ABSTRACT
Springs of various types are used to a greater extent in mechanical components. Moulded Case Circuit Breaker (MCCB) is one such application where springs are used on larger scale. Helical springs are the ones which are used on the larger scale in MCCB. They are one of the critically weak links of any mechanism. Extension Springs are the most vulnerable of all the helical springs because of the presence of the hooks at the end of the spring body for attachment in components. Hooks are the critical weak regions where spring failure is mostly observed in case of extension springs. In the present study extension springs in MCCB mechanism with side hook geometry was studied and modified in order to reduce the induced stresses in the hooks and reduce the chances of the breakage which increase the life of the spring. Hook diameter larger than mean coil diameter, hook diameter equal to mean coil diameter, hook diameter smaller than mean coil diameter and springs with conical ends are compared in order to reduce the induced stressed in hook regions. Finite Element Analysis was carried out in order to determine the induced stresses in the hook region. Results show that the stresses induced in the hook smaller than mean coil diameter of the spring are the minimum among all the designs and stresses induced in the hook larger than mean coil diameter of the spring are maximum among all the designs. Stresses induced in the hooks equal to mean coil diameter of the spring and springs with conical ends lies in between the above two cases.
