What is the difference between the free angle and working angle of a torsion spring

Torsion springs are key components in mechanical transmission and torque control, and their design parameters directly impact their performance and lifespan. Free angle and working angle are two crucial concepts in torsion spring design and application. A thorough understanding of their differences and roles helps optimize spring performance and improve the overall reliability of mechanical devices.

What is free angle?

The free angle refers to the natural angular state of a torsion spring when no external force is acting on it. At this point, the spring is in a relaxed state, unloaded by torsional forces. The gap between the helical coils and the spring's geometry are determined by the natural state of the material. The free angle is typically determined by design requirements and manufacturing processes and serves as a baseline parameter for the spring's initial state.

The size of the free angle affects the spring's preload and assembly space during installation. If the free angle is too large, the spring may generate excessive prestress during installation, leading to stress concentration and premature fatigue. If the free angle is too small, it may not provide sufficient reaction force, affecting the operational stability of the equipment.

What is the working angle?

The working angle refers to the angular range of torsion within which a torsion spring can be twisted during actual use, also known as the effective angle. The working angle is the angular displacement of the spring from the free angle after being twisted by an external force. This angle directly determines the torque output and degree of deformation of the spring.
The working angle is related to the spring's elastic limit and service life. Exceeding the allowable elastic deformation range of the spring material will lead to plastic deformation and failure. Therefore, properly determining the working angle range is a critical step in torsion spring design, ensuring the spring operates within a safe range and improving its reliability.

The Difference Between Free Angle and Working Angle
The free angle is a static geometric parameter of the spring, representing its initial state and describing its natural shape. The working angle is a dynamic parameter, indicating the range of angular variation under the action of external forces. The free angle is determined during design and manufacturing, while the working angle varies according to actual operating conditions.
The free angle primarily affects the spring's preload and assembly conditions; the working angle determines the spring's actual torsional deformation and output performance. The difference between the two reflects the transition process from the spring's static to loaded state.

The Impact of Free Angle on Spring Performance
Excessively large free angles may cause the spring coils to be too widely spaced, leading to unstable assembly or vibration during operation. Excessively small free angles may cause the spring coils to contact closely, affecting the spring's flexibility and cushioning effectiveness. In high-precision machinery, precise control of the free angle can prevent excessive preload during spring installation, reduce residual stress, and improve the spring's fatigue life. The material's elastic modulus and manufacturing process affect the stability and consistency of the free angle.

The Relationship between Working Angle and Spring Life
The working angle directly determines the stress amplitude during spring use. A reasonable working angle ensures that the spring operates repeatedly within its elastic range, avoiding the plastic deformation zone and minimizing fatigue cracking.
Exceeding the designed working angle will accelerate spring fatigue failure and shorten its service life. Torsion springs of different materials and specifications have different maximum working angles, and the design must be appropriately matched based on the specific operating conditions.

Matching Free Angle and Working Angle in Design
Torsion spring design must consider both the free angle and the working angle. The free angle should ensure that the spring is neither too loose nor too tight during assembly, providing a good foundation for achieving the desired working angle.
Sufficient working angle margin is generally required in the design to accommodate changes in external loads and performance degradation due to spring fatigue. Precise control of the free angle and working angle helps the spring achieve the desired torque output and long-term stable operation.