Self-Plugging Rivets (Mechanical Lock)
Self-plugging (mechanical lock) rivets are similar to self-plugging (friction lock) rivets, except for the manner in which the stem is retained in the rivet sleeve. This type of rivet has a positive mechanical locking collar to resist vibrations that cause the friction lock rivets to loosen and possibly fall out. [Figure 5-45] Also, the mechanical locking type rivet stem breaks off flush with the head and usually does not require further stem trimming when properly installed. Self-plugging (mechanical lock) rivets display all the strength characteristics of solid shank rivets and in most cases can be substituted rivet for rivet.
Bulbed Cherrylock Rivets
The large blind head of this fastener introduced the word “bulb” to blind rivet terminology. In conjunction with the unique residual preload developed by the high stem break load, its proven fatigue strength makes it the only blind rivet interchangeable structurally with solid rivets. [Figure 5-43]
Wiredraw Cherrylock Rivets
There is a wide range of sizes, materials, and strength levels from which to select. This fastener is especially suited for sealing applications and joints requiring an excessive amount of sheet takeup. [Figure 5-44]
Huck Mechanical Locked Rivets
Self-plugging (mechanical lock) rivets are fabricated in two sections: a head and shank (including a conical recess and locking collar in the head), and a serrated stem that extends through the shank. Unlike the friction lock rivet, the mechanical lock rivet has a locking collar that forms a positive lock for retention of the stem in the shank of the rivet. This collar is seated in position during the installation of the rivet.
Self-plugging (mechanical lock) rivets are fabricated with sleeves (rivet shanks) of 2017 and 5056 aluminum alloys, Monel, or stainless steel.
The mechanical lock type of self-plugging rivet can be used in the same applications as the friction lock type of rivet. In addition, because of its greater stem retention characteristic, installation in areas subject to considerable vibration is recommended.
The same general requirements must be met in the selection of the mechanical lock rivet as for the friction lock rivet. Composition of the material being joined together determines the composition of the rivet sleeve; for example, 2017 aluminum alloy rivets for most aluminum alloys and 5056 aluminum rivets for magnesium.
Figure 5-46 depicts the sequences of a typical mechanically locked blind rivet. The form and function may vary slightly between blind rivet styles and specifics should be obtained from manufacturers.
Self-plugging mechanical locked blind rivets are available in several head styles depending on the installation requirements. [Figure 5-47]
Shank diameters are measured in 1/32-inch increments and are generally identified by the first dash number: -3 indicates 3⁄32 inch diameter, -4 indicates 1⁄8 inch diameter, and so forth.
Both nominal and 1⁄64-inch oversize diameters are available.
Grip length refers to the maximum total sheet thickness to be riveted and is measured in 1⁄6 of an inch. This is generally identified by the second dash number. Unless otherwise noted, most blind rivets have their grip lengths (maximum grip) marked on the rivet head and have a total grip range of 1⁄16 inch. [Figure 5-48]
To determine the proper grip rivet to use, measure the material thickness with a grip selection gauge (available from blind rivet manufacturers). The proper use of a grip selector gauge is shown in Figure 5-49.
The thickness of the material being riveted determines the overall length of the shank of the rivet. As a general rule, the shank of the rivet should extend beyond the material thickness approximately 3⁄64 inch to 1⁄8 inch before the stem is pulled. [Figure 5-50]
Each company that manufactures self-plugging (friction lock) rivets has a code number to help users obtain the correct rivet for the grip range or material thickness of a particular installation. In addition, MS numbers are used for identification purposes. Figures 5-51 through 5-54 contain examples of part numbers for self-plugging (friction lock) rivets that are representative of each.