I. Core Judgment Methods
1. Torque-Angle Method: Tighten to the specified torque, then rotate through a specified angle to ensure the bolt enters the plastic zone. Suitable for high-strength bolts.
2. Direct Measurement Methods:
Strain Gauge Method: Attach a strain gauge to the bolt and calculate the preload by measuring the change in resistance. High accuracy.
Ultrasonic Method: Measure the change in the propagation time of ultrasonic waves in the bolt to calculate the preload. Non-destructive and fast.
3. Indirect Judgment Methods:
Torque Wrench Verification: After tightening, lightly tighten with a torque wrench in the opposite or same direction. If a "click" sound is heard and there is no additional rotation, the preload is sufficient.
Marking Line Inspection: Mark lines on the bolt head, nut, and connected parts. After vibration, check for misalignment. Misalignment indicates insufficient preload.
II. Key Precautions
1. Torque Coefficient (K): The relationship between actual torque and preload is affected by the coefficient of friction. It needs to be obtained according to standard testing or by consulting a manual. 2. Effects of Anti-loosening Measures: Anti-loosening measures (such as spring washers) may reduce the effective preload; this must be considered during installation.
3. Environmental Factors: High temperatures, corrosive environments, etc., will accelerate the decay of preload; regular checks are necessary.
III. Operational Recommendations
1. Important Connections: Prioritize the torque-angle method or direct measurement method to ensure accuracy.
2. Batch Operations: Use a torque wrench for spot checks, combined with marking lines for quick judgment.
3. Maintenance and Inspection: Regularly re-inspect using the marking line method or a torque wrench to ensure long-term reliability.
