Aerospace fastener
2008-08-06

Acument Global Technologies, Inc. announced it will re-enter the high-performance aerospace threaded fastener market with the opening of a production complex in Rockford, Illinois. The facility will create jobs and open a new chapter in the city's long history of supplying assembly systems and technology to global producers of commercial and military aircraft.
Producing fasteners for the aerospace industry requires a greater focus on quality and various techniques to meet high performance expectations.
Various techniques have been used in the aerospace industry to ensure that threaded fasteners are secured with the requisite torque and that they stay secured during use. An example is the product known as the HI-LOK fastener in which a wrenching collar is attached to a fastener collar by a frangible section such that when the application torque exceeds the design torque for the fastener, the wrenching collar separates, leaving the fastening collar in place. Although this application technique insures that the fastener collars are initially applied at the requisite torque, there is no assurance that with use and vibration the fastener collars will not loosen. 
Various techniques have been used to prevent loosing of the fastener collars or nuts in the aerospace industry. These have included mechanical locking devices such as mechanically upset threads on the nut or bolt fastener, typically slightly elliptical threads on the nut fastener. This, however, imparts a permanent drag to the application of the fastener and precludes free-spinning fasteners, thus encumbering the aircraft assembly. Additionally, the upset threads cause galling in the threads of the fasteners during application, particularly with titanium and certain stainless steel fasteners. Other mechanical locking devices include plastic or elastomer inserts in a portion of the threads of the nut or bolt fastener. Another disadvantage of the mechanical lock fasteners such as HI-LOK or HI-LITE, etc., is that they cannot be reused, contributing to high maintenance costs of the aircraft.
Various patents have been issued for adhesive compositions such as U.S. Pat. No. 4,164,971 to Strand for an adhesive coating having a microencapsulated solvent which, upon application of the fastener, is released to cure the adhesive coating on the bolt or nut. Another patent, U.S. Pat. No 4,325,985 to Wallace discloses an uncured resin which is coated with a ultraviolet-degradable film and which is activated by ultraviolet radiation during the application process. Other patents relating to adhesive systems are U.S. Pat. No.3,814,156 to Bachmann and 3,163,338 to Reike.
The design and application of threaded fasteners for commercial aircraft is closely regulated by the aerospace industry rules, such as paragraph 5 of the Boeing part specification for self-locking nuts (BPS-N-70) which specifies that a nut is considered installed when a minimum of one thread plus the chamfer of the male thread extends beyond the top of the nut. The purpose of this rule is two-fold; it permits easy visual inspection to confirm that the fastener has been applied correctly and it provides additional threaded length to assure that the mechanical locking element of the fastener has been penetrated by the bolt fastener.
Basically, the aerospace fastener industry has consolidated since 2000, led by Alcoa, the chief supplier of bolts for the 787, which acquired Huck Fasteners and Fairchild Fasteners and makes the bolts for the 787 at plants in southern California