Chromate Plating for Machined Parts

Chromate plating, also known as chromating or chromating conversion coating, is a common surface treatment used in the aerospace, automotive, and other industries to provide corrosion resistance, improve paint adhesion, and enhance the appearance of metal parts. It is often applied to machined parts made from aluminum or zinc-plated steel. Here’s an overview of the chromate plating process for machined parts:

  1. Cleaning and Pre-Treatment: Before chromate plating can begin, the machined parts must be thoroughly cleaned to remove any contaminants such as oil, grease, dirt, or rust. This is typically done through a series of chemical baths and rinses.
  2. Surface Preparation: The machined parts are then etched or prepared to ensure proper adhesion of the chromate coating. This may involve using an acid solution to roughen the surface slightly, improving the coating’s adherence.
  3. Chromate Bath: The parts are immersed in a chromate bath, which contains a solution of hexavalent chromium compounds. The exact composition of the bath can vary depending on the desired finish and performance characteristics. Common types of chromate coatings include yellow, clear, and olive drab.
  4. Immersion or Electroplating: Chromate plating can be accomplished through immersion or electroplating processes. Immersion involves simply dipping the parts into the chromate bath, while electroplating uses an electrical current to deposit the chromate onto the parts. Electroplating typically provides a more uniform and controlled coating.
  5. Rinsing: After chromate plating, the parts are thoroughly rinsed to remove any excess chromate solution and contaminants. Multiple rinsing steps may be required to ensure the parts are clean.
  6. Drying: The coated parts are dried using air or heat to remove any remaining moisture.
  7. Quality Control: It’s essential to perform quality control checks to ensure the chromate plating meets the required specifications. This may include measuring coating thickness, adhesion tests, and visual inspections.
  8. Sealing (Optional): Some applications may require a sealing step to further improve corrosion resistance and protect the chromate coating. Sealing can involve using various types of sealers or topcoats.
  9. Post-Treatment: Machined parts may undergo additional processes such as assembly, labeling, or packaging, depending on the specific application.

Chromate plating is known for its ability to provide excellent corrosion resistance and adhesion properties. However, it’s essential to note that hexavalent chromium compounds, which are commonly used in chromate baths, are toxic and pose environmental and health concerns. As a result, there has been a push towards using alternative, less toxic coatings such as trivalent chromium-based processes.

Additionally, regulations regarding the use of hexavalent chromium have become increasingly stringent in many regions, so it’s important for manufacturers to stay compliant with environmental and safety standards while conducting chromate plating operations.

Related surface treatment:

Cleaning and Degreasing
Powder Coating
Chemical Conversion Coating
Plasma Nitriding
Case Hardening
Laser Surface Treatment
Shot Peening
Ultrasonic Impact Treatment (UIT)