In praise of mechanical fasteners

Tom Shelley hears the case for mechanical fasteners as the joining method of choice to speed assembly and aid recycling

In the words of Barry Tibble, sales director of TFC (formerly The Fastener Centre): "People will always have to hold things together. The majority of the parts we sell are geared to ease and speed of assembly and a lowering of in-place costs. Although we do offer conventional threaded products, our carbon spring steel and injection moulded ranges of fasteners very often offer faster and easier assembly. “Fasteners continue to change as the materials to be joined change. Innovation is constantly required and there is now a phenomenal range of fasteners available - our portfolio now includes around 100,000 line items. Manufacturers encounter specific assembly problems and it is up to people like us to come up with solutions." Typical of recent developments introduced by TFC are the Scrivet, a nylon device with a screw that can be pushed in to fasten but unscrewed to unfasten in the traditional way, steel and plastic clips that can also support pipes and cables, and the nylon breakstem rivet. The latter is used to secure plastic to a fibrous material in Vauxhall cars. The sides open out like butterfly wings, except it has three of them, and Mr. Tibble says the devices can also be used to join acrylic components without cracking. Unlike adhesives, which he describes as "not kind to a manufacturing environment", fasteners inserted in holes automatically locate parts together in space and allow very immediate joining. And, compared with both adhesives and welding or brazing, they also allow assemblies to be easily disassembled. This is no small matter in the light of regulations on vehicle disposal due to come into force in 2003, when manufacturers will become responsible for end of life disposal and recycling. TFC is expanding its business at an annual rate of about 15%, although it has had to broaden its range to do this. One area into which it has expanded is 'crest to crest' or sinusoidal wave wound springs made from flat wire. Technical director Brian Goode explains that these are, "primarily to apply pre-loads" in minimal space, as an alternative to disc springs. And speaking of springs and fasteners generally, he adds: "We are often the last port of call, but we prefer to work with the designer from the beginning." The company has two design engineers who, in Mr Tibble’s words, “often get involved in the design and development of new products as well as looking for sources". It seems customers often need technical support above and beyond the information contained in a catalogue. Examples include ‘crest to crest springs for a range from devices a few mm across developed to fit on the drive shaft of a refrigeration pump for a cold drinks dispenser through to devices for car steering columns and on to a 600mm diameter bearing retainer for a steel mill. Designs are available with different numbers of crests or flat top and bottom elements for even force distribution. And all are part of a deliberate process of enabling "customers to rationalise their supply base by needing only to go to one vendor". TFC Brian Goode