This is the ultimate guide to specifying aerospace fasteners.
And let’s be very clear:
This is not a product guide (you can find our full stock card here).
Here you will learn about the the key specifications for aerospace fasteners.
You will also learn the performance characteristics that these specifications, manufacturing materials and techniques result in.
Aerospace fasteners are designed to withstand the extreme environments that they often experience.
There are various standard fasteners employed across the aerospace industry, all sharing the same names as stadard fasteners.
These include:
• Screws;
• Rivets;
• Nuts;
• Bolts;
• Collars.
But there is a difference.
Aersospace fasteners need to be durable and resistant to corrosion. They also need to withstand extreme pressure and dramatic temperature changes.
As a result of these exacting needs, there are various different designs for high-quality fasteners which have been developed.
Aerospace fasteners are always made to the most demanding specifications.
Performance Characteristics
The key characteristics include the following:
• Resistant to corrosion and oxidation (even in extreme conditions);
• Durable and strong with high shear and fatigue strength;
• Lightweight (often there is a careful balance to be found between lightweight for optimization of aircraft performance, loss of strength that comes with some lightweight materials, and the cost);
• Temperature resistant (they need to function optimally in a large temperature range).
Typical Aerospace Fastener Materials
As we’ve already mentioned, there are various designs for different fasteners which are dependent on the desired characteristics of the fastener and the type of extreme conditions it will experience.
An instrumental part of a fastener’s characteristic are the materials that the fastener is made of.
Some of the more commonly used materials in aerospace fasteners include:
• Steel
• Aluminium
• Titanium
• Super-alloys
Steel
Steel and steel-based alloys typically feature greater strength than other materials. However, this extra-strength comes at a cost.
Steel is heavier, which can cause issues, especially when designing and constructing aircraft.
Serious careful consideration needs to be taken when using steel as a part in aerospace design.
Normally when steel is used for aerospace applications, they mean stainless steel or particular steel alloys.
Certain steel alloys are susceptible to heat damage, however, which makes it doubly important that the proper series of stainless steel is chosen for the specific requirements of its aerospace application.
Three examples of this are:
• Series C300: This series is corrosion resistant (CRES) stainless steel. It doesn’t, however, have the same heat resistance as other types of stainless steel but is often used for covers.
• CRES series 400: This series features much greater heat resistance than the series C300 but as a trade-off of sorts it’s more susceptible to corrosion.
• Precipitation-hardened (PH) stainless steels of various grades are also used for some fastener applications.
There are also surface treatments that can be used on steels to improve their performance.
Aluminium
Aluminium has obvious benefits for the aerospace industry. It being much lighter than metals like steel.
However, it isn’t as strong and to attain industry acceptable performance characteristics it must be cold-heat formed and then undergo additional surface treatments.
Unfortunately, whilst these processes increase its strength and corrosion resistance, aluminium remains highly sensitive to dramatic temperature changes – and doesn’t operate well above around 125 degrees Celsius.
Titanium
Some of the advantages of using titanium are that it is lightweight (compared to steel), has strength that is comparable to steel, and it is resistant to heat and cold.
Specified operating temperatures range between -200C – 430C. This makes it a good material choice under certain circumstances.
Superalloys
High-performance alloys, as they are also known, are frequently used in the aerospace industry due to their broad range of specifications and their high-performance qualities.
They can withstand the many different types of stress that fasteners experience in aerospace equipment, whilst maintaining their structure and surface integrity.
Common super-alloys include:
• A286: an iron-nickel-chromium alloy which can withstand temperatures ranging between minus 420 and 1200 degrees Fahrenheit. It 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 super-alloy 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 super-alloy, 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 super-alloy 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.
Fastener Covers
An aspect of the aerospace fastener industry that ironically often gets overlooked is fastener covers.
These are required for the purpose of protecting fasteners from additional stress. Fastener covers are made from a broad array of different materials, which like the fasteners themselves are used for their specific characteristics.
Examples of materials used for fasteners covers include, but are not limited to:
• Phosphate;
• Zinc;
• Nickel;
• Silver;
• Black Oxide;
• Cadmium.
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For more about aerospace fastener terminology, don’t forget to keep checking back on our blog.
We have been manufacturing and supplying aerospace fasteners since the 1950s.
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