Using Electroplating to Increase Surface Thickness

In some situations, it may be necessary to increase the thickness of the surface of a workpiece. A thicker coating can improve the durability of the substrate and make it more difficult for potentially destructive forces — such as corrosion or exposure to harsh chemicals — to impact product quality. Increased coating thickness can also add bulk to the finished product, which may be a requirement in construction and similar heavy-duty applications.

Electroplating is one of the best methods for coating a metal object when maximum thickness is required. The electroplating process provides better control over coating thickness than many other metal finishing techniques. Additionally, electroless plating — which entails the application of the coating via autocatalytic reaction instead of an electrical current — offers even greater influence over coating thickness.

What Are the Results of Insufficient Coating Thickness?

The failure to apply the appropriate coating thickness for the application can result in several issues:

• Void: A void, referred to as porosity on a micro level, is a condition where the surface of the workpiece or underlying coating is visible. A void can increase the risk of corrosion and detract from the finished product’s aesthetic appeal. It can also shorten the timeframe in which an additional coating application will need to be applied. Salt spray and nitric acid vapor testing can detect the existence of voids.
• Pinpoint rusting: Pinpoint rusting can happen when the coating is too thin to provide sufficient cathodic protection for the substrate. Rusting may appear at the surface areas with the least protection.
• Cracking/brittleness: When a coating is applied below the desired thickness level, it can negatively affect the coating’s physical properties. This can result in a brittle surface that is more susceptible to cracking.

Attempting to correct a deficient coating thickness after the fact is often problematic, as adding thickness can jeopardize the structural integrity of the coating. Scarification — a modification process that entails scratching, etching or burning — may be necessary.

Consequences of Excessive Coating Thickness

While a coating that is too thin can affect the quality of the finished product, a coating that is too thick can also have unintended consequences. Excessive coating thickness is often the result of an application error and can lead to:

• Flaking/Peeling: A coating that is too thick can become brittle and flake or peel off even before the object is put into service.
• Cracking: Excessive coating thickness can result in a high internal stress level that causes cracking or delamination.
• Roughness: An excessively thick deposit can create a rough surface texture that can detract from the piece’s appearance or make it more difficult to apply a secondary coating.