Rivet Specifications and Standards PDF

Rivet Specifications and Standards Rivets Specifications and standards for aircraft hardware are generally identified by the organisation originating them. Some of the most common are: AN – Air Force-Navy NAS – National Aerospace Standard MS – Military Standards. A rivet is any type of fastener that...

Rivet Specifications and Standards Rivets Specifications and standards for aircraft hardware are generally identified by the organisation originating them. Some of the most common are: AN – Air Force-Navy NAS – National Aerospace Standard MS – Military Standards. A rivet is any type of fastener that obtains its clamping action by having one of its ends mechanically upset. When an MS20470-AD4-4 rivet is required, specifications have already been written for it and are available to both the aircraft manufacturer and the rivet producer. These specifications stipulate the material to be used as well as the rivet dimensions. By using these specifications and calling for standard hardware, aircraft manufacturers are able to build reproducible aircraft at an economical cost. Solid rivets 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 177 of 229 Rivets, Hi-locks and bolts/nuts 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 178 of 229 Solid-Shank Rivets The solid-shank rivet has been used since sheet metal was first utilised in aircraft and remains the single most commonly used aircraft fastener today. Unlike other types of fasteners, rivets change in dimension to fit the size of a hole. When a rivet is driven, its cross-sectional area increases along with its bearing and shearing strengths. Solid-shank rivets are available in a variety of materials, head designs and sizes to accommodate different applications. Installed solid shank rivet cross section view 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 179 of 229 Rivet Codes Rivets are given part codes that indicate their size, head style and alloy material. Two systems are in use today: the Air Force-Navy (AN), and the Military Standards 20 (MS2O). While there are minor differences between the two systems, both use the same method for describing rivets. Rivet codes The first part denotes numbering system. The second part describes head style (for examples, 470 is universal head and 426 is countersunk). The third part is a one- or two-digit letter code representing rivet alloy material. Fourth is the shank diameter, indicated in 1/32-in. increments. Finally, the length is indicated in 1/16-in. increments. 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 180 of 229 AN 470 and MS20470 universal head Rivet codes - AN 470 and MS20470 universal head The length of a universal head (AN470) rivet is measured from the bottom of the manufactured head to the end of the shank. However, the length of a countersunk rivet (AN426) is measured from the top of the manufactured head to the end of the shank. 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 181 of 229 Diameter of a shank Rivet Head Design As mentioned, solid-shank rivets are available in two standard head styles: universal and countersunk, or flush. Joints utilising countersunk rivets generally lack the strength of protruding-head rivet joints. One reason is that a portion of the material being riveted is cut away to allow for the countersunk head. Another reason is that, when riveted, the gusset may not make direct contact with the rivet head if the rivet hole was not countersunk or dimpled correctly. Rivet head design 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 182 of 229 AN426 countersunk rivets were developed to streamline aerofoils and permit a smooth flow over an aircraft’s wings or control surfaces. However, before a countersunk rivet can be installed, the metal must be countersunk or dimpled. Countersinking is a process in which the metal in the top sheet is cut away in the shape of the rivet head. On the other hand, dimpling is a process that mechanically ‘dents’ the sheets being joined to accommodate the rivet head. Sheet thickness and rivet size determine which method is best suited for a particular application. Countersunk and Dome head rivets 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 183 of 229 Rivet Alloys Most aircraft rivets are made of aluminium alloy. The type of alloy is identified by a letter in the rivet code and by a mark on the rivet head itself. Rivet alloys 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 184 of 229 1100 Aluminium (A) Rivets made of pure aluminium have no identifying marks on their manufactured head and are designated by the letter A in the rivet code. Since this type of rivet is made out of commercially pure aluminium, the rivet lacks sufficient strength for structural applications. Instead, 1100 rivets are restricted to non-structural assemblies such as fairings, engine baffles and furnishings. The 1100 rivet is driven cold, and therefore its shear strength increases slightly as a result of coldworking. Rivet 1100 A Unused 1100 A rivets 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 185 of 229 2117 Aluminium Alloy (AD) The rivet alloy 2117-T3 is the most widely used for manufacturing and maintenance of modern aircraft. Rivets made of this alloy have a dimple in the centre of the head and are represented by the letters put in rivet part codes. Because AD rivets are so common and require no heat treatment, they are often referred to as ‘field rivets’. The main advantage of using 2117-T3 for rivets is its high strength and shock-resistance characteristics. The alloy 2117-T3 is classified as a heat-treated aluminium alloy but does not require re-heat treatment before driving. Aluminium alloy 2117 Unused Aluminium alloy 2117 rivets 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 186 of 229 5056 Aluminium Alloy (B) Some aircraft parts are made of magnesium. If aluminium rivets were used on these parts, dissimilar metal corrosion could result. For this reason, magnesium structures are riveted with 5056 rivets, which contain about a small amount of magnesium. These rivets are identified by a raised cross on their heads and the letter B in a rivet code. Aluminium alloy 5056 Unused Aluminium alloy 5056 rivets 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 187 of 229 2017 Aluminium Alloy (D) 2017 aluminium alloy is extremely hard. Rivets made of this alloy are often referred to as D-rivets and were widely used for aircraft construction for many years. These rivets are extremely hard and must be heat treated before use. Aluminium alloy 2017 Unused Aluminium alloy 2017 rivets D-rivets are identified by a raised dot in the centre of their head and the letter D in rivet codes. 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 188 of 229 Rivets made of 2017 can be kept in this annealed condition by removing them from a quench bath and immediately storing them in a freezer. Because of this, D-rivets are often referred to as icebox rivets. These rivets become hard when they warm up to room temperature, and may be re-heattreated as many times as necessary without impairing their strength. 2024 Aluminium Alloy (DD) DD-rivets are identified by two raised dashes on their head. Like D-rivets, DD-rivets are also called icebox rivets and must be stored at cool temperatures until they are ready to be driven. The length of time the rivets remain soft enough to drive is determined by the storage temperature. Aluminium alloy 2024 Unused Aluminium alloy 2024 rivets 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 189 of 229 7050-T73 Aluminium Alloy (E) The letter E is used to designate this alloy, and the rivet head is marked with a raised circle. 7050 alloy contains zinc as the major alloying ingredient and is precipitation heat-treated. Aluminium alloy 7050 Unused Aluminium alloy 7050 rivets 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 190 of 229 Corrosion-Resistant Steel (F) Stainless steel rivets are used for fastening corrosion-resistant steel sheets in applications such as firewalls and exhaust shrouds. They have no marking on their heads and are designated with the letter F. Unused corrosion-resistant steel rivets Monel (M) Monel rivets are identified by two recessed dimples in their heads. They are used in place of corrosion-resistant steel rivets when their somewhat lower shear strength is not a detriment. Unused M rivets (Monel) 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 191 of 229 Rivet Heat Treatment When an alloy is allowed to cool at room temperature, it is referred to as natural ageing and can take several hours or several weeks. This process can be accelerated by carrying out ‘precipitation heat-treatment’, also known as artificial ageing and precipitation-hardening. It applies a slightly elevated temperature for an extended period to attain the required temperature in the shortest time possible. Rivet heat treatment and driving times 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 192 of 229 Special Rivets and Fasteners Special (Blind) Rivet Applications Conventional solid-shank rivets require access to both ends to be driven. However, special rivets, often called blind rivets, are installed with access to only one end of the rivet. While considerably more expensive than solid-shank rivets, blind rivets find many applications in today’s aircraft industry. Installed blind rivets cross section view 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 193 of 229 Friction-Lock Rivets One early form of blind rivet that was the first to be widely used for aircraft construction and repair was the Cherry friction-lock rivet. Originally, Cherry friction-locks were available in two styles: hollow-shank pull-through and self-plugging types. The pull-through type is no longer common; however, the self-plugging Cherry friction-lock rivet is still used for repairing light aircraft. Cherry friction-lock rivets are available in two head styles: universal and 100° countersunk. Furthermore, they are usually supplied in three standard diameters, 1/8, 5/32 and 3/16 in. The friction-lock rivet assembly consists of a shell and mandrel or pulling stem. The stem is pulled until the header forms a bucktail on the blind side of the shell. At this point, a weak point built into the stem shears and the stem breaks off. After the stem fractures, part of it projects upwards. The projecting stem is cut close to the rivet head and the small residual portion is filed smooth. Friction-lock rivet 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 194 of 229 Types of Mechanical-Lock Rivets Mechanical-lock rivets were designed to prevent the centre stem of a rivet from falling out as a result of the vibration encountered during aircraft operation. Unlike the centre stem of a friction-lock rivet, a mechanical-lock rivet permanently locks the stem into place and vibration cannot shake it loose. Mechanical-lock rivets include: Huck-Loks Olympic-Loks CherryMAX. Mechanical lock rivet (red) installed 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 195 of 229 Huck-Loks Huck-Lok rivets were the first mechanical-lock rivets and are used as structural replacements for solid-shank rivets. However, because of the expensive tooling required for their installation, HuckLoks are generally limited to aircraft manufacturers and some large repair facilities. Huck-Lok 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 196 of 229 Olympic-LOKs Olympic-Lok blind fasteners are lightweight, mechanically locking spindle-type blind rivets. OlympicLoks come with a lock ring stowed on the head. As an Olympic-Lok is installed, the ring slips down the stem and locks the centre stem to the outer shell. These blind fasteners require a specially designed set of installation tools. Olympic-Lok rivets are made with three head styles: universal, 100° flush, and 100° flush shear. Rivet diameters of 1/8, 5/32 and 3/16 in. The installation tools fit both countersunk and universal heads in the same size range. Installed Olympic-Lok rivet - cross section view 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 197 of 229 CherryMAX™ The CherryMAX rivet is economical to use and strong enough to replace solid-shank rivets size for size. The economic advantage of the CherryMAX system is that one size puller can be used to install all sizes of CherryMAX rivets. A CherryMAX rivet is composed of five main parts: a pulling stem, a driving anvil, a safe-lock locking collar, a rivet sleeve and a bulbed blind head. CherryMAX rivets can be used in extremely high temperatures. They are available in diameters of 1/8, 5/32, 3/16 and 1/4 in. and are also made with an oversize diameter for each standard diameter listed. Unused CherryMAX rivet Installed CherryMAX rivet - cross section view 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 198 of 229 Hi-Shear Rivets The Hi-Shear rivet has the same strength characteristics as a standard AN bolt. In fact, the only difference between the two is that a bolt is secured by a nut and a Hi-Shear rivet is secured by a crushed collar. The Hi-Shear rivet is installed with an interference fit, where the side wall clearance is reamed to a tolerance determined by the aircraft builder. When properly installed, a Hi-Shear rivet has to be tapped into its hole before the locking collar is swaged on. Hi-Shear rivets are made in two head styles: fiat and countersunk. As the name implies, the Hi-Shear rivet is designed especially to absorb high shear loads. The Hi-Shear rivet is made from steel alloy with the same tensile strength as an equally sized AN bolt. The lower portion of its shank has a specially milled groove with a sharp edge that retains and finishes the collar as it is swaged into the locked position. Installed Hi-shear rivet - cross section view Special Fastener Applications Many special fasteners have the advantage of producing high strength with light weight and can be used in place of conventional AN bolts and nuts. When a standard AN nut-and-bolt assembly is tightened, the bolt stretches and its shank diameter decreases, causing the bolt to increase its clearance in the hole. Special fasteners eliminate this change in dimension because they are held in place by a collar that is squeezed into position instead of being screwed on like a nut. As a result, these fasteners are not under the same tensile loads imposed on a bolt during installation. 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 199 of 229 Hi-Loks Hi-Lok bolts are manufactured in several different alloys, such as titanium, stainless steel, steel and aluminium. They possess sufficient strength to withstand bearing and shearing loads and are available with flat and countersunk heads. A conventional Hi-Lok has a straight shank with standard threads. Although wrenching lock nuts are usually used, the threads are compatible with standard AN bolts and nuts. To install a Hi-Lok, the hole is first drilled with an interference fit. The Hi-Lok is then tapped into the hole and a shear collar is installed. A Hi-Lok retaining collar is installed using either specially prepared tools or a simple Allen and box-end wrench. Once the collar is tightened to the appropriate torque value, the wrenching device shears off, leaving only the locking collar. Installed Hi-Lok fasteners - cross section view 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 200 of 229 Jo-Bolt Fastener Patented high-strength structural fasteners known as Jo-Bolts are used in close-tolerance holes where strength requirements are high but physical clearance precludes the use of standard AN, MS or NAS bolts. The hole for a Jo-Bolt is drilled, reamed and countersunk before the Jo-Bolt is inserted and held tightly in place by a nose adaptor of either a hand tool or a power tool. A wrench adaptor then grips the bolt’s driving flat and screws it up through the nut. As the bolt pulls up, it forces a sleeve up over the tapered outside of the nut and forms a blind head on the inside of the work. When driving is complete, the driving flat of the bolt breaks off. Installed Jo-Bolt - cross section view 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 201 of 229 Removal of Special Fasteners If special fasteners require removal the following process is used; remove the washer-nut or locking collar, by turning them with the proper size box end wrench or a pair of vise-grips use a mallet to tap the remaining fastener out of its hole If a flush-type jo-Bolt requires removal the following process is used; drill a pilot hole into the bolt slightly deeper than the inside of the head of the nut use a drill bit of the same size as the shank, to drill to the depth of the pilot hole drive the remainder of the shank and blind head from the hole using a pin punch of the proper size Removal of Jo-Bolt - cross section view 2022-05-18 B-06a Materials and Hardware CASA Part 66 - Training Materials Only Page 202 of 229