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About Coil Springs

Coil springs are made utilizing a helical coil winding shape. This is the primary design of most springs. Typically, coil springs are formed as a constant diameter cylinder. Coil springs can be cold-coiled or hot-coiled. Cold-coiling is the process in which helical winding of the material takes place at a low temperature after the spring has already been hardened and tempered. Material that is under 3/8” in diameter is generally cold-coiled. Bar stock that is over 5/8” is hot coiled. Hot coiling is the process in which the spring is wound at or above the recrystallization temperature of the bar stock. Material with a diameter from three- to five-eights inch can be either hot- or cold-coiled.

The majority of the cost of coil springs lies in the material used. Most coil springs are made from bars of carbon or alloy steel. Coil springs that are used in applications in which they will be subjected to corrosive environments with elevated temperatures are made from exotic alloys, such as precipitation hardening stainless steels and tungsten bearing tool steels. Coil springs can be coated with cadmium or zinc plating to protect, for example, against pitting caused by rust. Coil springs also typically undergo shot peening to increase work hardness. However, if a coil spring is hardened too much, it can shatter under a constant load.

The chief types of coil springs are torsion, extension and compression. A torsion coil spring is made to provide force or torque in a desired application. An extension coil spring is created to resist pulling or extension. The purpose of a compression spring is to withstand pressure or load. Coil springs in general are used for the storing and absorption of energy and the maintaining of tension or force. Coil springs are utilized mostly in the transportation industry, as well as by agricultural implement manufacturers and construction equipment builders. Other applications include railways, control and safety valves, excavating and earthmoving equipment, heat exchangers, turbines and cranes.

To order coil springs it is necessary to know the free length and the maximum and minimum lengths, as well as the controlling diameter, including the outside maximum and the inside minimum diameters. Also determine the number of coils needed and the wire size and material (including kind and grade). What are the loads at deflected positions? Should the spring be right- or left-hand wound and what style do the ends need to be? Other specifications include the finish, maximum solid length and frequency of the coil.

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Image Provided by Patrick Manufacturing, Inc.

Types

• Belleville washers are flat metal doughnuts whose insides are higher than the 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.
  
• Cold-coiled springs are generally made from material with a diameter of less than 3/8”.
  
• 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 closed coiled helical springs that are 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.
  
• Hot-coiled springs are made from material that is over 5/8” in diameter. Hot-coiled springs are typically wound to a length greater than the necessary finished length, treated with heat and then compressed to a solid at least one time in order to bring them to the required length.
  
• Leaf springs, also called “semi-elliptical” or “cart springs,” have a slender arc-shaped form. Leaf springs are a simple form of spring that is used mostly in heavy vehicles, such as vans, trucks and railway carriages.
  
• Parabolic leaf springs have fewer leaves whose thicknesses vary 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.
  
• Spiral springs, also referred to as “spiral torsion” or “brush springs,” operate without any contact between the coils.
  
• Torsion springs exert pressure along a path which is a circular arc, providing torque. The wire itself is twisted when the spring is compressed or stretched.