Apparatus for producing foamed plastic insulated wires

摘要

An apparatus for producing a foamed plastic insulating coating in a wire. A gaseous foaming agent is mixed with a resin and passed through a high pressure narrow passage and then through a lower pressure wide passage. The release of pressure, when the resin enters the wide passage, results in a foaming of the resin. The foamed resin is thereafter extruded through an orifice onto a wire. In one embodiment a chemical is added to serve as a nuclei for the gas bubbles formed during foaming. In a second embodiment, a second chemical is added to provide a smoother extruded surface. In still a further embodiment, the pressure in the wide passage is automatically controlled to remain at a predetermined preferred pressure.