Five top tips to help in maximising spring life
Nick and Dan Goss share a few tips on maximising spring life, focusing on material choice, temperature, stress and shock considerations, manufacturing processes, and the importance of natural frequency.
There are numerous factors that can impact on spring life, but with over 65 years experience in design and manufacturing industrial springs and press parts, it is fair to say that Goss Springs father and son team Nick and Dan know a thing or two about maximising spring life for their customers.
“Material choice is crucial” says Nick. “Whilst it is fair to say that a more expensive material can equate to longer life and better performance, it does not mean that a customer should always go for the most expensive material possible. The type of application that the spring is to be used in will of course determine life expectancy, performance requirement and, depending on what the life expectancy might be, the type of material used.
“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. The extreme environment of the offshore industry means that Inconel or Phynox is usually the material of choice. Inconel alloys are oxidation and corrosion resistant materials well suited for service in extreme 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.”
With regard to temperature, Dan argues that two considerations should be borne in mind. “On the one hand it is true that in higher temperature applications springs can relax over time as loss in spring load occurs so if possible the operating temperature of the application should be minimised,” he says. “By the same token some applications may call for the spring to have been inoperative for long periods of time and it is essential that storage should take place in reasonable ambient temperature conditions.”
Stress and shock are no good for springs either. “If possible the selection of a larger wire diameter can reduce undesirable stress or using a lower final load will relieve unwanted stress in the spring,” says Nick. Focusing on shock, he adds: “Shock loading occurs when the load is suddenly increased or accelerated. The speed at which the load is dropped onto a spring can cause damage to the spring and so if it is possible to minimise these effects the life of the spring will be increased.
It is not always appreciated that manufacturing processes can help extend life, with shot preening and pre-stressing being two good examples. “With shot preening, the surface of the spring is ‘dimpled’, which helps the spring become more resistant to stress,” explains Dan. “Another process, pre-stressing the spring, increases the elastic limit in the torsion and thus makes the spring stronger and less subject to stress.
Frequency can also be a factor to consider. “If the natural frequency of the spring matches the frequency of the operating speed, it will resonate leading to vibration which ultimately may make the spring break,” says Nick. “So it is important to ensure that the operating frequency of the spring is significantly lower than the natural frequency of the spring.
With such a wealth of experience in designing and manufacturing springs for both standard industrial applications and the most extreme and arduous applications in a wide range of industries from automotive and aerospace through to the military and medical industries the team at Goss are well placed to offer the right advice on spring design to ensure customers get the maximum life out of the product.
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