There are so many springs types available that it would be impossible to mention more than just a fraction of these, so here we take a look at three types – disc springs, wave springs and spiral springs – and the applications and industries these are being used in
Springs are available in a diverse variety of types, suiting different applications and industries, many of which require specific certification. In fact there are so many spring varieties available that this article will concentrate on just three: disc springs, wave springs and spiral springs.
Christian Bauer (the parent company of Bauer Springs), for instance, manufactures disc springs as well as customised spring pack assemblies. Disc springs, used singly or in pack form, are unique in the mechanical energy storage capacity they provide after compression for short stroke applications, claims the company. This, it continues, is particularly useful where safety critical conditions require a guaranteed mechanical force to be generated, even in the event of total power failure, typically for the operation of safety valves. Many industries use these reliable sources of stored energy for fail-safe operations.
Recently, Christian Bauer achieved full certification as an approved supplier of these products to the nuclear industry.
There has been an upsurge in interest in nuclear power generation, and component suppliers to this market will need to ensure they have full compliance with the latest specifications that have moved on from those in place for the earlier generations of plant.
As a result, the company’s certifications include ISO 9001:2000 plus KTA 3204 – the German standard covering aspects of manufacturing, quality control, testing and inspection for approved suppliers to the nuclear industry. These are supplemented with KTA 1401 and AVS D 100/50 – a higher certification covering nuclear engineering codes – which can only be achieved when KTA 3204 has been obtained.
Government based legal requirements for suppliers to this industry, these standards have been established to ensure that such suppliers and their personnel have the technology to produce parts of appropriate quality.
The company also supplies disc springs and spring packs which conform to the DIN 2093 specification, as well as other standards and special requirements.
To ensure the quality of its products, however, the company has also developed a comprehensive protocol for the corrosion and crack testing of its products. This approach towards elimination or minimisation of corrosion effects enable the products to be used for arduous or safety critical applications, including offshore oil and gas, aerospace, medical, marine, and in remote installations where a high degree of fit and forget reliability is needed.
As a result, the company instigated a research proposal on its product range – designated as AVIF Proposal Number A210. This covered ‘Investigations on the corrosion behaviour of disc springs and disc spring stacks’, advised by the Spring Association, Subcommittee on Disc Springs, via the University of Darmstadt, Institute for Materials. Systematic results on the behaviour and durability of disc springs under application related corrosive conditions were then determined.
The corrosion testing procedures included: Full immersion experiments without stress; VDA alternating test; Stress crack corrosion experiments with constant stress; Stretch-induced stress crack corrosion experiments; Vibration crack corrosion experiments; and VDA alternating tests with mechanical stress.
Testing protocols were determined for different metals and combined with alternative corrosive media and test procedures to suit the operating conditions and stress factors involved.
When a manufacturer of pipeline recovery tools required springs that would operate in a 700mm bore, provide in excess of 12,000 Newton force, but still be capable of offering over 200mm of travel, within a radial cavity of around 20mm, it turned to TFC for a solution.
As the radial restrain prevented the use of pocketed coil springs or stacked disc spring sets, TFC designed its biggest ever Smalley Crest-to-Crest wave springs to meet requirements. Comprising of over 55 turns and with over 15 waves per turn, the spring was able to provide the necessary load and travel with a free height less than 600mm.
According to the company, its Smalley Crest-to-Crest wave springs can maintain the same force and load specification of round wire coil springs yet occupy 50% or less axial space.
In a more unusual application, the company’s Smalley flat wire wave springs are being used for cushioning in the soles of athletic and casual shoes. Such springs provide an accurate and repeatable load in both the heel and ball of shoes, explains the company. In fact a single Crest-to-Crest wave spring in the heel and two parallel wave springs in the ball of the shoe absorb the impact associated with athletic activities, reducing stress on the joints.
The springs are manufactured in corrosion resistant 17-7 stainess steel and are said to handle the extensive cycle life associated with shoe wear. According to the company, the Smalley wave springs offer accurate, repeatable loads for the duration of the spring life, and will outlast the shoe itself.
William Hughes has added spiral springs to its product offering – spiral springs are a type of torsion spring. The use of profiled or square wire allows high performance parts to be engineered for applications in awkward or confined spaces, with typical applications including in the electrical and automotive industries, such as seat folding mechanisms.
Often soft wire is used for spiral springs which is then hardened and tempered to give the required characteristics. The company, however, is using CNC technology to process spring hard wire into the required shape. The spring is then stress relieved and finished, resulting in a product with better performance characteristics.
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