Aerospace Fasteners

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The aerospace industry employs a variety of standard fasteners, including screws, rivets, nuts, bolts, pins, and collars. As aerospace equipment and technology is often subjected to extreme environments—e.g., high pressures and temperatures from leaving the earth’s atmosphere or exposure to burning rocket fuel—they must be designed and constructed to withstand these conditions, even down to the fasteners which hold them together. As a result, several different designs of high-quality fasteners have been developed which are suitable for the specifications and standards of the aerospace industry, each of which exhibits different characteristics and qualities.

Some of the characteristics which aerospace fasteners typically exhibit include:

• High corrosion and oxidation resistance
• High tensile, shear, and fatigue strength
• Lightweight construction (to help optimize lift in planes and minimize the fuel costs of rockets)
• Operational capabilities in extreme environments (e.g., low and high temperatures and pressures)
• Self-sealing and self-locking capabilities (to prevent fluid and pressure leaks and loosening during operation)

The AS9100 and AS9120 quality management standards have wide use in the aerospace sector. AS9100, BS9100, and EN9100 are standards for organizations designing and manufacturing aerospace goods, such as parts, components, and assemblies. On the other hand, AS9120, BS9120, and EN9120 are standards for manufacturers and distributors of aerospace parts.

 There are some fasteners for aerospace that have wide applications in the commercial aviation industry. Also, there is an overview of the different types of fasteners for aircraft and how they compare and differ.

• Aircraft bolts: These are made of unplated corrosion-resistant steel, zinc plated corrosion-resistant steel, cadmium, or anodized aluminum alloys. Moreover, the commonly used bolts for aircraft are MS bolts, close tolerance bolts, NAS internal wrenching, and AN bolts.
• Aircraft nuts: These are threaded fasteners made of cadmium plated carbon steel, stainless steel, or anodized 2024T aluminum alloy. Besides, they are always used in conjunction with a mating bolt or screw. There are two types of aircraft nuts: non-locking and self-locking.
• Aircraft screws: These fasteners are the most common thread fastening method with a helical ridge, called an external thread. They are often composed of lower-strength materials than bolts and inserted with a loose-fitting thread.
• Aircraft rivets: These fasteners have a smooth cylindrical shaft with a head on one end and are used to join two or more metal sheets, plates, or pieces of material. The rivet’s shank is placed into matched holes in two pieces of material, and the tip is upset to produce a second head that securely clamps the two parts together.
• Aerospace Collars (Lock Bolt Rivet): These fasteners fit seamlessly with lock bolt rivets (available separately). They aid in attaching the rivet or bolt to the object and have compatible metal alloy bodies.
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As outlined above, aerospace fasteners exhibit several different characteristics. The characteristics demonstrated by a fastener are primarily determined by the material chosen for the particular fastener’s construction. Some of the common materials used for aerospace fasteners include:

• Aluminum
• Steel
• Titanium
• Superalloys

Although typically used in atmospheric planes, aluminum also has applications in the aerospace industry— albeit in the latter case, it requires additional surface treatment to attain the proper performance characteristics. For example, although aluminum rivets are common, achieving aerospace standards for these components requires that the lightweight material be cold-head formed. Unfortunately, even after being subjected to this process, the material remains highly sensitive to temperatures above 250 degrees Fahrenheit, as well as to stress-induced corrosion.

Steel and steel alloys typically feature high strengths and surface hardnesses. However, they are also heavier than other materials which can create issues when designing and constructing aircraft and spacecraft so careful consideration must be taken when using steel materials for aerospace parts and components.

Stainless steel and alloy steels are the main types of steel used in aerospace applications. Certain types of stainless steels, however, are susceptible to heat damage and failure, so it is essential to select the proper series of stainless steel for the specifications and requirements of the aerospace application. For example:

• Series C300 corrosion resistant (CRES) stainless steel, while not as heat resistant as other types available, is often used for aerospace screws and bolts and some fastener covers.
• CRES series 400 features greater heat resistance, but it is also more susceptible to corrosion.
• Precipitation-hardened (PH) stainless steels of various grades are also used for some fastener applications.
• Alloy steels express high levels of durability but are also susceptible to corrosion.

There are several surface treatments available for steels to prepare them for aerospace applications. However, these same treatments can also decrease the material’s carburization and resistance to tension corrosion.

In certain cases, titanium can serve as an alternative to aluminum material in the construction of aerospace fasteners. Some of the advantages of using titanium are its strength being comparable to that of steel and alloy steel, relative lightness, and resistance to heat and cold with operating temperatures ranging between -350–800°F.

Superalloys, or high-performance alloys, are commonly used in aerospace fasteners due to their ability to withstand the many different types of stresses experienced by aerospace equipment and components. Characteristics of superalloys include high versatility, the ability to maintain their structural and surface integrity in extreme environments, and their resistance to creep factors. Some of the types of superalloys available for use in the aerospace industry include:

• A286: an iron-nickel-chromium alloy which can withstand temperatures ranging between -420 and 1200 degrees Fahrenheit and exhibits high strength and corrosion and oxidation resistance. Suitable for use in engines, superchargers, and turbines.
• H-11: a 5% chromium tool steel alloy which exhibits high impact resistance and surface hardness. Suitable for use in structural and highly stressed components, such as landing gears.
• Hastelloy® (a registered trademark of Haynes International, Inc.): a nickel-molybdenum-chromium superalloy which exhibits high corrosion resistance. Suitable for use in combustion and exhaust components.
• Inconel 718® (a registered trademark of Special Metals Corporation): a nickel-based superalloy, retains a 220ksi (kilopound per square inch) tensile strength up to 900 degrees Fahrenheit.
• Monel® (a registered trademark of Special Metals Corporation): a nickel-copper alloy which exhibits high tensile strength and corrosion resistance. Suitable for use in structural components, as well as combustion and exhaust equipment.
• Waspaloy® (a registered trademark of United Technologies Corp): a nickel-based superalloy capable of withstanding temperatures up to 1600 degrees Fahrenheit, as well as exhibiting high corrosion and oxidation resistance.
• MP35N® ( a registered trademark of SPS Technologies, Inc.): a nickel-cobalt based alloy which exhibits high tensile strength, surface hardness, and corrosion resistance. Suitable for use in structural components.