FORMING TOOL FOR PRODUCING OPEN CONTAINERS BY THERMOFORMING FOAM SHEETING

摘要

Open containers of thermoformable sheet material are produced by drawing or deep drawing the preheated sheeting. If the sheeting consists of or contains at least one layer of foamed plastic material, the container walls may be expanded also by applying a reduced pressure. The inventive tool (1.2, 2.2) serves for a drawing process in which the sheeting is drawn with the help of a pair of forming tools which are moved relative to each other. During this movement the pressure on at least one side of the sheeting is reduced such that it reaches a value below ambient pressure which is low enough for expansion of the foam material when the male tool reaches its end position in the recess of the female tool or immediately afterwards. For preventing faulty containers due to air tight contacts between sheeting and tool surface combined with air cushions between tool surface and sheeting, the tool shows on the surfaces to come into contact with the sheeting a pattern of surface openings which openings are smaller than 0.5 mm and are spaced from each other by at the most 20 mm. Through these openings air is removed from between the tool surface and the sheeting for establishing the reduced pressure necessary for expanding the foam material. The inventive tool is e.g. made from a sintered material which has open pores connected to each other and forming fine channels in all directions through the material.