Adam Binding of Lee Spring considers the use of springs

Surely all springs are the same aren’t they?
Not really. There are many different types, each designed to suit specific applications. The most common types are compression, extension and torsion springs or derivatives of these such as die springs and instrument springs. Other forms include Belleville spring washers, also known as disc springs,  constant force springs plus battery, wave, conical, swivel  hook and drawbar springs.

Is there some kind of standard calculation formula that a designer can use if they know what mass or weight they have to move from A to B, and in what time and at what rate?
Yes, spring theory is normally developed on the basis of spring rate or load and the formula for this is the most widely used in spring design. Other formulas exist to determine spring index, stress correction factor and shear stress. The formula for spring rate is:

S ₌ ?F ₌ Gd ⁴

      ?L   8nD ³

 Do you sell more of the springs that are used for pulling things together, or pushing things apart?
Push type (compression) springs are the most widely sold type of springs, followed closely by extension and torsion spring types.

How many ‘generic’ families of spring types are there in existence?
As mentioned earlier mainly there are three kinds – compression, extension, torsion and each one can have different configurations. Other types include wave spring, constant force spring, clock spring, drawbar spring, garter spring, spring washers.

What material choices are there for designers?
A very wide variety is available to suit most applications. The list includes music wire, stainless steel (different types), carbon steel, phosphor bronze, beryllium copper, gold, Nitinol wire and alloys such as Monel, Hastelloy, Inconel, Elgiloy, Waspalloy and Nichrome.

What is the best spring material for corrosion resistance?
It depends on the application. Stainless steel is better than carbon steel for corrosion resistance.

What is the best spring material type for applications in very low temperatures?
There are different grades of alloy steels available for very low temperature applications. Steel types A201 and T-1 can operate at -45°C while nickel steels with 2.25% Ni can go down to -59°C and with 3.5% Ni extending to -101°C. The only alloy steel recommended for cryogenic use is 9% nickel steel which has a service temperature of -195°C and is used for transport and storage of cryogenics because of its low cost and ease of fabrication.

What is the best spring material type for high temperature applications?
Again different grades of alloy steels are available to suit high temperature applications. Inconel is very widely used as are Nimonic and Elgiloy alloys and tungsten tool steels.

Does the integrity of a spring deteriorate with usage or time? If so, can this be calculated at the design stage?
Yes in certain circumstances. Correct stress calculations can minimise the problem. This deterioration is called ‘creep’. A spring can deteriorate slightly under creep (either time or load). It depends on the design stresses. If the stresses are low and well within the limits, the creep would be negligible.

Are there any key performance issues that spring uses should bear in mind?
Spring failures are rare but these can occur in the ends of extension springs which absorb and store energy by offering resistance to a pulling force. To maximise the life of this type of spring the path of the wire should be smooth and gradual as it flows in to the end. A minimum bend radius of 1.5 times the wire diameter is recommended. Designing the correct leg configurations and loadings on torsion springs can also be a source of frustration for users. We recommend checking with a specialist to ensure product service life requirements are met.

Tell us about some of the more unusual applications that you have been involved with.Some that spring to mind include: ultimate quality roulette wheel mechanisms, tray dispenser systems for use in airport security systems, a very demanding high performance application in a Yamaha clutch and ejector seat mechanisms for use in ‘life or death’ situations.

How big are the biggest springs you can supply? And the smallest?
We go up to 16mm (0.625ins) wire diameter and down to 1.45mm (0.57ins) on standard products. However using micro coiling techniques it is possible to produce springs from wire no thicker than a human hair.

In your experience, do most engineers fully understand ‘spring technology’?
Usually, engineers understand spring technology with some help in the form of tutorial/manual. We offer an engineers’ guide which discusses all the elements involved in designing and specifying compression, extension and torsion springs.

Do you offer any assistance to engineers who might need advice or is it a case of “Find it on our website”?
Yes, we do offer assistance to engineers: by phone, email and of course via our website. Most spring companies, including ours, have dedicated engineering specialists on hand to respond to technical enquiries.

Does the industry as a whole have ‘minimum order quantities’?
Most do on stock spring selections but not on custom spring orders.

What about prototyping, or the production of specials? Do you get involved with these?We have always offered prototyping services to help customers with spring design through to production. Any spring manufacturer will require a drawing, cad file, a sample or a technical specification to create a custom design. Performance, operational and environmental conditions are essential. Most reputable manufacturers use cad systems to generate and present custom spring designs to customers.

To return to the media centre, click here