Thursday, April 5, 2012

Aerospace Fasteners Types and Materials

The aerospace fastener industry has been around since before the airplane, having serviced the once-emergent dirigible market of yesteryear prior to Kitty Hawk. As aerospace technology developed to introduce commercial, business, shipping and military airplanes and jets, as well as space-destined rockets and ballistic missiles, aerospace fasteners evolved, too. Heavier-than-air travel is a combination of physics and engineering, requiring stringent adherence to top quality design and manufacturing standards. As a result of this long tradition of high quality, aerospace fasteners are not necessarily fasteners dedicated to aerospace equipment, but rather a term of quality assessment for the fastener industry as a whole. For this article, though, the focus will be on fasteners used in the aerospace industry.

Overview

The aerospace industry utilizes all sorts of standard fastener types, including screws, rivets, bolts, pins, collars and many more. The key difference is quality. Aerospace products need to be more durable in order to withstand a lot of high pressure and temperature environments, such as leaving the earth’s atmosphere or exposure to burning rocket fuel. Additionally, aerospace products must be lightweight. This helps with lift for planes and fuel costs for rockets. As a result of these concerns, research and development teams working for the government and private companies have created many types of equipment and metal treatment methods in order to get high quality fasteners airborne.

Aluminum

Aluminum is a lightweight metal used more in atmosphere-based planes, although it does feature in applications in the aerospace industry. However, it requires extra treatment. Aluminum rivets are very common, for instance, but the aluminum itself must be cold-head formed. Unfortunately, even after this process it is still sensitive to heat upwards of 250 degrees Fahrenheit, as well as stress induced corrosion.

Steels

Steels are very strong, hard alloys, but they are also very heavy, which can cause problems for air- and spacecraft. The main types of steel used in aerospace applications are stainless steel and alloy steels. Certain types of stainless steels are too susceptible to heat damage or even failure, so it is a top priority to select proper series stainless steel. Series C300 corrosion resistant (CRES) stainless steel, while not as heat resistant as other types, is often used for aerospace screws and bolts, as well as some fastener covers. CRES series 400 can also be used, because it is more heat resistant, but it can rust. Precipitation-hardened (PH) stainless steels of various grades are also used for some fastener applications. Alloy steels are very durable, but they can corrode easier. Fortunately, there are several treatments available, although some of these treatments can decrease carburization and resistance to tension corrosion.

Superalloys

Superalloys, or high-performance alloys, are very common as aerospace fasteners due to their versatility, ability to maintain integrity in high temperature environments, and their resistance to creep factors. A286, for instance, can withstand temperature extremes between -420 and 1200 degrees Fahrenheit. Inconel 718, a nickel-based superalloy, retains a 220ksi (kilopound per square inch) tensile strength up to 900 degrees Fahrenheit. In general, there are superalloys for many different types of stresses. Other superalloys include:

H-11 Waspaloy Hastelloy Monel K-Monel A286 Inconel 718 Waspalloy Haynes MP35N MP159

Titanium

Aerospace rivets are sometimes made from titanium instead of aluminum, because of its similarities to steel and alloy steel strength, but its relatively light weight. Additionally, Titanium is more heat and cold resistant than steel, with a spread between -350 and 800 degrees Fahrenheit.

Fastener Covers

In addition to fasteners themselves, the aerospace industry requires a lot of fastener covers. These covers are made from a wider variety of materials with different resistances to the types of environment experiences outside of our atmosphere. These materials include:

Cadmium Black Oxide Zinc Nickel Silver Phosphate

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