Chromium Plating Defects and Its Causes
Chromium plating is widely used for decorative and/or protective finishing. It has excellent corrosion resistance, good wear resistance and excellent tarnish resistance. Despite its many benefits, there are still some defects that occur in chromium plating and failure to identify these defects can lead to quality problems.
Before delving into the defects and their causes, it is important to understand the electroplating process. In chromium plating, an electric current is used to plate chromium onto a surface. This process is repeated until a desired thickness of chromium is reached. The first step is the application of a coating, which serves as the foundation for the plating. It is then coated with a chromium bath, which typically contains sulfuric acid, chromic acid and oxide. The part is then electroplated and subjected to a series of rinsing and washing steps.
One of the most common defects in chromium plating is pinholing. This occurs when minute holes are present in the coating after the process. These holes are caused by the presence of hydrogen bubbles, which form on the surface as a result of the plating solution’s reaction with the metal’s surface. The hydrogen bubbles become trapped underneath the chromium and cause the coating to lift off, which results in the pinholing. The presence of air bubbles in the chromium bath and improper stirring of the bath before plating can also lead to this defect.
Another common defect in chromium plating is formation of nodules, or thick patches on the metal surface. These occur when there is an uneven plating solution distribution across the metal surface, which can happen due to the irregular shape of the metal part or uneven current passing through the bath. These nodules can result in pinholes, which will induce corrosion and other defects in the finished part.
Whiskering, another type of defect found in chromium plating, occurs when small, feather-like deposits of chromium form on the metal surface. This is typically caused by an excessive buildup of chromium ions in the bath, which can occur when the bath is not adequately cleaned between runs. Whiskers are difficult to remove, which can lead to a rough surface when the part is polished, causing further defects.
Improper dipping and rinsing can also lead to defects in chromium plating. If the part is not adequately rinsed after being dipped in the plating solution, there will be a build-up of chromium on the part, which will result in poor adhesion and poor quality. Another common defect can occur when the part is not completely submerged in the bath during plating, resulting in uneven plating.
Given all the potential defects, it is important that the chromium plating process is properly monitored and monitored. This includes inspecting the part before and after the process and performing regular maintenance on the plating bath. By being aware of the potential defects and their causes, it is possible to reduce the risk of quality problems in the finished product.
