Common Hard Chrome Plating Defects and Causes
Each of these coating failures can be very expensive. Many are caused by factors that are not apparent to the plating shop personnel. It is very important for them to recognise each failure, and understand its causes.
Pitting
Pits – Small Craters on the Surfaces: These types of coating failure can be caused by hydrogen gas bubbles which stick to the surfaces during the plating process. These spots are not coated with the deposit. Bad bath chemistry, especially with organic contamination, can cause pitting.
Poor Adhesion
Lift, Flake, or Peel of Chrome Coating. If your chrome coating lifts, flakes, or even peels, then it can only mean that the surface preparation prior to plating did not achieve the required bonding. In fact, typically surface preparation failures such as these result in coating failures.
Burning and Edge Roughness
Burning and Edge Roughness: High-current areas, such as sharp edges, corners, and protrusions, are subject to excessive current density. Therefore, rough, burnt, or nodular surfaces can develop at these locations. However, by using conforming anodes, or by reducing current density in problem areas, the required surface finish can often be obtained.
Cracking and Crazing
Hard chrome plating produces a very hard deposit that is under great amounts of tensile stress. Fines cracks and crazing in a surface network pattern are typical above a certain thickness. Through thickness, coarse cracks indicate excessive current density, overheat in the plating bath, and/or too fast deposit formation.
Low or Uneven Deposit Thickness
Thin patches can be due to a number of reasons. The main causes are poor anode positioning leading to a number of shielded low-current areas in the cathode. Additionally, a bath that has a low chromic acid concentration can cause a number of areas to receive a thin deposit. This can be resolved by checking the cathode-to-anode distance and ensuring that the bath chemistry is within the specified limits.
Nodular Growth or Treeing
Rough, branching nodules on the surface of a part indicate high current density and/or a chromium plating solution that has cooled below the working temperature of the solution. Such growths concentrate on edges of parts and are particularly a problem where there is a requirement for the final surface to be of a precise tolerance and require grinding.
Understanding each of the chrome plating defects will help you figure out if the problem is with your chrome plating solutions, your chrome plating set up, or your chrome plating pre-treatment.
