Torsion Spring: Definition, Types, and Uses

What is A Torsion spring?

Torsion springs can store and release angular energy or statically hold a mechanism in place by deflecting the legs about the axis of the body’s centerline. They offer resistance to torsion or rotationally applied force. Such a spring will reduce the diameter of the body and slightly increase the length of the body when deflected in the preferred direction of the manufactured wind.

Torsion springs are helical springs that exert a torque or rotary force. The ends of a torsion spring are attached to other components, and when those components rotate around the center of the spring, the spring tries to push them back to their original position. Although the name implies otherwise, torsion springs are subject to bending stresses rather than torsional stresses.

This type of spring normally has a closed wound, but may have a pitch to reduce friction between the coils. They offer resistance to torsion or rotationally applied force. Depending on the application, torsion springs can be designed to run either clockwise or counterclockwise, thus determining the direction of the wind.

Torsion Springs Characteristics

The torsion spring configuration is created for the purpose of storing and releasing angular energy or for the purpose of statically holding a mechanism in place by deflecting the legs around the axis of the body’s centerline. Such a spring will reduce the diameter of the body and slightly increase the length of the body when deflected in the preferred direction of the manufactured wind.

The direction of the fabricated wind can also be important for torsion spring applications because the location of the leg bearing/attachment must be on the left or right side during assembly.

A torsion spring is normally supported by a rod (mandrel) that matches the theoretical hinge line of the final product.

Torsion spring

Types of Torsion Springs

A torsion spring is a spring that works by rotating its end along its axis; that is, a flexible elastic object that stores mechanical energy when twisted. When twisted, it exerts torque in the opposite direction, proportional to the amount (angle) it twists. There are several types:

  • A torsion bar is a straight bar of metal or rubber bar that is subjected to twisting (shear stress) around its axis by a torque applied to its ends.
  • A more delicate form used in sensitive instruments, called torsion fiber, consists of a silk, glass or quartz fiber under tension, which is twisted around its axis.
  • A helical torsion spring, is a metal rod or wire in the shape of a helix (coil) that is subjected to torsion around the axis of the coil by lateral forces (bending moments) applied at its ends, twisting the coil tighter.
  • Clocks use a spirally wound torsion spring (a form of helical torsion spring in which the coils are wrapped around each other rather than stacked) sometimes called a “clock spring” or colloquially called a mainspring. These types of torsion springs are also used for attic ladders, clutches, and other devices that need near-constant torque for large angles or even multiple revolutions.

Uses of Torsion Springs

Some familiar examples of uses are strong helical torsion springs that operate clothespins and traditional spring-loaded bar mousetraps.

Other uses are in the large coiled torsion springs that are used to counter the weight of garage doors, and a similar system is used to help open the trunk (trunk) cover on some sedans.

Small coil torsion springs are often used to operate pop-up doors found in small consumer goods such as digital cameras and compact disc players.

Other more specific uses:

  • A torsion bar suspension is a thick steel torsion bar spring attached to the body of a vehicle at one end and to a lever arm that is attached to the wheel axle at the other. Absorbs road bumps when the wheel goes over bumps and uneven road surfaces, cushioning passenger travel. Torsion bar suspensions are used in many modern cars and trucks, as well as military vehicles.
  • The sway bar used in many vehicle suspension systems also uses the torsion spring principle.
  • The torsion pendulum used in torsion pendulum clocks is a wheel-shaped weight suspended from its center by a wire torsion spring. The weight rotates about the axis of the spring, twisting it, instead of swinging like an ordinary pendulum. The force of the spring reverses the direction of rotation, so the wheel oscillates back and forth, driven at the top by the clock’s gears.
  • Torsion springs consisting of twisted ropes or sinew, were used to store potential energy to power several types of ancient weapons; including the Greek ballista and the Roman Scorpio and catapults like the onager.
  • The balance spring or hairspring in mechanical watches is a fine, spiral-shaped torsion spring that pushes the balance wheel back toward its center position as it rotates back and forth. The balance wheel and spring function similarly to the torsion pendulum above in keeping time for the watch.
  • The D’Arsonval movement used in mechanical pointer-type meters to measure electric current is a type of torsion balance (see below). A coil of wire attached to the pointer twists in a magnetic field against the resistance of a torsion spring. Hooke’s law ensures that the angle of the pointer is proportional to the current.
  • A DMD or digital micromirror device chip is at the heart of many video projectors. It uses hundreds of thousands of tiny mirrors on tiny torsion springs fabricated on a silicon surface to reflect light onto the screen, forming the image.