Abstract: Process for the production of filters whose active filtering part is made up of a folded filter material web, preferably made from paper, which folded web is delimited in the process by side edges at which the folds terminate, and end edges at which a first or last fold is located, so that in this way filter units (49) are formed. The filter units (49) are produced in an automatized process in which the filter material web is creased and pushed together to form the folds. The spacings between the folds are maintained constant by means of a screw element with threads pushing down between the folds and forming spacing elements between these. The screw element is rotataed during forward movement of the folded web. Glue-coated strips are pressed onto the said side edges of the web, so that the ends of the folds are covered over by the strips.

Abstract: A method and apparatus for the manufacture of filters in which a filter material in the form of a continuous length (5) is folded to form pleats (39). The pleats are attached to their ends along the lateral edges of the filter material and are sealed in this way one against the other so as to form a flow path for the medium which is to be filtered into the spaces between the pleats on one side of the filter material, through the material, and out into the spaces between the pleats on the other side of the filter material. During the process of attaching the ends of the pleats to one another, the pleats are kept separated from one another by a pre-determined distance between their outer folded edges by means of a device (18) provided with a number of combs (20) which extend inside the pleats and hold them in this way at the aforementioned pre-determined distance from one another.