Buckles – buttons – clasps – etc. – Cord and rope holders – Sheathed strand
Patent
1987-09-10
1990-04-03
Sakran, Victor N.
Buckles, buttons, clasps, etc.
Cord and rope holders
Sheathed strand
24136R, 403248, F16G 1100
Patent
active
049128159
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the field of clamp assemblies for securing the ends of longitudinal, tensile load-bearing elements and finds particular application in armour clamps for submarine telecommunications cables.
It is sometimes necessary to secure the ends of longitudinal elements which are required to carry large tensile loads. The means used to secure their ends must be designed to do so without introducing weakness.
Where a submarine telecommunications cable is concerned, tensile load-bearing elements may be present as one or more annular layers of wires, known as armour wires, wound helically along the cable. For example, shallow water telecommunications cables are generally provided with such armour wires for protection against damage by trawlers. These armour wires between them may have to take tensile loads of the order of 100 tons if a trawler should pick up a cable in error. At a repeater housing loads of up to for instance 3 tons may have to be borne by individual wires as the repeater housing is wound onto a cable drum. Hence any clamp assembly used in clamping the ends of the armour wires, known in this context as an armour clamp, must be capable of reliably withstanding total loads on the wires of the order of 100 tons and, if used at a repeater housing, of more than 3 tons on individual wires.
A first known type of armour clamp comprises a pair of coaxial rings. The inner ring has a cylindrical hole but presents a conical exterior, its walls being rounded at their thicker end. The outer ring presents a conical hole, complementary to the exterior of the inner ring. In use, the ends of the armour wires are each fed through the inner ring and bent back over its conical exterior, round the thicker end of its walls. The outer ring is seated on the wires, its conical hole clamping them against the exterior of the inner ring. The outer ring can then be appropriately mounted to anchor the cable as required, for example, to a repeater housing.
This assembly is self-tightening in use. The surface of the conical hole of the outer ring is profiled so as to grip the armour wires while the exterior of the inner ring is smooth. Any tensile load on the armour wires then acts to pull the outer ring towards the thicker end of the inner ring and so tends to increase the clamping effect on the wires themselves, between the two rings. However, unfortunately, the assembly has been found unsatisfactory. The bend produced in each armour wire has led to failure of the clamp owing to shear breakage under unacceptably low tensile loads.
In order to overcome the problem recognised in the above assembly, a second known type of armour clamp is designed to operate without requiring the armour wires to be bent. Such a clamp is described in British patent GB 2122245. In this assembly, a rigid sleeve is inserted under the straight ends of the armour wires. Coaxial rings having complementary conical surfaces are again used but, in this case, both conical surfaces are smooth and the inner ring is in four separate segments, divided along radial planes of the ring.
The segments of the inner ring are mounted on the armour wires over the rigid sleeve, and the outer ring is then mounted over the segments.
In this second type of armour clamp, which is again self-tightening, when tensile load is applied to the armour wires the two rings are loaded such that the inner ring is pulled towards the end of the outer ring having the narrower opening. The segments of the inner ring are thereby clamped more tightly onto the armour wires, against the rigid internal sleeve.
Although the second type of armour clamp has been found to offer acceptable reliability at loads of up to 82 tons on the armour wires, it also has drawbacks, including cost, owing to the number of components involved, and the need to insert the rigid sleeve under the straight ends of the armour wires. This means that the diameter of parts of the cable which lie within the armour wires must be reduced to give access for the rigid sleeve.
A further problem, common to
REFERENCES:
patent: 1758218 (1930-05-01), Carlson
patent: 1885316 (1932-11-01), Astley
patent: 4127344 (1978-11-01), Kwiatkowski
patent: 4507008 (1985-03-01), Adl et al.
patent: 4516830 (1985-05-01), Guazzo
patent: 4598443 (1986-07-01), Ostling et al.
British Telecommunications public limited company
Sakran Victor N.
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