Highly Engineered Fastener Coatings

Mark C. Thurber

Coating and plating materials should not be taken for granted and must also evolve to meet the increased performance that is required by new applications and markets.

In the past, when the subject of specialized coatings has been discussed, it most often has focused on platings and corrosion preventatives. Today, specialized coatings are asked to address far, far more than corrosion, and need to deliver several specific properties all at once. As industry has evolved into more and more specialized products, the demands made on the corresponding components also requires highly engineered materials to meet new performance needs.

Carbon fiber molded parts have long ago carved out their place in sporting equipment and professional motor racing. The unique lightweight, super-strength character of carbon fiber is hard to beat. Only recently have components of this nature found a place in the mainstream consumer automobile market, led by General Motors and BMW. Naturally, with the pursuit of increased fuel economy and high performance, weight reduction is a highly valued feature. One peculiar, undesired and overlooked property of carbon fiber construction is its ability to conduct electricity, very unlike nearly all other polymer-based items.

Although at first blush, this may seem inconsequential, this characteristic suddenly becomes a very significant game changer when considering galvanic corrosion. In an assembly where the carbon fiber component is used, it may be completing a circuit to multiple other metallic elements, all connected through the, also metallic, fastening site.

Tectorius and Maelstrom Chemical Technologies have addressed this issue directly by offering coating products designed specifically to act as a dielectric barrier for carbon fiber assemblies.

The strength of carbon fibers is nothing short of amazing. However, just like any other molded composite composed of fiberglass, boron or inorganic fillers, it has an unfavorable trait making it impossible to be used for certain specialized applications: particle generation. Any molded composite that utilizes fiber or other filling materials, is prone to shedding microscopic particles protruding from the surface of the molded item.

Generating particles is of little consequence to most applications such as automotive pieces. However, it is a nightmare for clean-room type and sensitive assemblies. For some applications, a stray particle is the equivalent of a semi-truck on the tracks at a railroad crossing—devastating failure is very likely. In other instances, tiny carbon strands released from any carbon-filled composite are conductive, thereby acting as random electrical contact bridges and increasing the occurrences of short circuits where electronic items are being assembled.

Tectorius Tec-Kote™ 7000 is one example of products that are designed to seal composite materials after molding and finishing, to prevent particle generation.

Of course, as one considers the use and assembly of these high tech composite and plastic components, one must always arrive back to the means by which the component will be attached— the fasteners. Certainly, adhesives can be used for many of the attachments, but they also have their shortcomings including fixturing, cure time, nonserviceability and outgassing. Clearly these considerations ensure fasteners remain the backbone of composite component assembly. Still, they often require a little help. More specifically: lubrication.

Naturally, lubricants reduce friction, which diminishes abrasion, and in turn reduces the generation of particles from mating parts. As such, lubricants would seem to be an essential part of the picture to reducing particle generation and perfect a given assembly.

Not so fast! We are not just bolting together some run-ofthe- mill hardware store parts. These are highly engineered, ultra-sensitive components going into everything from aircraft guidance systems to medical devices. One must consider the lubricants themselves very carefully before throwing yet another variable into the program.

Reviewing the obvious compatibility effects the chosen lubricants might have on the composite components and mating parts is not enough. Engineers must ponder the potential fallout that could result from some of their standard lubrication choices. First, the lubricant itself must not produce particles. Many dry film choices contain Teflon™, graphite or other solids, and though microscopic, will dislodge from the fastener surface during installation. In such a case, the lubricant could compound the original problem rather that help resolve it.

Secondly, most lubricants will contain volatile or semivolatile ingredients that will end up as airborne particles collecting on surfaces throughout the cleanroom. Just like the common cold, airborne contamination is far harder to contain than surface particles, this is further multiplied by their tendency to be released over time rather than only once during installation. It takes only one visit to a commercial painting facility to understand that silicone-based lubricants are well known for such airborne contamination.

Technology development has accelerated far beyond what has been seen in prior history, especially in the field of electronics. One cannot expect to take strides in product advances by using the same old material choices that have been available for prior decades. Support materials should not be taken for granted and must also evolve to meet the increased performance that is required by new applications and markets. Www.tectorius.com

Teflon® is a registered trademark of DuPont® Corporation 

Tec-Kote™ is a trademark of Maelstrom Chemical Technologies™

Carbon fiber material for molded parts.

Clip parts coated with Tec-Kote from Maelstrom Chemical Technologies.

Date : 12.12.2016