Different Types of Finishes and Plating for Nuts, Bolts, Screws, and Fasteners

October 25, 2016

Fastener manufacturers use industrious processing methodologies when they coat their products in fine finishes. Obviously, the nuts, screws, and bolts must fulfill their primary design purpose, so the finish cannot interrupt function. It needs to be thin enough to promote the full range of features offered by the product, but it still has to deliver reliable surface protection. In order to fully appreciate the engineering acumen that drives this challenging procedure, we need to look at the different types of finishes and plating processes that can be applied to fasteners.

Zinc Electroplating

A very thin layer of protective zinc is deposited on the fastener's outer surface. At its heart, this is an electrical process, so the fastener gains its plated finish by acting as an electrode in a circuit. Currents flow, the zinc accumulates on the screw, bolt, or nut, and the anodizing current is removed. Electroplating is commonly used to deposit zinc on corrosion-prone objects, but chrome and nickel plating is also available. Plated coatings improve the corrosion resistance characteristics of a target object.

Hot-Dip Galvanizing

A galvanizing bath deposits a thin layer of zinc on the body of the fastener. Heated to its molten state, the 450°C molten metal bonds deeply with the underlying metal to form a hard-to-damage finish. It also deposits as a thicker coating, so it's an ideal product for outdoor applications. Hot-dip galvanized fasteners are robust and very corrosion resistant. They look a little duller than shiny zinc-plated products, but this matte finish is very much sought after when adverse conditions come calling.

Colourful Finishing Techniques

Yellow zinc plating bonds metal to oxygen to create a zinc chromate compound. Highly resistant to saltwater, fasteners in the yellow zinc family are popular in marine applications. Meanwhile, black zinc finishes compete with black oxides for consumer attention. Black oxide is attractive but not a proficient rust fighter, though it does function better when it's oil-coated. Meanwhile, blue phosphate finishes enhance bolts and screws by adding inbuilt lubricity to the mix, all thanks to the elements natural crystalline structure.

Oily and black oxide finishes look good, but their mechanical armoring capabilities are limited. Likewise, the zinc plating on a bolt or screw displays a shiny gloss, but its corrosion resistance rating is middling. For true outdoor mechanical fortitude, a galvanized or properly rated stainless steel fastener is the best choice, but newer coatings are on the horizon. These include fluoroelastomer finishes and other toughened plastic coatings.

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TCI Fasteners - Topcope
13 Slater Parade, Keilor East VIC 3033 Australia

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