Tension Springs

Tension springs, also known as extension springs and expansion springs, are typically coiled closely together when at rest and are designed to give a specific pull force when extended to a specific length.

The coils hold an initial tension in order to keep them together and store energy when a force pulls them apart.

As expert heavy duty tension spring manufacturers, our springs operate throughout a whole host of heavy tension spring applications across multiple industries including construction, robotics, lifting equipment, agriculture, elevators and heavy plant machinery as well as speciality equipment.

What are heavy duty tension springs?

Heavy tension springs are tightly wound coils that allow for an outside force to create tension through an end fitting or loop, using this energy to pull components back together when reverting back to their original tension spring shape.

Our division specialises in the heavy tension spring which is the largest of the tension spring range.

As heavy duty extension springs suppliers we design and manufacture heavy duty tension springs UK wide and across the globe for a wealth of diverse industries and applications.

How do tension springs work?

Tension or extension springs are similar to compression springs but with one distinct difference, the load direction is reversed – a tension (pulling) force, instead of a compression (pushing) force, causes the deflection via an end fitting.

The tension spring works as a link or an attachment between two components, drawing them together when another force separates them. An extension spring, for example, would be used on a trampoline to secure the matt to the frame but more significantly provide the energy required through its tension to give the trampoline its bounce. A high rated tension spring would give additional energy and bounce compared to a lower rated tension spring.

Types of extension spring end fittings

Extension springs with hook ends or loops formed from the spring body, with an equal diameter as the spring body, are the most common and cost-effective extension coil spring end design for customers. There are a number of different types of end loops and hooks available as options for expansion springs, as well as a wide range of other mechanical attachment possibilities, including:

Extension Spring With German Loops

Extension Spring With Half Hooks

Extension Spring With English Loop

Extension Spring With Extended Hooks

Extension Spring With Side Hooks

Extension Spring With Side Loops

Extension Spring With Screw Plugs

Extension Spring With Crew Shackles

Extension springs with round-end hook and extension springs with a V-hook are our most popular range but below shows the options available including extension springs with extended eyes, loops and swivel hooks. Each can be applied to suit the application required.

Extension spring manufacturing processes

Our teams are expert extension spring manufacturers offering hot coiling and cold coiling manufacturing capabilities across some of the most advanced spring technologies in the industry.

Our hot coiling facilities can manufacture extension springs up to 65mm wire diameter with our cold coiling starting at 3mm wire diameter.

Advanced CNC coiling and grinding machines deliver quality, accuracy and the best production run rates and efficiencies across an extensive wire range.

In-line shot peening facilities improve a component's shelf life and fatigue performance and large-scale, fully automated powder coat lines offer a zinc phosphate coating option in advance of powder coating, delivering 1000 hours of corrosive salt spray resistance.

Investment in spring technology is crucial and we have recently secured the largest Wafios cold coiling machine in the world, guaranteeing us as leading heavy-duty extension springs suppliers.

Tension spring materials

We hold the largest stock of chrome silicon in the world and work with carbon steels, low and high alloyed steels which enables our engineers to source the right material for the right application and work environment of your tension spring.

When considering industrial tension springs we need to evaluate the tension spring material for chemical composition, surface properties, tensile strength and wire diameter.

Our material scientists are leaders in their field and are on hand to consult with our engineers on the properties of all our metals including:

  • Carbon Spring Steel
  • Chrome Silicon
  • Chrome Vanadium
  • Stainless Steel
  • Nickel Alloys
  • Titanium Alloys
  • Copper Alloys
  • Surface Finish

The Lesjöfors Heavy Springs teams are positioned to consult on the benefits of each extension spring material for the maximum performance of your application. Our processes are adapted according to specific extension spring material needs, including heat treatment, shot peening and pre-setting. Our materials page has more information and advise on surface treatments for corrosion resistance and aesthetics.

How to start designing a tension coil spring

Customer consultation enables us to work out how to calculate spring tension for your product by using a tension spring design calculator. We also analyse what material would work best and if the spring requires loops or hooks.   The maximum initial tension that can be put into a tension spring during manufacturing is limited and therefore it is crucial that we understand the parameters of your extension spring so that we can optimise its use in your product. Our innovative teams deliver exceptional engineering expertise and are solution providers, custom designing your spring to your specifications.

To achieve the best results in developing your tension springs, our engineers ask a number of questions:

  • What are the spring dimensions required?
  • What end fitting is required?
  • What force is required?
  • Can we find the maximum tension of the spring?
  • What is the expected working environment of the expansion spring?
  • What is its expected spring fatigue life?

There are occasions where none of this is known, where customers are not sure of the parameters of their coil spring needs and that’s where our extension spring engineers investigate further, discovering the customer’s tension spring purpose.

Tension spring design often goes through many cycles to guarantee the right design for the right purpose. Designing prototypes that evolve as your product design evolves and manufacturing material samples before full production runs, is all part of the customer care and product service culture we believe in. Our engineers are leaders in their field, ensuring the extension spring performance achieves maximum success.

What are tension springs used for?

Due to the nature of the design of an extension spring, their application is often found in environments where they are needed to absorb energy to create a resistance to a pulling force.

Across the world, many people start their day with a tension spring. They might pull back the curtains using a spring tension curtain rod or access their car via garage door tension springs and if they cycle to where they need to go, bike brake spring tension will get them there safely.

If going to the office, you’re likely to access the building using a door tension spring and sit at your place of work on chair tension springs.

The expansion spring simply says what it does; it expands to a required length and provides a return force to the components it is fitted between.

Used across domestic and industrial applications, our tension springs are installed across every function from garage doors to canopies in football stadiums to heavy plant machinery.

Tension spring FAQs

What is the difference between a compression spring and an extension spring?

As helical coiled springs they might seem similar. However, the big difference is how they absorb force. Compression springs are made to keep components apart and tension springs are designed to keep components together – compression springs absorb force when compressed and an extension spring returns a force when stretched.

How to use tension springs?

Any lever-based mechanism requires a tension spring. Take a look at our section on what are tension springs used for. Garage doors, curtain rods and trampolines are classic examples of how to use a tension spring.

How to install a tension spring?

Once we’ve designed, manufactured and dispatched your product, the install element is individual to need, and we suggest you visit YouTube to discover hands-on applications of tension spring installs.

How to measure a tension spring?

A digital vernier caliper is the most effective tool for this. Start by measuring the outside coil diameter. It is difficult to secure an accurate reading for the inside coil diameter with the caliper because of the hook/loop ends.  

Use the caliper to measure the wire ends in line with the axis and at a 90 degree angle from the axis, and use the average of these two dimensions to secure the wire diameter.

Then measure the free length - the length of the spring inside the loops and the length of the spring body and the length of the overall spring (from the end of the hook/loop to the other).  Find out more about our spring terminology.

How do I order a custom spring?

Speak to our experts on 01726 861444 or email heavysprings@lesjoforsab.com. They will talk you through every step of the process to ensure we maximise your spring application's success.

Do you require a tension spring? Get in touch and discover how we can help you. 

Contact us today

Does your business require a different custom spring?

Lesjöfors Heavy Springs offers a consultancy service to discuss your heavy spring specifications - where our team will assist you with your engineering queries. Explore our Heavy Duty Torsion Spring and Compression Spring pages.

We are world-leading heavy duty spring manufacturers, delivering the greatest expertise in compression, torsion and tension spring manufacturing.

Delivering impact to every industry, we guarantee spring solutions that will optimise your performance and success.

Get in touch
crossmenuplus-circle linkedin facebook pinterest youtube rss twitter instagram facebook-blank rss-blank linkedin-blank pinterest youtube twitter instagram