publication_number US 4408865 A abstract a corona discharge device for electrophotographic printing is provided in which erasing and primary charging functions are performed by a single device a screened charging arrangement is used for ion steering while simultaneous illumination by light produces charge carriers in the photoconducting layer of the drum in one embodiment a photochemically etched stainless steel screen is used application_number US 32433981 A description referring now to fig1 a shield 100 preferably of extruded aluminum houses a set of corona wires 102 which are supported at the ends by insulating end blocks 104 in the preferred embodiment corona wires 102 are made of tungsten with a diameter of about 0 003 inches insulating end blocks 104 must be able to withstand the 6 7 kilovolts d c which will be applied to wires 102 despite possible high temperatures and humidities in addition the material chosen for end blocks 104 must not support combustion if an electric discharge occurs the preferred material for end block 104 is thus a mixture of mica and glass which can be molded and sintered such as the material sold under the trademark mycalex of the spaulding fiber company other materials such as glass ceramics or thermoplastics are also suitable if capable of withstanding the conditions described a cap 106 is provided for each end block 104 only four caps are shown in fig1 two caps having been omitted to reveal the endblock beneath for clarity of presentation caps 106 may be molded from polytetrafluoroethylene such as that sold under the trademark teflon caps 106 and end blocks 104 are preferably about 4 cm in length the inside surfaces of shield 100 are preferably coated with an insulator such as epoxy or an insulating.