DEVICE FOR SMOOTHING OUT THE THICKNESS OF A SHEET

摘要

A device for smoothing out the thickness of a sheet of thermoplastic material which includes a sheet die and a heating device which is integrated with the upper die lip of the sheet die. The heating device includes a hollow box filled with a liquid and a bar which projects laterally beyond the endfaces of the hollow box. The inlet and outlet openings of the bar in the hollow box are sealed. Arranged on the underside of the bar are small hot plates which are electrically heated. The liquid in the hollow box serves as a heat transfer medium and typically is an oil having a boiling point higher than 280 DEG C. The thickness profile of the extruded sheet is controlled, on the one hand, via controlling elements and, on the other hand, remaining thick and/or thin points of the sheet profile are smoothed by the bar of the heating device, in which the bar is progressively moved transversely with respect to the running direction of the sheet across the sheet width with the aid of a motor into a position in which the small hot plates are aligned with the thick/thin points to be smoothed. The corresponding thick/thin points of the sheet are smoothed by exposing the small hot plates to different temperatures or heating powers.