Inspection and Testing of Springs

Springs will generally be required little in the way of maintenance. It is important that any exposed springs are carefully inspected for signs of either of the problems of corrosion and overheating. Those that are in exposed areas can become corroded over time and those in areas of high temperature can lose their temper and cease to have the necessary mechanical compliance to satisfy the task for which they were designed. Corrosion, which occurs on static springs, can reduce the loads that the spring can carry. Whilst if a spring that carries cyclic loads becomes corroded, then the combination of fatigue and corrosion can result in a serious loss of fatigue strength.

In extreme circumstances, overheating can show a change of colour of the metal due to the loss of temper. In this event, it must be assumed that the spring is not suitable for the designed task.

In some instances, springs have to be checked against figures or graphs to prove whether they are in a suitable condition to continue in service. Some checks have to be done out at prescribed intervals whilst others are done on an ‘opportunity basis’, such as when a brake unit a hydraulic actuator is dismantled for overhaul.

The most common check, done on coil springs is on its static measurement. The manufacturer will publish the exact dimension of the unloaded spring with some small tolerance, whilst the servicing technician will accurately measure the spring’s length and compare the two dimensions. Providing that the spring is within the published figures, then the spring is considered to be serviceable.

The other check is the load/deflection check that is usually completed in a workshop environment. A special test rig is used, to load the spring with either a compressive, tensile or a torsional loading and a meter on the rig will display the load versus deflection figures. Subsequently, a series of loads are applied to the spring and the relevant deflections noted.

On completion, the figures are compared to a graph, published by the spring manufacturer, to establish the serviceability of the spring. If a spring fails any of these checks, it is simply replaced by a serviceable item.