Torsion springs are helical springs that exert a torque or rotary force. 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 a 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.
Torsion springs are commonly used in clothes pins, clipboards, swing-down tailgates and garage doors. Other application types include hinges, counterbalances and lever returns. Sizes range from miniature, used in electronic devices, to large torsion springs used in chair control units. The 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, which is also referred to as a mandrel. The designer should consider the effects of friction and arm deflection on the torque.
Torsion springs are designed and wound to be actuated rotationally and to provide an angular return force. There are many options for leg configuration so the spring can be attached in different ways. Leg specifications to consider for torsion springs include leg angle, leg length, and legend style. Springs that are straight or parallel on the same side are considered to have a 0º leg angle the increasing angle is in the unwinding direction. Legend style choices include straight torsion, straight offset, hinged, short hook ends, and hook ends. Torsion spring ends can be custom bent, twisted, hooked or looped to suit your project needs. Lee Torsion Stock Springs are offered in a choice of 90 degrees, 180 degrees, 270 degrees and 360-degree free leg position with straight legs.
Custom double torsion springs consist of one set of coils coiled right hand and one set of coils coiled left hand. These coils are connected, usually with an unwound section between the winds and work in parallel. The sections are designed separately with the total torque being the sum of the two.
Relevant Torsion Spring Parameters
Inside Diameter, Outside Diameter, Wire Diameter and Body Length
- The Inside Diameter is specified when the spring is required to slip over a mandrel with sufficient clearance to operate freely.
- The Outside Diameter is specified when the spring is required to fit into a circular hole with sufficient exterior clearance to operate freely, or if there are outer housing clearance issues.
- The Body Length is the length of the spring coil at rest.
Spring Rate, Maximum Deflection, Maximum Load and Wind Specifications
- Spring Rate is the angular return torque provided per unit of angular displacements, such as inch-lbs per degree.
- Maximum Deflection is the maximum rated angular deflection of spring to overstress.
- Maximum Load is the rated load at the rated maximum deflection.
- The Wind of the torsion spring can be right hand, left hand, or double torsion. Lee Spring Stock Torsion Springs are offered with legs of equal length oriented at varying unloaded angles.