Mechanical Galvanizing

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Mechanical plating and galvanizing are departures from the more familiar methods of depositing a metal. Instead of using electrical energy to deposit a metal as in electroplating, chemical energy as in electroless or immersion plating or molten metal as in the case of hot-dip galvanizing, a mechanically-plated or galvanized coating uses mechanical energy, literally pounding the coating onto the substrate. The mechanically plated or galvanized coating is not decorative, but rather functional.

The difference between mechanical plating and mechanical galvanizing is a subtle one – mechanical plating is for coatings up to 1 mil (25 microns or 0.001”) and mechanical galvanizing is for coatings over 1 mil. Both use the same process outlined below to achieve those coating thicknesses, although mechanical galvanizing can take longer to complete. Originally developed in the 1950s, mechanical plating (and/or galvanizing) is another means other then electroplating or hot-dip galvanizing, of depositing zinc onto substrate metals, particularly steel. Done in a rotating barrel, the parts to be plated are immersed in a water slurry containing the coating metal in the form of fine particles, 3 to 20 μm in size, spherical glass beads to do the mechanical work, with mesh sizes from 4 up to 100 (4 mesh is approximately ¼”; 100 mesh is about 1/100 inch in diameter); and proprietary chemicals, which inhibit oxidation of the particle and substrate surfaces so coatings will adhere to the substrate and to one another.

The rotating barrel produces a tumbling action, physically similar to the motion encountered in an electroplating barrel, but of course there is no need for a dangler to conduct electricity. The mechanical energy produced by the rotation is transmitted through the beads, which impact the parts in the barrel. This impact energy results in the cold-welding of the metal powder particles to the substrate, and to each other. In the process, the particles coalesce and an adherent, coherent coating is formed on the substrate.

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