Global Fastener News

PRODUCT NEWS: From Earth to Saturn: Getting a Grip on Vibration, Shock, and Extreme Temperature

John Wolz

Spiralock Corporation: A new internal thread form is helping manufacturers combat vehicle vibration, shock, and temperature extremes not only on earthbound applications but also on the frigid surface of Saturn�s largest moon.
When the Cassini-Huygens spacecraft enters Saturn�s orbit in July 2004, it will have endured – for the first time in human history – not only the vibration, shock, and temperature extremes of a Titan IV rocket launch, but also a seven-year journey from earth across more than 750 million miles of space. The probe will measure atmospheric composition down to Titan�s frigid surface.
Inherent in any threaded fastening system is the necessity for clearance. Unfortunately, the radial clearances between traditional male and female 60� �vee� threads permit relative sideways or lateral movement when shock, vibration, or transverse loading occurs. Any sideways movement in the conventional threaded hole reduces locking friction between the thread flanks and then the male fastener generates self-loosening movement.
Common stripping or shearing problems can occur when conventional 60� �vee� threads position the majority of the clamp load on the first engaged thread, permitting subsequent male threads to virtually �float� within the female threads. Testing has found that the first two threads carry as much as 80% of the load. When the load is applied, the male fastener stretches between the head and the first engaged thread. As clamp load continues to increase, the second thread takes some of the load. In many cases, however, the force required to transfer a significant amount of the load to the third and fourth threads begins to shear or strip the first thread.
Through the physics of the thread itself, Madison Heights, Mich.-based Spiralock introduced a thread form designed to address the fastener loosening and stripping problem caused byvibration, shock and temperature extremes. Spiralock�s thread form is a 30� �wedge� ramp cut at the root of the female thread. Under clamp load, the crests of the threads on any standard bolt are drawn tightly against the wedge ramp. This causes thread contact forces to be applied at approximately 60� from the bolt axis, rather than 30� away as in a standard thread form. The angular relationship between the wedge ramp and male thread restricts bolt or screw movement.
The wedge ramp allows the fastener to spin freely until clamp load is applied. At that point, the crests of the standard male thread form are drawn tightly against the wedge ramp, eliminating radial clearances and creating a continuous spiral line of contact along the entire length of thread engagement. This spreads the clamp force more evenly over all engaged threads.
The Shuttle orbiter�s three main engines develop 400,000 lb. of thrust and terrific vibration and NASA wanted a 15-cycle reuse capability per fastener. Under its own test, NASA determined that the fasteners in Spiralock-threaded holes did not back off or loosen when subjected to ten times shuttle-specified vibrations, and they stayed that way ten times longer than called for. Each shuttle engine carries no fewer than 757 Spiralock fasteners. Web: spiralock.com
Product News
J.W. Winco Inc., a supplier of standard industrial machine components, now offers steel socket screws with full, flat, or serrated ball point ends and steel set screws with a brass or nylon tip. Web: jwwinco.com
The Metal Powder Industries Federation published a 40-page 2003 Suppliers Directory with 163 companies and organization producing ferrous and nonferrous metal powders. Web: mpif.org
Nylok Corporation introduced a high-temperature self-locking patch material which �frees designers from the 250�F maximum of traditional materials and allows them to use self-locking fasteners with multiple cycle reuse capabilities in areas never before possible. �By maintaining torque and clamp load stability in temperatures up to 450�F the patch is for assembly applications in aerospace, automotive, appliances, small engines and other areas. Web: nylok.com
Ready Rivet & Fastener, Ltd., of Kitchener, Ontario, a Canadian manufacturer of specialty cold formed products, offers a solution to making stainless steel parts, cost effectively, that have to be cold headed and subsequently machined or fabricated from the same feed stock. Typically, most stainless steels with excellent heading characteristics do not machine well when secondary fabrication is required. Similarly, a stainless alloy designed to provide exceptional machining properties is not a likely candidate for cold heading. Ready Rivet found that it could get superior cold forming and machinability performance from a single stainless grade used to mass produce ball studs for an automotive application. The shop increased productivity by two thirds and tool life by 50% by using 302HQ-FM(R) stainless (S30431), an alloy developed by Carpenter Technology Corporation. ReadyRivet.com or cartech.com
Spaenaur Inc. is distributing Loctite�s new thread treatment sticks. The new products offer more flexibility in overhead or hard-to-reach applications, on components that cannot be moved and for pretreating bolts. Web: spaenaur.com
The Aerospace Fasteners Group of SPS Technologies introduced new high-strength Aerlite 160 and 180 titanium alloy fasteners for aerospace applications. The product line offers higher tensile and shear strength in sizes previously unavailable. The aerospace group also published a warning report on the MS/NAS socket screw products issue. The report is designed to promote understanding of MS and NAS standards and associated specifications, describe problem areas, including dimensional requirements, mechanical properties, plating and quality assurance. Web: spstech.com/aero\�2003 FastenerNews.com