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An Overview of Coatings and Finishes for Enhanced Bolt Performance

Blake Marciszewski

Blake Marciszewski

Metric Bolt is a family run company with an inventory of military fasteners.

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In the high-stakes world of aerospace, military, and precision engineering, every component’s performance is paramount. Bolts, often the unsung heroes of these sectors, are no exception. 

When you’re dealing with machinery that must withstand extreme conditions, there’s no room for error or compromise. This is where the power of advanced coatings and finishes comes into play. 
Offering enhanced durability, corrosion resistance, and performance, these treatments are crucial for bolts destined for challenging environments. So, let’s explore bolt coatings and finishes tailored for such specialized applications in further detail.

Why Do Bolts Need Coatings?

  • Protection from corrosion – In extreme environments, especially with exposure to elements like saltwater, bolts need a strong shield against rust. Coatings serve as this protective barrier.
  • Robustness in extreme conditions – For military and aerospace applications, bolts often face high temperatures, pressures, and other extreme conditions. A suitable coating ensures they remain steadfast and durable.
  • Enhanced lubrication – Certain coatings reduce friction, facilitating smoother assembly in intricate machinery and ensuring longevity.

A Closer Look at Popular Fastener Coatings

In the dynamic world of aerospace, military, and precision engineering, understanding the nuances of various bolt coatings is critical. 

Here’s a more detailed exploration of some widely employed coatings:

Zinc Plating

Overview – Zinc plating stands out as one of the most utilized coatings. Its primary role? Guarding against corrosion. When you have zinc on your bolt’s side, you essentially equip it with a barrier against rust.

How it’s done – The process, known as electroplating, involves submerging the bolt in an electrolyte solution rich in zinc. When an electric current is passed through this solution, zinc ions migrate and adhere to the bolt, creating a protective layer.

  • Advantages:
    • Offers robust corrosion protection in standard environments.
    • Economically viable for large-scale applications.
    • Maintains the bolt’s dimensional accuracy as the layer is relatively thin.
  • Limitations:
    • Not ideal for extremely aggressive or marine environments, as its protection might fall short.

Hot Dip Galvanizing

Overview – Imagine giving your bolt a thick, impenetrable zinc armor. That’s hot dip galvanizing for you. It’s especially beneficial when you need an extra robust protective shield.

How it’s done – The bolt is cleaned thoroughly to remove any impurities. It’s then dipped into a kettle of molten zinc. Upon withdrawal, the bolt is coated with a thick layer of zinc.

  • Advantages:
    • Outstanding corrosion protection, especially for bolts destined for outdoor or aggressive environments.
    • Due to its thickness, the coating is self-healing, meaning minor damages can “heal” with zinc oxidation.
  • Limitations:
    • Not suited for bolts with fine threads, as the thick coating might alter threading details.
    • A tad bulkier in appearance compared to zinc plating.

Cadmium Plating

Overview – Cadmium plating, the darling of the aerospace sector, is known for its brilliance both in appearance and corrosion resistance, especially in saltwater scenarios.

How it’s done – Similar to zinc plating, the bolt is immersed in a cadmium-rich solution and electrified. This electroplating process causes cadmium ions to cling to the bolt’s surface, forming a shiny protective layer.

  • Advantages:
    • Superior resistance to corrosion in marine environments, making it a prime choice for aerospace applications.
    • Offers galvanic compatibility with several metals, which is a plus in reducing galvanic corrosion.
    • Aesthetically pleasing due to its natural luster.
  • Limitations:
    • Cadmium is toxic. Its use and disposal demand caution and adherence to safety guidelines.
    • Generally pricier than zinc-based coatings due to environmental and health concerns.

The Finishing Touch

A protective coat is sometimes accompanied by a finish for added benefits:

  • Chromate – Applied over zinc or cadmium, chromate boosts corrosion resistance and imparts a distinct rainbow or yellowish tint to the bolt.
  • Phosphate – Phosphate’s fine-textured surface, usually black or grey, is ideal for bolts meant to be painted, ensuring optimal paint adherence.
  • Xylan – Known for its low-friction properties, Xylan is a top pick for bolts in machinery that demands regular adjustments.

Choosing the Right Coating for Your Bolt

  1. Identify the application – Is the bolt for an aircraft exposed to saltwater? Or high-pressure machinery?
  2. Assess the environment – Consider external factors like humidity, temperatures, or potential chemical exposures.
  3. Size and thread details – Coatings like hot dip galvanizing may not align with fine-threaded bolts’ requirements.
  4. Budgetary constraints – Balancing cost with desired performance or appearance is essential.

If you’re struggling to decide which type of coating will be best for you, please do not hesitate to get in touch with our friendly and experienced team at Metric Bolt.

Coatings and Finishes for Enhanced Bolt Performance

In sectors where precision, reliability, and durability are non-negotiable, understanding the role and nuances of bolt coatings becomes indispensable. These coatings and finishes not only bolster bolt performance but also ensure they stand up to the unique challenges they’ll face in aerospace, military, and beyond. Whether you’re procuring for defense, aviation, or other specialized industries, being informed about these treatments can significantly impact your projects’ success.

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