Electrospark Punching of Holes in a Moving Web.

Rapidly moving paper can be perforated with holes of various shapes by the explosive pressure wave produced by an electric spark. The shape of the holes punched in the paper is determined by a ceramic die which is in close proximity to one surface of the web. The spark is generated on the opposite side of the web. Thermal expansion of spark-heated air generates a gas pressure of 25 to 50 atmospheres and drives the paper punching out through the hole in the die. Approximately 2 joules of electrical energy is sufficient to punch a 9/32-inch diameter hole in a web moving at 20 feet per second. Electrospark equipment now in production use can be programmed to punch holes approximately every nine milliseconds, but faster repetition rates could be obtained if necessary.