Aerospace fasteners typically are treated with some forms of coating to protect them from corrosion and in some cases, to provide better lubricity.
Common coatings for aerospace fasteners include:
-Cadmium plating – for Carbon Steel and Alloy Steel fasteners.
-Aluminized coatings such as NAS4006 – for titanium alloys, A286 High Temperature Corrosion Resistant Steel and Inconel Alloys.
-Silver plating – for A256 High Temperature Corrosion Resistant Steel (CRES)
-Ion Vapour Deposited Aluminum (IVD) – for Titanium Alloys
-Solid Film Lube – for A286 High Temperature CRES, Inconel Alloys and as secondary coating in addition to cadmium plating.
In addition to protecting the fasteners from corrosion, these coatings also provide lubrication for nut or collar installation on threaded products and for installation of fasteners in interference fit applications.
These coatings do not have a storage life limit. However, they should be protected from damage during shipping and storage in plastic bags and cardboard boxes by the Manufacturer, by the Distributor, and by the OEM End User. They can be left in open fastener racks on the assembly line.
However, often these fasteners are treated with an additional coating of Cetyl Alcohol. Cetyl Alcohol provides some degree of corrosion protection, but its main purpose is lubrication. These fasteners depend on the presence of Cetyl Alcohol for proper installation.
The Cetyl Alcohol coatings are different in three ways. First, Cetyl Alcohol is not a ‘primary’ coating as the ones listed above. Second, Cetyl Alcohol will sublime with time when exposed to the atmosphere. Third, Cetyl Alcohol is easily removed by handling of the fastener.
Manufacturers of Lockbolt Pins and Threaded Pins rely on the Cetyl Alcohol to assist in interference fit installation, and it is used on Pins and Collars to assist the installation of the Collars onto Threaded Pins.
Cetyl Alcohol is also used on Blind Fasteners such as Blind Rivets and Blind Bolts. The Cetyl Alcohol reduces friction between the Core Bolt or Pull Spindle and the Body. There have been cases of incomplete installation of Blind Rivets due to the lack of Cetyl Alcohol.
Precautions must be taken to prevent the sublimation of Cetyl Alcohol. Sealing in plain plastic bags is sufficient for this, even in the fastener racks on the assembly line. This also prevents removal by handling. DO NOT store fasteners with Cetyl Alcohol loose where sublimation or handling can remove it!
Disclaimer
Avicast does not guarantee any results and does not incur any liability with regards to the information provided in this article. Avicast cannot and does not warrant the accuracy, correctness or completeness of the information and interpretation in this article.
