I. Precise Judgment Using Professional Tools
1. Torque Wrench Verification: Set the torque wrench to the standard torque value corresponding to the specified specification. Apply force slowly. A "click" sound accompanied by slight vibration indicates that the tightening force is adequate.
2. Torque Value Verification: Refer to the corresponding standard. For example, the standard tightening torque for an 8.8 grade M12 lock nut is 86.9 N·m, and the lock nut for a motor shaft needs to reach 160 N·m. A measured torque deviation within ±10% is considered qualified.
3. Professional Instrument Verification: In critical safety connection scenarios, bolt axial force sensors and ultrasonic preload measuring instruments can be used to directly read the actual bolt preload, confirming that it reaches at least 40% of the design requirement's guaranteed load.
II. Appearance and Simple Operation Verification
1. Fit Check: After tightening the nut, the supporting surface must be completely fitted with the connected part, with no visible gaps. The spring washer opening should be completely flattened, without any warping or incomplete compaction.
2. Hand Rotation Test: After removing the wrench force, if the locking nut cannot be turned by hand and can only be rotated with a tool, it indicates that the basic preload has met the standard.
3. Line Mark Reset Verification: For critical fasteners, first mark the original position of the nut and the connected part. Loosen the nut by 30° and then retighten it until the marked line is completely aligned. The torque value measured at this time meets the standard, indicating it is qualified.
III. Special Working Condition Adaptability Judgment
1. Low Torque Scenarios: For soft connections such as shock absorber piston rods, after tightening, if the connected part shows no obvious plastic deformation, no crushing or denting marks, and the nut has no looseness, the tightening force is appropriate.
2. High preload scenario: When the preload reaches 70%~90% of the lower limit of the bolt's yield strength, and the thread shows no stripping and the bolt shows no obvious tensile deformation, the tightening force is within a safe and reasonable range.
3. Toothed lock nut scenario: After tightening, the nut teeth are fully embedded in the surface of the connected parts without slippage or lifting, and there is no excessive cutting of the connected parts' surface; this indicates that the tightening force is up to standard.
