. I think it's simply a matter of SAE recognizing that it's possible to electroless nickel plate strips that are so extremely thin that 4X their thickness would still be next to nothing. So rather than requiring that the plating withstand essentially a tight hammered crease, they don't require bending over a mandrel smaller than 0.4"
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Previous closely related Q&A's starting in:2007
Q. What exactly is the bend test on electroless nickel? What size is appropriate? Can I buy it off the shelf, and what exactly is a mandrel?Jake Diemer
electroless nickel - Buffalo, New York
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A. Hi Jake,
Bend testing is described in ASTM B733 [affil. link to spec at Techstreet] (para. 9.4.1) & ASTM B571 [affil. link to spec at Techstreet] (para. 3.1) and Mil-C-26074 [link is to free spec spec at Defense Logistics Agency, dla.mil]E (paragraphs 4.5.2 & 3.3). A summary:
"4.3.2 Separate specimens. When the coated parts are of such form as to be not readily adaptable to a test...The separate specimens shall be of a basis material equivalent (see 6.6) to that of the parts represented....The separate specimens shall be strips approximately l-inch wide, 4-inches long, and 0.04-inch thick...These specimens shall be introduced into a lot at regular intervals prior to the cleaning operations preliminary to coating and shall not be separated therefrom until after completion of the processing."
[Note ASTM B733 size: approx. 25-50 mm wide, 200-300 mm long, and 3-6 mm thick]
"4.5.2 Adhesion test. The test specimen shall be bent 180° over a mandrel diameter 4 times the thickness (0.4 inch minimum) of the specimen."
Adhesion is then evaluated per MIL-C-26074E para. 3.3 or the referenced ASTM paragraphs.
For this purpose, a mandrel is a round bar or pipe (typically, clamped in a vise), 0.4" OD for thin strips up to 0.1" thick or 0.5" OD for 0.125" thick strip. To my knowledge, nobody uses strip thicker than 0.125" or 3 mm.
Laboratories doing salt spray & thickness qualification testing can furnish test panels -- the same size can be used for bending & thickness tests, or a 4x6" panel (salt spray test size) can be cut into 4 bend test panels. The panel material(s) must ~match the production material(s) in chemical composition and surface finish prior to coating application, MIL-C-26074E, para. 4.3.2 & 6.6, and ASTM B733, para. 8.3.
- Goleta, California
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