Supplied B1 Module 07A textbook: PDF pages 241–246.
Types and functions
Compression springs resist shortening, extension springs resist stretching and torsion springs resist angular movement. Leaf and disc springs provide other forms of controlled deflection. The installed function may be to return a mechanism, maintain contact, absorb vibration or apply a specified force. Match the complete spring specification: free length alone does not prove equivalence. Coil diameter, wire size, material, number of active coils and end form affect behaviour. Maintain orientation where the spring's ends or load direction are defined.
What loading does a torsion spring primarily resist? Angular displacement.
Visual inspection
Inspect for corrosion, cracks, wear, distortion and damaged hooks or seating ends. Surface damage can become a fatigue initiation site. Check that a spring is seated correctly and does not rub adjacent parts through its travel. Do not straighten, grind or heat a spring as an informal repair; these actions can alter material properties and geometry. A spring with correct free length may still have cracks or an unacceptable load characteristic. Compare condition with the specified inspection limits.
Why can corrosion be serious on a spring? It can reduce section and initiate fatigue cracks.
Free length and permanent set
Free length is measured without the applied working load. Permanent set is a lasting change after loading and may indicate that the spring has been overstressed or otherwise degraded. Check free length with the ends correctly supported and compare against the applicable limits. Do not interpret a shorter spring automatically as usable because it still fits. A preload requirement may mean the spring never operates near zero force in service, but free-condition dimensions remain relevant to its acceptance test.
What is permanent set? A lasting deformation after removal of load.
Load-deflection tests
A spring test relates force to deflection at specified points. For an ideal linear spring, force change equals spring rate multiplied by deflection change. Use a calibrated test rig and the stated compression, extension or angular positions. Do not exceed the specified test travel. Check the force at each required point: a free-length check cannot substitute for a load test. Real mechanisms may include preload, non-linear springs or friction, so apply the actual test method rather than a universal straight-line assumption.
For an ideal linear spring, what is spring rate? Change in force divided by change in deflection.
Handling stored energy
A preloaded spring can release energy as a retainer or cover is removed. Establish its loaded condition and use the prescribed restraint or compression tool before disassembly. Keep the body and hands out of the possible release path. Inspect the restraint and engage it correctly; an improvised clamp can slip. Release preload gradually as the task requires. Stored spring energy remains a hazard after electrical or hydraulic supplies have been isolated.
What must be controlled before removing a spring retainer? Stored mechanical energy and the release path.
Replacement and functional checks
Fit the specified spring, orientation and associated hardware. Check seats, guides and retaining features, because a sound spring installed on a damaged guide can fail in service. Lubricate only where required; unwanted grease can attract abrasive dirt. Verify the mechanism's travel, return action and required forces after assembly. Record the replacement or inspection under the maintenance task. If measurements fail limits, replace or process the spring under approved data rather than selecting another spring by visual similarity.
What should be verified after spring replacement? Correct seating, retention and mechanism operation.
Apply the knowledge
Work through these examples before starting the quiz. Explain why the other choices would not meet the requirement.
A linear spring's force rises by 120 N over 15 mm. What is its rate?
8 N/mm — Rate is force change divided by deflection change.
A spring meets free-length limits but fails the specified loaded-force test. What is correct?
Treat it as failing acceptance — Dimensional and load requirements are separate.
A cover retains a compressed spring. What is appropriate before removal?
Apply the specified restraint and disassembly sequence — Preload must be safely controlled before releasing retention.
A spring is cracked but still returns the lever. What does this show?
Functional movement alone does not establish serviceability — Cracks require assessment and normally rejection under the applicable criteria.