Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – Composite article making
Patent
1981-12-14
1984-07-24
Anderson, Philip E.
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
Composite article making
156 48, 174 23R, 174 23C, 249160, 264 469, 2642711, 2642791, B29D 2704
Patent
active
044617364
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
This invention relates to a method of producing a dam for a communication cable, and more particularly to a method of forming a gas-tight or water-tight dam by filling a portion of the communication cable with resin.
2. Background Art
In general, there has been employed a method of maintaining an underground laid communication cable in which a gas having a pressure higher than atmospheric pressure is filled in the communication cable in order to prevent water or moisture from intruding into the cable through a damaged portion of its sheath. Meanwhile, an aerially laid communication cable is not provided with the aforementioned gas maintenance means. A gas-tight dam is provided at the portion of the cable which extends upwardly from the underground laid cable to the aerially laid cable so as to prevent the gas in the former cable from flowing into the aerially laid cable.
In the case of a communication cable having no gas maintenance, water or moisture intruding into the cable through a damaged portion thereof diffuses in a longitudinal manner so that the cable is not able to be used along a large portion of its length. In order to prevent this, moisture-tight dams have been provided at intervals so that the damage does not spread beyond the distance between the adjacent dams.
Furthermore, in the case of the communication cable drawn into a feeder distribution interface, water or moisture intruding into the cable through the damaged sheath portion intrudes through the cable into the feeder distribution interface where it corrodes connectors in the interface. To prevent this, a moisture-tight dam has been provided at the place where the communication cable is introduced into the feeder distribution interface.
In the prior art, such dams for communication cables have been formed at the actual sites where the communication cables are laid. However, since the environment for operation varies widely at the actual sites, it is difficult to form the dams reliably in their gas or water tightness. Therefore, of late, dams have been formed at the portion or portions of the communication cables in factories where the enviroment for operation is better controlled. In this case, the products have been taken up on drums in the form of communication cable having a dam provided therein.
In order to make such a communication cable having a dam provided therein, exposed portions of insulated conductors of the communication cable which are formed by stripping the sheath (and which may be connected portions of the insulated conductors) are covered with a mold which is placed between the ends of the sheath portions on both sides of the exposed portions of the insulated conductors. Resin is injected into the mold so that the gaps or interstices among the insulated conductors are filled with the resin. Thereafter, the resin is cured so as to form a dam in the communication cable. The resin for the dam may be polyethylene, epoxy resin, urethane resin and so on.
In case that polyethylene is used as the dam resin, it takes substantial time to preheat and chill the mold at every cycle because of the large volume of the product to be formed, and also it is required to chill the mold while it is pressurized so that voids are never formed within the product. As a result, it takes 3 to 5 hours until the mold is removed from the communication cable, which reduces the productivity. In case that epoxy resin is used as dam resin, the curing reaction must be delayed to control heat so that insulators (which are usually composed of polyethylene) for the conductors are never melted by the heat generated from the curing reaction. Thus, it takes 8 to 24 hours after the resin is injected until the mold is removed, which also causes a reduced productivity. In comparison with this, since urethane resin generates less heat than epoxy resin on curing, it can be cured at a higher speed, but it has a problem of gas-tightness because it has no adhesion to polyethylene from which the insulators for the conductors are made.
REFERENCES:
patent: 2320506 (1943-06-01), Bennett et al.
patent: 2957038 (1960-10-01), Greenidge et al.
patent: 3427393 (1969-02-01), Masterson
patent: 3582533 (1971-06-01), Albright et al.
patent: 3710440 (1973-01-01), Nevin et al.
patent: 3872233 (1975-03-01), Rocton
patent: 3955043 (1976-05-01), Palmer et al.
patent: 3992569 (1976-11-01), Hankins et al.
Masterson, J. B., "Pressure Dams in Communication Cables", in Wire & Wire Products, May 1970, pp. 61-65.
Bender, Rene J., Handbook of Foamed Plastics, Libertyville, Ill., Lake Publishing Corp., .COPYRGT. 1965, p. 166.
Anderson Philip E.
The Furukawa Electric Co. Ltd.
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