In an earlier post on structural fasteners, we began discussion on lockbolts. A lockbolt is a 2-piece, permanent, mechanically locked structural fastener. Their primary benefit is that they offer long-lasting vibration resistance and won't loosen even under the most extreme vibration. This is because an installed, fully swaged (cold-formed collar on the grooved pin) lockbolt has no gaps between the grooves of the pin and the swaged collar, as found in threaded fasteners such as nuts and bolts. It's essentially a best-of-both-worlds hybrid of a bolt and a rivet.
A more detailed description, as defined by Engineering360 concludes, "Lockbolts are two-piece fasteners that consist of a headed, parallel-shank pin with a serrated end and collar. An assembly tool is used to swage the collar onto the serrated grooves in the pin and break the stem flush to the top of the collar. Shear strength, tensile strength, collar style, grip range, and diameter are important specifications to consider when selecting lockbolts."
As outlined at assemblymag.com, lockbolts "…are installed using a direct tension technique, in which the pin is pulled while the collar is simultaneously swaged into the locking grooves of the pin, deforming the collar into the grooves."
This creates a permanent, stable joint that can withstand high loads and heavy vibration.
A common use of lockbolts is as an alternative to welding. Welding was the primary, if not only, fastening method used to ensure joint integrity in heavy load, high vibration structures for many years. Today, direct-tension, swaged lockbolts are not only a viable alternative but might be superior in many applications.
While welding is a sure process for securing a joint, it is an expensive process when compared to lockbolt technology. Welding requires expensive controls as well as highly trained, highly skilled workers. Adding to the cost is the fact that the process is time-consuming.
Lockbolts are more forgiving to vibration and racking forces, whereas welds might fail under such circumstances. The heat associated with a weld can weaken the metals being joined and can be dangerous to the operator. Additionally, removal and rework of a welded joint, should that become necessary, is extremely difficult
Lockbolts offer several options for materials and head styles. They're typically manufactured from steel, stainless steel, and aluminum, with head styles including round, brazier, truss, and countersunk. Collars are available both with and without flanges.
The process of installing lockbolts also makes them cost-effective.
Reasons for this include:
- -Lockbolts maintain extremely consistent clamp load over time without the need for secondary devices such as lock washers, wires, or thread-lockers.
- -Lockbolts are quick and easy to install - Installation cycle time can be as short as 2 seconds (not including time to drill the hole) because the tool grabs the pin very quickly.
- -Unlike welding, which requires extensive operator training, a lockbolt installer requires minimal training.
- -With certain lockbolts, a quick visual inspection is all that's needed to confirm proper installation.
Another benefit of lockbolts is that they can be used to join virtually any metal, including dissimilar metals, as thermal expansion of joining dissimilar metals, which is often an issue for different types of fasteners, are of no consequence when using lockbolts.
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Austin Hardware® is a tier-1 master distributor for Huck Fasteners, which offers one of the largest and most innovative assortments of lockbolts for every industry. Shop online or contact your nearest Austin Hardware® location for more information. For immediate customer assistance, log on to our website, www.austinhardware.com, and engage our online chat product specialists.