Torsion Springs

torsion springs

 

 

 

 

Torsion springs

Torsion Springs: Overview

Torsion Springs are a type of helical springs that exert a torque or rotary force. This name implies that 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.
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.
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.
This type of spring is normally close wound but can have pitch to reduce friction between the coils.

Applications of Torsion Springs:


Common torsion springs are used in clothes pins, clipboards, swing-down tailgates and garage doors,. They are used for hinges, counterbalances and lever return applications. 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. They perform best when supported by a rod or tube. The designer should consider the effects of friction and arm deflection on the torque.

How Torsion Springs are configured:


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, equal leg length, and leg end 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. Leg end style choices include straight torsion, straight offset, hinged, short hook ends, and hook ends. Torsion spring ends can be bent, twisted, hooked or looped to suit your project needs.

The double torsion spring consists 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.

The Parameters of Torsion Springs:

Physical parameters
• d (wire diameter): This parameter describes the diameter of wire used as material for spring.
• Dd (Shaft): This parameter describes maximal diameter of spring shaft in industrial applications.
• Di (internal diameter): Internal diameter of a spring. It can be calculated by subtracting the wire diameter multiplied by 2 from the external diameter of a spring. Internal diameter in this type of springs decreases while the spring is working even up to shaft diameter.
• De (external diameter): External diameter of a spring. It can be calculated by adding the wire diameter multiplied by 2 to the internal diameter of a spring. External diameter decrease while the spring is working.
• L0 (Free Length): WARNING: Free Length decrease while spring is working.
• Ls (Leg Length): It is the distance from the center axis of the coil body to the end of the springs' leg.
• An (Maximum angle): Maximum acceptable rotation angle for the spring in degrees.
• Fn (Maximum force): Maximum acceptable force that can operate at the end of spring's leg.
• Mn (Maximum torque): Maximum acceptable torque (Newton * mm).
• R (Spring rate): This parameter determines spring's resistance, while it is working. It is measured in Newton * mm / degree.
• A1 & F1 & M1: (angle at torque or force) The following equation calculates the angle as a function of the torque: A1 = M1/R. In order to calculate the torque from the force, we use this equation: M = F*Ls
• Leg position There are 4 types of torsion springs' leg positions: 0, 90 ,180 or 270 degrees (see picture above).
• Helix direction: A right-hand-wound spring loads in a counter-clockwise direction. A left-hand-wound spring loads in a clockwise direction. Both types are available in all sizes.
Dimensions: Inner Diameter, Outer Diameter, Wire Diameter, and Spring Length.
• The Inner Diameter is specified when the spring is required to slip over a mandrel with sufficient clearance to operate freely.
• The Outer 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 Spring Length is the length of the spring coil.

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