Abstract: Apparatus and methods for coating an article on a flat line, powder coating system comprises a powder coating booth with a reduced inlet opening for articles to be coated and an enlarged outlet opening for coated articles. Powder spray guns of the tribo-electric type, or having internal charging electrodes, are arranged in rows with parallel tube spray heads and are disposed at a shallow angle with respect to the conveyor to spray powder onto the articles generally in the direction of conveyor movement. Baffle plates are installed under the spray guns so that any powder which collects on the spray guns does not fall on the articles being coated. Oversprayed powder is collected from a part of the booth intermediate the spray guns and the enlarged outlet opening. Preferably, the thickness of powder coating on the articles in the precured condition is measured and the system is controlled so that the coating thickness is uniform and of the desired thickness.