Passivation for machined parts

Passivation is a chemical process used to enhance the corrosion resistance of machined parts, particularly those made from stainless steel or other corrosion-resistant alloys. The goal of passivation is to remove surface contaminants and create a protective oxide layer on the part’s surface. Here’s a guide on passivation for machined parts:

  1. Material Selection: Passivation is most commonly applied to stainless steel parts. It is essential to ensure that the material used is indeed a corrosion-resistant alloy.
  2. Cleaning: Before the passivation process, clean the machined parts thoroughly to remove contaminants such as oil, grease, dirt, and machining residues. Use an appropriate cleaning method, which may include solvent cleaning, alkaline cleaning, or ultrasonic cleaning.
  3. Preparation: The parts must be properly prepared for passivation. This often involves soaking or immersing them in a mild acid solution, such as citric acid or nitric acid. The acid helps to remove any remaining iron and other contaminants from the surface.
  4. Passivation Bath: The passivation process typically involves immersing the parts in a passivation bath or tank containing the passivation solution. The solution can be a proprietary mixture of nitric acid and other chemicals or a citric acid-based solution.
  5. Temperature and Time: The temperature and duration of the passivation process depend on the specific passivation solution being used and the type of stainless steel. The process is typically performed at a controlled temperature for a specific period to ensure the formation of the protective oxide layer.
  6. Rinsing: After the passivation process, thoroughly rinse the parts with clean, deionized water to remove any residual passivation solution.
  7. Drying: Dry the passivated parts using clean, dry air or by placing them in an oven. Drying is essential to prevent water spots and ensure the formation of a uniform oxide layer.
  8. Quality Control: Perform quality control checks to ensure that the passivation process has been effective. This may include checking the thickness and appearance of the oxide layer, conducting salt spray tests, or other corrosion resistance tests.
  9. Verification: It’s important to verify that the passivation process complies with industry standards and specifications, as well as any customer requirements.
  10. Packaging and Storage: Once passivated and verified, package the machined parts in a clean and controlled environment to prevent recontamination. Proper storage conditions are also important to maintain the corrosion resistance of passivated parts.

It’s worth noting that passivation is a highly effective method for enhancing the corrosion resistance of stainless steel parts, but it must be done correctly and in compliance with relevant industry standards and regulations. Additionally, the choice between nitric acid and citric acid passivation should take into consideration environmental and safety factors, as nitric acid is considered hazardous and regulated in many regions, leading to a preference for citric acid-based passivation in some cases.

Common surface treatment methods:

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