Installation Steps for Torsional Shear Type High-Strength Bolts:
1. Bolt Insertion: The bolts should freely fit into the holes without forceful hammering. The washer should be placed on the nut side, with the chamfered side of the washer facing the nut. It must not be installed in reverse.
2. Handling Difficult Insertions: If the bolt cannot fit freely, avoid using gas cutting to enlarge the hole. Instead, use a reamer to enlarge the hole. Ensure the layers of the plate are tightly aligned to prevent iron filings from entering the seams. After reaming, use a grinder to remove burrs from the hole edges and clear away any iron filings.
3. Consistent Bolt Insertion Direction: Bolts should be inserted in a consistent direction. After tightening the bolts with a wrench, remove the temporary bolts and replace them with high-strength bolts. Avoid installing bolts in rainy conditions, and ensure the friction surfaces remain dry.
4. Tightening Process:
• Use of Specialized Tools: Tighten the bolts using a special electric wrench. In cases where manual operation is required, a manual torque wrench may be used. The tightening process should be done in two stages.
• Initial Tightening: Tighten to 60%-80% of the standard axial force (design pre-tension) of the bolt. The initial torque value should not be less than 30% of the final torque value.
• Final Tightening: During final tightening, the plum blossom head should be twisted off, indicating that the bolt has reached the required pre-tension. The process is complete when the head at the tail end of the bolt breaks off.
5. Sequential Tightening: To ensure even stress distribution across the bolt group, both initial and final tightening should follow a specific sequence. Generally, tighten from the center of the bolt group outward, from areas of higher joint stiffness to the unconstrained free end, and from the center of the bolt group outward.
Importance of Electric Torque Wrench
The electric torque wrench ensures that the torsional shear type high-strength bolts achieve the required pre-tension. The plum blossom head will only twist off when the specified torque is reached, guaranteeing the bolt's performance. This allows for a simple visual check of the bolt’s effectiveness. The bolts are designed for single-use, ensuring their reliability in securing structures.
