Abstract: The present invention related to an optical cable in which an optical fiber unit is covered with plural pieces of plastic warn and an outer covering such that the transmission characteristics of optical fibers does not deteriorate even if the plastic yarn longitudinally shrinks with time or with temperature. An optical fiber unit is covered with plural pieces of plastic yarn applied by clockwise-counterclockwise stranding.

Abstract: The present invention relates to an optical cable in which an optical fiber unit is covered with plural pieces of plastic yarn and an outer covering such that the transmission characteristics of optical fibers does not deteriorate even if the plastic yarn longitudinally shrinks with time or with temperature.

Abstract: A tension control apparatus includes at least two guide rollers and at least one dancer roller disposed so as to be movable relative to said guide rollers, and applies a predetermined amount of tension to a linear body wound about the guide rollers and dancer roller. This apparatus has a tension control device for variably controlling the tension applied to the linear body by adjusting an angle between a vertical line and a line connecting respective rotational centers of the guide rollers and dancer roller.

Abstract: Torsional fixation portions holding an SZ slotted body having spiral grooves turning over alternately in the surface of its column body are provided to prevent the SZ slotted body from being distorted, and between the torsional fixation portions, a groove fixation device with one or more protrusion projecting into the spiral grooves of the SZ slotted body to prevent the grooves front turning in the sectionally circumferential direction in provided. The SZ slotted body is passed through the groove fixation device while the SZ slotted body advanced straight. Optical fibers are introduced and stored into the grooves of the SZ slotted body in the vicinity of the groove fixation device, and immediately a pressing winding consisting of yarn, tape or the like is given onto the SZ slotted body.

Abstract: The present invention provides an extruder for highly foamed plastic material for coating a central conductor of a coaxial insulated cable with an insulator made of a mixture of a plastic material, preferably polyethylene, and an inert gas, such as nitrogen gas, to serve as a foaming agent. An inert gas is introduced approximately halfway down the extruder through a lead-in portion. At the lead-in portion of the extruder is a vent portion wherein the screw is provided with a plurality of stirring blades extending radially from the screw toward the inner surface of the extruder. These stirring blades provide a mechanism by which the inert gas is mixed thoroughly into the plastic material. The above invention provides an apparatus for producing an insulating material in which an inert gas (such as nitrogen), rather than hydrocarbon chloride fluoride, is used as a foaming agent, thus avoiding potential harm to the ozone layer.