Western Electric Company, Inc.

At&t Technologies, Inc.

Timothy S Dougherty

Manuel Ramon Cereijo

Montri Viriyayuthakorn

Glenn Lewis Schmehl

John J Kissell

William M Flegal

Greg Astfalk

Extruder tooling for directing plastic materials to enclose a conductor (26) being advanced along a path of travel through a core tube (97) and aligned dies includes disc-like flow passages (107, 129) which are disposed concentrically about and perpendicularly to the conductor. This arrangement minimizes conductor tension in a pressure extrusion arrangement by significantly reducing the length of the plastic-to-conductor contact within the extruder. The length and width of each flow passage normal to and along a path of travel are sufficient to provide a uniform distribution of plastic material circumferentially about the conductor and to dissipate stresses which have been induced in the plastic materials. In a tubing arrangement, the length of a cantilevered portion of the core tube is reduced significantly which results in improved concentricity of the plastic material about the conductor.

Methods of and apparatus for insulating a conductor with a plastic

A cable which is suitable for use as a riser cable in buildings comprises a plurality of conductors each of which is covered with a composite insulation. The composite insulation comprises an inner layer of an expanded polyethylene material and an outer layer of a polyvinyl chloride material with the percent expansion of the inner layer and the thickness of the outer layer being such as to optimize several cable parameters. The resultant cable is one which has excellent fire-retardant properties such as, for example, an unusually low fuel content. Advantageously, this same cable lends itself to color coding for inside wiring and is capable of having a relatively high pair count density. All these parameters are optimized within the framework of specific transmission requirements.

Compositely insulated conductor riser cable

Capacitance unbalance-to-ground between conductors of a twisted pair, each of which may be insulated with at least a layer of cellular plastic insulation, is maintained within acceptable limits by controlling the extrusion of the insulation to maintain the measured coaxial capacitance and associated outside diameter of the insulated conductors within a range of values which correspond to acceptable capacitance unbalance-to-ground values.

Methods of and apparatus for controlling capacitance unbalance-to-ground

Methods are provided for processing expandable thermoplastic materials with a typical compression relief design extruder screw having a helical flight for advancing and working a thermoplastic material. The screw is modified to shorten the feed and compression sections and to include a plurality of force-producing components in at least the compression section of the screw such that at least some portion of the components in any one turn of the flight lie in one plane essentially normal to the axis of rotation of the screw and such that the walls of the flight are uninterrupted. This arrangement controls the location of the rupturing or fragmenting of what is referred to as the solid bed and controls the manner in which it is fragmented to provide an extrudate at a die end of the extruder which has a constant temperature and which is uniform throughout each successive section of the thermoplastic material. Further, corresponding portions of the successive sections of the thermoplastic material at the die end are caused to have substantially identical time-temperature profiles which is particularly advantageous when extruding expandable insulation in minimizing amplitude of variation in the coaxial capacitance and the diameter of the insulated conductor.

Methods of working expandable thermoplastic materials in an extruder

A typical compression relief design extruder screw having a helical flight for advancing and working a thermoplastic material is modified to shorten the feed and compression sections and to include a plurality of force-producing components in at least the compression section of the screw such that at least some portion of the components in any one turn of the flight lie in one plane essentially normal to the axis of rotation of the screw and such that the walls of the flight are uninterrupted. This arrangement controls the location of the rupturing or fragmenting of what is referred to as the solid bed and controls the manner in which it is fragmented to provide an extrudate at a die end of the extruder which has a constant temperature and and which is uniform throughout each successive section of the thermoplastic material. Further, corresponding portions of the successive sections of the thermoplastic material at the die end are caused to have substantially identical time-temperature profiles which is particularly advantageous when extruding expandable insulation in minimizing amplitude of variation in the coaxial capacitance and the diameter of the insulated conductor.

Apparatus for working expandable thermoplastic materials

The capacitance and diameter-over-dielectric of successive sections of a conductor having a layer of cellular plastic insulation extruded thereon are monitored continuously. The monitoring provides a continuous indication of the capacitance and the diameter with respect to the percent expansion of the cellular plastic insulation and the weight of the insulation per unit length of the conductor. This facilitates the regulation of process variables to maintain the capacitance and diameter-over-dielectric within acceptable ranges of values.

Apparatus for monitoring cellular dielectric material

The capacitance and diameter-over-dielectric of successive sections of a cellular plastic material are monitored continuously. The monitoring provides a continuous indication of the capacitance and the diameter with respect to the percent expansion of the cellular plastic material and the weight of the material per unit length of the conductor. This facilitates the regulation of process variables to maintain the capacitance and diameter-over-dielectric within acceptable ranges of values.

Sensing capacitance and thickness of insulated cable to provide outputs

First and second concentric insulating sheaths of plastic materials are formed continuously around a filamentary core advancing longitudinally through an extrusion chamber. The core is passed axially through a tapered entrance portion and a coaxially aligned tapered throat portion formed in a separable die disposed in the chamber. Fluent plastic material for the first sheath is delivered from a main extrusion bore, impinging on the core circumferentially at the entrance portion of the die, the flow thereof being developed as it passes into the throat portion thereof. Fluent plastic material for the second sheath is delivered from an auxiliary extrusion bore flowing through a plurality of dividing channels formed in the die and radially inward at a plurality of circumferentially spaced points around the die axis into an annular manifold or reservoir where the fluid pressure of the plastic achieves a steady state condition. The plastic is forced from the manifold circumferentially, flowing in a frustoconical channel formed in the die which terminates in an annular fluid inlet formed in the throat portion of the die to impinge circumferentially around the first sheath, forming both sheaths simultaneously around the core.

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Roswell, GA, United States of America

Timothy S Dougherty