The invention provides a method of generating a high voltage in an electrostatic powder coating gun with a high-voltage generator having a transformer and a high-voltage cascade arrangement. The primary coil of the transformer is fed with an a.c. supply voltage operating at a working frequency. During operation of the coating gun, the frequency of the supply voltage is continuously varied about the working frequency, the current intensity of the primary coil current of the transformer is also continuously detected and the direction of frequency variation is reversed every time an increase in the current intensity of the primary coil current is determined. An electrostatic powder coating gun operating with the present high-voltage generating method includes a current detection circuit for continuously detecting the current intensity of the primary coil current of the transformer, a sweep generator for continuously varying the frequency of the supply voltage about the working frequency, and a control for controlling the operation of the sweep generator.
In a powder coating apparatus a pulse signal S2 of a low voltage generated by a pulse signal generation circuit (7) is boosted to a high voltage by means of a high voltage impression circuit (8), so that it is impressed upon corona electrodes (5). As a result, a corona discharge is intermittently generated from the corona electrodes (5) toward an object to be coated, whereby powder coating material sprayed from a nozzle opening of a gun main body in a forward direction is charged with negative ions developed by the corona discharge, whereafter it is directed toward the object to be coated, and is deposited on a surface of the object.
The present invention provides a method of operating a powder coating system, comprising at least one coating device, a coating compartment and a suction system in the coating compartment. In the method, a workpiece is passed through a coating compartment. The coating powder is discharged by the coating device to the workpiece and excess coating powder is sucked off from the coating compartment, wherein the powder mass flow of the coating powder discharged by the or each coating device is detected and the suction system is controlled in accordance with the powder mass flow. For this purpose the invention provides a powder coating system comprising a measuring means for detecting the powder mass flow of the coating powder discharged by the or any coating device, and an actuator means for setting the suction system in accordance with the powder mass flow.
The invention refers to a method of detecting workpieces in an electrostatic coating system, comprising at least one electrostatic coating device, which applies a high voltage to a high voltage electrode, in which the high voltage electrode generates a spray current including electrostatic charges for charging particles of a coating medium to be sprayed, an electrically conductive workpiece to be coated is moved past the coating device, the spray current of the high voltage electrode is determined and it is detected in accordance with the magnitude of the spray current whether the workpiece is in front of the coating device.
The invention refers to a method of controlling a coating device, which discharges a coating medium such as a powder or wet lacquer to a workpiece, in which in accordance with the shape of the workpiece the shape of the cloud of the coating medium discharged is automatically adjusted by changing at least one of the velocity, and the quantity, and the mass flow of the coating medium discharged or shaping air. The invention further refers to a coating installation capable of operating by this method.
