Torsion springs are a specific type of spring that reacts to rotational forces called torque. Torsion springs exert torque in a circular or rotating arc with the spring arms rotate about the central axis. They can store and release angular energy or statically hold a mechanism in place by deflecting the legs about the body centerline axis. They offer resistance to twist or rotationally applied force. The legs can be at any position and have virtually any bend twist or loop in them. The stress is in bending, not in torsion. A spring of this type will reduce in body diameter and increase slightly in body length when deflected in the preferred direction of the fabricated wind. 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 wire spring is most often used with forces of rotation similar to those found in a motor or drive unit with a rotating shaft or something as simple as a clothespin. In either application, the wire is formed to provide resistance to torque, thus the name torsion spring.
These springs are a type of torque spring that has two coils separated by a space to minimize friction. These consist of a right-hand and a left-hand coil section connected together and working in parallel. The sections are designed separately with the total torque exerted being the sum of the two, thus called double torsion springs. Spring
How a spring reacts to torque or rotational forces depends on how the spring is designed. The problem is that the combination of formulas, wire sizes and shapes can provide an endless selection of torque springs to choose. This can further be complicated Springs - 4by ordering stock or custom springs to best solve the application solution.
Ace Wire Spring & Form solves this problem by providing design assistance to our customers and assists them in designing the right spring for their specific application. With our manufacturing process and skilled craftsman, we can provide stock or custom springs in any quantity and still provide the fast turnaround time and consistent quality usually associated with only large production runs.
Torsion Springs and Double Torsion Springs Design Considerations
Torsion Springs - 2After determining the force of torque required a designer usually estimates a suitable space or size limitations. The space should be considered approximate until the wire size and number of coils have been determined. The wire size depends solely on the torque.
Torsion Springs and Double Torsion Springs Specifications
When Ordering a Torsion Springs or Double Torsion Springs Spring Remember to Give The Following Information As Completely As Possible:
Inside or Outside Diameter. Torsion Springs - 3
If spring works on a rod, give size of same, as spring must not bind when wound up to its limit of travel.
Free length and number of coils. If spring cannot increase in length as wound up, allow sufficient space between coils.
Right or Left Hand Wound.
Wire Size. Decimal size if possible. Material, Kind and Grade.
Style of Ends, (see illustrations). Number of turns deflection to hold given load and radius of loaded arm. This length may be the length of the arm, or the arm may be attached to a movable machine member, in which case the length to point of application of load is given.
Finish, Plain unless otherwise specified.
Torsion Springs - Double Torsion Springs Design Hints
Proportions: Spring index, inside diameter divided by wire diameter between 4 and 14 is best. The larger the ratio the more the average tolerance. Ratios of 3 or less often cannot be coiled on spring coiling machines because of arbor breakage.
Spring Index: Spring index must be used with caution.
Total coils: Torsion springs with less than 3 coils buckle and difficult to test. Best to specify to the nearest fraction in eights or quarters whenever possible.
Rods: Torsion springs should be supported by a rod running through center.
Diameter Reduction: Should compute the reduction of inside diameter during deflection. Double Torsion Springs Allowances should be considered for normal spring diameter tolerances.
Winding: Coils of a torsion spring may be closely or loosely wound. Should not be wound with coils pressed tightly together. Tight-wound springs with initial tension in coils do not deflect uniformly and are difficult to test accurately. A space between 20 to 25 percent of wire thickness is desirable.
Hand: Hand or direction of coil should be specified. Deflecting the spring in an unwinding direction causes high stress and early failure. When spring is sighted down the longitudinal axis it is right hand when direction of wire into spring takes clockwise direction or angle of coils follow angle similar to threads of bolt or screw, otherwise it is left hand. A spring must be coiled right hand to engage threads of a standard machine screw.
Arm Length: All wire in a torsion spring is active between the points where the forces are applied. Deflection of long extended arms can be calculated by allowing one third of the arm length from the point of force contact to the spring body converted in coils. If the length of arm is equal or less than one half the length of one coil it can be safely neglected in most applications.
Bends: Arms should be straight as possible. Sharp bends are stress raisers that cause early failure. Bend radii should be as large as practicable. Hooks tend to open during deflection. Hook stresses can be calculated in the same way as for extension springs.
Double Torsion: Consistence of a left-hand-wound series of coils and a series of right-hand-coils connected at center. Torque and stress calculations, each series is calculated separately as individual springs, then torques are added together but deflection are not added together.
Torsion Springs - 5Torsion Springs Design Formulas and Specifications Torsion Springs - 6
The basic formulas for torque or Moment (M) and bending stress (S) used in designing torsion springs are shown below.
In the formulas the constants 10.8 and 6.6, while strictly theoretical, give results closer to the actual values obtained.
Here is a video on torsion springs