Extension Springs

Manufacturing Extension Springs

Extension springs can be tailored for various loads, applications, or specific conditions by adjusting the coil size, wire size, or spring length. Typically made from round wire and close-wound with initial tension, these springs present a challenge for customization. Stock manufacturers can deliver large quantities quickly but may lack the customization needed for specific products or applications. Conversely, small custom manufacturers often struggle with turnaround times and consistent quality.

At Ace Wire Spring & Form Co., Inc., we bridge this gap by offering both specialty and stock springs with the design assistance and customization typical of a small shop, along with the quality and fast delivery of a larger company. Our state-of-the-art technology and in-house design expertise, backed by years of manufacturing experience, enable us to produce both small custom runs and large stock runs of extension springs. This is especially valuable in the custom gun springs industry, where precision and reliability are critical. As a certified member of the National Shooting Sports Foundation (NSSF), we are committed to meeting high-quality and industry standards.

Custom Services & Finishes

Take a moment to explore the variety of additional services Ace Wire Spring & Form Co. Inc., can perform on any type of spring or wire form to enhance performance and durability. From heat treatment, deburring, and painting to many more offerings, our secondary services are designed to meet your specific needs. Please include the secondary services you would like to add in the comment section of your request for quote, and our engineers will return an accurate and timely quotation with the added services. Visit our Secondary Services Page to learn more.

To review springs and wire form finishes such as e-coating, zinc plating, passivation, and many more, visit Wire Size and Material Range Page.

Initial Tension & Measuring Rate

Extension Springs are springs which absorb and store energy by offering resistance to a pulling force. Typically, extension springs are made from round wire and are close wound with initial tension. Extension applications include tape cassette players, balance scales, garage doors, washing machines and applications which requiring various types of tensioning devices. Various types of ends are used to attach the extension spring to the source of the force.

Initial Tension of Extension Springs

Most extension springs are wound with initial tension. This is an internal force that holds the coils tightly together. The measure of the initial force and just start coil separation. Unlike a compression spring, which has zero load at zero deflection, an extension spring can have a prelude at zero deflection.

This build-in load, called initial tension, can be varied within limits, decreasing as the spring index increases. There is a range of stress (and, therefore, force) for any spring index that can be held without problems. If the designer needs an extension spring with no initial tension he should design the spring with space between the coils.

Unlike compression springs, extension springs don’t have a solid stop to prevent overloading. Because of this design stress levels are lower for extension springs than for compression. A special type of extension spring is called a Drawbar spring, it has a solid stop and is a type of compression spring with special hooks.

Design & Specifications

It is important to include specifications for extension springs in both spring design as well as in placing an order for extension springs. The following information is designed to provide assistance with building specifications for extension springs.

Length, Maximum, Minimum, (Over all, Over coil, Inside Hooks).
Controlling Diameter: Outside Diameter Max. Inside Diameter Min.
Wire Size. Decimal size if Possible. Material, Kind and Grade.
Number of Coils.
Style of Ends – Right or Left Hand Wound.
Finish (Plain unless otherwise specified).
Load Required, Length Inside Hooks (Length of Coil if wire size not specified).
Maximum Extended Length (Over all, Over coil, Inside Hooks).
Deflection or Distance of Travel.

Frequency of Extension. Is Position of Ends important? (Making the ends of springs bear a definite relation to each other usually adds to the cost of manufacture.)

Note: Extension springs made from tempered or hard-drawn wires can be and usually are wound with initial tension. Such tension may average 20% of the total safe stress of the springs, but will not increase the elastic limit.

Remember that as the space occupied by the machine loop is shortened, the transition radius is reduced and an appreciable stress concentration occurs. This contributes greatly to shortening spring life and premature failure. Most extension spring failures occur in the area of the end. To maximize the life of the extension spring, the path of the wire should be smooth and gradual as it flows into the end. Tool marks and other stress concentrations should be held to a minimum. A minimum bend radius of 1 1/2 times the wire diameter is recommended. In the past, many ends were made as a secondary operation. Today, with modern mechanical and computer controlled machines, many ends can be made as part of the coiling operation. Due to the large variety of machines available for coiling and looping in one operation, it is recommended that the spring manufacturer be consulted before a design is concluded to assist and review extension spring design and specifications.

Extension Springs Design Method Specification

The fundamental formulas involving load/deflection (rate) and stress also apply to helical extension springs. The only unique property is that a solving for and including initial tension in the concept and method. Given a certain volume of space in which the spring will act and a certain maximum load (P) the basic design approach is to find a wire diameter (d) based on trial value of mean diameter (D) assumed on the basis of the available space, and a reasonable stress (S). Remember that an extension spring is not normally present and must be designed within torsion proportional limit of the material. This value will be about 40 percent of the tensile strength of the material. Extension Springs – 4 After a wire size is determined, establish the load deflection relationship and find out if the wire size picked will allow the extension spring to fit in the volume of space available. Involved in this decision is the solution for rate, number of coils and initial tension. The rate is found by the load/deflection relationship. The final step would be to determine whether the available initial tension (Pi), plus the load added by deflecting to L1, will add up to the first load required (P1).

Extension Springs Videos

This video shows how Extension Springs are manufactured.

For more information about extension springs or to talk to one of our experts call 1-800-828-3353.

Manufacturing Extension Springs

Can be made with specialized ends
Can be made from a variety of materials including stainless steel and carbon steel
Up to 5/8″ wire diameter

Ace Advantage

ACE specializes in custom precision springs and wire forms, offering a distinct advantage by utilizing the most advanced spring design software. ACE validates each existing and new design, notifying the customer with our recommendations.