Apparatus for applying dust particles by contact type electric field curtain

Claim 1

Apparatus by which finely divided particulate material from a source thereof can be coated onto a cylindrical surface of an elongated workpiece, said apparatus comprising: A. an elongated tubular guide element of electrical insulation material having a cylindrical surface which can oppose said surface of the workpiece all around the same so that said guide element can be disposed in telescoping relationship to the workpiece, said surface of the guide element having a diameter such that said opposing surfaces are radially spaced apart when the guide element and the workpiece are concentric to one another; B. means for holding the tubular guide element and the workpiece in concentric telescoped relationship to one another and for effecting relative axial motion between the guide element and the workpiece; C. means for introducing finely divided particular material from said source thereof into the interior of the tubular guide element from one end thereof; D. a plurality of electrodes extending circumferentially around the tubular guide element and arranged in axially spaced relation to one another; and E. conductor means connecting each electrode with only one terminal of an alternating voltage source, axially adjacent electrodes being connected with different terminals so that a varying potential difference exists between each pair of axially adjacent electrodes to produce an electric field that controls the motion of said material in the direction lengthwise of the guide element.