Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Torque responsive nut or bolt driving connection – Frangible connection
Reexamination Certificate
1999-08-17
2001-01-23
Saether, Flemming (Department: 3627)
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Torque responsive nut or bolt driving connection
Frangible connection
C411S393000
Reexamination Certificate
active
06176659
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a tear-off cap or shearable screw.
For connecting, branching off and plugging of cables, in particular underground cables, screw connectors, cable connecting clamps or cable lugs are conventionally used, into which tear-off cap screws are inserted for fixing or contacting of the conductors, respectively.
WO 96/31706 discloses a shearable screw comprising a plurality of thread portions and a cap portion connected with the thread portions by means of a predetermined breaking point, wherein further predetermined breaking points in the form of cross-section tapering are provided between the thread portions. The predetermined breaking points are configured such that the predetermined breaking point being most remote from the cap features the largest cross-section tapering, whereas the point being closest to the cap features the slightest cross-section tapering or cutting depth. Due to this configuration, a tear-off torque results which always increases from the thread portion that is most remote from the cap portion towards the cap portion.
A plurality of disadvantages are, however, entailed therewith. The less the shearable screw penetrates the cable connector to clamp the conductor inserted therein, the less is the corresponding tear-off torque, i.e. correspondingly less is the force acting thereagainst. This means that the least pressing force is available for the largest conductors and the strongest pressing force is available for the smallest conductors. In the one case, namely that of the least pressing force, there is the risk that the conductor will not be clamped sufficiently and thus the danger of lacking contact, whereas in the other extreme case, i.e. the smallest conductor with strongest pressing force, a squeezing of the smallest conductor may be possible, which may result in the failure of the cable connection.
A similar shearable screw is known from EP 0 692 643 A1, where the tear-off torques of all predetermined breaking points are to increase or decrease from the cap portion towards the last or front thread portion, respectively. Possibly they are, however, substantially equal. In the case of decreasing, the afore-mentioned disadvantages result. In the case of increasing, there is the risk of the tear-off cap screw to tear off before the tear-off torque required for the respective conductor has been reached, and this does not only result in a possibly insufficient clamping of the conductor, but also entails a very disadvantageous projecting of the broken remaining portion of the tear-off cap screw from the outer contour of the cable clamp.
SUMMARY OF THE INVENTION
It therefore is an object of the present invention to improve a tear-off cap or shearable screw of the kind initially mentioned such that the disadvantages of prior art are overcome and a tear-off cap screw is provided which enables optimal clamping and tearing off for a plurality of different cross-sections of cable conductors.
The present invention is directed towards a shearable screw comprising a plurality of thread portions and a cap portion connected to the thread portions via a first predetermined breaking point, wherein further predetermined breaking points in the form of cross-section tapering are provided between the thread portions. The tear-off torques both increase and decrease from the most remote thread portion towards the cap portion, thereby forming at least one stepped predetermined breaking point.
Due to the fact that the tear-off torques both increase and decrease from the most remote thread portion towards the cap portion, this forming at least one stepped predetermined breaking point, it is achieved that safe tearing off at the desired position is ensured on the one hand and too high torques are avoided with small conductor cross-sections on the other hand.
Advantageously, the tear-off cap screw is configured such that the tear-off torque of the stepped predetermined breaking point is smaller than that of the following predetermined breaking point located at a more remote position from the head. This ensures that the tightening moment during the further screwing in of the tear-off cap screw becomes smaller, and thus a smaller conductor is not compressed even stronger than the correspondingly larger conductor. Advantageously, the tear-off torque then increases again from predetermined breaking point to predetermined breaking point from the stepped predetermined breaking point towards the cap portion, so that the perfect functioning of the tear-off cap screw is guaranteed.
In accordance with the invention, a different tool engages at the stepped predetermined breaking point than engages at the thread portions that are more remote from the stepped predetermined braking point away from the cap portion. This ensures the correct engagement for tearing off at the correct predetermined breaking point.
Preferably, the cap portion comprises a hexagon insert bit as tool engagement face, and an inner excess, for instance a hexagon socket or Torx, etc. is provided which extends from the cap portion to the thread portion below the stepped predetermined breaking point. This ensures that the tool introduced into the inner excess produces the tear-off torque for the predetermined breaking points below the stepped predetermined breaking point, whereas for the predetermined breaking points positioned above, the cap portion produces the tear-off torque.
With a particular advantage, a corresponding adaptation to the various conductor cross-sections can additionally be achieved by the fact that the height of the thread portions is optional. Correspondingly flexibly and exactly can the tear-off cap screw be adapted with its predetermined breaking points to the cross-sections of the cable conductors which, according to standardization, do not alter continuously, but step-wise.
Another advantage of the present invention results from the fact that the tear-off cap screw comprises 3 to 10, preferably 4 to 8 predetermined breaking points, at least one of which is configured as stepped predetermined breaking point. This advantageously provides for the considerable flexibility and adaptability of the tear-off cap screw to the most various fields of application, in particular to the most various conductor cross-sections that can be clamped safely by means of the tear-off cap screw according to the invention, and the tear-off cap tears off at the correct predetermined breaking point.
Further details, features and advantages of the invention result from the following description making reference to the drawings.
REFERENCES:
patent: 3444775 (1969-05-01), Hills
patent: 3512447 (1970-05-01), Vaughn
patent: 3963322 (1976-06-01), Gryctko
patent: 4504180 (1985-03-01), Ishii
patent: 5697929 (1997-12-01), Mellinger
patent: 0634811 A1 (1995-01-01), None
patent: 0692643 A1 (1996-01-01), None
patent: 2140523 (1984-11-01), None
patent: 2281599 (1995-03-01), None
patent: 2299640 (1996-10-01), None
European Search Report dated Jan. 11, 1999.
Hardt Falk
Markgraf Volker
Gardner Carton & Douglas
Gerhard Petri GmbH & Co. KG
Saether Flemming
LandOfFree
Shearable screw does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Shearable screw, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Shearable screw will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2458197