Experimental Extrusion of Aluminum Cable Sheath at Bell Telephone Laboratories

In recent years considerable attention has been focussed on the possibility of using aluminum instead of lead as cable sheath. Over fifteen years ago German publications 1,2 described activities abroad. It was emphasized at that time that for a given temperature, aluminum would require much higher extrusion pressures than lead. Also, the pressure required for extrusion of commercially pure aluminum (99 per cent) was reported to be considerably higher than that for super purity aluminum (99.99 per cent) under a given set of conditions. The possibility of obtaining lower pressures by raising the temperature is limited by the danger of scorching the paper or other organic insulation of the core. It is evident, therefore, that improvements in extrusion techniques are required. Progress in this respect has been reported recently. 3,4 " 5 " 6 Lower cost is an important part of the incentive for using aluminum instead of other types of sheath. In the telephone industry lead has already been supplanted to a sizable extent by composite sheaths, such as alpeth or stalpeth. The former consists of a thin corrugated aluminum sheath covered with extruded polyethylene-carbon black compound. The overlap seam in the aluminum is sealed with an organic adhesive. Stalpeth has a thin corrugated aluminum inner sheath without overlap or seal. Outside of this there is a sheath of corrugated tinned, steel sheet 529