A closed end spring is designed to resist stretching and twisting. To “close” the ends, the space between the last two coils is reduced so they touch. In some applications, such as with Landrum springs, the closed ends are then flattened to ensure a stable contact surface.
How are spring ends flattened?
Flat end springs are achieved in two different ways, ground or forged. Ground end springs are the best way to get complete spring squareness. When this is done correctly, spring rates and reactions can be more accurately predicted which in turns makes the chassis more predictable. Also, there will tend to be less stress on the spring and spring related components because the pressure will be equally distributed throughout the spring and chassis. The lesser desired method is the forged or stamped method.
Landrum Spring feels that forging has more negative than positive effects and should not be used in racing applications where accurately rated springs are crucial. Forged ends are only desirable when mass production of a loose tolerance spring is acceptable, for example, the agriculture or industrial industry.
Why does forging the ends weaken the spring?
To accomplish a forged flat end, the spring material has to be heated more than once. The first heating of the material comes when the end of the wire is stamped, and the second heating process is when the wire is being rolled to a coil form. Every time that the material is heated, it removes carbon from the material. The more carbon removed from the material, the more “hardness” is removed from the wire. As a result, the spring will tend to fail under loads. Simply grinding the spring flat after forging it is like putting excessive ketchup on a bad hamburger. It doesn’t solve the problem of multiple heat runs it simply tries to hide the fact.
How can forged ends affect spring pre-load consistency?
Another negative effect of forged end springs is the fact that the chassis settings may change. For example, if the spring is beveled on the flat end instead of ground flat then the spring is not coming in true contact with the jack bolt plate. To check if the spring and jack plate is making true contact, simply inspect the contact points. Not having true continuity between spring and jack plate is an undesirable trait. The spring will not have any consistent spring pre-load from one spring to another; as a result, the chassis will not respond consistently.
How to tell if a spring is ground or forged
Inspect the end of the spring wire, if it appears to be splayed or tapered you can rest assure the ends have been forged.
