A small compression spring used in the actuation of an electromechanical switch will be expected to perform faultlessly for thousands of cycles. The compression spring in an aircraft ejector seat mechanism, on the other hand, stored under compression, will be expected to perform once to order.
For many standard duties, a spring produced from range 3 music wire or high tensile stainless steel is perfectly adequate. In operation, the material is subject to various degrees of stress and therefore must be highly tensile.
A spring manufacturer such as Goss has to consider the sheer extremes of the demands on an application, which, in turn, will influence design of the component, the material selected and the manufacturing process.
For instance, a standard stainless steel will operate in conditions of up to 300 degrees Centigrade. However, some grades of stainless steel have restricted environmental operating conditions. The basic ‘music wire’ used for producing springs is, however, available in different grades.
NOT ALWAYS STAINLESS STEEL
Here is a good example of the detailed consideration of the most suitable material that needs to take place, states Goss. “Type 302 stainless should not be used in conditions where acids are present, making it unsuitable for applications processing citrus fruits where, instead, type 316 should be used. Incidentally, this is also suitable for medical applications where contact with blood and tissue may occur or in low salt conditions.”
Components used in the medical industry are often made from platinum; iridium or 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.”
Extreme operational environments put quite different demands on the component. In the offshore industry, for example, Inconel is usually the material of choice, because of the specific properties of Inconel alloys, which render them oxidation- and corrosion-resistant, and so well suited for service in such environments – and which may be subject to pressure and heat. When heated, Inconel forms a thick, stable, oxide layer protecting the surface from further attack.
