I. Basic Visual Inspection
1. Alignment: The nut end face should be completely flush with the workpiece surface, without tilting or gaps, and 2-3 threads should be exposed.
2. Thread Condition: The threads should be free of stripped, misaligned, or chipped teeth. The nut should turn smoothly without any jamming or abnormal loosening.
3. Surface Condition: The hexagonal head of the nut should not show signs of rounding, cracking, or deformation from the wrench. The surface anti-corrosion layer should not be extensively damaged.
II. Torque and Force Verification
1. Torque Verification: Re-inspect using a calibrated torque wrench. A deviation of ±10% from the design torque is considered acceptable.
2. Tapping Test: Gently tap the edge of the nut with a 0.3-0.5 kg hammer. With your finger close to the washer, a slight, even vibration is felt. Excessive vibration indicates under-tightening, while no vibration indicates over-tightening.
III. Special Scenario Verification
1. High-strength Nuts: Mark the corresponding positions on the nut and screw. Loosen the nut by 60° and then retighten until the marks coincide. If the torque deviation is within the allowable range, it is considered qualified.
2. Vibration Condition Nuts: Perform a simulated vibration test after installation. If the nut does not loosen on its own and the anti-loosening structure (nylon ring, locking washer) is fully in place, it is considered qualified.
3. Welded Hexagonal Nuts: If the welded parts are free of porosity and incomplete welds, and the nut does not deform after cooling, and the threads can still be smoothly screwed on, it is considered qualified.
IV. Final Functional Verification
If the connecting parts have no relative displacement or loosening, the overall structure is evenly stressed, and the load-bearing and sealing requirements under operating conditions are met, the installation is considered completely correct.
