Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Externally threaded fastener element – e.g. – bolt – screw – etc. – Thread or shank structure
Reexamination Certificate
1999-06-04
2001-07-03
Saether, Flemming (Department: 3627)
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Externally threaded fastener element, e.g., bolt, screw, etc.
Thread or shank structure
C411S399000
Reexamination Certificate
active
06254326
ABSTRACT:
The invention relates to a screw for mutual fastening of at least two components, comprising a shank equipped if necessary at its free end with a boring part or a penetrating point, which shank is provided with a thread extending over part of its length, and also comprising a screw head, wherein an unthreaded shank portion is provided adjoining the screw head.
Screws of this type are used among other purposes for mutual fastening of thin components, such as two sheet-metal parts. The end region of the thread adjacent to the screw head is for practical purposes truncated such that it follows a plane disposed perpendicular to the screw axis, so that the components to be fastened to each other are disposed in the unthreaded shank portion after such a screw has been finally set and bear on both sides against a stop. The one stop then forms the underside of the screw head and the other stop forms the thread end truncated such that it is aligned at right angles to the screw axis. Such a fastener is driven into the components to be joined to each other until the thread on the shank has been passed fully through both components. Thereby threaded engagement is no longer present in the components, and therefore the screw can also be further driven without resulting in over-torquing of the thread in one of the two components.
Such screw designs are already known (for example from U.S. Pat. No. 984,969, U.S. Pat. No. 2,172,258, U.S. Pat. No. 2,321,378, U.S. Pat. No. 2,321,379 and U.S. Pat. No. 2,353,030). In these known embodiments, however, an exact fit between the screw to be inserted and the components to be fastened together is always needed. The length of the unthreaded shank portion between the underside of the screw head and the end of the thread functioning as a stop must be matched exactly to the thickness of the two components. For tolerance reasons, however, and also for reasons of various possible uses of such screws, no other screws can be used for each tenth graduation in thickness of components, and so such known solutions have only limited applicability.
The object of the present invention is to provide a screw of the type mentioned in the introduction, which screw can be used for components having various thicknesses within a specified range and with which over-torquing and mutual contact pressure between the components nevertheless take place.
According to the invention, this is achieved by the fact that the end region of the thread adjacent to the unthreaded shank portion tapers at a sharp angle relative to the screw axis with at least approximately constant thread pitch, the tapering end region of the thread forming a kind of frustoconical envelope surface upon rotation of the screw.
By means of these features according to the invention, the end region of the thread is able to engage to a variable depth in one or even in both components, the thread becoming over-torqued in the engaging part and thereby forming a kind of frustoconical opening at least in the second component. The thread flights of the sharply tapering end region of the thread are braced in this frustoconical opening, which is formed at least in the second component, thus guaranteeing optimal mutual fastening between the two components.
Since it is always guaranteed during the over-torquing process that the components to be mutually fastened will press against each other, it is also ensured in the finally set condition of the screw that the components to be mutually fastened will be mutually fastened in such a manner that they bear tightly against each other.
By means of the sharply tapering end region of the thread, it is possible to span a correspondingly large range of thicknesses of the two components to be fastened to each other, since it is inherently immaterial how deeply this sharply tapering end region of the thread now penetrates into the second component or even into the second and the first component.
During over-torquing of the screw, the mating thread in the components in question is destroyed, while the sharply tapering end region of the thread for practical purposes forms a kind of milling cutter, which makes a kind of frustoconical opening during corresponding rotation of the screw. The sharply tapering end region of the thread then becomes disposed in the manner of a wedge or in the manner of a taper sleeve in the formed frustoconical opening, and so spontaneous reverse rotation of the screw is made impossible. Thus not only is a mutual secure joint between the two components possible, but also the screw is correspondingly locked, so that turning and thus also loosening of the screw is prevented.
To achieve a particular optimal effect, it is provided that the end region of the thread tapers to zero in the unthreaded shank portion. Thereby a correspondingly long end region of the thread can be made to taper sharply as viewed in the axial direction of the screw shank, and so a relatively large range of thicknesses of the components to be fastened can also be spanned with a single fastener.
In one alternative embodiment it is provided that the envelope surface of the tapering end region of the thread is formed by straight generating lines. The thread height in the sharply tapering end region therefore decreases linearly, at least as far as the thread crest at a specified axial sectional plane of the screw is concerned. Thus an opening which for practical purposes is exactly frustoconical is made in at least one of the two components.
Within the scope of the invention it is also possible, however, for the envelope surface of the tapering end region of the thread to be formed by curved generating lines. The opening formed in the component in question by the tapering end region of the thread thereby has a cross section which for practical purposes is curved, so that a kind of bowl shape is cut out in which the end region of the thread is then braced after final setting.
It is further proposed that the minor diameter of the thread in the tapering end region of the thread increases to the same extent as the major diameter of the thread becomes smaller. Thereby the minor diameter merges into the unthreaded shank portion at what for practical purposes is also the correspondingly sharp angle, and so the unthreaded shank portion establishes the centering of the screw in the first component, or in other words in that component on which the screw head eventually bears.
In one alternative embodiment of the invention, it is proposed that the thread is made with multiple flights. With such a design the milling effect of the sharply tapering end region of the thread is further improved, and additional bracing regions are obtained between the tapering end region and the surface of the formed frustoconical opening.
In one particular alternative embodiment it is proposed that a shoulder with diameter larger than that of the remaining unthreaded shank portion be disposed directly adjoining the screw head in the unthreaded shank portion. In this way even more improved centering of the screw in the first component and on the whole even more improved mutual contact pressure between the components to be joined to each other are possible, since corresponding pressure is applied from both sides. On the one hand the larger shoulder must be pressed into the formed opening in the component, and on the other hand the frustoconical opening is milled in the other component, against which opening the sharply tapering end region of the thread can be correspondingly braced.
In this connection it is advantageous for the diameter of the shoulder directly adjoining the screw head to be larger than the boring diameter of a boring part formed at the free end of the shank. The shoulder partly compresses at least the thread portions formed in the first component, and so a corresponding fit is achieved. In this way it is additionally ensured that the components to be fastened to each other are also retained in such a way that they cannot slip transversely relative to the screw axis.
Within the scope of the invention, and especial
Saether Flemming
SFS Industrie Holding AG
Volpe and Koenig P.C.
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