1. Visual Inspection
Mark Line Inspection: Draw a mark line at the junction of the nut and bolt. If the mark line is misaligned, it indicates looseness.
Gap and Rust Inspection: Check for increased gaps between the nut and the component, or for accumulation of rust powder (oxidation discoloration indicates looseness).
Coating Condition: High-quality bolts should have an even zinc coating; plating loss may indicate looseness.
2. Manual Testing
Wrench Tightening: Use a suitable wrench to tighten the bolt. If it turns easily, it is loose; if it requires firm torque, it may be tightened.
Tap and Listen: A crisp sound indicates tightness; a dull or noisy sound indicates looseness.
3. Tool Testing
Torque Wrench: Set a standard torque value. If the torque is not reached, it is loose (refer to the maintenance manual). Color Marking Method: After tightening, apply a color mark. If deflection occurs after testing, it indicates rotational looseness; if no deflection occurs, it indicates non-rotational looseness.
4. Special Scenarios
High-Temperature Environments: Consider non-rotational looseness caused by thermal expansion and regularly check the preload.
Vibrating Areas: For engines and tower cranes, use lock washers or self-locking nuts.
5. Comprehensive Recommendations
Prioritize the marking method and torque wrench combination for testing. Critical areas (such as the brake system) must strictly follow the manual.
During regular maintenance, focus on checking for rust, thread damage, and the condition of the marking lines.
