Helical springs used to apply a torque or store rotational energy are commonly referred to as torsion springs. The ends of torsion springs 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 subjected to bending stress rather than torsional stress. They can store and release angular energy or statically hold a mechanism in place by deflecting the legs about the body centerline axis.
This type of spring is normally close wound but can have pitch to reduce friction between the coils. They offer resistance to twist or rotationally applied force. Depending on the application, torsion springs can be designed to work in a clockwise or counter-clockwise rotation, thus determining the direction of the wind.
Applications: Common torsion springs are used in clothes pins, clipboards, swing-down tailgates, garage doors, window shades, counterbalance mechanisms, ratchets and various types of machine components. Torsion springs are used for hinges, counterbalances and lever return applications. They are also used as couplings between concentric shafts, such as in a motor and pump assembly. Torsion springs are generally mounted around a shaft or arbor, and must be supported at three or more points. Various kinds of ends are available to facilitate mounting.
Sizes range from miniature, used in electronic devices, to large torsion springs used in chair control units. Load should be applied in the direction of wind; unwinding from the free position is not recommended. As they wind up, torsion springs reduce in diameter and their body length becomes longer. This should be considered when design space is limited. Torsion Springs perform best when supported by a rod or tube. The designer should consider the effects of friction and arm deflection on the torque.
Torsion Spring Terminology
Angular Deflection - is the angle of rotation as measured from the free position to the installed, intermediate or final positions.
Free Angle - is the angle between the arms of a torsion spring when the spring is in the unloaded position.
Leg Length - is the length of legs as defined from the axis of the spring body to the outermost point.
Mandrel - is a rod or shaft over which a torsion spring operates.
Radius - is the bend radius at which a load is applied to a leg. The radius is usually assumed to be equal to ½ the leg length.
Torque - is a twisting action in torsion springs which produces rotation, equal to the load multiplied by the distance from the load to the axis of the spring body.
Maximum Deflection – is the maximum rated angular deflection of spring before damage.