Small iron and steel parts may be coated by drum tumbling with a mixture of proprietary promoter chemicals, zinc powder, and glass beads. After cleaning the parts usually limited in size to about 8-9 inches (200-300mm) and weighing less than one pound (0.5 kg) they are flash copper coated and loaded into a plating barrel. Then the barrel is filled with chemicals, glass beads, and zinc powder and tumbled. The tumbling action causes the beads to peen the zinc powder onto the part. Thickness is regulated by the amount of zinc charged to the plating barrel and the duration of tumbling time. After coating, the parts are dried and packaged, or post-treated with a passivation film, then dried and packaged.

Materials mechanically plated must be simple in design. Complex designs with recesses or blind holes may not be thoroughly coated because of inaccessibility to the peening action of the glass beads. It is also important that the compaction agents (glass beads) are large enough to avoid being lodged in any cavities, recesses, or small threads in the parts.

See Also:
Zinc Coatings Publication