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Finishings

The final step in the fabrication process is deciding on a finish to maintain a high-quality appearance and provide protection to your parts. Three common finishing techniques are powder coating, wet painting, and plating.

Powder Coat

Powder coating applies a layer of free-floating, dry organic powder by electrostatic attraction to metal. The piece is first cleaned thoroughly to ensure even adherence of the powder. The powder can be polyester, polyurethane, polyester-epoxy, epoxy, or acrylic. After grounding the piece, a surge of high voltage electricity charges the dry powder. The charged powder is sprayed evenly over the entirety of the metal piece. To complete the process, curing occurs for 10-15 minutes in an oven up to 400 °F. During the curing process, the powder sets, polymerizes, and flows around the object forming a thick protective layer.

The benefits of powder coating are abundant. First, powder coating results in a thick, dense finish that is resistant to scratches, chipping, and splintering. If bending or denting occurs, the powder coating will remain intact where a traditional wet paint would chip fall off. The durable coating is long lasting. Another benefit is the ease of use and cleanup. Most projects only require one coat to achieve a perfect finish free of drips or brush marks. Because no is solvent involved, any excess powder can be swept or vacuumed up. This also makes the process environmentally safe.

There are only two major drawbacks to the powder coating process. If a thin finish is necessary, powder coating is not ideal. Thinning the polymer produces a bumpy finish rather than the slick coating produces with thick layers. Secondly, smaller jobs might prefer a less expensive finishing process, as powder coating requires spray materials, electrostatic booth, and a dedicated oven, all which can be expensive startup costs. Maintenance, while not required as often as wet paint, is more difficult. Touch ups to damaged areas are more difficult than simply touching up with a can of paint.

Wet Painting

Wet painting is a traditional process of applying liquid paint to a metal. Unlike painting a bedroom, wet paint in industrial settings is often applied with spray, pump, or pressurized vessels to ensure even coating.  The piece is first cleaned thoroughly. Following this, paint is applied. Unlike powder coating, wet paint may require multiple coats to ensure an even finish.

Wet painting is relatively cheap, especially when looking at startup costs. It also allows for thinner coats that are out of the question for powder coating. Wet paint can also be used on rubber or other heat-sensitive materials since curing occurs at room temperature. If the product becomes scratched or damaged, touch ups are much simpler than powder coating. Wet paint also provides a greater range of colors and finishes.

There are a few drawbacks to wet paint. It is by no means as durable as powder coating. If bending or scratching occurs, the paint is liable to chip or splinter. Because of this, maintenance over time will be greater than powder coat. Multiple coats are also needed in wet paint; however, only one coat is needed in powder coating. Because of the wet application, drips or other imperfections in the finish are possible.

Plating

Plating involves depositing metal on a conductive surface, providing a thin and durable corrosion resistant surface. Common metals used in plating are zinc, chrome, nickel, and silver. There are many different ways to plate metal pieces. One technique involves submerging a piece in an ion solution containing the plating metal.Electricity is passed through the system which leads to the deposition of plating metal on the piece.

Using different plating metals leads to a wide array of benefits. Plating can improve corrosion resistance, add decorative appeal, increase solderability, enhance strength, reduce friction, alter conductivity, increase magnetism, or enhance paint adhesion.

Although determining the downsides to plating is somewhat dependent on the plating metal, there are some general downsides to plating. The coats are very thin, so if thicker layers are desired, multiple coats may be necessary. This could be a time consuming and expensive process. The uniformity of each coat is not always ideal. Lumps or bumps may form uneven surfaces. Depending on the plating metal, the coating may tend to be brittle and easy to crack which leaves the piece open to impurities such as rust.

Summary

ProcessPowder CoatWet PaintPlating
CostMediumLowVaries
MaintenanceLowHighVaries
EaseHighMediumMedium
MaterialOrganicOrganicMetal
HeatHighLowVaries
ThicknessThickThinThin  
Corrosion ResistanceHighMediumVaries

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