The external sheath of power cables and communication cables has to protect the internal elements from mechanical damage and from environmental influences.
Lead cable sheaths have been extruded directly onto cable cores for more than 100 years, since the invention of cable sheathing by Borell in 1879.
Today, approximately 10% of overland and underseas cables are sheathed with metal, usually Lead.
The thickness of cable sheath is standardized and is usually between 1 and 3 mm the sheath has to be completely tight and protect the internal conductor and insulation layers against moisture as well as mechanical, chemical and thermal influences.
Further requirements are:
A narrow wall thickness tolerance is prescribed in the standard. The mean value should be at least equal to the nominal value.
Stop marks (known as bamboo rings) can form when the press is stopped and reloaded.
These marks are undesirable because of the associated wall thickness deviations.In Lead cable sheathing, liquid metal is poured into a vertical container. Usually, it is filled from an electrically heated crucible containing several tons of the melt through a floor valve with various flow systems at a maximum temperature of 450 C.
The cast Lead should bond well with the discard from the previous filling on the die head to prevent possible defects from inclusions. Air blisters should not form during filling. The Lead is, therefore, usually filled under vacuum together with a lost head that is sheared after solidification at the top edge of the container.
The metal solidifies in water cooled container under a small load applied by the steam within 5 to 10 minutes after which the extrusion process can begin.

The external sheath of power cables and communication cables has to protect the internal elements from mechanical damage and from environmental influences.
Lead cable sheaths have been extruded directly onto cable cores for more than 100 years, since the invention of cable sheathing by Borell in 1879.
Today, approximately 10% of overland and underseas cables are sheathed with metal, usually Lead.
The thickness of cable sheath is standardized and is usually between 1 and 3 mm the sheath has to be completely tight and protect the internal conductor and insulation layers against moisture as well as mechanical, chemical and thermal influences.
Further requirements are:
A narrow wall thickness tolerance is prescribed in the standard. The mean value should be at least equal to the nominal value.
Stop marks (known as bamboo rings) can form when the press is stopped and reloaded.
These marks are undesirable because of the associated wall thickness deviations.In Lead cable sheathing, liquid metal is poured into a vertical container. Usually, it is filled from an electrically heated crucible containing several tons of the melt through a floor valve with various flow systems at a maximum temperature of 450 C.
The cast Lead should bond well with the discard from the previous filling on the die head to prevent possible defects from inclusions. Air blisters should not form during filling. The Lead is, therefore, usually filled under vacuum together with a lost head that is sheared after solidification at the top edge of the container.
The metal solidifies in water cooled container under a small load applied by the steam within 5 to 10 minutes after which the extrusion process can begin.