Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Impact driven fastener – e.g. – nail – spike – tack – etc. – Including integral locking means
Reexamination Certificate
2000-11-28
2003-12-09
Saether, Flemming (Department: 3679)
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Impact driven fastener, e.g., nail, spike, tack, etc.
Including integral locking means
C411S456000, C411S477000, C411S478000
Reexamination Certificate
active
06659700
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to fasteners and more particularly to a metal piercing fastener for securing one or more metal
on-metal layers to at least one metal layer and retaining the secured layers in their positions permanently under adverse conditions.
PRIOR ART
Many fastener designs exist in the prior art and generally these designs can be placed into two different categories. The first are fasteners used in an environment where the fastener is accessible from both sides of the work pieces being joined together, which include traditional nut and bolt or the like. The other group or category of fasteners are those which must operate in environments wherein the fastener is usually only accessible from one side of the work pieces and may be manipulated from one and only one of its ends to accomplish its fastening task. This is called “blind” fastening and the present invention is directed to fasteners in this category.
In this latter category, there are many varieties of such fasteners. Traditional examples of such fasteners, including those capable of penetrating sheet metal, can be grouped into two categories. The first grouping consists of self-piercing and self-drilling threaded screws. The second grouping consists of brads, staples, nails, drive pins and the like. In the first group of fastening devices, a high rpm electric screw gun is usually used for installation. In the second grouping, a pneumatically actuated tool is normally utilized to cause the fastener to penetrate the work pieces and secure them together. In many instances where U-shaped, staple-like fasteners, brads, nails, drive pins, and the like have been employed, such fasteners are provided in an elongated continuous member or ‘stick’ with the penetrating points all facing in a common direction. These sticks are inserted into the magazine of a tool. The tool is placed at a desirable position over one of the work pieces being fastened to the other, is activated and a driving element is forcibly driven against the end of the fastener on the end opposite the point driving the fastening element through the work pieces to secure the same together.
In the case wherein a metal self-piercing screw is utilized, the screw is secured into the end of a power-driven rotating chuck attached to an electric screw gun. The tool, upon being activated, rapidly rotates the screw at approximately 2500 to 4000 rpm. Upon application of significant physical force by the installer, the rotational friction of the screw against the work piece heats the metal to a softened state thereby allowing penetration of the work piece. The helical threads engage the metal pulling the fastener through and securing the work pieces together. In the case wherein a metal self-drilling screw is utilized, it is secured into a similar tool as is used with self-piercing screws except this type of electric screw gun rotates the self-drilling screw at approximately 1800 to 2500 rpm. Also, similar to self-piercing screws, application of a significant force by the installer is required to press the cutting flutes into the metal to achieve a drilling operation. After a hole is drilled, the fastener then engages helical threads to secure the work pieces together.
With these examples of prior art, it should be noted that the threaded fastener advancement rate for the piercing or drilling operation is slower than the advancement rate when the fastener threads are engaged. This not only implies that these types of ‘blind’ fasteners have much slower installation rates and require considerable force to be applied by the operator but their self-piercing or self-drilling function must be completed before any of their threads become engaged within the substrates.
When a non-metal work piece is to be attached to a light-gauge metal substrate or two or more pieces of metal are to be attached, the bottom sheet may be pushed away from the top piece to be attached before the penetration and fastening process is completed. In the construction trades and fastener arts, this phenomenon is termed “oil canning”. Fastener “oil canning” is a function of fastener velocity, the metals' deflection properties and the ratio of the substrate mass being displaced to the fastener mass. The current state of art utilizes helical threads to pull the two separated sheets together. The lack of some mode of clamping component within nails, drive pins or staples precludes such fasteners from successfully tightening substrates to light gauge metal(s) or two or more light gauge metals together. Prior art metal penetrating fasteners and particularly metal penetrating and self-drilling screws demonstrate various disadvantages. Significant training and installation experience is required to bring the installer skill to an acceptable level.
For example, when attaching a work piece such as drywall, it is important that the work piece not be damaged and be properly clamped to the metal stud substrate without overdriving the fastener crown into the workpiece or tearing the work piece paper laminate. Use of such screws is labor intensive and requires physical pressure against the installation tool, both of which contribute to worker fatigue. Another disadvantage of conventional self-piercing and self-drilling threaded fasteners is that their threads achieve contact with the thin sheet metal base substrate at only one or two relatively small contact areas along the slanting helical threads. A single thread only touches the material on one side and a twin-lead thread will have just two contact points. This small area of contact (deemed “thread engagement”) frequently contributes to a fastening failure mode referred to as “thread strip-out.” This can occur when a slight over-torqueing of the fastener causes this relatively small contact point in the metal to rapidly fatigue resulting in the destruction of the mechanical interlock between the thread and metal substrate. In addition, there is an industry trend towards the use of even thinner metals which will acerbate this problem.
With other conventional fasteners, such as nails, drive pins or staples, there is no effective device or means to provide a gripping and clamping action on the backside of the bottom substrate being fastened. Therefore, adequate clamping of sheets is not always assured. Even more lacking is their withdrawal or ‘pull-out’ resistant values that are dependent on lateral friction forces between the fastener's contact points with the pierced holes. It has been determined that effective withdrawal or ‘pull-out’ values for these types of fasteners is not attained until the thickness of bottom substrate metal exceeds a thickness of 0.1250″ or that of a 11 gauge metal sheet. In addition, prior to the fastener of this invention, only drive pins within this category of blind fasteners have been able to consistently pierce metals of this thickness. The failure of these types of blind fasteners during severe conditions such as hurricanes, tornadoes, and earthquakes to effectively hold fastened substrates together has resulted in many of these types of fasteners being de-certified for light gauge structural metal construction applications. Additions of non-resilient spiral threads, flutes, undercuts, barbs or teeth to these products tend to only increase the physical dimensions of the substrate penetration pattern by ripping or removing the actual metal required to provide adequate clamping and holding.
Another consequence of this low thread-engagement condition is the lack of requisite friction to increase “back-off” resistance. When a threaded fastener is subjected to vibration or withdrawal stresses this “back-off” resistance is the force which keeps the fastener in place. In such thin materials and with such minor thread engagement, the “back-off” resistance is minimal and the fastener frequently becomes loose, thereby sacrificing the integrity of the fastened joint.
Furthermore, with conventional nails, staples, or drive pins designs, such fasteners lack an effective method to clamp
Farrell Mark A.
Farrell Michael E.
Evening Star International, Inc.
Fulbright & Jaworski L.L.P.
Saether Flemming
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