Electrostatic coating of metal powder on metal strip

Claim 1

Apparatus for applying a metal powder coating on metal stRip comprising means including non-electrically conductive wall means defining an elongated passageway having an entrance opening and an exit opening, means for continuously moving metal strip to be coated through the passageway in a direction from the entrance opening to the exit opening and in out-of-contact relation with the wall means, a plurality of charging wires in the passageway spaced longitudinally of the passageway in the direction of movement of the metal strip through the passageway, each charging wire extending transversely of the passageway and of the metal strip moving through the passageway, a charging circuit for the charging wires including the metal strip and a source of charging potential connected to the charginig wires, means for supplying a stream of carrier gas, means for holding a supply of metal powder, means for controlling flow of the metal powder from the last claimed means, means for flowing metal powder from the supply into the carrier gas to suspend metal powder in the carrier gas to form a cloud of metal powder, means for introducing the cloud of metal powder into the entrance opening of the passageway generally in the direction of the movement of the strip through the passageway, with metal powder suspended in gas passing between the charging wires and the metal strip, and means including a source of gas suction for withdrawing metal powder suspended in gas at a point contiguous to the strip exit end of the passageway, the means for introducing the cloud of metal powder into the entrance opening including nozzle means located contiguous to the entrance opening and having a discharge opening facing in the direction of the entrance opening, the cross-sectional area of the nozzle at its discharge end being substantially less than the crosssectional area of the entrance opening of the passageway, means for feeding the metal powder suspended in the carrier gas to the nozzle means, the relative shapes and dimensions of the nozzle means at the discharge end and the entrance opening of the passageway, acting with the source of gas suction, causing the carrier gas and suspended metal powder to induce ambient air to flow into the entrance opening.