Wrapping

Wrapping is laid above stranded core for form saving and fastening, and also for mechanical and thermal protection from the next processes: shielding, filler adding, cable sheath laying, cable armouring (hot bitum spraying). Because of wrapping, electric strength of insulated cores  increases relative to a metal sheath or a cable screen.

In air-space paper insulation cables it is used as wrapping: 10-100 pairs – two tapes of telephone-cable paper (thickness 0.05 mm); more than 100 pairs – cable paper (thickness 0.12 mm). In cables with polyethylene insulation as a wrapping it is used one or two plastic tapes (depends on cable’s diameter): polyvinilchloride, polyethylene and polyethylene terephthalate. Polyvinilchloride plasticised (PVC) film, polyethylene (PE) or polyethylene terephthalate (PET) film.

Fundamental properties of the films (PVC, PE, PET) are shown in the table below.

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Polyethylene film has a good insulation properties, though because of the high softening temperature (108…112 °C) it sweats while passing an extruder orifice in the process of polyethylene cable-sheath laying. The most common is polivinilchloride film. It is possible to use two types of film (for example: PVC and PET).Wrapping is laid spirally, with overlapping by width 15…50%, or lengthwise. A winding angle can change in a wide range: from 80º for the thinnest cables and to 20º for the thickest cables.