While the mechanical spring is a component of simplistic beauty, they’re also one of the most efficient methods of storing low-level mechanical energy. But there is also more variants to this basic design than most people realize.
With so many different types of springs available on the market, there is a need for a formal means of classification which includes a set of terminology used to depict specific models and designs. Within this guide, we look at some of the key ways in which springs are cataloged and as such, some of the defining features of the mechanical spring.
Common Types of Springs
The simplest place to begin is the actual form that the spring takes. As a flexible structure which stores and releases mechanical energy, coil springs are the most commonly used in everyday life, with the compression spring and the tension (or extension) spring the inverse structure to this.
These springs are typically formed so that they have the same diameter throughout the length of their coil. However, conical, concave (in the shape of an hourglass) and convex (a barrel shape) forms are also widely available.
Other popular spring forms include:
- torsion spring
- constant force spring
- Belleville washers
- clip springs
All of these are unique to each other in the way in which their structure handles the return force stored within its design both in the direction and the speed of release.
A final major difference commonly used to differentiate types of springs is the way in which they are crafted. They can either be wire-wound or machined, which provides certain additional qualities by machining the structure. This comes at an increased cost due to the extra work and equipment required to produce them.
Structural Deviations
Aside from the standardized coil structures, compression springs, in particular, can also be created in alternative shapes and forms. While the volute spring (conical) allows use within narrower and tighter confines due to its ability to compress into the width of a single coil of wire, the square and rectangular based springs are chiefly used to provide additional strength and compactness in operation, as well as preventing the spring from slipping or to allow it to fit into a bespoke space.
This square spring, of course, refers to the cross section of the coil that can be shaped from oval to any conceivable shapes and does not refer to the square finishing. While many types of springs come with a connector, hook or some other form of fastening the spring in place, many are used without this. The finishing process itself is when just a simple spring is required without an attachment and this has an effect on the physical appearance of the spring, as the ends can be shaped to better fit a need and comes in four main styles:
- Plain end
- Plain and ground
- Squared end
- Squared and ground
Another increasingly popular choice is to incorporate waves into the design. This reduces the total length of a traditional compression spring whilst delivering an equal amount of force and deflection.
A Matter of the Physical
The diameter and actual shape of the wire used to create the coil is also a factor to consider. Although shaped wire is a more expensive option, they offer additional strength and durability because of the increase in material density compared to a similar round wire design.
The material that the wire is composed of is perhaps one of the biggest single factors in the performance of the spring. Although typically made from steel alloys, springs can also be manufactured from other metals such as:
- Aluminium
- Titanium
- Rubbers and plastics
- Carbon
- Other materials that can be shaped without creating residual stresses in its structure
Coatings are another consideration when choosing a suitable material, as this too can have a desirable effect on performance. Whether it’s to make the spring conduct electricity, magnetic, or less corrosive and protected against the environment it will be employed in. A coating will also have an effect on the final capabilities of the spring and so needs to be carefully incorporated into the design process.
The Heart of the Performance
The coatings also can be used to make a direct impact on the output of the spring, using shot peening to add extra durability and resistance to fatigue in the design, oiled finishes which reduce frictional forces, or powder coatings to add abrasive qualities.
While the size and load of the spring are usually the first requirements needed to plan a design, there are categories within this to specify the spring by type. Whether a compression spring is anywhere between bantam to a heavy duty die spring, the spring rate or total load is only one factor to consider with the end output.
The difference between the free length (without any load applied to it) and the solid height (at maximum capacity) can easily be calculated and tweaked while the initial tension, the number of active coils and the coil angle – often measured as a pitch which is the height between coils in the free length – are both also easily modified to produce a product that fits your purpose.
Identification of Types of Springs
While many people only view spring identification as a colour-coding process between different products to visually establish which is which, there is more to spring identification than this.
All OEM’s will have individual ident numbers for any and all parts that they manufacture, including springs, which are used within their equipment. This is to ensure the highest level of consistency with their products at all stages of its lifecycle, meaning that parts can be swapped and replaced whilst retaining the originally intended output.
As there is no clear industry standard for this process, all individual manufacturers have their own classification system which can be sourced but they do not align with each other as such.
While high-quality spring manufacturers having access to this with the OEM’s permission, they can also create new designs to meet specific, bespoke stipulations and so with enough information, they could, in theory, produce exactly the same spring from a list of criteria rather than a set of blueprints.
With identification codes playing an important part in continuity and consistency, however, it is highly advisable to buy any replacement parts either through the OEM or a registered and approved supplier of that company.
With the integrity of the equipment at stake, it’s always wise to use the equipment as intended to produce the best possible results and this applies to maintenance of the equipment as much as anything else.
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