Joints and connections – Thread adaptor
Reexamination Certificate
2000-03-14
2001-12-11
Browne, Lynne H. (Department: 3629)
Joints and connections
Thread adaptor
C403S305000, C403S307000, C403S368000, C403S374100
Reexamination Certificate
active
06328499
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates generally to a screwed connection for threaded rods which is suitable in particular for sleeve connections and end anchorages of reinforcing rods.
About thirty years ago a new connection system for concrete reinforcing rods was put onto the market under the name GEWI® sleeve connection or DYWIDAG® system. A multi-rib reinforcing rod, on which the ribs are rolled in the form of a thread over the full rod length, is used in this connection system. A screwed sleeve connection can be made with a suitably designed threaded sleeve between two GEWI® reinforcing rods cut to length as required.
However, the external thread hot-rolled on to the reinforcing rod can be produced only with relatively rough tolerances. It follows that the sleeve connection is subject to significant axial slip under load. DIN 1045 specifies that the deformation of a screwed sleeve connection (slip at both sleeve ends) under service load occurring in addition to the elastic strain may be at most 0.1 mm.
According to the DYWIDAG® system the required slip limitation is achieved by locking the threaded sleeve at each end by a lock nut. The two lock nuts are tightened by a torque wrench with a locking torque specified as a function of the nominal diameter, so that the screwed connection is prestressed with a predetermined force. Such lock nuts are used in a DYWIDAG® sleeve connection with tensile load or with combined tensile and compressive load. The two lock nuts can be dispensed with in a sleeve connection with exclusive compressive load. The end faces of the two rod ends are then braced against each other in the sleeve, so that the compressive forces are transmitted directly from rod end to rod end.
The two lock nuts increase the cost of the DYWIDAG® screwed sleeve connection and also make it more difficult to produce. In fact the lock nuts are not always easily accessible for the torque wrench, and the torques to be produced are already 950 Nm for a nominal diameter of 28 mm, i.e. at the strength limit of an average worker.
To save the two lock nuts in a screwed sleeve connection WO 98/10158 suggests to eliminate the thread play by pouring cement slurry into the screwed-on threaded sleeve. However, this method is relatively unreliable compared to the DYWIDAG® system with lock nuts. For example, it is not ensured that the thread play is always satisfactorily filled on the construction site.
There is a long felt need for a screwed connection between a rod end with a coarse external thread and a threaded sleeve, which is screwed on to the external thread of the rod end, in which the axial slip caused by the rough tolerances of the outer thread is reduced in an inexpensive and simple, but reliable manner.
SUMMARY OF THE INVENTION
In a screwed connection according to the invention a cotter is driven through a lateral opening in the threaded sleeve in such a way that it bears both on the threaded sleeve and on the rod end face near this opening in order to press the external and internal threads axially against each other by the wedge effect. It should be noted that the cotter can bear on the threaded sleeve or on the rod end face either directly, i.e. by direct contact between cotter and threaded sleeve or cotter and rod end face, or indirectly, i.e. via one or more interposed parts. By driving a wedge essentially at right angles to the longitudinal axis of the threaded sleeve the flanks of the external thread on the rod are pressed with high force against the opposite flanks of the internal thread on the sleeve, so that the screwed connection is reliably prestressed without expensive lock nuts. It should also be noted that when the cotter is driven in, substantially smaller friction resistances have to be surmounted in contrast to tightening of the conventional lock nuts, and also no additional torsional stresses are produced in the connection. To achieve adequate prestressing of the screwed connection the cotter need be driven only a specific length into the threaded sleeve. Less space and less force are required to drive this cotter than to tighten the conventional lock nuts with a torque wrench.
A screwed connection according to the invention is particularly suitable for a sleeve connection between two rod ends with tensile load or combined tensile and compressive load. With such a sleeve connection between two rod ends each of the two screwed connections could, of course, be prestressed individually with a separate cotter. In an advantageous embodiment of such a screwed sleeve connection, however, only a single cotter is required to prestress both screwed connections. The threaded sleeve used for this purpose has a continuous channel with an internal thread, the rod ends to be joined being screwed into the threaded sleeve in such a way that their end faces are axially opposite each other in the threaded sleeve. A single cotter is then driven through the lateral opening of the threaded sleeve between the two rod end faces, wherein it bears on the two opposite end faces in order to press the external thread of the two rod ends axially against the internal thread of the threaded sleeve by the wedge effect and thus prestress both screwed connections at the same time.
A screwed connection according to the invention is likewise highly suitable for securing an end anchorage to a rod end with a rolled-on external thread. A threaded sleeve or cap nut screwed on to the rod end forms the end anchorage. The cotter is driven through a lateral opening in the threaded sleeve or cap nut in such a way that it bears on the rod end face and on the threaded sleeve or cap nut in order to press the external and internal threads axially against each other by the wedge effect and thus prestress the screwed connection.
The cotter is preferably self-locking, so that it need not be secured. It can be designed as a single part, but is preferably a double wedge or even better a triple wedge with parallel supporting surfaces. A triple wedge can, for example, advantageously be designed as a one-piece drive-in dowel. One or more marks on the cotter enable the driving depth to be determined.
The opening for the cotter in the threaded sleeve is advantageously designed as a guide slot, in which the cotter is guided laterally. The threaded sleeve advantageously has at least two openings for the cotter offset in the circumferential direction, so that the cotter can be driven in more easily in different angular positions of the threaded sleeve.
REFERENCES:
patent: 2679414 (1954-05-01), Hornschuch
patent: 3831297 (1974-08-01), Lanz et al.
patent: 4127354 (1978-11-01), Mixon
patent: 4997306 (1991-03-01), Kunoki
patent: 5606839 (1997-03-01), Baumann
patent: 5746555 (1998-05-01), McEvoy
patent: 895 952 (1983-06-01), None
patent: 16 09 867 (1970-06-01), None
patent: 0 867 578 (1998-09-01), None
patent: 342 078 (1904-08-01), None
patent: 213 333 (1924-03-01), None
patent: 98/10158 (1998-03-01), None
Reding Henri
Rehm Gallus
Ares S.A.
Browne Lynne H.
Dunwoody Aaron
Smith , Gambrell & Russell, LLP
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