General
Mechanical galvanizing is similar to hot-dip galvanizing in that they both apply a thick coating of zinc metal which provides sacrificial or cathodic protection to the steel. Because zinc is more reactive than iron, the zinc galvanized coating corrodes first, protecting the steel substrate. Mechanical galvanizing results in a very uniform coating thickness reducing thread fit issues at assembly, making it a preferable coating for structural applications. Not only does mechanical galvanizing provide excellent coating uniformity, but the process is consistent from batch to batch and within each batch.
The Mechanical Galvanizing Process
Mechanical galvanizing is a room temperature process in which zinc coatings are applied to fasteners without electricity (which is used for electroplating) and without heat (which is used for hot-dip galvanizing). Fasteners are placed in a large rotary barrel along with zinc powder, special promoters, and glass impact media. The mechanical energy generated from the barrel’s rotation is transmitted through the glass impact media and causes the zinc powder to be mechanically welded to the surface of the fasteners. With a proper glass media size mix, all exposed surfaces can be coated very uniformly, and the buoyancy of the glass media cushions the fasteners in the rotating barrel to minimize thread nicking. The room temperature process ensures no chance of re-tempering or softening high strength fasteners and guards against hydrogen embrittlement because the fasteners are also never exposed to acid pickling in the process.