Mechanical plating or Mechanical Galvanizing are an effective means of applying zinc, tin, or other ductile metals or mixtures of ductile metals to a metal substrate — usually steel. In the mechanical plating or mechanical galvanizing process, impact energy is transferred from a rotating open-ended oblique barrel through glass beads, resulting in the cold-welding of fine metal dust particles to the substrate. The resulting deposit is slightly porous, has a matte finish, and provides corrosion protection to the articles plated without introducing hydrogen embrittlement into the part. It is therefore used widely to provide corrosion protection to high-strength fasteners, particularly those above about Rockwell C40.
The most important reason for mechanical plating is the assurance of product reliability by the elimination of hydrogen-embrittlement. Mechanical plating is the method preferred by many engineers for hardened fasteners and stressed components.
Mechanical plating eliminates the lengthy pre-plating and post-plating baking cycles. The ASTM issued standard practices B849 and B850 which recommend baking cycles before and after electroplating to prevent hydrogen embrittlement. For extremely hard parts, baking cycles can be quite extensive — in some cases, as long as 40 hours.
Mechanical plating is the best way to avoid the extra expense of long baking cycles. Customers can visually confirm that parts have been mechanically plated —something that cannot be done to confirm baking cycles. Mechanical plating has a matte finish easily distinguishable from electroplating's bright finish. In addition, mechanical plating has the ability to plate sintered metal parts (power metallurgy) without costly impregnation.
Mechanical plating gives you the ability to plate parts that tangle; the glass impact media used in the process tends to prevent parts from tangling. This mechanical plating process characteristic makes this technology an ideal choice for plating hardened steel springs.
Mechanical plating gives you the ability to plate flat parts; the media prevents flat parts from masking one another. This makes mechanical plating an ideal process for plating flat stampings and washers.
Because mechanical plating consumes all the chemistry in each process cycle, there is no build-up of contamination in the bath. This assures users of long-term product and process consistency.
Mechanical plating allows you to apply leachant-sealants after the application of a hexavalent chromate or a trivalent passivate to enhance the corrosion protection of the process with little incremental expense. A zinc deposit of 0.0005`` with Hyperguard™ 326™ and a leachant-sealant topcoat will get over 500 hours of ASTM B117 salt spray protection, and coatings that deliver over 1,000 hours of protection are achieveable.
Mechanical plating offers an attractive economic advantage for coating thicknesses above 0.0005.`` This is due primarily to the fact that the process for thick coatings takes only slightly longer than the cycle for thin coatings (unlike electroplating, where the plating time is directly proportional to the plating thickness). The cost of additional plating thickness in mechanical plating is only slightly more than the cost of the plating metal.