Machine Design

Tubular Rivets

Nonthreaded fasteners often are simple designs, but they solve a wide range of fastening problems.

Rivets and pins can be used as inexpensive alternatives to threaded fasteners in automated assembly. Pins are used where ease of disassembly is desired, while disassembly usually destroys rivets. Retaining rings and washers are also common nonthreaded fasteners, but they are used for more specialized purposes.

There are two basic families of rivets: tubular and blind. The main difference between them is that blind rivets require access to only one side of the assembly for installation.

Economics, not performance, determines the optimum diameter for tubular rivets. Rivet shank length, however, is fixed by the amount of the rivet material needed for clinching and the total material thickness. To minimize initial costs, a rivet of standard shank diameter, length increment, and tolerances should be specified. Some high-volume rivet sizes are particularly inexpensive. For example, 0.125 in. is by far the most popular nominal shank diameter. A 0.125-in. carbon-steel rivet can cost less than rivets with shank diameters from 0.085 to 0.089 in. Unless limited by load requirements, the 0.125-in. rivet should be used. Inventory can be reduced if one rivet with a large grip range is used for several joints of different thicknesses.

Larger rivet shank diameters are more efficiently fed in automatic assembly operations, and low-carbon steel and brass rivets are most easily handled in riveters. Extremely soft, low-density rivet materials can cause feeding and clinching difficulties.

Rivet length-to-diameter ratio should be limited to a maximum of 6:1 when possible, so standard barrel hoppers can be used. Higher length-to-diameter ratios may require special feeding devices, such as continuous hopper drives or vibratory feeders. For rivets above the 6:1 ratio or with long shanks, the head diameter should be about twice the shank diameter for efficient automatic handling.

Steel, aluminum, and brass are considered standard cold-heading materials. Almost any soft grade of aluminum can be cold formed into rivets. Carbon steels from grades AISI 1006 through 1035, 1108, and 1109 provide good strength at reasonable cost.

The location of the rivet in the assembled product influences both joint strength and clinching requirements, with edge distance and pitch distance being the important dimensions.

TAGS: Fasteners
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