Springs

View A Video on Springs - A Quick Introduction

Springs are available in many configurations. Large, thick wire is used to make industrial springs, while thin, bendable wire can make small springs that can be invisible to the naked eye. Many clock spring varieties are examples of small springs. Compression springs, extension springs and torsion springs are all coil springs, or helical springs, meaning they are formed by winding spring wire around a cylinder into helically shaped metal springs, often steel springs or stainless steel springs for specialty applications. Each of these springs performs a very different function. Compression springs, as their name suggests, act as a cushion for a downward acting force; extension springs, also known as tension springs, act in reverse by giving resistance to outward acting forces, elongating when pulled by attached hooks at either side; torsion springs store mechanical energy within a twisted coil and act by exerting a twisting force, or torque. The most common examples of each are compression bed springs, extension springs used to keep screen doors closed and mousetrap torsion springs. Compression, extension and torsion springs are commonly manufactured as miniature springs to be used as precision medical springs in medical devices.

Other springs, such as flat springs and constant force springs, are not fabricated with coiled wire. Flat springs are simple devices constructed of flat strips of metal or plastic that have been tempered with a specific curvature in order to give resistance and shock absorption in simple applications. Flat springs fabricated with multiple layers of tempered metal strips are called leaf springs and are used most commonly in vehicle suspension. Constant force springs are constructed of one long sheet metal strip that has been wound, coiled and then heat treated to retain this coiled shape. Unlike coil and flat springs, constant force springs act as retracting mechanisms, providing even, uniform load through its entire travel length as it is uncoiled and recoiled. Constant force springs can also provide mechanical motion in applications such as clock springs, which must be rewound once the spring length has run out; they are also used in applications such as electric motors, fitness equipment, gardening equipment, toys, medical devices and commercial planes. In general, springs are used for the storing and absorption of energy (as in the case of a suspension system) and the maintaining of tension or force. Other applications include alarms, aviation, circuit breakers, electronics, furniture, hardware, instruments and gauges, office/business machines, solenoid valves and writing instruments.

Spring manufacturers use various metals and types of wire to make their products. While springs can be made from a wide range of metals, cold rolled spring steel is often used to form the wire into springs. Spring steel is a medium carbon steel with high yield strength, known for its excellent elastic properties. It is specifically made for spring fabrication. Music wire is also common. It is inexpensive high-carbon steel that is cold drawn with uniform tensile strength. For applications within the food and beverage, medical or pharmaceutical industries, stainless steel is used because it is non-contaminating, chemically resistant and easy to sterilize because of its smooth surface. Other metals commonly cold rolled to make coil springs and flat springs are copper, bronze, stainless steel, titanium, molybdenum, hastelloy and magnet wire. Although it is unusual, thermoplastics are sometimes used to fabricate springs when they must be quiet and corrosion-resistant. The elasticity of a spring facilitates the return of a piece to its original position; while springs made from properly tempered spring steel may retain their elasticity indefinitely, overextending the springs and heavy use can cause springs to lose recoil after time. Braided wire is used to make springs that can handle sudden significant loads, such as military applications. Wire up to 5/8" in diameter may be cold rolled, while huge, straight bars of steel up to 6" in diameter may be hot rolled and coiled around special machinery to be used as heavy duty shock-absorbers. Lightweight wire commonly used in commercial applications is generally as fine as .01", but micro-coilers can be used to wind wire as fine as .002". While most springs are made from round wire, flat and square wire can also be used to form springs, providing a stronger spring. Tubular stock can be formed into springs as well.

Although springs employ very simple, mechanical principles, their function within equipment and machinery across consumer and manufacturing industries is extensive and nuanced. Springs, such as constant force springs, can provide kinetic energy to other pieces of equipment without any external power source. Compression and leaf springs provide essential shock absorption in suspension transportation applications, while extension and torsion springs provide doors, windows and many types of equipment with necessary resistance. As metalworking and heat treating technologies have improved, spring manufacturing has improved as well, turning out springs with more durable elasticity and greater load resistance. All springs are defined as devices that store potential energy by using an elastic material. The potential energy is at a minimum when the spring is at its relaxed length. Carefully pairing a spring with its intended application will help to ensure the spring's effectiveness and longevity.

Image Provided by HyTech Spring and Machine

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Spring Types

• Belleville washers are flat metal doughnuts whose insides are higher than their outsides. While not a coiled spring, mounting a bunch of belleville washers together forms a very strong spring.
  
• Clock springs, also known as "power," "motor" or "flat coil springs," are made from wide, flat stock and are used in clocks, retractor reels and other machinery. Clock springs are coiled up like the shell of a snail and have the ability to store great amounts of rotational energy.
  
• Coil springs are made by wrapping wire around a cylinder in a helical pattern. Coil springs are the most standard type and shape of spring.
  
• Compression springs are open coiled, helical springs that offer resistance to compressive loading.
  
• Conical compression springs have a cone-shaped design that provides a solid height that is lower than a regular spring. Conical compression springs also provide near constant spring rate.
  
• Constant force springs are a special variety of extension springs that are well-suited for long extensions with no load build-up.
  
• Die springs are a form of compression springs that are engineered to give predetermined pressure at a given compression reliably and consistently.
  
• Extension springs are a closed coiled helical spring that is resistant to a pulling force.
  
• Flat springs include a wide range of springs manufactured from flat strip material which, on being deflected by an external load, will store and then release energy.
  
• Garter springs are either helical extension or compression springs that are typically used in oil seals. The ends of garter springs are connected so that each spring becomes a circle and exerts radial forces.
  
• Gas springs provide controlled motion and speed for elements, such as lids and doors, that open and close. There is normally a gas, such as nitrogen, in the chamber to provide absorption.
  
• Helical springs, also called "spiral springs," are the most common type of spring and can be used in torsion, tension, extension or compression.
• Industrial springs are tools used for the storage or transmission of force in industrial products and processes.
• Leaf springs, also called "semi-elliptical" or "cart springs," have a slender arc-shaped form. Leaf springs are a simple form of spring used mostly in heavy vehicles, such as vans, trucks and railway carriages.
• Metal springs are tools used for the storage and transmission of force; a typical metal spring is composed of some variety of steel wire that has been coiled in a cylindrical configuration.
• Parabolic leaf springs have fewer leaves, the thicknesses of which varies from the center to the ends of the spring, following a parabolic curve. Contact between the coils is made only at the ends and at the center.
  
• Power springs, also called "clock" or "motor springs," store and release rotational energy in the form of torque.
• Small springs are tools used for the storage and transmission of force that are characterized by their small size.
• Spiral springs, also referred to as "spiral torsion" or "brush springs", operate without any contact between the coils.
• Stainless steel springs are tools made of stainless steel that are used for the storage and transmission of force. They are valued for their qualities of strength and corrosion resistance.
• Steel springs encompass the wide spectrum of types of springs made from different varieties of steel.
• Torsion springs exert pressure along a path that is a circular arc, providing torque. The wire itself is twisted when the spring is compressed or stretched.

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Springs Terms

Active Coils - Coils that are free to deflect under load.

Arbor - Also called a "mandrel," it is the round, hardened shaft about which springs are wound.

Closed Ends - Ends of compression springs in which the pitch of the coil ends is reduced to the degree that the end coils touch.

Close-Wound - Referring to the coiling of a spring so that its adjacent coils are touching.

Coil - A round shape formed by a series of concentric circles.

Deflection (F) - Motion of spring ends or arms under the application or removal of an external load (P).

Free Angle - Angle between the arms of a torsion spring when the spring is not loaded.

Free Length (L) - The overall length of a spring in the unloaded position.

Frequency - The lowest inherent rate of free vibration of a spring itself, typically expressed in cycles per second, with ends restrained.

Helix - The spiral form (open or closed) of compression, extension and torsion springs.

Hooke's Law - Load is proportional to displacement. Most springs obey this law.

Hooks - Open loops or ends of extension springs.

Hysteresis - The loss of mechanical energy during the cyclic loading and unloading of a spring.

Lathe - A machine that rotates stock against which other tooling is brought to bear. Lathes are used to wind springs.

Load (P) - The force applied to a spring that causes a deflection (F).

Loops - Coil-like wire shapes at the ends of extension springs that provide for attachment and force application.

Pitch (p) - Also referred to as "coils per inch," it is the distance from center to center of the wire in adjacent active coils.

Rate (R) - Change in load per unit deflection, generally given in pounds per inch (N/mm).

Shot Peening - A cold-working process in which a metal surface is impacted with a high-velocity stream of metal shot or glass beads. Shot peening is used for cleaning or improving resistance to stress corrosion by producing a compressive stress.

Spring Index - Ratio of mean coil diameter (D) to wire diameter (d).

Stress Relieve - To heat treat springs under low temperatures in order to relieve residual stresses.

Torque (M) - A twisting action in torsion springs that tends to produce rotation, equal to the load multiplied by the distance (or moment arm) from the load to the axis of the spring body.

Torsion - A twisting force that can result in shear stresses and strains.

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