In our latest blog Tim Page, our Managing Director, will look at situations that require the manufacture of conical compression springs.
When space is limited, or a spring application requires a non-linear spring rate, a conical spring is recommended for use. When the spring is coiled it creates the non-linear spring rate, once the spring is deflected the coils begin to contact.
As the larger coils move further, they have the lowest spring rate, they will contact sooner. This results in the number of active coils reducing and then increasing the spring rate. A compressed conical spring can also be coiled so the coils lie inside of each other, this will result in the spring having a solid length of one wire diameter. This can be very useful when space is restricted.
Designing a conical compression spring is much more complex than that of parallel sided springs. An approximation of the spring’s behaviour can be sought from the calculations, as small changes in the pitch of the spring can result in large changes in the load/deflection characteristics.
What are the benefits of nested springs?
A nesting spring is one that has one or more springs sitting inside a larger spring. The spring manufacturer can design a spring to achieve more loadbearing material into a fixed space. This will result in the nested spring being able to support a greater load than one spring on its own could withstand.
The working life of the spring can be increased as the working stresses within each nested spring are reduced, the length of the spring can also be reduced by the spring manufacturer resulting in less chance of buckling.
Tangling in operation can occur if the springs adjacent to each other are not coiled in different directions. In situations where high loads and long fatigue life are needed, particularly in a small space, then nested springs are widely used.
Next month our Sales Manager, Jon Davies will look at ‘wire forms’.
In our latest blog Mike Hales, our Production Manager, will look at the benefits of prestressing when manufacturing springs.
Prestressing can increase the load-carrying capability and the spring’s ability to withstand stress ultimately improving the fatigue life of a spring.
Dimensional changes will take place when a spring is prestressed during its manufacture. The process of prestressing a compression spring is relatively simple. The manufacturing process involves the spring being coiled, stress relieved and ground. After this process has taken place, the spring is placed on a press and compressed to a fixed or solid position which is greater than its maximum working position.
Repeating this process at least three times will result in the spring being shorter than the coiled spring, with the correct initial set-up it will be possible to achieve the required final length.
Tension and torsion springs can also utilise prestressing during the spring manufacturing process. When it comes to the manufacture of tension springs, the amount of initial tension is reduced and is therefore not often carried out.
In order to successfully prestress torsion springs, special jigs are required. The leg relationship will change (the number of coils slightly increases).
As prestressing is an additional operation in the manufacture of a spring, this will increase its unit cost. However, the benefits of prestressing during the manufacturing process will generally outweigh the additional cost.
Next month our Managing Director, Tim Page will look at the use of conical compression springs.
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.