Flat Spiral Springs used in Toys

Design and Principles of Flat Spiral Spring

1. Flat Spiral Springs used in Toys

2. Abstract Flat spiral springs  are also known as spiral torsion, clock springs or brush springs. Generally it consists of rectangular cross-section, which is wound in form of spiral ,it is also called Power spring. These Springs are designed to customer requirements and are used in the toys, automotive, medical, industrial and office equipment markets.

3. Introduction In this spiral springs the inner end of this strip is fixed and the arbor which is at the center. The outer end is clamped to the drum called ‘ Retaining ’ drum. The spring is wound by rotating the arbor and during the winding process, energy is stored in the spring. This energy is released as mechanical torque through the drum when it gradually rotates and unwinds the spring. Spiral springs are widely used in watches ,cameras , instruments and automatic weapons , toys etc.

4. Methodology Thickness of the spring ( t ) = 0.1mm Distance of Center of Gravity ( r ) = 22 mm ∴ This is the flat spiral spring used in toys . The inner end is fixed to arbor. The outer end will be clamped to the drum or any fixed support to allow the spring to rotate on its axis.

5. Methodology ∴Flat spiral spring suspended freely ∴ Angular deflection in Flat spiral spring suspended under load.

6. Design Procedure Notations :- P= Force induced at the outer end A due to winding of the arbor (N). r = Distance of the center of gravity of spiral from the outer end(mm). t = Thickness of the strip(mm). b = Width of the strip perpendicular to plane of paper(mm). l = Length of the strip from outer end to the inner end(mm).

7. The Bending moment M due to the force P acting at a distance r is given by ∴ Maximum Bending stress induced at the point B is given by ∴ Deflection of one end of the spring with respect to other is given by ∴ where E= Modulus of Elasticity The Strain Energy ( U ) stored in the spring is given by ∴

8. Observation Materials : - Generally the strip is made of high quality steel. - It is very thin which results in high flexibility and enable the arbor to have large angular deflection. - Materials will be Alloyed or unalloyed, pre-hardened or hardened and tampered after coiling. - Steel alloys are the most commonly used spring materials. The most popular alloys include high-carbon , oil-tempered low-carbon, chrome  silicon,  chrome vanadium, and stainless steel. Features : - For reset or measuring applications these springs are manufactured with gaps between the coils. - These can be used where we require constant force. - Mostly used in Preloaded conditions.