from 76 to 8 inch. The diameter is measured as shown in figure 6-21.
Cable Fittings Cables may be equipped with several different types of fittings such as terminals, thimbles, bushings, and shackles.
Terminal fittings are generally of the swaged type. They are available in the threaded end, fork end, eye end, single-shank ball end, and double-shank ball end. The threaded end, fork end, and eye end terminals are used to connect the cable to a turnbuckle, bellcrank, or other linkage in the system. The ball-end terminals are used for attaching cables to quadrants and special connections where space is limited. Figure 6-22 illustrates the various types of terminal fittings.
The thimble, bushing, and shackle fittings may be used in place of some types of terminal fittings when facilities and supplies are limited and immediate replacement of the cable is necessary.
AN663 Double shank ball end terminal AN664 Single shank ball end terminal AN665 Rod end terminal AN666 Threaded cable terminal Turnbuckles A turnbuckle assembly is a mechanical screw device consisting of two threaded terminals and a threaded barrel. Figure 6-23 illustrates a typical turnbuckle assembly.
Turnbuckles are fitted in the cable assembly for the purpose of making minor adjustments in cable length and for adjusting cable tension. One of the terminals has right-hand threads and the other has left-hand threads. The barrel has matching right- and left-hand internal threads. The end of the barrel with the left-hand threads can usually be identified by a groove or knurl around that end of the barrel.
When installing a turnbuckle in a control system, it is necessary to screw both of the terminals an equal number of turns into the barrel. It is also essential that all turnbuckle terminals be screwed into the barrel until not more than three threads are exposed on either side of the turnbuckle barrel.
After a turnbuckle is properly adjusted, it must be safetied. The methods of safetying turnbuckles are discussed later in this chapter.
PUSH-PULL TUBE LINKAGE Push-pull tubes are used as linkage in various types of mechanically operated systems. This AN667 Fork end cable terminal AN688 Eye end cable terminal FIGURE 6-22. Types of terminal fittings.
type linkage eliminates the problem of varying tension and permits the transfer of either compression or tension stress through a single tube.
A push-pull tube assembly consists of a hollow aluminum alloy or steel tube with an adjustable end fitting and a checknut at either end. (See figure 6-24.) The checknuts secure the end fittings after the tube assembly has been adjusted to its correct length. Push-pull tubes are generally made in short lengths to prevent vibration and bending under compression loads.
PINS The three main types of pins used in aircraft structures are the taper pin, flathead pin, and cotter pin. Pins are used in shear applications and 144
Length (Threads flush with ends of barrel) Swaged terminal - Pin eye FIGURE 6-23. Typical turnbuckle assembly.
for safetying. Roll pins are finding increasing uses in aircraft construction.
Taper Pins Plain and threaded taper pins (AN385 and AN386) are used in joints which carry shear loads and where absence of play is essential. The plain taper pin is drilled and usually safetied with wire. The threaded taper pin is used with a taper-pin washer (AN975) and shear nut (safetied with cotter pin) or self-locking nut.
Flathead Pin Commonly called a clevis pin, the flathead pin (MS20392) is used with tie-rod terminals and in secondary controls which are not subject to continuous operation. The pin is customarily installed with the head up so that if the cotter pin fails or works out, the pin will remain in place.
Cotter Pins The AN380 cadmium-plated, low-carbon steel cotter pin is used for safetying bolts, screws, nuts, other pins, and in various applications where such safetying is necessary. The AN381 corrosionresistant steel cotter pin is used in locations where nonmagnetic material is required, or in locations where resistance to corrosion is desired.
Rollpins The rollpin is a pressed-fit pin with chamfered ends. It is tubular in shape and is slotted the full length of the tube. The pin is inserted with hand tools and is compressed as it is driven into place.
Pressure exerted by the roll pin against the hole walls keeps it in place, until deliberately removed with a drift punch or pin punch.
SAFETY METHODS Safetying is the process of securing all aircraft, bolts, nuts, screws, pins, and other fasteners o that they do not work loose due to vibration. A familiarity with the various methods and means of safetying equipment on an aircraft is necessary in order to perform maintenance and inspection.
There are various methods of safetying aircraft parts. The most widely used methods are safety wire, cotter pins, lockwashers, snap-rings, and special nuts, such as self-locking nuts, pal nuts, and jamnuts. Some of these nuts and washers have been previously described in this chapter.
Safety Wiring Safety wiring is the most positive and satisfactory method of safetying capscrews, studs, nuts, boltheads, and turnbuckle barrels which cannot be safetied by any other practical means. It is a method of wiring together two or more units in Self-aligning, anti-friction rod end assembly, adjustable Tube, steel or Clevis, Rod end, Check nut Rod end-threaded aluminum alloy adjustable OUD ОлЮт FIGURE 6-24. Push-pull tube assembly.
6 8 FIGURE 6-25. Safety wiring methods.
such a manner that any tendency of one to loosen is counteracted by the tightening of the wire.
Nuts, Bolts, and Screws Nuts, bolts, and screws are safety wired by the single-wire or double-twist method. The doubletwist method is the most common method of safety wiring. The single-wire method may be used on small screws in a closely spaced closed geometrical pattern, on parts in electrical systems, and in places that are extremely difficult to reach.
Figure 6-25 is an illustration of various methods which are commonly used in safety wiring nuts, bolts, and screws. Careful study of figure 6-25 shows that:
a. Examples 1, 2, and 5 illustrate the proper method of safety wiring bolts, screws, squarehead plugs, and similar parts when wired in pairs.
b. Example 3 illustrates several components wired in series.
c. Example 4 illustrates the proper method of wiring castellated nuts and studs. (Note that there is no loop around the nut.)
d. Examples 6 and 7 illustrate a singlethreaded component wired to a housing or lug.
e. Example 8 illustrates several components in a closely spaced closed geometrical pattern, using a single-wire method.
When drilled-head bolts, screws, or other parts are grouped together, they are more conveniently safety wired to each other in a series rather than individually. The number of nuts, bolts, or screws that may be safety wired together is dependent on the application. For instance, when safetywiring widely spaced bolts by the double-twist method, a group of three should be the maximum number in a series.
When safety-wiring closely spaced bolts, the number that can be safety-wired by a 24-inch length of wire is the maximum in a series. The wire is arranged so that if the bolt or screw begins to loosen, the force applied to the wire is in the tightening direction.
Parts being safety-wired should be torqued to recommend values and the holes aligned before attempting the safetying operation. Never over torque or loosen a torqued nut to align safety wire holes.
Oil Caps, Drain Cocks, and Valves These units are safety wired as shown in figure
6-26. In the case of the oil cap, the wire is anchored to an adjacent fillister head screw.
This system applies to any other unit which must be safety wired individually. Ordinarily, anchorage lips are conveniently located near these individual parts. When such provision is not made, the safety wire is fastened to some adjacent part of the assembly.
Oil caps Drain cocks Note: The safety wire is shown installed for right-hand threads. The safety wire is routed in the opposite direction for left-hand threads.
Valves FIcURE 6-26. Safety wiring oil caps, drain cocks, and valves.
Electrical Connectors Under conditions of severe vibration, the coupling nut of a connector may vibrate loose, and with sufficient vibration the connector may come apart. When this occurs, the circuit carried by the cable opens. The proper protective measure to prevent this occurrence is by safety wiring as shown in figure 6-27. The safety wire should be as short as practicable and must be installed in such a manner that the pull on the wire is in the direction which tightens the nut on the plug.
Turnbuckles After a turnbuckle has been properly adjusted, it must be safetied. There are several methods of safetying turnbuckles; however, only two methods will be discussed in this section. These methods are illustrated in figure 6-28 (A) and 6-28 (B).
The clip-locking method is used only on the most modern aircraft. The older type aircraft still use the type turnbuckles that require the wire-wrapping method.
AN3102 receptacle Bulkhead AN Standard fillister head screw (drilled head) AN3106 plug "AN3057 adapter FIGURE 6-27. Safety wiring attachment for plug connectors.
Straight end Hook shoulder
- Loop end Hook lip- - Hook loop Hook end Lock clip NAS 651 Direction of pull for inspection (A) AN161 or AN162 Turnbuckle fork Lock wire Turnbuckle barrel AN155 - 4 turns wrap Cable 4 turns wrap Tumbuckle eye AN170 - Thimble AN100 Lock wire 4 turns wrap Swaged terminal (B) AN666 or AN669 FIGURE 6-28. Safetying turnbuckles;
(A) Clip-locking method; (B) wire-wrapping method.
Double-wrap Method Of the methods using safety wire for safetying turnbuckles, the double-wrap method is preferred, although the single-wrap methods described are satisfactory. The method of double-wrap safetying is shown in figure 6-28 (B). Use two separate lengths of the proper wire as shown in figure 6-29.
Diameter of Material (annealed Cable size Type of wrap safety wire condition) (in.) (in.)
·16- Single - 020 Stainless steel 332- Single - 040 Copper, brass!
8-- Single - 040 Stainless steel 78- Double - 040 Copper, brass' 7/8- Single . 057 min Copper, brass' 32 and greater. Single - 057 Stainless steel
1. Galvanized or tinned steel, or soft iron wires are also acceptable.
FIGURE 6-29. Turnbuckle safetying guide.
Run one end of the wire through the hole in the barrel of the turnbuckle and bend the ends of the wire towards opposite ends of the turnbuckle.
Then pass the second length of the wire into the hole in the barrel and bend the ends along the barrel on the side opposite the first. Then pass the wires at the end of the turnbuckle in opposite directions through the holes in the turnbuckle eyes or between the jaws of the turnbuckle fork, as applicable. Bend the laid wires in place before cutting off the wrapped wire. Wrap the remaining length of safety wire at least four turns around the shank and cut it off. Repeat the procedure at the opposite end of the turnbuckle.
When a swaged terminal is being safetied, pass the ends of both wires, if possible, through the hole provided in the terminal for this purpose and wrap both ends around the shank as described If the hole is not large enough to allow passage of both wires, pass the wire through the hole and loop it over the free end of the other wire, and then wrap both ends around the shank as de- Single-wrap Method The single-wrap safetying methods described in the following paragraphs are acceptable but are not the equal of the double-wrap methods.
Pass a single length of wire through the cable eye or fork, or through the hole in the swaged terminal at either end of the turnbuckle assembly.
Spiral each of the wire ends in opposite directions around the first half of the turnbuckle barre: so that the wires cross each other twice. Thread both wire ends through the hole in the middle of the barrel so that the third crossing of the wire ends is in the hole. Again, spiral the two wire ends in opposite directions around the remaining half of the turnbuckle, crossing them twice. Then, pass one wire end through the cable eye or fork, or through the hole in the swaged terminal. In the manner described above, wrap both wire ends around the shank for at least four turns each, cutting off the excess wire.
An alternate to the above method is to pass one length of wire through the center hole of the turnbuckle and bend the wire ends toward opposite ends of the turnbuckle. Then pass each wire end through the cable eye or fork, or through the hole in the swaged terminal and wrap each wire end around the shank for at least four turns, cutting off the excess wire. After safetying, no more than three threads of the turnbuckle threaded terminal should be exposed.
General Safety Wiring Rules When using the safety wire method of safetying, the following general rules should be followed:
1. A pigtail of ¼ to ½ inch (three to six twists) should be made at the end of the wiring. This pigtail must be bent back or under to prevent it from becoming a snag.
2. The safety wire must be new upon each application.
3. When castellated nuts are to be secured with safety wire, tighten the nut to the low side of the selected torque range, unless otherwise specified, and if necessary, continue tightening until a slot aligns with the hole.
Optional Preferred FIGURE 6-30. Cotter pin installations.
4. All safety wires must be tight after installation, but not under such tension that normal handling or vibration will break the wire.
5. The wire must be applied so that all pull exerted by the wire tends to tighten the nut.
6. Twists should be tight and even, and the wire between the nuts as taut as possible without overtwisting.
7. The safety wire should always be installed and twisted so that the loop around the head stays down and does not tend to come up over the bolthead, causing a slack loop.
Cotter Pin Safetying Cotter pin installation is shown in figure 6-30.
Castellated nuts are used with bolts that have been drilled for cotter pins. The cotter pin should fit neatly into the hole, with very little sideplay.
The following general rules apply to cotter pin safetying:
1. The prong bent over the bolt end should not extend beyond the bolt diameter. (Cut it off if necessary.)
2. The prong bent down should not rest against the surface of the washer. (Again, cut it off if necessary.)
3. If the optional wraparound method is used, the prongs should not extend outward from the sides of the nut.
4. All prongs should be bent over a reasonable radius. Sharp-angled bends invite breakage. Tapping lightly with a mallet is the best method of bending the prongs.
Snaprings A snapring is a ring of metal, either round or flat in cross section, which is tempered to have springlike action. This springlike action will hold the snapring firmly seated in a groove. The external types are designed to fit in a groove around the outside of a shaft or cylinder. The internal types fit in a groove inside a cylinder. A special type of pliers is designed to install each type of snapring.
Snaprings can be reused as long as they retain their shape and springlike action.
External-type snaprings may be safety wired, but internal types are never safetied. Safety wiring of an external type snapring is shown in figure
6-31.
RIVETS An aircraft, even though made of the best materials and strongest parts, would be of doubtful value unless those parts were firmly held together.
Several methods are used to hold metal parts together; they include riveting, bolting, brazing, and welding. The process used must produce a union that will be as strong as the parts that are joined.
Aluminum and its alloys are difficult to solder.
To make a good union and a strong joint, aluminum parts can be welded, bolted, or riveted together. Riveting is satisfactory from the standpoint of strength and neatness, and is much easier to do than welding. It is the most common method used to fasten or join aluminum alloys in aircraft construction and repair.
A rivet is a metal pin used to hold two or more metal sheets, plates, or pieces of material together. A head is formed on one end when the rivet is manufactured. The shank of the rivet is placed through matched holes in two pieces of material, and the tip is then upset to form a second head to clamp the two pieces securely.
together. The second head, formed either by hand or by pneumatic equipment, is called a "shop head." The shop head functions in the Snapring Single-wire method Shaft FIGURE 6-31. External type snap ring with safety wire installed.
same manner as a nut on a bolt. In addition to their use for joining aircraft skin sections, rivets are also used for joining spar sections, for holding rib sections in place, for securing fittings to various parts of the aircraft, and for fastening together.
Two of the major types of rivets used in the aircraft are the common solid-shank type, which must be driven using a bucking bar, and the special (blind) rivets, which may be installed where it is impossible to use a bucking bar.
Solid-Shank Rivets Solid-shank rivets are generally used in repair work. They are identified by the kind of material of which they are made, their head type, size of shank, and their temper condition. The designation of the solid-shank rivet head type, such as universal head, roundhead, flathead, countersunk head, and brazier head, depends on the cross sectional shape of the head (see figure 6-33). The temper designation and strength are indicated by special markings on the head of the rivet.
The material used for the majority of aircraft solid-shank rivets is aluminum alloy. The strength and temper conditions of aluminum alloy rivets are identified by digits and letters similar to those adopted for the identification of strength and temper conditions of aluminum and aluminum alloy sheet stock. The 1100, 2017-T, 2024-T, 2117-T, and 5056 rivets are the five grades usually available.
The 2017-T and 2024-T rivets are used in aluminum alloy structures where more strength is needed than is obtainable with the same size 2217-T rivet. These rivets are annealed and must be kept refrigerated until they are to be driven.
The 2017-T rivet should be driven within approximately 1 hour and the 2024-T rivet within 10 to 20 minutes after removal from refrigeration.
The 5056 rivet is used for riveting magnesium alloy structures because of its corrosion-resistant qualities in combination with magnesium.
Mild steel rivets are used for riveting steel parts. The corrosion-resistant steel rivets are for riveting corrosion-resistant steels in firewalls, exhaust stack brackets, and similar structures.
Monel rivets are used for riveting nickel-steel alloys. They can be substituted for those made of corrosion-resistant steel in some cases.
The use of copper rivets in aircraft repair is limited. Copper rivets can be used only on copper alloys or nonmetallic materials such as leather.
Metal temper is an important factor in the riveting process, especially with aluminum alloy rivets. Aluminum alloy rivets have the same heattreating characteristics as aluminum alloy sheet stock. They can be hardened and annealed in the same manner as sheet aluminum. The rivet must be soft, or comparatively soft, before a good head can be formed. The 2017-T and 2024-T rivets are annealed before being driven. They harden with age.
The 1100 rivet, which is composed of 99.45 percent pure aluminum, is very soft. It is for riveting the softer aluminum alloys, such as 1100, 3003, and 5052, which are used for nonstructural parts (all parts where strength is not a factor).
The riveting of map cases is a good example of where a rivet of 1100 aluminum alloy may be The 2117-T rivet, known as the field rivet, is used more than any other for riveting aluminum alloy structures. The field rivet is in wide demand because it is ready for use as received and needs no further heat-treating or annealing. It also has a high resistance to corrosion.
The process of heat treating (annealing) rivets is much the same as that for sheet stock. Either an electric air furnace, a salt bath, or a hot oil bath is needed. The heat treating range, depending on the alloy, is 625° F. to 950° F. For convenient handling, rivets are heated in a tray or a wire basket. They are quenched in cold water (70° F.) immediately after heat treating.
The 2017-T and 2024-T rivets, which are heattreatable rivets, begin to age-harden within a few minutes after being exposed to room temperature.
Therefore, they must be used immediately after quenching or else be placed in cold storage. The most commonly used means for holding heat- 151
treatable rivets at low temperature (below 32° F.)
is to keep them in an electric refrigerator. They are referred to as "icebox" rivets. Under this storage condition, they will remain soft enough for driving for periods up to 2 weeks. Any rivets not used within that time should be removed for re-heat treating.
Icebox rivets attain about one-half their maximum strength in approximately 1 hour after driving and full strength in about 4 days. When 2017-T rivets are exposed to room temperature for I hour or longer, they must be subject to re-heat treatment. This also applies to 2024-T rivets exposed to room temperature for a period exceeding 10 minutes.
Once an icebox rivet has been taken from the refrigerator, it should not be mixed with the rivets still in cold storage. If more rivets are removed from the icebox than can be used in 15 minutes, they should be placed in a separate container and stored for re-heat treatment. Heat treatment of rivets may be repeated a number of times if done properly. Proper heating times and temperatures are:
Heating time-air furnace Time at Heat treating Rivet alloy temperature temperature 2024_ 1 hour 910° F.-930° F.
2017- 1 hour 925° F.-950° F.
Heating time-salt bath 2024- 30 minutes 910° F.-930° F.
2017_ 30 minutes 925° F.--950° F.
Most metals, and therefore aircraft rivet stock, are subject to corrosion. Corrosion may be the result of local climatic conditions or the fabrication process used. It is reduced to a minimum by using metals which are highly resistant to corrosion and possess the correct strength-toweight ratio.
Ferrous metals placed in contact with moist salt air will rust if not properly protected.
Nonferrous metals, those without an iron base, do not rust, but a similar process known as corrosion takes place. The salt in moist air (found in the coastal areas) attacks the aluminum alloys.
It is a common experience to inspect the rivets of an aircraft which has been operated near salt water and find them badly corroded.
If a copper rivet is inserted into an aluminum Group A Group B 1100 2117 3003 2017 5052 2124 6053 7075 FIGURE 6-32. Aluminum groupings.
alloy structure, two dissimilar metals are brought in contact with each other. Remember, all metals possess a small electrical potential. Dissimilar metals in contact with each other in the presence of moisture cause an electrical current to flow between them and chemical by-products to be formed. Principally, this results in the deterioration of one of the metals.
Certain aluminum alloys react to each other and, therefore, must be thought of as dissimilar metals. The commonly used aluminum alloys may be divided into the two groups shown in figure Members within either group A or group B can be considered as similar to each other and will not react to others within the same group. A corroding action will take place, however, if any metal of group A comes in contact with a metal in group B in the presence of moisture.
Avoid the use of dissimilar metals whenever possible. Their incompatibility is a factor which was considered when the AN Standards were adopted. To comply with AN Standards, the manufacturers must put a protective surface coating on the rivets. This may be zinc chromate, metal spray, or an anodized finish.
The protective coating on a rivet is identified by its color. A rivet coated with zinc chromate is yellow, an anodized surface is pearl gray, and the metal-sprayed rivet is identified by a silvery-gray color. If a situation arises in which a protective coating must be applied on the job, paint the rivet with zinc chromate before it is used and again after it is driven.
Identification Markings on the heads of rivets are used to classify their characteristics. These markings may be either a raised teat, two raised teats, a dimple, a pair of raised dashes, a raised cross, a single triangle, or a raised dash; some other heads have 152
no markings. The different markings indicate the composition of the rivet stock. As explained previously, the rivets have different colors to identify the protective surface coating used by the manufacturers.
Roundhead rivets are used in the interior of the aircraft, except where clearance is required for adjacent members. The roundhead rivet has a deep, rounded top surface. The head is large enough to strengthen the sheet around the hole and, at the same time, offer resistance to tension.
The flathead rivet, like the roundhead rivet, is used on interior structures. It is used where maximum strength is needed and where there isn't sufficient clearance to use a roundhead rivet.
It is seldom, if ever, used on external surfaces.
The brazier head rivet has a head of large diameter, which makes it particularly adaptable for riveting thin sheet stock (skin). The brazier head rivet offers only slight resistance to the airflow, and because of this factor, it is frequently used for riveting skin on exterior surfaces, especially on aft sections of the fuselage and empennage. It is used for riveting thin sheets exposed to the slipstream. A modified brazier head rivet is also manufactured; it is simply a brazier head of reduced diameter.
The universal head rivet is a combination of the roundhead, flathead, and brazier head. It is used in aircraft construction and repair in both interior and exterior locations. When replacement is necessary for protruding head rivets-roundhead, flathead, or brazier head-they can be replaced by universal head rivets.
The countersunk head rivet is flat topped and beveled toward the shank so that it fits into a countersunk or dimpled hole and is flush with the material's surface. The angle at which the head slopes may vary from 78° to 120°. The 100° rivet is the most commonly used type. These rivets are used to fasten sheets over which other sheets must fit. They are also used on exterior surfaces of the aircraft because they offer only slight resistance to the slipstream and help to minimize turbulent airflow.
The markings on the heads of rivets, indicate the material of which they are made and, therefore, their strength. Figure 6-33 identifies the rivet head markings and the materials indicated by them. Although there are three materials indicated by a plain head, it is possible to distinguish their difference by color. The 1100 is aluminum color; the mild steel is a typical steel color; and the copper rivet is a copper color. Any head marking can appear on any head style of the same material.
Each type of rivet is identified by a part number so that the user can select the correct rivet for the job. The type of rivet head is identified by AN or MS standard numbers. The numbers selected are in series and each series represents a particular type of head. (See figure 6-33.)
most common numbers and the types of heads they represent are:
AN426 or MS20426-countersunk head rivets AN430 or MS20430-roundhead rivets.
AN441-fathead rivets.
AN456-brazier head rivets.
AN470 or MS20470-universal head rivets.
There are also letters and numbers added to a part number. The letters designate alloy content;
the numbers, rivet diameter and length. The letters in common use for alloy designation are:
A-Aluminum alloy, 1100 or 3003 compo- AD-Aluminum alloy, 2117-T composition.
D-Aluminum alloy, 2017-T composition.
DD-Aluminum alloy, 2024-T composition.
B- Aluminum alloy, 5056 composition.
C- Copper.
M-Monel.
The absence of a letter following the AN standard number indicates a rivet manufactured from mild steel.
The first number following the material compo.
sition letters expresses the diameter of the rivet shank in 32nds of an inch. Examples: 3, 3ands;
5, 5/32nds; etc. (See figure 6-34).
The last number(s), separated by a dash from the preceding number, expresses the length of the rivet shank in 16ths of an inch. Examples: 3, 16ths; 7, 16ths; 11, 116ths; etc. (See figure
6-34.)
An example of identification marking of a rivet is:
AN470AD3-5-complete part number.
AN-Air Force-Navy standard number.
470-universal head rivet.
AD-2117-T aluminum alloy.
3-⅔2nds in diameter.
5-16ths in length.
ANG28 AN442 Univeral Material Marking нево Material Code AN Sunk Head Counter- Sunk Head MS20426 * Sunk Head MS20427 * Counter- MS20470* MS20613* MS20470 * Head M$20470* MS20470* MS20470* Before Using Heat Treat Shear itrengti P.S.I. P.S.I. searini MS20615* No 10000 25000 AD No 30000 100000 (o D Yes 34000 113000 D No 38000 126000 DD Yes 41000 138000 No 27000 90000 No MS20813* No 35000 90000 MS20613* No 65000 90000 No 23000 M No 49000
60) c MS20815* No 49000 MS20815* No MS 20426 No 95000 * New specifications are for Design purposes FIGURE 6-33. Rivet identification chart.
Special (Blind) Rivets There are many places on an aircraft where access to both sides of a riveted structure or structural part is impossible, or where limited space will not permit the use of a bucking bar.
Also, in the attachment of many nonstructural parts such as aircraft interior furnishings, flooring, deicing boots, and the like, the full strength of solid shank rivets is not necessary.
For use in such places, special rivets have been designed which can be bucked from the front.
They are sometimes lighter than solid-shank rivets, yet amply strong for their intended use.
These rivets are produced by several manufacturers and have unique characteristics that require special installation tools, special installation procedures, and special removal procedures.
That is why they are called special rivets. Because these rivets are often inserted in locations where Protruding Countersunk one head (usually the shop head) cannot be seen, head head they are also called blind rivets.
Countersunk - FIGURE 6-35. Self-plugging (friction lock) rivets.
angle Length of rivet Dia. of shank Dia. of shank FIcURE 6-34. Methods of measuring rivets.
Mechanically Expanded Rivets Two classes of mechanically expanded rivets will be discussed here:
(1) Non-structural
(a) Self-plugging (friction lock) rivets
(b) Pull-thru rivets
(2) Mechanical lock, flush fracturing, selfplugging rivets.
Self-Plugging The self-plugging (friction lock) blind rivets are manufactured by several companies: the same general basic information about their fabrication, composition, uses, selection, installation, inspection, and removal procedures apply to all of them.
Self-plugging (friction lock) rivets are fabricated in two parts: A rivet head with a hollow shank or sleeve, and a stem that extends through the hollow shank. Figure 6-35 illustrates a protruding head and a countersunk head self-plugging rivet produced by one manufacturer.
Several events, in their proper sequence, occur when a pulling force is applied to the stem of the rivet: (1) The stem is pulled into the rivet shank;
(2) the mandrel portion of the stem forces the rivet shank to expand; and (3) when friction (or pulling action pressure) becomes great enough it will cause the stem to snap at a breakoff groove on the stem. The plug portion (bottom end of the stem) is retained in the shank of the rivet giving the rivet much greater shear strength than could be obtained from a hollow rivet.
Self-plugging (friction lock) rivets are fabricated in two common head styles: (1) A protruding head similar to the M520470 or universal head, and
(2) a 100° countersunk head. Other head styles are available from some manufacturers.
The stem of the self-plugging (friction lock) rivet may have a knot or knob on the upper portion, or it may have a serrated portion as shown in figure 6-35.
Self-plugging (friction lock) rivets are fabricated from several materials. Rivets are available in the following material combinations: stem 2017 aluminum alloy and sleeve 2117 aluminum alloy; stem 2017 aluminum alloy and sleeve 5056 aluminum alloy; and stem steel and sleeve steel.