Fasteners are the engineering world’s equivalent of drummers in a band. They are not glamorous, but many everyday products would simply fall apart without them.
There are many ways of fastening components together, perhaps the most familiar being that used on cars, where mechanical methods hold just about all the non-welded parts in place. Audi’s A4 and A5 models, for example, feature a bonnet latch fastened to the bodywork by Profil’s RSN and RND rivet nuts.
These are fully encapsulated in 30 per cent glass-reinforced Polyamide 6 to form an integral part of each vehicle’s impact crumple zone as part of the installation process, and are designed to provide high-strength fastening. The manufacturers claim they are suitable for use with up to 1,200MPa high-strength steels.
The latches are considered to be a ‘safety critical’ part of the structure, and require high-integrity fastening, as the prospect of the bonnet opening at high speed on a motorway is not an option.
Latches are also fitted on racing cars for the speedy removal of panels and parts when in the pits. Radical Sportscars uses Protex fasteners, especially the company’s over-centre latches, to secure body panels on its range of high-performance track cars.
These latches sit flush to the body, which is essential for the car’s aerodynamics, and offer positive panel location together with a simple locking action designed to be easily operated by hand.
The fasteners are used to secure the car’s nose, centre section and rear bodywork, ensuring rigid retention of the composite moulded panels under high aerodynamic and cornering loads.
Torsion springs, either single or paired where higher forces are required, are also used in many places within cars to ensure components stay in place.
William Hughes, for example, custom manufactures torsion springs for a car’s centre console, glove box, cup holders, grab handles, sun visors and door mechanisms.
When involved in the development of a special torsion spring to release an armrest catch on a car’s central console, the company was asked to come up with a mechanism that had to be designed to slow the movement of the console to make it open gently and to ‘feel right’.
The design the company came up with was derived at using CAD software and specialised spring data, and incorporated a custom-designed and optimised single torsion spring to ensure the unit could be assembled quickly and easily. The design was finalised for volume production after prototyping — an example of where an enormous amount of expertise is used for what most would consider one of the simplest pieces of engineering in the vehicle.
Aircraft also require fasteners of all sorts in large numbers. TFC supplies several aircraft manufacturers with Smalley Crest to Crest wave springs and retaining rings to secure aircraft passenger service units, preloading the lighting, heating and to hold in place air-conditioning elements above passenger seats.
The springs’ reduced dimensions enable the lighting mechanism to be designed with a smaller footprint and offer a greater degree of movement, allowing the light to be more accurately focused by passengers. This has led to their use in the heating and air-conditioning systems on aircraft such as the A380 Airbus and private passenger jets.
But fasteners are not restricted to use in cars and aircraft. Alcoa Fastening Systems is supplying a fastener developed from experience gained in the Mojave Desert, California for the construction of a major solar power plant in Egypt.
The power generation process at the Kuryamat plant, due for completion next year, uses solar panels — in the form of U-shaped parabolic glass mirrors — to track the sun from east to west.
Alcoa’s C50L30 Huck fastener is being used to fasten the platform holding the mirror structure in place so that it holds fast in this extreme environment where the temperatures can vary between 45ºC in the day and -30ºC at night.
Dean Bradley, Alcoa’s sales manager for the region, said: ‘Because of the extreme weather conditions during construction and operation, where the mirrors invert to protect the glass during winter sand storms, as well as radical variations in temperature threatening thermal loosening of the fastener, our aim was to assure the joint’s integrity.
He calimed: ‘Consequently, the solution we are providing through a combined European team effort will be quick and easy to install, require no maintenance and meet the 30-year warranty as specified in the original design.’
Another extreme application features the use of special tension control fasteners on heat exchangers at Poland-based petrochemical giant PKN Orlen. The fasteners, made by James Walker Rotabolt, are designed to secure components in situations where pressure, vibration and fatigue could lead to failure if bolted joints were employed.
The heat exchangers at the company’s ZA Pulawy plant in Poland are in its ammonia plant, where the fasteners are used both on heat exchanger systems as well as on high-integrity flanges. Before the introduction of the Rotabolt tension control systems there were problems with bolt failure, causing shutdowns at the melamine plant. Since the installation of the new system, it has been running at full capacity without any shutdowns.
As well as application at PKN Orlen, the technology has also been applied on three of the main flanges at Poland’s Siekierki combined heat and power plant and the world’s largest steel producer is scheduled to fit Rotabolt technology at four of its Polish plants during this year.
Components used in cars, aircraft and a solar power plant in Egypt could benefit from a wide range of next-generation latches and fasteners. Colin Carter reports.