By Dr. Jody Muelaner
A rivet is a mechanical fastener with a plane unthreaded shaft that’s inserted through holes to join two or more parts together. A permanently formed head at each end prevents the rivet from removal from the hole. The shaft prevents any radial movements of the components.
Depending on the type of rivet, and its ability to support shear load, it can resist considerable forces. The heads prevent axial movements of the parts, although less force is supported in this way.
The function of a rivet is similar to that of a nut and bolt. However, while nuts can readily unscrew for disassembly and reassembly, typically rivets are broken or damaged before removal. They are, therefore, designed for permanent or semi-permanent joints, fulfilling the same role as structural adhesives or welding. Benefits are their ability to resist vibration and can secure joints with short clamp lengths.
A rivet has a pre-formed head at one head, called the factory head. Another head is formed after insertion and it’s referred to as the shop head. The factory head is similar to the head at one end of a bolt while the shop head is like a nut, which forms a temporary head at the other end of a bolt.
The end of a rivet’s shaft, which is formed into the shop head is called the tail. The process for forming the tail into a head is known as upsetting or bucking, which means it is deformed. By doing so, the tail expands, allowing it to securely hold the rivet in place. The two heads on each end of an installed rivet let it support tension loads (two forces pulling on opposite directions) and shear loads (the force is parallel to the surface or axis of the shaft).
Solid rivets are one of the oldest, most popular and commonly used types of fasteners. They are highly safe and reliable fasteners, with proven effectiveness in critical applications. For these reasons, they are widely used in the construction of aircraft. In such cases, a form of hammer and anvil are required to form the factory head of a solid rivet. Both sides of the hole also require access for installation, so that the anvil is against one end of the rivet and the hammer strikes the other end. Hand hammers are rarely used for this process. Instead, modern manual riveting operations use hand-held air hammers.
Automated drilling and riveting machines are also typical in aerospace manufacturing. These incorporate hydraulic or electromagnetic presses. Semi-tubular rivets are solid over the main part of the shaft, which carries the shear load, but are hollow at the shop end to make it easier to form the shop head.
In construction industries, such as when joining steel structures for bridges or steel-framed buildings, solid rivets have largely been replaced by bolts. This is because rivets are more time-consuming to install and remove, offering limited clamp load.
Blind rivets are hollow with a mandrel on a stem that runs through a central hole. By drawing the mandrel back through the rivet’s body, the factory head can be formed from the opposite side. This means it’s possible to install them from one side — or into a blind hole.
However, special-purpose riveting tools are required to install blind rivets. Manual tools are divided into plier-type riveters, which tend to be less costly and more compact, and lazy tong rivet tools. Lazy tongs are capable of installing strong rivets that require great force.