Mechanical Plating Equipment,Mechanical Plating Equipment,Mechanical Plating Equipment,Mechanical Plating Equipment
Mechanical plating is accomplished in mild steel or stainless steel variable-speed tumbling barrels. Because the entire
process takes place at low (1 to 2) pH, the barrels must be lined with an inert, abrasion-resistant protective coating such as
neoprene, polypropylene, polybutylene, or urethane. The lining is usually applied at a thickness of 19 to 25 mm (0.75 to 1
in.); thicker linings may be used in high wear areas such as the inner base of the barrel.
Typical tumbling barrels have capacities of 0.04 to 1.13 m3 (1.5 to 40 ft3), where capacity is the total available working
volume, which is typically about 25 to 35% of the total volume. For example, a 0.57 m3 (20 ft3) plating barrel will hold
approximately 910 kg (2000 lb) of 25 mm (1 in.) long steel threaded fasteners or about 680 kg (1500 lb) of 8d common
nails. After the parts are loaded in the barrel, approximately 1000 kg (2200 lb) of glass beads are added with sufficient
water to form a slurry.
The tumbling of part on part and glass bead on part creates kinetic energy that serves to cold weld the spheroidal metal
particles to the substrate. The diameters of the most commonly used glass beads are nominally 5 mm (0.187 in.), 1.5 mm
(0.056 in.), 0.7 mm (0.028 in.), and 0.25 mm (0.010 in.). The ratio of glass beads to parts is about 1.5:1 by weight, but
varies depending on the part mass and geometry and on the coating thickness required (greater thicknesses sometimes
require a higher ratio of beads to parts and the use of larger beads). The barrels rotate at a surface speed of 43 to 75 m/min
(140 to 250 ft/min) and at a tilt angle of about 30° from horizontal.
The glass plating beads perform a number of functions. They:
· Assist cleaning and oxide removal through a mildly abrasive scrubbing action
· Facilitate mixing and displacement of the chemicals
· Consolidate the metallic coating
· Protect and separate parts from one another, thereby preventing edge damage and tangling
· Help push the plating metal into corners, recesses, and blind areas
Glass beads are constantly reused and recycled through a glass bead recovery and pumping system, which is part of the
standard mechanical plating equipment package.
Process Steps
The mechanical plating process requires a series of chemical additions. The quantity depends on the total area of part
surface. The total area must be determined prior to each cycle. All of the plating steps are performed in the same barrel,
normally without rinsing or stopping the rotation. The only exception is removal of heavy oil or scale; these contaminants
should be removed before parts enter the plating barrel.
The first process steps include a series of chemical and metal additions designed to mildly acid clean and activate the
substrate and then to apply a thin, uniform copper strike. The copper strike provides a clean, galvanically receptive part
surface. The next step involves adding an "accelerator" or "promoter" agent, which creates a chemical environment that
controls the rate of deposition and subsequent bonding of the plating metals. A defoaming agent is used during the
process to control foaming and to prevent any associated loss of plating solution.
The plating metal is added as a dry, fine powder or a water slurry containing the powder. Platers add metal in a series of
steps and in amounts proportional to the coating thickness desired. Commercial plating thicknesses of 5 to 12.5 μm
(0.0002 to 0.0005 in.) usually require two to three additions of metal, while greater thicknesses or "galvanized" coatings
can demand eight or more.
The following represents a typical sequence of operations for mechanical plating:
1. Alkaline or acid preclean (if necessary)
2. Prepare surface
3. Copper strike

4. Add accelerator/promoter
5. Add plating metal
6. Add plating metal
7. Add plating metal
The plating cycle is carried out at temperatures between 15 and 32 °C (60 and 90 °F). A pH between 1 and 2 is required at
all times to ensure proper adhesion and a high plating efficiency. The low pH level acts to maintain an oxide-free
condition at all times on both the part surface and the surface of the plating metal particles. These temperature and pH
conditions facilitate mechanical bonding ("cold welding"). The process has an efficiency of about 92%; that is,
approximately 92% of the plating metal added is actually plated on the parts.
The mechanical plating process usually takes about 45 min. At the conclusion of the cycle, the slurry of glass beads,
coated parts, and water discharges into a vibrating surge hopper under the plating barrel. The capacity of this hopper
should be large enough to accept the entire load, thereby freeing the barrel to begin plating the next load. The slurry
dumps onto a vibrating screen or magnetic separator. Water sprays are used to wash and remove glass beads from the
parts. A glass bead handling system consisting of a sump, a double-diaphragm pump, and an overhead conical storage
reservoir with a pinch valve at the bottom is used to recycle the beads. More than one batch of glass beads can be used to
speed production.
As described above, the mechanical plating process can be used to apply a variety of metals and codeposits with varying
coating thicknesses, all with the same equipment. This capability offers advantages in equipment cost and space
utilization over other forms of plating.
Process Capabilities
Plating Thickness. The thickness of mechanical plating deposits ranges from 5 to 75 μm (0.2 to 3 mils). The heavier
coatings are referred to as mechanical galvanizing or cold-impact galvanizing coatings. Because the coating thickness is
somewhat independent of cycle time and is controlled by the plating metal additions, a heavy "galvanized" coating
thickness can be applied in almost as little time as thinner commercial coating thicknesses. Mechanical galvanizing
provides uniform, smooth, and adherent coatings, and the coated parts require no thread chasing.

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