A guide to security factors affecting fasteners

Jon Lawson

When a manufacturer or design engineer is considering security issues around fasteners, generally there are three aspects: the ability of the fastener to securely do its job and withstand problems such as vandalism; how secure the fastener will be in service (for example, will it seal or retain components and/or fluids?); and how confident they can be in their selection and the supply chain.

These are vital matters addressed by the company Challenge Europe. Within its product portfolio is the Hafren range of security fasteners – a range of anti-vandal, anti-tamper screws and nuts proven in applications from architectural and street furniture, to marine and industrial equipment. Vandal-resistant fasteners such as two-hole headed (otherwise known as pignose or snake eye) A2 stainless screws, bolts and self-tappers provide a versatile and clean look to installations while deterring vandals and keeping installations safe. Likewise, shear-nuts in zinc plated steel, galvanised, A2 and A4 stainless steel. Other important items include six-lobe driven threaded fasteners in A2 stainless steel with centre pin, in self-tapping, machine screw, self-drilling, barrel nut and floor anchor formats. Both countersunk and dome headed types are available.

Regarding security of retention and sealing, Challenge Europe offers impressive performance with Dubo products, which flow into the threads of the bolt and the nut, where they create a particularly effective frictional resistance with the bolt. This prevents rotation of the retaining ring around the bolt, by wrapping around the flats on the nut and thereby effectively prevents the nut from loosening by filling all free spaces, while sealing against leakage. Applications range from use in preventing leakages from transformer oil reservoirs to more demanding roles within the power generating industry and elsewhere.

Because Dubo retaining rings possess plastic-flow characteristics they absorb vibrations arising in the bolt assembly and exhibit excellent sound-deadening properties and durability. Thus they neither deteriorate nor wear and may be re-used without loss of performance.

Dubo retaining rings are chemically resistant to alkalis, to solutions of neutral inorganic salts, also to oils, fats, petrol, benzine, alcohol, acetone, diluted acids and sea water. Consequently, they are able to prevent electrolytic corrosion between two different metal surfaces and prevent fatigue in the bolt material while  insulating and protecting the surfaces.

An addition to the system is the Dubo toothed collar ring, which is intended for use in combination with high quality steel nuts (8.8). The toothed collar ring enables any desired bolt tension without damaging the retaining ring through high bolt and nut loads. This design permits the use of any nut as a locking nut, which can then be re-used. Constraining the retaining ring into this toothed-collar ring ensures that optimum deformation of the ring is obtained after tightening the nut, which provides a secure and long lasting locking and tightening effect according to the Dubo principle.

This high level of product performance is of little value however, unless backed by an experienced team working to BS EN ISO standards – manufacturers’ confidence in their supplier is crucial to the reliable consistent output of any production facility.

A process may additionally include supporting the engineering operation by initiating the supply chain, working from engineering drawings to determine the components/assemblies required. Confidence comes from partnering design and commissioning new component tooling for improved efficiency.

Ultimately, as a concept consultant a fastener supplier can advise on optimal design-for-production (DFP) values at the concept stage and provide specification consultancy with pre-production advice on the handling of components, kits and sub-assemblies. This allows greater confidence in the development process, leading to reliable, high-quality outcomes.

Further along the product lifecycle into enhancement, production engineers will want to look at on-going product improvement – a process that can be made easier by a supplier that can suggest components of alternative materials or how to reduce component counts and shorten assembly times.

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