Why It’s Important to Select the Right Coating

Since fasteners are used to connect multiple components, they are essential to the structural integrity of assemblies. Nut and bolt plating, bolt coatings, and other types of finishing services protect metal fasteners and safeguard their performance lifespan. This is particularly important for applications that involve exposure to water, chemicals, or other harsh environmental factors that can damage metal and alloys. With the right coating, you can ensure you get the most possible value out of your investment by improving fastener performance, strength, and longevity.

Zinc Coatings for Fasteners

Zinc is one of the most widely used coating materials for fasteners. It offers high corrosion resistance and is inexpensive to apply. Zinc-coated fastening products perform reliably in humid environments and better resist rust formation. There are several zinc plating options to choose from, depending on your performance requirements.

Zinc Plating

Using an electroplating technique, zinc can be applied to aluminum alloys, brass, bronze, copper, iron, steel, and many other commonly used alloys. The electroplating process causes the zinc to oxidize in a thin, tightly adhered layer that is referred to as zinc oxide. Zinc oxide plating is a good option for small fasteners that are used within indoor environments or minimally intensive outdoor applications. The zinc-plated fasteners take on a shiny, silver-gray appearance.

Black Oxide Coating

Black oxide coating is a light plating option that offers basic protection from corrosion and abrasion. To achieve maximum corrosion resistance, it can be oiled or waxed for added protection. Since black oxide prevents rust, it is mostly used on fasteners that will be installed in outdoor environments. The most common metal substrate for this type of coating is steel, however, stainless steel fasteners are sometimes also used. Unlike with galvanized coatings, black oxide does not change the fasteners’ dimensions. This makes it an ideal choice for close-tolerance machined parts.

Hot Dip Galvanizing

Hot-dipped galvanized coatings offer a thicker layer of zinc on the fastener’s surface than a standard zinc plating would. For this reason, hot-dipped galvanized coatings are better at resisting corrosion. Also known as HD, this type of coating is ideal for fasteners that will be used outdoors. With its reliable corrosion resistance, it is particularly well-suited to coastal areas where there is greater exposure to salt. HD-coated fasteners will resist corrosion much longer than products with other coatings.

Electro Galvanized

Commonly referred to as EG, this type of coating involves applying a thin layer of zinc for moderate corrosion protection. EG fasteners are used in areas where minimal corrosion protection is required, such as inside kitchens or bathrooms. Many roofing fasteners are also electro-galvanized.

Mechanical Plating (Mechanical Galvanizing)

With mechanical plating, fasteners are tumbled in a drum that contains water, glass beads, zinc powder, and other chemicals. This abrasive environment creates a cold welding process that attaches the zinc powder evenly onto parts.

Zinc Flake Coating

This process involves covering small fasteners with two layers of zinc and aluminum flakes. After the base and top coat are set, the coating will provide reliable corrosion resistance. The top coat acts as a preventative layer that shields the interior from damage.

Nickel Coatings for Fasteners

The nickel plating process involves electroplating a thin layer of nickel onto the desired substrate. While the coating is thin, it is substantial enough to help with corrosion resistance and wear resistance while also creating an attractive appearance. It’s also possible to apply a thicker coat onto undersized fasteners to improve their fit.

Since nickel coatings are more corrosive and costly than other varieties, they’re not ideal for certain applications. For example, since they are not resistant to nitrogen, they are not typically used in agriculture applications. However, nickel plating comes in many varieties and is used throughout many industries:

  • Watts Nickel Plating. This process creates a bright, decorative finish with corrosion-resistant properties.
  • Nickel Sulfamate. This coating offers highly efficient corrosion resistance and is used in engineering applications.
  • All-Chloride, Sulfate-Chloride, and All-Sulfate. These options have similar characteristics and run at low voltages with higher stressors. They’re typically used to plate the inside of pipes and pipe fittings.
  • Hard Nickel. Hard nickel coatings offer high tensile strength.
  • Black Nickel. Black nickel coatings feature a non-reflective surface that’s ideal for decorative and visual military purposes. This coating is typically plated onto brass, bronze, or steel.

Hard Chrome (Chromium) Coatings for Fasteners

Hard chrome coatings are one of the best methods of protecting fasteners from wear and tear. While this plating technique is more costly than other methods, it results in a durable, attractive finish that’s easy to clean and improves surface hardness. Chromium coatings are applied using electroplating techniques and are used throughout many diverse applications, including:

  • Motorcycle parts
  • Automotive hydraulic cylinders
  • Weapons manufacturing
  • Molds
  • Dies

Phosphate Coatings for Fasteners

Phosphate-coated fasteners are created using a crystalline conversion coating that is formed on the metal base of the fastener. Phosphate reduces friction and prepares surfaces for further coatings, like oils, sealers, or paints. On its own, phosphate coatings do not offer any corrosion resistance, however, they are an excellent base for painting.

Phosphate coatings are lightweight and should only be used on fasteners that will be used within indoor or interior settings. They are typically used on steel fasteners, but they are compatible with many other materials, including aluminum. Phosphate-coated fasteners are commonly used in airplane parts and automobile wheels.

Stainless Steel Fasteners

While stainless steel is not used as a coating material, fasteners crafted from this type of metal feature a similar level of durability, corrosion resistance, and chemical resistance. There are over 150 grade types and finish variations for stainless steel, however, 304 and 316 grades are the most commonly used. 304 stainless steel is used in more commercial settings while 316 offers marine-grade effectiveness. Stainless steel fasteners are ideal for high-temperature environments, outdoor use, food and medical applications, and other demanding settings.

Contact Us for Help Choosing Fastener Coatings

Associated Fastening Products has over 30 years of experience manufacturing and distributing fasteners for the OEM market. Whether you need a standard product or a completely custom solution, we offer an extensive range of capabilities designed to meet even the most demanding performance requirements.

No matter what challenges your application involves, our team can help you identify the most suitable coating and obtain reliable, high-quality products at a great price. If you have any questions about fastener coatings, reach out to our team. To get started on your next project, request a quote today.