What are the Consequences of Unsuitable Pre-Tightening of Threaded Fasteners?

As a Rail Bolt Manufacturer, share with you. The pre-tightening force of the threaded fastener connection is the effect of the pre-loaded force before the threaded fastener connection is subjected to the working load. This pre-loading force is the pre-tightening force. Proper pre-tightening force is an important prerequisite for enhancing the reliability and tightness of fastener connections. If the pre-tightening force fails to meet the specified requirements, there will be gaps or relative slippage between the connected parts after being loaded, resulting in loosening of the fasteners, and even making the whole machine unable to work normally. If the pre-tightening force is too large, it will cause man-made parts damage. For example, if the pre-tightening force of the O-ring seal is too large, the O-ring will be damaged and the seal will fail.

Track Bolt

The improper pre-tightening force of the threaded fastener connection will bring the following consequences:

1. Static damage of threaded fasteners connected parts

If the threaded fasteners are over-tightened, that is, the pre-tightening force is too large, it will cause man-made parts to be damaged, the bolts may be twisted, the coupling parts may be crushed, seized, twisted or broken, and the threaded teeth may be damaged. The shape is clipped and tripped.

2. The connected parts slip, separate or the fasteners loosen

For ordinary bolted connections that bear lateral loads, the pre-tightening force produces positive pressure between the connected parts, which rely on friction to resist the external load, so the size of the pre-tightening force determines its carrying capacity. If the pre-tightening force is insufficient, the connected parts will slip, resulting in misalignment, skew, and wrinkles of the connected parts, and the bolts may be sheared. For bolted connections subjected to axial load, the pre-tightening force produces a pressing force on the joint surface, and the remaining pre-tightening force after being subjected to an external load is the pressing force when the joint surface is working. If the pre-tightening force is insufficient, it will cause the joint surface to loosen, and even cause the serious consequences of the separation of the two connected parts. At the same time, the insufficient pre-tightening force will also cause strong lateral vibration and cause the nut to loosen.

3. Fatigue damage of bolts

Inappropriate pre-tightening force will cause bolt failure due to fatigue in most cases. Although reducing the pre-tightening force can reduce the average value of the total cyclic load on the bolt, it increases the load variation. Therefore, the overall effect is mostly to reduce the fatigue life of the bolt and cause fatigue damage.

Therefore, the pre-tightening force range must be determined in the assembly process. Our company also has Track Bolt on sale, welcome to contact us.