The Complete Guide to Square and Rectangular Springs
Rectangular and square springs are types of high-performance helical coil springs fabricated from wire with a rectangular cross-section, rather than the traditional circular wire. They are commonly used in high-load and impact applications. Their versatility extends to industrial machinery, heavy-duty machines, and mechanisms across various industries. Die springs found in industrial tooling, such as stamping presses, are the most widely recognized type of rectangular spring.
They are excellent options for short, high-load, high-travel environments where design space is limited. Additionally, the flat surfaces of the rectangular shape increase the stability of the spring during compression. When thoughtfully designed, rectangular wire springs deliver reliable performance in mechanisms where conventional round-wire springs fall short.
This article will profile the primary performance characteristics of rectangular and square wire springs in comparison to traditional round wire helical coil compression, extension, and torsion springs.
What Makes Square and Rectangular Springs Different?
The primary distinction between common round-wire helical coil springs and rectangular or square wire helical coil springs is the shape of the material that forms the coils. Traditional helical coil springs are formed by round wires that have a circular cross-section, while rectangular or square spring coils are formed by wires with a rectangular cross-section.
Rectangular and square cross sections are common in large structural components, such as beams. The rectangular wire spring incorporates the structural benefits of this shape into helical coil springs, with the primary effect being that it has a larger spring rate and lower stress for the same applied load. The increased cross-sectional area means that the other dimensions and design parameters of the spring, such as the outer diameter, solid height (in compression springs), and total coil count, can be smaller, making the rectangular spring more compact.
The basic idea behind why you would consider a rectangular or square spring for your application can be summarized as “more force in less space”. This also means that choosing square and rectangular springs in some instances may help you reduce the total weight of springs and related components, optimizing your machine design.
Advantages of Square and Rectangular Springs
The large cross-sectional area (compared to comparable circular wire springs) of rectangular or square springs allows them to store more energy per unit of spring deformation, meaning they can accommodate larger forces in a more compact envelope.
It follows that, compared to traditional helical spring coils, rectangular wire springs have larger spring rates for the same coil count, without increasing coil count or solid height. Such a feature is especially valuable in short-travel, high-load systems and space-constrained applications with large cyclic loads.
Furthermore, in rectangular and square compression springs, the large, flat surfaces of the rectangular wire provide a large, stable bearing area, thereby increasing the spring's stability and reducing the risk of buckling failure.
Such characteristics make rectangular or square wire springs the preferred option for high-performance mechanisms such as heavy-duty industrial tools, where rigidity and load-bearing strength are essential. An excellent example of such an application is the Die Spring, a type of Heavy-Duty compression spring found exclusively within industrial stamping and forming tooling and equipment. Rectangular springs operate reliably in the most demanding mechanical operating conditions.
Limitations and Considerations
The corners and flat sections of rectangular and square wires are geometric stress concentrations that may become sites for crack initiation and propagation, reducing the fatigue life of rectangular wire springs compared to circular wire springs. Conversely, the round, uniform profile of traditional helical coil springs does not exhibit such concerns.
To mitigate such concerns, rectangular wire springs require precision manufacturing to ensure that the corners are rounded and the surface finish is smooth. In some cases, it may be possible to round the edge of the rectangular spring. Still, the more material that is removed from the corners, the more you lose the advantage of the increased cross-sectional area of the spring to carry force.
Surface dents, even at the microscopic level, can become stress concentrations that significantly affect the spring’s fatigue life, a crucial property in safety-critical mechanisms, such as those found in aerospace or military equipment. For such applications, especially those involving large cyclic loading magnitudes and frequencies, design and manufacturing engineers must carefully account for such limitations. In part because of this, rectangular and square springs routinely require custom heat treatments.
Such requirements lead to manufacturing challenges, which may increase total production time. Often, custom rectangular wires are required to meet the tight dimensional specifications necessary for such applications. Manufacturing costs for square and rectangular wire springs are typically significantly higher than a comparable round wire spring because rectangular springs usually require custom-ordered raw wire material, which necessitates a custom tooling setup, which can be labor and time-intensive to set up. In general, this translates to long procurement lead times and higher product costs when compared to standard round wire springs.
Applications of Square and Rectangular Springs
At a high level, square and rectangular wire springs are used in high-load assemblies where space is limited and spring stability is crucial.
Rectangular wire springs are commonly used in short-deflection scenarios because they can support high loads under these conditions. Furthermore, the large bearing surface and the spring ends create a stable load path through the spring, making rectangular springs well-suited for dynamic or cyclic loading environments.
For example, rectangular wire springs are commonly found in production tooling (die springs), aerospace actuators, and precision stamping tools, which are systems that must accommodate large forces in a compact footprint. Typical square wire spring applications include fire dampers in HVAC ductwork, commercial roll-up door mechanisms, and mechanized industrial latching systems.
Rectangular springs deliver compact performance, stability, and reliability for such applications.
Design Considerations for Non-Round Wire Springs
Wire Selection and Cross-Section Geometry
When comparing square and rectangular spring cross-sections with round wire spring cross-sections, the differences between the two springs are evident in key performance properties, such as stiffness (or spring rate) and fatigue resistance.
Rectangular springs have larger spring rates than comparable circular wire springs because they have a larger cross-sectional area, allowing them to accommodate more force per unit of deflection. However, this advantage comes with a key trade-off related to the spring’s fatigue life because non-circular profiles have a non-uniform profile at the corners. Sharp-edged rectangular wires can deliver maximum force output but have stress concentrations that can negatively impact the fatigue life of the spring, which is a concern for applications with high-frequency cyclic load profiles.
Rounding the corners of the rectangular wire can improve the spring’s durability by eliminating potential crack initiation sites, but removing too much edge material may negate the structural benefits of the rectangular cross-section. You should carefully assess whether this trade-off can be tolerated for your application. However, in many instances, round and rectangular wire springs are fabricated from custom wire stock, meaning the radii of the edges can be directly specified as needed. This eliminates the need for a separate material removal operation and allows for tighter control of such dimensions.
Solid Height and Spring Rate
The increased cross-sectional area of rectangular and square spring wires translates to a higher spring rate or spring stiffness compared to similar circular wire springs. They also have a relatively small solid height because the increase in stiffness of the spring means they need fewer active coils compared to traditional round wire helical coils.
Because fewer active coils are needed to reach a desired force output, this directly reduces the spring’s total height as well as the fully compressed (or solid) length for compression springs. Because of this, rectangular wire springs are ideal for compact, high-load applications.
Material Considerations
The most common round and rectangular spring materials are music wire and stainless steel. However, because such springs are commonly specified for high-load applications, sometimes a high-strength material is needed. For example, chrome silicon is a common die spring material because it is a high-strength alloy that offers excellent performance even at elevated temperatures, making it suitable for shock or impact loading environments. Similarly, oil-tempered steel is an economical die spring material that offers excellent fatigue and temperature resistance.
There can be challenges associated with cold forming and shaping rectangular wire springs from certain hard materials. For this reason, most rectangular springs undergo a heat treatment process after forming, such as annealing. This process involves slow, controlled heating performed in a furnace, followed by slow cooling in air. Annealing is performed to increase the ductility of the wire spring.
We also offer additional custom rectangle spring materials, as well as various surface finishes, including powder coating, nickel plating, and shot peening.
Please contact us for a custom spring solution if you believe you require a custom rectangular wire spring material or a specific surface finish.
FAQs About Square and Rectangular Springs
What is the advantage of square springs over round springs?
Square (and rectangular) wire springs have a larger cross-sectional area when compared to round wire springs of the same wire diameter. In short, this means the square spring can achieve the same deformation profile with fewer coils when compared to round wire diameter springs. In compression springs, fewer active coils means the spring can have fewer coils and is therefore more compact than standard round wire helical springs.
Are rectangular wire springs stronger than round ones?
Rectangular and square wire springs have a larger cross-sectional area when compared to round helical wire springs. This means that the spring is stiffer, meaning it deforms less under the same loading conditions as a traditional round helical wire spring. Because the deformation is lower for a given load, the rectangular wire springs generally have a longer fatigue life. Additionally, the rectangular wire springs also have a larger maximum load capacity because they can therefore accommodate more deformation.
Therefore, it is correct to say that a rectangular wire spring has a larger maximum permitted displacement and load than a comparable traditional round wire spring.
Where are square and rectangular springs used?
In short, rectangular and square springs are ideal for applications with extremely high loading (static or shock) and limited available space to fit a standard wire coil spring that would be required to withstand such loading. The most common rectangular wire springs are die springs used in production tooling, which are specialized compression springs designed to withstand extreme temperatures, high cycling shock loading, and exposure to corrosive machine fluids. Rectangular wire torsion springs are used in garage or large commercial roll-up door mechanisms because they provide high torque and are far more compact than a typical torsion spring door mechanism.
Can I customize square compression springs for my application?
Yes. Our team of spring design experts is ready to partner with you today to develop a custom square wire compression spring. In addition to custom compression springs, we also offer custom square and rectangular torsion spring design services.
For all spring types, our skilled engineers can assist you through all phases of product development, from initial concept design to final optimization, to create custom solutions tailored to both your spring’s performance requirements and operational environment.
Century Spring: Your Trusted Source for Precision Square and Rectangular Springs
Century Spring is a quality-first manufacturer with decades of experience designing and manufacturing reliable square and rectangular springs for the most demanding applications and industries. As the most trusted name in spring and wire form products, our dedicated technical support teams can show you how to shop for springs by spring rate and can help you calculate spring deflection for your application. We offer design expertise for compression, extension, and torsion springs, as well as recommendations for optimizing load-deflection, corrosion protection, and fatigue resistance tailored to your specific application.
We are ISO 9001-certified and produce high-quality springs that deliver unrivaled performance, engineered to resist common spring failure modes in any application or environment. Our state-of-the-art manufacturing capabilities have positioned us to offer unmatched service to industries that require large volumes of customized spring designs in accelerated development programs.
We offer rapid turnaround, shipping, and delivery on over 40,000+ stock springs available to ship today. In custom spring development programs, we are committed to minimizing the total turnaround time, passing on time savings to you through reduced procurement lead times.
All our springs are always made in the USA.