In our latest blog, Steve Blunt examines the popular compression spring.
Widely used throughout the industry, compression springs are very popular due to the relatively simple method of production and their excellent static and dynamic properties. As the most commonly used helically wound spring, this blog will look at compression springs.
Just like extension springs, compression springs are stressed in torsion. Just like a torsion bar, when wound helically they can reduce the space taken up. This does limit the materials which can be used due to their ultimate tensile strength.
The stress limit in torsion is 49% of the ultimate tensile strength when an unprestressed compression spring is manufactured from a BS5216 spring steel. The minimum working position (at most) of a compression spring is usually 84% of the total deflection available. To go further than this would result in the coils contacting each other, reducing the effective number of active coils leading to an increasing spring rate. Also, fretting (wear) can happen between the faces of the coils as they make contact.
If there are two or more working positions the free length tolerances are generally not specified as they will be determined by the tolerances on the working loads (unless they are required for assembly purposes).
Compression springs have a number of options for end coil formation, a closed and ground spring will require more manufacturing time than a simple closed or open spring. However, a ground spring will provide more stability as the wire diameter to mean diameter ratio is high, the end formation can be considered as relatively stable.
The end formation of a spring will affect its tendency to buckle which renders the spring useless in most applications. If the end formation has closed coils, this can reduce the number of active coils (those that deflect and contribute to the spring’s rate).
When measuring the number of active coils with a spring, there can be a certain level of uncertainty, thus the British Standard tolerances do not apply to a spring with less than 3.5 total coils.
There are a number of factors to take into account when deciding on the best type of spring to use, these can include anticipated working requirements; its fittings; the wire diameter; the spring diameter and the cost of the end product:
• Throughout the life of the spring it’s important to maintain a force within close limits, if the temperature is to increase the amount of relaxation that will take place should be quantified.
• Any environmental factors that may affect the performance of the spring or the end product must also be factored in. These can include corrosive environments, elevated temperatures, the ability to conduct electricity and magnetic fields which will all affect the choice of material
• When applying tolerances to a spring component it’s best to consult the spring designer/manufacturer as standard drawing tolerances can increase the cost of the component.
Now that you know a little about the production process of a compression spring, please do get in touch if you would like to know more, email us or call 01425 611517.
Next month our Production Manager, Mike Hales will look at ‘the use of conical compression springs’.
Steve Blunt, Director of Quality
Southern Springs & Pressings manufacture a wide range of springs, wire forms, flat strip components and tailor made metal products to meet your needs. We also provide specialist services such as tooling, assembly and design solutions to help deliver your products to market.