Design Specifications for Torsion Springs

Critical Design Specs for Torsion Springs
Torsion and double torsion springs offer resistance to an externally applied torque, created when their ends are rotated in “angular deflection”.

Twisting a torsion spring creates normal stress, which is different than bending stress. Because of the additional stress to the wire due to bending the spring (bending stress), spring designers must consider the effects of friction and arm deflection on the torque applied to the spring’s wire.

• Spring Index/Proportions (define the ratio and limits of inside, outside and mean diameters)
• Diameter Reduction (compute the inside diameter during deflection and allow for normal tolerances)
• Total Number of Coils (total round coils)
• Wire Size
• Wire Material (round wire is preferred over rectangular wire for cost reasons; however, rectangular wire will bend more efficiently)
• Rod Diameter (if spring will operate over a rod)
• Bends (bend radii should be as large as possible to reduce stresses)
• Body Length
• Free Length
• Arm Length (calculating for deflection)
• End Style (end styles are unlimited)
• Winding
• Hand (Direction) – Right or Left Hand
  (For example, to engage the threads of a standard machine screw, the torsion spring must be coiled right hand)
• Finish (stress relieve, shot peen, passivate, plate, powder coat, electropolish, baked enamel or plastic coat) **

** Be mindful if plating or coating is in the design finishing, as this will increase its total solid height.

Stress relieving or heat treating affects torsion springs as follows:

1. Reduction in initial tension
2. Low temperature stabilizes position of ends