Production of insulated electrical conductors

Apparatus for forming a covering layer of substantially constant diameter upon an electrical conductor, the layer formed from composite material comprising magnetically permeable particles homogeneously mixed with a fluid carrier, the apparatus comprising:

• a container for holding a reservoir of the fluid composite material;
• a die means at the top of the container having a die orifice providing an outlet from the container to provide a fluid phase of the covering layer upon the conductor moving out of the container in a vertical direction along a feedpath;
• an annular baffle extending downwardly from the die means to horizontally separate composite material within the baffle from that outside the baffle;
• monitoring means for monitoring the diameter of the covering layer downstream from the die means and for transmitting a signal corresonding to a monitored diameter;
• means to apply gas pressure upon the composite material to ensure the material applies a pressure at the die orifice;
• valve means to control and adjust the gas pressure and thereby control and adjust the pressure of the composite material at the die orifice;
• and control means comprising analyzing means for receiving the signal from the monitoring means and for comparing it with a datum signal corresponding to a desired diameter of covering layer upon the conductor, the control means operable to transmit a control signal to the valve means when the monitored diameter differs from that desired to effect operation of the valve means to adjust the gas pressure appropriately to alter the rate of passage of the material through the orifice and effect a change in diameter towards that desired.