When a catalogue spring won’t do the job you have in mind
09 March 2018
Industrial springs are often seen as just a component or forming part of a sub assembly.
For the potential user or equipment designer there appears to be a simple choice to start the selection process.
Nick Goss of Goss explains; “there are essentially just two ways for a customer to look for and select the appropriate spring for his job: either he looks in a standard spring catalogue and selects the spring from the catalogue which most closely meets his requirements, if possible. Or, turn to a specialist manufacturer who will offer a complete design advisory service.
Long life expectancy is a must – choice of material crucial
The type of application that the spring is to be used in will determine life expectancy and performance. Generally, Nick Goss, “the more expensive the material we use, the longer the life of the component”. A typical application for a compression spring in an engine valve might involve 8,000 cycles per minute and the best material to guarantee this sort of performance is chrome silicon.
In the extreme environment of the offshore industry Inconel is usually the material of choice. Inconel alloys are oxidation and corrosion resistant and well suited for service in extreme environments. When heated, Inconel forms a thick, stable, oxide layer protecting the surface from further attack.
Must perform, even with extremely low duty cycle
A spring design may be required for an application 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 here a high tensile spring or stainless steel will be selected. To illustrate this case, without putting too fine a point on it, the compression spring deployed in an aircraft ejector seat mechanism has to work, just that one time.
Standard materials are fit for many purposes
However says Nick; “for many standard duties the spring, which is storing energy, is produced from range 3 music wire, or high tensile stainless steel. In operation the material is subject to 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 where instead type 316 should be used.
In the medical industry components are often made from platinum; iridium or gold especially in applications involving sub-cutaneous sites the material must be resistant to the corrosive effects of blood.
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.
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