Recent European Directives and, consequently, national regulations and legislation have put a new emphasis on the importance of fasteners, especially for designers of vehicles and electrical/electronic equipment. Conscientious manufacturers of other products are also adopting similar ‘best practice’ guidelines as part of their corporate social responsibility policies.

The three Directives of most importance are the End of Life Vehicle (ELV) Directive, the Waste Electrical and Electronic Equipment (WEEE) Directive, and the Restriction of the use of certain Hazardous Substances in electrical and electronic equipment (RoHS) Directive.

When the European Commission introduced the ELV Directive the aim was to reduce the amount of waste arising from vehicles (cars and vans) when they are finally scrapped, as end-of-life vehicles currently generate 8–9million tonnes of waste in the Community. For automotive manufacturers and their suppliers, this has resulted in the restricted use of certain hazardous materials and has encouraged vehicles and components to be designed for ease of dismantling. This is similar in many ways to the WEE and RoHS Directives. While the RoHS Directive is concerned with materials of construction, the WEEE Directive encourages a design-for-disassembly philosophy.

With both automotive and electrical/electronic products, there almost an assembly/fastening hierarchy:

• Design-out fasteners. This can be achieved through actions such as redesigning assemblies so they are single components, using moulded snap-fits instead of separate fasteners, and redesigning assemblies so that fewer fasteners hold more parts together. However, although adhesive bonding, welding, heat-staking and similar processes are cost-effective to apply instead of fasteners, they usually make disassembly and recycling more difficult.
• Use removable fasteners. Clips are easiest to remove, followed by threaded fasteners. Rivets are more problematic, and threaded inserts can be hard to remove from plastics.
• Commonise screw heads. The smaller the number of screwdriver types and sizes required to disassemble a product, the quicker and easier the task becomes.
• Consider materials and finishes. If a product is covered by the RoHS or ELV Directives, there are restrictions on the materials that can be used for fasteners and their finishes.

Lead is restricted by both the ELV and RoHS Directives. Nevertheless, small amounts are permitted as alloying elements in steel and brasses, as it is recognised that lead plays a significant role in the machinability of these metals. Lead is exempted from the RoHS Directive as follows: as an alloying element in steel containing up to 0.35percent lead by weight, aluminium containing up to 0.4percent lead by weight and as a copper alloy containing up to 4percent lead by weight. Harwin, for example, is promoting its nickel-plated brass spacers as being RoHS-compliant, with only 3percent lead content in the grade of free-machining brass used (Fig.1).

Depending on the mechanical and electrical properties required from the spacers, it should be borne in mind that replacing the metal components with plastic alternatives – such as the nylon 6/6 Metric Hex and Hex Tapped spacers from Micro Plastics International – can bring additional benefits such as reduced weight and the ability to colour-code (Fig.2). For more demanding applications, plastic fasteners are also available from some manufacturers in a wide range of engineering polymers – including Isoplast, Peek, and Ultem – that offer outstanding mechanical strength, thermal stability and chemical resistance. Of course, plastics are not immune from RoHS concerns, as this Directive restricts the use of polybrominated biphenyl (PBB), polybrominated diphenyl ether (PBDE), pentabromodiphenyl ether (PentaBDE), and octabromodiphenyl ether (OctaBDE), all of which are flame retardants.

If metal fasteners have to be used because they cannot be designed out of assemblies, their material and finish have to be considered. One of the most popular finishes prior to the recent Directives was zinc plating with a hexavalent chrome passivation. However, the use of hexavalent chrome is now banned. One option is to specify stainless steel instead of plated steel, though this has cost implications. An alternative is to source fasteners from a supplier that can offer a RoHS-compliant plating such as zinc plating with trivalent chromium passivation (Fig.3).