Apparatus for perforating thermoplastic sheet materials with an electric arc

Claim 1

An apparatus for forming perforations in a thermoplastic sheet comprising: a. means for continuously advancing a thermoplastic sheet; b. positioned above one side of the advancing sheet, multiple electrically charged discs having at least one pin mounted on the periphery of each disc, said discs spaced laterally across the sheet at intervals corresponding to the desired lateral spacing of the perforations and rotating to cyclically move said pins toward the surface of the advancing sheet to initiate an arc and then away from the surface of the advancing sheet to extinguish the arc; c. positioned above the opposite side of the advancing sheet and opposing each electrically charged disc, multiple grounded discs having at least one grounding pin mounted on the periphery of each disc, said grounded discs synchronously rotating with the electrically charged disc electrodes providing a grounding pin to oppose the electrically charged pins; d. a high-voltage electrical power source to supply electrical power to the rotating discs and the cyclically moving electrically charged pins, wherein the electrical power is connected to the discs through a current-limiting choke to provide a controlled high current density arc discharge at a relatively low maintenance voltage in the gap between a charged disc pin and a grounded disc grounding pin when the charged disc pin and grounding pin directly oppose each other; and e. means for controlling the size of the perforations and their spacing along the length of the moving sheet within predetermined limits by controlling the current density and time duration of the arc discharge at preselected values to produce the desired hole size and preselecting the cyclic frequency of the moving electrode in relation to the speed of sheet advance to produce the desired hole spacing along the sheet.

Claim 2

An apparatus for forming perforations in a thermoplastic sheet comprising: a. means for continuously advancing a thermoplastic sheet; b. positioned above one side of the advancing sheet, multiple electrically charged discs having at least one pin mounted on the periphery of each disc, said discs spaced laterally across the sheet at intervals corresponding to the desired lateral spacing of the perforations and rotating to cyclically move said pins toward the surface of the advancing sheet to initiate an arc and then away from the surface of the advancing sheet to extinguish the arc; c. positioned above the opposite side of the advancing sheet and opposing each electrically charged disc, multiple grounded discs having at least one grounding pin mounted on the periphery of each disc, said grounded discs synchronously rotating with the electrically charged disc electrodes providing a grounding pin to oppose the electrically charged pins; d. a high-voltage electrical power source to supply electrical power to the rotating discs and the cyclically moving electrically charged pins, wherein the electrical power is connected to the discs through a current-limiting choke to provide a controlled high current density arc discharge at a relatively low maintenance voltage in the gap between a charged disc pin and a grounded disc grounding pin when the charged disc pin and grounding pin directly oppose each other; and e. means for controlling the size of the perforations and their spacing along the length of the moving sheet within predetermined limits by controlling the current density and time duration of the arc discharge at preselected values to produce the desired hole size and preselecting the cyclic frequency of the moving electrode in relation to the speed of sheet advance to produce the desired hole spacing along the sheet.