Seeking and selecting a spring
09 May 2016
There are several ways a customer can seek and select a spring.
Browse the plethora of standard spring catalogues for a close match, or seek out a supplier who is prepared to offer a complete design advisory service whether it is for the design of a new component or even optimising an existing design.
One such supplier is Goss Springs and its press and multi-slide tooling subsidiary, PMT who have built a reputation for their design and manufacturing expertise. So, what are the key criteria for spring selection?
The type of application in which a spring is to be used will set the criteria for life expectancy, mechanical performance and, the type of material used. According to managing director, Nick Goss, as a general rule of thumb, the more expensive the material used, the longer the life of the component. A typical application for a compression spring in an engine valve, for example, might involve 8,000 cycles per minute and the best material to guarantee this sort of performance is chrome silicon.
The extreme environment of the offshore industry means that Inconel is usually the material of choice. Inconel alloys are oxidation and corrosion resistant materials well suited for service in extreme environments that may also be subject to pressures and temperatures. When heated, Inconel forms a thick, stable, oxide layer protecting the surface from further attack.
Goss Springs is also well qualified to develop a suitable design, and select the appropriate material and manufacturing process for a spring which might not be in use constantly, but must be ready to work when called upon. There are many applications where the spring will be held and stored for long periods of time, usually in a compressed state and in such cases a high tensile spring or one made from stainless steel will be selected.
Standard materials are fit for many purposes
For many standard duties the spring, which basically acts to store energy, is produced from range three music wire, or high tensile stainless steel. In operation the material is subject to various degrees of stress and therefore must be highly tensile.
A standard stainless steel will operate in conditions of up to 300°C. Some grades of stainless steel have, however, restricted environmental operating conditions. The basic ‘music wire’ used for producing springs is available in different grades: type 302 stainless should not be used in conditions where acids are present and is thus unsuitable for applications processing citrus fruits; type 316 should be used instead – which, incidentally, is also suitable for operations where contact with blood may occur or in low salt conditions.
Indeed, components used in the medical industry will often be made from platinum or iridium - gold may also be used. A readily worked alloy, platinum–iridium is much harder, stiffer, and more resistant to chemicals than pure platinum, which is relatively soft. Platinum–iridium is also very resistant to high-temperature electric sparks and is widely used for electrical contacts.
However, it’s not all to do with highly specialised alloys and complex designs. Goss Springs is equally at home developing high volume, simple components for every-day products. Basic compression springs are made in their thousands - for example, to be used as positional devices in oil and water filters where they retain the position of filter components.
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