I. Simple Sensory Quick Inspection
1. Tapping Test: Hold the handle of a hammer and tap the horizontal surface of the nut. A clear sound and noticeable vibration in your hand indicate proper tightening; a dull sound and no vibration suggest looseness.
2. Manual Tightening Test: Try to slightly tighten the nut with an appropriate wrench. If it turns easily, it's loose; if the wrench cannot turn it at all or the rotation is less than half a turn, the tightening is acceptable.
3. Visual Inspection: Directly observe the contact surfaces of the nut and the fastener. Obvious gaps, nut misalignment, or spring washer openings not fully flattened indicate looseness.
II. Marking Auxiliary Verification Methods
1. Paint Marking Method: After installation, draw a continuous straight line with paint on the surface of the nut and the fastener. If the line is misaligned or broken during operation, the nut has become loose due to rotation.
2. Line Mark Realignment Verification: Draw a baseline at the corresponding position of the nut and bolt head. Loosen the nut slightly and then retighten until the line marks are perfectly aligned. If the measured torque is significantly lower than the standard value, it indicates loosening.
III. Precise Instrument Testing Methods
1. Torque Wrench Re-inspection Method: Use a torque wrench with an indication error ≤ ±3% to re-inspect according to the standard torque value. If the wrench rotates before reaching the preset torque, it indicates insufficient preload and loosening of the nut.
2. Vibration Data-Assisted Judgment: If the vibration meter shows a significant increase in vibration velocity during equipment operation, but no significant change in vibration acceleration, prioritize checking if the locking nut is loose.
IV. Professional Anti-Loosening Performance Testing
1. Lateral Vibration Test Method: For locking nuts under critical operating conditions, a Junker lateral vibration test can be performed according to GB/T 10431 standard. If the preload retention rate is less than 50% of the initial value, it indicates anti-loosening failure and loosening.
2. Preload Sensing Detection: The real-time preload of the bolts is directly collected by equipment such as strain gauges and fiber optic sensors. If the preload decreases by more than 30% compared with the initial installation value, it can be determined that loosening has occurred.
