Cylindrical Tension Springs - Tensile coiled metal spring


Pension spring with hook eyelet

Cylindrical tension springs are widely used and versatile components in the world of mechanics and spring technology.
The structure of a cylindrical mainspring consists of a cylindrical wire wound in regular coils around a central axis.

Cylindrical extension springs are characterized by their cylindrical shape and their ability to create a pulling force and create a counter force respectively when lengthened.
Cylindrical tension springs usually have different spring ends, such as eyelets, hooks or plugs. In the case of tension springs, the spring ends can vary depending on the application.

Differences to the compression spring:
The main difference between cylindrical extension springs and compression springs is their reaction to loading. While tension springs are stretched or lengthened under tensile load and generate a tensile force, compression springs work under pressure and generate or absorb a compressive force a pressure load. This distinction is decisive for the respective area of application and the requirements of the application. When manufactured, the compression spring has a coil spacing a(mm) >= 0. While the tension spring has no coil spacing in the as-manufactured state a(mm) = 0.

There are different types of cylindrical extension springs to choose from based on application needs:

Cylindrical tension springs:
The simplest form is the cylindrical tension spring. These have an even coil and generate a linear force-displacement curve along the longitudinal axis of the spring body. They are used in a variety of applications such as industrial machinery, automobiles, home appliances and electronic products.
Cone-shaped tension springs:
Tapered mainsprings are tapered in shape and produce a progressive tensile force that increases as the mainspring lengthens and causes a progressive force-displacement curve along the longitudinal axis of the spring body. Conical tension springs are found in industry, mechanical engineering, medical technology or in special applications, where a progressive spring characteristic under tensile load is important.
Barrel tension springs:
Barrel-shaped tension springs have a barrel-shaped form that allows them to absorb tensile forces. With increasing elongation of the tension spring, the tensile force increases and also causes a progressive force-displacement curve along the longitudinal axis of the spring body. The barrel-shaped tension springs can be found in industry, in mechanical engineering, in medical technology or in special applications, where a progressive spring characteristic under tensile load is important.

extension-spring-tension-spring-round-straight-form-half -German-eyelet

Maintenance spring with half German eyelet

Cylindrical extension springs offer some special features that make them particularly suitable for certain applications:

High spring force:
Cylindrical Tension Springs can generate high spring force, making them ideal for applications where high tensile forces are required.
Long suspension travel:
Cylindrical extension springs can bridge large spring deflections, which makes them ideal for applications where greater spring deflection is to be achieved with an increase in force.
Space-saving design:
Due to their cylindrical, barrel-shaped or conical shape, tension springs can absorb large spring forces and bridge large spring deflections in a relatively small installation space. This is particularly advantageous in applications where the available space is limited.
Clamping force:
Preload force refers to the initial force required to stretch the mainspring and bring it into the loading range. The preload force is the force that the spring receives during manufacture through the special way in which the spring wire is wound. The preload force is critical as it determines the home position of the mainspring and affects its performance.
Spring Ends:
There are different attachment methods for tension springs. The installation space and the application are decisive for the choice of the right fastening method. The spring ends represent the attachment method (suspension) for extension springs. They act as force application points and thus create the connections with the actual spring body. The spring body stores the spring energy or releases the stored spring energy again.

Cylindrical tension springs are used in numerous applications. Their use and possible uses depend on the spring ends of the tension springs selected. The spring ends for extension springs have been specially designed for their attachment and integration with the spring body.

The different shapes of the spring ends of extension springs and their characteristics and uses are as follows:

Half German eyelet [LH ≈ (0.55 ... 0.8) * Di]:
The half German eyelet is a common attachment method for extension springs. It features a semi-circular eyelet attached to one end of the spring. This eyelet allows for easy assembly and provides a secure attachment point for the tension spring.
Whole German eyelet [LH ≈ (0.8 ... 1.1) * Di]:
In contrast to the half German eyelet, the whole German eyelet consists of a whole circular spring coil, which is attached over the entire diameter of the tension spring body. The entire German eyelet offers a large contact surface and thus high stability and resilience.
Double German eyelet [LH ≈ (0.8 ... 1.1) * Di]:
The double German eyelet consists of two whole German eyelets attached to the ends of the mainspring. The double German eyelet offers additional security and durability of the attachment. This ensures very high stability and resilience.
Entire German eyelet raised sideways [LH ≈ 1.0 * Di]:
Whole German eyelet with a raised eyelet on the side is an alternative fastening option or spring end shape for the tension springs. It is often used when space is limited or a specific orientation of the spring is required.
Double German eyelet raised at the side [LH ≈ 1.0 * Di]:
Double German eyelet with side raised eyelet has higher stability and resilience than single whole German eyelet with side raised eyelet. It is often used when there are space constraints or a specific orientation of the spring is required.
Hook eyelet [LH >= 1.5 * Di to approx. 40 * d]:
The hook eye is a simple yet effective method of attaching extension springs. At one end of the spring is a curved hook that can be securely hooked into a suitable bracket.
Hook eyelet raised at the side [LH >= 1.5 * Di to approx. 40 * d]:
This variant of the hook eyelet is raised on the side and allows for attachment options. It is particularly useful when the tension spring needs to be mounted in a specific orientation or especially when space is limited.
English eyelet [LH ≈ 1.1 * Di]:
The English eyelet is a common type of spring attachment for extension springs. It consists of a bent wire loop attached to one end of the tension spring. It offers easy installation and a reliable connection.
Hook rolled up:
In this version, the end of the tension spring is curled into a hook. This allows direct attachment to other components or brackets.
Threaded bolt rolled in:
Instead of a hook, a threaded bolt is rolled into the end of the tension spring with this type of spring end. This enables easy attachment to other components that have the appropriate threads.
Note: Approximately nx (3 to 5) spring coils of the threaded bolt are used in the mainspring for curling, so these coils must not be added to the spring coils when calculating the tension spring.
Thread plug screwed in:
This type of spring end consists of a threaded plug that screws into the end of the mainspring. The number of windings of the threaded plug can vary and serves to provide additional security for the attachment.
Note: Approximately nx (2 to 4) spring coils of the threaded plug are used in the tension spring for screwing in, so that these coils must not be added to the spring coils when calculating the tension spring.

Explanation of the most important parameters and formula symbols for eyelets for tension springs:
Di (mm): Inner diameter of the spring body of the tension spring
LH (mm) = eyelet length approx. LH ≥ 0.5 * Di to 40 * d
m (mm) = eyelet opening approx. m ≥ 2 *d

The selection of the appropriate spring end depends on the specific requirements of the application, such as space limitations, mounting options and load requirements. The variety of spring ends available allows technicians and engineers to choose the optimal mounting solution for their extension springs and ensure a safe and reliable attachment.


Mainspring with half German eyelet

Cylindrical extension springs are an important component in many industrial applications and play a crucial role in various industries. Their ability to generate or store tensile forces makes them extremely versatile.

The various areas of use and applications of cylindrical tension springs:

The automotive industry is one of the main users of extension springs. They are used in vehicles for various purposes such as suspension, chassis system, steering, brakes and clutch. Tension springs ensure precise function and safety in vehicle operation.
Mechanical Engineering:
Cylindrical tension springs are widely used in mechanical engineering. They are used in machines and devices to enable movement, balance loads, dampen vibrations and secure components. Examples are presses, elevators, conveyor belts and machine tools.
Tension springs are also frequently used in the electronics industry. They are used in electronic devices and components, such as switches, relays, contacts and connectors, to ensure electrical contacts and the to ensure function.
Medical technology:
In medical technology, tension springs are essential. They are used in medical devices, instruments and implants. Tension springs contribute to the precise movement and function of medical instruments, surgical devices and prostheses.
Tension springs are used in various areas of construction. They are used in doors, gates, hatches and other moving parts, to allow the opening and closing movements and to ensure proper tension and function.
Household appliances:
Extension springs are also used in household appliances such as washing machines, dishwashers, irons and vacuum cleaners. They enable the movement of flaps, doors and other components, contributing to the reliability and functionality of these devices.
Toys and sports equipment:
Tension springs also play an important role in the toy and sports equipment industries. They find use in toys, skipping ropes, fitness equipment, and other sports and recreational equipment to enable movement and action.

The use of extension springs in these different areas illustrates their importance as a versatile and indispensable elastic component. When selecting and designing extension springs, engineers, technicians and designers should consider the specific requirements of the application, such as material, spring force, Check spring deflection, environmental influences and service life carefully. Precise design, calculation and construction ensure safe and long-lasting operation. This enables optimal usability for the different applications.

extension-spring-tension-spring-round-straight-form-double -German-eyelet

Maintenance spring with double whole German eyelet

When designing cylindrical extension springs, there are several important considerations to ensure optimal spring performance and reliability:

Preload [F0 (N)]:
The preload F0 is the preload force introduced into the spring coil by the winding process. The preload force is the force that is necessary to prevent the spring coils of the spring from being lifted from each other. Adequate preload is important to prepare the spring for the desired travel and to ensure sufficient rebound force.
Eyelet shapes:
The shape of the spring ends, especially in extension springs, plays a crucial role in their functionality, use and assembly. The different eyelet shapes offer a wide range of different options for attachment and thus determine the intended use. The choice of the appropriate eyelet shape depends on the requirements of the application.
Fatigue strength [Tau (N/mm²]):
Extension springs are subject to cyclic loading, so fatigue strength is an important consideration. It is critical to choose a material with high strength and fatigue resistance that can withstand the repeated stresses without losing performance. Correct sizing and design of the spring, taking into account loads and safety factors, is also of great importance.
Vibrational behavior:
The vibration behavior of a tension spring can be important in many applications. Careful design, including selection of wire gauge, number of turns, and spring geometry, can help Minimize unwanted vibrations, resonances or dynamic loads and ensure stable and reliable performance of the spring.
Relaxation refers to the loss of tension or spring force in a metal spring over time at constant strain. This effect occurs due to material fatigue and the adaptation of the metal spring material to the load. At elevated temperatures, the relaxation properties of a spring material can increase, which can lead to a faster loss of tension and spring force. This can be a concern, especially with metal springs that work at high temperatures. The origin of relaxation lies in the material structure and the bonding mechanisms at the atomic level.
Creep refers to the slow and permanent deformation of a spring material under constant load. As temperature increases, a material's tendency to creep increases, which can lead to accelerated deformation and possible loss of resilience. This effect is particularly relevant when spring materials are exposed to high temperatures over a long period of time. It occurs due to the diffusion of atoms in the material, as a result of which the bonds gradually change their position. Creep is favored by high temperatures because atomic mobility increases at elevated temperature.
Hysteresis occurs in spring materials during the loading and unloading phases. It describes the difference in spring force between applying a load and removing that load. At higher temperatures, the elasticity of the spring material can change, which can lead to a change in the hysteresis curve. This can cause the spring force to shift and potentially affect the ability to precisely control the force. It arises due to energy dissipation in the material, for example due to elastic deformation and friction effects. Hysteresis can also be caused by internal stresses and microstructural changes in the material.

By considering these aspects when designing metal springs, optimal performance, durability and reliability can be achieved be guaranteed. It is important to consider the specific requirements of the application, norms and standards, as well as best design practices, to ensure that the springs meet the necessary requirements.

Relaxation, creep and hysteresis are important effects that can occur in spring materials. These effects can be affected by a variety of factors, including operating temperature.

The key differences between these effects lie in their underlying cause and specific usage implications:
Relaxation refers to the loss of tension or springiness over time and can lead to a gradual reduction in strength.
Creep refers to the slow and permanent deformation of a spring material under constant load, resulting in a possible decrease in spring length and spring force.
Hysteresis describes the difference in spring force between loading and unloading and can affect the precise control of spring force.

At elevated temperature, these effects (relaxation, creep, hysteresis) tend to increase because the thermal conditions affect the properties of the spring material. It is therefore important when selecting spring materials to consider the temperature dependent properties and where appropriate Take measures to minimize the effects of relaxation, creep and hysteresis.


Pension spring with hook eye
Condition of manufacture, installation condition, load condition and at maximum load condition

To minimize the effects of relaxation, creep and hysteresis in spring materials, there are several ways that can be applied:

Material selection:
Choosing the right spring material is crucial to achieve the desired properties. There are special spring materials that have a lower exhibit relaxation and creep. For example, high-strength steels or special alloy steels known for their good spring performance can be used.
Heat treatment:
The properties of the spring material can be optimized through targeted heat treatments. Such treatment can reduce relaxation and creep. For example, stress relieving can improve the internal stress state of the material and reduce relaxation.
Spring Construction:
The design of the feather itself can have an impact on the effects. A careful design of the spring geometry, such as choosing the right wire gauge, coil count and spring pitch, can help minimize the effects.
Surface treatment:
A special surface treatment such as coating or finishing the spring material can reduce friction and wear. This can help reduce hysteresis and increase spring life.
Temperature control:
The operating temperature can have a significant impact on the effects. If possible, temperature control can be a way to reduce the effects of relaxation, creep and hysteresis. This can be achieved through the use of heat protection measures or targeted cooling.

Pension springs with different force-displacement curves - three common curve types:

Linear gradient:
With a linear tension spring or a linear force-displacement curve, the spring force increases evenly over the entire spring travel. These tension springs are referred to as cylinder tension springs or cylindrical tension springs. These springs have a constant rate of spring force regardless of the amount of elongation. A linear force-displacement curve is used in many applications where a consistent and predictable spring force is required, such as in mechanical assemblies or tools.
Progressive gradient:
With a progressive tension spring or progressive force-displacement curve, the spring force increases more with increasing spring travel than with a linear curve. This means that the spring force does not increase linearly, but increases more rapidly as the spring deflection expands. This course is achieved by a special wire winding. Progressive springs provide increasing resilience with heavier loads and are often used in applications where increased resilience or increased load capacity is required, such as in industrial machinery or equipment.
Tension springs with a progressive force-displacement curve are, for example, barrel-shaped tension springs.
Declining gradient:
With a degressive tension spring or degressive force-displacement curve, the spring force decreases more with increasing spring travel than with a linear curve. This progression is achieved through a special wire winding or through changes in the spring geometry.
These three curve types are the most common variants for cylindrical tension springs with non-linear force-displacement curves. Choosing the right gradient depends on the specific needs of the application. It is important to carefully analyze the technical requirements and, if necessary, to develop a tailor-made spring in order to achieve the desired force-displacement curve.

In the case of tension springs, the spring wire is mechanically subjected to torsion.
The strength of tension springs is calculated using the analytical torsion equations for wire. Here, the G-modulus is an important material property. In addition, tension springs are usually designed for fatigue strength. Fatigue strength diagrams for torsion of the spring material or spring wire are of crucial importance.

extension springs

Different types of tension springs

Your contact for the production of technical metal springs :
Christian Neumann
Phone: 0212 / 3824187-3