Global Fastener News

1980 FIN – Corrosion Resistant Fastener Coatings

July 28
00:00 2010

By Dick Callahan

March 15, 1980 FIN – There is increasingly strong emphasis in the U.S. on corrosion resistant coatings for steel fasteners. As paradoxical as it may seem there is also a Federal government “edict” that there shall be no cadmium in the effluent in the U.S. by the year 1983.

Contrary to possible popular opinion, however, this does not constitute a ban on cadmium-plated fasteners (or other metallic components for that matter), but rather is designed to eliminate the toxic effect of cadmium in the effluent wastes from the cadmium plating process itself.

In essence, what it does create are the expenditures and efforts required to develop practical and efficient process methods for either “deactivating” the cadmium sludge in the effluent from the cadmium plating process operations, or by developing a closed-loop type of cadmium plating line that will prevent effluent cadmium sludge.

In as much as the costs of developing and installing cadmium sludge de-activating systems and/or closed-loop cadmium plating lines would be very significant, the net result is that we can expect to see a dramatic reduction in the availability of cadmium-plated fasteners over the next three years.

Zinc plating – although not as resistant to salt air exposure as cadmium plating – would seem to be the logical alternative to the virtual future elimination of cadmium plating, but there are other corrosion resistant coatings for fasteners, such as: zinc/tin composite coatings; tin over zinc coatings; various formulations or organic coatings; Ion vapor deposited (IVD) aluminum coatings, etc. Many of these do have excellent corrosion resistant properties but the plating or coating costs can be high.

In my opinion, zinc plating for fasteners will remain – at least for the time being – as the most popular of the corrosion resistant fastener coatings. Of importance, however, is the fact that as the use of heat-treated higher strength fasteners continues to increase, the problems of hydrogen absorption – associated brittle fractures also continues to increase.

The subject of corrosion resistant fastener coatings plus the attendant problems of hydrogen embrittlement failures and stress corrosion cracking is of vital concern to all suppliers and users of fasteners. Hydrogen-induced fastener failures are becoming a factor of concern in product liability investigations and litigation.

The ASTM F-16 Committee on Fasteners has established Sub-Committee F 16.03 on corrosion-resistant coatings for fastener manufacturers to explore the alternatives for cadmium plating and investigate these alternative methods.

At the Williamsburg meeting of ASTM, Dick Harris of Bethlehem Steel ably and efficiently set up and conducted a Symposium of Effects of Hydrogen on Steel Fasteners. There were reports and comments presented by six panelists relative to comparative corrosion resistance characteristics of zinc and/or zinc composite coatings, the influence of process-induced hydrogen, and the influence of environmental hydrogen. There was extreme interest in, and active questioning from the audience.  ©1980/2010 Fastener Industry News

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