The invention relates to a screw with an at least partially threaded shank as well as a screw head.
Screws of the type mentioned at the outset are known in the most different embodiments for various special applications.
The object of the invention is to provide a screw such that in particular thinner metal sheets can be connected to one another laterally with as high a degree of protection as possible from becoming loosened.
This is achieved according to the invention such that a section free from threads is provided between the screw head and the thread and that the thread is provided with at least one groove, notch, slot, or the like crossing the thread at the end region of the shank facing the screw head.
Through providing a thread-free section below the head, the screw is screwed into the sheet metal until it contacts below the head, with the bottom of the head acting as a stop. The second metal sheet is further screwed in. This ensures that the two metal sheets are pulled against one another. This achieves a higher degree of pre-tension of the screw. A reduction of this pre-tension is prevented by a groove being provided crossing the thread. Here, the groove in the thread creates a connection that is protected from being loosened. The edges of the groove act as engaging elements and thus contribute to an anchoring of the thread engaging at least the second metal sheet.
In one embodiment of the screw, the thread-free section has a smaller diameter than the root diameter of the threaded shank. This ensures that the sheet metal at the screw head does not cause resistance and thus the bottom of the head is used as much as possible as a stop during screwing down. If intentionally a form-fitting connection or one free from play is to be achieved below the head the diameter of the thread-free section may be equivalent to the diameter of the root diameter of the threaded shank or perhaps selected even slightly larger without creating any negative influence on the safety from being screwed loose.
In another embodiment of the screw, the width of the thread-free section is equivalent to a thickness of the metal sheet positioned next to the bottom of the head. This embodiment achieves an optimal condition with regard to the entire connection, because while the screw in the metal sheet next to the screw head can be freely rotated the second metal sheet is pulled against the first metal sheet with maximum force during the further screwing down of the screw.
In another embodiment of the screw, the width of the thread-free section is approximately equivalent to the thickness of all metal sheets to be connected to one another. This is a useful, simple way to prevent the reverse rotation of the screw in metal sheets which have entered the thread-free section in their entirety. In this case it is prevented that one of the two metal sheets can reengage the thread during the reverse rotation and loosening, respectively. Thus, no torque can be transferred between the metal sheets and the screw. A secure tightening without any torque-wrench is therefore easily possible in this embodiment. Security from loosening is also ensured in this case. This is also supported by the groove(s) crossing the thread.
In another embodiment of the screw, the groove tapers off in the thread-free section. This results in that a maximum effect of the groove being achieved, because particularly in thin metal sheets it is possible for the connection between the thread and the metal sheet to be created by less than one thread rotation. Only a groove tapering off in the thread-free section can ensure that the groove is engaging, if possible by the geometric conditions.
In another embodiment of the screw, the grooves, notches, slots, or the like are embodied U-shaped, V-shaped, or trapezoidally, or in any other shape forming a hollow space and form recesses in the teeth of the threads. The shape is selected such that it supports the forming of the thread and that the reverse rotation of the screw is possible only with very high reverse torque.
In another embodiment of the screw, two or more grooves are provided. This enhances the effect of the groove with regard to the reverse torque and the position. An enhancement can be achieved with each additional groove at the circumference of the thread. However, it must be taken into account that the function of the thread per se shall not be compromised by the implementation of an excessive number of grooves. In practical use, two to five grooves have proven useful, in particular.
In another embodiment of the screw, the groove extends parallel to an axis of the shank. This is technically easy to produce and fulfills the above-mentioned requirements.
In another embodiment of the screw, the groove, notch, slot, or the like extends clockwise and/or counter-clockwise in reference to the shank. In this manner, the effect can be adjusted more precisely to the application and thus the above-described requirements can be fulfilled even better. Particularly advantageous is a clockwise rotating groove, notch, slot, or the like with a low incline. In this embodiment the groove, notch, slot, or the like crossing the thread is created in the thread with an acute or obtuse angle. The acute angle leads to a higher reverse rotational torque of the screw and the acute angle reduces the milling of the sheet metal and thus increases the pulling torque of the screw.
Further, it is suggested that the groove, notch, slot, or the like are preferably provided to the depth of the root diameter of the thread. This way the limiting edge at the transfer between the teeth sides of the thread and the groove are provided in a length at which a maximum security from reverse torque is achieved by the length of the limiting edge.
In another embodiment of the screw, the groove, notch, slot, or the like is deeper than the core diameter of the thread. This ensures a very good shape of the sheet metal during the engagement.
In another embodiment of the screw, a binding and/or adhesive coating is applied at least on the part of the tread adjacent to the thread-free section. Through this coating, the binding effect, which is also determined by the geometric shape, is influenced in an extremely positive manner. A reverse rotation is hardly possible after a short period of time. Therefore, this can be called an optimum fastening.
It is known from professional literature that screwed connections can loosen, for example by interaction between tensions and compressions, heat-related expansion, shock and vibration related stress, wind vibrations, shaking, dynamic stress (swelling or alternating), reduced self resistance in multiple threads or by the application of circular springs. In the present invention an optimal, additional protection from the connection loosening can be yielded particularly by implementing grooves or by filling the hollow spaces with a binding and/or adhesive coating.
In addition to this short-term effect during the fastening process, the filling of the grooves, notches, slots, or the like with a coating is also used to constantly apply a coating to the thread during the screwing down process. This process already increases the reverse torque after a short period of time. In this way, a connection protected from reverse rotation is achieved already in metal sheets having a thickness of less than 0.5 mm.
In an additional embodiment of the screw, a clamping and/or adhesive coat is applied to the thread-free section and/or below the head. In thin metal sheets the coat acts in the tightened condition only in a very small area of the thread. By applying the coat to the thread-free section, prevention of the screw being moved by a low torque can be achieved. Even if the screwed connection cannot be loosened, the advantage of this embodiment comprises that the additional fixation of the screw prevents any unnecessary movement. This also prevents any potential jingling and/or vibration like the ones caused by wind impinging a façade.
In another embodiment of the invention, it is provided for the coat to be applied in form of a two-component adhesive of the like. Here, any known or newly developed adhesives can be applied which support the desired effects.
In another embodiment of the screw, plastic or the like is applied as a coat. Plastics can also be adjusted to the requirements of the screw connection and thus offer an ideal alternative to other coatings, e.g., in a liquid form.
In another embodiment of the screw wax, polytetrafluoroethylene (PTFE), plastics, or the like are applied as a lubricating coat at the end section of the shank facing away from the screw head. In order to reduce the thread-forming moment, a lubricating or gliding layer can be applied during the screwing down process at those points of the thread no longer in direct contact with one of the metal sheets after the connection has been tightened. This way the forming torque can be reduced. A screw connection is therefore enabled with a lower strength means, such as machine drills, among others. It provides a manual screwing down processes that allows less force to be applied while the screw can be screwed in faster.
In another embodiment of the screw, a coat is applied partially or covering the entire circumference. Even a partial coating acts to prevent a reverse torque. However, even partially applied lubricants are possible. Also, any combinations might be useful. They can be adjusted in any fashion to the requirements of the screw connection.
In another embodiment of the screw, the thread is arranged in an out of true manner at the end section of the shank facing away from the screw head. In addition to the non-cutting production of the female thread, this is also cold-hardened. A low screwing in moment results by a low material displacement.
In another embodiment of the screw the thread is embodied trilobularly. A form-fitting connection of the screw and the sheet metal is achieved by the high level of overlapping with teeth sides of the threads. This is a particularly important condition in thin metal sheets in order to accept high axial tensile forces.
In another embodiment of the screw, the shank is provided with a conical thread section at the end region of the shank facing away from the screw head. If pre-punched fastening holes are provided, an additional centering of the holes can be achieved thereby.
In another embodiment of the screw, the thread tapers off at the end facing away from the screw head. This way during the assembly process, pre-punched thin metal sheets up to almost the size of the diameter of the hole can be centered by the tip of the screw and thus forced into the correct position. This function is ensured even if the thread is not tapering off entirely at the tip. Even a cone-shaped tip can perform this function.
In another embodiment of the screw, a self-drilling or self-inserting tip is mounted at the side facing away from the drive connection, by which the hole is simultaneously created during the assembly process in already aligned metal sheets. This not only enhances the efficiency but also ensures that the diameter of the bore is ideally adjusted to the subsequent threading and tightening of the connection.
In the following, exemplary embodiments of the invention are explained in greater detail with reference being made to the drawings. They show:
A screw 1 shown in
In a variant of the exemplary embodiment according to
In another embodiment,
The term “clockwise” and “counter-clockwise” indicate a clockwise or counter-clockwise alignment in reference to shank 7 and are to be interpreted in the same manner as “clockwise” and “counter-clockwise” for threads.
Another embodiment relates to the shape of the groove.
In
In another embodiment of the screw, according to
Another variant of the exemplary embodiment is shown in
In
Number | Date | Country | Kind |
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10 2004 034 246.6 | Jul 2004 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP05/07443 | 7/9/2005 | WO | 10/31/2006 |