When using threaded fasteners, the choice of machine screws, rivets, and others is often dependent on many factors and made even more complex by the vast range of fasteners that are available. This blog will look at two fasteners, screws/bolts & rivets, and examine the most ideal situations to use each fastener.
Screw and bolts are similar types of fastener usually made from metal and characterized by a helical ridge, known as the external thread or male thread. These fasteners are used to fasten materials by the engagement of the screw thread with a similar internal/female thread in the matching component. The main advantages of screws and bolts are their simplicity of assembly and disassembly, their ability to be reused, and their wide availability.
A rivet is a permanent mechanical fastener that consists of a smooth cylindrical shaft that features a head on one end and a plain, opposite end called the tail. Upon installation, the rivet is placed in a punched or drilled hole, and the tail is deformed such that its diameter expands, holding the rivet in place.The advantages of rivets are their resistance to vibration, low-profile heads, and fast & low-cost assembly when large numbers of fasteners are required.
In common workshop applications, where pop rivets are commonly used, threaded fasteners will often provide superior strength. This is due to pop rivets’ use of a hollow shaft, which reduces their ability to resist shear loads. The strength of materials used also depends on the power of the riveting tools being used. Certain tools can only be used with very strong materials. Light-duty riveting tools can only be used with aluminum rivets, which do not offer high-strength fastening. Adversely, heavy-duty rivet tools can install high strength fasteners from materials such as stainless steel. However, their strength is limited by their need for a hollow shaft. Despite their weakness, hollow shafts are beneficial in that they provide relatively easy removal. For example, a drill bit can be easily placed in the hollow end and used to remove the fastener.
Solid rivets, on the other hand, are among the strongest mechanical fasteners available. They are available in materials such as high-strength steel and aerospace alloy, and their solid shafts allow them to transmit the greatest possible shear force for any given hole size. This shear force is even greater than what is possible for a threaded fastener because their threads can create potential areas of crack initiation. Additionally, once the heads of a solid rivet are formed, the hold is so tight that the fastener is almost entirely immune to vibration.
For these reasons, solid rivets remain the ideal fastener for important applications such as steel bridges, aircraft, structures, and more. The disadvantage of solid rivets is that they often require sophisticated and expensive installation equipment. This often requires access from both sides of the assembly, making installation more difficult. Furthermore, their strength makes them difficult to remove. Bolts and machine screws both offer a useful combination of high strength, versatility, and easy assembly & disassembly. Their main disadvantage, poor resistance to vibration, can be addressed by the addition of vibration-resistant or locking nuts, as well as threaded locks.