What are technical springs? Fundamentals, history & applications of spring manufacturing
Technical springs are elastic objects usually made of metals (typically steel) which are capable of stretching out by applying a certain force, then returning to their natural form. By changing their shape, technical springs can accumulate mechanical energy. Springs may also be used to connect different elements.
Probably the best known types of springs are coil springs such as the helical ballpoint pen springs wound from thin wire and the much bigger suspension springs in vehicles and railway carriages. Due to their shape and their design for pressure loading, these springs are called helical compression springs. Helical extension springs, on the other hand, are designed for tensile load. A well-known application can be found in trampolines where helical extension springs connect the jumping surface with the trampoline frame. When someone jumps on the jumping surface, these springs are pulled apart. Simultaneously, force is exerted which makes them want to go back to their original length, thus giving the jumping person the force to fly up into the air.
When helical springs are compressed or stretched, they exert an opposing force which is – within a certain range – proportional to their change in length. The relation between the load (force) and the deformation is described by their spring characteristic curve.
Another type of coil springs are torsion springs which, e.g., are used for clothespins.
Besides coil springs there are many other types of springs, for example spiral torsion springs which are inserted in alarm clocks, volute springs which, e.g., can be found in pruning shears, flat form springs which act in electric switches and leaf springs which are part of the suspension system of delivery vans and trucks. Spring washers, which have the shape of a saucer, are used to apply a constant tensile force on a screw connection. Also bent or stamped metallic parts can be designed to act as springs.
Moreover, there are non-metallic springs, for example rubber bands which act like tension springs, and gas or fluid springs which use compressed gas (or fluid) contained within an enclosed cylinder.
History of technical springs
Simple springs were used throughout human history, for example in bow and arrow devices. In early phases of the history dress fibulas made of bronze were used to close upper garments. These fibulas can be seen as the forerunners of safety pins. In the late Middle Ages coiled springs were used for door locks, and clocks powered by spiral springs appeared. Last but not least springs played – and play – a decisive role in firearms.
In 1676 the British physicist Robert Hooke defined a physical law which later was named after him: Hooke’s law. It states that the force a spring exerts is proportional to its extension. Coil springs correspond to this law. There are, however, also other types of springs which generate forces that vary non-linearly with displacement.
Spring manufacturing process
Different kinds of machines are used to form metallic springs such as spring coilers, spring formers or bending machines using a complicated interaction of wire and tool movements. A spring former is a very versatile machine. It has several tooling slides enabling it to perform bends, loops, hooks, radius and various wire shapes on the ends of the springs or on the wire form. Today, many spring manufacturing machines work electronically controlled.
Depending on the wire diameter, the shape-forming process is carried out or at elevated temperatures or at room temperature and one speaks of “hot forming” or “cold forming”. After the forming process, springs normally are heat treated to hold their elastic shape and can be subjected to a surface treament in order to get enhanced physical properties.
Springs and their applications
Technical springs including coil springs, torsion springs, disc springs and spiral springs are used in the automotive industry, mechanical engineering, the electrical industry, solar and wind energy technology, measurement technology, building technology, optics, office equipment, furniture and upholstery industry, watch industry, toy industry and in the fittings industry. About half of all produced springs are installed in motor vehicles. A modern passenger car, for example, contains several 1,000 springs.
Manfred Meissner, Hans-Jürgen Schorcht, Ulf Kletzin: Metallfedern. Grundlagen, Werkstoffe, Berechnung, Gestaltung und Rechnereinsatz (Metallic springs. Basics, materials, calculation, design and use of computers; in German). Springer Verlag Berlin, Heidelberg, 3rd ed. 2015.
Print ISBN: 978-3-642-39122-4
Electronic ISBN: 978-3-642-39123-1
Neil Sclater: Mechanisms and Mechanical Devices Sourcebook. Chapter 11: Spring and screw devices and mechanisms. New York, McGraw Hill, 5th ed. 2011.
Print ISBN 978-0-07-170441-0
Electronic ISBN: 978-0-07-170442-7
Manfred Meissner, Friedhelm Fischer, Klaus Wanke, Manfred Plitzko: Die Geschichte der Metallfedern und der Federntechnik in Deutschland (The history of metallic springs and of springs technology in Germany; in German). TU Ilmenau Universitätsbibliothek, Ilmenau, 2009.
Print ISBN 978-3-939473-64-0
Robert O. Parmley: Illustrated Sourcebook of Mechanical Components. Section 16: Springs: Drawings, designs and discussion of various springs and spring mechanisms. New York: McGraw Hill, 2004. ISBN 0071436871
The information has been compiled by Dipl.-Ing. Konrad Dengler, technical journalist and translator specialised in industrial topics.