TABLE 4-8. AIRCRAFT RIVET IDENTIFICATION (CONTINUED) Material Carbon Corrosion- Copper Monel Monel Brass Titanium Steel Resistant Nickel- Steel Copper Alloy Head Recessed Recessed Plain Plain Recessed Plain Recessed Marking Triangle Dash Double Large and Dots Small Dot AN Material F M c Code AN425 78• Counter- Sunk Head AN426 100• Counter- MS 20426 Sunk Head MS20426 AN427 100• Counter- Sunk Head MS20427 AN430 Round Head MS20470 AN435 Round Head MS20613 MS20615 MS20613 MS20613 MS20615 MS20615 AN 441 Flat Head AN 442 Flat Head MS20470 AN 455 Brazier Head MS20470 AN 456 Brazier Head MS20470 AN 470 Universal Head MS20470 Heat Treat Before Us- No No No No No No No ing Shear Strength 35000 65000 23000 49000 49000 95000 psi Bearing Strength 90000 90000 psi Par 4-57 Page 4-23
Par 4-57 Page 4-24
(3) An example of identification marking of a rivet follows:
MS 20470AD3-5 Complete part number MS Military standard number 20470 Universal head rivet AD 2117-T aluminum alloy 3 3/32 inch in diameter 5 5/16 inch in length
(4) Countersunk head rivets (MS20426 supersedes AN426 100-degree) are used where a smooth finish is desired. The 100-degree countersunk head has been adopted as the standard in the United States. The universal head rivet (AN470 superseded by MS20470) has been adopted as the standard for protruding-head rivets, and may be used as a replacement for the roundhead, flathead, and brazier head rivet. These rivets can also be purchased in half sizes by designating a “0.5” after the main length (e.g., MS20470 AD4-3.5).
b. Replace rivets with those of the same size and strength whenever possible. If the rivet hole becomes enlarged, deformed, or otherwise damaged; drill or ream the hole for the next larger size rivet. However, make sure that the edge distance and spacing is not less than minimums listed in subparagraph 4-57c. Rivets may not be replaced by a type having lower strength properties, unless the lower strength is adequately compensated by an increase in size or a greater number of rivets. It is acceptable to replace 2017 rivets of 3/16 inch diameter or less, and 2024 rivets of 5/32 inch diameter or less with 2117 rivets for general repairs, provided the replacement rivets are 1/32 inch greater in diameter than the rivets they replace.
c. Rivet edge distance is defined as the distance from the center of the rivet hole to the nearest edge of the sheet. Rivet spacing is the distance from the center of the rivet hole to the center of the adjacent rivet hole. Unless structural deficiencies are suspected, the rivet spacing and edge distance should duplicate those of the original aircraft structure. If structural deficiencies are suspected, the following may be used in determining minimum edge distance and rivet spacing.
(1) For single row rivets, the edge distance should not be less than 2 times the diameter of the rivet and spacing should not be less than 3 times the diameter of the rivet.
(2) For double row rivets, the edge distance and spacing should not be less than the minimums shown in Figure 4-5.
(3) For triple or multiple row rivets, the edge distance and spacing should not be less than the minimums shown in Figure 4-5.
FIGURE 4-5. RIVET HOLE SPACING AND EDGE DISTANCE FOR SINGLE-LAP
SHEET SPLICES
STRENGTH THROUGH THIS SECTION IS 75% OF SHEET WITHOUT HOLES.
D = DIAMETER OF
• RIVET (PREFER- ABLY ABOUT 3x 7 THICKNESS OF
THICKER SHEET) 20 → L40= -20 (A) DOUBLE ROW
STRENGTH THROUGH THIS SECTION IS 83% OF SHEETL WITHOUT HOLES.- 6D 3D 20- +3D+30=<30+ * 2D (B) TRIPLE OR MULTIPLE ROWS
d. The 2117 rivets may be driven in the condition received, but 2017 rivets above 3/16 inch in diameter and all 2024 rivets are to be kept packed in dry ice or refrigerated in the "quenched" condition until driven, or be reheat-treated just prior to driving, as they would otherwise be too hard for satisfactory riveting. Dimensions for formed rivet heads are shown in Figure 4-6, item (a), together with commonly found rivet imperfections.
Par 4-57 Page 4-25
FIGURE 4-6. RIVETING PRACTICE AND RIVET IMPERFECTIONS
(a) DIMENSIONS FOR FORMED RIVET HEADS.
65D (ID MIN.) (MIN.) (TO MIN.)
(b) RIVETING TOOLS
INCORRECT CORRECT SHAPE FOR RIVET SET.
BUCKING BAR
OR DOLLY (C) RIVET IMPERFECTIONS
RIVET DRIVEN AT SLANT, RIVET DRIVEN CORRECTLY, DOLLY RIVET FLAT ON ONE SIDE OR DOLLY HELD HEAD AT SLANT. FLAT.
BODY OF RIVET TOO RIVET NOT PULLED RIVET TIGHT, PLATES SHORT. CLOSING HEAD TIGHT, CLINCHES BULGED ON ACCOUNT SHAPED TOO MUCH BETWEEN PLATES, OF POOR FIT.
WITH SNAP DIE. CLOSING HEAD TOO FLAT.
RIVETED TOO MUCH. RIVET BODY CLINCHED TOO MUCH, HEAD CRACKED.
PLATES CLINCHED AT RIVET MATERIAL TOO AND DRIVEN APART. HARD WHEN
RIVETING TOOL FORMED
DAMAGED PLATE
e. When solid shank rivets are impractical to use, then special fasteners are used. Special fastening systems used for aircraft construction and repair are divided into two types, special and blind fasteners. Special fasteners are sometimes designed for a specific purpose in an aircraft structure. The name "special fasteners" refers to its job requirement and the tooling needed for installation. Use of special fasteners may require an FAA field approval.
f. Blind rivets are used under certain conditions when there is access to only one side of the structure. Typically, the locking characteristics of a blind rivet are not as good as a driven rivet. Therefore, blind rivets are usually not used when driven rivets can be installed.
NOTE: Blind rivets shall not be used:
• In fluid-tight areas; or
• On aircraft in air intake areas where rivet parts may be ingested by the engine, on aircraft control surfaces, hinges, hinge brackets, flight control actuating systems, wing attachment fittings, landing gear fittings, on floats or amphibian hulls below the water level, or other heavily stressed locations on the aircraft.
Par 4-57 Page 4-26
Par 4-57 Page 4-27 CAUTION: Fo r metal repairs to the airframe, the use of blind rivets must be specifically authorized by the airframe manufacturer or approved by a representative of the FAA.
(1) Self-plugging friction-lock cherry rivets. This patented rivet may be installed when there is access to only one side of the structure. The blind head is formed by pulling the tapered stem into the hollow shank. This swells the shank and clamps the skins tightly together. When the shank is fully upset, the stem pulls in two. The stem does not fracture flush with the rivet head and must be trimmed and filed flush for the installation to be complete. Because of the friction-locking stem, these rivets are very sensitive to vibrations. Inspection is visual, with a loose rivet standing out in the standard “smoking rivet” pattern. Removal consists of punching out the friction-locked stem and then treating it like any other rivet. (See Figure 4-7.)
FIGURE 4-7. SELF-PLUGGING FRICTION-LOCK CHERRY RIVETS (
2) Mechanical-lock rivets have a device on the puller or rivet head which locks the center stem into place when installed. Many friction-lock rivet center stems fall out due to vibrations; this, in turn, greatly reduces its shear strength. The mechanical-lock rivet was developed to prevent that problem. Various manufacturers make mechanical-lock fasteners, such as Bulbed CherryLOCK, CherryMAX, Olympic-Loks, and Huck-Loks.
(3) Bulbed CherryLOCK Rivets. One of the earlier types of mechanical-lock rivets developed were Bulbed CherryLOCK blind rivets. These blind rivets have as their main advantage the ability to replace a solid shank rivet size for size. (See Figure 4-8.)
(a) A Bulbed CherryLOCK consists of three parts: a rivet shell, a puller, and a lockring. The puller or stem has five features which are activated during installation: a header, a shank expanding section, a lockring indent, a weak or stem fracture point, and a serrated pulling stem. Carried on the pulling stem, near the manufactured head, is the stem lockring. When the rivet is pulled the action of the moving stem clamps together the sheets of metal and swells the shank to fill the drilled hole. When the stem reaches its preset limit of travel, the upper stem breaks away (just above the lockring) as the lockring snaps into the recess on the locking stem.
Par 4-57 Page 4-28 The rough end of the retained stem in the center on the manufactured head must never be filed smooth, because it will weaken the strength of the lockring and the center stem could fall out.
(See Figure 4-8.)
FIGURE 4-8. MECHANICAL-LOCK (BULBED CHERRYLOCK) CHERRY RIVET STEM
STEM IS PULLED
INTO RIVET SLEEVE
LOCKING BEFORE AND STARTS TO FORM
COLLAR PULLING BULB BLIND HEAD BEGINS RIVET
- HEAD SHEET
GAP ) CLAMP-UP AND
HOLE FILL
ACTION BEGIN SHEAR RING
FORMATION OF BLIND
CLAMP-UP COMPLETED HEAD AND HOLE FILLING
AS STEM CONTINUES TO ARE COMPLETED
BULB OUT BLIND HEAD
SHEAR RING NOW SHEARS
FROM STEM CONE TO ALLOW
STEM TO PULL FURTHER INTO
RIVET HEAD RIVET
FIRMLY SEATED
BLIND SIDE BULB HEAD
IS FORMED BELOW SHEAR RING GUARANTEES
MINIMUM GRIP BLIND SIDE BULBED HEAD (IN MINIMUM GRIP SHEAR
RING MAY NOT SHEAR)
SHEAR RING HAS MOVED
DOWN STEM CONE UNTIL
PULLING HEAD AUTOMATICALLY STOPS STEM BREAK NOTCH COMPLETELY INSTALLED BULBED CHERRYLOCK
FLUSH WITH TOP OF
RIVET HEAD
PULLING HEAD HAS
LOCKING COLLAR IS NOW INSERTED LOCKING
READY TO BE INSERTED COLLAR AND STEM
HAS FRACTURED FLUSH
WITH RIVET HEAD (MAXIMUM GRIP
ILLUSTRATED)
BLIND SIDE
BULBED HEAD Par 4-57 Page 4-29
Par 4-57 Page 4-30
(b) The Bulbed CherryLOCK rivets are available in two head styles: universal and 100-degree countersunk. Their lengths are measured in increments of 1/16 inch. It is important to select a rivet with a length related to the grip length of the metal being joined.
(c) The Bulbed CherryLOCK rivet can be installed using a G30 Cherry Rivet Hand Puller or a pneumatic Bulbed CherryLOCK pulling tool.
(4) The CherryMAX rivet (see Figure 4-9) uses one tool to install three standard rivet diameters and their oversize counterparts. This makes the use of CherryMAX rivets very popular with many small general aviation repair shops. CherryMAX rivets are available in four nominal diameters: 1/8, 5/32, 3/16, and 1/4 inch; and three oversized diameters. CherryMAX rivets are manufactured with two head styles: universal and countersunk. The CherryMAX rivets consists of five parts: bulbed blind header, hollow rivet shell, locking (foil) collar, driving anvil, and pulling stem. The blind bulbed header takes up the extended shank and forms the bucktail on a CherryMAX rivet stem. Rivet sleeves are made from 5056 aluminum, Monel, and INCONEL 600. The stems are made from alloy steel, corrosion resistant steel (CRES), and INCONEL X-750 stem. CherryMAX rivets have an ultimate shear strength ranging from 50 thousands of pounds per square inch (KSI) to 75 KSI.
FIGURE 4-9. CHERRYMAX RIVET (
5) An Olympic-Lok rivet (see Figure 4-10) is a light three-piece mechanically locked, spindle-type blind rivet. It carries its stem lock integral to the manufactured head. While installing, the lockring is pressed into a groove on the pulling stem just as the rivet completes drawing the metal together. After installation is completed, never file the stem of an Olympic-Lok rivet, because it will weaken the lockring attachment. The Olympic-Lok fastener is available in three head styles: universal protruding, 100-degree flush countersink, and 100-degree flush shear; and three diameters: 1/8, 5/32, and 3/16 inch. The three diameters are available in eight different alloy combinations of 2017-T4, A-286, 5056, and Monel.
Olympic-Lok lock spindles are made from the same material as the sleeves.
FIGURE 4-10. OLYMPIC-LOK RIVET
SLEEVE REDUCED INTERNAL DIAMETER TO DOUBLE
PRECISELY ALIGN THE LOCKING GROOVE TAPER DESIGN
FULLY SERRATED STEM CONTINUOUS INTEGRAL
FOR INCREMENTAL PULL-UP LOCKING COLLAR RV 1201 SERIES
COUNTERSUNK
HEAD STYLE 1/16 INCH GRIP VARIATION CAPABILITY
DESIGNED INTO FASTENER
LARGER SECOND SHANK RV 1200 SERIES FLUSH BREAKING STEM DIAMETER FOR EXTRA
PROTRUDING SLEEVE EXPANSION AND
HEAD STYLE GREAT BLIND-SIDE
BEARING AREA
GREATER LOCKING COLLAR VOLUME PROTRUDING HEAD
DRIVEN INTO LOCKING GROOVE UNDERCUT ELIMINATES
DEBURRING When the stem travel is Continued pulling breaks Olympic-Lok blind rivet is Tool jaws grip the stem and stopped by the sleeve's inter- the stem flush to the fasteninserted into a prepared pull it into the sleeve, closing nal step, the integral locking er head. Flushness is hole. Note the clearance the sheet gap, expanding the collar shears free and is assured by the positioning between the rivet and the sleeve to fill the hole, and forced into the stem locking of the break-groove when sides of the hole and the forming a consistently larger groove. This forms a stem travel is stopped by gap between the sheets. blind side bearing area. permanent mechanical lock. the sleeve's internal step.
(6) Huck rivets (see Figure 4-11) are available in two head styles: protruding and flush.
They are available in four diameters: 1/8, 5/32, 3/16, and 1/4 inch. Their diameters are measured in increments of 1/32 inch and lengths are measured in 1/16 inch increments. They are manufactured in three different combinations of alloys: 5056 aluminum sleeve with 2024 aluminum alloy pin, A-286 corrosion-resistant steel sleeve with an A-286 pin, and a Monel 400 sleeve with an A-286 pin. The Huck fastener has the ability to tightly draw up two or more sheets of metal together while being installed. After the take up of the Huck fastener is completed, the lockring is squeezed into a groove on the pulling stem. The anvil or footer (of the installation tool) packs the ring into the groove of the pulling stem by bearing against the lockring.
Par 4-57 Page 4-31
Par 4-57 Page 4-32 FIGURE 4-11. HUCK RIVET (
7) Common pull-type POP rivets, produced for nonaircraft related applications, are not approved for use on certificated aircraft structures or components.
g. Design a new or revised rivet pattern for strength required in accordance with one of the following:
(1) The aircraft manufacturer’s maintenance manuals.
(2) The techniques found in structural textbooks and using the mechanical properties found in MIL-HDBK-5 or MMPDS-10.
(3) The specific instructions in subparagraphs 4-58g through 4-58n. When following the instructions in subparagraphs 4-58g through 4-58n, the general rule for the diameter of the rivets used to join aluminum sheets is to use a diameter approximately three times the thickness
Par 4-57 Page 4-33 of the thicker sheet. Do not use rivets where they would be placed in tension, tending to pull the heads off; and backup a lap joint of thin sheets with a stiffener section.
4-58. REPAIR METHODS AND PRECAUTIONS FOR ALUMINUM STRUCTURE.
Carefully examine all adjacent rivets outside of the repair area to ascertain that they have not been harmed by operations in adjacent areas. Drill rivet holes round, straight, and free from cracks. Deburr the hole with an oversize drill or deburring tool. The rivet set used in driving the rivets must be cupped slightly flatter than the rivet head. (See Figure 4-6.) Rivets are to be driven straight and tight, but not overdriven or driven while too hard, since the finished rivet must be free from cracks. Information on special methods of riveting, such as flush riveting, usually may be obtained from manufacturer’s service manuals.
a. Splicing of Tubes. Round or streamline aluminum alloy tubular members may be repaired by splicing. (See Figure 4-12.) Splices in struts that overlap fittings are not acceptable.
When solid rivets go completely through hollow tubes, their diameter must be at least one-eighth of the outside diameter of the outer tube. Rivets which are loaded in shear should be hammered only enough to form a small head and no attempt made to form the standard roundhead. The amount of hammering required to form the standard roundhead often causes the rivet to buckle inside the tube. (Correct and incorrect examples of this type of rivet application are incorporated in Figure 4-12.)
FIGURE 4-12. TYPICAL REPAIR METHOD FOR TUBULAR MEMBERS OF
ALUMINUM ALLOY L = 20 SPACES 3 d EACH TOTAL NO. OF RIVETS - 18 (9 EACH SIDE OF SPLICE) B+ -C A = ORIGINAL TUBE C = REPLACEMENT TUBE B = SLEEVE USE 2117-T "45" ALUM. ALLOY RIVETS SMALL HEAD
HAMMER STANDARD SPLICES MAY BE USED ON LIGHTLY- 2dl ROUND HEAD LONGERONS OR WEB MEMBERS.
CORRECT WAY INCORRECT WAY d MUST NOT BE LESS THAN D/8.
R = 3 d 00 1000
STREAMLINE M/3 EACH- (USE BASIC ROUND SIZES IN TABLE FOR SIZE OF RIVETS ETC.)
A, C* 3/4 7/8 1 1-1/8 1-1/4 1-/3/8 1-1/2 1-/5/8 1-3/4 1-7/8 065 .065 .065 .065 058 .058 .058 .058 .058 .058 B 7/8 1 1-1/8 1-1/4 1-3/8 1-1/2 1-5/8 1-3/4 1-7/8 _2 ALL .058 THICK RIVET DIA 5/32 5/32 3/16 3/16 3/16 3/16 1/4 1/4 1/4 1/4 L 9-3/8 9-3/8 11-1/4 11-1/4 11-1/4 11-1/4 15 15 _ 15 15 * INCLUDES ALL THICKNESSES UP TO AND INCLUDING MAXIMUM SHOWN.
NOTE. USE SAME MATERIAL AS ORIGINAL FOR SLEEVE AND REPLACEMENT TUBE.
b. Repairs to Aluminum Alloy Members. Make repairs to aluminum alloy members with the same material or with suitable material of higher strength. The 7075 alloy has greater tensile strength than other commonly used aluminum alloys such as 2014 and 2024, but is subject to somewhat greater notch sensitivity. In order to take advantage of its strength characteristics, pay particular attention to design of parts to avoid notches, small radii, and large or rapid changes in cross-sectional areas. In fabrication, exercise caution to avoid processing and handling defects, such as machine marks, nicks, dents, burrs, scratches, and forming cracks. Cold straightening or Par 4-58 Page 4-34