Extrusion lines in the cable industry. - Manufacturing steps

Electrical or telecommunications conductors or wires must be electrically insulated in order to be used. Elastomers or thermoplastics with the appropriate dielectric properties provide this insulation to produce the final cable.

Extrusion is a manufacturing process for producing parts with a constant cross-sectional area. In most cases, the shaping of cable insulation materials is performed using a single-screw extruder. The extruder’s function is to plasticize the insulation material in order to push it into the extrusion (or forming) die, where the insulation is deposited onto the conductor passing through it.

However, the extruder alone is not enough to guarantee product quality. Other components along the production line play an important role. In addition to the extrusion unit (extruders and die), all lines include pay-offs, cooling tanks, diameter measurement devices, and winders. A production line is specific to the type of production intended. Production types can be classified into various sectors of the cable market. These correspond to ranges of cable diameters.

In this article, we provide an overview of the various mechanical components used along cable lines.

The process begins with the supply of cables or wires that have been pre-wound onto reels using one or more pay-offs (for small diameters) or a gantry (for diameters greater than a few millimeters).

Depending on the type of cable being produced, substrate preparation may take place in a step prior to extrusion. For conductors, this may involve annealing or preheating, sometimes preceded by wire drawing, or the stranding of wires. For pre-insulated wires, SZ-type stranding may be performed. A tape application step (taping) may also be included.

Extrusion itself is the next step. It involves applying one or more layers of polymer to the substrate. The output of the extrusion line must match the requirements of the final product (insulation or sheath cross-section × line speed).

Next, this insulation or sheathing layer must be cooled sufficiently in cooling tanks to ensure that it does not deform during subsequent stages. The larger the insulation or sheathing cross-section and the higher the line speed, the longer the cooling section must be.

A line-pulling device (capstan or track) controls the speed of the finished product. This line speed, combined with the type of cable (diameter), determines the rotational speed of the extruder. For this fixed rotation speed (or speeds) of the extrusion unit, the line speed will be adjusted to achieve the desired diameter.

Finally, the last step will involve winding the finished product...