A rivet is a mechanical fastening device that secures two or more components together in a semipermanent fashion.
A rivet comprises a wide head and a narrower tail. The tail is inserted into holes in the components to be fastened together so that it extends out at the rear; the tail is then deformed by some mechanical means that squeezes the components together.
This fastening process depends on the ability to access both sides of the rivet. The blind or "pop" rivet was developed to allow rivets to be installed where it's not possible to access the rear of the rivet.
Pop Rivet Structure
A pop rivet has a two-piece structure. The rivet body has a head and a tail similar to a solid rivet, but is hollow. A mandrel runs through the rivet, extending forward from the rivet head. The mandrel has a bulge at the rear or tail end of the rivet and is also notched inside the rivet body to enable the mandrel to break at a predetermined point during installation.
The rivet body is usually a relatively soft material, such as aluminium or copper. The mandrel is usually a harder material such as steel.
Installing a Pop Rivet
Pop rivet installation requires a specially designed rivet gun. The rivet is inserted into the hole drilled through the components that will be secured, then the rivet gun is placed over the rivet mandrel. When the gun is operated, the mandrel is drawn through the rivet tail. The bulge on the end of the mandrel deforms the tail of the rivet and squeezes the components together. When the force needed to pull the mandrel increases sufficiently, the mandrel breaks at the notch leaving a well-formed rivet in place.
Types of Pop Rivets
There are many kinds of pop rivets. They vary in material, size, construction and so on. However, according to Emhart Fastening Teknologies, the company that owns the "POP" rivet brand name, most are categorised into three main structural types and three main styles of rivet head, as follow:
Open end: The mandrel extends all the way through the rivet. The mandrel head is retained within the rivet body after the stem has broken. Open-end rivets are used where pressure or fluid retention is not required.
Closed end: The end of the rivet body is closed and therefore the rivet itself is sealed. The mandrel head is retained within the rivet body after the stem has broken. Closed-end rivets are used where pressure or fluid retention is required.
T rivets: The mandrel, rather than just deforming the rivet tail, actually splits the tail into three wide sections that form a large clamping force on the components.
Dome: The most common type of pop rivet. The head is twice the diameter of the tail of the rivet, and protrudes above the surface of the material being secured.
Large flange: The head is oversized to form a large bearing surface. Used to secure soft or brittle material.
Countersunk: The head is flat and countersunk into the material being secured. This type is used where low aerodynamic drag or a good appearance is important.
Benefits of Pop Rivets
Pop rivets have several benefits in use, as follow:
Inexpensive Quick assembly Single operator Portable tools for setting rivets Strong clamping force Versatile Low risk of damaging component surfaces
Testing Pop Rivet Strength
Pop rivets are manufactured using many different materials and dimension tolerances. Inexpensive rivets from your local hardware store may be perfect for repairing your garage door, but not strong enough for use in an aeroplane.
There are two tests for assessing the strength of a rivet: a shear test and a tensile test.
A shear test exerts a sideways force on the rivet. A rivet is set in place to clamp together two sheets of a hard material. Each sheet is then pulled in opposite directions to determine the force at which the rivet will break.
A tensile test exerts a force on the rivet perpendicular to the surface of the clamped material to determine the force at which the rivet will fail.
Note that these tests are to assess the strength of the rivet itself and not the riveted assembly.