Module 7 (Maintenance Practices) Sub Module 7.10 (Springs).pdf

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PIA TRAINING CENTRE (PTC) Module 7 - MAINTENANCE PRACTICES

Category A/B1 Sub Module 7.10 Springs

PTC/CM/B1.1 Basic/M7/03 Rev. 00 7.10 Mar 2014

MODULE 7

Sub Module 7.10

SPRINGS




PTC/CM/B1.1 Basic/M7/03 Rev. 00 7.10 - i Mar 2014

Contents

INSPECTION AND TESTING OF SPRINGS ----------------------- 1




PTC/CM/B1.1 Basic/M7/03 Rev. 00 7.10 - 1 Mar 2014

INSPECTION AND TESTING OF SPRINGS Springs will generally require little in the way of maintenance. Those that are in exposed areas can become corroded over time and those in areas of high temperature can, if they become overheated, lose their temper and cease to have the necessary mechanical compliance to satisfy the task for which they were designed. Corrosion that 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. Overheating, usually shown as blistering of the surface protection can, in extreme circumstances, show a change of colour of the metal due to the loss of temper. It must be assumed in this event that the spring is not suitable for the designed task. It is important that any exposed springs are carefully inspected for signs of either of the problems of corrosion and overheating. 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 springs 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, usually completed in a workshop environment, is the load/deflection check. 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. A series of loads are, subsequently, 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. Springs must be examined for: Corrosion

Overheating

Fatigue checking / expected life measurement

Static Measurement

Load / Deflection Check

Spring Testing Rig





Corrosion Corrosion, that 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.

A corroded spring Overheating Overheating, usually shown as blistering of the surface protection can, in extreme circumstances, show a change of color of the metal due to the loss of temper. It must be assumed in this event that the spring is not suitable for the designed task. It is important that any exposed springs are carefully inspected for signs of either of the problems of corrosion and overheating.

Fatigue checking / expected life measurement 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. Static measurement 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 springs length and compare the two dimensions. Providing that the spring is within the published figures, then the spring is considered to be serviceable. Load / deflection check The other check, usually completed in a workshop environment, is the load/deflection check. 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.





A series of loads are, subsequently, 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.

Module 7 (Maintenance Practices) Sub Module 7.10 (Springs).pdf

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Transcript of Module 7 (Maintenance Practices) Sub Module 7.10 (Springs).pdf