The role of aviation fasteners: the tens of thousands of functions of the aircraft: the tens of thousands of parts of the aircraft are connected to form a whole; when carrying, the load is transmitted and the deformation is coordinated.
Threaded fastener
Threaded fasteners: bolts, screws, washers and nuts - multiple disassembly and assembly of spirals - moving points on the surface of a cylinder, rotating at equal speed around the axis, while axially The trajectory of the speed movement.
Thread ------The plane pattern moves along the helix, and when the motion is maintained, the pattern passes through the axis of the cylinder, and the thread is obtained.
Thread type, mating level and identification symbolFirst, the thread type
Standard: AmericanNational Coarse
American National Fine
American Standard United Coarse
American Standard United Fine
The difference is as follows: 1. The coarse thread series of the same size number has the same thread nominal diameter as the thread of the fine thread series, except that the number of teeth per inch length is different, the tolerance distribution is different; and the diameter is 1 inch. The thread rules are different:
NF regulations - 14 teeth per inch, expressed as 1 - 14 NF UNF regulations - 12 teeth per inch, expressed in 1 - l2UNF
Second, the level of cooperation• The thread is also graded. The grade of the thread indicates the degree of tightness of the thread pair. It has five levels:
• Level 1 - loose fit (just turn the nut easily with your fingers)
• Level 2 - Free fit (used by aviation screws)
• Level 3 - Moderate fit (used by most aviation bolts)
• 4, 5 - tight fit (requires a wrench to tighten the nut)
The greater the number of grades, the tighter the tightening of the thread pair.Third, the identification symbol
Marking: bolt diameter, length, material, etc.
Note: The diameter measurement unit is 1/16in, and the rod length measurement unit of the body bolt is 1/8 in; the manufacturing material of the bolt is expressed by English letters or symbols, such as • “C†means stainless steel;
• “DD†means 2024 aluminum alloy;
• “-†indicates nickel alloy steel.Types of threaded fasteners and application bolts - transfer shear and tensile load applications: large concentrated loads or parts that need to be disassembled: tension-based shearing
First, standard aviation bolts
1, universal bolt
• A bolt with a hexagonal head that is widely used in aircraft structural assembly to withstand tensile and shear loads. These bolts are manufactured to AN model specifications and the threads of the bolts are fine thread (NF). • Bolt material: chrome-plated nickel steel Stainless steel 2024 aluminum alloy bolt mark:
AN series bolt AN 3 DD 14A as an example:
AN---Standard bolt "3" for the US Air Force Navy specification - indicates the body bolt with a bolt diameter of 3/16in
DD--- indicates that the bolt is made of 2014 aluminum alloy "14"--- indicates that the bolt length is 1.5in
A---- indicates that there is no safety hole at the end of the screw
AN 6 H 34 A :
AN---Standard bolt "6" for the US Air Force Navy specification - indicates the body bolt with a bolt diameter of 6/16in
H-- indicates that the bolt is used to fix the propeller blade on the flange "34"--- indicates that the bolt length is 3.5in
A---- indicates that there is no safety hole at the end of the screw2. Engine bolts for head drilling
AN73 to AN81 MS20073 MS20074The shape of the engine bolt is the same as that of the body bolt, except that its head is slightly thicker and has a through hole for the fuse. It has the same tensile and shear strength as the body bolts.
The threads of the engine bolts are:
Fine thread (no "A" letter)
Coarse thread (number of thread diameter followed by letter "A")3 , tight tolerance bolts (AN173 ~ AN186 and NAS80 ~ NAS86)
The diameter of the bolted rod section is higher than that of the universal type. The bolt is ground or ground, and its diameter error is between 0 and -0.0005 in.
4. Hexagon socket head bolts (MS20004~MS20024)
Construction: The head of the bolt is cylindrical or truncated, and the inner hexagonal hole is formed on the bolt head.
Material: Made of high-strength steel, its strength is higher than that of the AN series hex head bolts, so it is not interchangeable with the AN series hex head bolts.
Application: Hexagon socket head bolts are mainly used to withstand tensile and shear composite stresses. Its head and screw joints have rounded corners to avoid sharp corners and improve fatigue life.
Note: 1. When installing on steel, the installation hole should be nested to make the round hole sink into the hole;2. When installing on aluminum alloy parts, install MS20002C gasket under its head.
Model specification code: MS20004 ~ MS20024
The last two digits are 04, 05, 06, 07, 08, 09, 10, 12, 14, 16, 18, 20, 22, and 24, which indicate bolt diameters from 4/16" to 24/16". That is 1/4 inch to 3/2 inches.
5, slotted flat head bolts (AN2l ~ AN36)
Features: The head of the pin bolt is a round head with a word or cross groove on the round head. There is usually an empty sipe between the polished rod part of the screw and the threaded rod section.
Thread: Fine thread (NF).
Model specification code:
The second digits "1", "2", and "3" in AN2l, AN22, and AN23 represent "6-40", "8-36", and "10-32" threads, respectively. The diameter of the screw from AN24 to AN36 is in units of 1/16 inch. The rod length of the pin bolt is also in 1/16 inch units.
Application: The axle pin bolt can only bear the shear load, which is often used as the pivot pin of the hinge point in the rotating part; the matching shear nut is closely matched with the bolt thread and is secured by the split pin.
Example: AN 2 4 - 14 A
“A†------ means that there is no safety hole at the end of the bolt rod. In this case, the nut that cooperates with the screw should use a self-locking nut. If there is no "A", it means that there is a safety hole at the end of the bolt.
"14"----bolt rod length 14/16" "-"----screw material is nickel alloy steel "4"----bolt diameter 4/16 inch "2"-----shaft pin Bolt "AN"----US Air Force Naval StandardSecond, the nut
1, standard aviation nut
l) AN310 slot top nut (castlenut)
Name: This type of nut is also called å ž nut application: it is used with AN3 ~ AN2O body bolts: NF (fine thread)
Material: nickel alloy steel, stainless steel and 2024 aluminum alloy "-", "C" and "D"
Example 1: Mark AN3l0 C 6
Expressed as: a slotted nut made of stainless steel for use with AN6 bolts;
(2) AN320
Name: Shearing the top nut (shear castlenut)
Application: The part with only shear stress, it is used with AN2l~AN36 shaft pin bolts.
Construction and manufacturing materials: the same as the AN310 nut, except that the thickness of the nut is slightly thinner.
Example: Mark AN320D6
It is expressed as: Shear type hexagonal slotted flat nut made of 2024 aluminum alloy and AN26 shaft pin bolt.3) AN315
Name: Ordinary nut application: For parts subject to large tension. Its disadvantage is that it must be replaced with a lock nut or a spring washer to ensure its tightness.
Material: Same as AN310 nut.
Thread: There are two types of right-handed and left-handed threads.
Example: Mark AN315-7R
Representation: Right-hand threaded nut made of nickel alloy steel and used with AN7 bolts.
Tag: AN3l5C4L
Represents: a left-hand threaded nut with a stainless steel thread and a 1/4 inch diameter.
(4) AN316
Name: Lock nut Features: This is a hexagonal lock nut in the double nut anti-loose measures. It is used on the AN315 common nut to prevent the normal nut from loosening. However, due to the increased weight compared to other types of anti-loose measures, it is currently rarely used on airplanes.(5) AN340 and AN345
• Name: Mechanical screw nut • Application: Used in conjunction with mechanical screws, so the thread size is manufactured to the specifications of the screw.
• Thread: AN340 is a coarse threaded nut; AN345 is a fine threaded nut.
• Materials: Carbon alloy steel (-), stainless steel (C), brass (B) and 2024 aluminum alloy (DD).
• Example: Mark AN340B6
Expressed as: a coarse threaded nut made of brass and used with a 6-32 mounting screw.(6) AN350
• Name: Butterfly Nut • Application: A fitting that is designed for quick disassembly and assembly and that can be tightened with just a finger. This nut can be used with mounting screws or bolts. The nut that fits the mounting screw is given by the number of the screw.
• Material: alloy steel or brass.
• Example: Mark AN350-6
• Indicates: a nut for use with the 6-40 mounting screws. The nut used with the bolt is given in 1/16 inch bolt size with a number of 16.2, self-locking nut (1) low temperature self-locking nut and locking principle Model: AN365, AN364
Locking principle: The low temperature self-locking nut inserts an elastic ring into the thread, and the inner diameter is slightly smaller than the matching thread. When the nut is turned to screw the bolt through the bottom section thread and the top section thread is to be entered, the resistance of the elastic ring must be overcome in order to coordinate the thread of the bolt with the thread of the top section of the nut. After the bolts are fully tightened, the elastic ring segments force the top thread to tightly bite the bolt threads for anti-loosening purposes.(2) High temperature self-locking nut and locking principle Model: AN363
Both of these self-locking nuts are opened and tightened after tightening, and are elastically locked. They can be reused many times, and because of their relatively simple manufacturing process, these two self-locking nuts are increasingly used on aircraft.
(3) Application of self-locking nut Application: Fixed anti-friction bearing, pulley of control system, engine rocker box cover, exhaust pipe Note:
1. The use of self-locking nuts in aircraft is limited and should meet the requirements;
2, low temperature self-locking nut using ambient temperature T "2500F;
3. When the self-locking nut is screwed into the bolt, it must have sufficient depth;
4. Bolts that are subject to rotating torque cannot use self-locking nuts.Third, the gasket
The role of the gasket:
1. The force is evenly distributed under the nut or bolt head.
2. It can be used to adjust the distance between the thread and the surface of the component.
3. It has the functions of locking, anti-loose, protection and pre-tightening instructions.
1, ordinary washer
AN960 is the most commonly used ordinary gasket (Fig. (a)).
Application: It is widely used under hex nuts.
Materials: Carbon, steel, brass, stainless steel and aluminum alloy.
Specifications: Available from the size of the 1st mounting screw to the 1" bolt.
2, AN935 open type elastic washer (figure (d))
3, AN936B type external gear type elastic washer (figure (e)
4, AN936A type internal tooth type elastic washer (fig (f))).
AN936 inner and outer toothed elastic washers have uniform elastic force and good anti-loose effect. There are many external tooth types.
Fourth, the screwThe material from which the screw is made is often lower than the strength of the material from which the bolt is made.
Because it is applied to non-structural connections and non-primary structures such as fairings and detachable panels.
Features:
1) Its structure is similar to that of bolts. The screw shaft is generally a full-threaded shaft, and the thread is manufactured with 2 levels of free fit precision.
2) There are two kinds of flat ends and pointed ends.
3) When installing, the screws are generally screwed into the screw holes on the components, and the screws are usually screwed for fastening purposes.
Classified by purpose: 1. Mechanical screw 2. Structural screw 3. Self-tapping screw
1. Mechanical Screws Mechanical screws are commonly used on non-structural parts, such as light and small parts and gearbox covers.
Features:
1) The screw groove on the end face of the screw head is the same as the structural screw
2) The screw shaft is a fully threaded rod segment
3) Threads are available in coarse and fine teeth: low carbon steel, stainless steel, brass and aluminum alloy.
Common models are:
(l) AN500 is a coarse-toothed head screw AN501 is a fine-toothed round head screw
(2) AN505 is a coarse tooth 82° countersunk screw AN507 is a fine tooth 82° countersunk screw
(3) AN515 is a coarse-toothed round head screw AN526 is a fine-toothed large round head screw2, structural screw material: alloy steel made features:
1) The tensile and shear strengths are the same as the AN-type bolts of the same size and material.
2) This type of screw has the same length as the same size bolt
3) The nail body has a polished rod (unthreaded) section, the thread is NF, and the matching precision of the screw is also the same as that of the AN type hexagonal head bolt, so it can be used as a structural bolt.
Head shape of the screw: It has a round head, a flat head, and a 100° countersunk head.
Screw head slot for screw heads: Phillips Phillips cross-shaped (Reed-prince) slot
The common structural screw models are:
(1) AN509 100° grub screw (2) AN525 washer head screw, which has a large head like a washer and has a large bearing area.
(3) AN502 and AN503 round head screws AN502 is a fine-toothed round head screw, and AN503 is a coarse-toothed round head screw. The round heads of these two kinds of screws have a slot on the head and have a small hole through the fuse.
3, self-tapping screws
Self-tapping screws are often used for fastening characteristics of thin metal plates, plastic plates, etc.
1) Fastened by tapping itself in the assembly hole.
2) The head shape of the self-tapping screws are: flat round head, 100° countersunk head, large flat round head, etc.
3) The tail is: pointed (type A) blunt (type B)
Common models are:
(l) AN504 and AN506 They are commonly used to mount detachable parts such as signage.
(2) AN530 and AN531 These are self-tapping screws for metal sheets. AN530 is a flat head, AN531 is a countersunk head tapping screw-B type4, screw model
Mark AN501B-416-7
Representation: 416 - diameter 4 / 16 inches, 7 - rod length 7 / 16 inches, B - indicates that the material is brass, AN - air, naval standard 501 - grooved cylindrical head, fine thread.
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