I. Preparation Before Installation
1. Verify Compatibility: Confirm that the specifications and strength grade of the lock nut and bolt are completely compatible, and that the threads are free of burrs and damage.
2. Clean Contact Surfaces: Clean oil and impurities from the bolt threads and the mating surfaces of the nut to avoid affecting the transmission of preload.
3. Prepare Matching Tools: Prepare a torque wrench with the appropriate range and an adapter wrench. In some cases, flat washers and anti-loosening washers may be required.
II. Installation and Tightening Steps for Different Types of Lock Nuts
1. Nylon Lock Nuts: First, place the flat washer onto the bolt and hand-screw the nut until you feel resistance from the nylon insert.
Tighten clockwise with a wrench. If the bolt head is movable, use another wrench to hold the bolt head in place while applying force.
Complete the final tightening to the corresponding torque value to avoid excessive deformation and failure of the nylon insert.
2. Double Nut Top Locking: First, screw in the lower, thinner nut, applying 80% of the standard tightening torque.
Then screw in the upper standard nut, applying 100% of the rated tightening torque to lock the two nuts together.
This method is suitable for low-speed, heavy-load applications requiring frequent disassembly.
3. Circular Slotted Locking Nut
Place the nut onto the shaft end thread and manually tighten it until it aligns with the end face of the part.
Use a hook wrench to gradually tighten to the specified torque, engaging the locking tab of the anti-loosening washer into the corresponding notch in the nut to complete the mechanical locking.
III. Key Points for Tightening Torque Control
1. The standard tightening torque for a standard 8.8 grade M12 bolt with a locking nut is 86.9 N·m. For other specifications, refer to the torque standard for the corresponding strength grade.
2. The tightening torque for non-metallic insert locking nuts should be controlled to 50% of the standard value for all-metal nuts to avoid damaging the nylon structure.
3. The total coefficient of friction is recommended to be controlled between 0.09 and 0.15 to ensure stable preload.
IV. Post-Installation Precautions
1. Tighten the bolts once 48 hours after the initial installation to eliminate material stress and deformation.
2. If the nut can be turned by hand, the entire set of nuts and bolts must be replaced; do not replace the nut alone.
3. Damaged threads in the foundation hole must be repaired with a thread insert; do not directly replace with a larger nut to avoid altering the stress distribution.
