EXTENSION SPRINGS
General Wire Spring is an extension spring manufacturer specializing in custom extension springs and custom extension spring ends which include machine loop and crossover loop ends, among other options to accommodate different tensions. Extension springs absorb and store energy by offering resistance to a pulling force. Various types of ends are used to attach the extension spring to the source of the force.
Extension Spring Ends
The variety of ends that can be put on extension springs is limited only by the imagination and may include threaded inserts, reduced and expanded eyes on the side or in the center of the spring, extended loops, hooks or eyes at varying positions or distances from the body of the spring, and even rectangular or teardrop-shapes ends. (The end is a loop when the opening is less than one wire size; the end is a hook when the opening is greater than one wire size.) By far the most common, however, are the machine loop and crossover loop shown on Table 1. These ends are made with standard tools in one operation and should be specified whenever possible to minimize cost.
It should be remembered that as the space occupied by the machine loop is shortened, the transition radius is reduced and an appreciable stress concentration occurs. This contributes greatly to shortened spring life and premature failure.
Most extension spring failures occur in the area of the end. To maximize the life of the spring, the path of the wire should be smooth and gradual as it flows into the end. Tool marks and other stress concentrations should be held to a minimum. A minimum bend radius of 1 1/2 times the wire diameter is recommended.
In the past, many ends were made as a secondary operation. Today, with modern mechanical and computer-controlled machines, many custom extension spring ends can be made as part of the coiling operation. Due to the large variety of machines available for coiling and looping in one operation, it is recommended that the spring manufacturer be consulted before a design is concluded.
