Aviation Fasteners & Aerospace Fasteners

When a screw wants to fly in space,what kind of test should it go through?

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Aviation Fasteners & Aerospace Fasteners

From life to production,fasteners,known as the “rice of industry”,are indispensable.

For example,a small screw,whether it is close to the palm of the smart phone or as far as the spacecraft to explore space,industrial society has its figure everywhere.

When a screw wants to fly in space,what kind of test should it go through?

Starting from the raw material,a thousand hammers,according to the highest standards of the thousands of selection,after a lot of procedures,a small screw is qualified to go to heaven.

Small products,big questions

Aerospace-grade products are half as light as civilian-grade products for screws of the same size.” Aerospace Precision Industry researchers hold up a screw to introduce it.
Upon closer examination,it is made of titanium alloy,with a blue-violet coating on the outside,which is as glossy and varied as the gradient color eyeshadow palette of a makeup artist.

According to the application area,fastener products can be divided into civil fasteners,type equipment level fasteners and astronautical fasteners three categories.
In the fasteners that can “go to heaven”,the most common is the high-strength rivets,the amount of use can reach hundreds of thousands of pieces.

The most important thing is that the rocket ignition takeoff time,must hold.” Researchers said,as a connection between the entire vehicle “sinews”,screws shape although small,but the role of great,fasteners on the spacecraft to withstand impact,vibration and variable loads,many of the joints to work at high or low temperatures.

Arrow body in the operating environment is complex,for which we specifically developed a ‘customized’ products,a plug,a sticky,a bracket can be installed.” The researcher added as he demonstrated the fasteners in his hand.

The majority of specialized structural fasteners employed within the station’s core module exhibit distinct advantages,including facilitated one-sided installation and swift assembly processes.

Researchers handle “conversational” bolts prevalent in high-speed rail systems,featuring a distinctive light band on their heads.A sensor,impressively thin at merely 5 microns,is skillfully integrated onto the bolt’s surface through an embroidery-like technique.

Combined with a special measuring instrument,it can accurately measure the preload force of smart bolts in real-time and in-situ,reminding users whether the bolts are installed in place,and improving the measurement accuracy by 10 times.

At the scene,the researchers also showed for the aircraft design “stealth bolts”,all products countersunk head height size is controlled within 0.05 mm,only 12 of a hair or so,so that after assembling the skin of the aircraft surface as smooth as satin.

High-temperature resistant bolts are processed with refractory alloys containing niobium,tungsten,tantalum,etc.,and an antioxidant ceramic coating is sintered on the surface of the bolts,so that the bolts wearing the “ceramic coat” are able to withstand high temperatures up to 1,800 degrees Celsius.

In the production workshop of Aisino Precision,after cold heading,thread forming,stamping,heat treatment,surface treatment and other processes,the rough raw material becomes a screw with different colors and perfect structure.

After testing and heavy test,a qualified screw can get the space “pass”,into the whole arrow,the whole star assembly link.

Basic knowledge of aviation fasteners

Fasteners with threads
Threaded fasteners:bolts,screws,washers and nuts
Helix – a moving point on the surface of a cylinder,while rotating at equal speed around the axis,while moving at equal speed along the axis of the trajectory.
Thread – plane figure along the spiral line of motion,the movement to maintain the figure through the axis of the cylinder,you get the thread.

Thread type,fit level and identification symbols
I.Thread types
Standard:AmericanNational Coarse
American National Fine
American Standard United Coarse
American Standard United Fine

Difference:1,the same size and number of coarse thread series and fine thread series of threads have the same nominal diameter of the thread,only the number of teeth per inch of length is different.2,the distribution of tolerances is different;there are also different regulations for 1-inch diameter threads.

Tolerances are distributed differently,and there is a difference in the specification for threads with a diameter of 1 inch:
NF regulations — 14 teeth per inch,with 1 — 14NF said
UNF regulation – 12 teeth per inch,with 1 – l2UNF said

Matching Grades
Threads are subject to grading,with their classification reflecting the level of tightness or looseness in the mating threads.This classification consists of five distinct grades.
Class 1 – Loose fit (easy to turn the nut with just a finger)
Grade 2 – free fit (used for aviation screws)
Grade 3 – medium fit (used in most aviation bolts)
Grade 4 & 5 – tight fit (requires a wrench to screw on the nut)
The larger the grade,the tighter the threaded sub-fit.
III.Marking symbols
Marking:bolt diameter,length,material,etc.
Note:Diameter measurement unit 1/6 in,the body bolts of the rod length measurement unit 1/8 in;bolt manufacturing material is expressed in English letters or symbols,such as
C” means stainless steel;
DD” indicates 2024 aluminum alloy;
“－”indicates nickel alloy steel.

Various types of threaded fasteners,including screws,bolts,nuts,and washers,serve diverse applications across industries.Screws are employed for securing wood,metal,and plastics,while bolts are used in structural assemblies.Nuts facilitate thread engagement,and washers distribute loads evenly,protecting surfaces from damage.These essential components ensure reliability in machinery,construction,and automotive engineering.

Bolts – Transmitting shear and tensile loads
Application:larger concentrated loads or parts to be disassembled
Classification:Tension-dominated

Shear-dominated
I.Standard aviation bolts
1、Universal bolts
A kind of bolt with hexagonal head,which is widely used in the assembly of aircraft structure and can withstand tensile and shear loads.This kind of bolt is manufactured according to AN type specification standard,the thread of the bolt is fine thread (NF).
Bolt material:chrome nickel plated steel stainless steel 2024 aluminum alloy
Bolt marking:
AN series bolt AN3DD14A is illustrated as an example:
AN – standard type bolts for USAF-Navy specifications
3″ – indicates that the bolt diameter of 3/16in airframe bolt
DD – indicates that the bolt is made of 2024 aluminum alloy.
14″ – denotes a bolt with a 1.5in shank length
A–Indicates that there is no safety hole in the end of the screw.

AN6H34A:
AN – is a standard type of bolt for US Air Force and Navy specifications.
6″ – denotes a 6/16in bolt diameter airframe bolt
H – indicates that the bolt is used to secure the propeller blade to the flange
34″ – denotes a bolt with a 3.5in shank length
A–Indicates that the end of the screw has no safety hole

2.Engine bolts with drilled holes in the head

AN73 to AN81 MS20073 MS20074 As shown:

The engine bolt mirrors the body bolt’s design,distinguished by a slightly thicker head and an integral through-hole intended for the fuse.Equipped with identical tensile and shear strengths,this component functions seamlessly alongside its counterpart.
Engine bolts are threaded with:
Fine thread (without “A”)
Coarse thread (thread diameter number followed by the letter “A”)

3、Tight tolerance bolts (AN173～AN186 and NAS80～NAS86)
Bolt diameter of the light rod section of the manufacturing accuracy than the general-purpose high,the bolt by grinding or grinding process,its diameter error between 0,-0.0005in.

4、hexagonal bolts (MS20004 MS20024)
Structure:the head of the bolt is cylindrical or conical table-shaped,in the head of the bolt made of internal hexagonal holes.

Material: Made of high-strength steel, its strength is higher than that of AN series hexagon head bolts, so it cannot be used interchangeably with AN series hexagon head bolts.

Application:Hexagon bolts are mainly used in parts subjected to tensile and shear composite stress.Its head is connected with the screw with rounded corners,avoiding the connection of sharp corners and improving the fatigue life.

Note:1.When installed on steel parts,the installation hole should be scratched so that the rounded corner is sunk into the hole;
2、When installing on aluminum alloy parts,it is necessary to install MS20002C washer under the head.
Model 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 that the bolt diameter of 4/16 inches to 24/16 inches,i.e.,1/4 inch to 3/2 inch.

5,with slotted flat round head bolts (AN2l AN36)

Characteristics:the head of the axle pin bolt is round,round head with a word or cross groove,screw part of the light rod and threaded rod section generally have an empty cutter groove between.

Thread:Fine thread (NF) is used.

Model specification code:

The second digit “1”, “2”, and “3” in AN2l, AN22, and AN23 indicate “6-40”, “8-36”, and “10-32” threads, respectively. The second digit “1”, “2” and “3” in AN22, and AN23 indicate “6-40”, “8-36” and “10-32” threads, respectively. Screw diameters from AN24 to AN36 are in 1/16-inch increments. Shaft pin bolts are also available in 1/16-inch rod lengths.

Applications:Shaft pin bolts are designed to withstand shear loads only and are often used in rotating parts as a pin at the point of articulation;the mating shear nut fits snugly into the bolt threads and is secured with a cotter pin.
Example:AN24 – 14A
A” – indicates that there is no safety hole at the end of the bolt,in which case the nut to be fitted to the bolt should be 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 1416 inch.
“-”screw material is nickel alloy steel
4″ – Bolt diameter 416 inch
2″ – Shaft pin bolts
AN” – U.S.Air Force Navy specification standards

Second,the nut
1、Standard aviation nuts

1) AN310 slotted top nut (castlenut)
Renamed as the battlemented nut,this particular variety earns its distinctive title.
Function:Designed for compatibility with AN3 to AN20 threaded body bolts.
Thread:NF (fine thread)
Material:Nickel-alloy steel,stainless steel,and 2024 aluminum alloy
“-“,”C”,and “D”
Revised:”The item is designated as AN3l0 C 6.”
Indicates:Slot top nuts made of stainless steel for use with AN6 bolts;

(2) AN320
Designation:shear castlenut
Application:only the part of shear stress,it is used in conjunction with AN2l AN36 shaft pin bolts.
Construction,manufacturing materials:the same as AN310 nuts,only the thickness of the nut is slightly thinner.
Example:Marking AN320D6
It is expressed as:2024 aluminum alloy and AN26 shaft pin bolts used in conjunction with shear-resistant hexagonal slotted flat nuts.

(3) AN315
Name:shear castlenut
Application:Used for parts subject to large tensile force.Its disadvantage is that it is necessary to use another anti-loosening nut or an elastic washer to ensure its tightness.
Material:same as AN310 nut.
There exist two distinct types of right-handed threads and their counterparts,left-handed threads.
Example:Marking AN315-7R
Indicates:Nuts made of nickel alloy steel with right-hand thread for AN7 bolts.
Marking:AN3l5C4L
Indicates:made of stainless steel,thread diameter of 14 inch left-hand thread nut.

(4) AN316
Name:Anti-loosening nut
Characteristics:This is a hexagonal anti-loosening nut with double-nut anti-loosening measures.It is used on top of AN315 common nut to prevent the common nut from loosening.However,due to the large weight increase over other types of anti-loosening measures,it is seldom used in airplanes at present.

(5) AN340 and AN345
Name:Mechanical screw nut
Application:Used in conjunction with machine screws,so the thread specifications are manufactured according to the specifications of the screws.
Thread:AN340 is a coarse threaded nut;AN345 is a fine threaded nut.
Constructed from high-quality materials,the product features carbon alloy steel,corrosion-resistant stainless steel,durable brass,and lightweight 2024 aluminum alloy.
Example:Marking AN340B6
Indicates a coarse threaded nut made of brass for use with 6-32 mounting screws.

(6) AN350
Name:Butterfly nut
Application:Designed for assemblies that are frequently disassembled and can be finger-tightened only.These nuts can be used with mounting screws or bolts.The nut to be used with the mounting screw is given by the number of the screw.
Manufactured from durable alloy steel or high-quality brass,ensuring strength and resilience.
Example:Marking AN350-6

Indicates:Nut for use with 6-40 mounting screws.The nut used with the bolt is given by the specification of the 1/16-inch bolt,and the number 16 is added at the same time.

2、Self-locking nuts
1) Low-temperature self-locking nuts and locking principle
Model:AN365,AN364
Locking principle:low-temperature self-locking nut in the threads inserted into an elastic ring,the inner diameter of the threads slightly smaller than the match.When the nut is turned so that the bolt is screwed through the bottom section of the threads and wants to enter the top section of the threads,the resistance of the elastic ring must be overcome in order to make the threads of the bolt and the top section of the threads of the nut to harmonize and engage.After all the bolts are tightened,the elastic ring section forces the top section threads to bite the bolt threads tightly to achieve the purpose of anti-loosening.

2) High-temperature self-locking nuts and locking principle
Model:AN363

These two kinds of self-locking nuts are tightened after the closure expansion,by elastic locking.They can be reused many times,due to its relatively simple manufacturing process,so these two kinds of self-locking nuts in the aircraft are increasingly widely used.

3) Application of self-locking nuts
Applications:fixing friction reducing bearings,pulleys of the maneuvering system,engine rocker box mouth cover,exhaust pipe.

Precautions:
1,aircraft use self-locking nuts have restrictions,should meet the requirements;
2,low-temperature self-locking nut use environment temperature T ≤ 2500F;
3,self-locking nut screwed into the bolt with sufficient depth;
4,bear the rotation torque of the bolt can not use self-locking nut.

Washers

The primary function of a washer is to facilitate effective cleaning by agitating and suspending污渍 from fabrics,enhancing the cleaning process in various laundry tasks.
1,is to make the nut or bolt head below the uniform force.
2,Adaptable in nature,it facilitates precise control over the thread’s proximity to the component’s surface.
3,there are locking,anti-loosening,protection and pre-tightening instructions and other roles.

1、Ordinary washers
AN960 for the most commonly used ordinary washers (Figure (a))
Application:It is widely used under hexagonal nuts.
Material:there are carbon,steel,brass,stainless steel and aluminum alloy.
Specification:There are from the specifications used with No.1 mounting screws to the specifications used with 1-inch bolts.
2、AN935 open type elastic washers (Figure (d))
3、AN936B type external tooth type elastic washers (Figure (e))
4、AN936A type internal tooth type elastic washers (Figure (f))
AN936 internal and external teeth type elastic washers,uniform elasticity,anti-loosening effect is better.External tooth type is more applications.

Four,screws

Manufactured from materials with inherent inferior strength,screws are commonly crafted from less robust elements compared to the materials employed for bolt production.

Because it is used in non-structural connections and fairings,removable panels and other non-major stress structures.

Features:

1) Its structure is similar to that of the bolt,the screw body is generally a fully threaded body,the threads are manufactured according to the grade 2 free fit accuracy.
2) Nail tail has two kinds of flat head and pointed head.
3) installation,screws are generally screwed in the component screw holes,usually turn the screw to achieve the purpose of fastening.

Classification by use:1,mechanical screws 2,structural screws 3,self-tapping screws.

1,mechanical screws
Mechanical screws predominantly serve in non-structural components,including delicate machinery components,lightweight assemblies,and precisely engineered gearbox covers,all fabricated from cast aluminum materials.

Features:
1) Screw head end face of the screwdriver slot with the same structure screws
2) Screw rod body is fully threaded rod section
3) Threads are available in coarse and fine threads

Material:mild steel,stainless steel,brass and aluminum alloy,etc.

Common models are:
1) AN500 for coarse thread round head screws AN501 for fine thread round head screws
2) AN505 for coarse thread 82 ° countersunk head screws AN507 for fine thread 82 ° countersunk head screws
3) AN515 for coarse thread round head screws AN526 for fine thread large round head screws

2、Structural screws

Material:made of alloy steel

Features:

1) its tensile and shear strength and the same size,material AN-type bolts the same
2) The type of screw has the same size bolt exactly the same length
3) The body of the nail rod has a light rod (unthreaded) section with NF threads,and the fit accuracy of the screw is also the same as that of AN type hexagonal head bolts,so it can be used as a structural bolt.

Screw head type:there are round head,flat round head,100 ° buried head and other types.
Screw head screwdriver groove:cross type (phillips) Pointed cross type (Reed-prince) a word groove

Common structural screw models are:
1) AN509 100 ° flat head screws
2)The AN525 washer head screws feature prominently their extensive washer-like heads,designed to accommodate substantial load zones.
3) AN502 and AN503 round head screws
AN502 for fine-threaded round head screws,AN503 for coarse-threaded round head screws,these two types of screws have a round head nail head with a slot and a small hole through the fuse.

3,self-tapping screws

Self-tapping screws are commonly used in thin metal plates,plastic plates and other fastening features:
1) by itself in the assembly hole tapping and fastening.
2) self-tapping screw head type:flat round head,100 ° buried head,large flat round head.
3) Nail tail:pointed (A type) blunt head (B type).

Common models are:
1) AN504 and AN506 they are often used to install such as signs and other removable parts.
2) AN530 and AN531 they are used for self-tapping screws for sheet metal.AN530 for flat round head,AN531 for countersunk head self-tapping screws – B type.

4,screw type
Marking AN501B-416-7
said:416 – diameter 4/16 inches,7 – rod length of 7/16 inches,B – that the material is brass,AN – — Empty,Navy Standard 501 — Recessed cylindrical head,fine thread.