| Rivets Many different metals and alloys of metals are used to make rivets. The material used for the majority of aircraft rivets is an aluminum alloy. Other metals used are steel and copper. Aluminum rivets have a silver-white color; steel rivets are a typical steel color; and copper rivets are copper color. Aside from their metal, rivets are divided into two main groups: solid-shank and blind rivets. The following paragraphs discuss the two groups in detail. Solid-Shank Rivets. Rivets are manufactured in two head styles: universal and countersunk (Figure 1-11). Both head styles are used in interior and exterior locations. The universal head is shaped like a mushroom. Because of the added strength of the head style, the universal head rivet is used extensively throughout the aircraft. The countersunk rivet is used where flushness is required. The top of the countersunk head fits flush with the surface of the riveted material. This is accomplished because the rivet is flat-topped and undercut to allow the head to fit into a countersunk or dimpled hole. When aerodynamics or clearance is required, the countersunk rivet is used. 
Figure 1-11. Head Styles for Solid-Shank Rivets.
Blind Rivets. This section covers only the most common types of self-plugging rivets. Information on other types of self-plugging rivets may be obtained from the United States Army Aviation Systems Command, 4300 Goodfellow Boulevard, St. Louis, MO 63120, or from the rivet manufacturer. When access to both sides of a riveted structure or structural part is impossible or when limited space does not permit using a bucking bar, blind rivets must be used. These rivets have characteristics that require special installation tools and installation and removal procedures. Because these rivets are often installed in locations where one head, usually the shop head, cannot be seen, they are commonly called blind rivets. The blind rivets used on Army aircraft and discussed here are self-plugging (friction and mechanical lock). Friction Lock. Self-plugging friction lock rivets consist of a rivet head with a hollow shank or sleeve and a stem that extends through the shank. The rivet head styles are the same as the solid-shank rivets. Two common styles, shown in Figure 1-12, are in use. The stem may have a knob on the upper portion or it may have a serrated portion. 
Figure 1-12. Mechanically Expanded Rivet Head and Stem Styles.
Mechanical Lock. Self-plugging mechanical lock rivets include the 3000-series CherryMAX and the 2000-series Cherrylock. Mechanical lock rivets may be substituted for solid-shank rivets when a solid-shank rivet is inaccessible for bucking. When substituting 3000-series CherryMAX rivets for solid-shank rivets, the new rivet may be the same diameter as the solid rivet it replaces. When substituting 2000-series Cherrylock rivets or bulbed Cherrylock rivets for solid-shank rivets, the new rivet must be one diameter size larger than the solid rivet it replaces. In 1979 the Army began replacing all self-plugging rivets by attrition with the 3000-series CherryMAX rivet. The change will reduce the inventory of installation tools and types of rivets required in the Army supply system. The 2000-series Cherrylock rivet is made in three parts: a hollow shank, a stem, and a locking collar. The 3000-series CherryMAX rivet has an extra part attached to the rivet stem: the driving anvil (Figure 1-12a). The head styles of the shank are the same as those in solid-shank rivets. The head also has a conical recess to accept the locking collar. The stem has an extruded angle and land to expand the sleeve for hole filling, a breakneck groove, a locking groove, and a head. The pull grooves on the protruding end of the stem fit the jaws of the rivet tool. The mechanical lock between the stem and sleeve gives these rivets approximately the same strength as common solid-shank rivets. 
Figure 1-12a. Self-Plugging (Mechanical Lock) Rivets.
Rivet Removal. When a rivet has to be replaced, it must be removed carefully so that the rivet hole will retain its original size and shape and the rivet will not need to be replaced with one of the next larger size. If the rivet is not removed properly, the strength of the joint may be weakened. Hand tools, power tools, or a combination of both may be used to remove rivets. Solid-Shank. To remove a solid-shank rivet, use a drill one size smaller than the rivet shank to drill through the rivet head. Be careful not to drill too deep because the rivet shank will then turn with the drill and cause a tear. Insert a drift punch diagonally into the drilled hole and knock the rivet head off by lightly striking the drift punch. Drive the rivet shank out with a drift punch slightly smaller than the diameter of the shank. On thin metal or unsupported structures, support the sheet with a bucking bar while driving out the shank. If the shank is unusually tight after the rivet head is removed, drill the rivet about two-thirds through the thickness of the material and then drive the rest of the shank out with a drift punch. Mechanical-Locking. To remove a mechanical-locking rivet, use the following steps. Use a small center drill to provide a guide for a larger drill on top of the rivet stem and drill away the upper portion of the stem to destroy the lock. See Figure 1-12b. 
Figure 1-12b. Rivet Removal.
Drive out the rivet stem, using a tapered steel drift pin or a spent stem. See Figure 1-12c. 
Figure 1-12c. Rivet Removal.
Drill nearly through the head of the rivet using a drill the same size as the rivet shank. See Figure 1-12d. 
Figure 1-12d. Rivet Removal
Break off the rivet head, using a drift pin as a pry. See Figure 1-12e. 
Figure 1-12e. Rivet Removal
Drive out the remaining rivet shank with a pin that has a diameter equal to the rivet shank. See Figure 1-12f. 
Figure 1-12f. Rivet Removal.
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