Bolt Tightening Techniques

• When slip resistant connections are not required, high strength bolts are tightened to a ‘snug-tight’ using an ordinary spud wrench.

• When slip resistant connections are desired with HDFC bolts, three methods are used:
> Turn-of-the-nut tightening (part-turn method) -Cheap, more reliable, and common method.
> Direct tension indicator tightening,
> Calibrated wrench tightening (torque control method).

Advantages of Bolted connections

Bolted connections offer the following advantages over riveted or welded connections:
  • Use of unskilled labour and simple tools.
  • Noiseless and quick fabrication.
  • No special equipment/process needed for installation.
  • Fast progress of work. Accommodates minor .
  • discrepancies in dimensions.
  • The connection supports loads as soon as the bolts are tightened (in welds and rivets, cooling period is involved).

Main drawback of black bolt is the slip of the joint when subjected to loading

Advantages of HSFG Bolts

•HSFG bolts do not allow any slip between the elements connected, especially in close tolerance holes, Thus they provide rigid connections.
• Because of the clamping action, load is transmitted by friction only and the bolts are not subjected to shear and bearing.
• Due to the smaller number of bolts, the gusset plate sizes are reduced.
• Deformation is minimized.
• Holes larger than usual can be provided to ease erection and take care of lack-of-fit. However note that the type of hole will govern the strength of the connection.
• Noiseless fabrication, since the bolts are tightened with wrenches.
• The possibility of failure at the net section under the working loads is eliminated.

Since the loads causing fatigue will be within proof load, the nuts are prevented from loosening and the fatigue strength of the joint will be greater than in welded/connections.
• Since the load is transferred by friction, there is no stress concentration in the holes.
• Unlike riveted joints, few persons are required for making the connections.
• No heating is required and no danger of tossing of bolt. Thus safety of the workers is enhanced.
• Alterations, if any (e.g. replacement of defective bolt) is done easily than in welded connections.

Call Us