Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Externally threaded fastener element – e.g. – bolt – screw – etc. – Head having counter-sinking means
Reexamination Certificate
1999-04-23
2001-01-30
Barrett, Suzanne Dino (Department: 3627)
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Externally threaded fastener element, e.g., bolt, screw, etc.
Head having counter-sinking means
C411S001000
Reexamination Certificate
active
06179538
ABSTRACT:
The invention relates to a screw for fastening metal and/or plastic sections or plates to a substructure, comprising a shank with a threaded portion and a drive portion for applying a driving tool.
The very act of fastening sections or plates to a substructure is problematic in that such parts must achieve a condition in which they press firmly against the substructure when fastened. These negative effects are intensified when relatively stiff sections or plates become further distorted under certain circumstances or exhibit a longitudinal twist. In this case it is usually not possible to work with a depth limiter for the driving device. Even if torque clutches are used, it is still difficult to stop the process at the precise time, since an associated torque increase occurs as soon as the screw head bears on the section to be fastened, thus stopping the driving device. Further driving movement is then stopped regardless of whether or not the metal and/or plastic section or plate to be fastened continues to bear on the substructure.
The object of the present invention was therefore to provide a screw of the type mentioned in the introduction, in the use of which the section or plate to be fastened bears snugly on the substructure in the finally set condition and torque-dependent stopping of the driving device is possible.
According to the invention, this is achieved by the fact that the portion of the shank adjacent to the drive portion flares toward the drive portion conically, in the manner of a stepped cone or following a curve as viewed in cross section, and that the diameter of the end of the flaring portion of the shank close to the drive portion is larger than the diameter of the borehole receiving the screw in the section to be fastened and thus is also larger than the core diameter of the threaded portion of the screw.
By virtue of these features according to the invention, the metal and/or plastic section to be fastened is subjected to initial tension directed toward the substructure and thus is pressed thereagainst as soon as the screw has been driven in by one or more rotations. Because of the associated friction in the borehole and of the flaring shape, the flaring portion of the shank exerts a force in the screwing direction on the section to be fastened.
It then becomes a simple matter to adjust an appropriate torque clutch such that it disengages only at appropriately high torque. By that time, however, the section to be fastened has already been pressed snugly against the substructure by the action of the flaring portion, and so all that remains is for the driving tool to be stopped as soon as the appropriate torque is reached. The torque is achieved by the high friction of the flaring portion against the wall of the borehole. Thus rapid, torque-dependent stopping is possible, or further driving will be safely prevented.
The action of the flaring portion on the borehole wall also produces extremely good locking against reverse rotation. The surface of the flaring portion is for practical purposes disposed in a snug-fitting seat in the borehole wall. Furthermore, in the particular case of sections that have become distorted or twisted in the process, said sections have a tendency to return to their initial condition. Thereby an additional resilient load is always exerted on the screw, intensifying the locking effect against reverse rotation, especially in view of the action of the conical portion.
It is intuitively obvious that the beginning of the flaring portion must extend from the shank or from an unthreaded portion of the shank, because this flaring portion, while following the shank, must be inserted easily into the borehole in the section to be fastened. Thereafter, however, it is necessary that the flaring portion engage as rapidly and effectively as possible with the borehole wall, so that thereby it can apply the axial initial tension optimally. In this way the tightening torque and therefore the axial initial tension are exerted on the section to be fastened as soon as the screw has been driven in a relatively short distance, before the process of driving the screw is fully accomplished.
Another advantage of the flaring portion is that optimum fastening to a substructure is possible even if said substructure comprises a thin metal sheet, other thin materials or a material of low strength, such as gas-formed concrete or even foamed material. Since the flaring portion for practical purposes represents the agency which initiates an associated torque increase, stripping of the thread in the substructure cannot occur.
In another proposal according to the invention, the flaring portion of the shank extends directly to the drive portion or to the underside of the drive portion formed as the screw head. This ensures that the borehole will be steadily widened until the screw is finally set. Thereby there is also achieved a steadily increasing torque, which can be sensed by a driving tool with an adjustable stopping reaction or else prevents further driving of the screw in some other way.
In this regard it is also important to note that torque-activated stopping must take place with great precision, since the engagement of the thread in the substructure can be damaged under certain circumstances, thus negating the fastening effect, if driving is stopped too late.
It is also advantageous if the diameter of the end of the flaring portion of the shank close to the drive portion is larger than the outside diameter of the threaded portion on the shank. It is immaterial for the optimal effect of the present invention whether there is present in the section or plate to be fastened a prebored borehole or else a threaded bore, in which the screw is driven. An appropriate axially directed initial tension is always produced by the flaring portion in the threaded borehole of the section to be fastened or else in a borehole which is larger than the outside diameter of the thread. If thread turns are present, they will be compressed against or pressed flat by the flaring portion, and thereby the friction between the flaring portion and the borehole wall is smaller at least in the first two rotations than if the borehole wall had been smooth. Under these conditions, therefore, it is ensured that the sections or plates to be fastened will be drawn together appropriately with the substructure before the driving tool is stopped or further driving of the screw is interrupted.
An advantageous embodiment is obtained when the drive portion comprises two regions disposed successively in axial direction with different structures for a tool drive. This therefore also permits tightening with a larger or smaller wrench size as needed and thus with larger or smaller torque transmission.
In this connection, a further advantageous embodiment is achieved when one region of the drive portion is designed for engagement of the driving tool and the other region is designed for application of a tool for reverse rotation of the screw if necessary, wherein a predetermined breaking point acting as a stripping safeguard is formed between the two regions of the drive portion. This creates the possibility that the screw can be driven in with the one region of the drive portion and, after the two parts to be joined to one another have been drawn appropriately together and the torque has been increased appropriately by engagement of the flaring portion of the shank, the torque is increased so much that this first region of the drive portion breaks off. In this way, further driving of the screw is suddenly prevented, and so stripping in the substructure, especially when it has small thickness and/or low strength, is prevented. Nevertheless, if it becomes necessary to loosen the screwed joint, an additional region of the drive portion is still present on which another tool can be applied.
In one advantageous embodiment, the end of the shank facing away from the drive portion is constructed as the boring part. Such an embodiment is advantageous in particular when the two structural members to be joined to
Barrett Suzanne Dino
SFS Industries Holding AG
Volpe and Koeing, P.C.
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