Enhancing Adhesion: The Role of Zinc Phosphate Coatings in Surface Preparation

Zinc phosphate coatings are a reliable solution for protecting steel components from corrosion and improving their durability. In this blog post, we delve into the specifics of zinc phosphate coatings, comparing them to black oxide coatings and nitride coatings. From application to understanding what makes them rust-resistant, we uncover more of what makes them a small but mighty form of protection for manufactured products and surface adhesion.

What is black phosphate coating?

Black oxide coatings have a long history of use to enhance the corrosion resistance of steel. Black oxide and black phosphate are easily mistaken as the same thing, but black phosphate is more effective than black oxide. By sacrificially protecting the steel, zinc phosphate coatings become a shield against corrosion. This sacrificial nature means the coating degrades, preventing the steel substrate from succumbing to rust and degradation. The most common use of black phosphate coatings is on drywall screws. When mixed with oil for added lubrication, black phosphate is also used on floorboard screws and frame bolts. This application is practical against rust in each case because it is not open to the elements and harsh environments. Zinc phosphate coating wins out on wear and tear resistance over black phosphate coatings.

What is the difference between zinc phosphate and nitride coating?

Zinc phosphate and nitride coatings serve distinct purposes. While zinc phosphate is renowned for its excellent adhesion and sacrificial protection, nitride coatings enhance wear resistance and reduce friction. Nitride coatings are particularly beneficial for moving parts, preventing galling and improving lubrication efficiency due to the creation of a hard coating.

Other types of steel conversion coatings include:

  • Black oxide
  • Zinc, iron or manganese phosphate
  • Aluminum chromate

How to measure zinc phosphate coating thickness?

Ensuring the proper thickness of zinc phosphate coating is crucial for its effectiveness. Cleaning the steel surface is mandatory to remove oils and grease, allowing the coating to adhere correctly. Thickness typically ranges between 0.0002 and 0.0006 inches, with x-ray fluorescence measurements. Additionally, scanning electron microscopy helps determine the grain size and uniformity of the coating.

Will phosphate-coated screws rust?

While zinc phosphate-coated screws are effective in preventing rust, they may still rust together, especially in harsh environments. These screws are recommended for indoor projects where they are less likely to be exposed to damaging conditions. In less demanding construction applications, zinc phosphate-coated screws provide reliable protection against rusting if not damaged or exposed to extreme conditions.

How to apply zinc phosphate coating

Zinc phosphate coating can be applied as a stand-alone coating through spray or immersion. The steel is immersed in a dilute phosphoric acid solution with iron, zinc, or manganese salts. Remarkably, the coating dries to the touch within half an hour at room temperature, with complete curing achieved in approximately 5-6 hours.

Adhesion is a critical factor in the performance of any coating, and zinc phosphate excels in this regard. The crystalline phosphates formed during the coating process create an ideal surface for the coating to adhere to. This superior adhesion ensures the coating stays firmly in place, offering long-lasting protection against corrosion, wear, and other environmental factors. Interested in learning more about zinc phosphate coatings? Check out our previous blog post!

Partner with Condor Machinery for your next project

Since 1985, we have provided reliable machining services in Edmonton and the surrounding area. We take pride in our projects and are committed to bringing you the highest quality manufactured products on time and within budget. We offer various in-house services, such as custom CNC machining, machine engraving, phosphate coatings, and more. 
If you are looking for zinc phosphate coating services, contact us today to discuss your manufacturing needs!

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