Maximising spring life

Nick Goss says: "Material choice is crucial, whilst it is fair to say that the more expensive the 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 8000 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."

Two considerations regarding temperature 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. 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.

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.

Manufacturing processes can help extend spring life. A process known as "shot preening" whereby the surface of the spring is "dimpled" which helps the spring become more resistant to stress. 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 be a factor. 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. 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 you the right advice on spring design to ensure you get the maximum life out of the product.

Go to www.goss-springs.co.uk to learn more.